Edexcel IAL biology Unit 2
protein synthesis - correct answer-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 - correct answer-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)
need for seed banks - correct answer-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 - correct answer-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.
cons for seedbank - correct answer-1. are not of interest to public.
2. cannot spread awareness/raise funds easily.
seedbank collection - correct answer-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 - correct answer-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 - correct answer-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 - correct answer-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 - correct answer-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.
meiosis importance - correct answer-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 - correct answer-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 - correct answer-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 - correct answer-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 - correct answer-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 - correct answer-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 - correct answer-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 - correct answer-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 - correct answer-1. spindle fibres break down.
2. nuclear membrane and nucleolus reforms.
3. centrioles reform and chromosomes unravel.
acrosome reaction - correct answer-1. when the sperm touches the ovum, acrosome
releases acrosin.
2. the acrosome fuses with cell surface membrane of sperm.
3. the acrosin will be released by exocytosis and will digest the zona pellucida and allow the
sperm to penetrate through the barrier.
protein synthesis - correct answer-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 - correct answer-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)
need for seed banks - correct answer-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 - correct answer-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.
cons for seedbank - correct answer-1. are not of interest to public.
2. cannot spread awareness/raise funds easily.
seedbank collection - correct answer-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 - correct answer-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 - correct answer-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 - correct answer-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 - correct answer-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.
meiosis importance - correct answer-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 - correct answer-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 - correct answer-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 - correct answer-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 - correct answer-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 - correct answer-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 - correct answer-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 - correct answer-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 - correct answer-1. spindle fibres break down.
2. nuclear membrane and nucleolus reforms.
3. centrioles reform and chromosomes unravel.
acrosome reaction - correct answer-1. when the sperm touches the ovum, acrosome
releases acrosin.
2. the acrosome fuses with cell surface membrane of sperm.
3. the acrosin will be released by exocytosis and will digest the zona pellucida and allow the
sperm to penetrate through the barrier.
