B2.3 - Photosynthesis

Photosynthesis: the chemical process where plants use light energy to produce glucose (food)

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

During photosynthesis

• light energy is absorbed by green chlorophyll found in plant cells
• this energy is used to convert co2 (air) and h2o (soil) into sugar (glucose)
• o2 is released as a waste/by product

Factors that may limit the rate of photosynthesis are:                                                 

TEMPERATURE

Until approx 45*, the temperature & rate of photosynthesis increases. Temperature is the limiting factor.

Aroud 45*, the rate falls to 0, enzymes controlling photosynthesis denature.

LIGHT INTENSITY

As light intensity increases, so does the rate of photosynthesis. It's the limiting factor. At a certain point, the rate of photosynthesis plateaus.

An increase in light intensity has no further effect - it's no longer the limiting factor.

CARBON DIOXIDE CONCENTRATION

As the co2 concentration increases, so does the rate of photosynthesis. Co2 is the limiting factor. At a certain point, the rate of photosynthesis plateaus.   

An increase in co2 concentration has no further effect - it's no longer the limiting factor.

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Greenhouses may be used to control the rate of photosynthesis. This can result in plants growing more quickly + becoming bigger and stronger.

GLUCOSE PRODUCED IN PHOTOSYNTHESIS:

-Converted into insoluble starch for storage in stem, leaves or roots

Plants can store large amounts of starch in their cells w/o having a large affect on the water balance of the plant

-Cellulose for cell walls

-Lipid, fats, oils for storage

-Combines with nitrates to make amino acids which are used to make proteins. W/o this - stunted plant growth

Plants need mineral ions -- nitrates&magnesium-- which they absorb from the soil through their roots.

Magnesium is needed for chlorophyll production. W/o - yellow leaves.