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Roll no.2122

Light and temperature of an ecosystemThe light factor

Light is a form of radiant energy. It is an essential factor for the

production

of the plant materials upon which all other living organisms depend

directly or indirectly.

The visible range of light is between 380 to 720 nm. The chloroplast absorb radiation

from 330 to 740 nm. Only 39% of total radiation reaching the earth from the sun is visible

light. 60% is infrared and 1%is ultraviolet.

Effects of light on plants1. Photosynthesis.

2. Transpiration.

3. Seed germination.

4. Photoperiodism.

5. Reproduction and growth.

6. Influence upon number and position of chloroplast.

7. Changes in leaf structure.

Sun leaf Shade leaf

Ecological Classification

• Heliophytes

• Sciophytes

• Facultative Sciophytes

• Facultative Heliophytes

Measurement of light intensity

The intensity of light is usuallymeasured

by an instrument called photometeror

lux meter.

Unit of MeasurementThe intensity or brightness of light is measured in terms of candle power.

The light intensity from standard candle at one foot distance is called foot candle (F.C) and at one meter distance is called lux (L) or meter

candle (M.C)

Radiometer

The Temperature Factor

Temperature is a measurement of the degree of hotness. The radiant energy received from the sun is converted to heat energy. Heat is measured in

calories.

Vernalization

The flower production under the effect of low temperature is called

vernalization.

ThermoperiodismA phenomenon in which growth or development is promoted by alternating day and night temperatures.

Importance of temperature to plant

1. Temperature and metabolism

2. Temperature growth and reproduction

3. Temperature favourable and unfavourable to plants

Optimum temperature

Maximum temperature

Minimum temperature

Ecological classes of plants based on temperature

1. Megatherms

2. Mesotherms

3. Microtherms

4. Hekistotherms

Measurement of temperature Maximum minimum thermometer

Thermograph

Thermocouples and thermistors (water)