(a) State four modes of nutrition in plants.
(b) Outline the process involved in the light and dark reactions of photosynthesis.
(c) Describe briefly the modifications and the mechanisms associated with the following feeding habits:
(i) filter feeding in mosquito larva; (ii) parasitic feeding in tapeworm.
Explanation
(a)Modes of nutrition in plants are:
(i) Autotrophic or holophytic nutrition — It is a process by which green leaves or plants manufacture their food using atmospheric carbon dioxide and soil water as raw materials with sunlight as the source of energy. This type of aytotrophic nutrition is the photosynthetic nutrition. The other type is the chemosynthetic nutrition where energy is derived from the breakdown of inorganic compounds.
(ii) Parasitic nutrition — It is a process by which some plants depend on other plants (as the host) for food and protection. A parasite harms its host by causing some set back during the relationship.
(iii)Mutualism (symbiosis) — This involves two organisms living together for the mutual benefit of each other. It may be between organisms which belong to the same group or different groups, e.g. nitrogen fixing bacteria, rhizobium and leguminous plants and fungi and algae in lichens.
(iv) Epihytic nutrition — This happens when plants attach themselves to other plants for support. They obtain minerals and water from the point of attachment to the host plants but manufacture their food through photosynthesis because they possess green leaves.
(b) (i) Light reaction occurs in the grana of the chloroplast which contains chlorophyll, a light absorbing pigment. The absorption of light energy by chlorophyll helps to split water molecule into hydrogen and hydroxyl ions: 4H(_2)O Light energy 4H(^{+}/) (_H)OH — 4OH(^{-}/)
→
The hydroxyl components react further to form water and oxygen: 2OH + 20H > 2H20 + 02 .
Summary of reactions: 4H(_2)O radiant energy 4H(^{+}/) + 2H(_2)O + O(_2) + 4e-
In the process, electrons are transferred to photo system I, two molecules of ATP are synthesized from ADP and inorganic phosphate. ADP + P1→ ATP (photophosphory— lotion) electrons move further to another photosystem 1. NADP is reduced to NADPH and two molecules of NADPH are produced.
(ii) Dark reaction takes place in the stoma of the chloroplast in the presence of NADPH and ATP. The Hydrogen (H) formed in the light reaction undergoes series of reactions in which they reduce carbon dioxide to form sugar (glucose): Co(_2) + 4H → CH(_2)O + H(_2)O. The reactions are catalysed by enzymes.
(c) (i) Filter feeding in mosquito: The head possesses brushes, mandible and maxillae. Ventral surface of the head is upward and this enables the pair of brushes at the sides of the mouth to sweep through water and entangle small food particles which are combed into the mouth by the maxillae and mandibles.
(ii) Parasitic feeding in tape worm: The head (scolex) possesses hooks, rostellum and suckers. The hooks and the suckers enable the organism to attach itself to the walls of the intestine of its host. The entire body is used to absorb digested food from its host.