Overview of Plant Cells

This article helps you to understand the concept of plant cells and clearing your many doubts. It is the most important topic of biology and many competitive exams like- SSC, Banking and PGT, and TGT ask questions from the same. Here we are discussing plant cell, Plant cell walls, their types, etc.

Plant Cell :

Plant cells are eukaryotic cells that are present in green plants. Photosynthetic eukaryotes belong to the kingdom Plantae and that means they have a membrane-bound nucleus. Both plant and animal cells consist of a true nucleus along with similar organelles to maintain the normal functioning of the cell. The existence of a cell wall outside of the cell membrane is one of the distinguishing characteristics of a plant cell.

Plant Cell

Plant Cell Figure : 

The plant cell is rectangular and usually larger than the animal cell. Despite the fact that both plant and animal cells are eukaryotic and share several cell organelles, plant cells are very different from animal cells in that they serve diverse purposes. When the cells are analyzed using an electron microscope, some of these variations may be clearly understood.

Plant Cell Structure : 

All cells are mostly made of the same materials and perform comparable biological functions despite varying sizes and complexity. These include a cellular division for reproduction as well as growth and metabolism. Subcellular structures that makeup cells are in charge of a variety of specialized functions. They are referred to as organelles. These organelles are found in both plant and animal cells in various numbers. The focus of this section will be on the parts that plants have. Similar to the many organs in the body, plant cells are made up of a variety of parts called cell organelles that serve varied purposes to keep the cell alive. These organelles consist of :

1. Cell Wall

The cell wall is a hard layer present on the outside of the plant cell which gives it strength and also maintains high stability. It is a tough layer that is made up of polysaccharides cellulose, pectin, and hemicellulose. It is situated upper side of the plasma membrane. The cell wall is mainly composed of cellulose, glycoproteins, and polymers along with other molecules such as hemicellulose, pectin, and lignins. cutin, or suberin.

The primary functions of the cell wall are to support and cover the cell. Additionally, the plant cell wall aids in giving the cell its shape and structure and protects it from mechanical stress. It also screens molecules as they enter and leave the system.

The formation of the cell wall is controlled by microtubules. Three layers make up this structure: the main, secondary, and middle lamellae. Enzymes lay down cellulose to create the main cell wall.

2. Cell membrane :

A cell membrane is a semi-permeable membrane that is found within the cell wall. This is a protective layer that is enclosed in each cell and differentiates it from its outside environment. The cell membrane is made up of a thin layer of protein and complex lipids (fats). The cell membrane is crucial in controlling how certain molecules enter and leave the cell. For instance, the cell membrane transports nutrition and vital minerals while preventing the entry of contaminants.

3. Nucleus :

The nucleus is a membrane-bound structure that is found only in eukaryotic cells. The nucleus is the ‘control centre’ of the cell and one of the most important functions of a nucleus is to store DNA or genetic material needed for cell division, metabolism, and growth. Prokaryotic cells lack nuclei (plural for nucleus), which are only present in eukaryotic cells. The Nuclear membrane is a specialized membrane that separates the cytoplasm from the nucleus.

4. Plastids :

They are membrane-bound organelles that have their own DNA. They are necessary to store starch and to carry out the process of photosynthesis in chloroplasts. Plastids provide essential metabolic and signaling functions. It is also used in the synthesis of many molecules, which form the building blocks of the cell. There are three types of plastids, which are chloroplast, chromoplast, and leucoplast.

• Leucoplasts – Leucoplasts are part of the plastids and these plastids are colorless or non-pigmented plastids. They lack photosynthetic pigments as opposed to chloroplasts consisting of chlorophyll (green pigment) and chromoplasts consisting of other photosynthetic pigments. Leucoplasts are often present in plant tissues that are not photosynthetic, such as seeds and roots. Leucoplast’s primary purpose is to store vital substances like protein, lipids, and carbohydrates.

• Chloroplasts – Chloroplasts are specific organelles present only in plants and some forms of algae. It is a prolonged organelle surrounded by a phospholipid membrane. The chloroplast is a disc-shaped structure that is enclosed by a double membrane. The outer membrane forms the outside surface of the chloroplast and is comparatively permeable to tiny molecules, giving permission for substances to enter the organelle. Just below the outer membrane, the inner membrane is less permeable to outside substances.
  There is a little intermembrane space, 10–20 nanometers in diameter, located between the outer and inner membranes. The stroma, a fluid matrix, is located in the core of the chloroplast and is enclosed by the double membrane. The fluid that contains circular DNA in the chloroplast is called the stroma. Chlorophyll, a pigment with a greenish color needed for photosynthesis, is found in every chloroplast. The sun’s light energy is captured by chlorophyll, which then uses it to convert water and carbon dioxide into glucose.

