After reading this article you will learn about the structure of animal cell. This will also help you to draw the structure and diagram of an animal cell.
Growth of Reproduction:
The cell has ability to increase in size. It also reproduces by dividing into two smaller cells.
Some animal cells have the power of movement.
Irritability and Conductivity:
The cell has the ability to detect and respond to changes in its environment. By these two properties the cell is active. When a cell is stimulated either by chemical physical, mechanical or nervous means, the cell responds.
Structure of the Cell:
All cells are made up of protoplasm, which consists of water, electrolytes, proteins, lipids, and carbohydrates. The protoplasm of the cell is composed of cytoplasm and nucleus.
All animal cells are surrounded by a protective membrane which is called as cell-membrane or plasma membrane. It is also called as cytoplasmic membrane. Plasma membrane is a thin, elastic and semi-permeable membrane.
It is mainly composed of 32% lipids, 12% protein, 6% carbohydrates and 20% water. The pores of the membrane allow the passage of water, oxygen, carbon dioxide and some other substances in and out of the cell.
Functions of the cell membrane:
1. Cell membrane is a natural protective boundary around the cell.
2. It provides a definite shape and mechanical support to the cell.
3. It regulates the exchange of materials between the cell and the outside environment which is called as “trans membrane transport.”
4. It plays an important role in maintaining the homeostatic balance of the cell.
5. It receives stimuli from the outside.
6. It takes the nutrients and excretes the waste products.
7. Cell membrane is rich in enzymes. Many important compounds are synthesized on the plasma membrane.
8. It acts as a receptor site for hormones.
9. Cell membrane maintains the correct chemical composition of protoplasm.
The protoplasm inside the cell membrane and outside the nucleus is known as cytoplasm. It is also called the cytosome. It contains a number of structures known as organelles of the cell. About 90% of cytoplasm is water and the rest 10% are enzymes, proteins, vitamins, RNAs, nucleotides, sugar residues, amino acids and other organic and inorganic substances. The cytoplasm is the store house of many vital compounds necessary for life.
The followings are the main organelles of the cell present in cytoplasm:
(4) Golgi Apparatus
(5) Ground cytoplasm
These are rod like structure which are the largest cytoplasmic organelle. The name mitochondria was given by Benda in 1898. Mitochondria are uniformly distributed throughout the cytoplasm. In some cells they are found in certain zones. They are closely connected with the catabolic process of the cell body.
1. Mitochondria are called the “Power House” of the cell.
2. This is the energy transporting system in the cell. It extract energy from nutrients and oxygen in the form of ATP (Adenosine triphosphate) This energy is made available for cellular activity.
3. This is the respiratory center of the living cell.
4. Mitochondria are associated with fat metabolism.
5. Some of the proteins required by mitochondria are manufactured in its own “Protein factory”.
6. Some Proteolytic enzymes regulate some of the activities inside the cell.
7. As mitochondria move freely in the cytoplasm they are able to regulate their own density.
8. They take part in the yolk formation.
9. Mitochondria store and regulate the concentration of calcium ions in the cell.
These are minute, granular bodies found scattered throughout the cytoplasm either singly or in groups. These are made up of RNA and protein and ribonucleoprotein in nature.
1. These are called as “Protein Factory” of the cell as they synthesize protein.
2. Ribosomes are rich in RNA. They may contain as much as 60% of total RNA in the entire cell.
3. Haemoglobin in the blood cell is synthesized in the ribosomes.
4. The aminoacids are transported to the ribosomes for the growth of the polypeptide chain during protein synthesis.
These are spherical and bag like structure. They are important cytoplasmic organell which are found only in animal cells. The cells of the liver spleen, thyroid gland and brain are particularly rich in lysosomes. Under certain conditions the lysosomes may digest its own cellular content and for this it is sometimes called as “Suicide Bag”.
Lysosomes exist in four forms:
(d) Auto-phagic vacuoles.
1. Lysosomes contain digestive enzymes and help in intracellular digestion, so it is called as “Digestive apparatus” of the cell.
2. Lysosomes are phagocytic in nature. So they kill the germs, bacteria and other foreign particles.
3. Aging, degeneration and dead-cells are removed by autolysis process of Auto-phagic Vacuoles forms of lysosomes.
4. The enzymes of the lysosome can destroy some biological inactive compounds.
5. The stored food like fat and carbohydrates are digested during prolonged starvation by lysosomal enzymes to provide energy.
