Advanced higher biology All extended response questions

Discuss the control of the cell cycle under the following headings.

(i) Phases of the cell cycle and the importance of cell cycle checkpoints

(ii) The role of cyclins and cyclin-dependent kinases

1. lack of control of the cell cycle can result in degenerative disease/cancer

2. Phases are G1, S, G2, M

3. G1 and G2 are growth phases

4. DNA replication in the S phase

5. mitosis and cytokinesis in M/mitosis phase

6. checkpoints at G1, G2, M

7. checkpoints regulate progression to the next phase

8. example of what is being assessed at a checkpoint

9. at G1 cells may enter G0/non-dividing state

a. cyclins accumulate (during G1)

b. cyclins combine with cyclin-dependent kinases (CDKs)

c. cyclins activate CDKs

d. (active) CDKs phosphorylate proteins that stimulate the cell cycle

e. if the a sufficient threshold of phosphorylation, the cell cycle progresses/passes the checkpoint OR Insufficient phosphorylation, the cell cycle is arrested/held at the checkpoint

f. retinoblastoma/Rb (protein)/ transcription factor inhibitor controlled by/phosphorylated by (G1) CDK

Discuss signalling between cells under the following headings.

(i) Hydrophilic signalling molecules and signal transduction

(ii) Insulin signalling and diabetes

hydrophilic signalling molecules include:

1. neurotransmitters

2. peptide/protein hormones

3. receptor is specific

4. receptors are transmembrane proteins

5. binding (to the receptor) at cell surface/ plasma membrane

6. binding to the receptor causes a conformational change

7. bringing about a response/change inside the cell

hydrophilic/transduced signals.

· activate enzymes/phosphorylation

· activate G-protein

· promote rearrangement of the cytoskeleton

· change secretion or uptake of molecules

· activate proteins that regulate gene transcription

Give details of the structure of proteins including primary, secondary, tertiary and quaternary levels. (10 marks)

1. Primary structure of a protein is the sequence of amino acids in the polypeptide chain.

2. Amino acids are joined together by peptide bonds.

3. Secondary structure of a protein is stabilised by hydrogen bonds.

4. α-helix and β-sheet are two types of secondary structure.

5. α-helix is a spiral with the R groups sticking outwards.

6. β-sheet has parts of the chain running alongside each other forming a sheet.

7. The R groups sit above and below the sheet.

8. β-sheet can be anti-parallel or parallel.

9. Turns are a third type of secondary structure.

10. The polypeptide folds into a tertiary structure.

11. Folding at this level is stabilised by many different interactions between the R groups of the amino acids.

12. Any two from: hydrophobic regions, ionic bonds, hydrogen bonds, London dispersion forces, disulfide bridges.

13. A protein may include prosthetic (non-protein) parts.

14. For example, haem in haemoglobin.

15. Quaternary structure exists in proteins with two or more connected polypeptide subunits.

Give an account of enzyme activation. (5 marks)

Modulators regulate the activity of the enzyme.

Modulators bind at allosteric sites.

Causes a conformation/shape change in the enzyme.

Alters the affinity of the active site for the substrate.

Positive modulators increase the enzyme affinity for the substrate.

Negative modulators reduce the enzyme's affinity for the substrate.

Phosphorylation/addition of a phosphate or removal of a phophate/dephosphorylation can alter enzyme activity.

Kinase enzymes carry out phosphorylation/adds phosphate.

Phosphatase enzymes carry out dephosphorylation/remove a phosphate.

Some enzymes are activated by phosphorylation while others are inhibited.

Describe the action of the sodium potassium pump. (10 marks)

The sodium potassium pump transports ions against a steep concentration gradient.

The sodium potassium pump requires energy from hydrolysis of ATP.

The maintenance of ion gradients by the pump accounts for a significant part of basal metabolic rate.

The protein has high affinity for sodium ions inside the cell/sodium ions from inside the cells bind.

The protein becomes phosphorylated by ATP...

