Rates of Photosynthesis

Rates Of Photosynthesis:

• Availability of carbon dioxide
• Water
• Light energy
• Temperature of the cell

- Never affected by all factors at any given moment. Just the limiting factor - limits the rate oat which photosynthesis can take place

- Changing the levels of the other factors will not affect the rate of photosynthesis - only changing the limiting factor will.

• Light required to provide the energy needed to excite electrons in the light-independent stage
• Light causes stomata to open (gaseous exchange/transpiration)
• Allows CO2 to enter leaves - H2O can be delivered to leaves from the roots

- When there is little to no light, GP cannot be reduced to TP - TP levels fall and GP accumulates

- This means that RuBp cannot be formed and, therefore, RuBp levels fall

'As light intensity increases, the rate of photosynthesis increase' (directly proportional)

• Is rarely a limiting factor due to the abundance of it within the atmosphere
• If levels of CO2 falls, RuBp cannot accept it within the Calvin Cycle so RuBp accumulates

This means that GP cannot be made and, therefore, no TP is generated

• Calvin Cycle consists of many enzyme-catalysed reactions so is sensitive to temperature

'As temperature increases, the rate of photosynthesis increases' (directly proportional)

'As temperature increases above 30, the rate of photosynthesis may decrease'

(at 30 degrees and above, O2 competes with CO2 for the active site of the enzyme RuBisCo)

Photorespiration - binding of oxygen to RuBisCo reduces the amount of CO2 accepted by RuBp. Reduced GP formed which reduced TP formed. If there is not enough TP. RuBp cannot be generated

- 45 degrees and above - enzymes involved in photosynthesis may denature. The tertiary structure of enzymes break down (bonds are broken) and therefore, the function of the enzyme decreases.

Sufficient water keeps plant cells turgid. Turgid guard cells help to keep stomata open for gas exchange

Insufficient water:

• Roots cannot take up enough water to replace water lost during transpiration
• Plant cells lose water and shrink (become plasmolysed)
• Causes plant to become flaccid and plant leaves wilt

- When there is limited water, plant roots produce abscisic acid (translocated to leaves) which causes stomata to close.

- This causes rate of photosynthesis to reduce as photolysis cannot occur and CO2 can no longer enter through the stomata.

Limiting Factors limit growth of plants, making ti unfavourable in agricultural farming as it prevents crops from growing quickly and fully

Controlling Limiting Factors Using Greenhouses:

• Clear - Allow as much light in as possible
• Artificial Bright Lights - Provide high light intensity and allows photosynthesis to continue beyond daylight hours
• Keep heat in
• Artificial Heater - Can be used to carefully control the temperature so that it is at its optimum for photosynthesis. Temp too high = denaturing of enzymes. Temp too low = slow reactions
• Paraffin Lamps - To add additional carbon dioxide (Cost Effective as they give off Co2 as well as providing heat and light)

(Features must be weighed against crop yield to see if they will actually bring in higher income)