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Note on The Cell

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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 cell theory

The theory of cell is summed up in the following points:

  1. All the living organisms are composed of small living units called cells.
  2. All the cells are fundamentally similar in chemical compositions and metabolic activities.
  3. The entire cell arises from pre-existing cell.
  4. The cells are structural and functional units of life.
  5. The growth of multicellular organism is occurred by cell division and that of unicellular organism is occurred by cellular growth.

Shape and size of the cell

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 and Eukaryotic Cells

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.

Parts of Eukaryotic Cells

Eukaryotic cells can be divided into following three major parts:

  • Cell wall and cell membrane
  • Cytoplasm
  • Nucleus
Cell wall and cell membrane

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:

  1. It provides fixed shape and mechanical strength.
  2. The cell wall of root caps absorbs water and minerals from the soil.
  3. It protects the inner content of the cell.

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:

  1. It helps in feeding and locomotion in a unicellular organism.
  2. It helps in excretion in a unicellular organism.
  3. It helps in transportation by the process of diffusion.

Cytoplasm

Cytoplasm

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:

Mitochondria

Mitochondria

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

Endoplasmic reticulum and ribosome

It is a doubled layered membrane. The major functions of endoplasmic reticulum are as follows:

  1. It increases the surface area in the cell for metabolism.
  2. It provides mechanical support to the cell.
  3. It provides the pathway for transportation of materials.

Ribosomes are small round structures found in the cytoplasm and consider as protein factories as they synthesize protein.

golgi-apparatus

Golgi bodies

The major functions of Golgi bodies are as follows:

  1. It stores, condenses and packages the materials like protein, lipids etc.
  2. It is involved in cell secretion.
  3. It forms lysosomes, hormones etc.

lysosome

Lysosomes

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:

  1. They help in digestion of unnecessary material inside a cell.
  2. They also help in extracellular digestion.

centrosome

Centrosome

They are found only in animal cells.

The major functions of centrosome are as follows:

  1. They form asters during cell division.
  2. It controls the movement of cilia and flagella.

Plastids

Plastids

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.

vacuole

Vacuole

They are fluid filled sacs bounded by a single membrane called tonoplast.

The major functions of vacuole are as follows:

  1. They balance amount of glucose and water in cells.
  2. They store waste products and helps in excretion.

Cell Nucleus

Nucleus

It is very important part of a cell. It is a spherical structure that consists of four major components of it. They are:

  1. Nuclear membrane: It maintains the shape of the nucleus and regulates the nucleocytoplasmic interactions.
  2. Nucleoplasm: It provides the site of enzyme activities .
  3. Chromatin fibers: They shorten and thicken during cell division and divide in particular members into the cells of particular organisms called chromosomes.
  4. Nucleolus: It controls all cellular activities of the cells and forms ribosomes.

Differences between plant cell and animal cell

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 outermost, rigid, protective layer found in cells is known as cell wall.
  • The non-crystalline, translucent substance found in between the plasma membrane and nucleus is known as cytoplasm.
  • Ribosomes are small round structures found in cytoplasm and consider as protein factories as they synthesize protein.
  • Usually animal cells are smaller and have irregular shape.
  • A cell can be defined as the protoplasm surrounded with cell membrane, which works as structural and functional unit of life
  • All the cells are fundamentally similar in chemical compositions and metabolic activities.
  • The cells may be prokaryotic or eukaryotic.
  • Eukaryotic cells can be divided into following three major parts: Cell wall and cell membrane, Cytoplasm and Nucleus.
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Very Short Questions

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.

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  • Which of the following are not found in plant cells?

    Glyoxysomes
    Mitochondria
    Centrosomes
    Golgi apparatus
  • Which of the fllowng organelles do plant and animals have in common?

    mitochondria,endoplasmic reticulum and cholorplast
    mitochondria, endoplasmic reticulum and golgi bodies
  • What do plant cell have that aniaml cells do not?

    plants have vacuole and nucleus


    plants have a nuleus and mitochondria


    plants have a nucleus and a cell membrane


    plants have a cell wall and choloplast


  • What is the function of the cytoplasm?

    a jelly-like substance that holds al the organelles in place


    contain the pigment called chlorophyll


    transport food, water and waste around and out the cell


    releases energy in the cell


  • The Levels of Organization of Living Organisms are ______.

    organ, tissue, cell, organism


    cell, organism, tissue, organ


    cell, tissue, organ, organism


    none of these


  • The fuction of the nucleus is to ______.

    Control all the activiities of the cell; act as the brain
    tranport materials around and out of the cell
    Control protein production
    ?release energy in the cell
  • What type of cells have a cell membrane?

    animal cell
    both
    plant cell
    none of these
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Yadiel

what is cellular respiration?


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guddu

write the types ofpermanent tissues in short


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