Reproduction: Biology 0610 (Cambridge O Level / IGCSE)

A rose bush is home to a large colony of aphids (small sap-feeding insects). Throughout the summer, every aphid in the colony is female. Each female produces many new aphids without mating with a male: every new aphid develops from a single egg cell inside her body, and each one is genetically identical to her. As autumn approaches, some females instead produce egg cells that must first be fertilised by a male aphid before they can develop into the next generation.

Which statement correctly compares these two ways in which the aphids produce new individuals?

A botanist compares two plant species growing in the same meadow: a bell-flower, whose brightly coloured flowers are visited by bumblebees, and a meadow grass, whose small green flowers have no petals and hang loosely in the wind.

(a) State the function of each of these structures found inside the bell-flower. (i) anther (ii) stigma (iii) ovule [3]

(b) The meadow grass produces huge numbers of small, light, smooth pollen grains. The bell-flower produces far fewer, larger, sticky pollen grains. Explain how each type of pollen grain is suited to the way it is transferred to a stigma. [2]

(c) The botanist collects seeds from both plants and sets up three sealed trays to test what seeds need in order to germinate. Tray 1 has moist soil at room temperature. Tray 2 has dry soil at room temperature. Tray 3 has moist soil, but all of the air inside the sealed tray has been replaced with nitrogen gas, at room temperature. State the germination requirement being tested by comparing Tray 1 with Tray 2, and the germination requirement being tested by comparing Tray 1 with Tray 3. [2]

A midwife runs a workshop for trainee health workers, using models of the human reproductive system and the developing fetus.

(a) State the function of each of these structures in human reproduction. (i) testes (ii) prostate gland (iii) oviduct [3]

(b) State one adaptive feature of a sperm cell, and state one adaptive feature of an egg cell (ovum). [2]

(c) A trainee asks why millions of sperm cells are released during ejaculation, yet only one egg cell matures and is released roughly each month. State the difference in number and the difference in motility between sperm cells and egg cells, and suggest why these differences are useful for successful fertilisation. [2]

(d) The midwife explains that once an embryo implants, the placenta forms in the wall of the uterus. Explain how the placenta allows a fetus to obtain oxygen and nutrients from its mother's blood, and state one other type of substance, besides oxygen and nutrients, that can also cross the placenta and may harm the fetus. [3]

A student researching human fertility reads the following description of one part of the menstrual cycle.

"Rising levels of one hormone cause an egg cell to mature inside a follicle in an ovary. A sharp rise in a second hormone then triggers the follicle to release the egg cell (ovulation). After ovulation, the remains of the follicle develop into a structure that produces a third hormone, which maintains the thickened lining of the uterus. If the egg cell is not fertilised, the level of this third hormone falls, and the lining of the uterus breaks down."

(a) Name hormone 1, hormone 2 and hormone 3 described above. [3]

(b) Name the structure in the ovary that develops from the remains of the follicle after ovulation. [1]

(c) Explain what happens to the level of hormone 3 if the egg cell is fertilised and implantation occurs, and explain why this change is necessary for the pregnancy to continue. [3]

(d) State two secondary sexual characteristics that develop in females during puberty as a result of rising oestrogen levels. [2]

A community health worker is designing a poster to help control the spread of sexually transmitted infections (STIs), including HIV, in a local town.

Which of these actions would be most effective in reducing the spread of STIs, including HIV, through unprotected sexual contact?

A gardener grows strawberry plants in two ways. Some new plants grow asexually from runners: long stems that creep along the ground and take root, forming new plants that are genetically identical to the parent plant. Other new strawberry plants grow sexually from seeds, which form after strawberry flowers are pollinated and fertilised.

(a) State two advantages to the gardener of producing new plants asexually, using runners, rather than from seed. [2]

(b) State two advantages of producing new plants sexually, from seed, rather than by runners. [2]

(c) A new fungal disease is introduced into the field. Explain why a population of strawberry plants produced only by runners could be more severely affected by this disease than a population produced from seed. [2]

A pea plant can be pollinated in two ways: self-pollination, in which pollen transfers from an anther to a stigma of the same flower (or another flower on the same plant), or cross-pollination, in which pollen transfers from the anther of one plant to the stigma of a flower on a genetically different plant of the same species.

(a) State one difference between self-pollination and cross-pollination, in terms of where the pollen comes from. [1]

(b) Describe what happens after a pollen grain lands on a compatible stigma, up to and including fertilisation. [3]

(c) After fertilisation, the ovule develops into a seed and the ovary develops into a fruit. State what happens to the petals and stigma of the flower once fertilisation is complete, and suggest one function of the fruit that forms around the seeds. [3]

A biology teacher describes what happens to a human egg cell after it has been fertilised by a sperm cell in the oviduct, up to the point where the resulting embryo has implanted in the wall of the uterus.

(a) State what is meant by the term fertilisation, and state where in the female reproductive system it normally takes place. [2]

(b) Describe what happens to the fertilised egg cell as it travels along the oviduct towards the uterus, before implantation occurs. [3]

(c) State what is meant by implantation, and explain why implantation must occur for the pregnancy to continue. [2]

A textbook describes the events of a typical 28-day human menstrual cycle in a woman who does not become pregnant that month.

Which statement correctly describes the sequence of events in this cycle?

A health clinic identifies three different routes by which HIV can be transmitted between people: through unprotected sexual contact, through contact with infected blood (for example, by sharing unsterilised needles), and from an infected mother to her child (for example, during pregnancy, birth or breastfeeding).

(a) For each of these three transmission routes, state one method that can be used to reduce the risk of transmission by that route. [3]

(b) Suggest why testing donated blood for HIV, before it is used in blood transfusions, is an important part of controlling the spread of HIV within a population. [2]

(c) State one reason why HIV can continue to spread within a population even in places where screening and treatment programmes are available. [1]