Chloroplast is an organelle found in all photosynthetic cells of plants. These are also found in some protists, for example, Euglena. Chloroplasts are the most common type of plastid. These are …
● Chloroplast is an organelle found in all photosynthetic cells of plants.
● These are also found in some protists, for example, Euglena.
● Chloroplasts are the most common type of plastid.
● These are absent in those plants which are not exposed to light.
● Chloroplast is derived from the Greek word “chloros”. It means green, and plastic,
which means form.
● Chloroplasts were first observed by Antony Von Leeuwehoek in 1679.
● The term chloroplast was given by Schimper (1883 A.D.)
● Chloroplast originated from proplastids found in the growing region of plants and are
surrounded by two membranes.
● When its size increases (up to 1µm) the inner membrane invaginates to form
vesicles in the presence of sunlight.
● They are very important for plants, because photosynthesis by which complex
organic food is manufactured, takes place in them.
● In the cytoplasm of plant cells, the chloroplast is well distributed homogeneously.
however, it is concentrated around the nucleus.
● Similarly, in certain cells, it is present just beneath the plasma membrane.
● They have a green color which helps to distinguish them from other types of plastid.
The green color is produced from the presence of two pigments, chlorophyll a and
chlorophyll b.
● Other types of plastids such as leucoplast and the chromoplast do not carry out
photosynthesis and have low concentrations of chlorophyll.
● Other pigments, carotenoids are also present in chloroplast which serve as
accessory pigments. Carotenoid trapping solar energy and passing it to chlorophyll.
● Like mitochondria, chloroplast has its own extra-cellular DNA, which is thought to be
inherited from the ancestor a photosynthetic cyanobacterium that was engulfed by an
early eukaryotic cell.
● They also produced lipids and proteins essential for the production of chloroplast
membrane.
● Chloroplast is moved around within plant cells, circulates, and is occasionally
compressed in two to reproduce.
Chloroplast Morphology
, ● Its size and shape vary from species to species. In higher plants chloroplast are
generally biconvex or planoconvex.
● However, in different plant cells, it may have various shapes such as filamentous,
saucer, ovoid, discoid, spheroid, star-like girdle-shaped, spiral ribbon-like, reticulate,
or cup-shaped.
● The size of the chloroplast is generally measured at about 5-10 µm in diameter and
2-3 µm in thickness.
● The chloroplast of cells of polyploid and shade plants are comparatively larger than
the chloroplast of cells of diploid and sun plants.
● From cell to cell, chloroplast’s numbers differ from one to another.
● It depends on the physiological state of the cell also. For example, Chlamydomonas
has only one chloroplast however 1-16 chloroplast in Spirogyra.
● According to a calculation, Ricinus communis leaf contains about 400,000
chloroplasts per square millimeter of surface area.
● The number of chloroplast gets increased by division when it’s inadequate in number.
● Similarly, degeneration takes place when it’s excessive in number.
Types of pigments
1. Chlorophyll
● Chlorophyll is a green pigment located within the chloroplast. More
specifically, it is found in the thylakoid membranes.
● The chlorophyll consists of 75% of chlorophyll a and 25% of chlorophyll b.
● The chlorophyll absorbs energy from sunlight and the synthesis of food
molecules in the chloroplast.
2. Carotenoids
● Carotenoids are the pigments present in chlorophylls which are located in the
thylakoid membrane. Pigments like yellow and orange are present in it.
● Carotenoids are related to vitamin A.
● They are important because they can absorb a certain wavelength of light that
can not be absorbed by chlorophylls.
● Carotenoids are involved in a function known as photoprotection.
3. Xanthophylls
● The carotenoids are carotenes and xanthophylls. Xanthophylls are present in
the brown and green algae.
4. Phycobilin
● Phycobilin is found only in red algae and Cyanobacteria. It has a relatively
narrow distribution.
● Phycoerythrin and phycocyanin are other accessory pigments belonging to
this family.
● Phycoerythrin makes red algae commonly red and phycocyanin causes the
Cyanobacteria to appear blue-green.
Chloroplast Structure
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