Science Class 11 - Cell Structure-And-Functions Notes

Cell: Structure and Functions

Welcome to the chapter on Cell: Structure and Functions for Class 11. In this chapter, you will learn about the basic unit of life—the cell, its structure, types, and the functions of its various organelles. By the end of this chapter, you will understand how cells work together to form living organisms and how their structure relates to their function.

Introduction

All living organisms are made up of cells. The cell is the smallest unit of life that can carry out all the basic functions necessary for life. Cells can exist as single-celled organisms (unicellular) or as part of multicellular organisms.

Discovery of the Cell

• Robert Hooke discovered cells in 1665 while observing a thin slice of cork under a microscope.
• Anton van Leeuwenhoek was the first to observe living cells.

Cell Theory

• All living things are made up of cells.
• The cell is the basic unit of structure and function in living things.
• All cells arise from pre-existing cells.

Types of Cells

• Prokaryotic Cells: Simple cells without a nucleus (e.g., bacteria).
• Eukaryotic Cells: Complex cells with a true nucleus (e.g., plant and animal cells).

Structure of a Cell

• Cell Membrane: Outer covering that controls what enters and leaves the cell.
• Cytoplasm: Jelly-like substance where cell organelles are found.
• Nucleus: Control center of the cell, contains genetic material (DNA).
• Cell Wall: (Plant cells only) Rigid outer layer that gives shape and protection.
• Chloroplasts: (Plant cells only) Contain chlorophyll for photosynthesis.
• Mitochondria: Powerhouse of the cell, produces energy.
• Endoplasmic Reticulum (ER): Network for transport of materials.
• Golgi Apparatus: Packages and distributes proteins and other materials.
• Vacuole: Storage space for water, food, and waste (large in plant cells).
• Lysosomes: Contain enzymes for digestion (mainly in animal cells).

Differences Between Plant and Animal Cells

• Plant cells have a cell wall and chloroplasts; animal cells do not.
• Plant cells have a large central vacuole; animal cells have small vacuoles.
• Animal cells have lysosomes; plant cells usually do not.

Functions of Cell Organelles

• Nucleus: Controls cell activities and stores genetic information.
• Mitochondria: Produce energy by breaking down food.
• Chloroplasts: Make food in plant cells by photosynthesis.
• Golgi Apparatus: Modifies, sorts, and packages proteins.
• Endoplasmic Reticulum: Transports materials within the cell.
• Vacuole: Stores water, food, and waste.
• Lysosomes: Digest unwanted materials.

Practice Questions

1. Who discovered the cell?
2. Name two differences between plant and animal cells.
3. What is the function of mitochondria?
4. What is the control center of the cell?
5. What is the basic unit of life?

Challenge Yourself

• Draw and label a plant cell and an animal cell. Mark at least five organelles in each.
• Explain why cells are called the "building blocks of life."

Did You Know?

• The human body has trillions of cells!
• Red blood cells do not have a nucleus when mature.

Glossary

• Organelle: A small part inside a cell with a special job.
• Prokaryote: A cell without a nucleus.
• Eukaryote: A cell with a nucleus.
• Photosynthesis: The process by which plants make food using sunlight.

Answers to Practice Questions

1. Robert Hooke
2. Plant cells have a cell wall and chloroplasts; animal cells do not. Plant cells have a large vacuole; animal cells have small vacuoles.
3. Mitochondria produce energy for the cell.
4. Nucleus
5. Cell

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Understanding cells helps us understand all living things. Explore the microscopic world!