Contents
Bioinformatics combines Biology Topics with computational methods to analyze large datasets.
What are the structures of the cell membrane?
A cell consists of a jelly-like material enclosed in a thin membrane. The jelly-like material which fills the cell is called ‘cytoplasm’ and the thin, outer covering of the cell is called ‘cell membrane’. A general diagram of an animal cell is shown in Figure. There are many bodies of different shapes and sizes inside the cytoplasm.
For example, there is a large floating body usually in the centre of a cell which is called the nucleus. The function of nucleus is to control all the activities of the cell (like cell growth, cell division, etc.). The nucleus contains a tiny round structure called nucleolus and a fibrous material called chromatin. It also has a nuclear membrane on the outside. Chromatin forms chromosomes during cell division. These chromosomes transfer characteristics from the parents to the next generation.
The cytoplasm and nucleus taken together form the protoplasm of the cell. Protoplasm is the living material of a cell. There are a number of small bodies called ‘mitochondria’ in a cell (The singular of mitochondria is mitochondrion). The function of mitochondria is to carry out respiration for releasing energy from food. Since mitochondria produce energy from food, they are a kind of ‘power-house’ of the cell.
The tiny air spaces in the cytoplasm of an animal cell are called vacuoles. The function of a vacuole in an animal cell is to hold air, water and particles of food. Most of the animal cells do not have vacuoles. But some of the animal cells have several small vacuoles. The cell membrane is a thin sheet of skin all around the cell.
The main function of cell membrane is to control the passage of materials which ‘go into the cell’ or ‘go out from the cell’. The cell membrane also protects the cell and gives shape to the cell. The cytoplasm is a transparent, jelly-like substance. It is a complex solution. The function of cytoplasm is to carry out all the activities of the life processes (or metabolism). We will now describe the structure of a plant cell.
We have just studied that the main parts of an animal cell are: cell membrane, cytoplasm, nucleus and mitochondria. All these parts are also present in plant cells. In addition to these, the plant cells have three more parts in them. These are: cell wall, chloroplasts and large vacuoles. These parts make the plant cells different from animal cells. A general diagram of a plant cell is given in Figure.
A plant cell consists of a jelly-like cytoplasm enclosed in a thin cell membrane. There is a large, floating nucleus in the cytoplasm (see Figure). The nucleus contains nucleolus and chromatin. It is surrounded by a nuclear membrane. Several mitochondria are also present in the plant cell. The mitochondria present in the plant cell carry out respiration and release energy from food. All the plant cells have a thick cell wall all around the cell membrane (see Figure).
This cell wall is made of a material called cellulose. The cell wall protects the plant cell, gives it a fixed shape and makes it rigid (strong). Even the single-celled organisms like bacteria have cell walls around them. The cell wall is not present in animal cells.
The plant cells contain green coloured plastids called chloroplasts. Chloroplasts are the green coloured bodies (or particles) in the cytoplasm of the plant cell. The chloroplasts make food in green plants by the process of photosynthesis. Chloroplasts are not present in animal cells. Some plant cells may contain plastids of different colours (other than green). The plant cells have very large vacuoles. These vacuoles are filled with cell sap. Cell sap is a solution of sugars and mineral salts. The animal cells either do not contain vacuoles or contain several small vacuoles. The animal cells do not contain a large vacuole.
Comparison of Plant Cells and Animal Cells
We have just studied that plant cells and animal cells are similar in many respects but they are also different in some respects. We will now give the important similarities and differences between plant cells and animal cells. The main similarities between plant cells and animal cells are given below :
- Plant cells and animal cells have a cell membrane (or plasma membrane) around them.
- Plant cells and animal cells have cytoplasm.
- Plant cells and animal cells have a nucleus.
- Plant cells and animal cells have a nuclear membrane.
- Plant cells and animal cells have mitochondria.
The main differences between plant cells and animal cells are given below :
| Plant cell | Animal cell |
| 1. A plant cell has a cell wall around it. | 1. An animal cell does not have a cell wall around it. |
| 2. A photosynthetic plant cell has chloroplasts in it. Other plant cells have different plastids in them. | 2. An animal cell does not have chloroplasts or other plastids |
| 3. A plant cell has a large vacuole in it. | 3. An animal cell has usually no vacuole. Only some animal cells have small vacuoles. |
The various parts of a cell are colourless and hence difficult to distinguish. So, in order to see the plant and animal cells with a microscope, they are stained (coloured) with dyes. The dyes stain the various parts of a cell with different colours due to which these parts can be seen more easily under the microscope.
Thus, staining of plant and animal specimens is done to identify the different components of a cell easily through the microscope. Some of the common dyes (or stains) used in the study of structure of cells are dilute iodine solution, methylene blue solution and safranin. Keeping these points in mind, we will now describe how plant and animal cells are studied with the help of a microscope.
To Study Plant and Animal Cells with a Microscope
We can observe the structure of plant and animal cells in the laboratory by using a microscope. Let us study the structure of onion peel cells and human cheek cells.
Activity 1
To Study Onion Peel Cells
Onion is a plant. So, onion peel cells are an example of plant cells. The onion peel cells can be studied as follows : We take an onion, cut it into pieces and separate the thin inner layer of any fleshy layer with our fingers.This thin layer is called onion peel. A small piece of onion peel is placed on a glass slide. Put a drop of water over the onion peel. Add a little of dilute iodine solution to the slide and cover it with a glass cover slip.
When we observe this slide under a microscope, we will see the structure of onion peel cells (as given in Figure). The chamber like structures shown in Figure are the cells of onion peel. We can identify the cell membrane, cell wall, nucleus, cytoplasm and vacuole present in the onion peel cell. The boundary of onion peel cell is the cell membrane. The cell membrane is covered by a thick covering which is the ! cell wall. The dense round body on the periphery (near the edge) of the cell is the nucleus. The jelly like substance between the nucleus and the cell membrane is cytoplasm. And the empty looking space in ; the centre of onion peel cell is the vacuole (see Figure).
Activity 2
To Study Human Cheek Cells
The human beings are animals. So, the human cheek cells are an example of animal cells. We can study the structure of human cheek cells as follows: We open our mouth and scrape the inner surface of our cheek lightly with a tooth-pick. This scraping is mixed in a drop of water placed on a glass slide. Add a little of methylene blue solution to the slide and cover it with a glass cover slip. If we observe this prepared slide under a microscope, we will see the structure of human cheek cells as shown in Figure 9. We can identify the cell membrane, nucleus and cytoplasm in the human cheek cells. There is no cell wall seen in the human cheek cells (see Figure).
Please note that the cells of plants and animals are extremely small in size due to which we cannot see them with the naked eyes (they can be seen only through a microscope). We can, however, see the plants and animals around us because they are made up of millions and millions of tiny cells joined together. Before we go further and discuss prokaryotic cells and eukaryotic cells, please note that the material which makes up the nucleus of a cell is called ‘nuclear material’.