Stuff to know Flashcards
Describe the steps of protein synthesis
1) An mRNA copy of the DNA is made in the nucleus via transcription
2) Proteins are synthesised in ribosomes on the RER via translation
3) Proteins undergo modification at the Golgi apparatus, where lipids or carbohydrates may be added
4) Some proteins are secreted from the cell membrane when transport vesicles fuse with cell surface membrane, some proteins work within the cell
what ribosomes do prokaryotes have?
70s
what ribosomes do eukaryotes have?
80s
Does a SEM have a lower resolution than TEM?
Yes
What is the resolution of a light microscope?
0.2 micrometres
what is the magnification of a light microscope?
X 1500
micrometers to centimetres?
/ 10,000
centimetres to millimetres?
X 10
micrometres to millimetres?
/ 1000
micrometres to nanometres?
X 1000
how do you calculate magnification?
image size/ actual object size
What are the advantages of cell staining?
- Makes the cell easier to see
- Increases the contrast
- Allows you to recognise the different parts of a cell
Describes the roles of the cytoskeleton
- Maintaining the shape of the cell
- The movement of the cillia
- Changing the shape of the cell (exocytosis, phagocytosis, pseudopodia)
- Movement of vesicles to plasma membrane
- The formation of the spindle fibres during mitosis
- Holding organelles in place
What are the roles of membranes within cells?
- compartmentalisation
- Isolation of the contents of the organelle i.e the hydrolytic enzymes.
- Site for the attachment of enzymes
- Controls what enters and leaves an organelle
- Creates concentration gradients
What is the secondary structure ?
-Hydrogen bonds form between the amino acids all along the polypeptide chain (this is due to the polarity of the CO and the NH groups).
-These hydrogen bonds cause the polypeptide chains to twist and fold into shapes .
-The twisted 3d shape formed can either be an alpha helix cylindrical shape or a beta pleated sheet .
-Both these structures are maintained by hydrogen bonds
What are globular proteins?
Proteins that have a roughly spherical shape
What are glucose and fructose?
Monosaccharides
What 2 polysaccharides are starch molecules made up of?
Amylose and amylopectin
What are examples of monosaccharides?
Glucose, galactose, fructose, ribose, deoxyribose, glyceraldehyde
What type of bond forms when monosaccharides like glucose bond?
Glycosidic bond
What make up maltose?
Alpha glucose + alpha glucose
What forms sucrose?
Alpha glucose + fructose
What is the molecular formula of sucrose?
C12 H22 O11
What forms lactose?
Alpha glucose + galactose
What does sucrose and sucrase make?
Alpha glucose + fructose
Is amylose a monosaccharide or a polysaccharide?
Is amylose a monosaccharide or a polysaccharide?
Is amylopectin a monosaccharide or a polysaccharide?
A polysaccharide
What is amylose?
A polymer of glucose joined by a -1,4- glycosidic bonds. Amylose is unbranched and helical
What is amylopectin?
polymers of glucose joined by -1,4- glycosidic bonds but with branches of 1,6 glycosidic bonds. This causes the molecule to be branched rather than helical
What is glycogen made up of?
Alpha glucose molecules with much shorter 1,4 chains and many more branches of alpha 1,6 glycosidic bonds than amylopectin
What reactions form the ester linkage?
Condensation reactions
What are the roles of lipids?
-Energy storage
-Insulation(electrical and thermal)
-Buoyancy(floating)
-Waterproofing
-Protection
-Membranes
-Source of water- from respiration
-Aids absorption
What is a difference between lipids from animals and those from plants?
Lipids from animals are saturated, whereas lipids from plants are unsaturated
what can the hydrophilic hydroxyl group on the cholesterol molecule interact with?
the head groups of phospholipids. the rest of the cholesterol molecule can interact with the hydrophobic fatty acid tails
what are the functions of cholesterol?
- producing steroid-based hormones.
- making vitamin D, this process takes place in the skin in response to ultraviolet light.
- producing bile in the liver.
- fluidity and permeability of cell membranes
What prosthetic group does haemoglobin have?
Haem, which binds to oxygen
What is a protein with a prosthetic group called
A conjugated protein
What are disulfide bonds?
strong covalent bonds that form between two cysteine R groups (as this is the only amino acid with a sulphur atom)
What is the strongest protein bond?
The disulfide bond
In which proteins are disulfide bonds common in?
proteins secreted from cells eg. insulin
Where do Ionic bonds form in a protein?
Ionic bonds form between positively charged (amine group -NH3+) and negatively charged (carboxylic acid -COO-) R groups
Where do hydrophobic interactions form?
between the non-polar (hydrophobic) R groups within the interior of proteins
What is a good way of distinguishing between fibrous and globular proteins?
SAFES (Shape, Amino acid sequence, Function, Examples and Solubility).
How do you calculate Rf values?
Rf value = distance travelled by sample / distance travelled by solvent
what type of covalent bond is present in proteins?
peptide
what type of covalent bond is present in lipids?
ester
what type of covalent bond is present in nucleic acids?
phosphodiester
what do reducing sugars do?
donate electrons and they reduce the soluble copper sulphate to insoluble brick-red copper oxide
what do non-reducing sugars do?
they cannot donate electrons, therefore they cannot be oxidised
summarise the test for proteins
1) Add sodium
hydroxide solution.
2) Add copper (II)
sulphate solution.
Colour change should be from blue to purple
summarise the test for starch
1) Add iodine in
potassium iodide
solution.
Colour change from
brown-orange to
blue-black.
summarise the test for lipids
1) Add ethanol.
2) Pour solution into
water.
A cloudy emulsion forms
summarise the test for reducing sugars
1) Add Benedict’s
reagent to a sample and
heat in a water bath
that’s brought to a boil.
Sample goes from blue to
green to yellow to orange
to brick red precipitate,
depending on the
concentration
summarise the test for non reducing sugars
1) Add dilute HCl.
2) Put in a water bath
brought to a boil.
3) Neutralise with
sodium hydrogen
carbonate.
4) Do Benedict’s Test
for reducing sugars.
Sample goes from blue to
green to yellow to orange
to brick red precipitate,
depending on the
concentration
summarise the test for glucose
1) Dip test strip in
solution.
Colour change will occur
if glucose is present.
Compare to chart of
known colour changes to
check for concentration.
What are the functions of hydrogen ions?
-hydrogen bonding
-ATP formation
-control of blood pH
-transport of carbon dioxide
What are the functions of calcium ions?
-bone and enamel structure
-cofactor in blood clotting
-synaptic transmission of nerve impulses
-muscle contraption
What are the functions of iron ions?
-transport of oxygen via haemoglobin
-transfer of electrons
What are the functions of sodium ions?
-electrolyte
-nerve transmission
-reabsorption of water into the kidneys
What are the functions of potassium ions?
-electrolyte
-nerve transmission
-reabsorption of water into the kidneys
-opening of the stomata
What are the functions of ammonium ions?
deamination of proteins
What are the functions of nitrate ions?
source of nitrogen for plants
What are the functions of hydrogen carbonate ions?
carbon dioxide transport in the blood
What are the functions of chloride ions?
maintaining pH balance during carbon dioxide transport
What are the functions of phosphate ions?
-component of the cell membrane(phospholipids)
-component of bones (calcium phosphate)
-component of ATP and nucleic acids
What are the functions of hydroxide ions?
bonding between biochemical molecules
What is the structure of collagen?
-Peptide bonds between amino acids
-Secondary structure is alpha helix
-Has high proportions of glycine
-3 polypeptide chains and hydrogen bonds between them
-No hydrophilic R groups on the outside of the molecules
-Adjacent molecules joined by crosslinks
-Crosslinks form fibrils
What is the structure of heamoglobin?
-Peptide bonds between amino acids
-Secondary structure is alpha helix, with small regions of beta pleated sheets.
-Hydrophilic R groups on the outside of the molecule
-4 polypeptide chains, 2 alpha, 2 beta
-4 haem groups per molecule
-Made up of a wider range of amino acids
Describe the ways in which the structure of collagen is similar to the structure of haemoglobin?
-Both have an acid amino chain
-Both have amino acids joined by peptides
-Both helical
-Both have a quaternary structure
-Both have more than 1 subunit
How does heamoglobin differ from collagen?
-Haemoglobin is globular, whereas collagen is fibrous.
-Haemoglobin has hydrophilic R groups on the outside, whereas collagen doesn’t.
-Haemoglobin has 4 polypeptide chains, whereas collagen has only 3.
-Haemoglobin has a high wider range of amino acids- not predominantly glycine like collagen is
What are the differences between glycogen and cellulose?
-Glycogen doesn’t have hydrogen bonding, whereas cellulose does.
-Glycogen has a- 1,4 bonds and a-1,6 bonds; whereas cellulose only has a-1,4 bonds.
-Glycogen is branched, whereas cellulose is helical.
-Glycogen doesn’t have fibrils, whereas cellulose does have fibrils.
-Glycogen has granules, whereas cellulose does not have granules.
-All glucose units in glycogen are in the same orientation, whereas adjacent glucose units in cellulose are in opposite orientation.
Why does glycogen make a good storage molecule?
- Glycogen is insoluble, so it doesn’t affect the water potential of the cell.
- Can be broken down easily.
- Has many branches for enzymes to attach to.
- It’s compact and so stores a lot of energy
What does methylene blue do?
stains the nuclei in animal cells to give contrast(stains blue)
What does crystal violet do?
It stains cell walls purple
What is the magnification?
How much bigger an image is than the specimen
What is the resolution?
The ability to clearly distinguish 2 points that are next to each other
What is specific heat capacity?
The amount of heat required to raise the
temperature of 1Kg of liquid by 1oC.
Why does it take a lot of energy to raise the temperature of water?
Because water has a very high specific heat capacity. This allows water to provide a very thermally stable environment for organisms to live in.
What is the specific heat capacity of water?
4200 J/Kg degrees Celsius
what is cohesion?
a force where water molecules stick together.
What is adhesion?
The attraction between non alike molecules
Why is the ability of water to act as a solvent important for the survival of organisms?
- Allows for metabolic reactions to occur
- Allows for transport in transport systems, such as the xylem, to occur.
- Allows for the dilution of toxic substances
Water has a high specific heat capacity so….
- A large amount of energy is needed to change the temperature of water.
- So, a thermally stable environment is provided for aquatic organisms because their internal body temperature will only change slowly, so metabolism will function correctly
What is the latent heat of vaportisation?
- the amount of heat energy required to vaporise a liquid
Water has a high latent heat of vaporisation so…
- a large amount of energy is required to change water from a liquid to a gas.
- this allows for evaporation to be an efficient cooling mechanism i.e sweating can cool organisms down.
Ice is less dense than water so….
- The surface of ice provides habitats for organisms like polar bears.
- The water beneath ice doesn’t freeze so aquatic organisms can swim beneath the ice
Water is an effective solvent so..
it is a medium for metabolic reactions
Water has high surface tension so….
it is a habitat for insects
water has a high density so…
this allows for certain organisms to float on water’s surface
What are the components of nucleotides?
A pentose sugar , either ribose or deoxyribose, a nitrogenous base, and a negatively charged phosphate group
What structure do purines have?
A double ring structure
Give some examples of purines
Adenine and guanine
What is the structure of a pyrimidine?
A single ring structure
What are some examples of pyrimidines?
Thymine and cytosine and uracil
What are the bases found in RNA?
Adenine, uracil, guanine and cytosine
What base replaces thymine in RNA?
Uracil
What bond forms between the phosphate group of one nucleotide and the hydroxyl group on the carbon 3 of the other nucleotide?
A phosphodiester bond
what does guanine pair with?
cytosine
what does adenine pair with?
thymine
what do purines pair with?
pyrimidines
how many hydrogen bonds do guanine and cytosine form?
3
how many hydrogen bonds do adenine and thymine form?
2
What are the steps or DNA replication?
-The enzyme DNA helicase attaches to the DNA molecule. DNA helicase causes the hydrogen bonds between complementary bases to break. This causes the 2 polynucleotide strands to separate from each other.
-Free nucleotides line up with their complementary bases on the DNA strands. At this stage, the free nucleotides are only held in place by hydrogen bonds between complementary bases, not phosphodiester bonds. The nucleotides are called activated nucleotides, as they have 3 phosphate groups.
