Biology - 8 Photosynthesis - 8.1 Photosynthesis & 8.2 The Rate of Photosynthesis

Photosynthesis word equation:

carbon dioxide + water → glucose + oxygen

Photosynthesis: endothermic or exothermic?

endothermic

Where is the sunlight absorbed within the plant?

into the chlorophyll in the chloroplasts

Photosynthesis symbol equation:

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Leaf adaptations for photosynthesis [5]:

- broad; big surface area for light to land
- thin; diffusion distances for gases are short
- contain chlorophyll in chloroplasts; to absorb light
- veins; take water in the xylem and remove products in the phloem
- guard cells; regulate gas exchange

Respiration word equation:

oxygen + glucose → water + carbon dioxide

Respiration symbol equation:

6O₂ + C₆H₁₂O₆ → 6H₂O + 6CO₂

Limiting factor

factor that restricts the rate of photosynthesis

Factors affecting photosynthesis [4]:

- light intensity
- temperature
- carbon dioxide concentration
- chlorophyll levels in leaf

How does light intensity affect the rate of photosynthesis?

if the light is more intense, more photosynthesis can take place and the rate increases

How does temperature affect the rate of photosynthesis?

if the temperature is higher, more photosynthesis can take place as it is an enzyme controlled reaction and the rate increases up to a point (at which enzymes are denatured)

How does carbon dioxide concentration affect the rate of photosynthesis?

if the carbon dioxide concentration is higher, more photosynthesis can take place as carbon dioxide is one of the reactants and the rate increases

How do chlorophyll levels in leaves affect the rate of photosynthesis?

if the amount of chlorophyll is limited , so too will be the rate of photosynthesis

What practical can we use to investigate photosynthesis?

Required practical 6: The effect of light intensity on the rate of photosynthesis in pondweed

Inverse square law

the intensity of radiation is inversely proportional to the square of the distance from the source of radiation

Light intensity ∝

1 ÷ (distance²)