BIOLOGY UNIT 4: EDEXCEL IAL TEST
PAPER AND ALL CORRECT
ANSWERS 2025-2026 UPDATED.
Describe the structures in a chloroplast that are involved in the light-dependent reactions of
photosynthesis. - Answer 1) ref. to thylakoids.
2) made of membranes.
3) arranged as stacks/grana/eq.
4) contain chlorophyll}/eq.
5) arranged as photosystems.
Suggest 2 advantages of growing crops of wheat in glasshouses with artificial lighting rather
than growing them in open fields. - Answer 1) crops can be grown out of season/all year
round/eq.
2) plants can photosynthesis 24 hours a day/eq.
3) idea of less physical damage from weather/animals/eq.
4) pest control easier/eq.
5) ref. to control of other named factor (e.g CO2, temperature, humidity, water supply).
Explain how the increases in CO2 and CH4 released into the atmosphere may be contributing
towards the estimated changes mean temperature. - Answer 1) CO2 and CH4 are both
greenhouse gases.
2) trap/absorb heat/IR/long-wave radiation /eq.
3) idea of reflected form Earths surface/ re-radiation.
4) mean temperature of Earths surface increases/eq.
Suggest why higher and lower estimates of global temperatures are made. - Answer
appropriate comment on changes in production of gases e.g higher estimate assumes no
change in production of gases/ lower estimate takes into account reduction in carbon emissions.
Name and describe the structures where the polypeptide chain of an enzyme would be
synthesised. - Answer 1) ribosomes/RER
2) descriptive feature e.g (for ribosome) - 2 subunits (for RER) ribosome attached to membrane.
Explain what is meant by gene mutation - Answer 1) change in DNA
2) ref. to change/deletion/addition/duplication/substitution/eq. of bases/nucleotides.
, Theory used in DNA profiling - Answer 1) DNA profiling assumes everyones DNA is
unique/different/eq.
2) apart from identical twins/eq.
3) ref. to DNA profiling analyses the introns/nc-blocks/short tandem repeats/eq.
4) nc-DNA is very variable/eq.
5) large number of introns/nc-blocks/eq.
6) idea of many combinations/eq. at each locus.
Explain why evidence from DNA profiles may not be absolutely conclusive. - Answer 1) ref. to
DNA profiling has several stages.
2) ref. to contamination/eq. can arise at any stage.
3) only a few sequences/small portion of DNA is analyses/eq.
4) ref. to possibility of 2 identical profiles form unrelated individuals.
5) identical twins/closely related individuals/eq. may show same profile/eq.
Suggest hoe DNA profiling could be useful to scientists who examine fossils of animals and
plants - Answer 1) comparisons made between DNA from fossils and other organisms.
2) to find genetic relationships/eq.
3) ref. to use in taxonomy/ classification/eq.
4) to understand evolutionary lines/ to determine common ancestors/eq.
State how the genetic material in HIV differs from the genetic material in the
bacterium Mycobacterium tuberculosis that causes TB. - Answer 1) RNA in HIV and DNA in
M.TB/eq.
2) comparative description of nucleic acid (e.g circular in M.TB and linear in HIV).
3) plasmids in M.TB and no plasmids in HIV.
Explain why unbroken skin is an effective barrier against HIV infection - Answer 1) keratin in
skin surface/epidermis.
2) idea of forms a hard/ impenetrable/ physical/ eq. barrier.
Explain the decrease in numbers of CD4 T-lymphocytes during the first 6 weeks after infection
with HIV. - Answer 1) glycoprotein on virus/ eq.
2) binds with receptors/CD4/eq.
3) on membrane of lymphocytes/ eq.
4) viral RNA enters the lymphocyte/ eq.
5) viral RNA used to produce viral DNA (in lymphocyte/eq.
PAPER AND ALL CORRECT
ANSWERS 2025-2026 UPDATED.
Describe the structures in a chloroplast that are involved in the light-dependent reactions of
photosynthesis. - Answer 1) ref. to thylakoids.
2) made of membranes.
3) arranged as stacks/grana/eq.
4) contain chlorophyll}/eq.
5) arranged as photosystems.
Suggest 2 advantages of growing crops of wheat in glasshouses with artificial lighting rather
than growing them in open fields. - Answer 1) crops can be grown out of season/all year
round/eq.
2) plants can photosynthesis 24 hours a day/eq.
3) idea of less physical damage from weather/animals/eq.
4) pest control easier/eq.
5) ref. to control of other named factor (e.g CO2, temperature, humidity, water supply).
Explain how the increases in CO2 and CH4 released into the atmosphere may be contributing
towards the estimated changes mean temperature. - Answer 1) CO2 and CH4 are both
greenhouse gases.
2) trap/absorb heat/IR/long-wave radiation /eq.
3) idea of reflected form Earths surface/ re-radiation.
4) mean temperature of Earths surface increases/eq.
Suggest why higher and lower estimates of global temperatures are made. - Answer
appropriate comment on changes in production of gases e.g higher estimate assumes no
change in production of gases/ lower estimate takes into account reduction in carbon emissions.
Name and describe the structures where the polypeptide chain of an enzyme would be
synthesised. - Answer 1) ribosomes/RER
2) descriptive feature e.g (for ribosome) - 2 subunits (for RER) ribosome attached to membrane.
Explain what is meant by gene mutation - Answer 1) change in DNA
2) ref. to change/deletion/addition/duplication/substitution/eq. of bases/nucleotides.
, Theory used in DNA profiling - Answer 1) DNA profiling assumes everyones DNA is
unique/different/eq.
2) apart from identical twins/eq.
3) ref. to DNA profiling analyses the introns/nc-blocks/short tandem repeats/eq.
4) nc-DNA is very variable/eq.
5) large number of introns/nc-blocks/eq.
6) idea of many combinations/eq. at each locus.
Explain why evidence from DNA profiles may not be absolutely conclusive. - Answer 1) ref. to
DNA profiling has several stages.
2) ref. to contamination/eq. can arise at any stage.
3) only a few sequences/small portion of DNA is analyses/eq.
4) ref. to possibility of 2 identical profiles form unrelated individuals.
5) identical twins/closely related individuals/eq. may show same profile/eq.
Suggest hoe DNA profiling could be useful to scientists who examine fossils of animals and
plants - Answer 1) comparisons made between DNA from fossils and other organisms.
2) to find genetic relationships/eq.
3) ref. to use in taxonomy/ classification/eq.
4) to understand evolutionary lines/ to determine common ancestors/eq.
State how the genetic material in HIV differs from the genetic material in the
bacterium Mycobacterium tuberculosis that causes TB. - Answer 1) RNA in HIV and DNA in
M.TB/eq.
2) comparative description of nucleic acid (e.g circular in M.TB and linear in HIV).
3) plasmids in M.TB and no plasmids in HIV.
Explain why unbroken skin is an effective barrier against HIV infection - Answer 1) keratin in
skin surface/epidermis.
2) idea of forms a hard/ impenetrable/ physical/ eq. barrier.
Explain the decrease in numbers of CD4 T-lymphocytes during the first 6 weeks after infection
with HIV. - Answer 1) glycoprotein on virus/ eq.
2) binds with receptors/CD4/eq.
3) on membrane of lymphocytes/ eq.
4) viral RNA enters the lymphocyte/ eq.
5) viral RNA used to produce viral DNA (in lymphocyte/eq.
