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BIOLOGY UNIT 4- EDEXCEL IAL PPQS
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BIOLOGY UNIT 4- EDEXCEL IAL PPQS
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BIOLOGY UNIT 4: EDEXCEL IAL PPQSDescribe the structures in a chloroplast that are involved in the light-dependant
reactions of photosynthesis. - Answers- 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. - Answers- 1) crops can be grown out of
season/all year round/eq.
2) plants can photosynthesise 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. - Answers- 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. - Answers-
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. - Answers- 1) ribosomes/RER
2) descriptive feature e.g (for ribosome) - 2 subunits (for RER) ribosome attached to
membrane.
State how the genetic material in HIV differs from the genetic material in the
bacterium Mycobacterium tuberculosis that causes TB. - Answers- 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 - Answers- 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. - Answers- 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.
6) by action of reverse transcriptase.
7) ref. to formation of new viruses.
8) lymphocytes destroyed when new viruses bud out of/ leave the cell/eq.
9) T-killer cells destroy T-helper cells.
Explain how CO2 + ammonia are formed during the first stage of decomposition
(putrefaction). - Answers- 1) ref. to MO/ microbes/ bacteria/ fungi/eq.
2) ref. to respiration of MO/ bacteria/ fungi/eq.
3) ref. to aerobic/ anaerobic respiration.
4) converts organic compounds/eq. to CO2.
5) converts nitrogen compounds/ proteins/ amino acids/ urea to ammonia/eq.
Suggest why time taken for decomposition changes at different times of the year. -
Answers- 1) correct ref. to temperature effect.
2) correct ref. to water availability.
3) correct ref. to water logging reduces O2 availability/eq.
4) correct ref. to frozen water.
5) ref. to more insects/ decomposers/ eq. in summer.
6) correct ref. to the growth rate of MOs/ eq.
7) ref. to rate of metabolism/ enzyme reactions.
Explain what is meant by gene mutation - Answers- 1) change in DNA
2) ref. to change/deletion/addition/duplication/substitution/eq. of bases/nucleotides.
Theory used in DNA profiling - Answers- 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. - Answers-
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 - Answers- 1) comparisons made between DNA from fossils and other
organisms.
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