Unit 1: The basis of life                                              1   2   3   4   5   6

4. Cellular nutrition

Cellular nutrition consists of all the processes in which cells obtain matter and energy to perform vital functions.

The matter which cells need to stay alive, are substances called nutrients. According to the type of nutrients taken in by the cell, there are two kinds of
nutrition:

      a) Autotrophic nutrition

    It is characteristic of cells which make their own organic matter from

    inorganic matter.

To make it, they need energy. There are two types of autotrophic nutrition, depending on the energy source used:

          - Photosynthesis.
              In this case the energy comes from the Sun.

              It takes place in most part of autotrophic organisms: Plants, Algae

              and some Bacteria.

          - Chemosynthesis.
              In this case, energy comes from chemical reactions.

              It takes place only in some Bacteria.

     b) Heterotrophic nutrition

It is characteristic of cells which feed on organic matter produced by

other living beings.

They transform this organic matter to obtain their own nutrients and energy.

Heterotrophic nutrition takes place in Animals, Fungi, Protozoa

and many Bacteria.

Once inside the cells nutrients are subjected to chemical reactions that are called cellular metabolism.

There are two types or metabolic reactions: anabolic reactions and catabolic reactions.

4.1. Photosynthesis

From glucose and mineral salts, plant cells can synthetise other organic compounds, such as starch, lipids, etc. Part of this organic matter is stored by the cell and other part is consumed in cellular respiration in order to stay alive.

The overall reaction of photosynthesis is this:

H₂O + CO₂ + Sunlight energy à Glucose + O₂

However, the real reaction takes place into two phases:

- Light phase. Energy of sunlight is caught by chlorophyll and changed

  into chemical energy.

- Dark phase. Inorganic matter is changed into organic matter, using
  the chemical energy obtained in the previous phase.

4.2. Cellular respiration

The overall reaction of respiration is this:

Glucose + O₂ à Energy + H₂O + CO₂

In absence of oxygen cells perform fermentation.

This reaction is similar to respiration but the amount of energy obtained is lesser. Fermentation can take place in all living beings, but is especially mportant in yeasts and some bacteria.

4.1. Answer these questions:

        a. Do plant cells perform cellular respiration? Why?

        b. Why is photosynthesis an anabolic reaction?

        c. Can all the cells of a plant perform photosynthesis? Why?

        d. When do cells perform fermentation?

4.2. Indicate the difference between:

         a. Chemosynthesis – Photosynthesis

   b. Anabolism – Catabolism.