Chapter 21. Cell division, chromosomes and genes
Page 182
1. a Gametes are reproductive cells.
(i) Plants. The male gametes are the pollen nuclei and are produced in the anthers.
The female gametes are the egg cells in the ovules which are produced by the
ovary.
(ii) Animals. The male gametes are the sperms which are produced in the testes.
The female gametes are the ova which are produced in the ovaries.
b At fertilisation the nucleus of the male gamete fuses with the nucleus of the female gamete.
c A zygote is the cell formed from the fusion of the male and female gametes. It develops
into an embryo.
Page 183
1.There will be 2 x 46 = 92 chromatids at this stage. (See p. 184).
2. The chromosomes are too thin to be seen by the light microscope.
3. Cells in the basal layer will be dividing and producing more epidermal cells. Mitosis will be
taking place in these cells.
4. It is not possible to answer this question without more knowledge than is provided here.
Page 184
1. a 46 b 40 c 46.
2. 46.
Page 186
1. a human 23 b fruit fly 4.
2. White blood cell - diploid. Male cell in pollen grain - haploid. Guard cell - diploid. Root hair
- diploid. Ovum - haploid. Sperm - haploid. Skin cell - diploid. Egg cell in ovule - haploid.
3. a testes b ovary c stamen and ovule.
4. a 20 b 20.
5. Asexual reproduction takes place by mitosis. The chromosomes in each cell and therefore in
each individual are identical. There can be no variation..
Page 190
1. alanine - alanine - valine - glycine - valine.
2. CAT must have taken the place of the triplet CCA.
3. The gene determines the sequence of amino acids in the protein molecule which, in turn,
forms the enzyme. The enzyme controls a certain chemical reaction in the cell which affects
the cell’s structure.
4. Radiation causes an increase in mutation rate. If a mutation occurs in a gamete, it will affect
the offspring.
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Section 1, Chapters 1-5
Section 2, Chapters 6-9
Section 3, Chapters 10-12
Section 3, Chapters 13-17
Section 3, Chapters 18-20
Section 4, Chapters 21-24
Section 5, Chapters 25-27
Section 5, Chapters 28-29
Section 6, Chapters 30-34
Section 6, Chapters 35-37
Section 7, Chapters 38-39
Section 8, Chapters 40-41
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