Class-9-Biology-Cell

Class 9 Science - The Fundamental Unit of Life (Cell)

CELL:-

Cells are the basic structural, functional, and biological units of all living organisms. They vary in size, shape, and function. Studying cells helps in understanding the life processes, growth, reproduction, and physiology of living beings.

HISTORY OF DISCOVERY OF CELL:-

1. 1665: Robert Hooke observed cell walls in cork tissue under a microscope and coined the term 'cell'. 2. Anton van Leeuwenhoek observed living cells in pond water and other sources.

3. 1838-1839: Schleiden and Schwann proposed that all plants and animals are made of cells.

4. 1855: Rudolf Virchow stated that all cells arise from pre-existing cells. 

CELL THEORY:- 

*All living organisms are composed of one or more cells.

* The cell is the basic unit of life, structure, and function.

* Cells arise only from pre-existing cells.

* The activity of an organism depends on the total activity of independent cells. 

TYPES OF CELL:-

1. Prokaryotic Cells:-

*No true nucleus or membrane-bound organelles. -

*Examples: Bacteria, Blue-green algae. 

2. Eukaryotic Cells:-

* Have a true nucleus and membrane-bound organelles.

* Examples: Plant cells, Animal cells, Fungi.

STRUCTURE OF A CELL AND ORGANELLES:- 

Cell Membrane: Semi-permeable, controls entry and exit of substances.

Cytoplasm: Jelly-like substance, supports organelles, site for metabolic reactions.

Nucleus: Contains DNA, controls cell activities, surrounded by nuclear membrane.

Nucleolus: Inside nucleus, produces ribosomes.

Mitochondria: Produces ATP through respiration.

Endoplasmic Reticulum (Rough & Smooth): Transport system, protein synthesis (RER), lipid synthesis (SER).- Ribosomes: Protein synthesis.

Golgi Apparatus: Modifies, stores, and packages proteins.

Lysosomes: Contain digestive enzymes to break down waste.

Plastids (Plant cells): Chloroplasts for photosynthesis, Chromoplasts for color, Leucoplasts for storage.-Vacuoles: Store water, nutrients, and waste; large in plant cells.  

DIAGRAMS:- 

Refer to NCERT Class 9 Science diagrams for Plant Cell and Animal Cell.

Key labels include: Nucleus, Nucleolus, Cell Membrane, Cytoplasm, Mitochondria, Chloroplast (plant), Vacuole, ER, Golgi Apparatus, Ribosomes. 

FUNCTION OF CELL ORGANELLES:- Nucleus: Controls all cellular activities. 

Mitochondria: Produces energy for the cell.

Ribosomes: Protein synthesis.

ER: Transport of materials.- Golgi: Packaging of proteins.

Lysosomes: Digestive functions. 

Chloroplasts: Photosynthesis (plant cells).

Vacuoles: Storage and maintenance of turgor pressure.

DIFFERENCES BETWEEN PLANT AND ANIMAL CELLS:-

PLANT CELL:-

*Cell wall is present.

*Vacuoles are generally larger. 

*They contain plastids.

ANIMAL CELL:-

*Cell wall is absent.

*Vacuoles are smaller in size.

*Plastids are absent.