These are small structures inside the cell and are called cell organelles. Endoplasmic reticulum, mitochondria, lysosome, Golgi Body and plastids are the important cell organelles.
Mitochondria: Mitochondrion is a capsule-like structure. It is bound by double membrane. The inner membrane is projected into numerous finger-like structures, called cristae. Mitochondria are the sites of cellular respiration. After cellular respiration, energy is stored in the form of ATP (Adenosine triphosphate) in mitochondria. Mitochondria have their own DNA and ribosomes and hence mitochondria can make their copy or replicate on their own. As mitochondria are the sites for generation of energy, they are also known as the Powerhouse of the Cell.
Endoplasmic Reticulum: Endoplasmic reticulum is a mesh-like structure which is composed of numerous tubes. It extends from the plasma membrane to the nuclear membrane. There are two kinds of endoplasmic reticulum, viz. smooth ER and rough ER. Rough ER has ribosomes on its surface which give it the rough appearance.
Function of ER: It serves as the transport channel in the cell. Substances are transported from cell membrane to cytoplasm and to nucleus and vice-versa. RER is also the site for some important biochemical processes.
Golgi Complex: Golgi Complex was discovered by Camillo Golgi. It is composed of many sac-like structures which are stacked one above another. Golgi complex is responsible for packaging of various substances in the cell.
Lysosome: Lysosome are small sac-like structures and they are derived from Golgi complex. Lysosome contains digestive enzymes.
Functions of lysosome: The enzymes in the lysosome digest foreign particles and thus destroy them. Sometimes, the lysosome may burst open and its content ends up digesting the contents of the cell. The cell gets killed in the process. Due to this, lysosome is also called the Suicide bag of the cell.
Ribosome: These are tiny dot like structures interspersed in the cytoplasm and also on the surface of Rough ER. Ribosome is responsible for protein synthesis.
Plastids: These are somewhat similar to mitochondria in appearance. Plastids are found in plant cells only. They are of two types, chromoplast and leucoplast. Colourful plastids are called chromomplast and colourless plastids are called leucoplast. Chloroplast is green in colour and is found in green parts of plants. Leucoplast are responsible for storage of substances. Plastids too have their own DNA and ribosome.
Vacuoles: These are fluid filled chambers and are often seen in many cells. Vacuoles are very large in plant cells. A plant cell usually has single but large vacuole. Such a vacuole fills almost the entire space inside the cell. Vacuoles are much smaller and very few in animal cells.
|Plant cell||Animal cell|
|Cell wall present||Cell wall absent|
|Plastids present||Plastids absent|
|Vacuole is usually very large and single||Vacuoles are much smaller an may be absent|
Cell division is necessary for growth and repair. As per the cell theory, any cell is formed from a pre-existing cell. There are two types of cell division, viz. mitosis and meiosis.
Mitosis takes place in all the cells which are responsible for growth and repair. After mitosis, two daughter cells are formed from a mother cell. The number of chromosomes in daughter cells is same as in mother cell.
Meiosis takes place during gametogenesis, i.e. formation of gametes. This means that pollen grains and eggs are formed through meiosis. Similarly, sperms and ovules are formed through meiosis. After meiosis, four daughter cells are formed from a mother cell. The number of chromosomes in daughter cells is half the number in mother cell.
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