[Biology Class Notes] on Plant Cell Pdf for Exam

The basic unit of life in all organisms is known as a cell. Like animals and human beings, an infinite number of cells also create plants. The plant cell is surrounded by a cell wall which is responsible for providing shape to the plant cell.

Different cellular activities are associated with cell walls and other organelles. To have a better understanding of the same, let us take a detailed look at the plant cell, its structure, and the functions of different plant cell organelles.

What is Plant Cell?

Plant cells can be defined as the eukaryotic cells with a true nucleus along with specialized structures called organelles that carry out certain specific functions. 

A cell wall surrounds the plant cell and provides a shape to it. The plant cell contains different components inside it, the cell wall, and these components have different functions.

Let us look at each of these components and their functions inside a plant cell in detail:

Components of the Plant Cell 

To understand the different parts of a plant cell, we need to have a look at its diagram as given below:

Plant cell includes different components inside it that are known as cell organelles. These organelles perform different functions that we will discuss in detail. The organelles are: 

1. Cell Well 

Definition: Plant cell wall is a tough layer that is made up of cellulose, glycoproteins, lignin, pectin, and hemicellulose located outside the cell membrane. The cell wall comprises proteins, cellulose, and polysaccharides. 

Function: The primary function of the cell wall is to protect and provide structural support to the cell as well as protect the cell against mechanical stress and to provide form and structure to the cell. The cell wall also filters the molecules passing that screens and lets the molecules in and out of the cell.

Structure: The formation of the cell wall is guided by microtubules which consists of three layers, namely, primary, secondary, and the middle lamella. The primary cell wall is made up of cellulose laid down by enzymes.

  

2. Cell Membrane 

Definition: Cell membrane is a semi-permeable membrane present in the plant cell.

Function:  It is one of the essential organelles as it regulates the entry and exit of different substances within the cell.

Structure: It is made up of a thin layer of protein and fat.

3. Nucleus 

Definition: The nucleus is a membrane-based organelle that is found in eukaryotic cells.

Function: This organelle helps produce ribosomes, protein-manufacturing structures and allows proteins and nucleic acids to pass through. 

Structure: Eukaryotes generally have a single nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei, and a few others including osteoclasts have many.

The nucleus has two parts: 

• The Nucleolus:  It helps in producing the ribosomes and protein manufacturing structures. 

• The Nucleopore:-  The holes that penetrate the membrane of a nucleus are called the nucleopores and these allow proteins and nucleic acids to pass through.  

4. Plastids

Definition: Plastids are double-membrane organelles that are found in the cells of plants and algae. It plays a vital role in photosynthesis. 

Function: These organelles play a crucial role in the manufacturing and storage of food. It also contains pigments that contribute to the process of photosynthesis. 

Structure: The pigments in plastids not only help in photosynthesis but can also change the color of the cell. 

Types of Plastids: 

To understand the different types of plastids, we will have to go into more detail.

Below are some of the important plastids and their Function:

• Leucoplasts: Leucoplasts are organelles in non-photosynthetic tissues of plants that store protein, lipid, and starch. 

• Chloroplasts: Chloroplasts are an elongated organelle enclosed by phospholipid membrane. Chloroplasts are disc-shaped organelles and filled with fluid called stroma that comprises the circular DNA. They also include the green-coloured pigment called chlorophyll, which the plants use in photosynthesis by transforming carbon dioxide and water into glucose.  

Let’s understand the Function of a chloroplast with a diagram below: 

• Chromoplasts: Chromoplasts are diversely coloured plastic. They synthesize the pigments and store essential nutrients in photosynthetic eukaryotic organisms. They have red, orange, and yellow coloured pigments which provide color to all the ripe fruits and flowers we see in our day-to-day lives. 

5. Central Vacuole 

Definition: This is the largest organelle found in plant cells. Surrounded by a membrane, it is there to store materials and wastes. 

Function: It not only stores materials and wastes but also provides proper structure to the plant, which maintains a proper pressure for a growing plant. 

Structure: It takes up to 30% of the cell’s volume in a fully mature plant cell. 

6. Golgi Apparatus 

Definition: Golgi apparatus also known as Golgi Complex. Golgi apparatus is an organelle found in eukaryotic cells and are responsible for distributing synthesized macro-molecules to the different parts of the cell. 

Function: Distributing synthesized macro-molecules to the different parts of the cell. 

Structure: It comprises a series of stacked and flattened pouches called Cisternae. 

Also Known as

7. Ribosomes

Definition: Ribosomes are organelles that are found in all living cells and work as a macro-molecular machine that synthesizes biological proteins. Ribosomes are also called the “Protein Factories of The Cell”.  

Function: A Ribosome is a macro-molecular machine that synthesizes biological proteins. 

Structure: Ribosomes appear flattened and spherical in shape and consist of two major components: the small and large ribosomal subunits.  

8. Mitochondria 

Definition: Often referred to as the “powerhouse of the cell,” mitochondria are the double-membraned organelles that provide energy to the cell by breaking down carbs and sugar molecules. We can find them in the cytoplasm part of all the eukaryotic cells. 

Function: It breaks down carbohydrates and sugar molecules to generate energy. 

Structure: Mitochondria are oval, tubular-shaped, double-membrane organelles. 

9. Lysosomes 

Definition: Lysosomes are membrane-bound cell organelles that contain digestive enzymes and are involved in various cell functions.  

Function: Lysosomes are responsible for functions like recycling old cells, digesting materials both inside and outside of the cell, and releasing enzymes. 

Structure: Lysosomes do not have a particular structure but appear globular or granular in appearance.

Different Types of Plant Cells

Plant cells are a type of eukaryotic cell which are found in organisms of the Plant Kingdom. As an organism grows, its cells become mature enough to perform specific functions. 

There are various types of plant cells namely: parenchyma cells, sclerenchyma cells, collenchyma cells, xylem cells, and phloem cells. Let’s know about the functions of these cells in detail:

• Parenchyma Cells: These are the cells that are majorly present in plants. They help in the metabolism and food production of a plant. These cells are very flexible as compared to other cells because of their thinness.

• Sclerenchyma Cells: Sclerenchyma cells give the maximum support to the plant because of their hardness. These cells are usually found in plant roots and do not live past maturity.

• Collenchyma Cells: These cells are also hard but not as hard as sclerenchyma cells. They also provide support to the plants when they are young. Their growth takes place with the plant’s growth and stretch.

• Xylem Cells: Xylem cells, also known as water conducting cells, are hard cells that bring water up to the leaves. They do not live past maturity but their cell wall continues to allow the water to flow freely through the plant.

• Phloem Cells: A sugar transporting cell produced by the leaves throughout the plant. These cells live past maturity. 

Functions of a Plant Cell 

Photosynthesis is the major function performed by plant cells, and therefore these are known as the building blocks of plants. Photosynthesis is the process that occurs in the chloroplasts of the plant cell. It is the process by which plants prepare their food utilizing sunlight, water, and carbon dioxide.