(a) State four characteristics of enzymes (b) (i) List two digestive enzymes produced in the duodenum of humans (ii) Name the substrate that each enzyme lis...

(a) Four characteristics of enzymes

• They are proteins.
• They act as biological catalysts, speeding up reactions without being used up.
• They are specific, each enzyme acting on only one substrate (or one type of reaction).
• They are affected by temperature and are denatured (destroyed) by high temperature.
• They work best at a particular (optimum) pH and temperature.
• They are required in very small amounts.

(b) Digestive enzymes of the duodenum

(Any two of the above are acceptable.)

(c)(i) Importance of chlorophyll

Chlorophyll traps (absorbs) light energy from the sun and uses it to manufacture food during photosynthesis.

(c)(ii) Two macroelements needed for chlorophyll formation

Magnesium and nitrogen (iron is also required for its synthesis).

(c)(iii) Deficiency symptoms

• Magnesium deficiency: yellowing of leaves (chlorosis), especially between the veins, and stunted growth.
• Nitrogen deficiency: yellowing of older leaves, poor stunted growth and small size.

(d) Testing for starch in a leaf

1. Dip the leaf in boiling water for about a minute to kill the cells and stop chemical activity.
2. Boil the leaf in ethanol (alcohol) in a water bath to remove the chlorophyll (decolourise it). Do not heat alcohol directly over a flame because it is flammable.
3. Dip the softened, brittle leaf in warm water to soften it.
4. Spread the leaf on a white tile and add drops of iodine solution over it.
5. Observation: the leaf turns blue-black where starch is present. A brown/yellow colour shows starch is absent.