P1+2: Module 2: Foundations Flashcards
Mucus is composed of water, carbohydrates, proteins and triglycerides. Mucus is secreted by goblet cells. Suggest how the role of the GA is relevant to the function of goblet cells
Modify and package proteins into vesicles; so that they can be secreted via exocytosis
A theory suggests that mitochondria may have evolved from bacteria that mitochondria may have evolved from bacteria that were taken inside other cells. These cells then evolved into eukaryotes. Give 2 structural features of mitochondria that support this theory (2)
Contain 70s ribosomes; May have plasmids
Explain why early eukaryotes were able to grow more quickly than cells that didn’t possess mitochondria (3)
Cells w/ mitochondria can respire aerobically; which produces more ATP; ATP is needed for active transport
The plasma membrane contains proteins, which are made within the cell. Outline the process and organelles involved in the translation of these proteins from RNA (4)
mRNA transported out nucleus; mRNA transported to ribosome; translation occurs at ribosome; tRNA brings specific AA; peptide bonds form between adjacent AA
Describe 3 cellular functions of cytoskeleton
Provides mechanical strength; holds organelles in position/ place; aids in transport of cell eg cilia
Tubulin is a globular protein that can polymerise to form the cell cytoskeleton eg formation of microtubules. Suggest two ways tubulin is essential to protein synthesis and protein secretion in eukaryotic cells (2)
Movement of vesicles from RER to GA; movement of mRNA from nucleus to ribosome
State how cytoskeleton moves organelles around the cell
Uses microtubules
Explain how the function of epitheilal cells in airways of mammals in defence against pathogens and suggest the importance of the cytoskeleton carrying out this function (4)
Goblet cells secrete mucus; mucus traps pathogen; ciliated epithelium sweep mucus; cytoskeleton moves up cilia
A transmission e- microscope image of WBC was studied it concluded that the cell stopped dividing at G2 checkpoint. Suggest two observations that support this conclusion (2)
No visible chromosomes; Nuclear membrane present
Give 2 ways a drawing of a cell can be improved
-No shading/ cross hatching
-Add a title
-Add a scale
Explain how to measure the diameter of the nucleus of one WBC when observing cells through a light microscope (4)
Use eyepiece graticule; calibrate graticule using stage micrometer; measure diameter of nucleus; repeat and calculate mean diameter
Discuss the benefits of using a stain when making slides for light microscopes (3)
Provides contrast; so more internal structures are visible; because they bind to stain allowing a clearer image to be obtained
Explain the interrelationships between the organelles involved in the production and secretion of proteins. (9)
-A complimentary copy of the DNA is made in the nucleus
-The mRNA leaves the nucleus through a nuclear pore
-mRNA attaches to a ribosome
-Protein synthesis occurs
-The proteins are folded and processed at the rough ER
-The proteins are packaged into vesicles
-Transported to the golgi apparatus
-The vesicles fuse with the cis face of the Golgi apparatus and the proteins enter.
-The proteins are structurally modified at the Golgi apparatus.
-The proteins leave the Golgi apparatus on the trans side in a vesicle.
-The vesicles are moved to the plasma membrane by the cytoskeleton
-Proteins released by exocytosis
Resolution
The shortest distance between two objects that are still seen as separate objects.
Magnification
How many times bigger a microscope image is compared to the original specimen.
