Plastids are the colored organelles within plant cells. Plastids are the largest among the organelles present in the cytoplasm. Under a microscope, they are easily visible. Plastids are not present in Fungi, Bacteria, and Animal cells.
Plastids are mainly of two types:
Leucoplastid or Leucoplast and Chromoplastid or Chromatoplast.
Leucoplast
They are colorless, as they have no pigment. Leucoplast may be converted into chromoplast or mainly chloroplast in contact with sunlight. Leucoplasts are present in organs where light cannot reach, eg-root, cortex, etc. They function in food storage.
Chromatoplast
Chromatoplasts are green or other colors; when green, it is called chloroplast, and when they are another color it is called Chromoplast.
Chromoplast
Other than green, they are mainly yellow and red. They even come in a variety of shapes. Colored sections of plants, such as petals, colored berries and seeds, carrot roots, and so on, use chromoplast. Flowers are colored and majestic as a result of their presence. They aid pollination and reproduction indirectly.
Chloroplast
They are green, and they have an abundance of the green dye chlorophyll.
Some pigments are used in small amounts.
One or more chloroplasts can be found in each cell.
Chloroplasts in higher plants have a lanceolate form.
Algal cells come in a variety of sizes, such as cup-shaped, spiral, reticulate, star-shaped, semicircular, and so on.
Their primary feature is photosynthesis.
Structure of Chloroplasts:
1. The chloroplast is fully encircled by a bi-layered semipermeable membrane.
2. There is a hygroscopic matrix encased in a membrane. The name for this matrix is the stroma.
3. There are 40-80 well-arranged barrel-shaped grana (sing: granum) in the stroma. There are 5-25 granum discs in each granum. There are openings inside the granum disk. This chamber is likely to contain chlorophyll and other photosynthetic materials.
4. Several granum disks of two adjacent grana are bound by stromal lamella, which is a minute tubular body.
5. The membrane of the grana disc contains a large number of crystalline bodies. Carbon dioxide is mostly assimilated in the quant some during the dark process of photosynthesis.
Photosynthesis, the process by which green plants produce energy, is their primary purpose.
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