-The second enzyme, DNA polymerase, moves up and down the polynucleotides and catalyses the formation of phosphodiester bonds between the activated nucleotides. This is a condensation reaction. When the phosphodiester bonds form, the activated nucleotides lose their extra 2 phosphate groups and this provides the energy for the reaction.
Why is DNA replication an example of semi-conservative replication?
because each DNA molecule contains one strand from the original DNA molecule and one strand which is brand new
what is conservative replication?
where a DNA double helix is formed containing 2 new strands. The DNA molecule contains more of the original DNA
What is the most common isotope of nitrogen
Nitrogen-14
which isotope of nitrogen is heavier, nitrogen-14 or nitrogen-15?
nitrogen-15
What does the position of the DNA band determine?
How heavy the DNA is
Is the DNA in prokaryotes circular or linear?
Circular with no free ends
Is the DNA in eukaryotes circular or linear?
Linear with 2 free ends
What are the 2 main steps of protein synthesis?
Transcription and translation
Describe all the steps of DNA transcription
1) DNA helicase breaks the hydrogen bonds between the 2 polynucleotide strands of DNA.
2) Complementary nucleotides move into place and form hydrogen bonds with the bases on the exposed nucleotides of one of the DNA strands.
3) RNA polymerase then joins the RNA nucleotides by forming phosphodiester bonds.
4) A strand of mRNA is now produced
5) Now that the mRNA has been synthesised, the RNA polymerase detaches from the DNA and the DNA goes back to its normal double helix structure.
6) The mRNA now moves out of the nucleus through a nuclear pore.
7) Once in the cytoplasm, the mRNA can now undertake translation
Because of the fact that most amino acids have more than one triplet that codes for them, what do scientists call the genetic code?
The “degenerate code”
What is meant by the fact that the genetic code is non-overlapping?
No base is read more than once
What is meant by the fact the genetic code is universal?
The same base triplets encode the same amino acid in the vast majority of living organisms.
Describe the stages of protein translation
1) The small subunit of a ribosome binds with the mRNA at the start codon.
2) a tRNA molecule with an anticodon complementary to the start codon attaches. This is held in place by hydrogen bonds between the complementary base pairs on the mRNA and tRNA
3)Now, a second tRNA molecule moves into place. The anticodon on this tRNA is complementary to the second codon on the mRNA.
4)Now, a peptide bond forms between the 2 amino acids produced. This forming of the peptide bond is catalysed by the enzyme peptidyl transferase. The formation of the peptide bond requires energy provided by ATP
5)Now, the ribosome moves to the next codon and forms a peptide bond with the next amino acid. The first tRNA molecule is now released (TRNA molecules that have been released are later attached to their amino acids by enzymes in the cytoplasm)
6) The ribosome continues moving down the mRNA, forming the polypeptide
7)When the ribosome comes to a stop codon, it detaches and the protein is released.
Why is ATP a nucleotide?
Because it contains 3 phosphate groups, a ribose sugar and the base adenine
What is the reaction that involves adding a phosphate back onto ADP called?
A phosphorylation reaction
What are anabolic reactions ?
Reactions that build larger molecules from smaller molecules
How many different codons (triplets) are possible?
64 (there’s 4 bases)
Does semi Conservative replication occur in preparation for mitosis?
Yes
Does the degenerate nature of the genetic code limit the amount of mutations possible?
Yes
What are the advantages of Complementary Base Pairing?
-Allows for identical copies of DNA to be produced.
-Prevents mutations.
-Allows DNA to be replicated without error.
Why does the fluid mosaic model describe cell membranes as fluids?
because…
-The phospholipids and proteins can move around via diffusion
-The phospholipids mainly move sideways, within their own layers
-The many different types of proteins interspersed throughout the bilayer move about within it (a bit like icebergs in the sea) although some may be fixed in position
how can phospholipids be chemically modified to act as signalling molecules?
by….
-Moving within the bilayer to activate other molecules (eg. enzymes)
-Being hydrolysed, which releases smaller water-soluble molecules that bind to specific receptors in the cytoplasm
describe intrinsic proteins
they’re fully embedded in the membrane from one side to the other. Because they pass right through the bilayer, intrinsic proteins have hydrophobic amino acids on the outside surface of the protein. These can interact with the hydrophobic fatty acid tails in the phospholipid bilayer.
what are 2 types of intrinsic protein?
carrier proteins and protein channels
describe protein channels
they run through the centre of the phospholipid bilayer. This channel is lined with hydrophilic amino acids and is filled with water molecules. They allow water -soluble molecules and ions to diffuse through (hydrophilic substances)
describe carrier proteins
they have a binding site for certain chemicals . When that chemical binds, it causes the tertiary structure of the carrier protein to change. This change in tertiary structure brings the chemical across the membrane where the chemical is now released
describe extrinsic proteins
they don’t span the membrane and are found on one side of the membrane or the other. They can sometimes be attached to intrinsic proteins
describe the functions of extrinsic proteins
- some play a structural role within the membrane.
- some act as enzymes
- some are receptors for other molecules, such as hormones
what are glycoproteins?
membrane proteins attached to a carbohydrate molecule
what are the functions of glycoproteins?
- allowing cells to attach to each other to form tissues such as nervous tissues
- presenting antigens to T cells
- acting as receptors for hormones
what are glycolipids?
carbohydrates attached to phospholipid molecules
what are glycolipids used for?
- contacting other cells. the glycolipids of one cell can be recognised by another cell and this can determine whether cells come into contact .
- they act as antigens e.g in determining blood groups
what 2 factors affect the permeability of the cell membrane?
temperature and solvent concentration
what happens to the lipids when the temperature of the phospholipid bilayer increases?
- The lipids become more fluid and so the cell membrane becomes a less effective barrier to polar molecules and so they can easily pass through.
- Diffusion takes place at a higher speed due to increased kinetic energy. So, more molecules pass through
what happens to the proteins in the cell membrane at really high temperatures (temperatures exceeding 40 degrees)?
the proteins in the cell membrane denature, which means that it can no longer form an effective barrier and so substances can freely pass through the disrupted membrane
why do organic solvents increase membrane permeability?
because they dissolve the lipids in the membrane, causing the membrane to lose its structure
why does membrane permeability also increase below 0 degrees Celsius?
-Increased permeability can be caused by channel or carrier proteins deforming at these low temperatures
-Ice crystals that form can also pierce the cell membrane, making it highly permeable
what is diffusion?
The net movement, as a result of the random motion of its molecules or ions, of a substance from a region of its higher concentration to a region of its lower concentration.
what factors is the rate of diffusion dependant on?
- concentration gradient
- surface area
- diffusion distance
how does the steepness of the concentration gradient affect the rate of diffusion?
The greater the difference in concentration between 2 areas, the greater the rate of diffusion
what does Fick’s Law state?
‘the rate of diffusion is proportional to both the surface area and concentration difference and the rate of diffusion is inversely proportional to the thickness of the membrane’.
what is the formula for the rate of diffusion?
rate of diffusion = surface area X difference in concentration / length of the diffusion path
what can increase the surface area of cell membranes?
folding e.g microvilli in the intestines or cristae in mitochondria
what 2 proteins enable facilitated diffusion?
Channel proteins
Carrier proteins
is facilitated diffusion a passive process?
yes
what is osmosis?
the movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane
what is the unit of water potential?
kilopascals
what type of water has the highest water potential?
pure water
what is the water potential of pure water?
0kPa
What is the water potential of solutions besides pure water?
less than 0
do more concentrated solutions have higher or lower water potential than a less concentrated solution?
lower water potential
isotonic meaning?
the concentration of solutes is the same inside and outside of the cell, meaning the water potential is equal. water will diffuse equally between locations
hypertonic meaning?
the solution has a higher solute concentration than the cell, meaning the water potential is lower outside the cell. Water will diffuse out of the cell
hypotonic meaning
the solution has a lower solute concentration than the cell, meaning the water potential is lower inside the cell. water will diffuse into the cell
describe the visking tubing diffusion practical
-Fill a section of Visking tubing with a mixture of starch and glucose solutions
-Suspend the tubing in a boiling tube of water for a set period of time
-Test the water outside of the visking tube at regular intervals for the presence of starch and glucose to monitor whether the diffusion of either substance out of the tubing has occurred
-the results should indicate that glucose, but not starch, diffuses out of the tubing
what happens if an animal cell is placed in a solution with a lower water potential than the cell (such as a concentrated sucrose solution)?
- Water will leave the cell through its partially permeable cell surface membrane by osmosis.
- The volume of the cell will decrease.
- The cell will consequently shrink/shrivel up.
what happens when an animal cell is placed in a solution with a higher water potential?
water will enter the animal cell through its partially permeable cell membrane by osmosis. The volume of the cell will increase. The animal cell has no cell wall to withstand the increased pressure created. The cell membrane will stretch out too far and will eventually burst.
what happens to animal cells in an isotonic environment?
The movement of water molecules into and out of the cell occurs at the same rate (no net movement of water) and there is no change to the cells
why is the loss and gain of water less severe in plant cells?
because plant cells have a supporting cell wall
what happens if a plant cell is put in a solution with a lower water potential than the plant cell?
- water leaves the cell through the partially permeable membrane by osmosis.
- The volume of the plant will decrease.
- The protoplast will shrink and pull away from the cell wall. The cell is now plasmolysed
what happens if a plant cell is put in a solution with a higher water potential than the plant cell?
- water will enter the plant cell through the partially permeable membrane by osmosis.
- The volume of the plant cell will increase.
- The protoplast will expand and push against the cell wall.
- The cell wall withstands the increased pressure created. The pressure increases until the cell is rigid and firm (turgid). The cell becomes fully inflated with water and no more can enter
what is it called when a plant cell is fully inflated with water and has become rigid and firm?
it is called turgid
why is turgidity important for plants?
as the effect of all the cells in a plant being firm is to provide support and strength for the plant – making the plant stand upright with its leaves held out to catch sunlight
what happens if plants do not receive enough water?
the cells cannot remain rigid and firm (turgid) and the plant wilts
What is active transport?
The movement of molecules/ions from a region of lower concentration to a region of higher concentration. Active transport requires energy in the form of ATP
Describe the steps of active transport in a cell
1)Ions bind to receptors on the carrier protein.
2) A molecule of ATP binds to the carrier protein.
3) The ATP undergoes hydrolysis, producing phosphate and a molecule of ADP.
4) The phosphate now attaches to the carrier protein and causes it to change shape.
5)This shape change causes the carrier protein to transport the molecule or ion to the other side of the membrane where it is released.
6)The phosphate now unbinds from the carrier protein, causing the carrier protein to return to its original shape.
7) The ADP and phosphate will later reform ATP during respiration.
What is active transport important in?
- The reabsorption of useful molecules or ions into the blood after filtration into the kidney tubules.
- The absorption of some products or digestion from the digestive tract
- The loading of sugar from the photosynthesising cells of leaves into the phloem tissue for transport around the plant.
- The loading of inorganic ions from the soil into root hairs
What are the 2 forms of bulk transport?
Endocytosis and exocytosis
What is bulk transport?
The use of active transport to move larger molecules and whole cells that cannot move through channel proteins
What is endocytosis?
The process by which the cell surface membrane engulfs material, forming an endocytic vacuole around it.
What are the 2 types of endocytosis?
Phagocytosis and pinocytosis
What is phagocytosis?
When material is taken into a cell in solid form
What is pinocytosis?
When material is taken into a cell in liquid form
What is exocytosis?
When materials are removed from or transported out of the cell in vesicles, which fuse with the cell membrane and release the materials out of the cell out of the cell
What is the role of the ileum in the small intestine?
To absorb the molecules produced by digestion. This includes glucose
How does the fact that the membrane of the microvilli is folded into a large number of microvilli help with the rate of diffusion and the rate of active transport?
This increases the surface area of the membrane, providing more space for the membranes needed for facilitated diffusion and active transport. So, both of their rates are increased.
What are enzymes?
Biological catalysts that increase the rate of reactions in living organisms
What reaction does catalase catalyse?
The breakdown of hydrogen peroxide into water and oxygen
What reaction does amylase catalyse?
The breakdown of starch into maltose
What reaction does trypsin catalyse?
The breakdown of proteins into peptides and amino acids
What is the induced fit model?
