Page 121 - General and Inorganic Chemistry for Advanced Secondary Schools Students Book Form Five and Six

Biology for Secondary Schools

food is called an autotroph. The term Photosynthesis
‘autotroph’ originates from two Greek
words ‘autos’ which means ‘self’ and Task 6.1
‘trophy’ which means ‘feed’; hence Search from the library and reliable
‘autotrophy’ means ‘self-feeding’. This internet sources the information on the
FOR ONLINE READING ONLY
means that autotrophs are organisms meaning of photosynthesis.
that are capable of making their own
food for their own use and for other Photosynthesis is the process by which

organisms. Examples of autotrophic green plants, some bacteria and protoctists
make their own food using water and
organisms include green plants, algae, carbon dioxide in the presence of sunlight
and some bacteria such as cyanobacteria. energy. Organisms that make their own
The autotrophs can be divided into two food are called primary producers or
groups based on how they obtain their autotrophs. They are the primary source
energy. These are chemoautotrophs and of food for all other organisms. During the
photoautotrophs. process of photosynthesis, six molecules
of carbon dioxide and twelve molecules
Chemoautotrophs are organisms that of water combine to form one molecule of
obtain their energy from chemical glucose (a simple sugar), six molecules of
substances like hydrogen sulphide, water, and six molecules of oxygen. The
iron, methane, and ammonia. They leaf is the main site for photosynthesis in
plants. However, photosynthesis can take
utilise these chemicals to make their place in other green parts of the plant,
own food in the form of carbohydrates such as stem. The following chemical
through a process called chemosynthesis. equation represents the photosynthesis
Examples of chemoautotrophs are some process in plants.

bacteria (archaebacteria) that live in harsh
6 H O
Sunlight
environments. Such environments include 6CO 2 12H O+ 2 → C (Glucose) 6 6O+ 2 + 6H 2 O
Chlorophyll
12
the deep sea and around volcanic sites Photosynthesis produces a six-carbon
where there is no sunlight and where sugar molecule (a hexose) called
many other organisms cannot survive. glucose. Plants convert these hexose
Photoautotrophs are organisms that obtain sugars into other carbohydrates,
their energy from sunlight in order to such as complex sugars, starch and
cellulose. Plants are also capable of
make their own food. They make their converting hexose sugars into other
food using water and carbon dioxide in organic compounds, such as proteins

the presence of chlorophyll and sunlight and fats. The food formed by plants
through a process called photosynthesis. during photosynthesis is stored in the
form of starch.

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