What are the correct uses for light microscope, TEM, SEM and laser scanning confocal microscope
-Light= whole cells and tissues
-TEM= organelles, 2D (denser parts look darker)
-SEM= cell surface, 3D
-Laser= object at a certain depth within a cell, 3D
Name one structure present in animal cells that aren’t present in plant cells
Centrioles
Ultrastructure
The detailed structure of cells visible only with an e- microscope
Name the carbohydrates molecules used to store energy in plants and animals
-Plants= starch
-Animal= glycogen
Describe and explain how the structure and properties of different carbohydrate and lipid molecules suit them to their role as energy storage molecules in plants and animal (9)
-CARBS; polymers of glucose- glucose used in respiration to release energy; large molecules- insoluble so doesn’t affect water pot. of cell; 1-4, GB- easy to hydrolyze to release glucose; coiled shape- compact so take up less space and can store more; glycogen more branched- allows more rapid release of monomers in animals
-LIPIDS; fats are insoluble- doesn’t effect water pot. of cell; fatty acids are long C chains- can be broken down to release 2 C groups; animal fats are saturated- used for insulation and energy storage
State a physical property of glucose that allows it to be easily transported in bloodstream
Glucose is soluble in water
Why do animals use glycogen instead of glucose (3)
Glycogen is insoluble so doesn’t affect water pot. of cell; its metabolically inactive and compact so lots can be stored in a small space
Give 3 properties of cellulose that make it suitable as the basis of cell walls
-Insoluble
-High tensile strength
-Flexible
Explain how the structure of phospholipids allow them to form a bilayer of plasma membrane
Hydrophillic heads + hydrophobic tails; hydrophobic tails repelled by water so face inwards: hydrophillic heads form H bonds w/ water so face outwards
Name the bond formed between glycogen and fatty acid
Ester
Name three functions of triglycerides in living organism (3)
-Energy storage
-Thermal insulation
-Buoyancy
Explain why lipids can increase buoyancy of aquatic animals
Lipids are less dense than proteins
Using the structure of triglycerides explain what’s meant by hydrolysis
Uses water; to break 3 ester bonds
A vet is concerned that a llama is unwell, the vet suspects there may be haemoglobin in the urine, explain how the vet could confirm this (3)
Add biuret and CuSO4 to urine; observe a colour change from blue to purple if protein is present (hB is protein)
There’s two Q in here:
1)Describe how to carry out a controlled experiment to test the hypothesis “the higher the conc of glucose in fruit juice, the sweeter it’ll be” w/o using a colourimeter (4)
2)Suggest a reason why results for this experiment above might not be able to support students hypothesis
1)Taste fruit juice to see how sweet it is, test a sample w/ Benedicts and observe a colour change then obtain rank orders for sweetness and compare rank orders for sweetness and glucose conc. Make sure this is a blind taste test to avoid bias
2)Taste is subjective
Chemical elements for carbohydrates, lipids, proteins and nucleic acids
C, H and O for carbohydrates
C, H and O for lipids
C, H, O, N and S for proteins
C, H, O, N and P for nucleic acids
What is the role of membranes in cells? (3)
-Acts as a barrier between areas
-Cell signalling
-Site of chemical reactions
Describe the role of cholesterol in cell surface membrane in human body
Cholesterol binds to phospholipid fatty acid tails increasing the packing of the membrane therefore reducing fluidity of membrane
Explain why progesterone can move across membranes (2)
Its a lipid so its hydrophobic; so can diffuse/ dissolve through phospholipid bilayer
Osmosis
Net movement of water across a partially permeable membrane down a water pot. gradient
Explain why glucose can’t pass through a cell membrane by simple diffusion (2)
Phospholipid acts as a barrier; glucose molecule is too large
Sulfur atoms are required for synthesis of which type of biological moleule?
Proteins
Describe how the structure of llama hB is likely to be diff. from camel hB w/ reference to 4 levels of protein structure (6)
llama hB must have a diff. order of AA in its primary structure; resulting in a diff. shape in its secondary structure as a diff. number of alpha helixes and beta pleated sheets form;
This leads to a diff. 3D globular shape in teriarty structure; as hB forms diff. hydrogen, ionic, disulphide bonds and iff. hydrophobic interactions;
This results in 4 polypeptide chains in quaternary structure to bond differently; so llama hB has a higher affinity for O2
State 3 properties of fiborous proteins that are diff. from those of a globular protein
Insoluble; Strong; Unreactive
Compare the properties and functions of fiborous and globular proteins in the body (6)
-Fiborous; PROP= insoluble, strong, flexible.
FUNC= eg to give elasticity to blood vessels or for
structure like collagen in cartilage
-Globular; PROP= contain prosthetic group, soluble, temp
sensitive
FUNC= eg to transport substances in blood like hB
(carries O2) and for receptors used for cell signalling
Suggest why collagen is a strong molecule
Has many H bonds between polypeptides
The primary structure of a protein consists of a chain of amino acids, describe how a second AA would bond to cysteine in forming the primary structure of a protein
Peptide bond forms; between amine group and carboxyl group; H from amine group combines w/ OH from carboxyl group; Water is created and this is a condensation reaction
Each amino acid has diff R groups. Describe how these R groups can interact to determine the tertiary structure of a protein (4)
Some R groups repel or attract e/o; disulphide bonds; between S atoms; ionic bonds between oppositely charged R groups;
Primary structure of a protein
Sequence of AA in a polypeptide
Secondary structure of a protein
Folding of polypeptide chain, held in place w/ alpha helixes, beta pleated sheets or H bonds between AA chain
Explain why water is a good solvent
Its polar; this enables water molecules to bind to solute molecules
Suggest what roles hydrogen ions and sodium ionsmay play in helping flowers last longer
-H+= H+ ions used to regulate pH
-Na+= Na+ ions used to regulate water pot.
