It is important to know the component of cell i.e Plasma Membrane, Cell Wall, Nucleus, Cytoplasm, Ribosomes, Golgi bodies, Mitochondria, Lysosomes, and Plastids etc.
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Therefore, the structure of the Cell consists of:
1. Plasma Membrane: It is the outer covering of each cell. Present in cells of plants, animals and microorganisms. It is a living and quite thin, flexible and selectively permeable membrane. Made up of lipids, proteins and a small number of carbohydrates. Its major function is to hold cellular contents and control the passage of materials in and out of the cell.
2. Cell Wall: It occurs in plants and presents outside the plasma membrane. It is nonliving, quite thick and rigid but generally permeable. It is made up of cellulose, hemicelluloses and pectin. Its major function is to provide protection and strength to the cell.
3. Nucleus: It is a spherical cellular component, centrally located in the cell and filled with a fluid namely cytoplasm. Bounded by two nuclear membranes forming a nuclear envelope. Space between the nuclear envelope is connected to the Endoplasmic reticulum (ER). It also separates the nucleus from the cytoplasm and its pores contain liquid known as nucleoplasm which is embedded with two structures – the nucleolus and chromatin material. It is rich in protein and RNA (ribonucleic acid). Also known as the factory of Ribosomes because of ribosome formation.
| Nucleus | Nucleolus |
| 1. It represents the whole eukaryotic complex that contains genetic information. 2. It is covered by a two membrane envelope. 3. It controls the structure and working of cells. | 1. It is a component of the nucleus. 2. It does not have a covering membrane. 3. It synthesizes ribosomal subunits. |
Inside the nucleus, chromatin material is present which is composed of a genetic substance DNA and is responsible for the transmission of characteristic features from one generation to another.
4. Cytoplasm: The part of the cell which occurs between the plasma membrane and nuclear envelope. The inner layer of it is known as the endoplasm and the outer is known as the cell cortex or ectoplasm. The cytoplasm consists of an aqueous substance cytosol in which a variety of cell organelles and other inclusions like insoluble waste and storage products (starch, lipid etc.) are present.
(i) Endoplasmic Reticulum (ER): Inside the cell, there exists a membranous network enclosing a fluid-filled lumen that almost filled the intracellular cavity. It is of two types:
(a) Rough Endoplasmic Reticulum (RER): with ribosomes attached on its surface for synthesising proteins.
(b) Smooth Endoplasmic Reticulum (SER): which is without ribosomes and is meant for secreting lipids.
ER forms supporting skeletal framework of the cell and also provides a pathway for the distribution of nuclear material from one cell to another.
(ii) Ribosomes: are dense, spherical and granular particles that occur freely in the matrix (cytosol) or remain attached to the ER. It plays an important part in the synthesis of proteins.
(iii) Golgi apparatus: It consists of a set of membrane-bounded, fluid-filled vesicles, vacuoles and flattened cisternae (closed sacs). It is absent in bacteria, blue-green algae, mature sperms and red blood cells of mammals and other animals. Its main function is secretory. It packages material synthesised inside the cell and dispatches them. It produces vacuoles or secretory vesicles which contain cellular secretions like enzymes etc. It is also involved in the secretion of cell wall, plasma membrane and lysosomes.
(iv) Lysosomes are simply tiny spherical sac-like structures evenly distributed in the cytoplasm. Its cells digest foreign proteins, bacteria and viruses. So, it is a kind of garbage disposable system of the cell. And also known as suicidal bags as when the cells get damaged, lysosomes may burst and enzymes eat up their own cells.
(v) Mitochondria: are tiny bodies of varying shapes and sizes, distributed in the cytoplasm. It is bounded by a double membrane envelope. The outer membrane is porous and the inner membrane is thrown into folds known as cristae having some rounded bodies known as F1 particles or oxysomes. Since mitochondria synthesize energy-rich compounds (ATP) so, known as powerhouse of the cell.
(vi) Plastids: Occurs in plant cells and is absent in animal cells. They have their own genome and have the power to divide.
They are of three types:
Chromoplasts (coloured plastids) imparts various colours to flowers to attract insects for pollination.
Chloroplasts (Green-coloured plastids) trap solar energy and utilises it to manufacture food for the plant.
Leucoplasts (colourless plastids) store food in the form of carbohydrates (starch), fats and proteins.
(vii) Chloroplasts: are present in green algae and higher plants. They have a green pigment called chlorophyll and help in the photosynthesis of food. So, known as “kitchens of the cell”.
(viii) Vacuoles: are fluid-filled or solid filled membrane-bound spaces. They are a kind of storage sacs. In animal cell vacuoles if present is small and temporary as compared to plant cell. It helps to maintain the osmotic pressure in a cell and provide turgidity and rigidity to the plant cells. They also store toxic metabolic by-products or end products of plant cells.
(ix) Peroxisomes: are small and spherical organelles containing powerful oxidative enzymes. They carry out some oxidative reactions like detoxification or removal of toxic substances from the cell.
(x) Centrosome: is found only in animal cells. As it helps in cell division. In plant cells, polar caps perform the function of centrioles.
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Difference between Plant and Animal Cell
| Animal Cell | Plant Cell |
| 1. Generally small in size. 2. Cell wall is absent. 3. Plastids are absent except euglena. 4. Vacuoles are small and temporary. 5. Single highly complex and prominent Golgi apparatus is present. 6. Centrosome and Centrioles are present. | 1. Larger than animal cells. 2. A rigid cell wall of cellulose i.e plasma membrane is present. 3. Plastids are present. 4. Mature plants have permanent and large central sap vacuoles. 5. Many simpler units of the Golgi apparatus called dictyosomes are present. 6. Centrosome and Centrioles are absent. |
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