What are the differences between plant cells and animal cells?

Plant cells: have cell wall (cellulose), chloroplasts, large central vacuole; no centrosome; fixed shape. Animal cells: no cell wall, no chloroplast, small vacuoles, have centrosome; irregular shape. Both have: nucleus, mitochondria, ER, Golgi apparatus, ribosomes.

What is the function of the nucleus in a cell?

The nucleus is the control centre of the cell. It contains chromosomes made of DNA which carry genetic information. It controls all cell activities, including growth and reproduction. The nucleolus inside the nucleus produces ribosomes. The nuclear membrane controls entry and exit of substances.

Why are lysosomes called the suicide bags of the cell?

Lysosomes are called suicide bags because they contain digestive enzymes. In normal conditions they digest old/damaged organelles. When a cell is damaged beyond repair, lysosomes rupture and release their enzymes, digesting the entire cell — effectively 'committing suicide' to protect the organism.

Cell Structure and Functions

The Fundamental Unit of Life • Class 9 Science • NCERT • CBSE

The cell is the fundamental structural and functional unit of all living organisms. Robert Hooke discovered cells in 1665. All cells have a cell membrane, cytoplasm, and genetic material (DNA). Cells can be prokaryotic (no nucleus) or eukaryotic (true nucleus).

Key Formulas

Osmosis: water moves from high concentration to low concentration through semi-permeable membrane
Plant cell = Cell wall + Cell membrane + Chloroplast + Large vacuole
Animal cell = Cell membrane + Small vacuole + Centrosome (no cell wall, no chloroplast)

Frequently Asked Questions

What are the differences between plant cells and animal cells?: Plant cells: have cell wall (cellulose), chloroplasts, large central vacuole; no centrosome; fixed shape. Animal cells: no cell wall, no chloroplast, small vacuoles, have centrosome; irregular shape. Both have: nucleus, mitochondria, ER, Golgi apparatus, ribosomes.
What is the function of the nucleus in a cell?: The nucleus is the control centre of the cell. It contains chromosomes made of DNA which carry genetic information. It controls all cell activities, including growth and reproduction. The nucleolus inside the nucleus produces ribosomes. The nuclear membrane controls entry and exit of substances.
Why are lysosomes called the suicide bags of the cell?: Lysosomes are called suicide bags because they contain digestive enzymes. In normal conditions they digest old/damaged organelles. When a cell is damaged beyond repair, lysosomes rupture and release their enzymes, digesting the entire cell — effectively 'committing suicide' to protect the organism.

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