• Chromoplasts – They are a type of colored, heterogeneous plastid that produces and stores pigment in photosynthetic eukaryotic organisms. Red, orange, and yellow pigments found in chromoplasts give all ripe fruits and flowers their color. Some angiosperms use the chromoplast-based coloration of their petals as a pollinator-attraction tactic. According to scientists studying evolution, the main function of chromoplasts is to attract insects and other animals so that seeds can be dispersed.
  

5. Central Vacuole :

Plant cells are special in that they have a large central vacuole. A vacuole is a tiny plasma membrane sphere found inside a cell that can contain liquid, ions, and other substances. Vacuoles are basically just large vesicles. They are present in the cells of a wide range of organisms. In an adult plant cell, it takes up around 30% of the total volume. A membrane called the tonoplast encircles the central vacuoles. The main function of the central vacuole aside from storage is to sustain turgor pressure against the cell wall. The central vacuole contains cell sap. It is a combination of salts, enzymes, and other substances.

6. Golgi Apparatus :

The majority of eukaryotic cells contain the Golgi apparatus, sometimes referred to as the Golgi complex, Golgi body, or just the Golgi. They are responsible for spreading synthesized macromolecules to different cell regions. Proteins and lipids are moved, altered, and packaged into vesicles by the Golgi apparatus and delivered to specific locations.

7. Ribosomes :

Ribosomes are the smallest membrane-bound organelles. They are the sites for protein synthesis, hence, also known as the protein factories of the cell. A ribosome is an intercellular structure created by both RNA and protein. The messenger RNA (mRNA) sequence is read by the ribosome, which then converts the genetic code into a specific string of amino acids that develop into extended chains and fold to create proteins.

8. Mitochondria :

Mitochondria are the double-membraned organelles present in the cytoplasm of all eukaryotic cells and that produced the entire chemical energy necessary to power the cell’s biochemical reactions. The mitochondria produce chemical energy that is stored in a tiny molecule known as adenosine triphosphate (ATP). Because they make energy by dissolving sugar and carbohydrate molecules, they are also known as the “Powerhouse of the Cell.”

9. Lysosome :

Since they contain digestive enzymes in a membrane-enclosed structure, lysosomes are often known as “suicidal bags.” By breaking down stale food, foreign objects, and worn-out organelles inside the cell, they carry out the task of disposing of cellular waste. The vacuoles play the lysosomes’ function in plants.

Types of plant cells

A mature and higher plant develops specialized cells that carry out specific crucial tasks that are necessary for their existence. A small number of plant cells are responsible for transporting nutrients and water, while others are responsible for storing food. Plant cells can produce five different forms of tissue, each with a unique set of capabilities. All three simple plant tissues—parenchyma, collenchyma, and sclerenchyma—contain only one type of cell.

Collenchyma Cells :
They are tough or inflexible cells, which perform the main role in providing support to the plants. A plant’s growth is constrained because primary walls lack a hardening agent.

Sclerenchyma Cells :
Due to the presence of a hardening chemical, these cells are more rigid than collenchyma cells. These cells are typically present in all plant roots and serve mostly to support the plants.

Parenchyma Cells :
In all plants, parenchyma cells perform a crucial role. They are the plant’s live cells, and they play a role in the development of leaves. Additionally, they have a role in the metabolism of cells, food generation, storage of organic materials, and gas exchange. Because they are thinner than other cells, these cells are usually more flexible.

Xylem Cells :
In vascular plants, the transport cells are called xylem cells. They aid in moving minerals and water from the roots of the plant to the leaves and other regions.

Phloem Cells :
Other transport cells in vascular plants are called phloem cells. They move the food that the leaves have prepared to other plant components. 

Plant Cell Functions

• The building blocks of plants are called plant cells. Plant cells’ primary job is to perform photosynthesis.
• In the chloroplasts of the plant cell, photosynthesis takes place. It is the method through which plants prepare food by utilizing water, carbon dioxide, and sunshine. ATP is created throughout the process, which releases energy.
• A small number of plant cells aid in the movement of nutrients and water from the roots and leaves to various sections of the plants.