1
Explain the significance of variation in asexual and sexual reproduction, highlighting its role in the survival of species. 5marks
2
How does the process of binary fission in Amoeba differ from multiple fission in Plasmodium in terms of the number of daughter cells produced and the plane of division? 3marks
3
Describe the process of budding in Hydra, including the role of regenerative cells and the development of the bud into a new individual. 3marks
4
Explain vegetative propagation in plants, providing two examples and detailing two advantages of this method over seed reproduction. 5marks
5
How is spore formation an effective mode of reproduction for organisms like Rhizopus, especially under unfavourable conditions? 2marks
6
Differentiate between self-pollination and cross-pollination in flowering plants, mentioning at least two agents of pollination. 3marks
7
Explain the process of fertilization in flowering plants, from the landing of the pollen grain on the stigma to the formation of the zygote. 5marks
8
Describe the male reproductive system in human beings, detailing the function of the testes, seminal vesicles, and prostate gland. 5marks
9
With the help of a labelled diagram, explain the structure and function of the female reproductive system in human beings, focusing on the role of ovaries and the uterus. 5marks
10
What are the hormonal changes that occur during puberty in boys and girls? Relate these changes to sexual maturation. 3marks
11
Explain what happens in the human female reproductive system if the egg is fertilised and if it is not fertilised, detailing the processes involved. 5marks
12
What is the function of the placenta in human pregnancy? How does it facilitate the exchange of substances between the mother and the developing foetus? 3marks
13
Explain how the male and female germ cells are formed and how their fusion ensures an equal genetic contribution from both parents to the progeny. 5marks
14
Describe any two methods of contraception. Discuss their effectiveness and potential side effects. 4marks
15
The creation of a DNA copy is an essential step in reproduction. Explain why this is so, and what are the potential consequences of inaccuracies in this copying process? 3marks
16
Observe the diagram of a flower showing pollination and fertilization. Identify the parts labelled A, B, and C and explain the process that occurs when B reaches C. 3marks
17
A student observes a yeast culture under a microscope and notices small outgrowths from the parent cells.(a) Identify the process of reproduction shown.(b) Explain how this process leads to the formation of new individuals. 3marks
18
A farmer wants to grow large quantities of disease-free banana plants.(a) Suggest the most suitable method of reproduction for this purpose.(b) Explain the process.(c) State two advantages of this method. 5marks
19
A student is studying the life cycle of Plasmodium, the malarial parasite.(a) What type of asexual reproduction does Plasmodium undergo?(b) Explain the process briefly.(c) Why is this method advantageous for the parasite? 4marks
20
Read the following passage: "The human population is a cause for concern for many people. This is because an expanding population makes it harder to improve everybody’s standard of living. However, if inequality in society is the main reason for poor standards of living for many people, the size of the population is relatively unimportant."(a) What is the primary reason for population growth discussed in the chapter?(b) How do contraceptive methods help in managing population size?(c) Discuss the health implications of early and unplanned pregnancies. 5marks
Answers
1
Variation is crucial for the survival of species. In asexual reproduction, while offspring are genetically identical, minor variations in DNA copying can lead to adaptability. In sexual reproduction, the mixing of genetic material from two parents generates significant variations, allowing species to adapt to changing environmental conditions. For example, if there is a new disease, a population with diverse variations has a higher chance that some individuals will be resistant and survive, thus ensuring the species' continuity. Without variation, a species might be wiped out if the environment changes drastically.
2
Binary fission in Amoeba involves the splitting of the parent cell into two approximately equal daughter cells in any plane. Multiple fission in Plasmodium involves the parent cell dividing into many daughter cells simultaneously. This occurs within a protective cyst, allowing rapid multiplication under favourable conditions, but the division can occur in any plane.
3
In Hydra, the process of budding begins with repeated cell division at a specific site on the parent body, forming a small outgrowth called a bud. This bud contains regenerative cells that proliferate and differentiate to form specialized tissues and organs, eventually developing into a miniature Hydra. Once fully developed, the bud detaches from the parent body and becomes an independent organism.
4
Vegetative propagation is a type of asexual reproduction where new plants are produced from vegetative parts like roots, stems, and leaves. For example, sugarcane can be propagated from stem cuttings, and roses from stem cuttings. Two advantages are:(i) Plants produced are genetically identical to the parent plant, retaining desirable traits like disease resistance or fruit quality.(ii) Plants raised through vegetative propagation often bear flowers and fruits earlier than those grown from seeds, making it economically beneficial.
5
Spore formation is an effective mode of reproduction for Rhizopus because the spores are enclosed within tough, resistant walls. These walls protect the spores from desiccation and mechanical damage, allowing them to survive unfavourable conditions like drought and extreme temperatures. When favourable conditions (moisture and nutrients) are encountered, the spores germinate and grow into new Rhizopus individuals.
6
Pollination is the transfer of pollen grains from the anther to the stigma of a flower. Fertilisation is the fusion of the male gamete (from the pollen grain) with the female gamete (egg cell) within the ovule. Agents of pollination include wind, water, and animals (like insects and birds).
7
After pollination, if the pollen grain lands on a compatible stigma, it germinates and grows a pollen tube down through the style towards the ovary. The pollen tube carries the male gametes. Upon reaching an ovule within the ovary, the pollen tube penetrates it and releases the male gametes. One male gamete fuses with the egg cell to form the zygote, and another male gamete fuses with the polar nuclei to form the endosperm. This fusion is called fertilization.
8
The male reproductive system in humans includes the testes, scrotum, vas deferens, seminal vesicles, prostate gland, and penis.
- Testes: Located outside the abdominal cavity in the scrotum, they produce sperms and the male sex hormone testosterone.
