Chloroplast: What does the term “chloro” mean? Is it the same as chlorophyll? Chloro is a term that represents the colour – green. Green-coloured plastids are called chloroplast. Chloroplasts perform an important role in the process of photosynthesis. It converts light energy from the sun into chemical energy for the plant.‌ Chloroplasts perform an important role in the process of photosynthesis. It converts light energy from the sun into chemical energy for the plant.

Chloroplasts also offer several metabolic activities for plant cells. It includes the synthesis of fatty acids, tetrapyrroles, membrane lipids, starch, and hormones. The chloroplasts are significant in nature as it acts as the cooking place for all the plants. In this article, we will provide you with all the information about Chloroplasts, their definition, functions, and more. Continue reading to find out more!

Chloroplasts: Overview

Plants are living things that produce their own food through the process called photosynthesis. These plants are also called autotrophs and producers. These plants have pigmented or non-pigmented double-membrane cytoplasmic bodies in plant cells associated with preparation or the storage of food material are called plastids.
Plastids are present in the cytoplasm of most plant cells. Plastids are of three types: Chloroplasts, Chromoplasts and Leucoplasts.

1. Chloroplasts: It is a plant organelle that contains the photosynthetic pigment called chlorophyll. It captures sunlight and converts it into useful energy, thereby, releasing oxygen from water.
2. Chromoplast: The plastids having a colour other than green are called chromoplasts which attract insects for pollination and impart various colours to various plant organs like petals, fruits, etc.
3. Leucoplast: The colourless plastids are called leucoplast. Leucoplast can be converted to chloroplast on exposure to sunlight and reconverted to leucoplast when kept in dark for a long time.

Chloroplast Definition

Chloroplast is a plant organelle that contains the photosynthetic pigment called chlorophyll that captures sunlight and converts it into useful energy, thereby, releasing oxygen from water. One of the most important functions of the Chloroplast is to absorb light energy for photosynthesis. Chloroplasts consist of Stroma, inner membrane, outer membrane, thylakoid membrane, and intermembrane space.

Chloroplast Analogy

An analogy for chloroplasts is that chloroplasts are like a kitchen of the cell. It is also known as the chef of the restaurant.

Chloroplast Diagram

The chloroplast, found only in algal and plant cells, is a cell organelle that produces energy through the process called photosynthesis. The word chloroplast comes from the Greek words ‘khloros’, meaning “green”, and ‘plastes’, meaning “formed”.
The diagram of Chloroplast is given below.

Fig: A Labeled Diagram of Chloroplast

Chloroplast Structure

Chloroplasts are roughly \(1 – 2\, {\rm{μm}}\) thick and \(5 – 7\, {\rm{μm}}\) in diameter and are seen in all higher plants. In different plants, chloroplasts have different shapes like some plants have filamentous or ovoid or saucer-shaped.

Fig: A pictorial representation of Chloroplast structure

A chloroplast comprises the following components:

Membrane Envelope

Like mitochondria, the entire chloroplast is bounded by an envelope which is made of a double layer membrane with outer and inner layers, between which is a gap called the intermembrane space. Across this double-membrane envelope, the exchange of molecules between chloroplast and cytosol takes place.

Stroma

The matrix or stroma fills most of the volume of the chloroplast and is a kind of gel-fluid phase that surrounds the thylakoids (grana). It contains DNA, proteins, and ribosomes. The stroma is the site of carbon dioxide fixation and where the synthesis of sugar, starch, fatty acids, and some proteins occurs. While the inner membranes of mitochondria have many folds called cristae to increase the surface area, the inner membranes of chloroplasts are smooth. Instead, chloroplasts have many small disc-shaped sacs called thylakoids within their stroma.

Fig: Stroma

Thylakoids

The thylakoids consist of flattened and closed vesicles arranged as a membrane network. Thylakoids may be stacked like a neat pile of coins forming grana. There may be \(40\) to \(60\) grana in the matrix of a chloroplast.

Fig: A image representing the pile of coins forming grana in thylakoids of chloroplast

Chlorophyll

Chlorophyll is responsible for the colour of the leaf, i.e., it is a green photosynthetic pigment that helps in the process of photosynthesis in plants.

Functions of Chloroplast

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. Some of the functions are given below:

1. Chloroplasts are photosynthesis sites, which comprise a set of light-dependent and light-independent reactions to harness solar energy and convert it into chemical energy.
2. The light reaction takes place in thylakoids. It is also known as Hill reaction or photochemical reaction or photosynthetic electron transfer reaction.
3. In light reactions, solar energy is trapped in the form of the chemical energy of ATP and NADPH.
4. During the light reaction process, oxygen is evolved by photolysis.
5. The dark reaction takes place in the stroma. It is also known as Calvin reaction, carbon fixation reaction or thermochemical reaction, or photosynthetic carbon reduction cycle.
6. The reducing capacity of NADPH and energy of ATP is utilized for the conservation of carbon dioxide to carbohydrates in dark reactions.
7. Chloroplasts, like the mitochondria, use the potential energy of the \({\text{H}}^ {\text{ + }}\) ions or the hydrogen ion gradient to generate energy in the form of ATP.
8. The components of chloroplast also participate in several regulatory functions of the cell as well as in photorespiration.
9. Production of ATP by photophosphorylation. NADPH₂ and ATP are the assimilatory powers of photosynthesis. Transfer of \( {\text{C}} { {\text{O}}_ {\text{2}}}\) obtained from the air to \(5\) carbon sugar in the stream during the dark reaction.
10. The chloroplasts with the nucleus and cell membrane and ER are the key organelles of pathogen defence.
11. Chloroplasts also provide diverse metabolic activities for plant cells, including the synthesis of fatty acids, tetrapyrroles, starch, membrane lipids, and hormones.
12. The chloroplast is very important as it is the cooking place for all the green plants. All heterotrophs also depend on plants for this food.

Fig: A Pictorial Representation of a Photosynthesis Reaction in Chloroplast

Summary

Chloroplasts are the site of photosynthesis in Eukaryotic Cells like plants and algae. There are no chloroplasts in animal or bacterial cells as they do not produce their own food using sunlight. Through this article, we got to know how green pigments called chlorophyll present in the chloroplast helps in imparting the green colour to plants. Plants also have life and they produce food for animals and human beings. We also learned that Chloroplasts performs several metabolic activities for plant cells, like tetrapyrroles, the synthesis of fatty acids, starch, membrane lipids, and hormones.

FAQs on Chloroplast

Q.1. What do chloroplasts contain?
Ans: Chloroplasts contain a pigment called chlorophyll, thylakoids, stroma, chloroplast DNA, etc.

Q.2. Why are chloroplasts found in plant cells?
Ans: Chloroplasts are found only in plant cells because chloroplasts contain chlorophyll which is essential for photosynthesis which is absent in animals.

Q.3. What are the two main functions of chloroplasts?
Ans: The two main functions of chloroplasts are:
i) It helps in the process called photosynthesis by capturing the sunlight.
ii) Production of ATP by photophosphorylation.

Q.4. How many Chloroplasts can a cell have?
Ans: The number of chloroplasts may differ from one cell to another. Usually, a cell from a leaf may contain around \(20\) to \(100\) chloroplasts.

Q.5. What are thylakoids?
Ans: The thylakoids consist of flattened and closed vesicles arranged as a membrane network. Thylakoids may be stacked like a neat pile of coins forming grana.

Q.6. Why are chloroplasts green in colour?
Ans: The chloroplast is green in colour because of the photosynthetic green pigment called chlorophyll.

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