Year 1 Model Answers Flashcards
Describe Condensation Reactions
Monomers are joined together producing a larger molecule forming a bond.
A molecule of water is formed in this process
Describe Hydrolysis
Polymers and dimers are split a part breaking bonds
A water molecule is formed in this process
Name the bonds in biological molecules
glucose + glucose –>
glucose + galactose –>
glucose + fructose –>
glucose + glucose –> maltose (malt sugar)
glucose + galactose –> lactose (milk sugar)
glucose + fructose –> sucrose (table sugar)
Describe the structure and function of starch
Alpha glucose monomers
Polysaccharide
Has 1-4 glycosidic bonds
Amylose is helical
Amylopectin is branched and has additional 1-6 glycosidic bonds
Insoluble so doesn’t effect water potential
Branched so accessible for respiration
Describe the structure and function of glycogen
Alpha glucose monomers
Polysaccharide
Has 1-4 glycosidic bonds
Is branched and has many additional 1-6 glycosidic bonds
Highly branched so accessible for respiration
Describe the structure and function of cellulose
Beta-glucose monomers
Polysaccharide
Has 1-4 glycosidic bonds with alternating molecules being rotated by 180 degrees
Straight, unbranched chains
Straight chains ideal for cell wall, have crosslinks for stability
Describe the test for reducing sugars
Add Benedict’s reagent
Boil in a waterbath
Brick red colour indicates a reducing sugar
E.g. glucose
Describe the test for a non-reducing sugar
Carry out benedict’s test and see a negative result
Boil in a water bath with hydrochloric acid
Neutralise the acid with sodium hydrogen carbonate
Carry out Benedict’s test – a brick red result indicates a reducing sugar.
E.g. sucrose (this is the only one you need to remember)
Describe the test for starch
Add iodine to food sample
Blue/Black indicates starch is present
Describe the structure of amino acids and how they are joined
Amino acids contain C, O, H and N
They have a carboxyl group and an amine group
They also have an R group which can change the properties of the amino acid
There are 20 amino acids
They react in a condensation reaction and are joined by a peptide bond
A polymer of amino acids is called a polypeptide
Describe protein structure
Proteins have a primary structure that is formed by a sequence of many amino acids that are joined by peptide bonds in a condensation reaction
The primary structure folds into a secondary structure of either alpha helix or beta pleated sheets and these are held together by hydrogen bonds
The secondary structure further folds into a tertiary 3D structure that is held together by hydrogen bonds, ionic bonds and disulphide bonds
Some proteins e.g. antibodies may form a quaternary structure of more than one polypeptide chain(some of these may have prosthetic groups e.g. haem)
Describe the test for protein
Add Biurets reagent to sample (copper sulphate and sodium hydroxide)
Mix and heat
Lilac colour indicates protein is present
Describe the structure and function of triglycerides
Condensation of one glycerol and three fatty acids forming and ester bond
Fatty acids have an R group that can be saturated(C-C) or unsaturated (C=C)
Triglycerides are non-polar
Insoluble
Can’t form a bilayer
Used for longer term energy storage
Describe the structure and function of a phospholipid
Condensation reaction forming ester bonds
One glycerol and two fatty acids
One fatty acid is replaced by a phosphate group
The phosphate group is polar
The fatty acids are non-polar
Insoluble
Used in the phospholipid bilayer
Describe the emulsion test
Mix sample with ethanol and shake
Add water
If lipid is present a milky white emulsion will be seen
Describe enzyme induced fit
Enzyme active site is complementary to the substrate
When substrate binds the enzyme changes shape slightly
This stresses the bonds in the substrate
Reducing the activation energy for the reaction
The reaction occurs quicker
Describe competitive inhibitors
Binds to active site
Blocks active site so substrate can’t bind
Fewer enzyme-substrate complexes form
Describe non-competitive inhibitors
Binds to allosteric site
Changes tertiary structure
Enzyme is no longer complementary to substrate
Fewer enzyme-substrate complexes form
Describe DNA structure
DNA is made of a polymer of nucleotides/polynucleotide
It is two molecules that are antiparallel to each other coiled into a double helix.