The idea that the tertiary structure of the active site actually changes as the substrate molecule binds with the enzyme. As the substrate starts to form bonds with the amino acids in the active site, the tertiary structure of the enzyme adjusts so that the active site moulds itself tightly around the substrate. This change in the tertiary structure of the enzyme ensures that the active site fits perfectly into the substrate.
What is Q10?
The temperature coefficient
What is the equation for the temperature coefficient?
Temperature coefficient= rate of reaction at temperature X at 10 degrees / rate of reaction at temperature X
What does the pH of a solution depend on?
The concentration of hydrogen ions (H+)
How do you workout the pH on a calculator?
pH = - log[H+]
How does a competitive inhibitor reduce the rate of reaction?
-The competitive inhibitor prevents the actual substrate from colliding with the active site.
-This reduces the frequency of successful collisions between the substrate and the active site.
-So less ESC’s are made and the reaction rate is lower.
What is succinate the substrate for?
An enzyme involved in respiration
What competitive inhibitor has a similar structure to succinate?
Malonate
What does malonate slow down the rate of?
Respiration
What is the name of a molecule that competes with substrate molecules for the active site?
A competitive inhibitor
Give 2 examples of competitive inhibitors
Methotrexate, which is a reversible competitive inhibitor used to treat certain cancers
Penicillin, which is an irreversible competitive inhibitor used to treat bacterial infections
Where do non competitive inhibitors bind?
To the allosteric site
What happens to the enzyme when the non competitive inhibitor bonds to the allosteric site?
The tertiary structure of the enzyme changes. This results in the shape of the active site changing and so the active site is no longer complementary to the substrate
Why do non competitive inhibitors reduce the rate of reaction?
Because they change the shape of the active site and so the substrate can no longer bond to the active site and form an ESC.
what is important in regulating metabolic pathways in cells?
End product inhibition
What is a metabolic pathway?
A series of reactions, all catalysed by enzymes
What type of cell division occurs in yeast?
Budding
What types of cells are found in the phloem?
- Sieve plates
- Companion cell
- Parenchyma
Discuss the ways in which genetic variation is produced, including the role of nuclear division
- Independent assortment of homologous chromosomes in metaphase 1, which allows for homologous chromosomes to have different alleles.
- Crossing over in Prophase 1, so that chromatids will have a new combination of alleles.
- Mutations, as they allow for changes in the DNA when DNA checks don’t recognise the damage.
- Fertilisation produces a large number of allele combinations as gametes aren’t genetically identical.
When does independent assortment occur in meiosis?
- Metaphase I
- Metaphase II
why does meiosis need to have twice as many stages as mitosis?
- because the chromosome number needs to be halved from 46 to 23.
- because the homologous pairs of chromosomes and sister chromatids need to be separated.
What feature of the DNA molecule is changed as a result of a mutation?
The sequence of bases
what are the effects a mutation can have on the structure and the function of a protein?
- can change the primary, secondary or tertiary structure of a protein.
- The protein could be shorter due to a deletion or longer due to an insertion.
- The protein could also remain unchanged due to a silent mutation.
- The function of the protein could either be worse or better than before.
Describe how the cells in a multicellular organism are organised
- Cells undergo differentiation and become specialised.
- A group of cells work together to form a tissue.
- A group of tissues work together to form an organ.
- A group of organs work together to form an organ system.
Why must the genetic material replicate before the division of the nucleus of the cell?
So that the daughter cells have all the identical genetic material.
What is a homologous pair of chromosomes?
- They have the same genes.
- The centromere is in the same position.
- They pair up in meiosis to form a bivalent.
What is a tissue?
A group of specialised cells working together to perform a particular function.
Whay cells are xylem made up of?
Vessel cells
What type of cells are phloem made up of?
Sieve tube elements, companion cells
How are the products of meiosis different from the peoducts of mitosis?
- In meiosis the cells produced aren’t genetically identical .
- In meiosis, haploid cells are produced ans they only contain 23 chromosomes.
- Meiosis produces gametes.
- Meiosis produces 4 cells
What happens during interphase?
- Genetic material is copied.
- DNA is checked for errors.
- Protein synthesis.
- Synthesis of more organelles.
- ATP production.
- Cell increases in size.
How is cell division in plants different to cell division in animals?
- In plants, cell plate forms between 2 new cells.
- in plants, cytokinesis starts from the middle of the cell.
- in plants, cell division only occurs in the merristem.
- no centrioles involved in the cell division of plant cells.
Describe the process of budding yeast
- Mitosis occurs.
- The cell bulges.
- The nucleus moves into the bulge
- Cytokinesis occurs and a new cell wall forms
State two other roles of mitosis in multicellular organisms.
- asexual reproduction
- growth and repair of tissues
- development of body plan
- proliferation of white blood cells
- producing gametes from haploid cells
- production of new stem cells.
Is the nucleolus visible in prophase?
No
what do opsonins do?
they bind to the antigen on a pathogen and make it easier for a phagocyte to bind.
are adult stem cells multipotent?
Yes
how thick are squamous epithelial cells?
one cell thick
2
Mitotic index = ?
Mitotic index = (the number of cells in mitosis/ the total number of cells) X 100
How does the crossing over of chromatids ensure genetic variation?
- The chromosomes of homologous pairs come together.
- In Prophase 1, the chromatids cross over.
- One chromosome from each homologous pair ends up in each cell.
- Each cell has a different chromatid and therefore a different set of alleles, which increases the genetic variation in the offspring.
How does the independent assortment of chromosomes ensure genetic variation?
- Each homologous pair of chromosomes is made up of a maternal and paternal chromosome.
- When the homologous pairs line up on the equator in Metaphase I and are separated in Anaphase I, it’s completely random which chromosome from each pair ends up in which daughter cell.
- So, the 4 daughter cells produced by meiosis have completely different combinations of those maternal and paternal chromosomes.
- This is called independent assortment (separation) of the chromosomes.
- This ‘shuffling’ of chromosomes leads to genetic variation in any potential offspring.
Where does crossing over occur in meiois?
prophase 1
Where does independent assortment occur in meiosis?
metaphase 1 and 2
do small organisms have a low or high surface area to volume ratio?
A high surface area to volume ratio
what is the surface of an insect covered with?
An exoskeleton
What is an insects exoskeleton make out of?
The polysaccharide chitin
Why do insects need spiracles on their exoskeleton?
So that gases like oxygen and carbon dioxide can diffuse into the insect
What do the spiracles lead to ?
The trachea
What are walls of the trachea in insects made up of?
Chitin
What are walls of the trachea in animals made up of?
cartilage
Why is there a short diffusion distance between the tracheoles and the insects cells?
-because tracheoles have a narrow diameter
-because tracheoles are extremely close to cells
Why does water from the tracheal fluid move into the insect cells during intense activity?
-Because during intense activity, cells around the tracheoles
undergo anaerobic respiration and this produces lactic acid.
-This lowers the water potential of the cells and causes water to move from the tracheoles into the cells by osmosis.
-This reduces the volume of the tracheal fluid, drawing air down into the tracheoles
what is a significant problem faced by insects?
Water loss
What is each spiracle surrounded by ?
A muscular sphincter
how are the gill lamellae adapted for the efficient diffusion of gases?
- they have a massive surface area for diffusion to occur
- there’s a very short diffusion distance between the walls of the lamellae and the bloodstream
- gill lamellae have an extensive network of capillaries
- The counter current exchange system
Describe the counter current exchange system
- Water and blood move in opposite directions
- Blood with a low concentration of oxygen passes into the capillaries of the gill lamellae
- As the blood passes through the gill lamellae, oxygen diffuses from the water into the blood
- Oxygenated blood passes out of the gill lamellae and leaves the gills
what is the major advantage of the counter current exchange system?
A steep concentration gradient is always maintained
Describe how bony fish maintain constant water flow through the gas exchange system
- A bony fish opens its mouth and water flows into the buccal cavity (the mouth space)
- The floor of the buccal cavity lowers and increases the volume available for water
- The fish then shuts the operculum and this increases the volume of the opercular cavity
- Due to the increased volume, the pressure in the opercular cavity falls and the floor of the buccal cavity moves upwards.
- This increases the pressure of water and so the water moves down a pressure gradient and flows over the gills in the opercular cavity.
- Now, the fish closes its mouth and opens the operculum.
- The sides of the opercular cavity squeeze inwards on the water.
- This increases the pressure of water and forces it out of the operculum
What are the 2 main adaptations of the trachea?
- The walls of the trachea contain cartilage. This prevents the walls of the trachea from collapsing when we inhale
- The trachea walls are lined with ciliated epithelia and goblet cells
what do the elastic fibres between the alveoli do during breathing?
they stretch and recoil
What happens during inhalation?
- The intercostal muscles contract
- The diaphragm contracts and flattens
- The volume of the thorax increases
- Air pressure in the lungs decreases
- Because air pressure in the lungs is now less than atmospheric pressure, air is drawn into the lungs
- Air consequently moves into the alveoli
What happens during exhalation?
- The intercostal muscles relax
- The diaphragm relaxes and becomes domed
- The volume of the thorax decreases
- Now, the air pressure in the lungs is greater than atmospheric pressure and so air is pushed out of the lungs
What is mass transport?
When molecules are carried in a transport medium, such as blood, through a circulatory system
Describe a single circulatory system
Blood only passes through the heart once in a single circuit
What’s a major problem with a single circulatory system?
Oxygen is delivered to the body cells a lot slower
Describe a double circulatory system
Blood passes through the heart twice in a single circuit. This ensures that blood moves to the body tissues rapidly and under high pressure
What is a closed circulatory system?
Where the blood is contained in blood vessels
What are the advantages of a closed circulatory system?
- The blood can move rapidly
- Oxygen can be delivered to respiring tissues quicker and carbon dioxide can be removed from the body quicker
Do insects have an open or closed circulatory system?
They have an open circulatory system
What do insects contain instead of blood?
A fluid called haemolymph
What does haemolymph carry?
Nutrients such as sugars, but not oxygen
Is the blood in the left side of the heart oxygenated or deoxygenated?
Oxygenated
Is the blood in the right side of the heart oxygenated or deoxygenated?
Deoxygenated
Describe the structure of an artery
- Very thick walls to allow the artery to withstand high pressure
- Collagen rich outer layer , which strengthens the artery wall against the pressure of the blood
- Smooth muscle layer. When this layer contracts, the diameter of the artery narrows and this allows the body to control how much blood flows to different organs
- elastic layer that is rich in elastic fibres. This allows the artery to recoil and stretch
- Lumen is lined with endothelial cells which allows for a very smooth surface and reduces friction
Describe the structure of an arteriole
-Collagen layer and the elastin layer are thinner than that of the arteries
-Thicker smooth muscle later than arteries because they control blood flow into the capillaries
Describe the structure of the capillaries
-Have a wall that is one cell thick allowing greater time for the diffusion of molecules to occur
-Capillary lumen is only slight bigger than the lumen of the red blood cells. This means that red blood cells can move slowly and in single file through the capillaries, allowing for more time for the diffusion of molecules to occur
-Capillaries have pores in their walls. These gaps allow tissue fluid to pass out of the blood. They also allow the white blood cells to leave the bloodstream
Describe the structure of veins
-Have thin walls because veins don’t have to withstand high pressure
-Large lumen to carry a great volume of blood
-Thinner elastic fibre layer because blood is under low pressure so veins don’t need to stretch and recoil
-Lumen has an internal lining of endothelial cells to create a smooth surface that reduces the friction between the blood and the wall of the vein
-Valves to ensure that there’s no backflow and that blood moves in the right direction
Describe the movement of fluid in and out of the capillary
- at the arterial end of the capillaries, hydrostatic pressure was greater than oncotic pressure, so fluid moves out of the capillary
- At the venous end of the capillary, hydrostatic pressure was lower than oncotic pressure , so fluid moves into the capillaries by osmosis
What happens to tissue fluid that isn’t reabsorbed back into the blood?
This fluid drains into lymph capillaries and becomes lymph fluid
Do lymph vessels have valves?
Yes
What adaptations do red blood cells have for transporting oxygen?
-Biconcave shape, to give a large surface area to carry the maximum amount of oxygen possible.
-Contains lots of haemoglobin.
-No nucleus to give more space for haemoglobin
How many polypeptide chains does haemoglobin have?
4
What is each of the 4 polypeptide chains in haemoglobin bound to?
