1. Membrane: Each chloroplast is covered by a bilayer membrane. Outer cover and inner cover. The outer layer is called the outer layer and the inner layer is called the inner layer. The space between the two coats is called the periplastidal space. Distance of periplastidal space is 6-8 nm. The outer coat contains porin proteins.
2. Stroma: The transparent, granular and semi-fluid material inside the chloroplast is called stroma. It is a colloidal and hydrophilic liquid. The stroma contains about 200 DNA, RNA and circular DNA or plasmids. It contains protein plastogaebuli, osmophilic granules, sugar, oil droplets, vitamins, mineral salts etc.
3. Thylakoid: The sac-shaped three-dimensional structure in the stroma is called thylakoid. It is called the structural and functional unit of chloroplast. Its width is 100-300 Å.
4. Granum: 10-100 thylakoids arranged in a row forming a stack is called granum. Some quantosomes are present on the inner surface of the granum cycle membrane. Each chloroplast contains 40-60 grana.
5. Stroma lamellae: Two adjacent thylakoids are connected by ducts called stroma lamellae or intergranular frets. Stroma lamellae contain chlorophyll.
6. ATP Synthase: The round or oval object in the thylakoid membrane is called ATP synthase. It contains enzymes for making ATP. It makes ATP for cells.
7. Photosynthetic Unit: Photosynthetic units are present on the thylakoids. It is called photosynthetic unit. Each photosynthetic unit contains 300-400 molecules of chlorophyll-a, chlorophyll-b, carotene and xanthophyll. It contains various enzymes, phospholipids, sulfolipids, metal ions, quinones, etc.
8. DNA: Chloroplasts contain short and circular DNA. DNA has its own characteristics. This is called chloroplastic DNA. Each chloroplast contains 200 cpDNA. Without cpDNA, photosynthesis cannot occur in chloroplasts.
9. Ribosomes: Chloroplasts contain 70S ribosomes. It synthesizes proteins.
10. Unidentified granules: Chloroplasts contain some unidentified granules.

In lower plants, old chloroplasts divide to form new chloroplasts. They originate from primitive plastids in higher plants. In the presence of sunlight, the original plastid transforms into a mature chloroplast. In the absence of sunlight, chloroplasts transform into leucoplasts.

Each cell contains one or more chloroplasts. Its number is 10-40 in higher plant cells. Spirogyra has 1-16 chloroplasts and Chara has hundreds of chloroplasts. Each cell of Mnium has 106 and Ricinus communis plant has 400,000 chloroplasts per square millimeter.

Green leaves, young green stems, unripe fruits, green shoots etc. contain chloroplasts in palisade cells. C3 plants have granulated chloroplasts. C4 plants have granulated and non-granulated chloroplasts.

The word Chloroplast is derived from the Greek word chloros meaning green. Chloroplast means green cell. Chloroplasts are the largest green colored organelles in the cytoplasm that produce sugary food in the process of photosynthesis. It is green in color because it contains more green pigment called chlorophyll. It is called the cell’s kitchen, carbohydrate food factory and energy conversion organ. A.F.W Schimper first observed it in plant cells in 1883 and named it chloroplast. Julius von Sachs (1832-1897), the father of plant physiology, discovered chloroplasts.

1. Leucoplasts store food like carbohydrates, proteins and lipids.
2. Chloroplasts produce carbohydrates.
3. Chloroplasts store carbohydrates.
4. Chromoplasts attract insects for pollination.
5. Chromoplasts attract animals for fruit and seed dispersal.
6. Chromoplasts have high food value.
7. Different types of chromoplasts are recreational materials in animals including humans.
8. Different types of colorful flowers are used in house decoration.
9. Flowers are widely used in all national festivals.
10. Flowers of different colors are used as religious or worship materials.

The varied colors of flower petals depend on pigments such as anthocyanins and betacyanins. Anthocyanins are a group of several complex compounds. It is incorporated into the cells as a glycoside. The color of the flower changes when the pH of the soil changes. If the pH of the soil is acidic, the color of the flower is red, if the pH is alkaline, the color of the flower is blue, and if the pH is neutral, the color of the flower is purple or dark blue.

Plastids are formed from important chemical compounds used in cells. Protocells and plastids have evolutionary similarities in origin. They both have double-stranded circular DNA. Plastids are thought to have originated from some endomitotic cyanobacteria. About 1.5 million years ago such mitosis evolved and made true cells photosynthetic.

Plastids are divided into three types based on the pigment content. These are-

1. Leucoplast : 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.

2. Chloroplast: Greek word Chloros means green. Green colored plastids are called chloroplasts.
3. Chromoplast : 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.