A cell can be defined as the protoplasm surrounded with cell membrane, which works as structural and functional unit of life. Each cell is capable of performing the basic functions of life such as respiration, reproduction, excretion, growth etc.
The theory of cell is summed up in the following points:
Due to different functions, cells are found in different shapes oval, round, rectangular, cylindrical etc. The shape of cells is influenced by factors like a cell wall, pressure, location etc.
The cells may be prokaryotic or eukaryotic. In prokaryotic cells, nuclear materials and organelles are not enclosed by membranes but in eukaryotic cells, nuclear materials and organelles are covered with membranes. A bacteria has the smallest cell and the largest cell is found inside an ostrich egg. The size of prokaryotic cells range from 102nm to 2 \(\times\) 103nm and size of eukaryotic cell ranges from 104nm to 105nm.
Prokaryotic Cells: Prokaryotic cells lack nuclear membrane. It also lacks membrane bound organelles. There is the absence of mitotic apparatus and nucleoli in a prokaryotic cell. Mitotic cell division is absent in prokaryotes. The cell organelles present in the prokaryotic cells are ribosomes which are of 70s type.
Eukaryotic Cells: the Eukaryotic cell is a type of cell that consists membrane bound organized nucleus and all other types of cell organelles. It contains all membrane bound organelles such as mitochondria, endoplasmic reticulum, golgi complex, centrosome, vacuoles, etc. The ribosomes found in eukaryotic cells are of the 80stype.
Eukaryotic cells can be divided into following three major parts:
The outermost, rigid, protective layer found in cells is known as the cell wall. It is absent in animal cells.
The main functions of cell wall are as follows:
The animal’s cells have fine cell coat at their surface, called as a cell membrane. It is made up protein and lipid.
The main functions of cell membrane are as follows:
The non-crystalline, translucent substance found in between the plasma membrane and nucleus is known as cytoplasm. Cell organelles and cell inclusions are found in it, which are jointly known as cytoplasmic structures. Some major cell organelles are described below:
They are made up of protein, lipids and a small amount of DNA. They contain different types of enzymes in which intracellular respiration occurs. The energy produced by this process is stored here in the form of ATP. Due to this reason, mitochondria are known as the powerhouse of a cell.
Endoplasmic reticulum and ribosome
It is a doubled layered membrane. The major functions of endoplasmic reticulum are as follows:
Ribosomes are small round structures found in the cytoplasm and consider as protein factories as they synthesize protein.
The major functions of Golgi bodies are as follows:
They are sac-like structures bound by a membrane made of lipid and protein and contain digestive enzymes in them. They carry the following functions:
They are found only in animal cells.
The major functions of centrosome are as follows:
They are found only in a plant cell. They are oval, round and in other shapes. On the basis of pigments found in them, they are divided into three types. They are chloroplast, chromoplasts, and leucoplast. Chloroplasts contain green pigment and help in preparation of food. Chromoplasts are found in coloured parts of plants and help in pollination. Leucoplasts are non-pigmented plastids which are concerned with storage of protein, starch, oil etc. in plant bodies.
They are fluid filled sacs bounded by a single membrane called tonoplast.
The major functions of vacuole are as follows:
It is very important part of a cell. It is a spherical structure that consists of four major components of it. They are:
|Plant cell||Animal cell|
|Centriole and centrosome are absent.||Centriole and centrosome are present except in invertebrates.|
|Its nucleus is pushed to one side by vacuole.||Its nucleus is located at the center.|
|Have plastids in them.||Usually plastids are absent in them.|
|Golgi bodies are smaller and scattered in cytoplasm.||Golgi bodies are bigger and found near nucleus in the form of a block.|
|It has a cellulosic cell wall surrounding plasma membrane.||The cell wall is absent. The cell is enclosed by the plasma membrane.|
|Mitochondria are usually fewer.||Mitochondria are usually numerous.|
|Usually plant cells are bigger and of regular shape.||Usually animal cells are smaller and have an irregular shape.|
The living structure of the cytoplasm is called organelles. They are: cell membrane, lysosome, centrosome, plastid, nuclear membrane, nucleolus, nucleoplasm, chromatin fibre. The non-living structure within at cell are called as cell inclusions. They are: cell wall, granule, vacuoles, fat drops.
The differences between cell membrane and cell wall are given below:
|Cell membrane||Cell Wall|
|i) It is made up of protein and lipid.||i) It is made up of cellulose.|
|ii) It is present in both plant and animals.||ii) It is present in plant only.|
|iii) It is semi-permeable in nature.||iii) It is permeable in nature.|
The non-crystalline, translucent and homogeneous colloidal substance found in between plasma membrane and nucleus is called cytoplasm.
The main function of mitochondria is to release energy by the oxidation of carbohydrate in the presence of enzymes and store in the form of ATP.
The full form of ATP is Adenosine triphosphate.
Mitochondria are called the power house of a cell because it releases energy and stores in the form of ATP which is used up for the different metabolic activities performed inside a cell.
Three functions of endoplasmic reticulum are as follows:
a) It increases the surface area in the cell for metabolism.
b) It helps in the formation of nuclear membrane and cell plate during cell division.
c) It provides mechanical support to cytoplasm.
The main function of ribosome is to synthesize protein.
Any two functions of Golgi bodies are:
i) It helps to make cell plate during cell division.
ii) It forms lysosomes, hormones etc.
The main function of lysosome is to help in digestion of unnecessary material inside a cell.
Lysosome is called suicidal bag because sometimes it digests cell organelles of a cell with the help of enzyme and ultimately cell dies.
Centrosome is found only in animal cell and plastid is found only in plant cell.
Plastids are of three types:
i) Chloroplast: It is green pigment containing chlorophyll which helps in preparation of food.
ii) Chromoplast : It is colour pigment except green which gives colour to flowers and fruits.
iii) Leucoplast : It is colourless which is present in root and store protein, starch, oil etc.
The functions of vacuole are as follows:
i) They regulate the amount of water and glucose in a cell.
ii) They store waste products and helps in excretion.
Vacuole is made up of fluid filled sacs surrounded by tonoplast.
Nucleus is formed by nucleoplasm, nucleolus and chromatin.
The major functions of nucleus are as follows:
i) It helps in both sexual and asexual reproduction.
ii) Nucleolus, present in nucleus, helps to form ribosome.
iii) It controls all the activities of a cell.
The differences between plant cell and animal cell are as follows:
|Plant cell||Animal cell|
|i) It contains cell wall.||i) It does not contain cell wall|
|ii) It is rectangular in shape.||ii) It is oval in shape.|
|iii) Plastids are present.||iii) Plastids are absent.|
|iv) It has single but large sized vacuole.||iv) It has numerous small vacuoles.|
What do plant cell have that aniaml cells do not?
plants have a nuleus and mitochondria
plants have a cell wall and choloplast
plants have a nucleus and a cell membrane
plants have vacuole and nucleus
What is the function of the cytoplasm?
a jelly-like substance that holds al the organelles in place
transport food, water and waste around and out the cell
releases energy in the cell
contain the pigment called chlorophyll
The Levels of Organization of Living Organisms are ______.
cell, tissue, organ, organism
cell, organism, tissue, organ
none of these
organ, tissue, cell, organism
The fuction of the nucleus is to ______.