...which changes the conformation (of the pump)

The affinity for sodium ions decreases resulting in sodium being released outside of the cell.

Potassium ions from outside the cell bind to the sodium potassium pump.

Dephosphorylation occurs...

...which changes the conformation (award once only).

Potassium ions are taken into the cell.

The affinity returns to the start.

Three sodium ions are transported out of the cell and two potassium ions are transported into the cell.

Give an account of cell signalling. (10 marks)

Some signalling molecules/hormones are proteins/peptides/hydrophilic.

Hydrophilic/protein/peptide signalling molecules/hormones cannot cross the membrane.

The receptor for hydrophilic signals is in the membrane.

Binding changes the conformation of the receptor.

Receptors cause transduction/trigger cell response.

Example - insulin triggers recruitment of GLUT4/glucose transporters to the cell membrane.

Hydrophobic signals/steroid hormones can pass through the membrane.

The receptor for hydrophobic signals/steroid hormones is inside the cytosol/nucleus.

The receptors for hydrophobic signalling molecules are transcription factors.

The hormone-receptor complex binds to specific DNA sequences called hormone response elements (HREs).

Binding at these sites influences the rate of transcription.

Each steroid hormone affects the gene expression of many different genes.

Describe the control of apoptosis. (5 marks)

Apoptosis is triggered by cell death signals that can be external or internal.

The production of death signal molecules from lymphocytes is an example of an external death signal.

External death signal molecules bind to a surface receptor protein (and trigger a protein cascade within the cytoplasm).

DNA damage is an example of an internal death signal.

An internal death signal resulting from DNA damage causes activation of p53 tumour-suppressor protein.

Both result in the activation of caspases (types of protease enzyme) that cause the destruction of the cell.

Cells may initiate apoptosis in the absence of growth factors.

Describe the cell cycle. (10 marks)

Consists of interphase and mitotic (M) phase.

Interphase involves growth and DNA synthesis.

Interphase is G1, S, G2.

G1 and G2 are growth periods.

DNA replication occurs during S phase.

Mitotic phase involves mitosis and cytokinesis.

During prophase - DNA condenses into chromosomes each consisting of two sister chromatids OR nuclear membrane breaks down.

Also during prophase spindle microtubules (extend from the MTOC and) attach to chromosomes (via their kinetochores in the centromere region).

During metaphase chromosomes are aligned at the metaphase plate (equator of the spindle/cell).

During anaphase sister chromatids are separated, and the chromosomes are pulled to opposite poles.

During telophase the chromosomes decondense and nuclear membranes are formed around them.

During cytokinesis the cytoplasm is separated into two daughter cells.

Give an account of meiosis. (10 marks)

1. Meiosis produces four haploid gametes...

2. ...from one diploid gamete mother cell.

3. Interphase is where DNA replications occurs.

4. During meiosis I, homologous chromosomes line up at the equator of the cell.

5. Homologous chromosomes are the same size and shape.

6. They carry the same genes at same gene loci...

7. ...but may carry different alleles / one from each parent.

8. They have their centromere at the same place.

9. During meiosis I, crossing over may occur...

10. ...at points called chiasmata.

11. This process shuffles sections of DNA between the homologous pairs, allowing the recombination of alleles to occur thus increasing variation.

12. Genes on the same chromosome are said to be linked.

13. There is a correlation between the distance between linked genes and their frequency of recombination / description or definition of chromosome mapping.

14. Independent assortment occurs as a result of meiosis I, with homologous chromosomes being separated irrespective of their maternal and paternal origin.

15. Homologous chromosomes are separated by spindle fibres.

16. This increases variation in the gametes.

17. During meiosis II, chromatids are pulled apart (and four haploid gametes are produced).

· sexual diamorphism; (4 marks)

· male-male rivalry; (1 mark)

· sneakers; (1 mark)

· lekking. (4 marks)

Sexual diamorphism (maximum of 4 marks):

Sexual dimorphism is the physical difference between males and females of the same species.

