What Is Chloroplast And Its Function? CBSE Class 11 Biology Notes

Plant cells are known as the fundamental building blocks of all plants. Both plants and animals have eukaryotic cells, which means they have a membrane-bound nucleus and cell organelles. Despite both being eukaryotic cells, there are several differences between them, and one such difference is plastids, which are not seen in animal cells. These plastids are double-membraned cell organelles that play an important role in producing and storing food in plants. Plastids are classified into three types:

• Chromoplasts are color plastids found in all flowers and fruits, primarily responsible for various colors.

• Chloroplasts are green-colored plastids containing green-colored pigments called chlorophyll within the plant cell.

• Leucoplasts are colorless plastids primarily employed to store carbohydrates, lipids, and proteins inside the plant cell.

This article will educate students on chloroplasts and their functions, which are vital for the CBSE Class 11 Biology Examination. Students must thoroughly prepare for this topic using the NCERT Solutions for Class 11 Biology and smart preparation strategies!

CBSE Class 11 Biology: Chloroplast

The term chloroplast came from the Greek words “khloros” (green) and “plates” (formed). These are the organelles present in plants that execute mainly the process of photosynthesis.

“A chloroplast is an organelle in green plants and algae containing the photosynthetic pigment, known as chlorophyll, which absorbs sunlight and transforms it into usable energy, releasing oxygen from water.”

Chloroplasts are circular, oval, or disk-shaped structures in plants that aid in producing and storing food and energy. Their primary function is to absorb and convert sunlight into useable energy. They can be found in green leaves and stems, but they are most abundant in the parenchyma cells of the leaf mesophyll. They feature a biconvex lens-like structure and are surrounded by a two-layered envelope. They are composed of smaller sections called thylakoids, grouped in stock-like formations known as grana. In the chloroplast matrix, there are 40-80 grana. Refer to NCERT Solutions for Class 11 Biology for further information on the topic.

CBSE Class 11 Biology: Functions of Chloroplast

Chloroplasts perform photosynthesis. The primary function of chloroplast is to provide a venue for light-dependent and light-independent reactions. Inorganic substances (carbon dioxide), water, and solar energy are transformed into food, i.e. glucose or carbohydrates (a sugar molecule). As a result, these cell organelles are essential for photosynthetic plants and algae to produce their food and not rely on other organisms for survival. 

Because oxygen is a byproduct of photosynthesis, chloroplasts are an important site for creating this gas, which is then discharged from the cell into the environment. Oxygen is biologically significant due to its function in various physiological and biochemical processes in animals and other complex species. Students must check the NCERT Solutions for Class 11 Biology for better clarity of concepts.

• The process of photosynthesis occurs in chloroplasts present in the leaves of the green plants and algae. Chloroplast performs various light-dependent and light-independent reactions that capture solar energy and convert it to chemical energy.
• Chloroplast components are involved in a variety of cell regulatory processes and photorespiration.
• Chloroplasts also support plant cells’ metabolic processes, such as creating fatty acids, isoprenoids, membrane lipids, starch, tetrapyrroles, and hormones.
• The chloroplasts are the primary organelles involved in pathogen defence, with the nucleus, cell membrane, and ER (endoplasmic reticulum).
• Chloroplasts have the potential to function as cellular sensors.

CBSE Class 11 Biology: Structure of Chloroplast

The chloroplast structure is enclosed by two 9-10 mm thick unit membranes. These membranes are separated by a space known as the periplast ideal space. Structurally, a chloroplast is split into two different parts, the grana, and stroma. 

Grana are made up of thylakoids, which are disc-shaped structures. The chloroplast’s grana comprise chlorophyll pigments and serve as the receptors for sunlight responses. 

The stroma, also known as the matrix, is a homogeneous matrix containing grana and is similar to the cytoplasm of cells in which all cell organelles are embedded. Stroma also contains enzymes, DNA, RNA, ribosomes, and other materials. Stroma lamellae aid in the connection of thylakoid sac stacks. Use NCERT Solutions for Class 11 Biology.

The chloroplast structure is made up of the following components:

Outer membrane: It is a semi-porous membrane permeable to tiny molecules and ions and allows for easy diffusion. Larger protein complexes cannot pass through the outer membrane.

Intermembrane Space: This is a narrow intermembrane space between the chloroplast’s outer and inner membranes, usually 10-20 nanometers wide.

Inner membrane: The chloroplast’s inner membrane forms a barrier to the stroma. It controls the flow of materials to and from the chloroplast. In addition to regulatory action, the inner chloroplast membrane synthesises fatty acids, lipids, and carotenoids.

Stroma: This protein-rich alkaline aqueous fluid is found within the inner chloroplast membrane. The stroma is the space outside of the thylakoid membrane. The stroma contains chloroplast DNA, starch granules, chloroplast ribosomes, the thylakoid system, and numerous proteins.

Thylakoid System: The stroma contains the thylakoid system. The system is made up of membranous sacs known as thylakoids. The chlorophyll is present in the thylakoids and serves as the site for the absorption of sunlight for the process of photosynthesis to occur. The thylakoids are grouped in grana, which are stacks of thylakoids. Each granum comprises between 10 and 20 thylakoids.

