Chloroplast- Definition, Structure, Types,
Functions, Diagram
● 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
Functions, Diagram
● 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
