Biology Paper 2 Que & Ans KCSE 2019|KCSE Paper 2| Biology Revision KCSE 2019 | Biology Revision 2019

7.Giving examples,describe the following interactions among organism: (20 marks) Predator-prey relationship Symbiosis Parasitism ANSWER Predator-prey relationship A predator is an animal that hunts/kills another/other animals (prey) for food; example, a dog and a hare; preys devise survival mechanisms in their habitats not to be eaten/killed; to survive and reproduce/propagate their lineage; to this end, they run faster (strong hind leg muscles); camouflage with environments; mimic the predators; or strong sense of smell to detect the predator; some emit chemicals/smell that turn away from the predators; while others, like porcupines, use quills/spines/ spikes to fight off predators; on the other hand, predators also evolve/ device means to be able to survive in such an ecosystem, for instance, running faster/camouflaging with the environment/mimicking preys/ sharp eyesight; some produce venom/poison; sharp/strong/long claws; Symbiosis Is a close, (long-term) association between two organisms of different species where the two mutually benefit from each other; for example, the bacteria in the rumen/gut/colon of herbivores; which help the herbivores digest cellulose; as they are sheltered by the herbivores; the bacteria found in the human digestive system/gut; are also sheltered by humans as they ensure microbial balance; the nitrogen-fixing bacteria on the root nodules of leguminous plants; benefit from the shelter offered by the plants; as they facilitate conversion of free atmospheric nitrogen into forms that can be readily absorbed by the plants; Parasitism Is a kind of(inter-specific) relationship/association where one member/ organism, the parasite, benefits while the other, the host is harmed/ loses; (also called antagonistic/antipathetic symbiosis) for example, a tick (parasite); sucking blood from a cow (host), making the cow to be anaemic/skin destroyed/malnourished; parasites can be external/ecto- parasite; or internal/endo-parasite; endo-parasites,for instance, liver fluke, suck blood/nutrients from the host and can cause death/bodily harm on the internal organs of the host, including blocking blood vessels; 8. Explain the effects of increased physical activity on the following organ systems: (20 marks) (a) Heart Increased physical activity results in increased heart beat/rate/cardiac frequency/increased blood pressure; pumping more blood to the muscles/peripheral blood vessels at a faster rate; supplying oxygen; nutrients; for continued oxidation/respiration; to yield energy needed to sustain the (vigorous) contraction/relaxation of muscles (during the physical activity); carbon (IV) oxide/lactic acids/other nitrogenous/ metabolic wastes produced during the process are also eliminated/ transported to the relevant excretory organs for elimination; the wastes, if left to accumulate, can also poison cells/cause muscle crump/ fatigue/pain; (b) Lungs The panting/increased breathing rate (during the physical activity) influences the lung volume/lungs expand/increase in volume, to take in more amount of air/oxygen retained (for the activity) or expelled (during the activity); they expand to take in more air/oxygen (into the body) and deflate to expel more carbon (IV); more oxygen is taken in (during exercise) to sustain the process of muscle respiration/to produce the required energy (for the constant muscle contraction and relaxation); (C) Kidneys Kidneys also maintain the blood plasma pH; and osmotic balance; by eliminating excess hydrogen ions(H“) that accumulate for instance, through the production of lactic acid/carbon (IV) oxide during exercise; to maintain the osmotic balance, the kidneys conserve sodium ions and reabsorb water (in the kidney tubules); leading to reduction in the volume of urine produced; during exercises, the kidneys tend to filter out more urea, releasing more in the urine; (d) Skin. Due to the increased muscle activity during physical exercises, one sweats (more); eliminating nitrogenous wastes/excess water (through the skin)/sweat pores; cooling the body; after water in the sweat evaporates; the increased internal body temperature also leads to the dilation of superficial blood vessels (vaso-dilation)/blood flowing to the skin; leading to loss of excess heat (to the atmosphere) by radiation/ convection; the hair on the skin surface also lie flat to allow for loss of heat (to the environment) by radiation/convection;