Chloroplasts: Diagram, Structure and Functions
Last Updated :
28 Mar, 2024
The structure and function of chloroplast are adapted for photosynthesis. Chloroplast is an eukaryotic organelle found in plant cells and some algal cells which forms the site for photosynthesis. Chloroplasts contain the pigment chlorophyll, which captures light energy and uses it to synthesize organic compounds, including sugars, from carbon dioxide and water.
Chloroplasts give plants their green colour and are essential for their growth and survival. In this article, we will cover the structure and function of chloroplast, along with their diagram.
Chloroplast Definition
Chloroplast is an organelle that consists of the photosynthetic pigment chlorophyll which absorbs sunlight and transforms it into usable energy, then, releases oxygen from water.
What is Chloroplast?
The chloroplast word originated from the Greek word “chloros”, meaning “green” and “plast”, meaning “form” or “entity”. All green plants and algae have chloroplasts inside their cells. They are the food producers of plants. They consist of a high concentration of chlorophyll that traps sunlight.
In higher plants, almost all chloroplasts are uniformly round, oval, flattened, or elliptical. Their length can be 2-5 µ or up to 100 µ while the width remains 3-4 µ. According to the personnel, their number should be up to 20-40 cans. Usually, their presence is close to the nucleus or cell wall. Chloroplast has its own extra-nuclear DNA and therefore is semiautonomous, like mitochondria. They also produce the lipids and proteins needed to make the chloroplast membrane.
Location of Chloroplast - Where are Chloroplast Found?
Chloroplasts are found in mesophyll cells, which are the green tissue of leaves. They are also present in other green parts of the plant, for example stems and unripe fruits. The chloroplasts in these cells are responsible for conducting photosynthesis. It is not found in animal cells; they are a unique feature of plant cells and some types of algae.
Also Read: Reason Why are Plants Green
Chloroplast Diagram with Label
This diagram of chloroplast shows the inner and outer membrane, intermembrane space, thylakoid membrane, stroma, and lamellae. The labeled diagram of chloroplast picture is given below:
Structure of Chloroplast
The structure of the chloroplast is explained as follows:
Double Membrane Envelope
The chloroplast is enclosed by a double membrane envelope. The outer membrane act as a barrier between the chloroplast and the cell. The inner membrane regulates the passage of molecules in and out of the chloroplast. The space between them is referred to as periplastidial space (intermembrane space). A matrix is present inside these membranes. Carbohydrates are formed in this part, that is, the dark reaction of photosynthesis occurs.
Thylakoid Membranes (Lamellae)
The system is suspended in the stroma. There are large number of flattened, sac-like structures called thylakoids. These contain pigments, like chlorophyll, which capture sunlight energy during the light-dependent reactions of photosynthesis. The thylakoids are arranged in stacks referred to as grana and each granum consists of approximately 10-20 thylakoids.
Grana
Thylakoid membranes are structured into stacks called grana. It increase the surface area for light absorption and have the component necessary for the light-dependent reactions. The number of grana in a chloroplast can be up to 40-60. The particles present in it are referred to as quantasome. Each quantasome is made up of 200 green molecules. The width of the grana lamellae found in the grana is less than that of the stroma lamellae.
Stroma
The stroma is an aqueous, protein-rich, colorless fluid that enclose the thylakoids. It contains enzymes and substances necessary for the light-independent reactions of photosynthesis. Stroma also consists of various enzymes, DNA, ribosomes, and other substances. Stroma lamellae function by connecting the stacks of thylakoid sacs or grana.
Chlorophyll
Chlorophyll molecules are present in the thylakoid membranes. They are responsible for capturing light energy and come in different types (chlorophyll a and chlorophyll b) which is essential for photosynthesis.
DNA and Ribosomes
Chloroplasts contains its own DNA and ribosomes. It encodes proteins required for chloroplast function. The ribosomes present are involved in chloroplast protein synthesis.