A prosthetic group called haem
Which iron ion does haem contain?
Fe2+
How many molecules of oxygen can one haemoglobin molecule bind to?
1 and as oxygen is diatomic, haemoglobin binds to 8 oxygen atoms altogether
What is on the y axis of the oxygen dissociation curve?
The percentage saturation of haemoglobin with oxygen
What is on the x axis of the oxygen dissociation curve?
The partial pressure of oxygen (Kpa)
At low partial pressures of oxygen…
Haemoglobin will have a low affinity for oxygen
Why does the affinity of hemoglobin for oxygen increase after one oxygen molecule has bound?
Because as one oxygen molecule binds , the polypeptide chain opens, exposing the other 3 haem groups. The affinity of the haem groups for oxygen therefore increases
The partial pressure of oxygen is high in the lungs so..
Oxygen readily combines with haemoglobin
The partial pressure of oxygen is low in the tissues so….
Oxygen is readily released by haem
What happens when the partial pressure of carbon dioxide is high?
Haemoglobin releases oxygen more readily and it’s affinity for oxygen decreases
Is the oxygen dissociation curve shifted to the left or to the right when there’s a high partial pressure of carbon dioxide?
The right
What is the Bohr effect?
Where a high partial pressure of carbon dioxide causes haemoglobins affinity for oxygen to decrease
Describe the carriage of carbon dioxide in the blood
- The carbon dioxide produced in respiring tissues diffuses into the blood where most of it enters the red blood cells.
- In the red blood cells, the enzyme carbonic anhydrase catalyses the reaction between carbon dioxide and water.
- Carbonic acid is produced. Carbonic acid is a weak acid and so dissociate into hydrogen ions and hydrogen carbonate ions.
- The hydrogen ions can combine with haemoglobin to produce haemoglobinic acid.
- Hydrogen ions act as a pH Buffer and when haemoglobinic acid is formed, the haemoglobin is forced to drop some of the oxygen it’s carrying
- Some of the carbon dioxide that enters the red blood cells doesn’t undergo the process described above and instead combines directly with haemoglobin to form carbaminohaemoglobin
How is fetal haemoglobin different to adult haemoglobin?
Fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin . This increases the oxygen transfer across the placenta from the mother to the baby
Does carbon dioxide from the foetus diffuse into the maternal blood?
Yes. This carbon dioxide lowers the oxygen affinity of the maternal haemoglobin
In which 3 ways is carbon dioxide transported around the body?
-Dissolved in the blood plasma
-Carried as carbaminohaemoglobin in red blood cells
-as hydrogen carbonate ions in the blood plasma
Do the ventricles have thicker muscular walls than the atria?
Yes
What are the atria separated from the ventricles by?
The atrioventricular valves (AV valves)
What is the left AV valve called?
What is the right AV valve called?
The tricuspid valve
What does the septum do?
It prevents any blood from passing directly between the 2 sides of the heart
What does the superior vena cava?
Brings blood from the head and other parts of the body back to the heart
What does the inferior Vena Cava do?
It brings deoxygenated blood back to the heart from lower parts of the body
why is the heart myogenic?
Because it triggers its own heartbeat- no external factors come to play
What is another name for the pacemaker?
The SAN
What is another name for the SAN?
The pacemaker
What happens when the cells in the SAN become electrically excited?
A wave of electrical excitement spreads across the atria and this causes the atria to contract
What is the contraction of the atria called?
Atria systole.
What is the AVN connected to?
Conducting fibres called Purkyne fibres
What is the Bundle of His?
Where the Purkyne fibres are bundled together
Where do the Purkyne fibres run down to ?
The apex
What happens after the AVN detects the electrical excitation passing over the atria?
The AVN then transmits the electrical excitation down to the Purkyne fibres. This electrical excitation causes the ventricles to contract
In which direction do the ventricles contract?
From the apex upwards
Why do the ventricles contract from the apex upwards?
To ensure that the maximum volume of blood is pumped out of the ventricles
Why is there a slight delay before the AVN triggers a wave of excitation down the Purkyne fibres?
To ensure that the ventricles contract after the atria have contracted
Describe the initiation and cooordinatiion of the action of the heart
1) A wave of electrical excitation spreads out from the SAN across both the atria. As a result, the atria contract and atrial systole occurs.
2) The electrical wave is stoppepd from passing through to the ventricles by the non consucting atriventricular septum.
3) The AVN picks up the electrical wave and after a short delay, sends an impulse down the bundle of His.
4) The electrical signal is down the bundle of His to the Apex. From the apex, the electrical signal branches into smaller Purkyne fibres,
5) Both ventricles contract from the ventricles upwards. This is ventricular systole.
What is the cardiac cycle?
The different steps involved in producing a single heartbeat
What does systole mean?
Contracting
What does diastole mean?
Relaxing
Describe the cardiac cycle
1) Blood flows into the atria through the vena cava and the pulmonary vein. This causes the pressure in the atria to rise.
2) At a certain point, the pressure in the atria is greater than the pressure in the ventricles.
3) This causes the Atrioventricular valves to open, allowing blood to flow down the atria and into the ventricles.
4) The atria then contract and atrial systole takes place. This pushes the remaining blood from the atria and to the ventricles
5) The ventricles then contract and enter ventricular systole. The pressure in the ventricles now rises rapidly and because the ventricular pressure is now greater than the atrial pressure, the atrioventricular valves close.
6) This prevents any blood from moving back into the atria from the ventricles
7) The semilunar valves in the aorta and pulmonary artery are also open. So blood is pumped from the ventricles and out of the heart .
8) Finally, the ventricles relax and enter ventricular diastole
9) At some point, the pressure in the ventricles falls below the pressure in the pulmonary artery and aorta. This causes the semilunar valves to shut and this prevents blood from flowing back into the ventricles.
10) The heart is now ready to enter the next cardiac cycle
What does ECG stand for?
Electrocardiogram
What does the P wave on an ECG trace show?
The contraction of the atria/ atrial systole
What does the QRS wave on an ECG trace show?
The contraction of the ventricles/ ventricular systole
What does the T wave on an ECG trace show?
the relaxation of the ventricles/ ventricular disastole
What is the heart rate?
Heart beats per minute
What is an ectopic heartbeat?
When it feels as though the herat has missed a beat
What is the cardiac output?
The volume of blood pumped into the circulatory system in one minute
What is the stroke volume?
The volume of blood pumped out of a ventricle during each contraction
What is a typical stroke volume?
Around 70cm^3
What is the equation for cardiac output?
Cardiac output (cm^3/min) = heart rate(bom) X stroke volume (cm^3)
What is the tidal volume?
The volume of air inhaled/exhaled during regular breathing
Q
What is the vital capacity?
The maximum volume of air inhaled/exhaled in 1 breath
Why is there always resdiual volume left behind in the lungs?
Because the lungs can’t be completely compressed
What does the smooth muscle do?
It constricts the airway and controls the flow of air
What do the elastic fibres do?
They stretch and recoil
How do you use a spirometer to measure the rate of oxygen uptake?
- You measure the volume of oxygen used in a given time
- You draw a line along the tips of peaks/troughs
- Divide volume by time taken
Why is a nose clip used when using a spirometer?
To ensure all the air breathed comes from the air chamber
What effect might tachycardia have on the heart?
-Less blood will leave the heart because ventricles won’t have time to fill before contracting
Why doesn’t tissue fluid contain erythrocytes?
because the erythrocytes are too big too fit through the pores in the capillary walls
Describe the role of haemoglobin in transporting oxygen around the body
- Haemoglobin has a high affinity for oxygen
- Oxygen binds to haemoglobin in the lungs.This forms oxyhaemoglobin
- The oxygen is released in respiring tissues
Describe the pressure changes in the blood as it flows through the circulatory system from the aorta to the veins?
-The pressure drops as the distance from the heart increases
- The greatest pressure drop is while the blood is in the arteries
- The pressure remains constant in the veins
What causes the overall changes in pressure as blood flows from the aorta to the arteries and from the arteries to the capillaries?
- blood flows into a larger number of vessels
- the total cross-sectional area of the arteries is greater than the aorta
- the total cross-sectional area of the capillaries is greater than the arteries
Explain why it’s important that the pressure changes as blood flows from the aorta to the capillaries?
Because the capillary wall is thin and it can’t withstand the high pressure
do multicellular plants have a high or low surface area to volume ratio?
They have a low surface area to volume ratio
Why can’t multicellular organisms rely on diffusion alone for the transport of molecules?
Because they have a low surface area to volume ratio
What are the products of photosynthesis?
Oxygen and glucose
What are the reactants used in aerobic respiration?
Oxygen and glucose
How can the metabolic rate of an organism be measured?What different apparatus can be used to measure the metabolic rate in organisms?
-Oxygen consumption
-Carbon dioxide production
-Heat production
What different apparatus can be used to measure the metabolic rate in organisms?
-Respirometers
-Oxygen/carbon dioxide probes
-Calorimeters
What 4 things do effective exchange surfaces have?
-A large surface area
-Short diffusion distance
-Good blood supply
-Ventilation mechanism
What are the 2 mass transport systems in plants?
The xylem and the phloem
What is the embryonic seed in leaves called?
Cotyledon
What happens to the cotyledon when a seed germinates?
The cotyledon unfurls, allowing the seed to carry out photosynthesis
What is an example of a plant that only has one cotyledon?
Grass
What are plants with only one cotyledon called?
monocotyledonous
What are plants with 2 cotyledons called?
dicotyledonous
What is an example of a plant that has 2 cotyledons?
Trees
Are trees and shrubs examples of woody dicotyledonous plants?
Yes
describe woody dicotyledonous plants?
They’re long-lived and have a woody stem
Describe herbaceous plants
they’re often fast growing and can be short-lived. unlike woody plants, they don’t have a woody stem
What are the 2 different transport systems in plants?
The xylem and the phloem
What does the xylem do?
it carries water and mineral ions from the roots of the plant up the stem to the leaves
what does the phloem do ?
The phloem transports organic molecules around a plant , from the source to the sink
are the xylem vessels and phloem vessels grouped together in vascular bundles?
Yes
is the arrangement of the vascular bundles the same in the roots, stem and leaves, or different?
Different
What is the centre of the root called?
The stele
In the roots where can the vascular bundle be found?
In the centre of the root (the stele)
where do the root hair cells in a root grow from?
A layer of external tissue called the epidermis
What does the cortex contain?
parenchyma cells
What is the vascular bundle in the root surrounded by?
A layer of cells called the endodermis
In the vascular bundle in the root, are the xylem vessels or phloem vessels in the centre of the root?
The xylem vessels are in the centre of the vascular bundle. (The phloem vessels surround the xylem)
how does the fact that xylem vessels are mechanically strong help the plant (in the root) ?
The xylem vessels are grouped together in the centre of the root and this prevents the root from being pulled out of the soil by strong winds
are xylem vessels mechanically strong?
Yes
how is the vascular bundle arranged in the stem?
The vascular bundles are arranged in a ring around the edge of the stem
What is the centre of the plant stem called?
The pith, which consists of parenchyma cells
What does the pith consist of?
parenchyma cells
What’s around the edge of the stem?
The epidermis and the cortex
in the vascular bundle in the stem, where is the phloem found?
around the edge of the stem
in the vascular bundle in the stem, where is the xylem found?
closer to the centre of the stem
What does the vascular bundle being closer to the edge of the stem help with?
helps the stem to withstand bending due to the wind
where in a leaf is the vascular bundle found?
In the midrib. This helps with transport in the leaf and helps support the leaf
is the leaf also supported by smaller vascular bundles connected to the main one?
Yes
in the vascular bundle of a leaf, where is the xylem found?
at the upper part of the vascular bundle
in the vascular bundle of a leaf, where is the phloem found?
at the lower part of the vascular bundle
Where in the leaf does photosynthesis take place?
In the palisade mesophyll, which is in the upper half of the leaf
what cells does the xylem consist of?
Tracheids and xylem vessel elements,which are both types of water- conducting cells
what is the function of lignified cell walls in the xylem vessel elements (mature cells)?
Adds strength to withstand the hydrostatic pressure so that the vessels don’t collapse
what is the point of xylem vessel elements having no end plates?
