1. At what stage of mitosis do chromosomes replicate to form daughter chromatid?
( 1 mark)
2. Fill in the blank spaces in the statement below
After fertilization of an ovule Integuments develops into a testa and triploid nucleus develops into endosperm. ( 2 marks)
3. State the difference between the composition of maternal blood entering the placenta and material blood leaving the placenta ( 3 marks)
- Blood entering placenta has more oxygen, more food substances, less nitrogenous wastes and less carbon dioxide. - Blood leaving placenta has less oxygen, less food substance, more carbon dioxide and nitrogenous wastes.
4. After four months of pregnancy the ovaries of a woman can be removed without terminating pregnancy. However during the first four months of pregnancy the ovaries must remain intact if pregnancy is to be maintained. Explain these observations ( 3 marks)
Corpus luteum in the ovary secretes progesterone, which maintains pregnancy/development of uterus after four months pregnancy is maintained by progesterone form placenta.
5. Name two mechanisms that prevent self pollination in flowers that have both male and female parts ( 2 marks)
- Protandry / protogyny / male and female parts mature at different times
- Stigma positioned higher than stamen
- Incompatibility /sterility.
6. State three characteristics that ensure cross pollination takes place in flowering plants ( 3 marks)
- Presence of special structures that attract agents of pollination.
- Protandry /protogyny
7. Give a reason why it is necessary for frogs to lay many eggs ( 1 mark)
- To increase the chances of fertilization and survival of species.
8. A flower was found to have the following characteristics
- Inconspicuous petals
- Long feathery stigma
- Small light pollen grains
(a) What is the likely agent of pollination of the flower? ( 1 mark)
(b) What is the significance of the long feathery stigma in the flower ( 1 mark)
To enable it trap pollen grains in the air.
9. State two ways by which the human Immuno Deficiency virus (HIV) is transmitted other than sexual intercourse? ( 2 marks)
- Blood transfusion
- Use of unsterilized instruments / sharing (contaminated) instruments.
- Infected mother to foetus; infected mother to newborn.
10. Explain why sexual reproduction is important in organisms ( 3 marks)
Bring about change or genetic material, which leads to variation that enables organisms to exploit new environment resistance to disease.
11. State two disadvantages of self- pollination ( 2 marks)
- Lack of variations
- Lack of hybrid vigour
- Disadvantageous traits are retained within species.
12. The chart below shows the number of chromosomes before and after cell division and fertilization in a mammal.
(a) What type of cell division takes place at Z? ( 1 mark)
(b) Where in the body of a female does process Z occur? ( 1 mark)
(c) On the chart indicate the position of parent and gametes ( 2 marks)
13. (a) What is meant by the terms
(i) Epigynous flower ( 1 mark)
Conditions where other floral parts arise / positioned above the ovary / inferior ovary.
(ii) Staminate flower (1 mark)
(b) How are the male parts of wind- pollinated flowers adapted to their function?
( 4 marks)
-Large anthers loosely attached to the filament to be easily shaken in the wind.
- Small / smooth / light pollen grains
– easily carried by wind
14. Name the part of a flower that developed into:
(a) Seed- Ovule ( 1 mark)
(b) Fruit- Ovary ( 1 mark)
15. (a) State two processes which occur during anaphase of mitosis ( 2 marks)
- Sister Chromates separates.
- Chromatids start moving to opposite poles with centromere first.
(b) What is the significance of meiosis? (2 marks)
- Ensure that gametes formed have half the number of chromosomes found in original cell.
- Formation of sex cells.
- Leads to variation of genetic material during crossover.
16. (a) Explain how the following prevents self- pollination:
(i) Protoandry ( 1 mark)
Stamens with pollen grains matures before carpel (stigma) of the same flower
(ii) Self- sterility ( 1 mark)
Pollen grain of anthers cannot grow into pollen tube on the stigma of the same flower.
(b) Give three advantages of cross- pollination ( 3 marks)
- Mixing of genetic composition of different plants.
- Offspring produced has high yield.
- Offspring is more resistant to disease and adverse conditions.
