What is Chloroplast
Chloroplast is an organelle that contains the photosynthetic pigment chlorophyll that captures sunlight and converts it into useful energy, thereby, releasing oxygen from water.
Chloroplasts are found in all green plants and algae. They are the food producers of plants. These are found in mesophyll cells located in the leaves of the plants.
They contain a high concentration of chlorophyll that traps sunlight. This cell organelle is not present in animal cells.
Chloroplast has its own extra-nuclear DNA and therefore are semiautonomous, like mitochondria. They also produce proteins and lipids required for the production of chloroplast membrane.
Function of Chloroplast
Following are the important chloroplast functions:
The most important function of the chloroplast is to synthesise food by the process of photosynthesis.
Absorbs light energy and converts it into chemical energy.
Chloroplast has a structure called chlorophyll which functions by trapping the solar energy and is used for the synthesis of food in all green plants.
Produces NADPH and molecular oxygen (O2) by photolysis of water.
Produces ATP – Adenosine triphosphate by the process of photosynthesis.
The carbon dioxide (CO2) obtained from the air is used to generate carbon and sugar during the Calvin Cycle or dark reaction of photosynthesis.
Structure of Chloroplast
Chloroplasts are found in all higher plants. It is oval or biconvex, found within the mesophyll of the plant cell. The size of the chloroplast usually varies between 4-6 µm in diameter and 1-3 µm in thickness. They are double-membrane organelle with the presence of outer, inner and intermembrane space.
There are two distinct regions present inside a chloroplast known as the grana and stroma.
Grana are made up of stacks of disc-shaped structures known as thylakoids or lamellae. The grana of the chloroplast consists of chlorophyll pigments and are the functional units of chloroplasts.
Stroma is the homogenous matrix which contains grana and is similar to the cytoplasm in cells in which all the organelles are embedded. Stroma also contains various enzymes, DNA, ribosomes, and other substances. Stroma lamellae function by connecting the stacks of thylakoid sacs or grana.
Membrane Envelope
It comprises inner and outer lipid bilayer membranes. The inner membrane separates the stroma from the intermembrane space.
Intermembrane Space
The space between inner and outer membranes.
Thylakoid System (Lamellae)
The system is suspended in the stroma. It is a collection of membranous sacs called thylakoids or lamellae. The green coloured pigments called chlorophyll are found in the thylakoid membranes. It is the sight for the process of light-dependent reactions of the photosynthesis process. The thylakoids are arranged in stacks known as grana and each granum contains around 10-20 thylakoids.
Stroma
It is a colourless, alkaline, aqueous, protein-rich fluid present within the inner membrane of the chloroplast present surrounding the grana.
Grana
Stack of lamellae in plastids is known as grana. These are the sites of conversion of light energy into chemical energy.
Chlorophyll
It is a green photosynthetic pigment that helps in the process of photosynthesis.
Plastid
Plastids are double membrane-bound organelle that helps in photosynthesis. They have some specific pigments thus giving specific color to the plants. Due to these pigments plastids are divided into three types chloroplasts, chromoplasts, and leucoplasts.
Chloroplasts are green-colored plastids that contain the pigment chlorophyll. The function of chloroplast is to help in photosynthesis. This type of plastid is present in photosynthetic parts of the plant such as the leaf.
Leucoplast is a colorless plastid. They are found in non-photosynthetic parts of the plant. For example roots, stems, and bulbs. They help store food such as starch, proteins, and fats.
Chromoplast has fat-soluble carotenoid pigments like carotene, xanthophylls, and others. The function of chromoplast is to give color to the plant parts. They are present in flowers, fruits, etc.