Because this allows the mass flow of water and dissolved solutes as cohesive (between water molecules) and adhesive forces (between water molecules and the walls) aren’t impeded.
what is the point of the xylem vessel elements having no protoplasm?(with organelles)
The organelles don’t get in the way of the mass flow of water and dissolved solutes (the transpiration stream )
what is the point of xylem vessel elements having pits in their walls?
This allows for the continual flow of water, in the case of air bubbles forming in the vessels
are xylem vessels living tissue or non living tissue?
Non-living tissue
Can organic substances(glucose) be transported both up and down the phloem ?
Yes
What is the fluid moving in the phloem referred to as?
Phloem sap
Is phloem made up of living or dead tissue?
Living
What 2 different cells does the phloem consist of?
Sieve tube elements and companion cells (also parenchyma for storage and strengthening fibres)
How are the sieve tube elements in the phloem arranged?
They consist of a long line of cells arranged end to end
What do the insides of sieve tube elements look like?
Almost all of the organelles have been lost , including the nucleus and the vacuole
Why do sieve tube elements have almost no organelles?
So that they have enough space to transport phloem sap and assimilates
Why are the end walls of sieve tube elements modified to contain large pores called the sieve plate?
to allow for the continuous movement of organic molecules
Why can’t sieve tube elements produce large amounts of essential molecules such as ATP?
because they’ve lost almost all of their organelles
what organelles do companion cells contain?
A nucleus and large amounts of mitochondria
why do companion cells have a large amount of mitochondria?
To provide ATP for the active transport of assimilates into or out of companion cells
What links the companion cell to the sieve tube elements?
The plasmodesmata
What is the role of the companion cells?
to provide essential molecules to the sieve tube elements cells.
why do companion cells have transport proteins in their plasma membrane?
To move assimilates in and out of the sieve tube elements
where on the root hair cell do root hairs grow?
from the epidermis of the root hair cell (the outer layer)
does water move into the root hairs via osmosis or via active transport?
Osmosis
Where does water move after it has entered the roots?
- From the root hair cells
- through the root cortex
- and to the xylem
Which 2 pathways can water move through the cortex?
the symplast pathway and the apoplast pathway
Describe the symplast path way in the roots
water moves from the cytoplasm of one cell to the cytoplasm of an adjacent cell. To do this, water moves through the plasmodesmata that links the adjacent cells. (osmosis )
What is the plasmodesmata?
Microscopic channels through the cell wall that connects the cytoplasm of cells
What is the symplast pathway drive by?
the water potential gradient between the root hair cells and the xylem
is the water potential of the root hair cells greater than the water potential of the cortex cells?
yes
is the symplast pathway quick or slow?
relatively slow
why is the symplast pathway relatively slow?
because the pathway for water in the cytoplasm is obscured by the organelles
describe the apoplast pathway in the roots
water moves between cell walls and the spaces between the cells by diffusion
what is the idea that water molecules are attracted to each other called?
Attraction cohesion
Why does attraction cohesion occur?
Because water molecules can form hydrogen bonds with each other and as water moves into the xylem and is carried away, more water moves along the apoplast pathway due to cohesion
which offers the least resistance to water flow- the symplast system or the apolast system?
The apoplast system
what runs around the cell wall of the endodermis of the root?
The casparian strip
What is the casparian strip?
waterproof and prevents water from moving through the apoplast pathway. Instead the water moves through the symplast pathway. This allows the cell membrane to control which substances can enter the xylem
What do cells in the endodermis of the root hair cell use to pump mineral ions into the xylem?
active transport
What happens when cells in the endodermis of the root hair cell pump mineral ions into the xylem?
the water potential of the xylem is lowered and water is triggered to move into the xylem by osmosis
Is root pressure an active or passive process?
It’s an active process, requiring energy from respiration
what happens to root pressure when you inhibit respiration using a metabolic poison such as cyanide OR when you prevent aerobic respiration by excluding oxygen?
Root pressure stops
What does the waxy cuticle do?
It reduces water loss from the surface of the leaf by evaporation
what is the pulling effect of water on xylem vessels called?
Tension
what is the transpiration stream?
The movement of water from the roots, up the xylem and out of the leaf
Can water form hydrogen bonds with molecules in the xylem vessel walls such as carbohydrates?
Yes and this attraction is called adhesion
What can be used to measure the rate of water uptake into a plant?
A potometer
What does a potometer consist of?
A fine capillary tube which is filled with water. The tube is connected to a plant which has been cut at the stem. The capillary tube is also connected to a syringe filled with water.
How can you measure the rate of water uptake by a plant using a potometer?
By measuring how far the air bubble moves in a given time
What are the 2 key features of guard cells?
-the cellulose cell wall on the inner side of the guard cell is thicker than on the rest of the cell
-some of the cellulose microfibrils in the cell wall are arranged in ring shapes
what do light conditions trigger to move into the guard cells?
solutes such as the potassium ion K +. This lowers the water potential of the interior of the guard cells.
What happens after light triggers solutes to move into the guard cell?
Because the water potential of the guard cell has been lowered, water now moves into the guard cells by osmosis and this causes the guard cells to swell. The guard cells are now turgid
What prevents the guard cells from expanding width-wise when water enters?
The rings of cellulose. So the guard cells expand lengthwise instead
does increasing humidity of the air outside of a leaf increase or reduce the rate of transpiration?
Decreases the rate of transpiration because there’s a smaller concentration gradient and so there’s no net loss of water vapour from the leaves
why does increasing the temperature increase the rate of transpiration?
Because at higher temperatures, water molecules have more kinetic energy. So, molecules will move faster out of the leaf
why does air movement, such as wind, increase the rate of transpiration?
because air movements increase the concentration gradient of water vapour
Why can the rate of transpiration also be affected by the level of water in the soil?
Because in drought conditions, the root of a plant produces a hormone. This hormone triggers the stomata to close . this reduces the rate of transpiration and reduces water lost by a plant
what are xerophytes
plants which are adapted to hot, dry conditions
What are 2 examples of xerophytes?
Cacti and marram grass
why do cacti have spines?
-because this reduces the surface area to volume ratio of the cactus and so reduces the rate of diffusion of water from the plant.
- The spines also trap moist air near the cactus, reducing the humidity and the rate of transpiration
what does sunken stomata help with?
This traps a layer of moist air around the stomata, increasing humidity, decreasing water potential gradient, and decreasing rate of transpiration
why do cacti have extensive shallow roots?
this allows the cacti to absorb water from lower levels of the soil
what are plants that can store water in their stem called?
Succulents
where are the stomata in maram grass found?
In sunken pits, with fine hairs projecting inwards towards the centre, ensures that moist air is trapped around the stomata, reduces conc gradient
which is more reactive- glucose or sucrose?
Glucose
what are molecules such as sucrose that are made as a result of photosynthesis called ?
Assimilates
what is the transport of assimilates around a plant called?
Translocation
assimilates are transported from sources to what?
Sinks
What are sources?
Where the assimilates are produced
what are examples of sources?
Photosynthesising leaves and storage organs e.g tubers
what are sinks?
Regions where assimilates are required
What is an example of a sink?
The roots and shoots
Why are the roots an example of a sink?
Because the roots carry out active transport and require the assimilate glucose for respiration
When can storage organs act as sinks?
When they’re refilling their carbohydrate stores
Describe translocation
- Proton pumps actively transport hydrogen ions out of the companion cell using active transport.
- This increases the proton concentration outside the companion cells.
- This creates a concentration gradient of hydrogen ions and so the hydrogen ions now diffuse through a co transporter protein, down the concentration gradient, and back into the cell. Whilst sucrose diffuses into the companion cell through the cotransporter protein.
- The sucrose now diffuses through the plasmodesmata from the companion cells and into the sieve tube element cells.
- This reduces the water potential of the sieve tube element cells. So, water moves into the sieve tube element by osmosis from nearby tissues such as the xylem.
- This increases the hydrostatic pressure inside the sieve tube element, so the phloem sap now moves down the sieve tube element and towards the sink.
- This bulk movement of phloem sap is called mass flow .
- At the sink, the sucrose moves out of the sieve tube element and is converted to glucose for use in respiration. Or, converted to starch.
xylem…
Where is the xylem located in the roots?
In the centre
Where is the phloem located in the roots?
surrounding the outside of the xylem
Where in the stems is the xylem located?
closer to the middle
Where in the stem is the phloem located?
outside the xylem
Where in the leaf is the xylem located?
on the
Where in the leaf is the phloem located?
on the inside
What’s happening at the P wave?
The atria are contracting
What’s happening at the QRS wave?
the ventricles are contracting (depolarising)
What’s happening at the T wave?
The ventricles are relaxing
Suggest why a bunch of flowers may survive longer if the ends of the stems are removed
immediately before the flowers are placed in water.
- Because air bubbles will be removed.
- This prevents there being a blockage in the xylem and the continuous column of water in the xylem will be restored
Describe and explain how water moves from the roots to the xylem to the leaves
- Water lost from the leaf by transpiration is replaced via the apoplast, symplast and vacuolar pathways.
- Lost water is replaced by water from the xylem.
- A pressure gradient is created in the xylem, with there being low hydrostatic pressure at the top of the xylem.
- Water moves down a pressure gradient and the water is under tension.
- Cohesion between water molecules and adhesion between water molecules and xylem walls helps water to move up the xylem by mass flow.
- Water moves up the xylem in a column of water.
6
What steps should be taken when setting up a potometer to ensure that the apparatus works correctly?
- Make sure that the shoot is healthy.
- Assemble the apparatus under water.
- Cut the end off of the shoot.
- Check that there are no air bubbles in the apparatus.
- Make sure that the apparatus is airtight and has no leaks.
- Make sure that the leaves are dry
State the adaptations of xerophytes
- Hairy leaves, to trap water vapour, decrease water potential gradient, and decrease transpiration rate.
- Stomata in sunken pits, to trap water vapour.
- Rolled leaves, trap water vapour.
- Thicker cuticle, is waterproof
- Fewer stomata, reduces the diffusion of water vapour.
- Stomata close during the day, to reduce the diffusion of water vapour.
- Most stomata are on the lower surface of the leaf, so that they experience a lesser exposure to the sun, so stomata will open less for gas exchange.
Define a parasite
- Lives on a host
- Obtains food from the host
- Harms the host
Why is malaria much more common in tropical areas than in other parts of the world?
Because the climate is warm enough and suitable for mosquitoes to survive in.
What are the differences between globular and fibrous prtoeins?
- Globular proteins are spherical, whilst fibrous proteins are linear.
- Globular proteins have hydrophilic R groups on the outside, whereas fibrous proteins have hydrophobic R groups on the outside.
- Globular proteins form hydrogen bonds with water and so are soluble in water, whereas fibrous proteins don’t.
- Globular prtoeins have a physiological role, whereas fibrous prtoeins have a structural role.
Describe how the structure of antibodies allows them to perform their function.
- Have 4 polypeptide chains that are held together by disulfide bridges.
- Have variable region, which have receptors that are specific and complemetnary in shape to antigens. This allows antibody to bind to complimentary antigens.
- Have more than one variable region. This allows antibody to attach to more than one antigen, also allows for agglutination to occur.
- Has constant region, which allows antibody to bind to the phagocyte.
- Has hinge region, which allows for flexibility of the antibody.
-
What is neutralisation?
- Where antibodies bind to toxins and prevent them from binding to the host cell.
What is agglutination?
- Where antibodies bind to many pathogens, making them too large to enter the host cell. This increases the likelihood of the pathogens being consumed by the phagocyte.
Why are phagocytes described as a secondary defence against pathogens?
because they engulf many different pathogens and because they do not have antigen-specific receptors
How are phagocytes able to pass from the blood to the tissue fluid?
- Phagocytes have a lobed nucleus and can also change shape. So, they can squeeze through the pores in the capillaries.
What can a pathogen be hydrolysed to?
amino acids and sugars. These products can then be absorbed into the cytoplasm.
What invective agent causes Tuberculosis?
M. bovis
How does a mosquito trasmit the malarial parasite to a human?
- Mosquito is a vector and so carries the parasite.
- Plasmodium is present in a mosquitoes salivary gland.
- The infected mosquito bites a human and plasmodium then passes from the saliva to the blood.
Why does the influenza vaccine have to be changed each year?
because the virus mutates each year and the antibodies will not match the antigens of the new strain of influenza.
