Structure of the cell–Cell Structure and functions Class 8 NCERT Notes

Cell Structure

Structure of the cell

Cell Structure

The cell is a tiny sac bounded by thin skin or membrane. It is filled with a semifluid substance call the cytoplasm.
Tiny living bodies called organelles lie suspended in the cytoplasm.

The basic components of the cell are

  • Cytoplasm

  • Cell membrane

  • Nucleus

  • Organelles

Cytoplasm

The word cytoplasm came from
kytos– means Hollow
plasma— means liquid

Cytoplasm is a thick substance that fills  each cell and is enclosed by the cell membrane.  It is mainly Composed of water, proteins etc.

Also Check–Shape and Size of Cell

Cell membrane

The cell membrane is also called as  Plasma membrane or Cytoplasmic membrane.   Cell membrane separates interior of all cells from the outside surroundings.

Functions of cell membrane

  • It protects the cell and gives it a shape.
  • It allows water, minerals and some other necessary substances to pass through it.

Plant cells have cell wall which is absent in animal cell. Since plants do not have  skeleton  for support.

Nucleus

  • A small spherical body floating   within the cytoplasm in the center of the cell is called as the  Nucleus( plural: nuclei).
  • Nucleus is separated from cytoplasmby a thin membrane called as nuclear membrane.
  • Nuclear membrane is porous and allows the movement of material between cytoplasm and nucleus.

What is there inside the nucleus??

  • Liquid which is present in nucleus is called as the Nucleoplasm.
  • A smaller spherical body present inside the nucleus is called as
  • Thread like structure present inside the nucleus are called as chromosomes.

Functions of chromosomes

  • Chromosomes carry genes which contains the information needed by the cell to reproduce for the cells of the next generation.
  • Genes are responsible for inheritance that is transferring of characteristics from parents to offspring.
  • The nucleus is the control center or brain of the cell.
    it Direct growth of the cell and controls all the activities that go on within the cell.

Protoplasm

The nucleus and cytoplasm together make the Protoplasm. It is the living substance of the cell.

The main constituent elements of Protoplasm are

  • Carbon

  • Hydrogen

  • Oxygen

  • Nitrogen and many other elements.

Organelles

In the cytoplasm there are small structures called organelles.

Different types of organelles of the Cell and their functions

Each organelle present in the cytoplasm have different functions some of these are as follows-

Mitochondria

Mitochondria are the powerhouse of the cell. The mitochondria oxidizes food to provide energy. They are small rod like structures.

Vacuoles

Vacuoles are sac like structures.  They store food water and waste. Plant cells have large vacuoles as compared to animal cells.

Plastids

Plastids are present in the cytoplasm of plant cell. They are in different colors and types. Green color plastids are called as chloroplasts. They contain the green colour pigment called chlorophyll which provides green color to the leaves.

Golgi bodies

Golgi bodies or Golgi apparatus is made up of membrane bound sacs present inside the cytoplasm of the cell.

Functions of Golgi bodies: –

  • It secretes many enzymes which are responsible to perform functions in the cell.
  • Golgi bodies work closely with endoplasmic reticulum that helps to transport substances proteins and lipids within the cell.
  • It also secretes ribosomes that makes proteins.
  • It secretes lysosomes that helps to destroy old cell structures.
  • It also secretes centrosomes that regulate cell division.

Cilia and flagella: –

Many cells have projections   called cilia or flagella on their outer surface which helps in the movement of the cells of the organisms. Example cilia in paramecium, flagellar in euglena.

Cilia of paramecium

Euglena with Flagella

Levels of Organisation in individuals.

Organelle level

  • Protoplasm, the living matter of the cell is made up of molecules of various compounds.
  • It is organized into various cell organelles such as the nucleus, mitochondria and the Golgi bodies.
  • Each of these organelles has its own functions, which it carries out in coordination with the other organelles in order that the cell may function efficiently.

Cellular level

  • The cell is the next level of organization. Each cell is made up of specific organelle helps to carry out all the life activities.
  • In unicellular organisms like bacteria and yeast this activity takes place within the single cell.
  • In multicellular organism all the cells of the body carry out the life activities independently they also perform some functions jointly. In higher plants and animals, there is division of labor among the cells.

Tissue level

  • The tissues may be defined as a group of cells which are similar in structure and perform a specific function.
  • There are many different types of tissues in the higher organism.
  • The cells of one type of tissue are different from those of another type. For example, the cells of our skin tissue are different from those of our muscle tissue.

Organ level

  • The organ is composed of different kinds of tissues which help it to perform its functions.
  • For example heart has epithelial tissue, which   forms a lining; muscular tissue, which helps it to contract and relax; and blood, which is also a tissue.

Organ system level 

  • An organ system consists of a group of organs which work together to carry out the specific function.
  • For example our respiratory system, excretory system, digestive system etc.

The organs comprising the digestive systems are

  • Mouth
  • Teeth
  • Pharynx
  • Oesophagus
  • Stomach
  • Liver
  • Pancreas
  • Small Intestine
  • Large Intestine
  • and various Digestive Glands

 

Plants do not have such organ  but if we consider leaves, roots, stems  and flowers as organs, we can speak of certain organ system that perform specific function for example the roots, stems  and please form the conducting system, which carries water from the soil and food from the leaves.

Organism level

  • The organ system collectively forms an organism.
  • Each organ system performs specific function in coordination with other organ system to help the organism lead its life.
Cell, Tissue, Organ, Organ System

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