(a)Why an athlete should be given glucose drink: Glucose is the simplest form of carbohydrates/soluble form of carbohydrate; an energy-giving food substance which does not require any form of digestion. - hence it is absorbed in the ileum/small intestine. - where it diffuses/enters into the blood stream/circulatory system. - it is then assimilated; and oxidized. - within the shortest time/quickly/immediately. - to give energy to the athlete. - bread is a complex carbohydrate/polysaccharide/starch. - which will require a series of digestive processes/hydrolysis. - which starts in the mouth; and ends in small intestine/ileum. - this takes a longer time to produce energy for use/cannot give immediate energy.
(b) Test for starch: -

Macerate/crush a piece of the food substance.
add water to the crushed food to form a solution/suspension/take a piece of food substance.
put a few drops of the solution/suspension/ piece of food.
on a white tile/watch glass/in test tube
add one or two drops of iodine solution
the solution/piece of food will turn blue black
indicating the presence of starch.

(c) Importance of water in human diet: -

Water is an essential part of living protoplasm; blood
it acts as a solvent; and transport medium in the body for food substances/gases/hormones.
transports waste excretory products
it is a medium for chemical reactions/digestive processes
it function in distribution of body heat
it is the main component of the synovial fluid of joints; amniotic fluid
serves a protective function in the brain
allows easy movement of food through the digestive tract.