Photosynthesis Revision Cards

  • Created by: abi_owen
  • Created on: 12-05-17 20:22

Photosynthesis Overview

Photosynthesis uses energy to change carbon dioxide and water into glucose and oxygen.

  • Takes place in chloroplasts

          - they contain pigments like chlorophyll that absorb light.

  • Energy is transferred to the chloroplasts from the environment by light.
  • Photosynthesis is endothermic - this means energy is transferred from the environment in the process. 

The word equation for photosynthesis is:


carbon dioxide + water ---->  glucose + oxygen

The symbol equation is:


Light Intensity Equation:

light intensity = 1/d^2

measured in a.u.

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Uses for Glucose in Plants

  • respiration to release energy for chemical reactions
  • making cellulose for structural growth, making new cell walls and increasing biomass
  • making amino acids and proteins for growth
  • stored as lipids 
  • stored as insoluble starch in leaves and storage organs, e.g. potatoes and seeds
  • sucrose (for transport) as it's more soluble than glucose
  • chlorophyll, made using magnesium ions and glucose
  • DNA, made using nitrates, phosphates and glucose
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Limiting Factors

A limiting factor slows the rate of photosynthesis, such as:

Light Intensity

  • light provides energy needed for photosynthesis
  • as light levels increase, the rate of photosynthesis increases steadily up to a point
  • beyond this point, the limiting factor has changed, even as light levels increase, the rate will no longer increase - it could be carbon dioxide concentration or temperature, but it is not light intensity

* the point where the graph constant is the point where the limiting factor changes


  • temperature provide the energy needed for enzymes to catalyse chemical reactions
  • if temperature is too low, enzymes don't have enough kinetic energy to catalyse reactions fast enough, so the rate of photosynthesis slows down
  • if the temperature is too high, enzymes can begin to denature, so the rate of photosythesis will slow down

Carbon Dioxide Concentration

  • raw material needed for the photosynthesis reaction (see Photosynthesis Overview)
  • as the carbon dioxide concentration increases, the rate of photosynthesis increases steadily up to a point
  • beyond this point, the graph falttens out - as the carbon dioxide concentration increases, the rate no longer increases and the limiting factor changes to either temperature or light intensity
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Photosynthesis Required Practical

Canadian pondweed can be used to measure the effect of light intensity on the rate of photosynthesis

  • The rate at which the pondweed produces oxygen corresponds with the rate of photosynthesis

              - the faster the rate of oxygen production, the faster the rate of photosynthesis


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Why Do Plants Need Minerals?

Lack of magnesium ions means...

  • yellow leaves

        - due to less chlorophyll, so less photosynthesis

Lack of nitrates means...

  • stunted growth

        - used to make amino acids ----> proteins

               > proteins needed for growth

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