Explain how properties relating to density of water contribute to survival of organisms (3)
Ice is less dense than water; ice provides habitats for some species; floating ice will insulate water below; so animals can move under ice
Properties of water (9)
-Ice is less dense than water
Ice will float and insulate the water underneath
The whole body of water does not freeze
-Water has a high specific heat capacity
Because the hydrogen bonds can absorb a lot of energy
Therefore it is thermally stable
Good habitat, particularly for ecotherms
-Water has a high latent heat of evaporation
Because it takes a lot of energy to break the hydrogen bonds
Therefore, can be used to cool organisms via sweating
-Water has high cohesion
Because it is a polar molecule
Therefore it flows by mass flow through the xylem and phloem
-Water is a good solvent
Because it is a polar molecule
Therefore ions and glucose easily dissolve and can be transported
Describe the effect of high temp on structure of cell membrane
Phospholipids vibrate as they have more kinetic energy; increasing number of gaps between phopholipids; bilayer becomes more fluid and proteins denature
Explain how cell surface membranes contribute to process of cell signalling
Release of signal molecule by exocytosis; proteins have receptors; signals are specific; to shape of receptor thats complementary; when they attach it causes a change
Outline how vesicles are moved from one organelle to another
Cytoskeleton provides a pathways for movement; vesicle moves along microtubule; this whole process uses ATP
Active transport
Movement of substances against conc gradient; using ATP
Cell signalling
Communication between cells to trigger a response
Explain how a glycoprotein can act as a receptor
Receptors have a specific shape; as theyre complementary to shape of trigger
Describe how DNA molecule replicates (7)
Semi conservative replication; double helix unwinds; H bonds between bases beak; each strand acts as the template for the formation of a new molecule; free DNA nucleotides align via complementary base pairing (purines and pyrimidines); H bonds reform; sugar phosphate backbone forms; DNA polymerase joins strands
How can you distinguish between RNA and DNA
-RNA= single stranded whilst DNA= double stranded
-RNA= contains uracil whilst DNA= contains thymine
Explain why mRNA molecule is shorter than DNA molecule
DNA comprises many genes, mRNA only codes for 1 protein
What do genes code for?
Proteins
Suggest how changing sequence of DNA nucleotides affect final product DNA codes for
Diff. sequence of AA means that there’d be diff. tertiary structure so product will have diff. functions
Function of DNA polymerase
Make phosphodiester bonds between adjacent nucleotides
A student tries to extract some DNA from a crushed banana at home, suggest a suitable substance the student could use to release DNA and explain why it should work
Detergent; works as an emulsifier; it’ll break up plasma membranes
A DNA molecule contains two polynucleotide chains, describe how these two chains are held together (3)
Two H bonds between A to T and three H bonds between C to G
Semi conservative replication
One original strand and one new strand; each strand of DNA acts as a template strands for new double helix
DNA helicase
Unzips DNA molecule
DNA polymerase
Forms phosphodiester bonds/ joins adjacent nucleotides
A teacher told his students that the human body makes the equivalent of its own mass in ATP everyday. Explain why at the end of the day only a small proportion of students mass was ATP (2)
Because ATP is hydrolyse to ADP; ATP is constantly recycled
A student mixed a plant sample w/ detergent, added salt, added protease enzyme then spool DNA ppt onto a glass rod.
Suggest whether this method would extract and purify DNA (3)
Yes because:
-Detergent breaks cell membrane
-Protease breaks down proteins around DNA
Describe the difference between intracellular and extracellular enzymes. Give an example of both. (4)
-Intracellular work inside cells; For example catalase
-Extra cellular enzymes work out of cells; For example amylase
Describe the difference between intracellular and extracellular enzymes. Give an example of both. (4)
-Intracellular work inside cells; For example catalase
-Extra cellular enzymes work out of cells; For example amylase
Explain why enzymes work as catalysts
-Enzymes lower the activation energy of the reaction.
