Class 10, Science, Chapter-5, Lecture-1, Photosynthesis (Notes)
NUTRIENTS:
A substance which is obtained by an organism from its surrounding and used as a source of energy or for biosynthesis of body parts is termed as nutrient.
Examples– carbohydrates, fats, proteins, mineral, vitamins, water.
NUTRITION:
The process by which living organisms obtain or synthesise food and change it into a simple absorbable form and utilise it as a source of energy or for biosynthesis of body parts is termed as nutrition.
STEPS OF NUTRITION:
- Ingestion
- Digestion
- Absorption
- Assimilation
- Egestion
MODES OF NUTRITION:
- AUTOTROPHIC NUTRITION:
The mode of nutrition in which organisms synthesise organic materials from the inorganic materials is termed as autotrophic
Examples– photosynthesis.
AUTOTROPHS:
The organisms, which synthesise organic materials from the inorganic materials, are termed as autotrophs.
Example– green plants, autotrophic bacteria. - HETEROTROPHIC NUTRITION:
The mode of nutrition in which energy is derived from the intake and digestion of the organic substances obtained from plants or animals is termed as heterotrophic nutrition.
Example– nutrition by animals , Nutrition by Bacteria , Nutrition by Fungi
HETEROTROPHS:
The organisms, which derive energy from the intake and digestion of the organic substances obtained from plants or animals, are termed as heterotrophs.
Examples– all animals, bacteria, fungi.
DIFFERENCES BETWEEN:
Autotrophs | Heterotrophs |
---|---|
The organisms, which synthesise organic materials from the inorganic materials, are termed as autotrophs. | The organisms, which derive energy from the intake and digestion of the organic substances obtained from plants or animals, are termed as heterotrophs |
Autotrophs contain CHLOROPHYLL | Heterotrophs do NOT contain Chlorophyll. |
PHOTOSYNTHESIS:
The process by which green plants make their own food from carbon dioxide and water by using sunlight in the presence of chlorophyll is termed as photosynthesis.
Overall equation:
STEPS INVOLVED IN PHOTOSYNTHESIS:
- Absorption of light energy by chlorophyll.
- Conversion of light energy to chemical energy.
- Splitting of water molecule into hydrogen and oxygen.
- Reduction of carbon dioxide to carbohydrates.
CONDITIONS NECESSARY FOR PHOTOSYNTHESIS:
- Presence of Chlorophyll
- Presence of light
- Presence of Carbon dioxide
- Presence of water
Experiment to Show that Chlorophyll is Necessary for Photosynthesis:
Steps:
- A potted croton plant, having variegated leaves, is kept in the dark for 72 hours to make the leaves starch free.
- After that, the plant is kept in sunlight for six hours.
- A leaf is plucked and dipped in boiled water to denature the enzymes.
- The leaf is boiled in alcohol to decolourise the leaf and then tested with iodine.
Observation:
The portion of the leaf that was initially green due to presence of chlorophyll, turns blue black confirming the presence of starch.
The non-green portion of the leaf does not turn blue black.
Conclusion:
Chlorophyll is necessary for photosynthesis.
Experiment to Show that Light is Necessary for Photosynthesis:
Steps:
- A potted plant is kept in the dark for 72 hours and another plant is kept in sunlight.
- One leaf from each is plucked and dipped in boiled water to denature the enzymes.
- The leaves are boiled in alcohol to decolourise them and then tested with iodine.
Observation:
The colour of the leaf kept in sunlight, turns blue black confirming the presence of starch.
The colour of the leaf kept in dark, turns brown.
Conclusion:
Sunlight is necessary for photosynthesis.
Experiment to Show that Carbon Dioxide is Necessary for Photosynthesis:
Steps:
- Two potted plants are kept in the dark for 72 hours.
- Each one of the potted plants is covered by bell jar. The arrangement is made airtight.
- Some potassium hydroxide (KOH) is placed in a watch glass to absorb the CO2 present inside the first
ell jar. - Each plant is kept in sunlight for six hours.
- One leaf is plucked from each plant and dipped in boiled water to denature the enzymes.
- The leaves are boiled in alcohol to decolourise and then tested with iodine.
Observation:
The colour of the leaf from second plant turns blue black confirming the presence of starch.
The colour of the leaf from first plant does not turn blue black.
Conclusion:
Carbon dioxide is necessary for photosynthesis.
Though the requirement of water for photosynthesis is very little, yet its deficiency reduces rate of photosynthesis.
Reason:
Under water deficient conditions stomata remain closed to reduce transpiration.
This restricts or stops the entry of carbon dioxide into the leaves.