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Biology · Class 9 · Chapter 4: Cells and Tissues

8 min

Key points

Cell is the basic structural and functional unit of life — all living organisms are made up of cells
Cell theory states: (1) All living things are made of cells (2) Cell is the basic unit of life (3) All cells arise from pre-existing cells
Prokaryotic cells lack membrane-bound nucleus and organelles — found in bacteria and blue-green algae
Eukaryotic cells have membrane-bound nucleus and organelles — found in plants, animals, fungi and protists
Cell membrane is selectively permeable — allows some substances to pass through while blocking others
Mitochondria is called powerhouse of cell — produces ATP energy through cellular respiration
Chloroplasts contain chlorophyll and carry out photosynthesis in plant cells
Tissue is a group of similar cells performing the same function
Meristematic tissue consists of actively dividing cells found at growing points of plants
Permanent tissues are formed from meristematic tissues and have lost the power of division

Definitions

Cell: Cell is the basic structural and functional unit of life. It is the smallest unit that can be called living.
Tissue: A tissue is a group of similar cells that perform the same function.
Prokaryotic Cell: Prokaryotic cells are those cells which lack membrane-bound nucleus and other membrane-bound organelles.
Eukaryotic Cell: Eukaryotic cells are those cells which have membrane-bound nucleus and other membrane-bound organelles.
Meristematic Tissue: Meristematic tissue consists of actively dividing cells and is found at the growing points of plants.

Worked example

Define tissue. Differentiate between simple and complex tissues in plants. (6 marks)

Tissue: A group of similar cells that perform the same function is called tissue. Simple Tissues: Tissues composed of only one type of cells are called simple tissues. Examples: Parenchyma, Collenchyma, Sclerenchyma. Complex Tissues: Tissues composed of more than one type of cells are called complex tissues. Examples: Xylem and Phloem.

Common mistakes

Students often confuse prokaryotic with eukaryotic — remember PRO means 'before' (before nucleus formation)
Writing incomplete cell theory — all three points must be mentioned
Confusing meristematic with permanent tissue — meristematic divides, permanent doesn't
Not drawing clear labeled diagrams of plant and animal cells
Mixing up functions of organelles — mitochondria for energy, chloroplast for photosynthesis

Quick recap

Cell is the basic unit of life existing as prokaryotic or eukaryotic types. Plant cells have cell wall, chloroplasts and large vacuole unlike animal cells. Tissues are groups of similar cells performing same function, classified as simple or complex in plants. Organs are made of different tissues while organ systems contain multiple organs working together.

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