Question 4
- (i)Explain briefly the term sickle cell anaemia. [4 marks]
(ii) State four transmittable characters in humans. [4 marks] - State three ways by which animals survive unfavourable conditions. [3 marks]
- Explain briefly the theory proposed by jean Baptiste Lamarck on evolution. [4 marks]
- State five evidences of evolution. [5 marks]
Observation
This question was not popular among candidates but those that attempted it fared well only in the transmittable characters and evidence of organic evolution.
The expected answers are:
(a) (i) Sickle cell anaemia
Is an inheritable disease; caused by an abnormality in the red blood cells/haemoglobin molecules; the red blood cell of the sufferer is sickle shaped/SS genotype; while the carrier is AS genotype; causing blocking/clogging of capillaries thereby reducing the amount of oxygen it carries; causing crisis in the sufferer.
(ii) Transmittable characters in humansSkin colour; eye colour; blood group; height; nose shape; hair colour; albinism; haemophilism; sickle cell disease; hairy earlobe; tongue rolling; intelligence; any correctly named character.
(b) Ways by which animals survive unfavourable conditions Hibernation; aestivation; migration; basking; encystment/encapsulation.
(c)Evolutionary theories proposed by Jean Baptiste Lamarck
- Theory of use and disuse of body parts; a body part that is constantly used enlarges/becomes efficient; the one that is not becomes weak and small/atrophied; e.g. Giraffes developed long neck overtime because they fed on the crown of trees; penguins’ wings became smaller because they are not used; development of thick muscles through constant exercise.
- Inheritance of acquired traits; new species evolved after several generations by acquiring new traits and losing old ones; e.g. in Giraffes, the longer necks traits were passed to the next generation.
Evidences of organic evolution Evidence from
- comparative anatomy;
- vestigial organs;
- physiology;
- fossil records/palaeontology;
- embryology;
- cytology;
- geographical distribution;
- serology;
- comparative biochemistry;
- adaptive radiation;
- molecular records.