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K.C.S.E Biology Q & A - MODEL 2019PP1QN16
State two benefits of mutation in living organisms.
answers
K.C.S.E Biology Q & A - MODEL 2019PP1QN13
A female human being was found to have an extra sex chromosome in her cells.
​(a) Give the total number of chromosomes in the female individual’s cells.
(b) Explain the possible cause of this condition. (c) State two physical characteristics observed in the female individual with such a condition.
answers
(a) 47
(b)Non-disjunction/failure of homologous chromosome to separate/segregate (in anaphase I) or failure of sister chromosome to separate/segregate (in anaphase II); resulting in an extra X sex chromosome, X chromosome in a cell having XXX instead of XX; (c) infertile / ovary abnormalities; Taller than average female; Development delays; (more pronounced) signs of obesity; Flat feet Abnormally curved fingers; Widely spaced eyes; Abnormally shaped breast bone;
K.C.S.E Biology Q & A - MODEL 2018PP2QN07
Describe the role of hormones in the human menstrual cycle.
answers
​After/at the onset of menstruation, (the anterior lobe of) the pituitary gland; secretes follicle stimulating hormone (FSH); the FSH causes the Graafian follicle; to develop into the ovary; and stimulate the ovary tissues to secrete oestrogen hormone; Oestrogen brings about repair/healing of the endometrium/uterine wall; its concentration increases to a level which stimulates the (anterior) pituitary gland; to secrete lutenizing hormone (L.H.) and stops further secretion of FSH;
The L.H. stimulates the maturation of the Graafian follicle; LH also stimulates the Graafian follicle to release an ovum into the (funnel of the) fallopian tube/causes ovulation; it also stimulates the remains of the Graafian follicle to form a yellow body/corpus luteum (in the ovary; The corpus luteum is stimulated by the L.H. to produce progesterone; Progesterone then stimulates the thickening of the endometrium/inner lining of the uterine wall; in readiness for implantation; as progesterone level increases, it inhibits (the pituitary gland) from secreting FSH; further increase in progesterone level inhibits the pituitary gland from secreting L.H. This causes the corpus Luteum to degenerate; this reduces the amount of progesterone; the sudden drop in secretion of progesterone causes the endometrium to slough off/menstruation occurs; and the cycle is repeated;
K.C.S.E Biology Q & A - MODEL 2018PP2QN07
Describe the mode of reproduction in a named fungus.
answers
Rhizopus/mucor/mould; reproduce asexually; by sporulation; spores develop from a single cell forming sporangium; which bursts on maturity releasing spores; which are dispersed by air currents/wind germinating; to form new generation/ form a mycelium (if it lands on a suitable medium); Or
Yeast/Saccharomyces/Schizosaccharomyces; reproduce asexually;by budding; parent cell forms an outgrowth/projection/bud; this is followed by division of the nucleus into two; one of the nuclei moves into the bud; which grows and develops into a new cell; K.C.S.E Biology Q & A - MODEL 2018PP2QN02
Below is a graphical representation of students’ height in a classroom.
​(a) Name the type of curve illustrated.
(b) (i) State the type of variation represented by the curve. (ii) State two meiotic processes that lead to variation among organisms. (iii) Explain the role of variation in organisms. (c) Explain the need for genetic counselling in present day health facilities.
answers
​a) Normal distribution curve;
b) i. Continuous (variation); ii. Independent assortment; Crossing over; iii. Organisms/individuals with advantageous traits/variations are favoured/selected by nature; and survive to reproduce/pass on/propagate the advantageous/favourable traits to their off-spring; Or Variation ensures propagation of desirable/favourable traits; to the future generations/off-spring, ensuring improved/quality population; c) Provides information/advice to individuals/families/communities about genetic disorders; Helps identify/test/advice families/communities on possible risks of genetic disorders; Provides supportive services/serves as patient advocates/refer individuals/families to relevant health professionals;
K.C.S.E Biology Q & A - MODEL 2017PP2QN04
State the significance of diploidy.
answers
K.C.S.E Biology Q & A - MODEL 2017PP2QN04
(i) Define the term diploidy.
(ii) Name the type of cell division that gives rise to diploid cells. (iii) Name the type of cells in which the process named in (b) (ii) above Occurs.
answers
​ i. State of being/having two sets of chromosomes and therefore two copies of genes (especially in somatic/body cells);
ii. Mitosis; iii. Body cells/somatic cells;
K.C.S.E Biology Q & A - MODEL 2017PP2QN04
Explain how the sex of a male child is determined in human beings.
answers
K.C.S.E Biology Q & A - MODEL 2016PP1QN30
State two advantages of hybrid vigour
ANSWERS
K.C.S.E Biology Q & A - MODEL 2016PP1QN10
State two functions of the placenta in mammals.
answers
K.C.S.E Biology Q & A - MODEL 2016PP1QN10
State two disadvantages of sexual reproduction in animals.
answers
K.C.S.E Biology Q & A - MODEL 2016PP1QN07
Explain how the following prevent self-pollination.
(i) Protandry (ii) Self- sterility.
answers
K.C.S.E Biology Q & A - MODEL 2015PP2QN07
Explain the various ways in which seeds and fruits are adapted to dispersal.
ANSWERS
Wind - dispersed seeds / fruits are light / small to be carried by air currents;
Some seeds / fruits have developed hairy structure feather-like projections; wing like structure which increase their surface area to be blown about /carried away by wind; open capsules; borne on long stalks, which are swayed by wind scattering seeds. Water - dispersed fruits / seeds are also light; to float on water; Some, (like coconuts) have fibrous /spongy mesocarps to trap air; making them buoyant/floating on water; Others (like the water lily) produce seeds whose seed coats trap air bubbles; making them float on water; Some have water-proof seed testa / pericarp; remain afloat without soaking /sinking immediately they are released from parent plants; Animal - dispersed fruits have developed hooks; to stick on (the fur of passing) animals; In some cases, fruits are succulent, brightly coloured / scented; to attract animals, birds; The seed coats (of some seeds) are hard; and resistant to the digestive enzymes; hence passing out through the gut undigested; Self dispersal by explosive mechanism; Fruits have sutures/lines of weakness; which split open when drying scattering seeds. K.C.S.E Biology Q & A - MODEL 2015PP2QN02
The diagram below illustrates the structure of the female part of a flower.
(a) Name the part labelled W.
(b) Describe what happens when the pollen tube enters the structure labelled V. (c) What do the structures labelled R and T develop into after fertilization? R T
ANSWERS
​ (a) W - ovary wall/ovary;
(b) Tip of pollen tube bursts open; one of the nuclei fuses with the egg cell nucleus; to form a diploid zygote; while the remaining male nucleus fuses with the polar nuclei; to form a triploid endosperm nucleus; (c) R - Endosperm/primary endosperm; T - testa/seed coat; K.C.S.E Biology Q & A - MODEL 2015PP1QN15
The photomicrographs below show the various stages of cell division in a certain plant.
​(a) (i) Name the type of cell division illustrated.
(ii) Give a reason for your answer in (a) (i) above. (b) (i) Name the stage of cell division labelled K. (ii) Give a reason for your answer in (b) (i) above.
answers
​(a) (i) Mitosis;
(ii) Formation of two daughter cells. (b) (i) Metaphase; (ii) Chromosomes are at the equator |
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