notes prepared by subhankar Karmakar
Cell : Cells are the basic units of life. All the living things both plants and animals, are made from cells. Cells are tiny basic unit of structure and function of all living organisms. Cells are the building blocks of plants and animals. Therefore, we can say a cell is the smallest unit of life which has a definite structure and performs specific function.
Microscope: The instrument used to study cells is called microscope.
Discovery of cell: an English scientist named Robert hooke discovered cell in 1665.
In 1838, a German scientist Schleiden first suggested that all plants are made of cells.
In 1839, another German scientist Schwann suggested that all animals are made of cells too.
Cell division: all cells arise from pre-existing cells by a method which is called cell division.
Classification of cell: All cells are primarily categorised into two main types. Animal cells and plant cells.
Structures of a cell: Each cell has a number of smaller parts or internal structures in it. Some of the structures are present in both animal and plant cells, while some structures are only present in plant cells, they are not present in animal cells. They are also called parts of a cell.
The parts of a cell present in both animal and plant cells:
Cell membrane or plasma membrane, Cytoplasm, Nucleus and Mitochondria. These basic parts are present in in both animal as well as plant cells.
The parts of a cells present in plant cells only:
Cell wall, Chloroplasts, Large vacuole are present in plant cell only.
1. Cell membrane or plasma membrane:
Every cell is covered by a thin sheet of skin which is called cell membrane or plasma membrane. The cytoplasm and nucleus are enclosed within the cell membrane. Therefore we can say, cell membrane encloses the living part of the cell which is known as protoplasm.
The cell membrane protects the cell and also gives shape to the cell. The cell membrane has tiny pores in it. Through this pores, the cell membrane controls the movement of substances "into the cell" and "out of the cell" like the dissolved glucose and oxygen can enter into the cell whereas the waste products like carbon dioxide can go out from the cell through this pores of the cell membrane.
Cell membrane separates the cell from other cells as well as from the surrounding medium. The cell membrane or plasma membrane is a living part of the cell.
2. Cytoplasm:
Cytoplasm is a transparent jelly like material which fills the cell between nucleus and the cell membrane. It acts like a chemical factory of the cell. In cytoplasm, new substances are built from materials taken into the cell and energy is released and stored. It is a place where most of the chemical reactions which keep the cell alive take place. Cytoplasm has many internal structures which are known as organelles. The most prominent internal structure in the cytoplasm is nucleus. It also contains mitochondria, Golgi bodies, ribosomes etc. Cytoplasm for plant cells also contain chloroplast. Cytoplasm and the nucleus taken together is called protoplasm.
3. Nucleus:
Nucleus is a large spherical organelle present in all the cells. In animal cell, nucleus lies in the centre of the cell whereas in plant cells the nucleus maybe on the periphery of the cell. Nucleus is separated from the cytoplasm by a membrane called nuclear membrane. Nucleus controls all the activities of cell. The transmission of characteristics from the parents to the offsprings is called inheritance and Nucleus plays a role in inheritance.
Chromosome: Nucleus contains thread like structure called chromosome. The function of chromosomes is to transfer the characteristics from the parents to the offspring through the genes and it is called inheritance.
Nucleolus: The nucleus also contains a tiny round structure called nucleolus. The nucleus containing chromosomes and nucleolus is bound by a membrane called nuclear membrane. Nuclear membrane has tiny pores for the exchange of materials with cytoplasm. Some cells like red blood cells do not have a nucleus.
Gene: Gene is a unit of inheritance in living organisms, which is transferred from parent to offspring during reproduction and determine some characteristic feature of the offspring. Thus genes control the transfer of hereditary characteristics from parents to offsprings.
Protoplasm: All the living matter in a cell is called protoplasm. Protoplasm is a liquid substance which is present inside the cell membrane. Protoplasm includes cytoplasm, nucleus and other organelles. Most of the protoplasm is made up of compounds of only 4 elements Carbon, Hydrogen, Nitrogen and Oxygen. It also contains water, carbohydrates, proteins, nucleic acids, fats and mineral salts.
4. Mitochondria:
Mitochondria are the tiny rod-shaped or spherical organelles which are found in all the cells. Mitochondria provide energy for all the activities of the cell. This energy is produced by the process of respiration in which food such as glucose is broken down by oxygen. Thus mitochondria use glucose and oxygen to produce energy. Mitochondria are found in large numbers in the cytoplasm in all the cells.
5. Cell wall: The plant cells have a thick cell wall around them outside the cell membrane. The cell wall is made of a tough material called cellulose. Cell wall gives shape and support to the plant cell. Cell walls also hold the plant cells together and give plants most of their strength. Plants need protection against high wind speed, variation in temperature and atmospheric moisture etc. Since plants are fixed at a place so they cannot move to protect themselves from the various changes in their surroundings. The tough cell wall present in plant cells provides protection to plants. Cell wall is not there in animal cells. The cell wall is a non living part of the plant cells.
6. Chloroplasts: Chloroplasts are the green coloured organelles present in the cytoplasm of plant cells. The process of food making by plants known as photosynthesis takes place in chloroplasts. The green colour of chloroplasts is due to the presence of a green pigment called chlorophyll in them. Chlorophyll can absorb sunlight energy. In the chloroplasts, carbon dioxide and water combine in the presence of sunlight energy to produce food such as glucose. And this process of food making is called photosynthesis.
The organelles containing pigments or colour matter present in the cytoplasm of plant cells are called plastids. Plastids can be of many different colours. The plastids containing green pigment or chlorophyll are known as chloroplasts. Chloroplast are present in the cells of leaves. It makes the leaves green. The plastids are may be of different colour like red colours of tomatoes are due to red plastids. Different colours of flowers are also due to this plastids.
7. Large Vacoule:
Vacoule is a space in the cytoplasm of a cell which is enclosed by a membrane and is usually contains substances dissolved in water. A vacoule appears as an empty space under the microscope. All the plant cells have a large vacoule. The vacuole is filled with a liquid called "cell sap" , which contains dissolve sugar and salts. The function of vacuole in a cell is to store various substances including waste products of the cell.
* In amoeba vacuoles contain food particles so they are called food vacuoles.
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