Page 115 - Biology_F5

Biology for Advanced Level Secondary Schools

Photoautotrophs or in their host (obligate parasitic bacteria),
Photoautotrophs bacteria need light as while others live as parasites in or on the
their source of energy in manufacturing host but obtain their food as saprophytes
their food. The light is trapped with the (facultative parasitic bacteria). Some
aid of chlorophyll 'a' and carotenoid other bacteria live in a mutual (symbiotic)
pigments. This type of photosynthesis is relationship with other organisms whereby
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much simple compared to that of plants. both partners benefit from the association.
Examples include blue-green bacteria. Examples of symbiotic association
include; Rhizobium bacteria that live in
Chemoautotrophs the root nodules of leguminous plants.
These bacteria acquire their energy by These bacteria have ability to fix nitrogen
oxidising simple inorganic substances, but into useful compounds such as nitrates
not from sunlight as in photoautotrophs. which are needed by these plants, and
The obtained energy is used to synthesise Escherichia coli, which live symbiotically
food in the presence of carbon dioxide. in the human gut and contribute to the
Important nitrogen fixing bacteria such as formation of vitamin B and K.
Nitrosomonas and Nitrobacter belong to
this group. Others include Iron bacteria 3.3.3 Bacterial reproduction
which oxidise Iron two (Ferrous Iron) to Task 3.3
Iron three (Ferric Iron), and the energy Search from the internet sources
released from oxidation is utilised during the simulations or videos showing
food synthesis.
bacterial reproduction. Note asexual
and sexual reproduction.
Heterotrophs
All bacteria, which cannot manufacture Bacteria reproduce both sexually and
food on their own as they lose the ability to asexually. Sexual reproduction involves
photosynthesise in the course of evolution two organisms/cells exchanging their
are heterotrophs (heterotrophic bacteria). genetic materials (not gametes, as they
Heterotrophs can be classified into have no reproductive structures) and
chemotrophs. They are named “chemo” produce daughter cells which differ in their
heterotrophs, when they obtain energy for genetic materials from that of the parental
their growth from organic compounds, cells. Sexual reproduction involves the
such as proteins and glucose. Heterotrophs process of genetic recombination through
can be further categorised into saprotrophs, cell to cell contact (Conjugation), while in
parasites and mutualists. The saprotrophs asexual reproduction the cell divides by
obtain their food from dead and decaying binary fission to form two daughter cells
organic matter, majority of them are with similar genetic materials as that of
decomposers, which are very important the parental cell.
in nutrient recycling. Parasitic bacteria
are pathogenic as they obtain their foods Asexual reproduction in bacteria
by living in or on other organisms thereby Most bacteria reproduce asexually. A
causing diseases and even death of their single bacterium can reproduce asexually
hosts. Some bacteria live permanently on by binary fission, which involves division

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