-It does this by holding the substrate molecule(s) in the active site
-This either reduces any repulsion between the substrate molecules
-Or puts strain on the bonds of the molecule
-This increases the rate of reaction
Lock and key model of enzyme action
-Each enzyme has a specific substrate
-That has a complementary shape to the active site
-This forms an enzyme substrate complex
-The substrate is converted into products
-To form an enzyme product complex
-The products leave the active site because it does not have a complementary shape
Difference between lock and key model and induced fit model (3)
-The substrate binds to the active site
-The enzyme changes shape slightly
-To fit the substrate more closely
Describe the difference between a reversible and non-reversible enzyme inhibitor. (6)
-Reversible inhibitors form weak bonds with the enzyme
-For example hydrogen or ionic
-Therefore the inhibitor does not bind permanently
-Irreversible inhibitors form strong bonds with the enzyme
-For example covalent
-Therefore they bind permanently
Product Inhibiton
The product of a reaction inhibits the enzyme that catalyses the reaction
Inactive precursors and give an example
-An inactive form of an enzyme that needs to be activated to work
-For example some protease enzymes are released as inactive precursors
-This prevents them from damaging the cells they are produced in
Coenzyme
Non protein organic molecule not permanently attached to an enzyme but needed to allow enzyme to function
Describe how a non competitive inhibitor works to inhibit the activity of an enzyme (2)
Inhibitor attaches to allosteric site of enzyme, this changes the shape of the active site of the enzyme this means that the substrate is no longer complementary to the enzyme so no more ESC can be formed decreasing the enzymes activity.
There are two models for the mechanism of enzyme action. Outline how changes in temperature can affect these mechanisms of enzyme action (6)
-Lock and key model, shape of substrate is complementary to active site of specific enzyme, this then forms enzyme substrate complexes
-Induced fit, enzymes active site changes shape to accommodate substrate once substrate binds
-An increase in temperature increases the kinetic energy of the molecules; resulting in more successful collisions so more ESC form
-Decrease in temp reduces kinetic energy of molecules; resulting in fewer successful collisions and fewer ESC forming
-Enzymes have a optimum temperature so if there’s a high temp the enzyme is at risk of denaturing.
A plant has leaves adapted to form water filled traps for insects. Which are attracted to by the plants nectar but then fall into the traps and drown. The plants digest the insects and absorb the mineral ions produced. Enzymes digest insects that fall into the plants traps. Is the mode of action of these enzymes extracellular or intracellular? (3)
Extracellular because:
-Digestion is occurring in the liquid in the trap not inside cells
-Enzymes are released by plant cells into trap
-Enzymes may also come from bacteria in the trap
In which stage of mitotic cell cycle does chromosomes line up at the equator of the cell?
Metaphase
The second division of meiosis is different from mitosis because…
…the separating chromatids of a pair aren’t the same
Bone marrow contains stem cells that can develop into erythrocytes, neutrophils and lymphocytes. Describe the changes that must occur inside these stem cells as they differentiate to form erythrocytes (2)
Synthesise alot of hB; remove nucleus and ribosomes associated with protein synthesis
What type of nuclear division in a zygote is mitosis and not meiosis? (2)
Mitosis is for growth of zygote which; which needs genetically identical cells; so not meiosis because gametes aren’t produced
Another stage of meiosis is metaphase 1. Explain how the organisation of homologous chromosomes during metaphase 1 increases genetic variation (3)
Random assortment; Homologous chromosomes line up on the equator of cell; Either one of homologous pair can end up in either daughter cell; so each chromosome of the homologous pair is genetically different
Mitosis is involved in growth and repair of tissues. State two other roles of mitosis in multicellular organisms
-Production of new stem cells
-Producing gametes from haploid cells
The use of stem cells is being evaluated for the treatment of certain human diseases. Name two potential sources of human stem cells and for one source, describe an ethical issue associated with use of stem cells (4)
2 sources: -Embryos
-Adult bone marrow
-An ethical issue for embryo being a possible source is that some may argue that its not ethically right as embryo is being killed
Cells from an embryo can be used for medical research and for research on the development of an organism. Suggest three ways in which the use of embryonic stem cells in research has practical benefits to biological knowledge (3)
-Can be grown into different types of tissue to test how effective new medicinal drugs are
-Can be grown into different tissues to test for side effects
-Can be grown and studied to see how they develop into diff cell types
Define the term magnification. (1)
Define the term resolution. (1)
How many times bigger a microscope image is compared to the original specimen.