Lipid and Starch Granules
Chloroplasts store lipids and starch granules. Lipids act as an energy reserve, and starch is a storage form of glucose that is produced during photosynthesis.
Envelope Pores
Protein channels present in the outer membrane, known as envelope pores, regulate the passage of molecules, such as ions and metabolites, into and out of the chloroplast.
Functions of Chloroplast (Role of Chloroplast in Plant Cells)
Some important functions of the chloroplast are mentioned below:
- Chloroplasts are the primary sites of photosynthesis in plant cells. They capture light energy and use it to convert carbon dioxide and water into glucose and oxygen.
- Chlorophyll pigments within chloroplasts absorb light energy, which is essential for the photosynthesis process.
- During photosynthesis, chloroplasts synthesize glucose and other organic compounds, which serve as an energy source for the plant and can be stored as starch.
- Oxygen is released as a byproduct of photosynthesis, which is vital for the respiration of both plants and animals.
- Chloroplasts can store energy in the form of lipids and starch granules, which can be used when needed by the plant.
Structure and Function of Chloroplast
The table given below shows the structure and function of each part of chloroplast:
| Structure | Function |
|---|
| Double Membrane Envelope | Acts as a barrier, regulating molecule passage. |
| Thylakoid Membranes | Contain pigments for capturing light energy during photosynthesis. |
| Grana | Stacks of thylakoids optimize light absorption efficiency. |
| Stroma | Protein-rich fluid housing enzymes for photosynthesis reactions. |
| Chlorophyll | Pigment responsible for capturing light energy for photosynthesis. |
| DNA and Ribosomes | Synthesize proteins required for chloroplast function. |
| Lipid and Starch Granules | Store energy reserves in the form of lipids and starch, respectively. |
| Envelope Pores | Regulate the passage of molecules, such as ions and metabolites, in and out of the chloroplast. |
Chlorophyll in Chloroplast
Chloroplasts and chlorophyll are present within plant cells and carry out photosynthesis. Chloroplasts, organelles enclosed by a double membrane, is the sites for photosynthesis.
The name chlorophyll originated from two Greek terms: Chloros which means “green” and phyllon which means “leaf”. It was first isolated in 1817 by the French chemist Joseph Bienname Caventeau and his co-workers. Chlorophyll is a pigment responsible for giving plants their green color, it helps plants make their own food through photosynthesis.
Chemical Formula of Chlorophyll
Chlorophyll contains proteins 50%, chlorophyll 3-10%, RNA-5%, DNA 0.02-0.01%, phospholipids 23%, carotenoids 1-2%, and various metals, such as Fe, Zn. mg. Cu and Mg etc. Each molecule of chlorohyll has a hydrophilic head that is made up of pyrole and a hydrophobic tail attached to a phytol chain.
There are many types of chlorophyll:
- Chlorophyll a: Its formula is C55H72O5N4Mg. It consists of the CH2 group. It is found approximately 75%.
- Chlorophyll b: Its formula is C55H70MgN4O6.In this, the CHO group is found in place of CH3. It gets up to about 25%.
- Chlorophyll c: It is found in place of Chlorophyll b in Bacillariophyceae and Phaeophyceae.
- Chlorophyll d: It is found in place of Chlorophyll b in Rhodophyceae.
- Chlorophyll e: It is found in Xanthophyceae in place of Chlorophyll b.
Also Read: Difference Between Chlorophyll A and Chlorophyll B
Conclusion - Chloroplasts
In conclusion, chloroplasts play a crucial role in the life of plants. They serve as the primary sites for photosynthesis. Chloroplasts contain the pigment chlorophyll, which captures light energy and converts it into organic compounds essential for plant growth. Through this process, chloroplasts produce oxygen, store energy, and contribute to the green coloration of plants. Understanding the structure and function of chloroplasts is fundamental to learning the vital role they play in sustaining life on Earth.
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