The answers to the end of chapter 12 questions of the CAPE Biology (Unit 1) textbook by Ramesar, Jones and Jones.Full description
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11 Ans Answers wers to end-of-chapter questi questions ons 1
C
[1]
2
B
[1]
3
B
[1]
4
C
[1]
5
C
[1]
6
B
[1]
7
C
[1]
8
D
[1]
9
C
[1]
10 C
[1]
Structured questions 11 a
b
c
I – fibrous layer II – vascular bundle III – tapetum IV – filament V – inner layer of fibrous layer VI – pollen mother cells / developing pollen grains Length of scale bar = 6 mm Therefore 6 mm = 200 μm Length from A to B = 104 mm Actual length = 104/6 × 200 = 3467 μm
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d
2 labels [1] [max 3]
Complete calculation [1] Partial [1]
Pollen mother cells undergo meiosis Each produces a tetrad of 4 haploid cells Cells absorb nutrients from tapetum Cells increase size Secretion of exine / outer walls Pollen grains separate Nucleus of each pollen grain divides by mitosis Produces generative and pollen tube nuclei Exine complete their development
Every 2 points [1] [max 4]
Meiosis occurs Produces gametes which contain haploid number of chromosomes • This is important because in sexual reproduction fertilisation of • gametes occurs • This allows for restoring of chromosome number / maintenance of a constant chromosome number / meiosis allows the chromosome number to remain constant in each generation Crossing over leads to genetic variation •
I – pollen tube II – locule III – nucellus IV – antipodal cells V – primary endosperm nucleus VI – egg cell VII – synergids VIII – funicle IX – placenta
Both serve as attachment points VIII attaches ovule to ovary wall / IX attaches ovary to rest of plant Haploid nucleus of pollen grain divides by mitosis Produces 2 nuclei – generative and pollen tube (B) The generative nucleus then divides by mitosis to give 2 male gametes (A) Both A and B are haploid
Any point [1]
4 points [3] 3 points [2] 2 points [1]
e
Micropyle allows pollen tube to enter the ovule so fertilisation can take place
[1]
f
•
[1] [1]
•
g
C / ovary becomes the fruit D / integuments become the testa
See diagram above / should be through the locule, close to ovary wall
Three of the four cells / megaspores nearest the micropyle degenerate Leaving one megaspore to develop
iii
Haploid (n) / one set of chromosomes
[1]
iv
Mitosis occurs three times
[1]
v
3 antipodal 2 polar 2 synergids 1 egg nucleus
vi
4 points [3] 3 points [2] 2 points [1]
Generative
[1]
vii 2 male nuclei 1 pollen tube nucleus b
•
[1] [1]
Separation of male and female plants / dioecious E.g. marijuana, pawpaw, chenet Monoecious / separation of male and female flowers but on same plant E.g. castor oil, corn, pumpkin Protandry / anthers mature before stigma E.g. rose-bay willow herb, fireweed Protogyny / stigmas mature before anthers E.g. avocado, soursop Self-incompatibility / if pollen grain with same allele as stigma, does not germinate E.g. tobacco, cabbage Any mechanism [1] Heterostyly: specialised pollination structures, pin and thrum example [1] E.g. red cordial, primrose [max 4]
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Essay questions 14 a • •
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b
i
Self-pollination meiosis occurs some genetic variation in offspring / crossing over produces gametes fertilisation produces seeds uses gametes / reproductive
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Biology for CAPE
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Asexual mitosis occurs genetically identical offspring / clones no gametes produced no fertilisation no seeds produced uses vegetative structures to multiply
Each comparison [1] [max 3]
Self-fertilisation Since plants are widely scattered, would not be close to other plants to pollinate / pollinating agents scarce No wastage of gametes Plants would be well adapted to the environment Can also be asexual
Since plants are widely scattered and rare, less likelihood of pollination / plants maybe adapted to the area, necessary to keep genetic information
Type [1] Reason [2]
Asexual Offspring genetically identical to parent therefore would be well adapted to the environment
Type [1] Reason [2]
Cross-fertilisation / cross-breeding Increases the amount of genetic variation in the population Better able to adapt to harsh environment / changing environment
Type [1] Reason [2]
Cross-fertilisation / cross-breeding Increases the amount of genetic variation in the population More resistant / less susceptible to diseases
Type [1] Reason [2] [max 12]
Pollination is the transfer of pollen from the anther, where it is made, to a stigma Fertilisation is the fusion of male and female gametes
[2]
b
stigma produces sucrose which helps in germination
•
pollen grain lands on stigma of same species • absorbs water • pollen grain starts to germinate •
