Chapter 8: Cell – structure and functions

These NCERT Class 8 Science Chapter 8 notes explain the structure and functions of cells in a clear and structured manner. The chapter focuses on the cell as the basic structural and functional unit of life.

It discusses the discovery of the cell, types of organisms based on number of cells and different parts of a cell such as cell membrane, cytoplasm and nucleus. It also explains cell organelles like mitochondria, ribosomes, plastids and vacuole.

Chapter 8 – Cell: Structure and Functions is important for understanding the basic unit of living organisms. It builds a strong foundation for school examinations and higher-level biology concepts.

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1. Introduction: what is a cell?

• A cell is the basic structural unit and functional unit of life.
• All living organisms like plants, animals and humans are made up of cells.
• Some organisms consist of a single cell, while others have many cells.
• Cells perform all life processes such as growth and reproduction.
• Just as bricks build a house, cells build the body of living beings.

2. Discovery of the cell

• The cell was discovered by Robert Hooke in 1665.
• He observed a thin slice of cork under a microscope.
• He saw small box-like structures and named them cells.
• The word cell means small room.
• Discovery of cells helped in understanding living organisms.

3. Types of organisms based on number of cells

• Unicellular organisms are made up of only one cell.
• In unicellular organisms, a single cell performs all life activities.
• Examples include Amoeba and Paramecium.
• Multicellular organisms are made up of many cells.
• In multicellular organisms, different cells perform different functions.

4. Shape and size of cells

• Cells differ in shape, size and function.
• Red blood cells are disc-shaped and help in transport of oxygen.
• Nerve cells are long and branched to transmit messages.
• Plant cells are generally rectangular in shape.
• Cell shape depends on the function it performs.

5. Main parts of a cell

• Every cell has three main parts: cell membrane, cytoplasm and nucleus.
• These parts work together to carry out life activities.
• Each part has a specific structure and function.
• Proper functioning of all parts keeps the cell alive.
• Cell structure is studied under a microscope.

6. Cell membrane and its function

• The cell membrane is the thin outer covering of the cell.
• It is also called the plasma membrane.
• It separates the cell from its surroundings.
• It controls the entry and exit of substances.
• It protects the inner parts of the cell.

7. Cytoplasm and its role

• Cytoplasm is a jelly-like substance present inside the cell.
• All cell organelles are suspended in the cytoplasm.
• Most life processes occur in the cytoplasm.
• It supports and protects organelles.
• Cytoplasm helps in movement of materials within the cell.

8. Nucleus and its importance

• The nucleus is usually round and located in the centre of the cell.
• It is surrounded by a nuclear membrane.
• The nucleus controls all activities of the cell.
• It contains genetic material responsible for heredity.
• The nucleus acts as the control centre of the cell.

9. Cell organelles and their functions

• Mitochondria are known as the powerhouse of the cell as they release energy during respiration.
• Ribosomes help in protein synthesis inside the cell.
• Endoplasmic reticulum (ER) helps in transport of materials and has rough and smooth types.
• Golgi apparatus modifies and packages proteins for transport.
• Vacuole is a storage sac that stores food, water and waste and is large in plant cells.

10. Plastids in plant cells

• Plastids are present only in plant cells.
• Chloroplast contains chlorophyll and helps in photosynthesis.
• Chromoplast gives colour to fruits and flowers.
• Leucoplast stores food materials.
• Plastids play an important role in plant nutrition.

11. Cell wall in plant cells

• The cell wall is present only in plant cells.
• It is made of a substance called cellulose.
• It gives strength and shape to the cell.
• It protects the plant cell from damage.
• Animal cells do not have a cell wall.

12. Plant cell and animal cell differences

• Plant cells have a cell wall, while animal cells do not.
• Chloroplast is present in plant cells but absent in animal cells.
• Plant cells have a large vacuole, while animal cells have small vacuoles.
• Plant cells usually have regular shape.
• Animal cells have irregular shape.

13. Prokaryotic and eukaryotic cells

• Prokaryotic cells do not have a true nucleus.
• Bacteria are examples of prokaryotic cells.
• Eukaryotic cells have a well-defined nucleus.
• Plant and animal cells are examples of eukaryotic cells.
• The presence or absence of nucleus is the main difference.

14. Key exam-oriented keywords explained

• Cell: Basic structural and functional unit of life.
• Microscope: Instrument used to observe very small objects like cells.
• Unicellular: Organism made of only one cell.
• Multicellular: Organism made of many cells.
• Cell membrane: Outer covering that controls entry and exit of substances.
• Cytoplasm: Jelly-like substance inside the cell where activities occur.
• Nucleus: Control centre of the cell containing genetic material.
• Mitochondria: Organelle that releases energy for the cell.
• Ribosomes: Organelle responsible for protein synthesis.
• Vacuole: Storage sac present inside the cell.
• Plastids: Plant cell organelles involved in food production and storage.
• Chloroplast: Plastid containing chlorophyll for photosynthesis.
• Cell wall: Rigid outer layer present in plant cells.

15. One-page summary for quick revision

• The cell is the basic unit of life.
• Organisms can be unicellular or multicellular.
• Cells vary in shape and size according to function.
• Cell membrane, cytoplasm and nucleus are main parts.
• Plant and animal cells differ in structure and organelles.

Understanding NCERT Class 8 Science Chapter 8 is essential to learn how living organisms are structured at the cellular level. The chapter clearly explains plant and animal cell differences and important cell organelles.

The concepts help students understand life processes and prepare for advanced biology topics. It is highly useful for school exams and foundation competitive preparation.

Continue reading NCERT Class 8 Science Chapter 9 – Reproduction in Animals to understand how living organisms produce new individuals.

FAQs

Q1. What is a cell?
A cell is the basic structural and functional unit of life.

Q2. Who discovered the cell?
The cell was discovered by Robert Hooke in 1665.

Q3. What is the difference between unicellular and multicellular organisms?
Unicellular organisms have only one cell, while multicellular organisms have many cells.

Q4. What is the function of the nucleus?
The nucleus controls all activities of the cell and contains genetic material.

Q5. Why is this chapter important for exams?
It explains the structure and function of cells, which form the foundation of biology and are important for school exams and competitive preparation.

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