6. Tissue degeneration is attributed by lysosomes activity.
7. Lisosomes bring about the death of cells to make space for new cells.
Golgi complex or golgi apparatus are situated near the nucleus. They look like a network of fine threads and are composed of an equal amount of protein and phospholipids. They also contain several enzymes like nucleotidase diphosphatase transferase, and other oxidative and lysosomal enzymes. Large numbers of Golgi complex are found in the secretory cells of salivary glands, Liver cells and other gland cells.
1. Golgi complex are associated with the secretory activities of the cell.
2. The material secreted by golgi complex helps in fertilization.
3. It Chemically modifies secretory products. It helps to form glycoproteins and glycolipids.
4. Golgi bodies are associated with the packaging and distribution of secretory materials to and from other parts of the cell.
5. Golgi bodies are associated with the synthesis of melanin and lipid metabolism.
6. It is an integral part of endo-membrane system for intracellular transport.
This is a highly complex collaidal substance in which other structures of cytoplasm are embeded.
It is connected with the anabolic activities of the cell.
This is a complicated net work of tubules which are connected with the nucleus and cell membrane. Chemically, Endoplasmic Reticulum is composed of 40% protein, 55% lipid with traces of enzymes and RNA.
There are two types of Endoplasmic Reticulum:
(1) Agranular or smooth
(2) Granular or rough endoplasmic Reticulum.
1. It transfers substances from one part of the cell to another.
2. It provides additional support to the cytoplasmic matrix.
3. Rough Endoplasmic Reticulum manufactures and stores protein.
4. Smooth Endoplasmic Reticulum is involved in the synthesis is of lipoproteins, steroids and glycogen.
5. It helps in detoxification of drugs and antigens.
6. It is involved in the conduction of intracellular impulse in muscle cell.
This is a minute dense part of cytoplasm, lying close to the nucleus. It consists of another specialized part of clear cytoplasm which is known as centrosphere. It is made up of two centrioles which are small and spherical bodies.
Centrioles play an important role in initiating and regulating cell division.
Nucleus was first discovered by Robert Brown in 1837. The study of nucleus is called karyology. It occupies a central position in the cell. It consists of a more compact mass of protoplasm. It is enclosed by the nuclear membrane and is separated from the cytoplasm.
This membrane is also porous and allows substances to escape from the nucleus into the cytoplasm or substances to pass into it. The nucleus is usually an oval body lying near the center of the cell. The nucleus is the controlling center of the cell and contains a special type of protein called as nucleoprotein. It controls both the chemical reactions that occur in cell and the reproduction of the cell. The nucleus contains a fine network of thread like fibers called the chromatic reticulum.
Functions of the Nucleus:
1. The nucleus is chemically very active. It influences the growth, repair and division of the cell.
2. The nucleus controls all the metabolic activities of the cell, so it is known as the control room of the cell.
3. It transmits hereditary information from one generation to another.
4. It influences the growth, repair and division of cell.
5. The cell would die without a nucleus. So it is known as the Commanding organelle of the cell.
6. It takes part in the synthesis of RNA.
7. It plays an important role in sexual reproduction.
(Chroma = Colour, Soma = body)
The nucleo protein consists of a number of thread like fibers called “Chromosomes” When the cell is in a non-dividing state the chromosomes are scattered throughout the nucleus which are called as “Chromatin”. In human cells, there are 23 pairs or 46 numbers of chromosomes. Each chromosome has a specific part which is active only during cell division.
Functions of Chromosomes:
1. The chromosomes carry smaller particles called “genes” which are node of a complex protein compound DNA. (Deoxyribo – Nucleic Acid)
2. They carry all the hereditary character of the parents and grand parents like colour of hair and eyes, height, body shape, blood group, nature, congenetal defects, heriditary disease etc.
3. Sex charmosomes determine the sex of the children at the time of conception.
4. Chromosomes duplicate and pass on the genetic information to the daughter cell.
General Functions of the Cell:
Although there are lot of differences in size and shape of various types of cells, basic similarities are there at the functional level.
The followings are some of the basic functions:
1. All cell maintain a barrier that protects the content of cells from the external environment. This barrier maintains the concentration of the solutes in the cell by regulating the transport of materials from in and out of the cells. Even the barriers are used to compartmentalize the cell for some special functions.
2. Inheritance and transmission of genetic material from one generation to another are performed in the cell through cell division. Actually, the genetic material is duplicated before cell division, so that newly formed cells can get a full set of genetic material from the mother cell.
3. All cells carry out series of chemical reactions for the synthesis of macromolecules, trapping energy, the degradation of some unused molecules, converting food substances into sugar etc. In other words, they are performing the most important processes known as metabolism, to perform all the essential or cellular activities.
4. Cells can show different types of motility starting from locomotion to the movement of some components at the cell.