Greek word Chroma means colored. Plastids of color other than green are called chromoplasts. It is colored due to carotene and xanthophyll. Chromoplasts probably evolved from chloroplasts. Flower petals, colored fruits and seeds, and carrots contain chromoplasts. Insects are attracted to the colors of flowers and leaves and help in pollination. Different types of chromoplasts are-

(i) Carotenoplast: The orange colored chromoplast is called carotenoplast. Monica Sánchez flowers, bignonia flowers and carrots contain carotenoids.

(ii) Rhodoplast : Red colored chromoplast is called rhodoplast. Rhodoplasts are present in spp.

(iii) Pheoplast: Yellow-brown colored chromoplast is called pheoplast. Diatoms and brown algae contain pheoplasts.

(iv) Xanthoplast: Yellow colored chromoplast is called xanthoplast. Dandelion flower, sunflower flower, golden flower, ginger flower, marigold flower, ripe fruit skin contain xanthoplast.

Greek word Leuco means colorless. Colorless plastids are called leucoplasts. In presence of light it can transform into chromoplast or chloroplast. It can be semicircular, rectangular or cylindrical in shape. Leucoplasts are found in plant roots, lower stems, seeds, dividing tissues, gametes etc. Polytoma algae contain leucoplasts. There are three types of leucoplasts. These are-

(i) Amyloplast : The leucoplasts that store starchy food are called amyloplasts. Amyloplasts are present in plants like rice, wheat, potato, bhutra, barley, cown etc.

(ii) Elioplast: The leucoplasts that store fatty food are called elaioplasts. Plants like mustard, coconut, Chinese almond, soybean, linseed etc. contain elaioplast.

(iii) Aleuroplast: All leucoplasts that store protein food are called aleuroplast or proteinoplast. Chickpeas, peas, kesari and lentils contain aleuroplasts.

Almost all plant cells contain plastids. Photosynthetic bacteria and blue-green algae have chromatophores. Fungi, myxomycetes and most bacteria do not have plastids.

In 1883, A.F.W Schimper first observed green colored plastids in plant cells and named them chloroplasts. In 1883, scientist Meyer described green plastids as autoplasts and other colored plastids as trophoplasts. In 1886 scientist Haeckel first used the term plastid. In 1923, scientists provided information about the location and function of plastids in female plant cells.

The Greek word plastikas means molded. The ovoid, plate-shaped, ribbon-shaped or star-shaped organisms located in the cytoplasm of plant cells are called plastids. It is the largest organelle in the cytoplasm. Fungi and bacteria do not have plastids, but do have chromatophores. Blue green algae or cyanobacteria (BGA) contain chlorophyll in their thylakoids. Animal cells do not have plastids.

1. Respiration Process: Krebs cycle and electron transport system of respiration process are completed in mitochondria. It is called mitochondrial respiration as it takes place in the mitochondria.
2. Energy production: ATP is produced in mitochondria. ATP is the source of energy.
3. Protein production: Mitochondria make proteins for the cell.
4. Nucleic acid production: It makes DNA and RNA. It plays a role in heredity.
5. Blood cell and hormone production: It helps in blood cell and hormone production.
6. Contains enzymes: It contains enzymes and co-enzymes required for respiration.
7. Ion balance: They maintain the correct concentration of calcium ions in different parts of the cell.
8. Metabolism: It metabolizes neurotransmitters and cholesterol or fat.
9. Control of apoptosis: Mitochondria control cell apoptosis.
10. Heredity: Mitochondria help in the formation of sperm and egg.
11. Energy regulation: It regulates the storage and release of energy in cells. ADP is converted into ATP and stored in the body by creating high energy bonds.
12. Cation storage: Mitochondria store Ca2+, S2+, Fe2+, Mn2+ etc.
13. Heat production: Mitochondria help in the production of excess heat in hibernating animals.
14. Production of chemical compounds: Mitochondria are capable of creating, breaking down and producing substances necessary for the cell. It produces compounds like cytochrome, ferridoxine, hemoglobin, chlorophyll, steroids, alkaloids etc.
15. Biosynthesis: It causes biosynthesis of iron and steroids in cells.
16. Transport: It is capable of active transport of calcium, potassium etc.
17. Disinfection: It participates in ammonia disinfection.
18. Pathogenesis: Mutations can occur in mitochondrial DNA that cause mitochondrial disorders. 100 such disorders are known. In old age, diseases like Parkinson’s, Alzheimer’s, type-1 diabetes etc. can occur. Proper health is dependent on the structure and function of mitochondria.