Each nucleotide is made of deoxyribose, a phosphate group and a nitrogenous base that can either be adenine, cytosine, thymine or guanine
The adjacent nucleotides are joined to each other between the sugar and phosphate groups in a condensation reaction forming a phosphodiester bond
Complementary base pairing holds the two strands together due to hydrogen bonds forming between A - T and C - G.
Describe DNA replication
DNA helicase breaks the hydrogen bonds causing the strands to separate
Both strands act as a template
Free nucleotides complementary base pair to the template A-T and G-C
DNA polymerase joins adjacent nucleotides together forming a phosphodiester bond
Hydrogen bonds form between the old strand and the newly synthesised strand
DNA replication is semi-conservative replication
Describe ATP structure
DNA helicase breaks the hydrogen bonds causing the strands to separate
Both strands act as a template
Free nucleotides complementary base pair to the template A-T and G-C
DNA polymerase joins adjacent nucleotides together forming a phosphodiester bond
Hydrogen bonds form between the old strand and the newly synthesised strand
DNA replication is semi-conservative replication
Describe the properties of water
It is a metabolite in hydrolysis/condensation reactions
A solvent so metablic reactions can occur
High specific heat capacity to buffer changes in temperature
High latent heat of vaporisation providing a cooling effect
Cohesion between molecules forms a continuous column of water in the xylem and surface tension for organisms to move on bodies of water
Describe 3 of the inorganic ions you need to know in A level Biology
Inorganic ions are dissolved in bodily fluids and cytoplasm
They typically have a specific role
H+ For Chemiosmosis and Oxidative phosphorylation and maintaining pH
Fe2+ Haemoglobin
Na+ Co-transport, depolarisation, sodium potassium pump in action potentials
K+ For sodium potassium pump
Ca2+ For NMJ, synaptic transmission and sliding filament
PO43- For phospholipid bilayer, DNA, RNA and ATP
NO3- For N-cycle and Nitrogen containing compounds e.g. amino acids, DNA, ATP etc
Describe adaptations of cells
Depends a lot on the context, but…
Many mitochondria for increased rates of aerobic respiration and ATP production
Microvilli to increase the surface area of the cell surface membrane to increase the rate of diffusion
More carrier proteins to increase the rate of active transport
More ribosomes to produce more proteins
Name the viral structures
A Attachment protein (binds to a receptor on host cell e.g. CD4 in HIV)
B Enzymes e.g. reverse transcriptase
D Genetic Material (RNA in HIV)
E Lipid Envelope
F Protein Capsid
Describe how an electron microscope works and the advantages and disadvantages of them
Electrons pass through the sample so it must be sliced thinly
Higher magnification
Higher resolution as the wavelength of electrons is shorter – so we can see smaller objects
Artifacts may be present
Can’t view live specimens
Can’t see colour images
Complex preparation
SCANNING shows 3D surface of the cell
TRANSMISSION shows a cross sections of the cell
What happens if the temperature is above an enzymes optimum
Too much kinetic energy
Breaks the hydrogen and ionic bonds
Tertiary structure denatures
Active site changes shape and the enzyme substrate complex can’t form
Reaction slows to a stop
What happens if the temperature is below an enzymes optimum
Not enough kinetic energy
Enzymes substrate complexes don’t form
Reaction slows
What happens to a reaction as you increase the substrate concentration
The reaction increases as the concentration of substrate increases
Eventually the rate plateaus as the reaction is limited by the number of enzymes
The active sites become saturated
What happens to a reaction as you increase the enzyme concentration
The reaction increases as the concentration of enzyme increases
Eventually the rate plateaus as the reaction is limited by the substrate concentration
How do you perform cell fractionation
Homogenise cells to break them open
Filter to remove large debris
Conditions must be:
Cold – To prevent enzyme activity damaging the organelles
Isotonic – To prevent shrinkage or osmotic lysis of the organelles
Buffered – To prevent enzymes and proteins denaturing due to pH changes
Spin cell extraction in a centrifuge at high speeds and pellet nuclei and more dense organelles
Remove supernatant and spin again to pellet the less dense organelles e.g. ribosomes
How do you prepare a temporary mount
Samples must be sliced thinly - to let light pass through them.
