ABOVE LEFT : Photosynthesis is an endothermic process that uses light as its energy source. Glucose is made in the process.
ABOVE RIGHT : The effect of different coloured light on the rate of photosynthesis.
Photosynthesis is an endothermic process which occurs in organisms that contain chlorophyll. The energy source for this process is light, and the products are glucose and oxygen.
The rate of photosynthesis depends on many factors, including the intensity and the colour of the light. White light from the Sun is made up of the colours of the visible spectrum.
Chlorophyll molecules absorb light strongly in the blue red regions of the spectrum, and poorly in the green region.
If plants are placed in an area covered with a green plastic roof, they will grow poorly. This is because the green roofing allows only the green light in the sunlight to pass through to the plants.
The rate of photosynthesis is much lower in green light than in other colours, causing poor growth in the plants. The chlorophyll in plant cells is contained in the chloroplasts.
Using an electron microscope, chloroplasts can be seen to contain granules. These can be stained with iodine, which indicates that they contain starch.
When plants are kept in the dark for some time, the chloroplasts no longer contain granules. This is further evidence that the granules contain starch which is made by photosynthesis.
ABOVE LEFT : The effect of light intensity on the rate of photosynthesis.
ABOVE RIGHT : A chloroplast viewed through an electron microscope. The white patches inside it are starch granules.