(a) (i) Name the two stages involved in photosynthesis. (ii) Write an equation to represent the first stage of photosynthesis. (b) (i) List six modes of nut...

Answer Details

(a)(i) Two stages of photosynthesis

The light stage (light-dependent reaction) and the dark stage (light-independent reaction / Calvin cycle).

(a)(ii) Equation for the first (light) stage

In the light stage, water is split by light energy (photolysis) to release oxygen, hydrogen and energy:

\[ 2H_2O \xrightarrow{\text{light energy / chlorophyll}} 4H^+ + 4e^- + O_2 \]

(In words: water is split in the presence of light and chlorophyll to give hydrogen ions, electrons and oxygen. The energy is trapped as ATP.)

(b)(i) Six modes of nutrition

Autotrophic (holophytic), heterotrophic (holozoic), saprophytic, parasitic, symbiotic, and chemosynthetic nutrition (carnivorous/insectivorous also acceptable).

(b)(ii) Feature that makes feeding possible

• I. Paramecium: cilia (which sweep food into the oral groove / gullet).
• II. Spirogyra: chloroplasts (containing chlorophyll for photosynthesis).
• III. Rhizopus: rhizoids/hyphae which secrete enzymes and absorb digested food (saprophytic feeding).
• IV. Tapeworm: hooks and suckers (scolex) for attachment, and a thin body surface for absorbing already-digested food from the host.

(c) Balanced diet

A balanced diet is a diet that contains all the classes of food (carbohydrates, proteins, fats and oils, vitamins, mineral salts and water) in the correct proportions needed by the body for good health.

(d)(i) Three characteristics of enzymes

• They are proteins and act as biological catalysts.
• They are specific in their action.
• They are affected by temperature and pH (denatured by high temperature).

(d)(ii) Ptyalin and pepsin