The Cell

Todays topic for ICSC|Chemistry|Class6 is Water. All living organisms i.e plants, animals,human beings and micro-organisms are made up of cells.So cells are called the building blocks of the body.Cells participate in all the body functions so the different functions or activities of the body are actually the result of activities of cells. Hence a cell is known as the functional and structural unit of life. A cell may or may not have its independent existence.

Cells are generally so small that we can't see them with naked eyes. They can only be seen with the help of a microscope. Microscope was invented by Anton Von Leeuwenhoek. It was a simple microscope as it consisted of only one lens. He was the first who observed bacteria, protozoa, blood cells in frog's capillaries but he didn't give them the name cell.

Robert Hooke discovered a microscope with two lenses known as the compound microscope. He studied the outer layer of a tree's bark known as cork and observed tiny box like structures in that bark. He called them 'cells'. So Robert Hooke discovered cell in 1665.The word cell was derived from a Latin word 'cellula' meaning small compartments.

All cells have definite life span. The life of organisms start from a single cell which grows and divide to form new cells. Group of cells form tissues . Similar tissues join together to form organs like brain, kidneys, larynx,heart etc. Organs with similar functions work together to form an organ system such as the respiratory system, the excretory system etc. All the organ systems work together and form an organism.

Depending upon the number of cells, there are two types of organisms -

(a) Single celled or unicellular organisms - They consist of only one cell. For example - amoeba, paramecium, bacteria etc.

(b) Multicellular organisms - They consist of more than one cell. For example - plants, animals, human beings etc.

Shape of the cells

Cells have different types of shapes -

1.Oval - These cells are egg shaped. For example - chlamydomonas, eggs etc.

2.Elongated - These cells are contractile and elongated in shape. They have the capacity of becoming longer and shorter. For example - muscle cells.

3.Oblong - These cells somewhat long and elliptical.For example - paramecium (slipper shaped).

4.Irregular - These cells don't have any particular shape. For example - amoeba, white blood cells.

5.Thread like - These cells are like bundles of threads or fibres. For example - nerve cells.

6.Flat cells - These cells are flat. For example - Cells found in the skin's outer layer in human beings and animals.

Size of the cells

Cells are of different sizes as mentioned below -

The unit used for measuring the size of the cell is micrometre or micron. Its symbol is μ.There are 1000 micrometres in 1 millimetre. The average size of the cell ranges between 0.0001 mm to 12 inches. For example -

1.The size of the cell of bacteria ranges from 0.2 to 0.5 μ.

2.The size of the cell of hen ranges from 6 cm.

3.The size of the cell of ostrich ranges from 23 cm.

5.The size of the cell of nerve cell of elephant ranges from 8 m.

Structure of the cell

All living organisms consist of cells. Cell is the smallest unit in the body which is responsible for all the functions and life processes. A cell consists of -

1.Cell wall

2.Cell membrane or plasma membrane

3.Cytoplasm

4.Nucleus

5.Cell organelles

1.Cell wall - It is found only in the plant cells. It is a thick, protective outer covering of the plant cells present around the plasma membrane. It allows the movement of substances inside and outside the cell without any hindrance as it is freely permeable.

2.Cell membrane or plasma membrane - It is thin and delicate and is present in both plant and animal cells. It forms the outer covering of the cells in animals while in plants it is present on the inner side or next to the cell wall. It only allows some selective substances to move in or out as it is selectively permeable. It helps in providing shape to the cell and protects it from injuries.

3.Nucleus - It is spherical or oval in shape. It controls the functioning of the cell. Hence it is known as the control centre of the cell. It is protected by a double membrane. This membrane encloses a fluid called nucleoplasm. Thread like structures present in the nucleoplasm form a network known as the chromatin network that forms the chromosomes. These chromosomes carry genes which are responsible for passing hereditary characters from parents to offsprings. Nucleus helps in the process of cell division.

4.Cytoplasm - The space between the nucleus and the plasma membrane is filled with a clear fluid known as cytoplasm. Cytoplasm always keeps on moving and helps in transferring nutrients within the cells.It also helps in exchanging materials between different cell organelles. Many chemical reactions take place in the cytoplasm.

Cell organelles

A cell organelle is a type of subcellular structure that performs one or more functions inside the cell. They are present in the cytoplasm.

*Mitochondria

They are also known as the powerhouse of the cell.They may be rod-shaped or spherical and consist of two membranes - inner and outer. The inner membrane of mitochondria is folded into finger shaped structures known as cristae. Cellular respiration takes place here which releases energy in the form of ATP. The full form of ATP is Adenosine Triphosphate.

Food + Oxygen ➡CO2 + H2O + Energy

*Endoplasmic Reticulum

ER or Endoplasmic Reticulum is a type of network that consists of channels with double membranes. They are present in the cytoplasm all over. ER is of two types. These are -

(a) Smooth ER - It doesn't have ribosomes on its surface.

(b) Rough ER - It has ribosomes on its surface.

*Ribosomes - They are known as protein factory as they help in the formation of proteins. They occur in the form of small granules in the cytoplasm or also found on the outer side of the ER.

*Golgi bodies

They consist of flattened, parallel discs. They are unconnected and small in size. In plant cells, they occur in large numbers. They can also be found attached with endoplasmic reticulum.They help in the formation of cell walls in the cells of plants.They help in the secretion of enzymes and hormones. They help in transferring nutrients or materials outside or within the cell.

*Lysosomes

They are also known as the suicide bags of the cell.They are small in size and consist of a single membrane. They consist of enzymes that help in the process of digestion of food within the cell. They can also produce enzymes that can digest other cell organelles.They also play the important role of protecting the cell from foreign bodies.

*Centrosome -

It is found only in the cells of animals. It is small in size, membraneless and occurs near the nucleus. It has two small granules known as centrioles. It controls the division of the cell.

*Plastids

They are found only in the plant cells and consist of two membranes.They are of three types -

(a) Chromoplasts - These plastids are found in fruits and flowers and impart orange, red or yellow colours to them. They don't give green colour.

(b) Chloroplasts- These plastids impart green colour to the leaves with the help of a pigment known as chlorophyll.

(c) Leucoplasts - These plastids are colourless. They mostly help in the storage of food in the form of proteins, fats and starch. They are mostly found in underground stems such as ginger or the roots of the plants.

*Vacuoles - They are found in both plant and animal cells and are filled with fluid. They consist of a single membrane. They are small in animal cells and large in plant cells. They have a single membrane known as Tonoplast. They give shape to the cell and help in the storage of nutrients and water.

Cell division

This process is important for the development and growth of the cell. In this process, two new daughter cells are formed by the division of a cell.

Hope this topic The Cell for ICSC|Chemistry|Class 6 would be quiet helpful for you. You can also practice Worksheets for Science related to this topic. Please share it and comment if you want article on any other topic.

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