PHOTOSYNTHESIS Class VII Subject Biology Part 4 To

PHOTOSYNTHESIS Class – VII Subject – Biology Part - 4

To show that oxygen is given out during photosynthesis Requirements: A beaker, a funnel, a test tube, conical funnel, pond water and twigs of an aquatic plant such as Hydrilla. Procedure: Fill some water in the beaker and put the twigs of hydrilla in it. Keep an inverted conical funnel so that it covers the twigs. Now, keep an inverted test tube filled with pond water over the funnel as shown in the figure. Put this apparatus in sunlight. Keep it for sometime and write your observation. Put this apparatus in a shaded area, keep it for sometime and write down your observation. Now, put the apparatus in a completely dark area, keep it for sometime and write your observation. Observations: You will observe that when the apparatus was in sunlight, there appeared more number of air bubbles from the twigs of hydrilla than when it was kept in a shaded area. In total darkness, no bubbles appeared at all. Inference: It proves that oxygen is given out during photosynthesis.

To find out the fact why most of the plants look green while there are plants which have leaves of different colours • The chlorophyll pigment in the leaves absorbs most of the blue and regions of the incident light. The pigments are not capable of absorbing the green region of the visible light, therefore, the green light is reflected from the plants and that is why they look green. • The leaves are green in colour because of the green pigment chlorophyll in them. The leaves other than green have other pigments which impact various other colours of the leaves such as red, yellow, orange, brown etc. • These pigments also give characteristic colours to flowers, fruits and roots. • Carotene is an orange pigment which do photosynthesis by transmitting light to chlorophyll molecule.

Significance of photosynthesis • It is the primary source of organic food and energy (ATP) for all forms of life. • Excess of sugars produced by photosynthesis are stored in the form of carbohydrates (starch) or used in the formation of other organic compounds. • Photosynthesis helps to purity air and also maintains the balance of oxygen and carbon dioxide in the ecosystem. • Photosynthesis process led to the origin of life on earth. • The energy stored in all these fuels is basically solar energy that was trapped and stored during photosynthesis millions of years in the primitive earth.

End of Part 4