- Seminal Vesicles and Prostate Gland: These glands secrete fluids that mix with sperm to form semen. This fluid provides nutrients, lubricates the passage, and makes sperm transport easier.
- Vas Deferens: A tube that carries sperm from the testes.
- Penis: The external male reproductive organ responsible for delivering sperm into the female reproductive tract.
9. The female reproductive system consists of ovaries, oviducts (fallopian tubes), uterus, and vagina. - Ovaries: Two oval-shaped organs that produce eggs (ova) and female sex hormones like estrogen and progesterone.
- Oviducts (Fallopian Tubes): Tubes that carry the egg from the ovary to the uterus. Fertilization usually occurs in the fallopian tube.
- Uterus: A muscular, hollow organ where the fertilised egg implants and the embryo/foetus develops.
- Vagina: A muscular canal that connects the uterus to the outside of the body; it receives sperm during sexual intercourse.
10. During puberty, boys experience changes like the growth of thick hair on the face, chest, and pubic areas, a deepening of the voice (cracking), enlargement of the penis, and increased muscle mass. Girls experience breast development, widening of the hips, growth of pubic and underarm hair, and the onset of menstruation. These changes are driven by hormones and signify sexual maturation, preparing the body for reproduction.
11. If the egg is fertilised, it implants in the thickened uterine lining, and the embryo begins to develop. The uterine lining is maintained to support the growing embryo and foetus. If the egg is not fertilised, it lives for about a day. The thickened uterine lining, which was prepared to receive the fertilised egg, is no longer needed. It breaks down and is shed from the body along with blood and mucous through the vagina in a process called menstruation.
12. The placenta is a disc-shaped tissue embedded in the uterine wall that connects the developing foetus to the mother's blood supply. It facilitates the transfer of nutrients (like glucose, amino acids, fats, vitamins, and minerals) and oxygen from the mother's blood to the foetus's blood. It also allows for the removal of waste products (like carbon dioxide and urea) from the foetus's blood and their transfer into the mother's blood for excretion.
13. Equal genetic contribution is ensured through sexual reproduction. In humans, males produce sperm containing half the number of chromosomes (23), and females produce eggs also containing half the number of chromosomes (23). During fertilization, a sperm fuses with an egg, combining their genetic material to form a zygote with the full complement of 46 chromosomes (23 pairs). This ensures that each parent contributes equally to the genetic makeup of the offspring.
14. Two methods of contraception are:
(i) Condoms: These are barriers placed over the penis (male condom) or inside the vagina (female condom) to prevent sperm from entering the female reproductive tract. They are effective in preventing both pregnancy and the transmission of sexually transmitted infections (STIs). Side effects are minimal, mainly related to potential allergies to latex.
(ii) Oral Contraceptive Pills: These pills contain hormones that prevent ovulation (release of eggs from the ovary) or alter the uterine lining, making it unsuitable for implantation. They are generally effective but can have side effects such as nausea, weight gain, mood changes, and hormonal imbalances. They do not protect against STIs.
15. DNA copying is essential in reproduction because it ensures the transmission of the genetic blueprint or "body design" from parents to offspring. This DNA contains the information for making proteins, which in turn determine the organism's traits. If DNA copying were absent, new individuals could not be generated. Inaccuracies in DNA copying (mutations) introduce variations. While small variations can be beneficial for adaptation, drastic errors can lead to non-viable DNA copies, resulting in the death of the new cell or organism.
16. In the given diagram:
A represents the Stigma.
B represents the Pollen grain.
C represents the Style.
When B (pollen grain) reaches A (stigma), pollination occurs. The pollen grain then germinates on the stigma and grows a pollen tube down through C (style) to reach the ovule, where fertilization takes place.
17. (a) The process of reproduction shown is budding.
(b) In budding, a small outgrowth (bud) develops from the parent yeast cell due to repeated cell division. This bud grows and matures, eventually detaching from the parent cell to become a new, independent yeast organism.
18. (a) Tissue culture is the most suitable method for growing large quantities of disease-free banana plants.
(b) In tissue culture, small pieces of tissue or cells are taken from a healthy banana plant and grown in an artificial nutrient medium under sterile conditions. These cells divide rapidly to form a callus (a mass of cells). The callus is then transferred to another medium containing plant hormones, which stimulate it to develop into plantlets. These plantlets are then transplanted into the soil to grow into mature plants.
(c) Two advantages of tissue culture are:
(i) It allows for the rapid multiplication of plants from a single parent, producing a large number of offspring in a short time.
(ii) It enables the production of disease-free plants, as the initial tissue is taken from healthy stock and the process is carried out under sterile conditions.
19. (a) Plasmodium undergoes multiple fission as its mode of asexual reproduction.
(b) In multiple fission, the nucleus of the Plasmodium parasite divides repeatedly to form many daughter nuclei. Each nucleus then gets surrounded by a small amount of cytoplasm and develops into a new daughter parasite. This process occurs within a protective covering called a cyst.
(c) Multiple fission is advantageous for Plasmodium because it allows for the rapid multiplication of the parasite, producing a large number of offspring simultaneously. This increases the chances of infecting new hosts when the cyst bursts and releases the numerous parasites.
20. (a) The primary reason for population growth discussed is the high birth rate. While the chapter acknowledges other factors like standard of living and inequality, the act of reproduction itself is the mechanism for population increase.
(b) Contraceptive methods help manage population size by preventing unwanted pregnancies. By reducing the number of births, these methods can help to slow down the rate of population growth, allowing resources and infrastructure to better meet the needs of the existing population.
(c) Early and unplanned pregnancies can have significant health implications for the woman. Her body may not be fully developed for childbirth, increasing the risks of complications during pregnancy and delivery. It also places immense physical, emotional, and financial strain on her, potentially impacting her overall health and well-being.
