Chloroplasts: Diagram, Structure and Functions

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.

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.

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.

FAQs on Chloroplast

What is a Chloroplast?

A chloroplast is a membrane-bound organelle known as a plastid that carry out photosynthesis mostly in plant and algal cells.

What is the Function of Chloroplasts?

Chloroplasts capture light energy and use it to convert carbon dioxide and water into glucose and oxygen through photosynthesis. It also produces important compounds such as amino acids, lipids, nucleotides, vitamins, and secondary metabolites.

What are the Components of a Chloroplast?

Chloroplasts have a double-membrane envelope, thylakoid membranes organized into grana, a stroma, chlorophyll pigments, and their own DNA and ribosomes.

Where are Chloroplasts Located in Plant Cells?

Chloroplasts are primarily found in the cells of leaves, especially in the green mesophyll tissue. They are also present in other green parts of the plant.

What is Grana in Chloroplast?

Grana are stacks of thylakoid membranes inside chloroplasts where light-dependent reactions of photosynthesis occur.

Where is Chloroplast Located?

Chloroplasts are located in plant cells, mainly in the mesophyll cells of leaves.

What is the Function of Chlorophyll?

Chlorophyll function to absorb light energy for photosynthesis and convert it into chemical energy.