Describe the process of gaseous exchange in terrestrial plants

-
  Gaseous  exchange  occurs  in  the  spongy  mesophyll;  During  the  day,  air  diffuses  into  large  air spaces  of  the  spongy  mesophyll;  through  the  stomata;  the  carbon  (IV)  oxide  in  the  air  diffuses into  photosynthetic  cells;  in  solution  form;  during  photosynthesis,  carbon  (IV)  oxide  is  used up;  while  oxygen  is  produced;  some  of  the  oxygen  is  used  in  respiration;  while  the  rest  diffuses out  of  the  leaf;  through  the  stomata;  During  the  night,  air  diffuses  into  the  air  spaces;  through the  stomata;  the  air  dissolves  into  the  film  of  moisture;  oxygen  in  the  air  diffuses  into  the  cells; and  is  used  for  respiration;  carbon  (IV)  oxide  produced;  diffuses  out  through  stomata;  due  to  a concentration  gradient/diffusion  gradient;  At  night,  carbon  (IV)  oxide  accumulates  in  the  leaf since  photosynthesis  does  not  occur;  some  gaseous  exchange  also  takes  place  through  the cuticle;  and  through  the  epidermis  of  young  leaves,  roots  and  stems;  some  plants  exchange gases  through  breathing  roots/pneumatophores;  older  stems  exchange  gases  through  lenticels; 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