The shortest distance between two objects that are still seen as separate objects.
Light microscope + key points about the image produced
Mainly used for whole cells or tissues
Transmission Electron microscope + key points about the image produced
2D images Denser parts look darker
Scanning Electron microscope + key points about the image produced
3D Shows the surface of the specimen
Scanning Confocal microscope + key points about the image produced
Shows objects at different depths within the specimen
Describe how to prepare slide to be used with a light microscope.
Cut the specimen very thinly
Use forceps to put it in the middle of the glass slide.
Pipette two drops of water onto the specimen.
Add a stain, if necessary.
Place a cover slip on top
Being careful not to create any air bubbles
Function of Nucleus, Nucleolus, Nuclear envelope
Nucleus Controls the cell’s activities Contains the DNA / chromosomes
Nucleolus Produces ribosomes
Nuclear envelope Double membrane around the nucleus Has pores that allow mRNA to leave the nucleus
Function of Rough ER, Smooth ER, Golgi apparatus, Ribosomes
Rough ER Processes and folds proteins
Smooth ER Synthesises and processes lipids
Golgi apparatus Processes and packages proteins into vesicles
Ribosomes Protein synthesis
Function of Plasma membrane, Centrioles, Cell wall
Plasma membrane Controls the movement of substances into and out of the cell Has receptor molecules used in cell signalling
Centrioles Pull the chromosomes / chromatids to opposite poles during cell division
Cell Wall Supports the plant cell
Function of Flagella, Cilia, Vesicle
Flagella Allow movement of the cell
Cilia move to move substances along the cell surface
Vesicle Transports substances in and out of the cell
Explain the interrelationships between the organelles involved in the production and secretion of proteins. (9)
A complimentary copy of the DNA is made in the nucleus
The mRNA leaves the nucleus through a nuclear pore
mRNA attaches to a ribosome
Protein synthesis occurs
The proteins are folded and processed at the rough ER
The proteins are packaged into vesicles
Transported to the golgi apparatus
The vesicles fuse with the cis face of the Golgi apparatus and the proteins enter.
The proteins are structurally modified at the Golgi apparatus.
The proteins leave the Golgi apparatus on the trans side in a vesicle.
The vesicles are moved to the plasma membrane by the cytoskeleton
Proteins released by exocytosis
Describe the three main roles of the cytoskeleton. (3)
Provide mechanical strength to cells,
Aid transport within cells
Enables cell movement
State the definition of a stem cell. (2)
An undifferentiated cell
That can differentiate into other types of cell
State four locations where stem cells are found in organisms and for each one state the types of cell that the stem cells can differentiate into. (4)
Early embryos – all the cells required for an animal (totipotent)
Bone marrow – erythrocytes and neutrophils
Meristems – new plant cells at the shoot tip and root tip
Cambium – xylem vessels and phloem sieve tube elements
Neutrophils function, Adaptation, How adaptation aids function
Neutrophil
Engulf pathogens
Contain lots of lysosomes Digestive enzymes break down the engulfed pathogen
Erythrocyte function, Adaptation, How adaptation aids function
Carry oxygen in the blood
Biconcave disc shape + No nucleus Increases the surface are for oxygen absorption More space for haemoglobin
Describe the structure of a triglyceride (include details of saturated and unsaturated fatty acids. (5)
One glycerol molecule
Three fatty acids tails
The fatty acids can be saturated or unsaturated
Saturated fatty acids only contain single bonds between the carbon atoms
Unsaturated fatty acids have at least one double bond between the carbon atom
Describe how triglycerides are formed. (6)
A condensation reaction occurs
Between the glycerol molecule and the fatty acids
A hydrogen atom is removed from the glycerol
An OH group is removed from the fatty acids
To form three molecules of water
An ester bond is formed
Describe the functions of triglycerides and explain how their structure aids the function. (5)
Energy storage molecules
They are insoluble
And therefore don’t affect the water potential of the cell
The fatty acid tails contain a lot of chemical energy
This energy is released when the bonds are broken
Describe the functions of phospholipids and explain how their structure aids the function. (4)
Form the bilayer in membranes
The phosphate heads are hydrophilic and the fatty acid tails are hydrophobic
Therefore the phosphate heads face outwards and the tails face inwards
The fatty acid tails act as a barrier to water soluble substances
Describe three properties of water. For each one, explain how it aids living organisms. (9)
Ice is less dense than water
Ice will float and insulate the water underneath
The whole body of water does not freeze
Water has a high specific heat capacity
Because the hydrogen bonds can absorb a lot of energy
Therefore it is thermally stable
Good habitat, particularly for ecotherms
Water has a high latent heat of evaporation
Because it takes a lot of energy to break the hydrogen bonds
Therefore, can be used to cool organisms via sweating
Water has high cohesion
Because it is a polar molecule
Therefore it flows by mass flow through the xylem and phloem
Water is a good solvent
Because it is a polar molecule
Therefore ions and glucose easily dissolve and can be transported
Define the term primary structure. (1)
The sequence of amino acids in a polypeptide chain
Describe how the secondary structure of a protein is formed. (2)
The polypeptide chains coil to form an alpha helixes
Or fold to form a beta pleated sheet
Describe how the tertiary structure of a protein is formed (include details of the different bonds that hold the protein in its tertiary structure).
