(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]

Describe how the following plants are adapted to their habitat
(a) Xerophytes
(b) Hydrophytes


(a) Xerophytes

• Xerophytes have roots that grow deep to absorb water far below;
• Some xerophytes have shallow roots that spread widely / extensively in order to trap water from any little shower of rain;
• Xerophytes have fleshy / succulent /juicy stems / roots for storage of water;
• Some xerophytes have photosynthetic stems that take the place of leaves; to reduce the surface area for transpiration;
• Some xerophytes have leaves that are needle like / reduced to spines; to reduce surface area thus reducing loss of water by transpiration;
• Some xerophytes have fewer number of stomata located only on the lower surface of the leaves to reduce transpiration rate;
• The stomata are also small in size to reduce loss of water by transpiration;
• Some xerophytes have sunken stomata which allow water vapour to saturate in the pits / depression; thus reducing water loss of transpiration;
• Xerophytes have thick waxy cuticle that is water proof; thus preventing excessive loss of water;
• Some xerophytes have a very short life cycle thus grow fast to use the little rain within a very shirt time;
• Some xerophytes have thorns on their stems / branches / midribs / leaves to protect the plant from predator / browsers / herbivorous animals;
• Some xerophytes roll their leaves to reduce surface area exposed thus reducing rate of water loss by transpiration;
• Some xerophytes have reversed stomatal rhythm where they open their stomata at night and close during the day to reduce water loss of transpiration;

b) hydrophytes

• Hydrophytes have large number of stomata on the upper surface / epidermis to increase
• transpiration rate;
• They have board leaves to increase the surface area for floating / bvoyancy;
• Hydrophytes have long fibrous roots to increase surface area for floating / absorption of mineral / salts;
• Hydrophytes have gerenchynia tissues that have large intercellular air spaces for storage of air to be used for gaseous exchange;
• They have aerenchyma tissues that also help the plant to float in water / buoyancy; hydrophytes have poorly developed supporting tissues because water provides the necessary support;
•  They have poorly developed conducting tissues / xylem and phloem since the plant get water by diffusion;
• Leaves of submerged hydrophytes are deeply dissected into thread-like straws to provide large surface area for absorption of light;
• Submerged hydrophytes have no cuticle and epidermal cells to enable them absorb water;