Edexcel A Level Biology Topic 4 Exam Questions

Explain how breeding programmes in zoos maintain the genetic diversity of captive populations. (3)

• M1: Animals are selected to prevent {breeding between closely related individuals/ inbreeding depression}

• M2: A stud book is used to {select individuals for mating/ keep a record of all breeding events}

• M3: Exchange of {animals/ gametes} between zoos

Describe how clinical trials of a vaccine would be conducted. (3)

• M1: small group of healthy volunteers are given the vaccine to test for side effects

• M2: Healthy volunteers tested for the presence of antibodies to the virus following vaccination

• M3: A group of people at risk of contracting the disease is given the vaccine

• M4: A number of people who develop the viral disease following vaccination are monitored

State suitable conditions for keeping seeds in a seed bank. (2)

• M1: cold

• M2: dry

Sterile nutrient agar is a medium used for growing microbes.

Describe how aseptic techniques are used when handling bacterial cultures. (3)

• M1: Working near a bunsen burner (to provide a convection current)

• M2: Sterilising work surfaces

• M3: Sterilising equipment with heat (eg. flaming of {forceps/ bottle necks/ inoculating loops})

• M4: Limiting time containers are open (only partially lifting lids from petri dishes)

Explain the role that a placebo and a double blind trial have in producing valid conclusions. (4)

• M1: Placebo because it provides a control group for comparison

• M2: therefore ensuring that the {active ingredient/ drug} is causing the effect

• M3: Double blind because neither doctors nor patients know who has been given the actual drug

• M4: therefore ensures that bias is removed from the trial.

Explain the advantages of drying seeds before storage. (2)

M1: Extends storage times of the seeds

M2: Because drying prevents {germination/ decomposition} of seeds

Explain why the bacteria are able to multiply in the bloodstream when they enter the body. (3)

• M1: {warm conditions/ water/ glucose/ amino acids/ ideal pH available}

• M2: suitable {temperature/ pH} for bacterial enzymes

• M3: Glucose used for {respiration/ energy}

• M4: Amino acids used for growth

Explain why the use of bamboo fibres to make coffee cups is sustainable. (2)

• M1: Available for future generations

• M2: Bamboo is renewable resource

• M3: More bamboo plants can be grown

Describe the role that zoos play in animal conservation. (3)

• M1: Role in protection (protection from poachers/ hunting)

• M2: Role in repopulation (increase numbers, breeding programmes, release back into wild)

• M3: Role in education (conservation)

• M4: Role in research (improving health, discovering better nutrition, developing a genetic data base)

Describe the structure of starch. (3)

• M1: Starch is a polysaccharide made from alpha glucose

• M2: Monomers in the chain are joined by 1,4-glycosidic links

• M3: Starch contains {unbranched chain/ amylose} and {branched chain/ amylopectin}

• M4: Branches are joined to chains by 1,6-glycosidic links

Explain the relationship between the structure and function of a granum in photosynthesis. (3)

• M1: (granum) is formed from many layers of thylakoid membranes to increase surface area for absorbing light.

• M2: Thylakoid membranes contain chlorophyll to absorb light

• M3: Electron carrier molecules in thylakoid membrane involved in ATP production (photophosphorylation)

Describe how nitrate ions are transported from the roots to the leaves. (2)

M1: Through xylem vessels

M2: in {water/solution} (allow via transpiration)

Compare and contrast the structure of cellulose and amylopectin. (3)

• M1: both are {polysaccharides/ polymers of glucose}

• M2: Both contain 1-4 glycosidic bonds

• M3: Cellulose contains {beta glucose} whereas amylopectin contains {alpha glucose}

• M4: Cellulose is {not branched/ does not contain 1-6 glycosidic bonds}

Explain why seedling needs a supply of magnesium ions. (2)

M1: Magnesium is needed to make chlorophyll

M2: Because chlorophyll is required for photosynthesis

M3: Because shoots need chlorophyll to carry out photosynthesis to grow.

Explain the role of the middle lamella when a plant cell completes mitosis. (2)

M1: Produced between adjacent new cells in cell plates

M2: because the middle lamella holds cell walls together

Explain the effects of a shortage of magnesium ions on a plant. (3)

M1: A shortage of magnesium ions limits the production of chlorophyll

M2: Lack of {glucose/ carbohydrate/ cellulose} due to less photosynthesis

M3: Therefore plant leaves may be yellow/ may be small (allow stunted growth/ slow growth)

State what is meant by the term tensile strength. (1)

• The pulling force that fibres can withstand before breaking

Describe how tensile strength of fibres can be measured. (3)

• M1: Tensile strength calculated as a factor of force divided by cross sectional area of fibre

• M2: Addition of {force/ weight/ mass} to a fibre

• M3: Measurement of {force/ weight/ mass} required to break fibre

• M4: Calculation of cross sectional area

Explain how the structure and properties of starch are related to its function as a storage molecule. (3)

• M1: Contains glucose needed for {respiration/ energy}

• M2: Insoluble so has {no osmotic effect/ remains in the cell}

• M3: Amylose is coiled making starch compact so more can be stored

• M4: Amylopectin is {branched/ contains 1-6 glycosidic bonds} so is rapidly hydrolysed.

Describe the positions in the stem of those tissues that contain lignin. (2)

• M1: Sclerenchyma fibres on the outer side of the {vascular bundle/ phloem}

• M2: Xylem vessels on the {inner side/ inside} of the vascular bundle

Describe the arrangement of glucose in a cellulose molecule. (2)

• M1: Monomers are connected by 1-4 glycosidic links

• M2: Alternate monomers are inverted

Explain how the structures of amylopectin and glycogen make them suitable for storing energy. (3)

M1: Branched therefore can be rapidly hydrolysed to produce glucose

M2: Compact so more energy/ glucose can be stored

M3: insoluble therefore does not affect osmosis

M4: Molecules too large to diffuse across cell surface membrane

What does the wall of the sieve tube element contain? (1)

• Hemicellulose, microfibrils, and pectin

Define endemic. (1)

• It is found only in one location/ geographical location

State what is meant by the term allele. (1)

• {alternative form/ different form/ version/ variation} of a gene

Describe what needs to be measured in order to compare the biodiversity of two rainforests. (2)

• M1: Counting the number of different species (measure species richness)

• M2: Counting number of individuals per species

Explain how two species of a snake could have arisen from a common ancestor. (4)

• M1: Mutations lead to {variation within the population of snakes}

• M2: Natural selection led to those snakes which were better adapted to survive and reproduce

• M3: Therefore giving rise to two populations with different allele frequency

• M4: As a result of natural selection, two populations become reproductively isolated

• M5: Sympatric speciation (in the context of new species developing in the same habitat)

Describe how molecular phylogeny can be used to show that these two populations are reproductively isolated. (3)

• M1: Comparing similarities/ differences in {DNA/proteins}

• M2: Comparison of {nucleotide sequences/ amino acid sequences}

• M3: The more the number of differences, the more likely they are to be reproductively isolated

State what is meant by the following terms:

1. Species Richness

2. Heterozygosity index

• M1: species richness measures the number of species in a habitat

• M2: Heterozygosity index is a measure of genetic diversity within a {species/ population}

State what is meant by the term species. (1)

• A group of organisms that can interbreed to produce fertile offspring

Explain how the Hardy-Weinberg equation can be used to show that natural selection is occurring in a population. (2)

• M1: Hardy-Weinberg equation shows allele frequency in a population

• M2: If natural selection is occurring, there would be a change in allele frequency over time