Chapter 2
Cellular Organisation of Plants & Animals
Class 7 Science • Exam Notes
Definitions • Key Points • Diagrams • Exam Questions • Quick Revision
Part 1 — Notes & Definitions
Lesson 1–2: General Structure of Cells
Key definitions
Cell: The basic structural and functional unit of all living organisms.
Cell wall: A hard, thick, non-living layer made of cellulose. Found ONLY in plant cells.
Protects the cell and sets its boundary.
Protoplasm: A semisolid, jelly-like living substance inside the cell. Contains 67–90%
water. Has 3 parts: cell membrane, cytoplasm, and nucleus.
Cell membrane (Plasma membrane): A soft thin membrane made of phospholipids
bilayer surrounding the entire protoplasm. Also called bio-membrane. Controls
movement of water, minerals and gases in and out of the cell.
Cytoplasm: Jelly-like substance outside the nucleus. Contains all cytoplasmic
organelles.
Nucleus: The densest part of protoplasm, surrounded by a membrane. Controls all cell
activities. Has 4 parts: nuclear membrane, nucleolus, nuclear reticulum, nucleoplasm.
Remember: A typical plant cell = Cell wall + Protoplasm. Animal cells have NO cell wall
— only a plasma membrane.
Lesson 3–5: Cytoplasmic Organelles (8 types)
, All 8 organelles — definitions
1. Plastid: Round or elliptical organelles found ONLY in plant cells. Functions:
synthesis, pigmentation & storage of food.
2. Mitochondria: Small rod-like organelles in both plant and animal cells. Surrounded
by two membranes (outer smooth, inner folded = cristae). Called the 'power house' of
the cell as it produces all energy for metabolic activities.
3. Golgi body: Round or thread-like organelles near the nucleus, covered by
membranes. Secretes enzymes and hormones.
4. Endoplasmic Reticulum (ER): A single-membrane reticulum inside the cytoplasm.
Two types: Smooth ER and Rough ER.
5. Ribosome: Found free in cytoplasm or as granules on the ER. Site of protein
synthesis — called the 'protein factory' of the cell.
6. Lysosome: Found in ANIMAL cells only. Enclosed in a bilayered lipoprotein
membrane. Contains hydrolytic enzymes.
7. Centriole: Two tube-like organelles near the nucleus, found in ANIMAL cells (absent
in most plant cells). Covered by non-granular cytoplasm called centrosome. Forms aster
during cell division.
8. Cell vacuole: Fluid-filled spaces containing cell sap. Plant cells have large vacuoles;
animal cells have very small or no vacuoles.
Remember: Lysosome + Centriole = animal only | Plastid + large Vacuole = plant only
| Mitochondria = power house | Ribosome = protein factory
Types of Plastids
Chromoplastids (coloured) — 2 kinds
• Chloroplast — Green colour, in green parts of plants. Contains chlorophyll pigment.
Main function: photosynthesis. Has 3 parts: covering membrane, grana, stroma.
• Chromoplast — Produces yellow, orange, and red colours in flower petals and fruits.
During fruit ripening, chloroplasts convert to chromoplasts.
Leucoplastids (colourless)
• Found in plant parts where light cannot reach (e.g. root cells).
• When exposed to sunlight, they convert to chloroplasts.
Remember: Real-life example: Red colour of tomato = lycopene pigment in
chromoplast. Grass turning white under a brick = chloroplasts converting to leucoplasts.
Brick removed = white grass turns green again.
Cellular Organisation of Plants & Animals
Class 7 Science • Exam Notes
Definitions • Key Points • Diagrams • Exam Questions • Quick Revision
Part 1 — Notes & Definitions
Lesson 1–2: General Structure of Cells
Key definitions
Cell: The basic structural and functional unit of all living organisms.
Cell wall: A hard, thick, non-living layer made of cellulose. Found ONLY in plant cells.
Protects the cell and sets its boundary.
Protoplasm: A semisolid, jelly-like living substance inside the cell. Contains 67–90%
water. Has 3 parts: cell membrane, cytoplasm, and nucleus.
Cell membrane (Plasma membrane): A soft thin membrane made of phospholipids
bilayer surrounding the entire protoplasm. Also called bio-membrane. Controls
movement of water, minerals and gases in and out of the cell.
Cytoplasm: Jelly-like substance outside the nucleus. Contains all cytoplasmic
organelles.
Nucleus: The densest part of protoplasm, surrounded by a membrane. Controls all cell
activities. Has 4 parts: nuclear membrane, nucleolus, nuclear reticulum, nucleoplasm.
Remember: A typical plant cell = Cell wall + Protoplasm. Animal cells have NO cell wall
— only a plasma membrane.
Lesson 3–5: Cytoplasmic Organelles (8 types)
, All 8 organelles — definitions
1. Plastid: Round or elliptical organelles found ONLY in plant cells. Functions:
synthesis, pigmentation & storage of food.
2. Mitochondria: Small rod-like organelles in both plant and animal cells. Surrounded
by two membranes (outer smooth, inner folded = cristae). Called the 'power house' of
the cell as it produces all energy for metabolic activities.
3. Golgi body: Round or thread-like organelles near the nucleus, covered by
membranes. Secretes enzymes and hormones.
4. Endoplasmic Reticulum (ER): A single-membrane reticulum inside the cytoplasm.
Two types: Smooth ER and Rough ER.
5. Ribosome: Found free in cytoplasm or as granules on the ER. Site of protein
synthesis — called the 'protein factory' of the cell.
6. Lysosome: Found in ANIMAL cells only. Enclosed in a bilayered lipoprotein
membrane. Contains hydrolytic enzymes.
7. Centriole: Two tube-like organelles near the nucleus, found in ANIMAL cells (absent
in most plant cells). Covered by non-granular cytoplasm called centrosome. Forms aster
during cell division.
8. Cell vacuole: Fluid-filled spaces containing cell sap. Plant cells have large vacuoles;
animal cells have very small or no vacuoles.
Remember: Lysosome + Centriole = animal only | Plastid + large Vacuole = plant only
| Mitochondria = power house | Ribosome = protein factory
Types of Plastids
Chromoplastids (coloured) — 2 kinds
• Chloroplast — Green colour, in green parts of plants. Contains chlorophyll pigment.
Main function: photosynthesis. Has 3 parts: covering membrane, grana, stroma.
• Chromoplast — Produces yellow, orange, and red colours in flower petals and fruits.
During fruit ripening, chloroplasts convert to chromoplasts.
Leucoplastids (colourless)
• Found in plant parts where light cannot reach (e.g. root cells).
• When exposed to sunlight, they convert to chloroplasts.
Remember: Real-life example: Red colour of tomato = lycopene pigment in
chromoplast. Grass turning white under a brick = chloroplasts converting to leucoplasts.
Brick removed = white grass turns green again.