A drop of water is typically added.
Often stains are applied to make them darker – iodine and methylene blue are examples.
Usually, a cover slip is applied gently at an angle.
The light passes through and when it hits the specimen it appears darker.
Describe the cell cycle
Interphase is split into G1,S and G2 phases – then the cell divides by mitosis and cytokinesis
G1 - Proteins are made, organelles are sythesised and the cell grows
S phase – DNA is replicated by semi-conservative replication
G2 – Organelles grow and divide and ATP is synthesised
Mitosis – Nuclear division
Cytokinesis – Division of the cytoplasm, two new cells are formed
Describe mitosis
DNA is replicated in S-phase of interphase
Prophase – Chromosomes condense and become visible, nuclear membrane dissolves
Metaphase – Spindle fibres pull chromosomes line up at the middle of the cell
Anaphase – Sister chromatids are pulled to the opposite poles of the cell as spindle fibres contract
Telophase – Chromosomes decondense and the nuclear envelope starts to reform around the two nuclei
Cytokinesis – The cytoplasm and surface membrane splits forming two new cells that are genetically identical
Describe binary fission
Bacteria an prokaryotes reproduce by binary fission
First the DNA (and plasmids) are replicated
Then the cytoplasm and cell membrane divides in two
Each daughter receives on copy of the circular DNA (and variable number of plasmids if present)
Describe the phospholipid bilayer
The phospholipid bilayer is made of phospholipids with hydrophilic/polar phosphate heads and non-polar/hydrophobic fatty acid tails
This bilayer limits the movement of substances through the membrane so that only small non-polar molecules like oxygen can freely diffuse through
Embedded in the membrane are transmembrane proteins that can act as carrier and channel proteins. Chanel proteins allow facilitated diffusion of ions, while carrier proteins can perform facilitated diffusion, they can also transport molecules across the membrane using energy from ATP in active transport
Glycoproteins are embedded in the membrane and act as antigens for cell recognition, they also increase stability and adhesion of the cells
Glycolipids are part of the membrane and increase stability and allow for adhesion of cells.
Cholesterol is also found in the phospholipid bilayer and acts to increase rigidity of the membrane.
Describe phagocytosis
Phagocyte recognizes antigen
Pathogen is engulfed into a phagosome
Lysosome fuses with phagosome forming a phagolysosome
Lysozyme enzymes Hydrolyse pathogen
Antigens from pathogen may be presented on the surface of the cell
Describe cell mediated immunity
Antigen is presented by an antigen presenting cell
Helper T Cells with the complementary receptor binds to the presented antigen
Helper T cell is activated and goes through mitosis
Forming – cytotoxic T cells and more Helper T cells
Cytotoxic T cells produce perforins to kill cells by making holes in their cell surface membrane, water enters causing cells to burst
Only works on whole cells e.g. cancer cells of those infected with viruses
Describe humoral immunity
T helper cells bind to the complimentary antigens presented by the specific B cell. Clonal selection.
T helper cells activate specific B cells.
The B cells rapidly divide by mitosis to produce plasma and memory B cells. This is clonal expansion.
These cloned plasma cells produce specific complementary antibodies to the antigens on the pathogen
Antibodies destroy the pathogen
Describe a vaccine
Vaccines contain antigens/weakened pathogen
Memory B cells are made
On second exposure memory cells are activated
Memory cells and plasma cells rapidly produce antibodies
Antibodies destroy pathogens
Some vaccines are only effective for a limited time as viruses can change the tertiary structure of their antigens
Describe the ELISA test
First antibody binds/complementary to the antigen of interest
Second antibody with an enzyme is added
Enzyme binds to substrate (e.g. first antibody/antigen)
Unbound antibody is washed away
Solution added and colour change seen
Describe HIV replication
HIV attachment proteins complementary to the receptors on the helper T cell
Virus nucleic acid enters the cell
Reverse transcriptase converts RNA to DNA and inserted into the host genome
DNA is transcribed and the HIV capsid (protein) and enzymes are made by host cell ribosomes.
