Question 1
- Suggest two reasons why cross pollination is considered advantageous over self pollination.
- State three mechanisms in plant that prevent self pollination.
- What are the functions of the following in a mammal?
i. Sominiferous tubules
ii. Oviduct
iii. Prostate glands
Answer
- 1. Genetic diseases can be easily eliminated.
2. Gene exchange /mixing leads to hybrid vigour. - 1. Heterostyl
2. Protogyny
3. Protandry -
i. Sominiferous tubules - Production of spermatozoa.
ii. Oviduct - Provides passage for the ovum to the uterus after fertilization; fertilization takes place in the upper region of the oviduct.
iii. Prostate glands - Produces an alkaline fluid that neutralizes acid in the vaginal/urethra (male), the fluid contains nutrients for the sperm and also activate sperms.
Question 2
Study the organism shown below and answer the questions that follows
- State the kingdom to which the organism belongs and give reason for your answer.
- Name the structure labelled A
- Give the function of the part labeled C
Answer
- Kingdom protoctista
Reason - Unicellular, eukaryotic, reproduce by a sexual fission - A - Cilia
- To get rid of excess water by osmosis.
Question 3
The diagram below shows the exchange site between circulatory system and body cells.
- Name the blood cell labelled B
- State the gas that diffuses from B to the tissue cell.
- How is tissue fluid formed?
- Name the cell labeled C
Answer
- B - Red blood cells.
- Oxygen
- Formed from part of blood minus blood cells and plasma that ultra filtrates to fill in channels and spaces between the cells.
- C- Leucocyte
Question 4
Hemophilia or bleeder’s disease is a condition in which blood takes a longer time than usual to clot. This is due to lack of a certain blood protein. The gene for hemophilia is recessive to the gene for normal clotting factor and is found on the X-chromosome.
- Explain why there are only female carriers for hemophilia and no male carriers for traits.
- A carrier female for hemophilia trait married a normal male. Work out the possible genotype of the children. Let letter H represent the normal gene, and let h represents the gene for hemophilia.
- Name one other disorder in humans that is determined by certain genes on the X-chromosome thatlack a corresponding allele on the Y chromosome.
Answer
- Female have two x chromosomes in a gamete while males have only one x chromosomes the gene for hemophilia is located on the x –chromosomes ,such that in heterozygous condition a female does not show the trait.
- H - Normal gene
H - Gene for hemophilia
Parental phenotype: carrier x normal;
Parental genotype: XHXh X XHY
- Colour blindness.
Question 5
Explain how comparative embryology is an evidence for organic evolution.
Answer
Vertebrates embryos have similar morphological features e.g. single circulatory system ;( segmented) myotomes notochord, gills, pharyngeal, cleft and a tail.