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

(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

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

EXPLAIN HOW ABIOTIC FACTORS AFFECT PLANTS. (20MKS)

-
 Explain how abiotic factors affect plants. (20mks) Abiotic factors. Wind; -On a windy day rate of transpiration increases since wind carries away water vapour leaving surrounding of leaves with low humidity; the lower the humidity the more the space in the atmosphere for water molecules to occupy. - Wind disperse fruits, seeds and spore; - Wind is an agent of pollination. - Strong winds break branches of trees and may even uproot some trees; Temperature; -Enzymes work best at optimum temperature; changes in temperature hence influence rate of photosynthesis/respiration; and other enzyme controlled biological reactions. -In aquatic environment temperature affects the percent of dissolved gases. Light; - green plants need light for photosynthesis; - some plants need light for flowering; photoperiodism; - some seeds (lettuce) require light for germination; - light affects opening and closing of stomata; which affects transpiration; gaseous exchange and photosynthesi...
Read more