Usually, males are more conspicuous than females / a suitable description.

Being inconspicuous mean that females can better protect their young due to camouflage.

Sexual dimorphism is a product of sexual selection.

Sexual dimorphism can be reversed in some species.

Male-male rivalry (maximum of 1 mark):

Males often use large size to out compete other smaller males for mates.

Some males use weaponry to win females / suitable description of horns or antlers.

Sneakers (1 mark):

Smaller males may still be successful using sneaker / satellite behaviour.

Lekking (maximum of 4 marks):

Lekking is where males collect in a display area and present to females.

The display area is called a lek.

A suitable example, e.g. grouse, capercaillie.

Females assess male fitness...

...and choose based on 'honest' signals...

...such as low parasite burden.

Discuss the concept of the parasite niche. (10 marks)

Parasites and hosts have a symbiotic relationship...

...that benefits the parasite at the expense of the host.

Parasite niche is a complex summary of tolerances and needs.

Parasites have narrow niche due to high host specificity.

Parasites are defined as degenerate due to loss of certain organs or structures.

Fundamental niche is the niche that exists in the absence of interspecific competition.

Realised niche is the niche that exists in the presence of interspecific competition.

Interspecific competition will result when two species have very similar niches.

Interspecific competition can lead to competitive exclusion principle, which is local extinction of one (the weaker) of the two competing species.

Resource partitioning allows two species to co-exist (by compromising).

Endoparasites live inside the host and ectoparasites live on the surface of the host.

A definitive host is the host where the parasite reaches sexual maturity.

An intermediate host may be a vector and is needed for the parasite to complete its life cycle.

Vectors have a role in parasite transmission from one host to another...

...such as the mosquito spreading the malaria parasite / any other suitable example of a vector.

Describe how mammals use immune responses to reduce the effects of parasites. (10 marks)

Defences can be non-specific / natural and specific / adaptive.

Physical barriers such as the skin prevent entry of parasites.

Chemical secretions such as mucus, tears, saliva and stomach acid.

Inflammatory response increases bloodflow and therefore phagocytes to site of injury or parasite.

Natural killer cells destroy abnormal cells.

Phagocytosis is where phagocytes engulf parasites into a vacuole/vesicle...

...and digestive enzymes in lysosomes digest the parasite.

White cells carry out 'surveillance'.

Phagocytes display foreign antigens to lymphocytes.

A specific lymphocyte is produced in response to each foreign antigen.

Lymphocytes undergo mitosis so are amplified.

This is called clonal selection.

T cells / T lymphocytes target infected or damaged cells.

T cells induce apoptosis (cell death).

B cells / B lymphocytes produce specific antibodies to specific antigens.

Some cloned lymphocytes act as immunological memory cells.

Discuss the statement that 'there are major challenges in the treatment and control of parasites'. (10 marks)

Parasites are difficult to culture in the laboratory.

Many parasites have rapid evolution rates...

...resulting in rapid antigen change.

This makes development of vaccines difficult.

Developing suitable drugs is also very difficult...

...due to the metabolism of the parasite and their host being so similar...

...since a drug intended to kill a parasite may also harm the host.

Control has been noted in areas with improved sanitation / civil engineering / sewage systems.

Where vectors are under control parasites are controlled too.

Control is particularly difficult in tropical climates / developing countries, ...

...places where there is war / refugee camps, ...

...areas facing natural disasters...

...and overcrowded regions.

Improving parasite control reduces child mortality.

Where there are improvements, children are likely to thrive / increase in child growth, development and intelligence.

As children develop / become educated, they can continue improving control methods in these countries.

Describe the role of genetic drift in the evolution of new species.