17. The diagram below represents a human foetus in a uterus
(a) Name the part labeled S ( 1 mark)
(b) (i) Name the types of blood vessels found in the structure labeled Q ( 2 marks)
– Umblical vein
- Umblical artery
(ii) State the difference in composition of blood in the vessels named (b) (i) above ( 2 marks)
Umblical vein – rich in nutrients and oxygen.
Umblical artery – rich in CO2 and waste like urea
(c) Name two features that enable the structure labeled P carry out its function ( 2 mark)
- Has thin membrane to reduce diffusion distance.
- Has villi which increase surface area for exchange.
- Highly vascularized.
(d) State the role of the part labeled R ( 1 mark)
- Cushions foetus against shock
- Supports the foetus
- Keeps foetus moist (prevent dehydration)
18. The diagram below represents a stage during cell division
(a) (i) Identify the stage of cell division ( 1 mark)
(ii) Give three reasons for your answer (a) (i) above ( 2 marks)
- Homologous chromosomes separate at the equator.
- Chromosomes start migrating to opposite poles
- Sister chromatids attached at the centromere.
(b) Name the structure labeled M ( 1 mark)
19. State two disadvantages of sexual reproduction in animals ( 2 marks)
- Harmful characteristics from the parents may be passed on to the off springs.
- Takes a longer time
- Few offsprings are produced at a time.
20 (a) What is meant by the following terms?
(i) Protandry ( 1 mark)
Stamens mature and pollen grains are shed off before the stigma matures
(ii) Self- sterility ( 1 mark)
Pollen grains from the anthers cannot grow on the stigma of the same flower or plant.
(b) The diagram below shows a stage during fertilization in plant
(i) Name the parts labeled Q, R, and S ( 3 marks)
Q- Antipodal cells
R- Polar body / polar nucleus
S- Egg cell
(ii) State two functions of the pollen tube ( 2 marks)
- Path through which the male gametes reach the embryo sac to enhance fertilization.
- Prevent other pollen grains from developing into pollen tubes hence no multiple fertilization of embryo sac.
(c) On the diagram, label the micropyle ( 1 mark)
21. (a) Describe how insect pollinated flowers are adopted to pollination
i) Large brightly coloured corolla / inflorescence / forests / tracts to attract insects.
ii) Scented to attract insects
iii) Have secreted nectar to attract that direct flowers secrete nectar to attract insects.
iv) Pollen grains rough/spiky sticky surface to stick on insect’s body.
v) Special shaped corolla tube to enable the insect land.
( 6 marks)
(b) Describe the role of each of the following hormones in the human menstrual
Repair / heal endometrium / wall of uterus, which is destroyed in menstruation. Stimulates pituitary gland to produce the luteinising hormone
Stimulates the thickening of the uterus, increases the blood supply to the endometrium. Inhibits the production of follicle stimulating hormone
(iii) Luteinizing hormone ( 3 marks)
Responsible for maturation of the graafian follicle / causes ovulation. Stimulates corpus luteum to secrete progesterone.
22. Describe the role of hormones in the human menstrual cycle (20 marks)
- Interior lobe of pituitary glands secretes follicle stimulating hormones (FSH). FSH causes Graafian follicle to develop in the ovary. It also stimulates tissues of ovary / all of graafian follicle to secrete oestrogen.
- Oestrogen causes repair /healing of uterine wall; oestrogen stimulates interior lobe of pituitary to produce Luteinsing Hormone which causes ovulation. It also causes graafian follicle to change into corpus luteum and stimulates corpus luteum to secrete progesterone.
- Progesterone causes proliferation of uterine wall in preparation for implementation. Oestrogen/progesterone inhibits the production of FSH by interior lobe of pituitary thus no more follicles develops and production reduces.
- In the next two weeks, progesterone level lowers and inhibits production of LH from interior lobe of pituitary.
- The corpus luteum stops secreting progesterone and menstruation occur when the level of progesterone drops. Interior lobe of pituitary start secreting FSH again.
23. What part does the placenta play in the
(i) Nutrition of the embryo
It forms a large surface area for the diffusion of nutrient from the maternal blood to the foetal blood. Glucose, amino acids and salts are transferred.
(ii) Protection of the embryo ( 4 marks)
The placenta isolates the foetus from the higher blood pressure of the mother and from direct connection of the two blood systems. Excretion materials can easily pass from foetus to mother.