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EDEXCEL IAL BIOLOGY UNIT 2
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EDEXCEL IAL BIOLOGY UNIT 2
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EDEXCEL IAL BIOLOGY UNIT 2protein synthesis - Answers- the ribosomes in the rough endoplasmic reticulum make
the proteins. the RER has a large surface area for the synthesis of the proteins. the
polypeptide chain is folded into a 3-D shape and then packaged into vesicles to be
transported to the Golgi apparatus. the proteins are modified in the Golgi
apparatus/enzyme is activated in the Golgi apparatus. carbohydrate is added to some
proteins to form glycoproteins. the proteins/enzymes are then enclosed in vesicles to
form lysosomes. the lysosomes fuse with the cell membrane and release the enzymes
out of the cell by exocytosis.
cellulose microfibrils - Answers- many beta-glucose units are held together by 1,4-
glycosidic bonds to form cellulose in a condensation reaction. every alternative
monomer unit has to be turned round/inverted so the bonding can take place. the
cellulose molecules formed are unbranched chains and these chains are held together
by hydrogen bonds. this is called cross-linking (holding neighbouring bonds together)
cons for seedbank - Answers- 1. are not of interest to public.
2. cannot spread awareness/raise funds easily.
seedbank collection - Answers- 1. seeds are collected from a large number of individual
plants to ensure a high genetic diversity.
2. seeds are x-rayed to check for fully formed embryos so that only viable seeds are
stored.
3. seeds are dried to prolong viability/survival and stored at -20dC to stop enzyme
activity and prevent germination and decomposition.
4. seeds are periodically germinated to make new seeds, replace dead and decaying
seeds and check for viability.
seedbank conditions - Answers- low temperatures and dry atmosphere-
1. reduces the enzyme activity and respiration in seeds.
2. the seed will thus be less likely to germinate/seed kept dormant.
3. this also reduces the enzyme activity and growth of bacteria/fungi/microorganisms.
4. this also decreases the rate of decomposition.
seedbanks and genetic diversity - Answers- 1. harvest the seeds from different plants
of the same species.
2. collect seeds from plants growing in different locations/countries.
3. this all will increase the variety of alleles in the plants by doin gthis a large gene pool
can be obtained.
zoos - Answers- 1. prevent extinction.
2. maintains breeding populations when habitats are lost.
3. breeding programmes increase numbers so endangered animals can be introduced
back into the wild.
4. zoos are used for research to gain a better understanding for conservation.
,5.zoos raise awareness to educate the public on endangered species.
captive breeding and genetic diversity - Answers- 1. '18 individuals is a small
population/small gene pool/low genetic diversity/may have been closely related.
2. captive breeding will increase population.
3. the animals can be taken care of in zoos.
4. they can also be exchanged from different zoos and may mate with other animals of
different zoos.
5. this will lead to an increase in their population size as more offspring will be
produces.
6. there will also be more genetic diversity.
7. stud books can be kept to select mates.
8. inbreeding must be prevented to avoid genetic drift.
9. IVF (pg 144) can be done to make sure fertilization is successful. the zygote can be
implanted into a surrogate mother.
10. genetic diversity can be measured using DNA profiling.
need for seedbanks - Answers- 1. food crop such as wheat, barley, rice and corn
(horticulture).
2. medicinal value.
3. materials, such as paper, clothing and building materials.
4. food for wildlife as plants are the base of all food chains.
5. recycling carbon dioxide and producing oxygen.
6. transpiration gives rise to rainfall.
pros for seedbank - Answers- 1. since seeds are small, they take up less space when
storing.
2. if large numbers of seed are stored there is greater genetic diversity.
3. seeds can also be stored for along time. because they can stay dormant for a long
time.
4. many different species of plants seeds can be stored easily and in similar conditions.
5. growing plants require more regular maintenance.
6. they are less expensive to keep than growing plants.
meiosis importance - Answers- 1. meiosis reduces the chromosome number in
gametes from diploid to haploid.
2. genetic variation is brought about in two ways :- crossing over and independent
assortment.
3. in crossing over, alleles/sections are exchanged between chromatids.
4. this leads to the formation of recombinants.
5. moreover, in independent assortment, the maternal and paternal genetic material is
completely randomly distributed into the gametes.
genetic variation in a species - Answers- 1. genetic variation is brought about in two
ways in meiosis.
2. in crossing over, sections of chromatids are exchanged.
, 3. this leads to the formation of recombinants.
4. errors in the progress lead to mutation which also introduces new combinations into
the genetic make-up of the species.
5. furthermore, in independent assortment, the maternal and paternal genetic material is
distributed completely at random.
6. moreover, a completely random ovum is fertilized by a completely different random
sperm.
specialized cells - Answers- 1. give a stimulus to the cell (e.g. chemical).
2. some genes are activated while others are deactivated.
3. only the active genes are transcribed to produce mRNA at those genes.
4. the mRNA is then translated to make a protein/polypeptide.
5. this protein permanently modifies the cell (and determines the structure and function
of the cell).
potential risks of stem cell treatment - Answers- 1. infection from donor/unsterilized
equipment.
2. increased suspectibility due to immunosuppressants.
3. risk of cancer/abnormal growth.
4. rejection.
role of the cell cycle - Answers- 1. in the cell cycle the organism grows as the number
of cells increase.
2. asexual reproduction or mitosis leads to the production of clones or genetically
identical daughter cells.
3. tissues are also repaired and the cells are replaced. (in phase- )
4. cell division is also controlled at checkpoints by enzymes called CDKs...
prophase - Answers- 1. nuclear membrane is disintegrated.
2. nucleolus is disintegrated.
3. chromosomes become shortened and thickened and more visible.
4. each chromosome now has two chromatids joined to a centromere.
5. centrioles start moving to the pole at late prophase.
metaphase - Answers- 1. centrioles reach the poles and form spindles. (plants do not
have centrioles but can form spindle fibres)
2. chromatids line up along the metaphase plate (equator) of the spindle.
3. centromeres of each chromatids attach with a separate microtubule of the spindle.
anaphase - Answers- 1. the overlapping microtubules (spindle fibres) contract - this
uses energy, pulling chromatids from each pair to opposite poles.
2. pairs of chromatids have been separated to opposite ends.
telophase - Answers- 1. spindle fibres break down.
2. nuclear membrane and nucleolus reforms.
3. centrioles reform and chromosomes unravel.
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