Organisms In the Environment

PHOTOSYNTHESIS

Photosynthesis can only be carried out by green plants and algae.  Chlorophyll in the choloroplasts absorbs the Sun's light energy.

Carbon dioxide + water ----> oxygen + glucose

6CO2 + 6H20 ------> 6O2 + C6H12O6

Carbon dioxide is taken in by the leaves and water is taken up by the roots.  The chlorophyll traps the light energy from the Sun and uses it for photosynthesis.  The energy is used to convert the carbon dioxide and water into glucose and oxygen.  Oxygen is released as a waste product of photosynthesis.  Some of the glucose is converted into insoluble starch for storage.

Leaves can be tested with iodine solution.  Variegated plants have patches of green where chlorophyll is present and patches of white where there is no chlorophyll.  Only the green patches turn the iodine solution blue-black to show that starch is present.

LIMITING FACTORS

A lack of light would slow the rate of photosynthesis as light provides the energy for the process. Even if it is sunny, light may be limited to plants that are shaded by trees.

If it is cold, then enzymes do not work effectively and this will slow down the rate of photosynthesis.

If there is little carbon dioxide, then the rate of photosynthesis will slow down.

Anything that puts a cap on the rate of photosynthesis is a limiting factor.

HOW PLANTS USE GLUCOSE

The glucose produced by photosynthesis may be converted into insoluble starch for storage. In addition, it used as a reactant in respiration, converted into fats and oils for storage, used to produce cellulose and to produce proteins.  Plant and algal cells also need a supply of mineral ions in order to produce protein.  Plants absorb mineral ions from the soil.

MAKING THE MOST OF PHOTOSYNTHESIS

Plant growers try to give their plants the best conditions for growth by controlling the environment.  They have to evaluate the benefits of increasing growth against the increased cost of heating and lighting or providing carbon dioxide.  Greenhouses and polytunnels can be constructed to grow plants in an enclosed space.  If the greenhouse has heaters and lamps…