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Cell is called the fundamental unit of life because it is solely able to survive with the help of its *organelles.
*Cell organelles:
Cell organelles works similar to the organs in our body. They help the cell to survive by providing it basic functionality such as respiration, digestion, food intake etc.
In 1665, Robert Hooke discovered the first cell. He observed the cork slice under the microscope, which was made by him. He observed that the structure of cork was similar to the bricks laid one on another to construct a wall. He named these structures as “Cell.”
There are basically two types of organisms:
These organisms are made of a single (independent) cell, which is able to perform all the necessary functions with the help of its organelles for survival. Example: Amoeba and Paramecium.
Multicellular organisms are made of millions or even billions of cells. These organisms have complex body structure, and they do possess organs that helps them to survive. Example: Humans, Animals.
*Every multicellular organism is infact made of single cells combined together.
Cells -> tissues -> organs -> organ system -> body
Almost every single cell has the following structure:
Plasma membrane is a thin membrane that covers the outer area of the cell. It is made of protein and lipids. It allows selective substance to enter or exit the cell. Therefore, it is also known as selectively permeable membrane.
Diffusion: Plasma membrane allows the exchange of gases such as CO2 by the process of diffusion. In cell, the exchange of gases takes place from higher concentration to lower concentration.
Osmosis: Plasma membrane also allows the movement of water by the process known as osmosis. Water, however, also move from higher concentration to lower concentration.
Endocytosis: In addition to water and gas, plasma membrane also allows the cell to take food from its external environment. This process is known as endocytosis.
Hypotonic solution: When there is a higher concentration of water outside the cell and lower concentration of water inside the cell, the water moves inside the cell, this solution is called hypotonic solution.
Isotonic solution: When the concentration of water inside the cell and its external environment is same, no movement take place such situation. This solution is known as Isotonic solution.
Hypertonic solution: When the concentration of water is high inside the cell and low in its external environment, the movement of water takes place from cell to the environment. This solution is known as hypertonic solution.
Cell wall is the outer most covering of the cell. The plasma membrane lies inside the cell wall. The cell wall is only present in plant cell. It protects the plant from harsh weather such as warm and cold. Cell was is made of cellulose which is a complex substance.
Plasmolysis: When the cell takes water the content of the cell came close to the cell wall. Similarly, when the cell loses water the content of the cell goes away from the cell. This contraction and expansion of cell is known as plasmolysis.
*The cell wall protects the cell from bursting. When a cell intakes water from its external environment, it expands and exert pressure on the cell wall. To maintain equal pressure the cell wall also exerts pressure on the swollen cell, which protects the cell from bursting.
Nucleus is the most important part of a cell. It works just like our brain but also helps in cell division. The nucleus has double layer covering which is called nuclear membrane. The nucleus contains chromosomes. These chromosomes contain DNA (Deoxyribo nucleic acid). Genes are present inside the DNA that contains the information of the parent cell. Normally, the DNA is present as chromatin material in the cell, but when the cell is about to divide this chromatin material is organized in chromosomes.
Functions of nucleus:
*Cellular reproduction:
When a single cell divides into two cells, this process is called cellular reproduction.
*Membrane biogenesis:
The lipid is used to build the plasma membrane of the cell. This process is known as membrane biogenesis.
Cytoplasm is a jelly like substance in which all cell organelles are present.
There are two types of cell:
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Prokaryotic cell |
Eukaryotic cell |
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1. |
Nucleus is not well defined |
Nucleus is well defined |
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2. |
Contains single chromosome |
More than one chromosomes are present |
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3. |
Cell organelles do not have membrane |
Cell organelles do have membrane |
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4. |
Size varies from 1-10 um |
Size varies from 50-100 um |
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5. |
Do not have specialize cell organelles |
It has specialize cell organelles |
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6. |
Example: Bacteria |
Example: Plant and animal |
Cell organelles are just like our body organs that performs specific function in a cell. In Eukaryotic cell, these organelles are surrounded with membrane.
The structure of Endoplasmic reticulum looks like tubes and sheets. It acts as a network system, which serves the protein to other parts of the cell. There are two types of Endoplasmic reticulum:
Smooth endoplasmic reticulum (SER) manufactures fats and lipids. One of the major roles of SER is to detoxify the poisons and drugs.
Rough endoplasmic reticulum (RER) manufactures proteins with the help of ribosome. The surface of RER looks rough because of this ribosome.
Camillo Golgi was the first to discover the Golgi apparatus in a cell. The function of Golgi apparatus includes packaging, modification, storage, and transportation of protein. The protein manufactured in ER is also transported inside and outside the cell via Golgi apparatus. It also helps in the formation of lysosomes.
Lysosmes include the digestive enzymes that help the cell in waste disposal. It also protects the cell from bacteria that may enter during the food intake. These lysosomes are called suicide bags because if the cell is damaged and the lysosome is burst, it can digest the whole cell.
Mitochondria are called the powerhouse of the cell because the energy required by the cell for all chemical process is released by mitochondria in the form of ATP also known as Adenosine triphopshate. Mitochondria have its own DNA and ribosomes thus it can produce its own protein.
Plastids are only present in plant cell. It has its own DNA and ribosomes. Its external structure is similar to mitochondria. There are two types of plastids:
Chromoplasts contain the chlorophyll, which is known as chloroplast. Chloropast helps plant in photosynthesis. The chloroplast is also responsible for the greenish color of plant’s leaves.
Leucoplast works as a storage unit that stores starch, protein granules, and oils.
Vacuoles are the storage sac of the cell. It stores every solid and liquid substance in it. There is only one big size vacuole in plant cell whereas in animal cell there are a number of small vacuoles. Vacuole stores organic acid, some protein, amino acid, and sugars. The vacuole in plant cell provides turgidity and rigidity.
Cell division is a process by which new cells are formed from an existing cell. There are two types of cell division:
In mitosis, the existing cell is divided into two cells which are identical and contains the same number of chromosome as parent cell.
In meiosis, the existing cell is divided into four cells and the numbers of chromosomes are half the number of chromosomes in parent cell.