1.Evolution is the change over time in the frequency of alleles in the gene pool of a population

2. Genetic drift is a random process

3. Named examples of random processes from: colonisation/ establishment of new populations/the founder effect; survivors of an environmental event/a volcanic eruption/an earthquake/a tsunami

4. A second named example

5. Genetic drift is more important in small populations (than large ones)

6. Alleles are more likely to be (completely) lost from the gene pool of a small population

A Describe the events of meiosis and how they lead to variation in gametes

1. Meiosis occurs in diploid gamete mother cells

2. There are two phases: meiosis I and meiosis II

3. In meiosis I, homologous chromosomes pair

4. The paired chromosomes undergo crossing over at chiasmata

5. DNA is exchanged and recombination occurs

6. Homologous pairs are separated

7. In meiosis II, sister chromatids are separated

8. Haploid gametes form [Any 5 for 1 mark each]

9. In meiosis I, homologous chromosomes separate independently

10. And irrespective of their maternal and paternal origin

11. Chiasmata formation is random

12. New combinations of alleles on linked chromosome are formed

Describe the basis of sex determination and how the sex of an organism might change during life.

1. Genetic factors can determine the sex

2. In live-bearing mammals sex chromosomes are involved

3. In mammals XX determines female/ homogametic sex

4. In mammals XY determines male/ heterogametic sex

5. The Y chromosome contains a gene/ SRY which causes maleness

6. XY males lack the homologous alleles on their Y chromosome

7. In Drosophila the XY chromosome system is also involved

8. Environmental factors can determine sex [Any 5 for 1 mark each]

9. Sex can change within an individual as a result of size/age

10. Competition

11. Parasitic infection

12. Some species are hermaphroditic/have both sexes present in one individual

Discuss factors that maximise the transmission of parasites.

1. Transmission is spread of parasites to host

2. Virulent parasites have high transmission rate

3. High host density

4. Vector in life-cycle can nullify the need for a healthy host OR eg of vector transmission

5. Transmission can be water-borne (even though host is incapacitated) OR eg.

6. Host behaviour is exploited

7. eg STD, ingestion during grazing, etc OR named example

8. Host behaviour can be modified

9. eg risk taking/habitat choice/anti-predator behaviour, etc OR named example

10. So (host behaviour) is extended phenotype of parasite

11. Suppression of host immune system

12. Modification of host size (infected hosts larger and so more spores)

13. Host reproductive rate modified (infected hosts breed less)

14. Rapid rate of evolution (ie overcoming host immunity improvements)

15. Asexual life-cycle phase allows rapid build-up of adapted parasites

Discuss photoreception in animal eyes under the following headings:

(i) photoreceptor system proteins;

(ii) triggering of a nerve impulse.

1. rhodopsin is the light-sensitive protein

2. (rhodopsin is) retinal combined with opsin

3. in membranes of retina/membrane location/photosensor

4. cones cells sense specific wavelengths/colours

5. (because of) different forms of opsin

6. rod cells absorb wider range of wavelengths

7. rods more sensitive in low light intensity

8. greater amplification in rod cells

9. amplification converts stimulation by photon into large effect on ion movement

10. photon stimulates change in conformation of rhodopsin

11. G protein/transducing activated

12. enzyme activated/phosphodiesterase

13. sufficient product/cyclic GMP to GMP/closes sodium channels

14. idea of increasing numbers

15. leads to nerve impulse

Discuss the movement of ions across membranes under the following headings:

(i) mechanism and functions of Na/KATPase;

(ii) nerve transmission

1. Ions pumped against concentration gradient OR ions moved by active transport

2. (3) sodium ions (pumped) out of cell and (2) potassium in

3. Pump uses/hydrolyses ATP

4. Phosphate attaches to protein/pump/NaKATPase

5. Phosphorylation alters conformation of protein

6. (Different conformations) have different affinity for sodium and potassium (Any 4)

7. Osmotic balance

8. Symports eg. sodium influx + glucose uptake

9. across nerve cell/resting potential

10. Ion gradients in nephrons

11. Resting potential across the plasma membrane

12. Ligand gated channel opens to allow ions in

13. Neurotransmitter is ligand

14. Ions enter and voltage (membrane potential) changes

15. Voltage change opens voltage-gated channels (nearby)

16. Sequence of v - gated channels open/wave of depolarisation

Describe how phosphate groups can affect the structure and function of proteins.

