Limiting factors LO Know the 3 limiting factors Describe photosynthesis graphs Evaluate growth conditions for optimum crop yield KW : photosynthesis; light intensity; carbon dioxide concentration; temperature

Three factors can limit the rate of photosynthesis - light intensity, carbon dioxide concentration and temperature. Write down the word equation for photosynthesis, what two limiting factors are directly involved in the reaction? Why does the third limiting factor also affect the rate of photosynthesis?

Without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the speed of photosynthesis. How could you increase the light intensity?

The rate of photosynthesis will increase until it reaches a threshold at which the rate cannot increase any further. Describe in 2 or 3 sentences what is happening to the rate of photosynthesis with an increase in light intensity.

Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient carbon dioxide. What could limit the amount of carbon dioxide in the air? How can we increase the proportion of carbon dioxide in a local environment? (think about when we don’t want carbon dioxide to be formed)

The rate of photosynthesis will increase until it reaches a threshold at which the rate cannot increase any further. Describe in 2 or 3 sentences what is happening to the rate of photosynthesis with an increase in carbon dioxide concentration.

If it gets too cold, the rate of photosynthesis will decrease If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesise if it gets too hot. The photosynthesis reaction cannot take place due to having a narrow temperature effectiveness window. This effectiveness window is different in different plants – ones that live in the arctic can photosynthesise at lower temperatures than desert plants. Suggest a range of temperatures that plants in a) the desert and b) the arctic can photosynthesise

Think about the shape of the light intensity and carbon dioxide concentration graphs. How do you think the temperature graph will differ? Sketch a possible graph in your books. ??

The peak of the graph would be at a higher temperature for a plant that is adapted to the desert, lower for a plant that is adapted to the arctic.

Maximising growth Farmers can use their knowledge of these limiting factors to increase crop growth in greenhouses. They may use artificial light so that photosynthesis can continue beyond daylight hours, or in a higher-than-normal light intensity. The use of paraffin lamps inside a greenhouse increases the rate of photosynthesis because the burning paraffin produces carbon dioxide, and heat too.