What are some differences between the primary and secondary immune response?
- The primary response has a longer delay before the response.
- The primary response is slower than the secondary response.
- The primary response produces fewer antibodies than the secondary response.
Why aren’t antibiotis used to treat viruses?
Because antibiotics are not effective against viruses. They are only effective against bacteria.
Suggest why researchers in Nepal concentrated their research on plants that had been used
in traditional medicine.
- Because the plants have already been identified to have medicinal properties and fewer side effects.
- Because this reduces time and effort in having to find new plants.
- Could reduce costs.
What infective agent causes AIDS?
HIV
What is meant by the term health?
When someone is free from disease and has good nutrition.
How does bacteria cause food shortage?
- Bacteria divide and increase in number.
- Bactera secrete enzymes which digest food. Proteins are broken down into amino acids.
- Bacteria release toxins which change the taste and smell of the food.
Why does food spoil at higher temperatures?
- Bacteria reproduce faster at higher temperatures, so more bacteria is present at higher temperatures.
- More toxins will be relased and more enzymes will be secreted.
- Enzymes work faster at higher temperatures, as they have more kinetic energy and so more ESC’s can be formed, and more food can be broken down.
How does salting work as a method of food preservation?
It results in there being a lack of water due to osmosis
How does sugar work as a method of food preservation?
It results in there being a lack of water due to osmosis
How does freeze-drying work as a method of food preservation?
prevents enzymes from mobilising and impairs intracellular transport
How does pickling work as a method of food preservation?
the low ph denatures enzymes
How does cooking work as a method of food preservation?
high temperatures denatures enzymes
How does ionising radiation work as a method of food preservation?
damages genetic material
How does smoking work as a method of food preservation?
food becomes exposed to antibacterial chemicals.
How does vacuum packing work as a method of food preservation?
prevents microorganisms from respiring aerobically
How does food being kept in low temperatures in a freezer or a fridge work as a method of food preservation?
denatures enzymes
Identify the type of immunity provided by antibodies in breast milk.
natural passive
what is the vector for the malarial parasite?
female Anopheles
Which human cells does the malarial parasite reproduce in?
liver cells and red blood cells
Suggest why adults who have survived malaria may lose their immunity when they leave a
malarial area
- They don’t have any further exposure to the parasite so they lose immunological memory
How does fossil evidence support the idea that evolution has taken place?
- Fossils show that organisms have changed over time
- Fossils can be dated.
- Fossils show intermediate forms
What causes variation?
- Mutation
- The environment
What are the characteristics of continuous variation?
- No defined categories.
- Intermediate values
- Influenced by environment
- Quantitative and so has to be measured.
Explain why it may become increasingly difficult to discover new drugs in the future.
because new drugs often come from plants and biodiversity is redeucing due to destruction of habiatas .
-What is the respiratory quotient?
The ratio of the volume of Carbon dioxide given out in respiration to the amount of oxygen used in unit time.
At what levels can gene expression be controlled at?
- The transcriptional level
- The post transcriptional level
- The post-translational level
What controls gene expression at the transcriptional level?
Transcription factors
What are transcription factors?
Proteins that bind to DNA and switch genes on or off by increasing or decreasing the rate of transcription.
What are the 2 types of transcription factors?
- Activators
- Repressors
What do activators do?
they increase the rate of trasncription
What do repressors do?
They decrease the rate of transcription
What determines whether a transcription factor can bind to DNA or not?
The shape of the transcription factor
In eukaryotes, where do transcription factors bind?
They bind to specific DNA sites near the start of their target genes.
In prokaryotes, where do transcription factors bind?
To operons
What is an operon?
A cluster of structural genes that are transcribed together, and also control elements and sometimes a regulatory gene.
What do the control elements include?
- A promoter
- An operator
What is a promoter?
A DNA sequence located before the structural genes that RNA polymerase binds to
What is an operator?
A DNA sequence that transcription factors bind to
What does the bacteria E.coli typically respire?
Glucose
What can the bacteria E.coli respire if glucose isn’t available?
Lactose
Where are the genes that produce the enzymes needed to respire lactose found?
On an operon called the Lac Operon.
What 3 structural genes does the lac operon have?
- lac Z
- lac Y
- lac A
What happens when lactose isn’t present?
- The regulatory gene produces the lac repressor.
- The lac repressor is a transcription factor that binds to the operator site when there’s no lactose present.
- This blocks transcription because RNA polymerase can’t bind to the promoter .
What happens when lactose is present?
- Lactose binds to the repressor.
- This changes the repressor’s shape so that the repressor can no longer bind to the operator site.
- RNA polymerase can now begin the transcription of the structural genes.
what structural detail of a polypeptide is altered by gene mutations?
the base sequence
how is it possible for a mutation to have no effect on the protein produced from that gene?
- Some triplets code for the same amino acid, so the amino acid sequence isn’t altered.
- Some alternative amino acids will not alter the shape of the protein.
- The mutation may occur in the intron.
How could a mutation alter the protein so that it no longer performs its correct function in the cell?
- An insertion or deletion may result in a frameshift mutation.
- All triplets downstream will be different.
- The protein will have a different sequence of amino acids.
- The tertiary structure of the protein will be different.
Describe and explain how a tiger with striped fur may have evolved from a non-striped ancestor.
- This may have occurred by natural selection.
- There may have been a selection pressure of prey availability.
- So the adaptation of striped fur may have helped tigers to camoflage and hide from prey.
- So striped tigers would have had a greater survival probability and so were more likely to reproduce.
- Advantageous alleles would have been passed on to the next generation.
- the allele frequency for the
relevant genes would have
increased with each generation
and after many generations, all tigers within a population were striped.
What do regulatory genes do?
code for proteins that control the expression of structural genes.
What do the structural genes do?
codes for a protein that has a function within a cell
How can transcription be controlled in eukaryotes?
- Hormone enters a cell and binds to a transcription factor.
- The transcription factor will then be activated and will bind to a promoter.
- This will allow RNA polymerase to bind to the promoter.
How can gene expression be regulated after transcription?
- The primary mRNA is modified.
- Introns are removed to make mature mRNA.
- Alternative splicing can produce different versions of mRNA.
Why are fruit flies chosen for research into genes controlling the development of the body plan?
- There’s less ethical concerns
- Low cost
- Rapid reproduction rate
- The genetics of fruit flies is well understood.
- They have a simple body plan
-
Why are mice usually used or research into genes controlling the development of the body plan, despite there being some ethical concerns?
- low cost
- share some genes with humans
- more than one species is needed to demonstrate the conservation of base sequences.
do species that have diverged recently share a similar base sequence?
Yes
Why do non-coding regions of DNA show more variation?
- Because they are not selected against
Do homeobox genes enable proteins to work as transcription factors?
Yes
WHat does RNA polymerase do?
- makes RNA via transcription
What does DNA polymerase do?
- Allows for DNA replicatio, where 2 polypeptide strands are produced.
What is programmed cell death?
Apoptosis
What do hox genes do?
They determine the identity of embryonic body regions along the anterior-posterior axis (i.e. the head-tail axis)
What is a homeobox gene?
A homeotic gene that initiates transcription and controls the development of the body plan.
Why has there been little change by mutation in homeobox genes?
Because these genes are very important so any mutations are likely to be lethal
Which animal kingdoms have similar homeobox genes?
Animals, fungi, plants
What feature of the DNA molecule is changed as a result of mutation?
The order of bases
What are the purposes of plant collection in a modern botanic garden?
- Saving endangered plants
- A gene bank
- Education
- Aesthetic value
What is the role of PCR?
To amplify copies of DNA, at a range of different lenghts
What is the role of electropheresis?
To put Dna pieces in size order, and to read the order of bases
What is the role of the digestion of DNA by restriction enzymes?
- To cut DNA into smaller fragments.
- To cut vectors
Why does a genome have to be fragmented before sequencing?
- Because the genome is too big
- Fragmenting genomes allows for better accuracy when sequencing, and allows the job to be divided over different labs
What is a regulatory gene?
A gene that makes transcription factors
What is a structural gene?
A gene that makes a protein, such as an enzymes
What is the relationship between regulatory genes and structural genes?
Regualatory genes control the expression of structural genes
How is gene expression regulated at the post-translational level?
- Certain molecules, like hormones, bind to cell membranes and trigger the production of cAMP inside the cell.
- cAMP then activates proteins inside the cell by altering their 3D structure.
- Altering the 3D structure can change the active site of an active site, making it more or less active.
How does cAMP activate PKA?
- cAMP binds to PKA and causes the shape of the enzymes 3D structure to change, releasing the active subunits.
- PKA is now active
Substtitution. Insertion. Deletion
Beneficial. Neutral. Harmful
What are the 3 main ways a mutation can occur?
- Substitution
- Insertion
- Deletion
What can form frameshift mutation?
Insertion and deletion
What is a function of the cerebellum?
- Coordination of posture
What is a function of the medulla oblongata?
- control of heart rate
What is a function of the hypothalmus?
- control of temperature regulation
What is a function of the cerebrum?
- control of speech
Somatic nervous system
- voluntary
- output to skeletal muscles
Autonomic nervous system
- involuntary
- output to smooth muscles and glands
Sympatheitc motor system
- ‘fight or flight
- neurotransmitter = noradrenaline
- adrenergic system
Parasympathetic motor system
- relaxing
- neurotransmitter = acetycholine
- cholinergic
Good
luck!
What do exocrine glands do?
They secrete substances into a duct
What do endocrine glands do?
They secrete hormones into the blood
What is adenyl cyclase?
An enzyme located on the inside of the cell surface membrane
Where is adrenaline released from?
Adrenal medulla
What is a first messenger?
A hormone that transmits a signal around the body
What does a secondary messenger do?
It transmits a signal inside the cell i.e cAMP
What cells secrete glucagon?
Alpha cells
What cells secrete insulin?
Beta cells
What does thyroxine do?
Accelerates metabolism
What is the difference between type 1 and type 2 diabetes?
- In type 1 diabetes, insufficient insulin is produced
- In type 2 diabetes, the body becomes resistant to insulin.
What is the difference between hormonal and neuronal communication?
- hormonal: chemical response, slow response, effect lasts longer
- neuronal: electrical impulse, fast response, effect lasts for a shorter period of time
What is the apical bud?
The shoot tip at the top of a flowering plant
What does auxin do?
It stimulates the growth of the apical bud and inhibits the growth of side shoots from lateral buds
Where is auxin produced?
In the tips and shoots of flowering plants
What is auxin used in?
- Weed killers
- Rooting powders
What are the functions of abscisic acid?
- Induced dormancy in some seeds
- Closes stomata during water shortage
- Helps defend against the attack of insects
- Inhibits stem growth in response to water stress
- Causes the synthesis of some storage proteins in seeds
What does ethene do?
- Causes leaves to drop off
- Speeds up ripening
- Controls cell division during plant growth
What inhibits giberellins ?
Abscisic acid
What are the uses of giberellins?
- seed germination
- promotes flowering in long-day plants
- prevents leaf abscission
- promotes the activity of amylase
What are the functions of cytokinins?
- Induces cell division
- Causes the growth of lateral buds
- Causes leaf expansion
- Delays leaf senescence
- Promotes cholroplast development in leaves
-
What are the uses of cytokinins?
- Used by farmers to increase the yield of crops
What is the function of a syringe in a respirometer?
To reset the respirometer
What is the respiratory quotient?
The ratio of the volume of CO2 given out in respiration to the volume of oxygen used in respiration
Is cystic fibrosis a mutation?
Yes
How does cyctic fibrosis affect the phenotype?
Cystic fibrosis causes there to be thick mucous in the lungs, and people with cyctic fibrosis are often small in size and have poor digestion
why is it important for mammals to be able to detect changes in their internal environment
- To allow for homeostasis to occur
- ## So that enzymes work efficiently
What receptors detect chemicals?
Chemoreceptors
What receptors detect pressure?
Mechanoreceptors (Pacinian corpuscle)
What receptors detect blood pressure changes?
Baroreceptors
What receptors detect changes in blood water potential?
Osmoreceptors
Describe the sampling techniques that biologists could use to show how the distribution and abundance of organisms change across a habitat
- They could identify the species present and use keys to do so.
- They could use a quadrat and place it randomly along a belt transect.
- They could use an abundance scale
- They could use capture recapture for animals.
