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Science Class 8 - Cell Notes

Comprehensive study notes for Class 8 - Cell olympiad preparation

Cell

Welcome to the chapter on Cell for Class 8. In this chapter, you will learn about the basic unit of lifeā€”the cell. You will understand the structure of cells, their types, and their functions. By the end of this chapter, you will be able to describe the parts of a cell and explain why cells are important for all living things!

Introduction

All living things are made up of tiny building blocks called cells. Cells are the smallest units of life and carry out all the basic functions needed for living.

Discovery of the Cell

The cell was first discovered by Robert Hooke in 1665 when he looked at a thin slice of cork under a microscope. He saw small box-like structures and called them "cells".

Types of Cells

  • Plant Cells: Found in plants. They have a cell wall and chloroplasts.
  • Animal Cells: Found in animals. They do not have a cell wall or chloroplasts.

Structure of a Cell

  • Cell Membrane: The outer covering that protects the cell and controls what goes in and out.
  • Cytoplasm: The jelly-like substance inside the cell where many activities happen.
  • Nucleus: The control center of the cell. It contains genetic material (DNA).
  • Cell Wall: Found only in plant cells. It gives shape and support.
  • Chloroplasts: Found only in plant cells. They help make food using sunlight.
  • Vacuole: Stores water, food, and waste.

Functions of Cell Organelles

  • Nucleus: Controls cell activities and stores genetic information.
  • Mitochondria: Produces energy for the cell (known as the "powerhouse").
  • Chloroplasts: Help plants make food by photosynthesis.
  • Vacuole: Stores materials needed by the cell.

Differences Between Plant and Animal Cells

  • Plant cells have a cell wall; animal cells do not.
  • Plant cells have chloroplasts; animal cells do not.
  • Plant cells usually have a large vacuole; animal cells have small vacuoles.

Cell Theory

  • All living things are made up of cells.
  • Cells are the basic units of life.
  • All cells come from pre-existing cells.

Fun Activity: Observe Onion Cells

Take a thin peel of onion and place it on a slide. Add a drop of water and cover with a cover slip. Observe under a microscope. Draw what you see!

Summary

  • Cells are the basic units of life.
  • Plant and animal cells have different structures.
  • Cell organelles have special functions.
  • Cell theory explains the importance of cells.

Practice Questions

  1. Who discovered the cell?
  2. Name two differences between plant and animal cells.
  3. What is the function of the nucleus?
  4. What does the cell membrane do?
  5. Why are mitochondria called the "powerhouse" of the cell?

Challenge Yourself

  • Draw and label a plant cell and an animal cell.
  • List three organelles found in plant cells but not in animal cells.

Did You Know?

  • Some organisms, like bacteria, have only one cell!
  • Red blood cells do not have a nucleus.

Glossary

  • Cell: The smallest unit of life.
  • Organelle: A small part inside a cell with a special job.
  • Nucleus: The control center of the cell.
  • Cell Membrane: The outer covering of the cell.
  • Chloroplast: The part that helps plants make food.

Answers to Practice Questions

  1. Robert Hooke
  2. Plant cells have a cell wall and chloroplasts; animal cells do not.
  3. It controls cell activities and stores genetic information.
  4. It protects the cell and controls what enters and leaves.
  5. Because they produce energy for the cell.

Cells are amazing! Explore more under the microscope and discover the building blocks of life.

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