Question 1
Paper 1A style
Which statement describes an advantage of asexual reproduction compared with sexual reproduction?
- It produces offspring with new combinations of alleles.
- It produces offspring that are well adapted if the environment changes.
- It produces genetically identical offspring of a parent adapted to an existing environment.
- It increases genetic variation within a population.
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Answer: C [1]
Question 2
Paper 1B style
The table shows the concentrations of four hormones in the blood of a woman on selected days of one menstrual cycle (arbitrary units, data for practice). (a) Identify the day on which ovulation most probably occurred. [1] (b) Explain the change in LH concentration between day 10 and day 14. [2] (c) Explain why the endometrium breaks down after day 26. [2]
| Day | FSH | LH | Oestradiol | Progesterone |
|---|---|---|---|---|
| 2 | 8 | 6 | 4 | 1 |
| 10 | 6 | 8 | 14 | 1 |
| 14 | 14 | 58 | 18 | 2 |
| 21 | 3 | 5 | 10 | 16 |
| 26 | 4 | 4 | 5 | 4 |
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- (a) day 14 / when LH peaks [1]
- (b) LH rises sharply / LH surge from 8 to 58 units [1]
- (b) oestradiol concentration rises to a high level / from 14 to 18 units [1]
- (b) high oestradiol stimulates (pituitary) LH secretion / positive feedback [1]
- (c) progesterone falls / from 16 to 4 units [1]
- (c) because the corpus luteum degenerates (no pregnancy / no hCG) [1]
- (c) progesterone no longer maintains the endometrium [1]
- [max 5]
Question 3
Paper 2A style
(a) Outline what happens to the sperm and egg nuclei after a sperm's membrane fuses with the egg membrane. [2] (b) Outline how hormones are used at the start of IVF treatment. [2]
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- (a) sperm nucleus enters the egg; tail and mitochondria destroyed [1]
- (a) nuclear membranes of sperm and egg nuclei dissolve [1]
- (a) chromosomes from both take part in one (joint) mitosis producing two diploid nuclei [1]
- (b) drug suspends normal secretion of (FSH/LH) hormones / down-regulation [1]
- (b) large / artificial doses of FSH injected [1]
- (b) to induce superovulation / many follicles develop [1]
- [max 4: max 2 for each part]
Question 4
Paper 2B style
Explain how flowering plants promote fertilization by gametes from different plants.
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- male gametes are inside pollen grains; female gametes are inside ovules [1]
- pollination is transfer of pollen from anther to stigma [1]
- cross-pollination is transfer to a different plant (of the same species) [1]
- pollen and stigma mature at different times (in the same flower) [1]
- separate male and female flowers on one plant (e.g. maize) [1]
- separate male and female plants (e.g. holly) [1]
- animals / insects carry pollen between plants, attracted by petals / scent / nectar [1]
- wind carries pollen between plants [1]
- self-incompatibility genes / S alleles cause pollen from the same plant to be rejected [1]
- pollen with an allele matching the stigma / style fails to germinate / tube stops growing [1]
- self-pollination leads to inbreeding, which reduces genetic diversity / vigour [1]
- pollen tube grows down the style to the ovule so the male gamete can fuse with the egg [1]
- [max 7]
Question 5
Paper 2A style
(a) Distinguish between seed dispersal and pollination. [1] (b) Outline how food reserves are mobilized when a seed germinates. [2]
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- (a) pollination moves pollen from anther to stigma (before fertilization) whereas dispersal moves seeds away from the parent plant (after fertilization) [1]
- (b) water absorbed, activating enzymes / gibberellin production [1]
- (b) amylase digests starch into maltose / sugars OR proteases digest proteins into amino acids [1]
- (b) soluble products transported to the embryo for respiration / growth [1]
- [max 3]
Question 6
Paper 1A style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanWhich feature occurs in oogenesis but not in spermatogenesis?
- Mitosis of germ cells
- Two divisions of meiosis
- Unequal division of cytoplasm during meiosis
- Differentiation of haploid cells
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Answer: C [1]
Question 7
Paper 2A style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels mean(a) Outline the role of the acrosome reaction in fertilization. [1] (b) Explain how a pregnancy test strip detects pregnancy. [3]
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- (a) acrosome releases enzymes that digest (a path through) the zona pellucida so the sperm can penetrate it [1]
- (b) detects hCG (in urine) [1]
- (b) hCG is produced by the embryo / developing placenta [1]
- (b) mobile monoclonal antibodies (with coloured marker) bind hCG [1]
- (b) immobilised antibodies in the test line bind the hCG complex producing a coloured line [1]
- (b) control line shows the test has worked [1]
- [max 4]
Question 8
Paper 2B style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanExplain the hormonal control of pregnancy and childbirth.
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- embryo / trophoblast secretes hCG [1]
- hCG maintains the corpus luteum [1]
- corpus luteum secretes progesterone (and oestradiol) [1]
- progesterone maintains the endometrium / prevents menstruation [1]
- progesterone inhibits contractions of the uterus / myometrium [1]
- placenta takes over progesterone secretion (after about 3 months) [1]
- at the end of pregnancy progesterone levels fall [1]
- allowing oxytocin secretion (by the posterior pituitary) to increase [1]
- oxytocin stimulates contractions of the myometrium [1]
- contractions / stretching of the cervix stimulate more oxytocin secretion [1]
- positive feedback so contractions become stronger / more frequent until birth [1]
- [max 6]