•
•
•
•
style – pollen tube pushes out from pit and grows down the style; digestive enzymes are secreted from tip generative nucleus divides by mitosis to produce 2 male nuclei pollen tube nucleus is at the tip of the tube guiding the tube towards the ovule ovule secretes chemicals to guide pollen tube / chemotaxis
•
•
•
Biology for CAPE
ovary – pollen tube enters the ovary wall; tissue of ovary wall is dense locule – has space for pollen tube to pass; it stays close to ovary wall (but in the locule) to obtain nutrients pollen tube enters the micropyle towards embryo sac
pollen tube nucleus disintegrates and tip ruptures to release male gametes
At least 4 drawings in correct sequence [3] Partial [2] Double fertilisation
1 annotation per drawing 1 mark [max 4] Ideas can be incorporated in fewer drawin s
products of fertilisation – diploid zygote and triploid endosperm in embryo sac
c
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• •
•
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•
•
Zygote undergoes repeated mitotic divisions to produce basal cell, suspensor and embryo Tissues differentiate Embryo consists of a plumule, radicle and one or two cotyledons Cotyledons act as food for future seed Basal cell absorbs nutrients from endosperm / nucellus / parent plant for embryo to grow Suspensor is a short stalk of cells which pushes embryo into the embryo sac It also aids in absorption of nutrients Endosperm nucleus divides repeatedly by mitosis to form the endosperm / undifferentiated cells Endospermous seeds – endosperm remains the food store / oils / starch / layer of protein Non-endospermous seeds – food is absorbed by 1 mark for each zygote [max 3] cotyledon 1 mark for each endosperm [max 3]
passes through filament / contains xylem and phloem
b
•
c
Pollen mother cells undergo meiosis • Each produces a tetrad of 4 haploid cells Cells grow in size • Cell wall patterns develop • Pollen grains separate • nucleus of each pollen grain divides by mitosis • • produces generative and pollen tube nuclei • generative nucleus divides by mitosis to produce 2 haploid male gametes
Drawing neat and clear [1] Drawing neat and clear Any 3 annotations[1] or more or [3] Any 3 annotations 2–3 annotations [2] more [3] 1 annotation[2] [1] 2–3 annotations Drawing with[1] no 1 annotation annotations but Drawing with no 3 labelsbut [1] annotations [max[1] 4] 3 labels
Advantages Increased genetic variation • Leads to increased heterozygosity / more likely to have two different alleles of any • gene More vigour / less susceptible to diseases / not all plants wiped out by diseases • Widens gene pool • Better adapted to changing environment / more evolutionary potential • Any valid point Any 2 points [2] • Disadvantages • Need another plant for fertilisation – not reliable if plants are widely scattered Wastage of gametes • May lose advantageous alleles / plants may be well adapted to a stable environment • May receive unfavourable alleles • Diseases may be transferred • • Any valid point Any 2 points [2]
nucellus – made up of parenchyma / undifferentiated cells / contains nutrients
vascular strand – contains xylem and phloem
Integuments – outer covering of ovule
embryo sac developed from a megaspore; haploid / consists of 3 antipodal cells, 2 polar nuclei, 2 synergids and 1 egg nucleus
funicle – a short stalk which attaches ovule to the ovary wall
micropyle – a pore in the integuments
b
• • • • • • • •
• • • •
Diploid megaspore mother cell in ovule / nucellus divides by meiosis Produces 4 haploid cells 3 cells degenerate Remaining cell absorbs nutrients from nucellus Grows into the embryo sac Haploid nucleus within embryo divides three times by mitosis Produces 8 nuclei 3 nuclei move to chalaza / opposite micropyle end to become antipodal cells 2 move to the middle to become the polar nuclei Polar nuclei can fuse to produce the diploid primary nucleus 3 nuclei at the micropyle end These are made up of the egg nucleus in the middle with 2 synergids on the ends
Biology for CAPE
Drawing neat and clear [1] Any 3 annotations or more [3] 2–3 annotations [2] 1 annotation [1] Drawing with no annotations but 3 labels [1] [max 4]
Advantages • Reliable, especially where pollinating agents are scarce or wildly scattered • Offspring genetically very similar to parent therefore would be well adapted to the stable environment Retention of valuable genotypes / preserves genetic makeup • No wastage of gametes • Any valid point Any 2 points [2] • Disadvantages • Less genetic variation • Leads to increased homozygosity / more likely to have the same two alleles of any gene Plant would not be well adapted in a changing environment / evolution restricted • Increases expression of unfavourable allele • Restricts gene pool • • Inbreeding depression • Any valid point Any 2 points [2]
