Page 28 - Biology_F5

Cytology

and products out. types, namely amyloplasts, proteinoplasts,
(d) The matrix contains appropriate and elaioplasts. Each of these has a
enzymes used in respiratory pathways distinctive function. For instance,

such as Kreb’s cycle. amyloplasts are responsible for storage
(e) Presence of windows or fenestra in the of starch, proteinoplasts are responsible
membranes facilitates the passage of for storage of proteins, while elaioplasts
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materials in and out. are responsible for storage of fats and oils
which are needed by plants. They are also
used for synthesis of amino acids and fatty
Plastids acids.
These are membrane bound organelles
found in the cells of plants, algae, and Chloroplasts: These are most commonly
other eukaryotic organisms. They often known plastids which play an essential role
contain pigments. The type of pigment in enabling plants and some algae to make
determines the cell colour. They are their own food through photosynthesis.
mainly responsible for activities related They are found in green parts of plants,
to making and storing food. The plastids mainly leaves and in some other organisms
include chromoplasts, gerontoplasts, such as photosynthetic bacteria and green
leucoplasts, and chloroplasts. algae. The term chloroplast comes from
two Greek words: chloros, meaning 'green'
Chromoplasts: These are pigmented and plast, meaning 'form'. It contains
plastids found in flowers, aging leaves, green pigment known as chlorophyll,
and fruits such as tomato and red pepper. enzymes and other molecules that play
They contain carotenoid pigments; mainly role in photosynthesis.
red, orange or yellow which give different
colours seen in different parts of the Structure of chloroplasts
plant. They assist in pollination and seed The contents of chloroplasts are portioned
dispersal. from the cytosol by an envelope consisting
of two membranes separated by a very
Gerontoplasts: These are plastids that narrow inter-membrane space. Inside
develop from the chloroplasts of the leaves
or other parts of the plant that are going the chloroplast is another membranous
through the ageing process (senescence) system in the form of flattened sacs called
or are converted into different organelles. thylakoids or lamellae. In some regions,
This occurs when such parts of the plant thylakoids pile up like a stack of coins to
are no longer carrying out photosynthesis. form grana (singular, granum). The fluid
outside the thylakoids is the stroma, which
Leucoplasts: These are colourless plastids contains the chloroplast DNA, ribosomes
found in non-photosynthetic parts of the (70s), starch granules as well as many
plant such as roots, seeds, and bulbs. They photosynthetic enzymes. The chlorophyll
are used for storage of starch, lipids, and and carotenoids are present in thylakoids
proteins particularly in roots and tubers. and grana (Figure 1.12).
They are subdivided into three different

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