1. Addition or removal of phosphate causes conformational changes in protein

2. form of post-translational modification

3. kinases add a phosphate group

4. phosphatases remove phosphate group

5. conformation changes affect protein activity

6. activity can be regulated in this way

7. some proteins are activated by phosphorylation, others are inhibited

8. phosphate group adds negative charge, which can change ionic interactions in the protein.

Give an account of the different classes of amino acids and explain their roles in the tertiary structure of proteins.

1. Classes depend on R groups: hydrophobic R group has no charge

2. hydrophobic attractions

3. London dispersion forces between hydrophobic groups

4. basic R group has a positive charge; form ionic bonds

5. acidic R group has a negative charge; form ionic bonds

6. polar R group balances tiny charges

7. form hydrogen bonds

8. sulfur-containing amino acids can form covalent bonds/ disulfide bridges.

Give an account of the glucose symport in intestinal cells.

1. Transports glucose and sodium together/ simultaneously

into intestinal cells from the intestine lumen

2. sodium moves down its concentration gradient

3. providing energy for glucose movement

4. against its concentration gradient

5. sodium-potassium pump maintains sodium gradient/low concentration of sodium in intestinal cells.

Discuss endoparasitic infections under the following headings:

(i) difficulties involved in their treatment and control

(ii) benefits of improved parasite control to human populations

1. endoparasite defined as living within host

2. rapid antigen change/high antigenic variation

3. vaccines difficult to design/ produce

4. (some) parasites difficult to culture (in vitro/laboratory)

5. similarity between host and parasite metabolism

6. difficult to find drugs only toxic to parasite

7. difficulty associated with vector control

OR

indirect transmission

8. transmission rate high in tropical climate/

overcrowded situations

9. overcrowding (can occur) in

refugee camps/rapidly growing cities (in LEDCs) 10. difficult/expensive to improve

sanitation

Maximum 7 from 1 to 10

(ii) Benefits of improved parasite control to human populations: a. reduction in child mortality b. improvements in child

development/intelligence c. body uses more resources for growth/development

Discuss cell membranes under the following headings:

(i) the phospholipid bilayer as a selective barrier

(ii) types of transport proteins and their functions.

a. Channels/pumps/transporters are transmembrane.

b. Control ion concentrations OR Create/maintain concentration gradients.

c. Different cell types/cell compartments have different channel/transporter proteins OR example.

d. Movement through channels is passive/by diffusion/down a concentration gradient.

e. Transporter proteins change conformation (to transport molecules across membrane).

f. Conformational change in active transport requires energy from (hydrolysis of) ATP.

g. Ligand-gated channels opened/closed by binding of signal molecules/ligand.

h. Voltage-gated channels opened/closed by changes in ion concentration.

i. One from: Na/KATPase Maintains osmotic balance in animal cells Generates ion gradient for glucose symport Generates and maintains resting potentials in neurons Generates ion gradient in kidney tubules. OR Aquaporin 2 /AQP2 Transports water in the collecting duct. OR GLUT4 Transports glucose in fat/muscle cells.

j. Second example from i

Discuss the formation of variable gametes during meiosis under the following headings:

(i) the activity of homologous chromosomes

(ii) meiosis II.

1. (Homologous chromosomes) have the same size/centromere position/genes at same loci.

2. Pairing of (homologous chromosomes).

3. Chiasmata form where chromosomes/(non-sister) chromatids touch.

4. Chromatids break and rejoin OR crossing over occurs.

5. Exchange of DNA between (homologous) chromosomes/ non-sister chromatids.

6. (Leads to) new combinations of/recombination of alleles (of linked genes).

7. (Homologous chromosome pairs) line up randomly on spindle/equator/metaphase plate.

