CBSE – 8th Standard Science

Cell Structure And Functions

Discovery of the Cell

  • Robert  Hooke in 1665 observed slices of cork under a simple magnifying device. Hooke coined the term ‘cell’

image001

The Cell

  • Cells in the living organisms, are basic structural units, cells are assembled to make the body of every organism. The egg of a hen represents a single cell and is big enough to be seen by the unaided eye.

 

Variety in Cell Number, Shape and Size

  • There are millions of living organisms. They are of different shapes and sizes. Their organs also vary in shape, size and number of cells

 

Number of Cells

  • Different groups of cells perform a variety of functions. Organisms made of more than one cell are called multicellular organisms.
  • The single-celled organisms are called unicellular organisms. A single-celled organism performs all the necessary functions that multicellular organisms perform.
  • A single-celled organism, like amoeba, captures and digests food, respires, excretes, grows and reproduces. Similar functions in multicellular organisms are carried out by groups of specialised cells forming different tissues. Tissues, in turn, form organs.

 

Shape of Cells

  • The different shapes are related to their specific functions, cells are round,
  • spherical or elongated , spindle shape Cells sometimes are quite long.
  • Some are branched like the nerve cell or a neuron.

 

image002

Size of Cells

  • The size of cells in living organisms may be as small as a millionth of a metre or may be as large as a few centimeters

 

Cell Structure and Function

  • Each living organism has many organs. Each organ is further made up of smaller parts called tissues. A tissue is a group of similar cells performing a specific function.

 

Parts of the Cell

image004

  • The basic components of a cell are cell membrane, cytoplasm and nucleus

Cell Membrane

 

  • The cytoplasm and nucleus are enclosed within the cell membrane, also called the plasma membrane. The membrane separates cells from one another and also the cell from the surrounding medium.

.

  • The boundary of the cell is the cell membrane covered by another thick covering called the cell wall.

 

Cytoplasm

  • The jelly-like substance between the nucleus and the cell membrane is called cytoplasm. Various other components, or organelles, of cells are present in the cytoplasm are mitochondria, golgi bodies, ribosomes, etc.

Nucleus

  • The central dense round body in the centre is called the nucleus.. Nucleus is separated from the cytoplasm by a membrane called the nuclear membrane. This membrane is porous and allows the movement of materials between the cytoplasm and the inside of the nucleus.
  • Small spherical body in the nucleus is called the nucleolus.
  • Nucleus contains thread-like structures called chromosomes. These carry genes and help in inheritance or transfer of characters from the parents to the offspring. .
  • Nucleus, in addition to its role in inheritance, acts as control centre of the activities of the cell.
  • The entire content of a living cell is known as protoplasm. It includes the cytoplasm and the nucleus. Protoplasm is called the living substance of the cell.
  • The cells having nuclear material without nuclear membrane are termed prokaryotic cells. The organisms with these kinds of cells are called prokaryotes bacteria and blue green algae.
  • The cells, having well organised nucleus with a nuclear membrane are eukaryotic cells.

image005

image007 image008 image010

 

CBSE 8th Standard Science

CTN’s handcrafted quick & easy revision notes to help the students understand the concepts and revise the chapters.

You will also get comprehensive question bank which will not only help the student prepare for the exams, but also get also secure better grades and marks.

CBSE 8th Standard Science Syllabus and Revision Notes

  • Crop Production & Management
  • Microorganisms – Friends & Foe
  • Synthetic, Fibers & Plastic
  • Materials – Metals & Non-Metals
  • Coal & Petroleum
  • Combustion & Flame
  • Conservation Of Plants And Animals
  • Cell Structure And Functions
  • Reproduction In Animals
  • Reaching The Age Of Adolescence
  • Force And Pressure
  • Friction
  • Sound
  • Chemical Effects Of Electric Current
  • Some Natural Phenomena
  • Light
  • Stars And The Solar System
  • Pollution Of Air And Water