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There are six main classes of nutrients that the body needs:
  • Carbohydrates
  • Proteins
  • Fats
  • Vitamins
  • Minerals, and
  • Water.
It is important to consume these six nutrients on a daily basis to build and maintain healthy bodily function. Poor health can be caused by an imbalance of nutrients, either an excess or a deficiency, which in turn, affects bodily functions cumulatively. To function, the human body must have these nutrients in appropriate levels.


Autotrophic Nutrition

Autotrophic nutrition involves the use of an external energy source to make the complex organic substances that we call food. Plants use light energy from the sun as their external energy to perform photosynthesis.


During photosynthesis carbon dioxide and water are used to convert into carbohydrate. Light energy is trapped by chlorophyll and with the help of carbon dioxide carbohydrate is prepared. Plants manufacture all the other organic substances that they need from these carbohydrates and very small quantities of minerals from the soil. It is the process of converting light energy into chemical energy and storing it in the bonds of sugar. This process occurs in plants and some algae. Plants need only light energy, CO2 and H2O to make sugar. The process of photosynthesis takes place in the chloroplasts, where the pyruvate breaks down to give carbon dioxide and water with the release of energy. The total energy fixed is around 1% of the total energy.

Photosynthesis takes place primarily in plant leaves and in stems. The parts of a typical leaf include the upper and lower epidermis, the mesophyll, the vascular bundle, and the stomata. The upper and lower epidermal cells do not have chloroplasts, thus photosynthesis does not occur there. They serve primarily as protection for the rest of the leaf. The stomata are holes, which are in the lower epidermis and are used for air exchange. The vascular bundles or veins in a leaf are a part of the plant's transportation system which transports water and nutrients for the plant as needed. The mesophyll cells have chloroplasts and this is where photosynthesis occurs. 


Collect three or four green leaves of any common plant such as spinach or radish and crush them with a grinding stone. Put this crushed pulp on a piece of white paper. A green patch will be formed on the paper. This is formed due to the pigment called chlorophyll.
The molecule of chlorophyll pigment present in organelles called chloroplasts has the unique property of trapping solar energy which is then utilized for the synthesis of food in the chloroplast. You will recall that white light consists of a range of wavelengths of light known as VIBGYOR. Maximum absorption of the red and blue wavelengths of the spectrum takes place due to chlorophyll. Photosynthesis is most efficient in these ranges of light. Chlorophyll reflects back the green wavelength and hence it appears green in colour.
Chlorophyll consists of four pigments. These are chlorophyll a and b which are green. The other two are xanthophylls and carotene which are yellow and orange, respectively. The overall green colour of the leaf is because of predominance of the green pigments.

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