Everything is assembled by the host cells RER and Golgi apparatus into new virus protein, capsid, enzymes.
Virus are assembled and released
Compare prokaryote and eukaryotic DNA
Prokaryote DNA is short Eukaryote DNA is long
Prokaryote DNS is circular Eukaryote DNA is linear
Prokaryote DNA has no introns Eukaryote DNA has introns
Prokaryote DNA is free floating Eukaryote DNA is in in the nucleus (and mitochondria and chloroplasts)
Describe gas exchange in small/simple organisms
Simple organisms (e.g prokaryotes) are very small and have a large surface area to volume ratio
Gasses can be exchanged by simple diffusion across their cell surface membrane
Why do large organisms need a gas exchange system
Large organisms need gas exchange systems as the diffusion pathway is too big and the rate of diffusion is too slow, they are also usually more metabolically active
Describe the relationship between SA:V and metabolism
Higher surface area to volume ratio means there is higher metabolism
This is because there is more heat energy lost
So, more respiration is needed to release heat as a byproduct
Describe the adaptations of the gas exchange surface in insects
Insects have spiracles and tracheae that branch into tracheoles
Gasses (e.g. Oxygen) diffuse through the spiracles and the tracheae/tracheoles
Tracheoles are very branched so have a large surface area and short diffusion pathway
Tracheoles are penetrate respiring tissue so have a short diffusion distance
Describe how insects are adapted to limit water loss
Cuticle exoskeleton that limits water loss
Spiracles can close to prevent water loss
Hairs around spiracles to prevent water loss
Describe the mechanism and benefits of counter current flow in fish
Fish have gills with many gill filaments and lamella to increase the surface area to volume ratio
Single layer of cells in lamella so short diffusion pathway
Blood flows in the opposite direction to water in a counter current flow
This maintains the diffusion gradient so O2 conc. Is always higher in the water than the blood
Diffusion occurs along the entire length of the lamellae/filament
Describe ventilation in mammals
Inhalation: External intercostal muscles and diaphragm contract internal intercostal muscles relax
Ribcage moves up and out diaphragm moves down
Volume in the thorax increases so pressure decreases and air moves in
Exhalation: External intercostal muscles and diaphragm relax internal intercostal muscles contract
Ribcage moves down and in diaphragm moves up
Volume in the thorax decreases so pressure increases and air moves out
Describe adaptations of the human gas exchange surface
Alveoli are a single layer of cells to reduce diffusion distance
Alveoli are branched so have a large surface area
Alveoli have a good blood supply so the oxygen diffusion pathway is maintained
Describe factors that affect gas exchange in plants
Humidity – affects the diffusion gradient of water
Temperature – affects the KE of molecules
Air movement – affects the diffusion gradient all molecules
Light intensity – can open and close stomata (using guard cells), increases photosynthesis affecting diffusion gradient
Describe complete digestion of starch
Amylase in saliva hydrolyses starch (by breaking the glycosidic bond) to maltose (alpha glucose disaccharide)
Amylase is denatured in the stomach – no carb digestion there
Pancreatic amylase is released and further hydrolyses any leftover starch
Maltose is hydrolysed to α-glucose by breaking the glycosidic bond in the ileum by the enzyme maltase which is a membrane-bound enzyme
Glucose is absorbed in co-transport
Describe the complete digestion of proteins
Hydrolysis of peptide bonds.
Endopeptidase act in the middle of protein/polypeptide in the stomach and produces shorter polypeptides, increasing the number of ends
Exopeptidases act at end of protein/polypeptide and in the stomach and produce dipeptides.