8. Independent assortment.

9. Separation of parental chromosomes irrespective of maternal and paternal origin.

Meiosis II

a. Chromosomes line up singly on equator.

b. (Sister) chromatids/chromosomes separate.

c. (And are) randomly distributed to the daughter cells/gametes.

d. (Four) haploid gametes formed.

Discuss animal reproduction strategies under the following headings:

(i) mating systems in animals (3)

(ii) courtship and female choice. (6)

1. Mating systems based on how many mates an individual has during one breeding season.

2. Monogamy: the mating of a pair of animals to the exclusion of all others.

3. Polygamy: individuals (of one sex) have more than one mate. 4. Polygyny: one male mates exclusively with a group of females.

5. Polyandry: one female mates with a number of males. (Any 3 from 1-5)

6. Listing all four system names without definitions.

a. Animals use courtship rituals to attract a mate

b. (Courtship behaviour can be a result of species-specific) sign stimuli and fixed action pattern (responses)

c. Sexual selection increases chance of mating

d. Sexual dimorphism a product of sexual selection

e. (In sexually dimorphic species) females are generally inconspicuous

OR (In sexually dimorphic species) males usually have more conspicuous markings/structures/ behaviours OR (In some species there is) reversed sexual dimorphism

f. Female choice involves females assessing honest signals

g. (Honest signals) indicate alleles that increase male fitness/the chances of survival of offspring

h. (Honest signals) indicate a low parasite burden (suggesting a healthy individual)

i. (In lekking species) males gather to display at a lek (where female choice occurs)

j. Dominant males occupy centre of lek* OR Subordinates and juveniles at the fringes as 'satellite' males.

Discuss changes in allele frequency under the following headings:

(i) Natural selection (4)

(ii) genetic drift (5)

1. Natural selection is non-random

2. (Natural selection) acts on/requires genetic variation in the population

3. Variation (in traits)/new alleles arise as a result of mutation/new sequences of DNA

4. Mutations can be beneficial/harmful (to the fitness of an individual)

5. Population produces more individuals than the environment can support

6. Individuals with favourable alleles/that are better adapted are more likely to survive and reproduce/produce offspring OR Individuals with favourable alleles/that are better adapted have higher fitness

7. Increase in frequency of advantageous alleles OR decrease in frequency of deleterious alleles

a. (Genetic drift occurs when) chance/random events cause unpredictable/random fluctuations in allele frequencies (from one generation to the next)

b. (Genetic drift) is more important in/more likely to affect small populations

c. Alleles are more likely to be lost from the gene pool (in small populations)

d. Population bottlenecks occur when a population is reduced (for at least one generation)

e. Founder effects occur through the isolation of a few members of a population (from a larger population)

f. Gene pool/allele frequency of new population is not representative of original

g. Alleles may be underrepresented/over-represented.

Describe courtship behaviours that affect reproductive success. (8)

1. Female choice assesses male fitness

2. Females assess honest signals (to assess fitness)

3. Fitness explained in terms of advantageous genes/low parasite burdens

4. Display behaviour of lekking species

5. Successful strategies of dominant and satellite males (in lekking species)

6. Example of lekking behaviour described

7. Male—male rivalry: large size/weaponry

8. Increases access to females through conflict

9. Behaviour of sneaker males

10. Importance of sign stimuli and fixed action pattern in birds/fish

11. Example of sign stimuli and fixed action pattern described

Describe the specific cellular defences that protect mammals from parasite infection.

1. Immune surveillance by white blood cells

2. T lymphocytes recognise antigens from pathogen

3. Antigens (from pathogen) displayed on the surface of infected cells

4. T lymphocytes destroy infected cells

5. T lymphocytes induce apoptosis

6. Phagocytes present antigens to lymphocytes

7. B lymphocytes produce specific antibodies

8. T lymphocytes/B lymphocytes amplified by clonal selection 9. A different lymphocyte is produced/selected for each antigen

10. Long-term survival of some members of T lymphocyte/B lymphocyte clones

11. Surviving lymphocytes act as immunological memory cells