- They could repeat the experiment and calculate a mean.
What is the importance of sampling in measuring the biodiversity of a habitat?
- It is impossible to count every individual, so sampling provides an estimate of the number of individuals in a species.
- And the sample will be representative of the whole area.
Outline the significance of a low value of Simpson’s Index of Diversity.
- The habitat is dominated by one species.
- The habitat is less likely to cope with change
Why it is sometimes necessary to conserve a plant species, such as N. thermarum,
outside its natural habitat (ex situ)?
- The natural habitat may be destroyed by deforestation.
- The population in the natural habitat may be very low.
- In the wild, sexual reproduction if difficult if the numbers are very low.
- Breeding ex situ can maintain the gene pool.
- Breeding ex situ allows protection from herbivores or grazers.
- Protects the plant species from disease
Outline an unbiased sampling method that can be used to measure the biodiversity of plant species in grassland.
- Use a random number generator to randomly generate coordinates.
- Use a quadrat and place the quadrat at the random coordinates.
- Count the number of different species in each quadrat.
- Use an identification key in order to identify the different species present in each quadrat.
- Use ACFOR to determine the abundance of each species.
- Repeat 2 more times in order to calculate a running mean.
- Sample at different times of the year.
What is the role of a gene?
a gene codes for a polypeptide
Suggest three ways that farmers can maximise the efficiency of the transfer of energy up food chains from primary consumers to humans
- keep animals, warm / indoors
- feed animals high, protein / energy, food
- selective breeding for improved animals
- slaughter animals just befoe they’re full size
What is excretion?
The removal of the waste products of metabolism from the body
What are the functions of the liver?
-The removal of excess amino acids
- The removal of harmful substances from the body
- Stores glycogen
How are excess amino acids broken down by the liver?
- The amino groups (NH2) are removed from proteins, forming ammonia and organic acids. This process is called deamination.
- Ammonia is then binded with CO2 in the ornithine cycle to create urea.
- The urea is then released from the liver into the blood . The kidneys then filter the blood and remove the urea as urine. The urine is then excreted from the body.
What harmful substances, other than urea, does the liver break down?
- Alcohol
- Drugs
- Unwanted hormones
Describe how the liver breaks down alcohol (ethanol)?
- Ethanol is a toxic substance that can damage our body cells
- The liver breaks down ethanol into ethanal.
- Ethanal is consequently broken down into a much less harmful substance called acetic acid, which is excreted from the body
What happens to us if there’s excess alcohol in the body?
- This can lead to cirrhosis of the liver.
- This is where the cells of the liver die and scar tissue blocks the blood flow
Why is paracetamol broken down by the liver?
Because excess paracetamol in the blood can lead to liver and kidney failure
What are the main veins, arteries, and ducts of the liver?
- The hepatic artery
- The hepatic vein
- The hepatic portal vein
- The bile duct
What does the hepatic artery do?
It supplies the liver with oxygenated blood from the heart, so the liver has a good supply of oxygen for respiration.
What does the hepatic vein do?
It takes deoxygenated blood away from the liver
What does the hepatic portal vein do?
- Brings blood from the small intestine rich in the products of digestion to the liver.
- This allows for any ingested harmful substances to be filtered out and broken down by the liver straight away.
What does the bile duct do?
It takes bile to the gallbladder to be stored
Is the hepatic artery narrower than the hepatic vein?
Yes, because it is transporting high pressure oxygenated blood from the heart to the liver
What is the liver made up of?
- Lobules.
- These are cylindrical structures made up of hepatocyte cells that are arranged in rows radiating from the centre
What does each lobule have in the middle?
A central vein that connects to the hepatic vein.
What are the hepatic artery and the hepatic portal vein connected to the central vein by?
Veins called sinusoids
How does blood run through the sinusoids?
- Past the hepatocytes that remove harmful substances and oxygen from the blood
- These harmful substances are broken down into less harmful substances by the hepatocytes and they then reenter the blood.
- The blood runs to the central vein and the central veins from all lobules conect up to form the hepatic vein
What are kupffer cells attached to ?
The walls of the sinusoids
What do kupffer cells do?
Remove bacteria and break down old red blood cells
Which cells in the liver produce bile?
The hepatocytes
What is a nickname for the kupffer cells?
The macrophages of the liver
Bile from hepatocytes->
Into canaliculi -> into bile ducts -> into gall bladder
What are the functions of the kidneys?
-to excrete waste products
Give an overview of how the kidney excretes waste products
- Blood enters the kidney through the renal artery and then passes through the capillaries in the cortex of the kidneys.
- As the blood passes through the capillaries, substances are filtered out of the blood and into long tubules that surround the kidneys. This process is known as ultrafiltration.
- Useful substances, like glucose, are reabsorbed back into the blood from the tubules in the medulla and the cortex. This is called selective reabsorption
- The remaining unwanted substances pass along the tubules, then along the ureter to the bladder, where they’re passed out as urine.
- The filtered blood passes out of the kidneys through the renal vein
What are nephrons?
the long tubules along with the bundle of capillaries where the blood is filtered out
Describe the process of filtration in the nephrons?
- Blood from the renal artery enters smaller arterioles in the cortex.
- Each arteriole splits into a structure called a glomerulus, a bundle of capillaries looped inside a hollow balled called the Bowman’s capsule.
- The glomerulus is where ultrafiltration takes place.
- The arteriole that takes blood in blood into each glomerulus is called the afferent arteriole, ad the arteriole that takes the filtered blood away is called the efferent arteriole.
- The efferent arteriole is smaller in diameter than the afferent arteriole, so the blood in the glomerulus is under high pressure.
- The high pressure in the glomerulus forces liquid and small molecules in the blood out of the glomerulus and into the bowman’s capsule.
- The liquid and small molecules pass through 3 layers to get into the Bowman’s capsule and enter the nephron tubule: the basement membrane and the epithelium of the bowman’s capsule.
- The liquid and small molecules, now called filtrate, pass along the rest of the nephron and useful substances are reabsorbed along the way.
- Finally, the filtrate flows through the collecting duct and passes out of the kidney along the ureter.
Where does selective reabsorption take place?
as the filtrate flows along the proximal convulated tubule (PCT), through the loop of Henle, and along the distal convulated tubule
is it true that useful substances leave the tubules of the nephrons and enter the capillary network that’s wrapped around them?
yes
why is the epithelium of the wall of the proximal convulated tubule covered in microvilli?
to provide a large surface area for the reabsorption of useful materials from the filtrate into the blood
what useful substances are reabsorbed along the proximal convulated tubule?
glucose, amino acids, vitamins, and some salts
why does water enter the blood surrounding the proximal convulated tubule by osmosis?
because the water potential of the blood is lower than that of the filtrate
Where does selective reabsorption take place?
As the filtrate flows along the proximal convulated tubule, through the loop of henle and along the distal convulated tubule
Why does the epithelium of the wall of the proximal convulated tubule have microvilli?
To provide a large surface area for the reabsorption of useful materials from the filtrate into the blood
What happens if the water potential of the blood is too low?
More water is reabsorbed by osmosis into the blood from the tubules of the nephrons. This results in the urine being more concentrated and less water being lost during excretion
What happened if the water potential of the blood is too high?
Less water is reabsorbed by osmosis into the blood from the tubules of the nephrons. This means that the urine is more dilute, so more water is lost during excretion
What 2 limbs is the loop of henle made up of?
The descending limb and the ascending limb. They have a mechanism called the countercurrent multiplier mechanism. This mechanism helps to reabsorbed water back into the blood
Describe the process of the countercurrent multiplier mechanism in the loop of henle
1) Near the top of the ascending limb, sodium and chloride ions are actively pumped out of the loop of henle and into the medulla.
The ascending limb is impermeable to water, so the water stays inside the tubule.
This creates a low water potential in the medulla because there’s a high concentration of ions in the medulla.
2) Because there’s a lower water potential in the medulla than in the descending limb, water moves out of the descending limb and into the medulla by osmosis.
As a result, the filtrate becomes more concentrated and the water in the medulla is reabsorbed into the blood through the capillary network
3) Near the bottom of the ascending limb, sodium and chloride ions diffuse out into the medulla
4) Hence, the ion concentration in the medulla massively increases and its water potential lowers.
This causes water to move out of the collecting duct by osmosis
The water in the medulla is reabsorbed into the blood through the capillary network
What type of receptors does the hypothalmus have?
osmoreceptors
When are hormones secreted?
When an endocrine gland is stiimulated
How can an endocrine gland be stimulated?
- By another hormone
- By electrical impulses
Is a hormone a first messenger?
Yes
Outline how the hormone adrenaline acts as a first messenger
- Adrenaline binds to specific receptors in the cell membrane of many cells.
- When adrenaline binds, it activates an enzyme in the cell membranae called adenyl cyclase.
- Activated adenyl cyclase catalyses the production of a second messenger called cAMP from ATP.
- cAMP then activates a cascade.
Where are the adrenal glands found?
Just above the kidneys
What is the outer part of the adrenal gland called?
The cortex
What is the inner part of the adrenal gland called?
The medulla
What does the cortex of the adrenal glands do?
the cortex secretes steroid hormones when you’re stressed e.g. cortisol, aldosterone
What are some examples of steroid hormones?
- Cortisol
- Adrenaline
Can the effects of steroid hormones be both short term and long term?
Yes
What are the functions of steroid hormones?
- Breakdown of proteins and fats into glucose. This increases the amount of energy available so that the brain and the muscles can respond to the situation.
- Increases the blood volume and pressure by increasing the uptake of sodium ions and water by the kidneys.
- Suppresses the immune system.
What does the medulla of the adrenal glands do?
- Secretes catecholamine hormones when you’re stressed, i.e adrenaline and noradrenaline.
What are examples of catecholamine hormones?
- Adrenaline
- Noradrenaline
What are the functions of catecholamine hormones?
- Increasing the heart rate and the breathing rate.
- Causing cells to break down glycogen into glucose.
- Constricting some blood vessels, so that blood is diverted to the brain and the muscles.
Is the pancreas and endocrine gland?
Yes
What is the area of the pancreas that contains endocrine tissue?
The islets of langerhan
Where are the islets of langerhan found?
In the pancreas
Is it true that the islets of langerhan are found in clusters around blood capillaries and so they secrete hormones directly into the blood?
Yes
What types of cells are found in the islets of langerhan?
Alpha cell and beta cells
What do alpha cells do?
They secrete a hormone called glucagon.
What do beta cells do?
They secrete a hormone called insulin
Should beta cells be stained darker or lighter?
Darker
Can ectotherm scontrol their body temperature internally?
No, so they change their behaviour
What is a behaviour carried out by ectotherms to increase their body temperature?
Basking in the sun
Is it true that ectotherms have a variable metabolic rate and that they generate very little heat themselves?
Yes
Is it true that endotherms constantly have a very high metabolic rate and that they generate a lot of heat from metabolic reactions?
Yes
What are mechanisms carried out by endothems to reduce the internal body temperature?
- Sweating. The water in sweat evaporates from the skin’s surface and takes heat from the body. This cools the skin.
- Hairs lie flat. This prevents a layer of hot air being trapped on the skin’s surface.
- Vasodilation occurs. Arterioles near the skin’s surface dilate, so more blood flows closer to the skin’s surface, and so more heat is lost.
What are mechanisms carried out by endothems to increase the internal body temperature?
- Shivering. Muscle contraction produces more heat by respiration.
- Less sweating. Less water evaporates from the skin’s surface.
- Hairs stand up. This traps more hot air and prevents heat loss.
- Vasoconstriction. Arterioles near the skin’s surface constrict, so less blood flows through the capillaries that are close to the skin’s surface. This reduces heat loss.
- Hormones such as adrenaline and thyroxine are produced. These hormones increase metabolism and result in more heat being produced.
What controls the internal body temperature?
The hypothalmus in the brain, which has thermorecepetors
What happens when the body temperature is too high?
- Thermoreceptors detect that the body temperature is too high.
- The hypothalmus sends signals to the effectors.
- A response is carried out in the form of vasodilation etc
- More heat is lost and less heat is produced by the body.
- Body temperature returns to 37 degrees celcius.
What happens when the body temperature is too low?
- Thermoreceptors detect that the body temperature is too low.
- The hypothalmus sends signals to the effectors.
