Nutrition and Transport in Plants etc.

2.17 describe the process of photosynthesis and understand its importance in the conversion of light energy to chemical energy
2.18 recall the word equation and the balanced chemical symbol equation for photosynthesis 


Overall equation for photosynthesis:


*Ignore the second equation!! It is unbalanced, and is there just to illustrate the thought process as you convert from a word equation to a symbol equation.*

What conditions are essential for photosynthesis?

· sunlight

· carbon dioxide

· chlorophyll

· a suitable temperature

· water

Photosynthesis depends on enzyme reactions in the chloroplasts. Remember the effect of temperature on enzyme activity-enzymes have optimum temperatures that vary between different organisms. (Optimum temperature=this is the temperature at which the enzyme is most active, catalysing the largest number of reactions per second.) --Certain enzymes in plants have a high optimum temperature. E.g. the optimum temperature of the enzyme papain found in papaya is about 65°C.

How do guard cells control the size of stomata?

In sunlight:

·         The concentration of potassium ions (K⁺) increases in the guard cells

·         Chloroplasts in the guard cells photosynthesise. The light energy is converted into chemical energy used to pump potassium ions into the guard cells from neighbouring epidermal cells. This lowers the water potential in the guard cells.

·         Water from neighbouring epidermal cells enters guard cells by osmosis so that they swell and become turgid.

·         The guard cells have a thicker cellulose wall on one side of the cell (the side around the stomatal pore). Hence, the swollen guard cells become more curved and pull the stoma open.

At night:

·         The potassium ions accumulated in the guard cells during the day diffuse out of the guard cells.

·         This increases the water potential in the guard cells and water leaves them by osmosis.

·BlogThis!