Dipeptidases are membrane bound enzymes in the ileum which act on dipeptides and produce single amino acids
Describe absorption of amino acids/glucose
Na+ is actively pumped out of the cell into the blood by the sodium potassium pump
This lowers the concentration of sodium in the epithelium cell
Na+ moves into the cell from the lumen by facilitated diffusion and glucose/amino acids are co-transported with it
Glucose/amino acids are then transported into the blood by facilitated diffusion
Describe lipid digestion
Bile salts emulsify lipids into micelles to increase surface area and solubility in water
Lipids/triglycerides are hydrolysed by lipases to form fatty acids and monoglycerides
Micelles contain fatty acids, monoglycerides and bile salts
They move through the ileum to the epithelium cells
Describe lipid absorption
Micelles contain bile salts and fatty acids/monoglycerides, making them soluble in water.
Fatty acids/monoglycerides are released to cell/lining of the ileum.
This maintains a higher concentration of fatty acids/monoglycerides outside the cell, so they are absorbed by simple diffusion.
Triglycerides are reformed in cells and form chylomicrons.
The chylomicron vesicles fuse with the cell membrane and are released by exocytosis.
Describe co-operative binding
As O2 loads to oxygen, its binding cause the haemoglobin to change shape
This change of shape makes it easier for more oxygen to load
Until all the haem groups are occupied and the haemoglobin is saturated (full)
This is called co-operative binding
Describe the impact of the bhor shift on haemoglobin
In exercising or organisms with high metabolism
CO2 in tissues reduces the affinity of oxygen to haemoglobin (it’s acidic/changes Hb shape)
In tissues where there is lots of respiration the oxygen is more easily unloaded – this makes the curve shift to the right.
This can replace used O2 easier
The impact of CO2 is called the Bohr Shift
Describe the effect on oxygen dissociation when the curve shifts left
Usually in low oxygen environments e.g. womb, high altitude, under water
Higher affinity for oxygen at low ppO2
Oxygen associates/loads more readily
More oxygen can bind where little oxygen is available e.g foetus
Describe the effect on oxygen dissociation when the curve shifts right
Usually in metabolically active organisms e.g. mice or runners
Lower affinity of oxygen at higher ppO2
Oxygen disassociates/unloads more readily
More oxygen available in tissues for More aerobic respiration
Describe how tissue fluid is formed
Higher hydrostatic pressure of blood at arterial end of capillary;
Water and soluble molecules pass out, but proteins / large molecules remain;
This lowers the water potential
Water moves back into venous end of capillary by osmosis;
The lymph system collects any excess tissue fluid which returns to the circulatory system
Describe the path of blood through the left side of the heart
Blood arrives at the left atrium from the pulmonary vein filling the atrium increasing the pressure.
The atrial muscle contracts reducing the volume and increasing the pressure in the atrium until it is greater than the ventricle – this forces the blood through the atrioventricular valve into the left ventricle.
The increase in pressure of the ventricle closes the atrioventricular valve, preventing back flow of blood.
Then the left ventricle muscle contracts reducing volume and increasing the pressure until it is greater than in the aorta, this forces the blood through the semilunar valve.
The pressure in the aorta increases causing the semilunar valve to close preventing back flow.
Describe the path of blood through the right side of the heart
Blood arrives at the right atrium from the vena cava filling the atrium increasing the pressure.
The atrial muscle contracts reducing the volume and increasing the pressure in the atrium until it is greater than the ventricle – this forces the blood through the atrioventricular valve into the right ventricle.
The increase in pressure of the ventricle closes the atrioventricular valve, preventing back flow of blood.
Then the right ventricle muscle contracts reducing the volume and increasing the pressure until it is greater than in the pulmonary artery, this forces the blood through the semilunar valve.
The pressure in the right pulmonary artery increases causing the semilunar valve to close preventing back flow.
Describe the structure and function of arteries, arterioles, veins and capillaries
Describe the movement of water through a plant
Water evaporates from the leaves/transpiration
Due to heat/kinetic energy from sunlight
Water diffuses out of the stomata from a high water potential to low
The diffusion of water causes tension in the xylem
This is due to water potential gradient
Cohesion tension forms a continuous column of water that is pulled through the xylem in a transpiration stream
Water’s adhesive properties aid the movement through the xylem
Transpiration stream lowers water potential in the root cells
Water is absorbed through the root hair cells by osmosis from a higher water potential to low.
