Explain the various ways in which a typical cell is adapted to its functions (20 marks)

-
Having a cell membrane; with pores; that regulates substances entering and leaving the cell;
Cytoplasm; contain sugars and salts; for maintaining its osmotic pressure; also has a liquid medium; for all biochemical reactions;
Having nucleus; contain chromosomes having hereditary material; and controls all the activities of the cell;
Having Ribosomes;  sites for protein synthesis;
Presence of golgi bodies/apparatus ; for secretion of hormones and enzymes; formation of lysosomes;
Presence of lysosomes; containlytic enzymes for breaking down worn-out organelles;
Having secretory vesicles ; formed from golgi apparatus for secreting substances;
Presence of smooth endoplasmic reticulum ; synthesizes and transports lipids;
Posses rough endoplasmic reticulum; transport proteins;
Nucleolus present; controls the activities of the nucleus; produces ribosomes;
Mitochondria present; form sites for energy production;
Centrioles presence; for formation of cilia and flagella; forms spindle fibres used in cell division;
Having plant sap vacuoles ; store salts and other dissolved substances; controls osmotic pressure and turgidity of cells;
Presence of food vacuoles; involved in digestion of engulfed food;
Chloroplasts presence; Are sites for photosynthesis in plant cells;
Have cellulose cell wall; rigid as to maintain the shape of the cell and offer mechanical support.
 Max. 20 mks

Comments

Post a Comment

Popular posts from this blog

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

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

KCSE 2010 Q8. Describe how a finned fish such as Tilapia moves in water. (20 marks)

-
The following describes how  a finned fish such as Tilapia moves in water . v       Water is denser than air. The density of water supports fish and provides a medium in which it swims. v       It has a streamlined body; reducing resistance, thus easily swims in the water. v       The scales overlap pointing backwards allowing water to pass over the fish without obstruction. Mucus is also secreted over the scales reducing friction during movement. v       They have a flexible backbone onto which segments of muscle blocks, myotomes, are attached. The muscles contract and relax bringing about undulating movements. v       The fish have fins that help in steering and balancing fish during swimming. v       The pectoral and pelvic fins are paired. They are used for braking, steering and v   ...
Read more