2.9

(a) Outline how light energy is used and how organic molecules are made in photosynthesis.

(5) Light Independent Reaction ATP and hydrogen (carried by NADPH) are products of the light dependent reactions They are used to fix carbon molecules together (add CO2 to basic carbon compounds) This allows for the production of more complex organic molecules (e.g. sugars) These organic molecules can then be stored to use in cellular respiration as required (Photosynthesis is a two step process: 1. The light dependent reactions convert the light energy into chemical energy (ATP) 2. The light independent reactions use the chemical energy to synthesise organic compounds (e.g. glucose) The organic molecules produced in photosynthesis can be used in cellular respiration to provide the energy needed by the organism)

2. Which variable has the least effect on enzyme activity? A. Temperature B. Light intensity C. pH D. Substrate concentration

B. Light intensity

3. What conclusion can be drawn from examining the action spectrum for a green plant shown below? A. Yellow light is the most effective at promoting photosynthesis. B. Every colour of light is equally effective at promoting photosynthesis. C. Light of wavelength 550 nm is least effective at promoting photosynthesis. D. Light in the green range is the most effective at promoting photosynthesis.

C. Light of wavelength 550 nm is least effective at promoting photosynthesis.

4. What is the source of the oxygen released into the air as a product of photosynthesis? A. Chlorophyll B. Carbon dioxide only C. Water only D. Both water and carbon dioxide

C. Water only

(b) Outline the role of chlorophyll and the effects of temperature, light intensity and carbon dioxide concentration on the rate of photosynthesis.

Chlorophyll is composed of a # of pigments -absorb different colors of light -mainly red and blue absorbed -green light reflected -temperature increases rate -up to a point where enzymes denature -light intensity increases rate up to a point where maximum absorbance can occur -carbon dioxide increases rate up to a point where fixation is at a maximum

6. A plant is exposed to increasing light intensity from very dim to bright light, while the carbon dioxide concentration and temperature are kept at an optimum level. What will happen to the rate of oxygen production? A. It will increase exponentially. B. It will remain constant. C. It will decrease to a minimum level. D. It will increase to a maximum level.

D. It will increase to a maximum level.

5. The photosynthetic activity of desert plants is often reduced in the middle of the day. What is the most reasonable explanation for this fact? A. Enzymes are denatured by the high temperatures. B. There is not sufficient water for photosystem I. C. Most of the light is reflected by the thick cuticle. D. The stomata close to preserve water and gas exchange decreases.

D. The stomata close to preserve water and gas exchange decreases.

1. Oxygen is produced during photosynthesis. What is the source of this oxygen inside the plant? A. Air spaces in the leaf B. Carbon dioxide C. Glucose D. Water

D. Water