- Crop Production & Management
- Microorganisms – Friends & Foe
- Synthetic, Fibers & Plastic
- Materials – Metals and Non Metals
- Combustion and Flame
- Conservation Of Plants And Animals
- Coal & Petroleum
- Cell Structure And Functions
- Reproduction In Animals
- Reaching The Age Of Adolescence
- Force And Pressure
- Chemical Effects Of Electric Current
- Some Natural Phenomena
- Stars And The Solar System
- Pollution Of Air And Water
- Question Bank – Chapter 1 – Crop Production & Management
- Question Bank – Chapter 2 – Microorganisms
- Question Bank – Chapter 3 – Synthetic Fibres and Plastics
- Question Bank – Chapter 4 – Metals and Non Metals
- Question Bank – Chapter 5 – Coal & Petroleum
- Question Bank – Chapter 6 – Combustion and Flame
- Question Bank – Chapter 7 – Conservation of Plants and Animals
- Question Bank – Chapter 8 – Cell Structure & Functions
- Question Bank – Chapter 9 – Reproduction
- Question Bank – Chapter 10 – Reaching the age of adolescence
- Question Bank – Chapter 11 – Force and Pressure
- Question Bank – Chapter 12 – Friction
- Question Bank – Chapter 13 – Sound
- Question Bank – Chapter 14 – Chemical Effects of Electric Current
- Question Bank – Chapter 15 – Some Natural Phenomena
- Question Bank – Chapter 16 – Light
- Question Bank – Chapter 17 – Stars and Solar System
- Question Bank – Chapter 18 – Pollution of Air & Water
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’
- 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.
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
- The basic components of a cell are cell membrane, cytoplasm and nucleus
- 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.
- 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.
- 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.