The alpha helixes and beta pleated sheets coil and fold further.
Held in place by lots of bonds:
-Ionic bonds between amino acids of opposite charge
-Hydrogen bonds between amino acids with slight charges
-Disulphide bonds that form between sulphur atoms in two cysteine amino acids
-Hydrophilic interactions – hydrophilic amino acids are found on the outside of the protein.
Describe two examples of where the tertiary structure of a protein is crucial to its function. (8)
- Enzymes
Shape of active site is specific
And complementary to the substrate
If the tertiary shape is altered, the enzyme can’t hydrolyse the substrate - Hormones
Shape is specific and complementary
To the receptor
If the tertiary shape is altered the hormone won’t combine with the receptor
Define the term quaternary structure. (1)
A protein made up of different polypeptide chains
Define the term conjugated protein. (2)
A protein with a non-protein group attached.
The non-protein group is called a prosthetic group
3 examples of a conjugated protein
Insulin, Amylase, Haemoglobin
Describe the general features of fibrous proteins. (3)
Insoluble
Strong
Structural proteins
3 examples of fibrous protein
Collagen, Keratin, Elastin
Describe the difference between intracellular and extracellular enzymes. Give an example of both. (4)
Intracellular work inside cells
For example catalase
Extra cellular enzymes work out of cells
For example amylase
Explain why enzymes work as catalysts. (5)
Enzymes lower the activation energy of the reaction.
It does this by holding the substrate molecule(s) in the active site
This either reduces any repulsion between the substrate molecules
Or puts strain on the bonds of the molecule
This increases the rate of reaction
Explain what happens to enzymes at temperatures above the optimum. (5)
The enzymes denature
This is because the extra kinetic energy makes the enzyme molecule vibrate more
This can break some of the bonds holding the enzyme in its tertiary structure
The active site changes shape
The substrate can longer fit into the active site.
Explain why enzymes are denatured in extremes of pH. (5)
Acidic solutions contain hydrogen ions H+
Alkali solutions contain hydroxide ions OH-
These ions interfere with the ionic and hydrogen bonds holding the tertiary structure in place
Therefore the active site changes shape
The active site is not complementary to the substrate
Describe the difference between a reversible and non-reversible enzyme inhibitor. (6)
Reversible inhibitors form weak bonds with the enzyme
For example hydrogen or ionic
Therefore the inhibitor does not bind permanently
Irreversible inhibitors form strong bonds with the enzyme
For example covalent
Therefore they bind permanently
Describe how a competitive enzyme inhibitor works. (4)
The inhibitor has a similar shape to the substrate
Therefore the inhibitor enters the active site and blocks it
No enzyme substrate complexes can be formed
The rate of reaction decreases
Describe how a non-competitive inhibitor works. (7)
The inhibitor binds to the enzyme
but not at the active site
It binds at an allosteric site.
The changes the tertiary structure of the enzyme
and therefore the shape of the active site.
Therefore the substrate can’t enter the active site.
The rate of reaction decreases.
Describe and explain what happens to an animal cell when it is placed in distilled water. (4)
The cell bursts
The water potential outside the cell is higher than the water potential inside the cell.
Water moves into the cell
By osmosis
Define the term osmosis. (3)
The net movement of water
From a high water potential to a low water potential
Through a selectively permeable membrane
Describe and explain what happens to a plant cell when it is placed in distilled water. (4)
The cell becomes turgid
The water potential outside the cell is higher than the water potential inside the cell.
