1. 1
   Broad bean seeds were soaked in water and kept at 20 °C. Each day, some seeds were separated into cotyledons and embryo axis (the young root and shoot), dried and weighed. Over 10 days, the dry mass of the cotyledons fell from 1.20 g to 0.55 g per seed, while the dry mass of the embryo axis rose from 0.02 g to 0.40 g. In a separate observation, burdock fruits were found covered in hooks and attached to the fur of a dog.

   (a)

   The hooks on burdock fruits are an adaptation for:

   [1 mark]

   • Apollination by animals
   • Bgermination in dry soil
   • Cwind pollination
   • Dseed dispersal by animals

   (b)

   Which process allows the starch stored in the cotyledons to reach the growing embryo axis?

   [1 mark]

   • ACondensation of starch into cellulose in the cotyledons
   • BHydrolysis of starch by amylase into sugars, which are transported to the embryo
   • CPhotosynthesis in the cotyledons
   • DDiffusion of starch molecules through the seed

   (c)

   Explain why the dry mass lost by the cotyledons (0.65 g) is greater than the dry mass gained by the embryo axis (0.38 g).

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A home pregnancy test contains a strip along which a urine sample flows. Near the start of the strip are mobile monoclonal antibodies that bind to human chorionic gonadotropin (hCG) and are attached to coloured particles. Further along, at the test line, a second type of anti-hCG antibody is fixed in place. Beyond that, at the control line, fixed antibodies bind the mobile antibodies themselves. A woman who is 10 days past ovulation tests her urine and two coloured lines appear.

   (a)

   What produces the hCG detected by the test?

   [1 mark]

   • AThe woman's pituitary gland
   • BThe corpus luteum
   • CThe embryo or developing placenta
   • DThe endometrium

   (b)

   Why does a coloured line appear at the test line?

   [1 mark]

   • AhCG bound to the coloured mobile antibodies is captured by the fixed anti-hCG antibodies
   • BhCG is itself coloured and collects there
   • CThe fixed antibodies bind the coloured antibodies whether or not hCG is present
   • DProgesterone in the urine reacts with the fixed antibodies

   (c)

   Explain how hCG prevents menstruation in early pregnancy.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Early observational studies followed large numbers of women after the menopause. Women who chose to take hormone replacement therapy (HRT) had a much lower incidence of coronary heart disease (CHD) than women who did not, and it was concluded that HRT protects against CHD. Women taking HRT in these studies tended to have a higher socioeconomic status. Later, a randomised controlled trial allocated about 16 600 women at random to receive either HRT or a placebo. Over about 5 years, the rate of CHD events was 37 per 10 000 women per year in the HRT group and 30 per 10 000 women per year in the placebo group.

   (a)

   Calculate the percentage difference in the rate of CHD in the HRT group compared with the placebo group, and state what this indicates.

   [3 marks]

   (b)

   Explain why the observational studies and the randomised controlled trial reached different conclusions.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   From puberty, a man's testes produce roughly 1500 sperm every second throughout his adult life. In a woman, all the cells that will become eggs have begun developing before birth, and only about 400 eggs are released in her lifetime. An egg is about 0.1 mm across, with a volume thousands of times that of a sperm. Of the millions of sperm released during intercourse, a few hundred reach the egg in the oviduct, yet only one fertilises it. About a week later, the embryo implants in the uterus.

   (a)

   Compare spermatogenesis and oogenesis, and explain how they result in the differences in the numbers of gametes and the amount of cytoplasm they contain.

   [6 marks]

   (b)

   Describe the events from the arrival of sperm at the egg to implantation, including how polyspermy is prevented.

   [6 marks]

   Total for question 4: 12 marks

End of questions