Book : Zoology
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Posted by: CHELSEA
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Animal Cell

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All animal cells are multicellular. They are eukaryotic cells. Animal cells are surrounded by plasma membrane and it contains the nucleus and organelles that are membrane bound. Animal cells are of various sizes and have irregular shapes. Most of the cells size range between 1 and 100 micrometers and are visible only with help of microscope. Trillions of cells are found in the human body. There are many different types of cells, approximately 210 distinct cell types in adult human body.

Cell membrane

It is a semi-permeable barrier, allowing only a few molecules to move across it. Electron microscopic studies of cell membrane shows the lipid bi-layer model of the plasma membrane, it also known as the fluid mosaic model. The cell membrane is made up of phospholipids which has polar(hydrophillic) heads and non-polar (hydrophobic) tails.


The fluid matrix that fills the cell is the cytoplasm. The cellular organelles are suspended in this matrix of the cytoplasm. This matrix maintains the pressure of the cell, ensures the cell doesn't shrink or burst.


Nucleus is the house for most of the cells genetic material- the DNA and RNA. The nucleus is surrounded by a porous membrane known as the nuclear membrane. The RNA moves in/out of the nucleus through these pores. Proteins needed by the nucleus enter through the nuclear pores. The RNA helps in protein synthesis through transcription process. The nucleus controls the activity of the cell and is known as the control center. The nucleolus is the dark spot in the nucleus, and it is the location for ribosome formation.


Ribosomes is the site for protein synthesis where the translation of the RNA takes place. As protein synthesis is very important to the cell, ribosomes are found in large number in all cells. Ribosomes are found freely suspended in the cytoplasm and also are attached to the endoplasmic reticulum.

Endoplasmic reticulum

ER is the transport system of the cell. It transports molecules that need certain changes and also molecules to their destination. ER is of two types, rough and smooth. ER bound to the ribosomes appear rough and is the rough endoplasmic reticulum; while the smooth ER do not have the ribosomes.


It is the digestive system of the cell. They have digestive enzymes helps in breakdown the waste moelcules and also help in detoxification of the cell. If the lysosomes were not membrane bound the cell could not have used the destructive enzymes.


It is located near the nucleus of the cell and is known as the 'microtubule organizing center' of the cell. Microtubules are made in the centrosome. During mitosis the centrosome aids in dividing of the cell and moving of the chromosome to the opposite sides of the cell.


They are bound by single membrane and small organelles. In many organisms vacuoles are storage organelles. Vesicles are smaller vacuoles which function for transport in/out of the cell.

Golgi Bodies

Golgi bodies are the packaging center of the cell. The Golgi bodies modify the molecules from the rough ER by dividing them into smaller units with membrane known as vesicles. They are flattened stacks of membrane- bound sacs.


Mitochondria is the main energy source of the cell. They are called the power house of the cell because energy(ATP) is created here. Mitochondria consists of inner and outer membrane. It is spherical or rod shaped organelle. It is an organelle which is independent as it has its own hereditary material.

Cilia and Flagella

Cilia and flagella are structurally identical structures. They are different based on the function they perform and their length. Cilia are short and are in large number per cell while flagella are longer and are fewer in number. They are organelles of movement. The flagellar motion is undulating and wave-like whereas the ciliary movement is power stroke and recovery stroke.

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