1. Protein: About 65% of the dry weight of mitochondria is protein. It contains both soluble and insoluble proteins.
2. Lipids: Mitochondria contain about 35% lipids. Of this, 90% are phospholipids and 10% are fatty acids and carotenoids. It contains glycerides 29%, lecithin and cephalin 4% and cholesterol 2%. Its inner membrane contains phospholipid called cardiolipin.
3. Pigments: Contains small amounts of carotenoids.
4. Nucleic acid: It contains DNA and RNA as nucleic acids. Each mitochondrion contains about 200 pieces of DNA. It contains 5% RNA.
5. Enzymes: It contains about 100 types of enzymes and co-enzymes.

1. Membrane: Each mitochondrion is covered by a bilayered membrane. Outer cover and inner cover. The outer layer is called the outer layer and the inner layer is called the inner layer. The outer coat is smooth and the inner coat is rough. Each coat is 40–60 Å thick. The space between the two membranes is called the perimitochondrial space. The distance of perimitochondrial space is 6-8 nm. It is composed of lipoproteins. It gives the mitochondria specific shape and protects them from external injury.
2. Chambers: Mitochondria have two types of chambers. Outer chamber and inner chamber. The compartment between the outer and inner envelope is called the outer compartment and the compartment between the inner envelope is called the endocompartment (70 Å wide). It is filled with various chemicals.
3. Matrix: The jelly-like substance inside the cell is called matrix. It is dense, homogenous and full of enzymes and co-enzymes.
4. CRISTIE: The inner membrane of the mitochondria folds inwards to form a number of finger-like extensions. It’s called Christy. The space between each cristae is called the intercristi space.
5. Oxysome or F1 Cells: Mitochondria have numerous fine granules like tennis bats on the inner envelope. These are called oxisomes or F1 cells. It consists of head, stem and base. There are two types of oxisomes. Sabrintak and Abrintak. The oxisomes which have a stalk are called stalked oxisomes and the oxisomes which do not have a stalk are called unstalked oxisomes. It has ATP-ase enzyme in its head.
6. ETS: Electron Transport System is abbreviated as ETS. It is called ETC (Electron Transport Chain). Christy has ETS on him. It transfers electrons from one place to another.
7. ATP-Synthases: All substances that synthesize ATP are called ATP-Synthases. Christy has spherical or oval ATP-synthases. It produces ATP.

There are three theories about the origin of mitochondria.
1. De novo origin: According to this theory, amino acids and lipids combine to form mitochondria. This doctrine is not accepted at present.
2. Cell membrane or endoplasmic origin: According to scientist Morison (1966), vesicles are formed from endoplasmic reticulum or cell membrane and mitochondria are formed from vesicles. This doctrine is now defunct.
3. Mitochondrial origin: According to this theory, during cell division, old mitochondria divide to form new mitochondria. The new mitochondria quickly change shape and move to other parts of the cell. It grows rapidly and divides to increase the number of cells to meet more energy.

Each cell has an average of 300-400 mitochondria. Advanced plant cells contain 100-3000 mitochondria. Liver and kidney cells contain 1000 or more mitochondria. Human sperm has 20 mitochondria. A sea urchin egg has 140,000 mitochondria, an amphibian egg has 300,000, and an Amoeba has 500,000. Mammalian red blood cells do not contain mitochondria.