Discuss the various evidences of organic evolution.

-
Comparative  anatomy/taxonomy;  members  of  a  phylum/group  show  similarities;  organs  have similar  structure/organs  performing  the  same  function  such  as  the  digestive  system,  urinary system,  vertebrate  heart;  homologous  structures  are  structures  with  the  same  embryonic  origin but  have  been  modified  to  perform  different  and  specific  functions;  show  a  form  of  divergent evolution;  e.g.  the  pentadactyl  limb  in  vertebrates  which  has  been  modified  for  racing; swimming  and  flight  or  beaks  of  finches  and  birds;  while  analogous  structures  are  those  with different  embryonic  origin  but  have  been  modified  to  perform  the  same  function  e.g.  wings  of insects,  bats  and  birds;  eyes  in  octopuses  and  humans;  show  a  form  of  convergent  evolution; vestigial  structures;  have  been  reduced  in  size  and  become  functionless;  in  the  course  of evolution;  e.g.  limbs  in  snakes,  human  hair  and  tail;  Cell  biology/cytology;  occurrence  of similar  organelles  such  as  the  mitochondria  and  the  endoplasmic  reticula  point  to  common ancestry;  Fossil  records/Paleontology;  remains  of  organisms  preserved  in  naturally-occurring materials  for  many  years;  fossil  records  show  morphological  changes  of  organisms  over  a  long period  of  time  e.g.  skull  of  humans  and  horse;  they  provide  a  direct  evidence  of  existence  of organisms  at  a  particular  ecological  era;  however,  since  only  hard  parts  are  preserved,  no evidence  is  available  for  existence  of  soft-bodied  organisms;  and  there  are  many  missing  links; since  remains  are  accidentally  preserved  in  rudimentary  rocks  and  resins;  Comparative embryology;  vertebrate  embryos  are  morphologically  similar  during  the  early  stages  of development;  suggesting  that  the  organisms  had  a  common  ancestry/origin  e.g.  larvae  of mollusks/annelids,  embryos  of  chicken,  humans,  sheep;  the  closer  the  semblance  between embryos,  the  closer  their  ancestral  backgrounds;  Geographical  distribution;  present  continents are  thought  to  have  been  a  large  land  mass  joined  together;  as  a  result  of  continental  drift; isolation  occurred  bringing  about  different  patterns  of  evolution;  where  plants  and  animals from  different  continents  yet  with  common  ancestry  can  no  longer  interbreed;  because  they evolved  into  different  species;  examples  of  animals  that  moved  to  different  areas  are  the jaguars  and  Llamas  in  south  America,  lions  in  Africa,  Tigers  in  Asia,  marsupials  in  Australia; Comparative  serology/physiology;  semblance  in  blood  components  such  as  blood  proteins, antigen-antibody  reactions,  structure  of  haemoglobin  in  all  vertebrates;  reveal  some  phylogenic relationship  among  organisms/show  common  ancestry;  Max.  20  mks 

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