Question

write the definition of cell​

Answer 1

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Cells are the structural and the functional units of life. All the living things are made up of cells. Cells are of two types:-

$\sf{\star}$ Prokaryotic cells:-

Those cells which have nuclear material without a nuclear membrane are known as prokaryotic cells. Eg:- bacteria, blue-green algae.

$\sf{\star}$ Eukaryotic Cells:-

Those cells which have nuclear material enclosed within a nuclear membrane are known ad eukaryotic cells. Eg:- plants, animal, etc.

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$\bf{\blue{\underline{\bold{Extra\:Information}}}}$

$\sf{\huge{\red{\star}}}$ Cell theory:-

The modern cell theory state:-

• All living organisms are made up of cells.
• All the cells arise from the pre-existing cells.
• Cells are the structural and functional unit of life.
• All the cells have similar chemical composition.
• Energy flow occur within the cells.

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$\sf{\huge{\blue{\star}}}$ Parts of a cell:-

(i) Cell membrane (or plasma membrane):-

Both plant and animal cells are covered by a layer called cell membrane (or plasma membrane). Cell membrane is the outermost covering of an animal cell.

(ii) Cytoplasm:-

Cytoplasm are jelly-like material which fill the cells between nucleus and cell membrane. Most of the chemical reactions of a cell take place in cytoplasm. It is present in both animal and plant cell.

(iii) Nucleus:-

It is a sphere - shaped organelle present in all the cell. It controls all the function of a cell. It contains thin thread-like structures called chromosomes which transfer the characteristic of a parent to its offspring.

(iv) Mitochondria:-

Mitochondria are sphere-shaped organelles found in all the cells. They are power house of the cells. Respiration occurs in the mitochondria organelle of a cell.

(v) Cell Wall:-

Cell wall are the cell organelles which are found only in plant cells. They are the outermost covering of a plant cell. They regulate the exchange of food materials and gases.

(vi) Chloroplasts:-

These are the cell organelles which are found only in plant cells. These cells contain a green pigment called chlorophyll which play a vital role in the process of photosynthesis.

(vii) Large Vacuole:-

Large Vacuoles are found only in plant cells. They are enclosed within a membrane and the substances in it are usually dissolved in water. It stores various substances including waste profucts of a cell. Most of the animal cell do not have vacuole. Some animal cells have small food vacuoles.

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Answer 2

A N S W E R :

Cell - Defination :

Cell : Cell is the smallest structural & functional unit of body. Body contains several billion cells, with different size, shape and function.

• Wall $\leftrightarrow$Represents $\leftrightarrow$Animal/Plant.
• Brick $\leftrightarrow$Represents $\leftrightarrow$Cell.

$\large\star$“Building blocks of life”

$\large\star$“Fundamental unit of life”

$\large\star$“Structural or functional unit of life”

❍ Prokaryotic cell :

Prokaryotic : Prokaryotic cell have incomplete cell and they do not have nucleus.

• Archae bacteria
• Cyano bacteria
• Bacteria

❍ Eukaryotic cell :

Eukaryotic : Eukaryotic cells have advanced and incomplete cell.

• Humans
• Plants
• Animals

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$~~~~~~~~~~~~~~~~~~~$ $\large\dag$ More Information :

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❍ Cell theory :

Cell theory : Developed by microbiologist Schliden & Schwonn about properties of cell.

❍ Modern concept :

Modern concept : Activity of an organism depends on total activity of independent cell. Energy flow Occuss in cells through breakdown of carbohydrates by suspisation. Cells contain information necessary for creation of new cells (hueditary information of DNA).

★ Function of cells :

• $\longmapsto$Provides support and structure

• $\longmapsto$Facilitate growth

• $\longmapsto$Transport of substances

• $\longmapsto$AIDS in reproduction

★ Parts of cell :

(i) Plasma membrane or cell membrane.

• This is the outermost covering of the cell that separates the contents of the cell from its external environment. The plasma membrane allows or permits the entry and exit of some materials in and out of the cell. It also prevents movement of some other materials. The cell membrane, therefore, is called a selectively permeable membrane.

(ii) Cytoplasm.

• We look at the temporary mounts of onion peel as well as human cheek cells, we can see a large region of each cell enclosed by the cell membrane. This region takes up very little stain. It is called the cytoplasm. The cytoplasm is the fluid content inside the plasma membrane. It also contains many specialised cell organelles. Each of these organelles performs a specific function for the cell.

(iii) Nucleus.

• Remember the temporary mount of online peel we prepared? We had put iodine solution on the peel. Why? What would we see if we tried observing the peel without putting the iodine solution? Try it and see what the difference is. Further, when we put iodine solution on the peel, did each cell get evenly coloured? According to their chemical composition different regions of cells gate coloured differentially. Some regions appear darker than other regions. Apart from iodine solution we could also use safranin solution or methylene blue solution to stain the cells. We have observed cells from an onion; let us now observe cells from our own body.

(iv) Mitochondria.

• Mitrochondria are known as the powerhouses of the cell. Mitochondria have two membrane coverings. The outer membrane is porous while the inner membrane is deeply folded. These folds increase surface area for ATP - generating chemical reactions. The energy required for various chemical activities needed for life is released why mitochondria in the form of ATP (Adenosine triphosphate) molecules. ATP is known as the energy currency of the cell. The body uses energy stored in ATP for making new chemical compounds and for mechanical work. Mitochondria are strange organelles in the sense that they have their own DNA and ribosomes. Therefore mitochondria are able to make some of their own proteins.

(v) Cell wall.

• Every cell has a membrane around it to keep its own contacts separate from the external environment. Large and complex cells, including cells from multicellular organisms, need a lot of chemical activities to support their complicated structure and function. To keep these activities of different kinds separate from each other, these cells use membrane - bound little structures (or 'organelles') within themselves. This is one of the features of the eukaryotic cells that distinguish them from prokaryotic cells. Some of these organelles are visible only with an electron microscope. We have talked about the nucleus in a previous section. Some important examples of cell organelles which we will discuss now are: endoplasmic reticulum, Golgi apparatus, mitochondria and plastids. They are important because they carry out some very crucial functions in cells.

(vi) Large Vacuoles.

• Vacuoles are storage sacs for solid or liquid contents. Vacuoles of small sized in animal cells have very large vacuoles. The central vacuole of some plant cells may occupy 50 - 90% of the cell volume.