Explain the different evidences of evolution. 20 marks

-
Comparative anatomy / taxonomy;
  • Members of a phylum / group show similarities ; organisms have structures / organs performing the same function ; e.g. digestive system ; nervous system same function etc (any correct example 1mk)
  • The pentactyl limb / any correct example; these are called homologous organs / structures; homologous (same origin but have different function;  Analogous structures / different structures performing the same function e.g. wings of insects, bat and birds; Analogous – different origin but performing same function;

Fossil records / Paleontology; 
  • remains of organisms preserved in naturally occurring materials for many years; show morphological changes of organisms over a long period of time; e.g. skull of man ( leg of horse)
Comparative embryology; 

  • embryos of vertebrates have similar morphology; suggesting the organisms have a common origin / ancestry ;
Geographical distribution; 

  • continents present are thought to have been a large landmass; joined together; as a result of continental drift; isolation; occurred bringing about different patterns of evolution; e.g. Ilamas in the amazons resemble the camel / any other correct example e.g. kangaroo in Australia Jaguar in S. America; camel in Africa;
Comparative serology / physiology ; 

  • antigen – antibody reactions / RH factor/ blood groups / haemoglobin structure reveal some phylogenetic relationship among organisms  / common ancestry.

Comments

Post a Comment

Popular posts from this blog

Explain how structures of the human ear are adapted to their functions. (20 marks)

-
Image
The pinna;- is funnel shaped to trap sound waves; cartilaginous to maintain the funnel shape; collects and directs sound waves into the external auditory meatus ear; The external auditory canal; - a tube connected to the pinna that directs sound waves from the pinna to the eardrum lining the auditory canal; has hair that trap foreign particles; The canal contains wax-secreting cells; and hair which traps dust particles; and pathogenic bacteria hence prevent them from getting into the ear; The eardrum; - has a thin tough membrane; that easily vibrates when hit by sound waves; transferring them into vibrations. The ear ossiscles; - they act like a layer and they easily move forward and backward to amplify sound vibrations that hit them; The suspensory ligaments; - suspends the ear ossicles and prevents excessive vibration that would otherwise damage the inner parts of the ear; The eustachian tube - it connects the middle ear with the pharynx; and it equalises air pressure between
Read more

DESCRIBE THE ADAPTATIONS OF THE ILEUM TO ITS FUNCTION (20 MARKS)

-
Has secretory glands/crypts of lieberkuhn which secretes enzymes (maltase/sucrase/lactase/peptidase/lipase to complete digestion of sugars/proteins/lipids. Goblet cells secrete mucus which allows for smooth movement of food and protect wall of ileum from action of digestive enzymes Very long to provide large surface area for absorption. Highly folded/coiled to slow movement of food to allow more time for digestion/absorption/ and to increase surface area for absorption. Has numerous villi which increase surface area for absorption/microvilli which further increase surface area for absorption. Ileum wall/villi have thin epithelium which is only one cell thick to reduce distance over which digested food has to diffuse. Villi are highly vascularised/have a rich network of blood capillaries for rapid transport from small intestines and maintain a steep concentration gradient for rapid absorption. Villi have lacteals for absorption of fatty acids and glycerol Cells of ileum wall h
Read more

(a) Define digestion. [2 m] (b) Describe the digestion of a piece of ugali in a human digestive system from the mouth until its assimilation. [18mks]

-
(a) Define digestion It is break down of complex insoluble; v food substance into simple soluble food substances; v 2max (b) Describe the digestion of ugali; Digestion of ugali begins in the mouth;v ugali is chewed by the teeth to increase large surface areav for action of salivary amylase / ptyalin; vThe food mixes with saliva produced by salivary glands;v Saliva contains mucus and enzyme ptyalin. Mucus moistens, softens and lubricates the food;v ptyalin speeds up the conversion of starch to maltose;v ugali is made into bolus in the mouth;v The bolus moves along the oesophagus and prestalsis / by contraction and relaxation of circular and longitudinal muscles into the stomach;v The digestion continues until ugali become acidic since the stomach does not contain carbohydrase / carbohydrate digesting enzymes no digestion of ugali takes place here.v Ugali now
Read more