Water moves into the cell
By osmosis
Describe and explain what happens to an animal cell when it is placed in a concentrated salt solution. (4)
The cell shrinks (becomes crenated)
The water potential inside the cell is higher than the water potential outside the cell.
Water leaves the cell
By osmosis
Describe and explain what happens to a plant cell when it is placed in a concentrated salt solution. (5)
The cell becomes plasmolysed
The cell membrane moves away from the cell wall
The water potential inside the cell is higher than the water potential outside the cell.
Water leaves the cell
By osmosis
State three key roles of plasma (cell surface) membranes. (3)
Partially permeable barriers – control which substances enter or leave the cell
Site of chemical reactions
Contain receptors where hormones and drugs can bind.
Describe three roles of membranes within cells. (3)
Control which substances enter or leave organelles
Site of chemical reactions
Compartmentalisation
What is the protein level of structure the statement is refering to?
Short α-helical sections are present
in both polypeptides because of
their high proline content
2
What is the protein level of structure the statement is refering to?
Intermolecular bonds form between
glutenin and gliadin polypeptides
4
What is the protein level of structure the statement is refering to?
Up to 45% of the amino acids in
gliadins are glutamine
1
What is the protein level of structure the statement is refering to?
Hydrophobic amino acids such as
glutamine and proline are not found
on the surface of gluten proteins
3
Explain why a process known as transcription is necessary for polypeptide synthesis
-gene transcribed, to (m)RNA
-mRNA goes to ribosome for protein synthesis
-DNA, is too large to fit through
nuclear pores
Compare the properties and functions of fibrous proteins and globular proteins in the human body (6)
FIBROUS PROTEINS
Properties:
- insoluble
- elongated / long / rods / filaments / ropes /
strands - strong / tough
Functions:
to give, elasticity / elastic properties
* elastin in, (named) blood vessels
- for protection
- keratin in, skin / hair / nails
- to give, elasticity / elastic properties
GLOBULAR PROTEINS
Properties:
- soluble
- spherical / ball-shaped
- ref. conjugated / contain prosthetic group
Functions:
* enzymes / metabolic role / to catalyse
reaction(s) / to lower activation energy
* named enzyme + its specific role described
- to transport substances in blood
- haemoglobin + role described e.g. carry
oxygen
Describe and explain why collagen is a fibrous protein.
-is long chain (of amino acids) ✓
-little / no, tertiary structure ✓
-insoluble / has many non-polar
amino acids
Suggest why collagen is such a strong molecule
Has many H bonds
Name the covalent chemical bond which links two cysteine amino acids
Disulphide bonds
Plan a method to compare the amino acids present in the urine of a person who has been following one of
these diets with that of a person who has not
(paper) chromatography (1)
Set, blots / AW, of the two (urine)
samples (1)
separate / AW, with (aqueous /
hydrophilic) solvent (1)
(use a) stain / ninhydrin to
visualise the spots (1)
compare patterns (of separated
components / colours) (1)
Explain why a protease enzyme is added to the mixture during the DNA purification process
Breaksdown histone proteins so they can be removed
The student used the following procedure to stain the sample:
* Use forceps to place the sample on a glass slide.
* Use a pipette to place two drops of the stain in the centre of the sample.
* Carefully lower a cover slip onto the sample, ensuring that the cover slip is
parallel with the slide as it is lowered.
Describe two improvements the student should make to their staining procedure
-lower cover slip at an angle / use mounted needle
-use blotting paper to, remove excess stain
Sago pondweed has evolved many adaptations to its aquatic environment. Three such
adaptations are described below.
Explain the advantage of each adaptation
-Waxy Cuticle
-Stem tissue contains air spaces
-Thin, flexible stem
-No WC, water loss is not a problem / wax production wastes
energy
-Stem tissue contains air spaces (allows it to) float, more
light near surface of water for photosynthesis
-Thin, flexible stem less support needed / move more (in water) without breaking
Prophase
- Chromosomes condense
- Chromosomes have become
visible (but are unordered) - Nuclear envelopeand nucleolus
have disappeared
Anaphase
- Spindlefibres are shortening
- Chromatids are separating and are
being pulled to opposite sides of
the cell
Telophase
- Chromatids have been pulled to
opposite sides of the cell - A new cell membrane is visible
down the centre of the cell - Cytokinesis/ thecell is beginning to
divide