- Response is carried out in the form of vasoconstriction etc
- More heat is produced.
- The body temperature returns to 37 degrees celcius.
What happens when the blood glucose concentration is too high?
- The pancreas detects that the blood glucose concentration is too high.
- Beta cells secrete insulin.
- Insulin binds to receptors on the liver and muscle cells.
- Cells take up more glucose; glucose is converted to glycogen ; cells respire more glucose.
- There is now less glucose in the blood.
What happens when the blood glucose concentration is too low?
- The pancreas detects that the blood glucose concentration is too low.
- Alpha cells secrete glucagon.
- Glucagon binds to receptors on liver cells.
- Glycogen is converted back to glucose; glucaneogenesis is activated; cells respire less glucose.
- Liver cells release glucose into the blood
When do beta cells secrete insulin?
When they detect high blood glucose concentrations
describe the role of beta cells in the secretion of insulin into the blood
- When the blood glucose concentration is high, more glucose enters the beta cells by facilitated diffusion.
- More glucose in a beta cell causes the rate of respiration to increase, making more ATP.
- The rise in ATP triggers the potassium ion channels in the beta cell plasma membrane to close.
- This means that Potassium ions can’t get through the membrane, so they build up beta inside the cell.
- This makes the inside of the beta cell less negative, so they build up inside the cell.
- This makes the inside of the beta cell less negative, so the plasma membrane of the beta cell is depolarised.
- Depolarisatiom triggers Calcium ion channels in the membrane to open, so Ca²+ ions diffuse into the beta cell.
- This causes the vesicles to fuse with the beta cell membrane, releasing insulin by exocytosis.
Describe type 1 diabetes
- No insulin is produced
- Is genetic
What are the treatments for type 1 diabetes?
- Regular insulin injections throughout the day.
- An insulin pump, which continuously delivers insulin into the body via a tube inserted beneath the skin.
- Islet cell transplantation
Describe type 2 diabetes
- linked to obesity
- the beta cells don’t produce enough insulin or the body cells don’t respond properly to insulin.
What treatments are used for type 2 diabetes?
- Metformin, sulfonylureas, thiazolidinediones
- Insulin therapy
Can human insulin be made from GM bacteria?
Yes
What are the advantages of using insulin from GM bacteria ?
- It’s cheaper than extracting insulin from animal pancreases.
- Large quantities of insulin can be produced using GM bacteria.
- GM insulin is less likely to cause allergic reactions.
- Some people prefer insulin from GM bacteria for ethical or religious reasons
Can stem cells be grown into beta cells?
Yes
Describe how stem cells can be grown into beta cells
- The beta cells would be implanted into the pancreas of a person with type 1 diabetes.
- This means that the person would be able to make insulin as normal.
What is homeostasis?
Maintaining a stable internal environment within narrow limits, even though the environment is changing.
What two systems does the nervous system consist of?
The PNS and the CNS
What does the PNS control?
The somatic nervous system and the autonomic nervous system
What does the Somatic Nervous system control?
Conscious activities
What does the Autonomic Nervous system control?
Unconscious activities
What does the Autonomic nervous system consist of ?
The sympathetic nervous system and the parasympathetic nervous system,
Describe the sympathetic nervous system
- ‘fight or flight’
- Releases the neurotransmitter noradrenaline
Describe the parasympathetic nervous system
- Calms down the body
- Releases the neurotransmitter acetylcholine
What neurotransmitter is released by the sympathetic nervous system?
Noradrenaline
What neurotransmitter is released by the parasympathetic nervous system?
acetylcholine
Where is the hypothalmus located?
Beneath the middle part of the brain
What is the role of the hypothalmus?
Maintaining body temperature
What hormones does the hypothalmus produce?
Hormones that control the pituitary gland
What part of the brain is the cerebrum?
The largest part of the brain
What is the role of the cerebrum?
Involved in vision, hearing, learning, thinking
Where in the brain is the pituitary gland found?
Beneath the hypothalmus
What is the pituitary gland controlled by?
The hypothalmus
What is the role of the hypothalmus?
Releases hormones and stimulates other glands to release hormones
Where in the brain is the Medulla Oblongata found?
At the base of the brain, at the top of the spinal cord.
What is the role of the Medulla Oblongata?
Automatically controlling the breathing rate and the heart rate
Where is the cerebellum found?
Underneath the cerebrum
What is the role of the cerbellum?
Muscle coordination, posture, co-ordination of balance
Describe the blinking reflex
- Sensory nerve endings in the cornea are stimulated by touch
- A nerve impulse is passed along the sensory neurone to a relay neurone in the CNS.
- The impulse is then passed from the relay neurone to the motor neurones.
- The motor neurones send impulses to the effectors.
- The orbicularis muscles that move your eyelids contract, causing your eyelids to close quickly and preventing your eye from being damaged.
Describe the knee-jerk reflex
- Stretch receptors in the quadriceps muscle detect that the muscle is being stretched.
- A nerve impulse is passed along a sensory neurone, which communicates directly with a motor neurone in the spinal cord.
- The motor neurone carries the nerve impulse to the effector, the quadricep muscle, causing it to contract, so that the lower leg moves forward quickly.
Describe the fight or flight response
- Nerve impulses from sensory neurones arrive at the hypothalmus, activating both the hormonal system and the sympathetic nervous system.
- The pituitary gland is stimulated to release a hormone called ACTH. This causes the cortex of the adrenal gland to release steroidal hormones.
- The sympathetic nervous system is activated, triggering the release of adrenaline from the medulla region of the adrenal gland.
is it true that the rate at whoch the SAN fires is unconsciuosly controlled by a part of the brain called the medulla?
Yes
What happens if a high blood pressure is detected?
- Baroreceptors in the heart detect a high blood pressure.
- Electrical impulses are sent to the medulla, which send impulses along the vagus nerve.
- This secretes acetycholine, which binds to receptors on the SAN.
- The heart rate then slows down to reduce blood pressure back to normal.
What happens if a low blood pressure is detected?
- Baroreceptors detect low blood pressure.
- Impulses are sent to the medulla, which sends impulses along the accelerator nerve.
- This secretes noradrenaline, which binds to receptors on the SAN.
- The heart rate speeds up to increase the blood pressure back to normal.
What is a conjugated protein?
- A protein that has a non-protein prosthetic group, which is attached to the protein by covalent bonds.
Why is a reduced heart rate sometimes seen in people who are very aerobically fit?
- Because they have an increased stroke volume.
- Because their heart muscle is stronger
What is glycogenesis?
The conversion of glucose into glycogen
What is gluconeogenesis?
Creating glucose from other molecules i.e amino acids.
What are the features of a good communication system?
- Covers the whole body
- Allows one cell to communicate with another specific cell.
- Allows a cell to communicate with many cells.
- Is fast
- Allows for both long term messaging and short-term signalling.
How is the structure of the mitochondrial membranes related to the function of a mitochondrion?
- Contains an electron transport chain.
- Location for chemiosmosis.
- Allows for the creation of proton gradients.
-
Do trachea have cartilage, elastic fibres, and goblet cells?
- Have cartilage
- Have elastic fibres
- Have goblet cells
Do bronchi have cartilage, elastic fibres, and goblet cells?
- Have cartilage
- Have elastic fibres
- Have goblet cells
Do bronchioles have cartilage, elastic fibres, and goblet cells?
- Don’t have cartilage
- Have elastic fibres
- Don’t have goblet cells
Do alveoli have cartilage, elastic fibres, and goblet cells?
- Don’t have cartilage
- Have elastic fibres
- Don’t have goblet cells
In sensory neurones, is the cell body in the middle ?
Yes
Does the autonomic nervous system contain sensory and motor neurones?
Yes
Are NAD and FAD examples of coenzymes?
Yes
In a respirometer, is the rate of the movement of the liquid in the capillary tube a measure of the rate of respiration?
Yes
Can water molecules pass through the casparian strip?
No
Which subdivision of the peripheral nervous system supplies to the SAN?
The autonomic nervous system
Why is the knee jerk reflex an example of a spinal reflex?
Because it only goes through the spinal cord
Why is the blinking reflex an example of a cranial reflex?
Because the pathway goes through the brain
Why are reflexes very fast?
Because they only involve one or two synapses, which are the slowest parts of nerve transmission
what statistical test is used when 2 means are being compared?
the t-test
What causes oncotic pressure?
The imbalance of large plasma proteins between the blood and tissue fluid.
What are the 3 types of muscle?
- Cardiac
- Involuntary (smooth)
- Voluntary
Where is cardiac muscle found?
In the heart
What is another name for involuntary musclce?
Smooth muscle
Where is involuntary muscle found?
- Arteries
- Veins
- Respiratory system
- Digestive system
What is another name for voluntary muscle?
Skeletal muscle
Is it true that skeletal muscle attaches to the bone and causes the skeleton to move?
Yes
What does the sarcoplasmic reticulum do ?
Stores calcium ions, which trigger muscle contraction
What do muscle cell smake up?
Muscle fibres
Is it true that muscle fibres are very long with many nuclei and mitochondria?
Yes
What is the muscle cytoplasm called?
The sarcoplasm
Do muscle fibres have a high number of myofibrils?
Yes
What 2 types of filament are myofibrils made up of?
- Myosin (thick)
- Actin (thin)
What repeating units are myofibrils divided up into?
Sarcomeres
I- band….
the lightest part with only actin fibres
A-band…
the darkest part with both actin and myosin fibres
H-zone…
in the centre of the A-band and has myosin fibres only
What happens to the I band during contraction?
It narrows
What happens to the H-zone during contraction?
It narrows
What happens to the sarcomere length during contraction?
It shortens
What happens to the distance between the Z line during contraction?
It shortens
What happens to the A-band during contraction?
It stays the same
Do myosin filaments have a globular head?
yes, and this globular head faces outwards
what are actin filaments made up of?
actin, tropomyosin, troponin
Describe the sliding filament theory
- An action potential arrives at the end of a motor neurone.
- Acetycholine is released and causes an action potential in the sarcolemma.
- The action potential is carried by invaginations of the cell membrane called T-tubules.
- The action potential causes the sarcoplasmic reticulum to release calcium ions into myofibrils.
- Calcium ions bind to troponin on thin filmanet (actin) which changes shape. This moves tropomyosin into a groove.
- Myosin heads bind to actin to form actomoyosin cross-bridge and the cross-bridge cycle can now take place.
- The myosin head is temporarily bound to ATP and it swivels to a new angle, using the energy from ATP. This causes the actin filaments to slide past myosin filaments.
- Myosin head remains attached until new ATP binds with it, this reprimes them for repeated movement as long as ATP and Ca2+ are present.
- Ca2+ actively taken back into vesicles of sarcoplasmic reticulum until next depolarization
During anaerobic respiration, pyruvate is converted to lactate by lactate fermentation. WHat is the problem with lactate build up in the muscles?
Can cause muscle fatigue
How is ATP made in muscle cells?
By phosphorylating ADP. The phosphate croup is taken from creatine phosphate.
Does creatine phospahte act as a reserve of phosphate?
Yes
Describe the ATP-CP system
it’s anaerobic and its alactic
WHEN TALKING ABOUT LIGNIN ALWAYS SAY PROVIDES SUPPORT
ATP is needed to break the links
between myosin and actin so they remain attached
When is primary metabolite production at its highest rate?
During the exponential phase
When are most secondary metabolites produced?
During the stationary phase
What is a primary metabolite?
- A molecule needed for the cell’s normal growth and development, for example, glucose.
Temperature and pH can be changed to optimum in a fermenter
Oxygen and nutrient concentration can be increased in a fermenter.
what is recombinant DNA?
DNA combined from 2 organisms
What is a primary metabolite?
A molecule needed for the cell’s normal growth and development, for example, glucose.
What are the disadvantages of animal cloning?
- There’s no genetic variation in a population, meaning that the population will be more susceptible to disease.
- Cloned animals may have shorter life spans.
- The cloning success rate is very poor.
- Cloning is very labour intensive.
What is biotechnology?
The large scale industrial use of living organisms
REDUCED DOWnstream processing
Immobilised enzymes
What are some disadvantages of immobilised enzymes
- Higher initial costs
- Fewer exposed active sites
- The immobilisation method may affect the shape of the active site
Features of an efficient exchange system
- A good blood supply to maintain the concentration gradient
- A short diffusion pathway
