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6 Sexual reproduction in mammals and plants
Answers to Exam practice questions
1 A and B
2 D
3 C
Middle piece/collar
Enables sperm to swim
Carries mitochondria/produces ATP/provides energy
(for swimming)
Carries chromosomes/carries DNA/has hydrolytic
For B, do not allow ‘produces energy’
b) Width of head measured as 10 mm = 10 000 μm;
Correct calculation using:
magnification =
size of image
size of object
= × 3333.3 ;
5 a) (Petal of flower) = 44;
(Zygote) = 44;
(Endosperm) = 66;
b) Nucleus formed by fusion/fertilisation of one male gamete and two polar nuclei;
All three nuclei are haploid/contain 22 chromosomes;
6 a) Capacitation of sperm must occur before sperm are able to fertilise secondary oocyte;
Capacitation) occurs in uterus/in oviduct;
(Without capacitation) glycoproteins remain on head of sperm;
(Without capacitation) no acrosome reaction occurs/no hydrolysis of zona pellucid;
b) Any four of the following points:
• The cortical reaction;
• Meiosis II is completed;
• Cleavage divisions produce more cells/blastomeres;
• Solid ball of blastomeres;
• Blastocyst is formed as a hollow ball of cells;
• (Blastocyst contains) inner cell mass and outer trophoblasts;
Credit appropriate descriptions of cortical reaction and meiosis II
© Hodder & Stoughton Limited 2015
6 Sexual reproduction in mammals and plants
Answers to Exam practice questions
7 a) Embryos and endosperm contain variable amount of water;
(Without water) can make valid comparisons of mass;
b) Heat to a temperature that evaporates water but does not burn the embryos or endosperm;
Until mass is constant;
Credit heat to any temperature between 80 °C and 100 °C
c) Subtract mass of embryo at day 0 from mass of embryo at day 4 and divide by 4;
(Give value as) g per day/g day ;
Credit (6.9 – 5.1) ÷ 4 as equivalent to 1 marking point
d) Growth of embryo uses amino acids to produce new protein/β-glucose to produce new
Growth of embryo uses ATP/energy from respiration;
Endosperm depleted as sources of amino acids/β-glucose/respiratory substrates used up; [3]
8 a) Pin-eyed have longer style/higher stigma than thrum-eyed;
Position of anthers in pin-eyed is halfway down the flower, in thrum-eyed anthers are near
the top of the flower;
b) i)
Cross pollination occurs when pollen from one plant lands on stigma of another plant;
Pollen from thrum-eyed flower sticks to top of bee’s mouthparts;
This pollen is not at the same level as this flower’s stigma;
If bee visits a pin-eyed plant, the pollen is at the same level as this flower’s stigma;
Allow converse descriptions of pollen sticking to mouthparts of a bee that visits a pineyed flower
Reduces likelihood of mutant alleles/alleles that are detrimental becoming homozygous;
Since half of plant’s gametes likely to contain a copy of the detrimental allele;
Maintains genetic diversity in population;
Stretch and challenge questions
9 a) 3.4 × 10 .
340 million is not acceptable, since an answer in standard form was required.
b) Chance of any sperm reaching the secondary oocyte is small; because uterus/oviduct is
hostile to sperm. With only 20 000 sperm mm , it is unlikely that any of this man’s sperm will
reach the secondary oocyte stage.
c) He is possibly fertile; since his fertility index is 10.
© Hodder & Stoughton Limited 2015
6 Sexual reproduction in mammals and plants
Answers to Exam practice questions
9 a) Use an eye-piece graticule; calibrated using a stage micrometer.
b) The length of the pollen tubes increases in (direct) proportion to time; the range of
lengths/variation in length increases as the tubes get longer.
c) Pollen tube growth involves production of new proteins; the difference between the normal
growth medium and the medium with actinomycin D is likely to be due to chance/not
(statistically) significant; because the standard deviations overlap; with actinomycin D, the
pollen tube is using mRNA (for protein production) already present in the pollen grain/is not
producing new mRNA; with cytochalasin, the existing mRNA cannot be translated/cannot be
used by ribosomes to produce new protein (for growth).
© Hodder & Stoughton Limited 2015