AQA A Level Biology 4/5/6
mark questions, (Certified
Answers)
Many different substances enter and leave a cell by crossing its cell surface
membrane. Describe how substances can cross a cell surface membrane.
(5)
1 (Simple / facilitated) diffusion from high to low
concentration / down concen...
AQA A-Level Biology long answer Qs,
AQA A Level Biology 4/5/6 mark
questions, TOPIC 2 AQA LONG ANSWER
Glucose is absorbed from the lumen of the small intestine into epithelial
cells. Explain how the transport of sodium ions is involved in the absorption
of glucose by epithelial cells. (5 marks) [Unit 1, June 16]
1. Na+ ions leave epithelial cell and enter blood;
2. (Transport out is by) active transport / pump / via carrier protein using
ATP;
3. So, Na+ conc. in cell is lower than in lumen (of gut);
4. Sodium/Na+ ions enter by FACILITATED diffusion;
5. Glucose absorbed with Na+ ions against their concentration/diffusion
gradient / glucose absorbed down an electrochemical gradient;
Oxygen and chloride ions can diffuse across cell-surface membranes. The
diffusion of chloride ions involves a membrane protein. The diffusion of
oxygen does not involve a membrane protein.
Explain why the diffusion of chloride ions involves a membrane protein and
the diffusion of oxygen does not. (5 marks) [Unit 1, June 16]
1. Chloride ions water soluble/charged/polar;
2. Cannot cross (lipid) bilayer (of membrane);
3. Chloride ions transported by facilitated diffusion OR diffusion involving
channel/carrier protein;
4. Oxygen not charged/non-polar;
5. (Oxygen) soluble in/can diffuse across (lipid) bilayer;
Blood leaving the kidney eventually returns to the kidney.
Describe the pattern of blood circulation in a mammal that causes blood to
return to the kidney. (6 marks) [Unit 2, June 16]
1. (blood flows from kidney along) renal vein to vena cava;
2. (along) vena cava to RIGHT atrium/side of heart;
3. (along) pulmonary artery to lungs;
4. (along) capillaries to pulmonary vein;
5. (along) pulmonary vein to RIGHT atrium/side of heart;
6. (along) aorta to renal artery (to kidney);
7. Blood may pass through several complete circuits before returning to
,subspecies has distinct coloured skin markings. Some biologists have
suggested that up to six of these subspecies should be classified as
different species.
Explain how different subspecies of giraffe may have evolved from a
common ancestor. Use information from the passage in your answer. (5
marks) [Unit 4, June 16]
1. No interbreeding / gene pools are separate / geographic(al) isolation;
2. Mutation linked to (different) markings/colours;
3. Selection/survival linked to (different) markings/colours;
4. Adapted organisms breed / differential reproductive success
5. Change/increase in allele frequency/frequencies;
Crops use light energy to produce photosynthetic products.
Describe how crop plants use light energy during the light-dependent
reaction. (5 marks) [Unit 4, June 16]
1. Excites electrons / electrons removed (from chlorophyll);
2. Electrons move along carriers/electron transfer chain releasing energy;
3. Energy use to join AFP and Pi to form ATP;
4. Photolysis of water produces protons, electrons and oxygen;
5. NADP reduced by electrons / electrons and protons / hydrogen;
Describe the advantages and disadvantages of using chemical pesticides
to control pests of crops. (5 marks) [Unit 4, June 16]
(Advantages)
1. Acts quickly;
2. Can apply to a particular area;
3. Kills all/most/wide variety of pests;
(Disadvantages)
4. Needs to be re-applied;
5. Not specific;
6. Pests can develop resistance;
7. (Bio)accumulation;
After harvesting, the remains of crop plants are often ploughed into the soil.
Explain how microorganisms in the soil produce a source of nitrates from
these remains. (5 marks) [Unit 4, June 16]
1. Protein/amino acids/DNA into ammonium compounds / ammonia;
2. By saprobionts;
,Describe and explain how cell fractionation and ultracentrifugation can be
used to isolate mitochondria from a suspension of animal cells. (5 marks)
[Unit 1, June 2015]
Any FIVE from:
1. Cell homogenisation to break open cells;
2. Filter to remove (large) debris/whole cells;
3. Use isotonic solution to prevent damage to mitochondria/organelles;
4. Keep cold to prevent/reduce damage by enzymes / use buffer to prevent
protein/enzyme denaturation;
5. Centrifuge (at lower speed/1000 g) to separate nuclei/cell
fragments/heavy organelles;
6. Re-spin (supernatant / after nuclei/pellet removed) at higher speed to get
mitochondria in pellet/at bottom;
Describe the principles and the limitations of using a transmission electron
microscope to investigate cell structure. (5 marks) [Unit 1, June 2015]
Principles:
1. Electrons pass through/enter (thin) specimen;
2. Denser parts absorb more electrons;
3. (So) denser parts appear darker;
4. Electrons have short wavelength so give high resolution;
Limitations:
5. Cannot look at living material / Must be in a vacuum;
6. Specimen must be (very) thin;
7. Artefacts present;
8. Complex staining method / complex/long preparation time;
9. Imagine not in 3D / only 2D images produced;
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The events that take place during interphase and mitosis lead to the
production of two genetically identical cells. Explain how. (4 marks) [Unit 2,
June 2015]
1. DNA replicated;
2. (Involving) specific/accurate/complemetary base-pairing;
3. (Ref to) two identical/sister CHROMATIDS;
4. Each chromatid/ moves/is separated to(opposite) poles/ends of cell;
A mutation can lead to the production of a non-functional enzyme. Explain
, 5. Change in ACTIVE SITE;
6. Substrate not complementary/cannot bind (to enzyme/active site) / no
enzyme-substrate complexes form;
On islands in the Caribbean, there are almost 150 species of lizards
belonging to the genus /Anolis/. Scientists believe that these species
evolved from two species found on mainland USA. Explain how the
Caribbean species could have evolved. (6 marks) [Unit 4, June 15]
1. GEOGRAPHIC(AL) isolation;
2. Separate gene pools / no interbreeding/gene flow (between populations);
3. Variation due to mutation;
4. Different selection pressures / different abiotic/biotic
conditions/environments/habitats;
5. Different(ial) reproductive success / selected organisms (survive and)
reproduce;
6. Leads to change/increase in ALLELE frequency;
/Anolis sagrei/ is a species of lizard that is found on some of the smallest
Caribbean islands. Describe how you could use the mark-release-recapture
method to estimate the number of /Anolis sagrei/ on one of these islands.
(4 marks) [Unit 4, June 15]
1. Capture/collect sample, mark AND release;
2. Method of marking does not harm lizard/make it more visible to
predators;
3. Leave sufficient time for lizards to (randomly) distribute (on island) before
collecting a second sample;
4. (Population =) number in first sample x number in second sample divided
by number of marked lizards in second sample/number recaptured;
We have an expert-written solution to this problem!
Large areas of tropical forest are still found on some Caribbean islands.
The concentration of carbon dioxide in the air of these forests changes over
a period of 24 hours and at different heights above ground.
Use your knowledge of photosynthesis and respiration to describe and
explain how the concentration of carbon dioxide in the air changes:
- over a period of 24 hours
- at different heights above ground. (5 marks) [Unit, June 15]
1. High concentration of/increase in carbon dioxide linked with respiration
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