Conclusion

Chloroplast is one of the plant cell organelles containing chlorophyll (the substance that gives plants their green colour) and is responsible for photosynthesis, allowing plants to turn sunlight into energy. Thus, without chloroplasts, plants won’t be able to produce energy and food, and without these green plants, humans would go hungry and vanish. Hence one can rightly say that chloroplast is essential for the survival of, growth and development of both plants and animals. Students must have a good grasp of the topic. Students must analyse the NCERT Solutions for Class 11 Biology AESL. They must strategically plan their CBSE Class 11 Biology syllabus to pass the Biology subject with flying colours!

FAQs

1. What happens to plants that lack chloroplasts?

Chloroplasts are necessary for both photosynthetic plants and algae. It supports the healthy growth and development of all green plants. Chloroplasts act as solar panels for green plants. They absorb light energy and transform it into energy that may be used to perform various functions inside the plant cells. So, what happens to plants that lack chlorophyll?

One such example is Rafflesia, a parasitic plant that takes nutrition from other plants, an example of such a type of plant is Tetrastigma vines. Rafflesia does not require its chloroplast because it obtains almost all energy from parasitising the other plant. Such plants have become so accustomed to this technique that they have lost the genes that code for chloroplast formation. It is the only plant species on land that does not have chloroplasts.

2. Describe the structure of chloroplasts in plants and algae.

Students can understand the structure of chloroplasts in plants and algae with the help of the following points.

• The chloroplast organelles found in plants are commonly in biconvex or plano convex shape.
• Chloroplasts in grown plants have an average diameter of 4-6 µm and a thickness of 1-3 µm.
• Chloroplasts are present in the mesophyll cells of plant leaves.
• The shape of chloroplast organelles varies significantly depending on the plants, from spherical to elongated saucer-shaped, discoid to ovoid.
• These organelles have a colourless core and are vesicular.
• Some chloroplasts have the structure of a club, with a thin centre zone and chlorophyll-filled tips.
• A single massive chloroplast can be structured like a web, a spiral band, or a stellate plate in algae.
• The size and structure of the chloroplast depend on the species and are stable within a cell type.

3. Describe the location of chloroplast in green plants and algae.

Chloroplasts are the cell organelles found in the cells of green plant leaves and stems and the cells of eukaryotic algae. All green plants have a plastid, unlike animal cells, a type of cell organelle, and chloroplasts are one such type of plastid. Sunlight penetrates the chlorophyll in these chloroplasts, resulting in the utilisation of light energy in useful chemical form. And it is through this process that sunlight enters the living ecosystem.

As students know, the chloroplast is surrounded by membranes. There are three membranes in chloroplasts. The outermost membrane is semipermeable and allows tiny molecules to pass through. The inner membrane is a somewhat less permeable layer, and the final membrane is known as the thylakoid membrane, which looks like a collection of flattened discs heaped on top of each other. Chlorophyll is located in the innermost thylakoid membrane.

4. Explain the process of the Calvin cycle.

The Calvin cycle is a metabolic mechanism by which plants convert carbon dioxide to produce carbohydrates or glucose. The process takes place in the absence of sunlight in the stroma of the chloroplast, which consists of the enzyme ribulose-1, 5-bisphosphate carboxylase oxygenase (rubisco).

Rubisco catalyses the first phase of carbon fixation in the Calvin cycle, the principal mechanism of carbon transport in plants, resulting in the formation of six-carbon intermediary molecules.

Then, six-carbon molecules are divided into three-carbon compounds in the following stage, transformed into glyceraldehyde-3-phosphate, or G3P. The Calvin cycle needs to be repeated three times to produce one molecule of G3P.

Following this, one G3P molecule remains in the Calvin cycle and travels to the cytoplasm to produce carbohydrates.

A total of 6 ATP and 6 NADPH are required in the reduction stage. In the regeneration stage, 3 ATP molecules are necessary. So to create one molecule of glucose, it takes six cycles, 18 ATP and 12 NADPH.

5. How does chloroplast perform the process of photosynthesis?

Carbohydrates or glucose are formed by the carbon diffusion process, which involves the combination of carbon dioxide, water, external energy, sunlight, chlorophyll, and the participation of oxygen. The following chemical reaction can explain photosynthesis.

The process of photosynthesis:

In equation form: 6CO2 + 6H2O + Light Energy = C6H12O6 + 6O2 +6H2O

In word form: (Carbon Dioxide) + (Water) + (Sunlight) = (Glucose) + (Oxygen) + (Water)

In the first stage, the chloroplast absorbs sunlight through chlorophyll and carotenoids to generate adenosine triphosphate (ATP), which fuels the cell’s energy, as well as nicotinamide adenine dinucleotide phosphate (NADPH), which takes charged electrons, in the reaction above (photosynthesis process). 

It is followed by the second stage, which consists of light-independent processes, commonly referred to as the Calvin cycle. NADPH takes the electrons in the Calvin cycle to transform carbon dioxide absorbed from air into organic matter in the form of glucose or carbohydrates. It is known as CO2 fixation. The residual carbohydrates or glucose and other organic molecules that are not consumed are stored and used later by the plant’s various systems.