Animal Cells and Plant cells –Cell Structure and functions Class 8 NCERT Notes

Animal cells

Let’s begin with the components of the animal cells:-

Cell membrane

A cell is always surrounded by a thin membrane called plasma membrane.

The membrane has the following functions:-

• It encloses the various cell structure and cytoplasm.
• It gives definite shape to the cell.
• It regulates the movement of substance into and from the cell. Only certain substances are allowed to enter or leave the cell so the membrane is selectively permeable membrane.

#Selectively permeable means something which is permeable allows material to pass in and out of it freely.

Nucleus 

• The the most important organelle which controls all the vital activities of a cell is the nucleus.
• It may be spherical or oval.
• It is enclosed by a membrane called nuclear membrane filled with nucleoplasm.
• It contains thread like structures arranged in a network called the chromatin
• At the time of cell division chromatin threads get called become shorter and thicker forming chromosomes, each of which carries large number of genes.

# Genes controls and organisms hereditary character which are   passed down from the parent cell to the new cell.

 Mitochondria 

• Mitochondria are the powerhouse of the cell they are essential for the completion of the respiratory process, which ends with the release of energy following the breakdown of food.
• Mitochondria is a simple rod shaped or spherical body with double membrane.
• The inner membrane has several folds which project inwards, forming   finger like structures called cristae.
  The cell may have a few hundred to a few lakh mitochondria.

Centrosome 

• This small body lies in cytoplasm close to the nucleus.
• It contains two minute granules called centrioles, which help in cell division.

Plant cell

A plant cell is enclosed not only by the plasma membrane but also by a wall called the cell wall.

Also Check –Cell Structure and Its Function

Cell wall of Plant cell

It is made of nonliving substance called cellulose, a kind of carbohydrate.

Functions of cell wall in  the plant cell

• It gives a definite shape to the plant cell.
• It makes the cell rigid and strong.
• Cell wall provides protection against variations in temperature, atmosphere moisture
• Prevents water loss.
• It protects the cell from injury.
• It allows all substance to enter and leave the cell.

Plant cells have all the structure mentioned in the animal cell except centrosome. In addition they have following organelles.

Plastids-

• Plastids are organelles containing pigment.
• They are covered by double membrane.
• Their shape varies from round to filamentous.

Plastids are of following types: –

Chloroplasts- 

These  Plastids have a green pigment called chlorophyll.  This gives plants their green colour.

Functions of chloroplast

• Chloroplasts plays Vital role in photosynthesis.
• Chloroplast helps the plant by trapping solar energy, which is then used to convert carbon dioxide and water to carbohydrates.
• Chloroplast are essential for survival of not only plants, but also all other organisms which depend on plants to fulfill their carbohydrate requirement.

Chromoplasts 

• All The Other color which we see in plants are produced by Chromoplasts.
• For example, red, orange and yellow of ripe fruits and flowers are produced by this color Plastids.

Leucoplasts

• These are colorless plastids found in roots and underground stems, such as potatoes and Ginger.
• They store food like  starch proteins and fats.
• Some leucoplasts turn into chloroplast when exposed to sunlight.

 Vacuoles

• This bodies are like sacs or cavities.
• The contain the fluid called  cell sap,  which consists of water ,sugar ,amino acids,  enzymes, salt, nitrogenous waste, and so on.

The functions of vacuoles are as follows

• It maintains the shape of the cell.
• It maintains the balance of water in the cell.
• It stores Chemicals, food, water and salts.

Nonliving substance

• A plant cell contains various non-living substances which are the products of its metabolic activities this substance as a whole are called cell inclusion.
• They Include various types of carbohydrates, proteins, fats, oils and some waste products like resin, gums and mineral crystals.