Describe the factors affecting transpiration
Humidity – increases or decreases the water potential gradient
Light intensity/stomata opening/no of stomata – more light more photosynthesise, stomata open in the day close at night
Temperature – increases kinetic energy, more diffusion
Wind movement - increases or decreases the water potential gradient
Describe translocation/massflow
Sucrose (and other solutes) are actively transported into phloem (or co-transported with H+) by companion cells
This lowers the water potential in the phloem and water moves in by osmosis
This creates high hydrostatic pressure leading to mass flow to respiring cells/storage organs
Solutes/sucrose is unloaded from the phloem by active transport
Describe chromosome structure
Chromosomes are wrapped around histone proteins forming a nucleosome
Replicated chromosomes are formed of two sister chromatids attached at the centre by a centromere
Describe how DNA codes for protein (don’t refer to transcription/translation)
DNA has a specific sequence of bases where a triplet of three bases codes for a specific amino acid.
The order of the triplets codes for a specific sequence of animo acids of a polypeptide/primary structure
Describe transcription
DNA strands are separated by breaking hydrogen bonds
Transcription is the synthesis of an mRNA copy of a gene;
The copy is complementary to the DNA template/antisense strand;
RNA polymerase attaches to DNA
RNA nucleotides matched to exposed complementary bases;
Adjacent nucleotides are joined by a phosphodiester bond together to make a strand of mRNA;
mRNA molecule separates from DNA
In eukaryotes only: mRNA is spliced to remove introns
Mature mRNA leaves the nucleus through nuclear pores
Describe splicing in eukaryotes
Eukaryotic DNA forms pre-mRNA when transcribed
Pre-mRNA contains introns (non-coding DNA) this must be spliced out
Pre-mRNA is spliced and introns are removed
Mature mRNA is transcribed
Describe translation
mRNA attaches to the ribosome at a start codon
tRNA with a complementary anticodon attaches to the mRNA codon
This tRNA is attached to a specific amino acid
Amino Acids are joined by a peptide bond
Using energy from ATP
tRNA is released from the ribosome and a new on enters
Ribosome moves along the mRNA to synthesise a complete polypeptide
Describe meiosis
DNA is replicated in interphase before meiosis begins
In the first division there is a separation of homologous chromosomes, halving the chromosome number
In the second division there is separation of the sister chromatids
This produced four genetically different daughter cells
How does meiosis lead to genetic variation?
Mutations can occur changing the base sequence leading to the formation of new alleles
In the first division of meiosis there is crossing over where homologous chromosomes swap DNA producing new combinations of alleles
In meiosis homologous chromosomes may be independently segregated, separating into different daughter cells producing new combinations of alleles
During fertilisation there is random fusion of gametes this produces new combinations of alleles
Describe how taxonomy techniques are used to classify organisms
Smaller groups within larger groups that are non-overlapping
Comparisons of DNA base sequences to identify similarities and differences
Comparisons of mRNA base sequences to identify similarities and differences
Comparisons of amino acid sequences to identify similarities and differences
Identify points of divergence/common ancestor
Use courtship behavior to identify species
Define species as organisms that can breed to produce fertile offspring
Describe natural selection
Mutation leads to variation in a species by developing a new allele
The new allele provides an advantage e.g. give an example from the question
Organisms with the new allele can survive and reproduce
Advantageous allele is passed on to offspring
The advantageous allele increases in frequency in the population
Define gene pool and genetic drift, then describe why genetic drift has a larger effect on small populations
Gene Pool – all of the alleles in a certain population usually measured as a frequency
Genetic drift – changes in the frequency of alleles caused by random chance
Why is genetic drift important in small populations?
Changes in population frequency is more pronounced in small populations because of genetic bottlenecks, founder effect, loss off and fixation of alleles.
Describe how and optical microscope works and the advantages and disadvantages of them
Light passes through the specimen so it needs to be a thin layer of cells
Has lower magnification
Lower resolution as the wavelength of light is too long (some organelles may be missed)
Can view live specimens
Can show images in colour via staining
Not very complex preparation
