General Science Notes Chapter 10 Cell and Cell Organelles Class 8 Maharashtra Board

Notes For All Chapters – General Science Class 8

1. Introduction to Cells

• The cell is the basic unit of life in all living organisms.
• Robert Hooke discovered the cell in 1665 while observing cork under a microscope.
• All living things are made of one or more cells.

2. Types of Organisms Based on Cells

3. Structure of a Cell

Each cell has three main parts:

1. Plasma Membrane (Cell Membrane) – The outermost layer that controls what enters and exits the cell.
2. Cytoplasm – A jelly-like fluid inside the cell that contains organelles.
3. Nucleus – The control center of the cell that contains DNA.

4. Cell Organelles and Their Functions

(A) Plasma Membrane

• The outermost layer of animal cells and found below the cell wall in plant cells.
• It is semi-permeable, meaning it allows only specific substances to pass in and out.

(B) Cytoplasm

• A jelly-like fluid where all organelles are present.
• Many chemical reactions occur here, helping the cell to function.

(C) Nucleus

• The brain of the cell that controls all activities.
• Contains chromosomes, which are made of DNA (genetic material).
• The nucleolus inside the nucleus produces ribosomes.

(D) Mitochondria (Powerhouse of the Cell)

• Produces energy (ATP) through cellular respiration.
• More mitochondria are found in active cells like muscle cells.

(E) Endoplasmic Reticulum (ER) – Transport System of the Cell

• Network of tubes that help in transporting substances inside the cell.
• Types:
  • Smooth ER – Produces lipids and fats.
  • Rough ER – Has ribosomes and helps in protein transport.

(F) Ribosomes – Protein Factories

• Small structures that make proteins needed for the cell.
• Found floating in cytoplasm or attached to the rough ER.

(G) Golgi Complex – Packaging Unit of the Cell

• Modifies, packages, and transports proteins and lipids.
• Helps in making enzymes and hormones.

(H) Lysosomes – “Suicide Bags” of the Cell

• Contain digestive enzymes that break down waste materials and damaged cell parts.
• If a lysosome bursts, it can destroy the whole cell, which is why it is called a suicide bag.

(I) Vacuoles – Storage Units of the Cell

• Store water, food, and waste.
• Large in plant cells to maintain turgor pressure, keeping the plant upright.

(J) Plastids – Color and Food Factories (Only in Plant Cells)

• Found only in plant cells and responsible for food production and storage.

Types of Plastids:

1. Chloroplasts – Contain chlorophyll, which helps in photosynthesis (green color).
2. Chromoplasts – Contain color pigments that give fruits and flowers red, yellow, and orange colors.
3. Leucoplasts – Store starch, proteins, and fats (colorless).

5. Differences Between Plant and Animal Cells

6. Functions of Important Pigments in Plants

7. Important Functions of the Cell Organelles