Welcome to our all-in-one guide on Class 9 Science Chapter 5: The Fundamental Unit of Life! Whether you’re a Class 9 student targeting top marks in your 2025 CBSE exams, a parent helping your child, or a teacher looking for detailed resources, this blog post has everything you need. We’ll cover the in-text questions and answers, exercise solutions, and detailed notes for Chapter 5, simplifying the biology of cells into clear, easy-to-understand concepts. By the end, you’ll master the structure and functions of cells—the building blocks of life—ensuring exam success and a strong foundation in Science!
Chapter 5 introduces the cell as the basic unit of life, exploring its discovery, structure, and role in living organisms. From unicellular to multicellular life, this chapter is a gateway to Biology. Let’s dive into the Class 9 Science Chapter 5 questions, answers, and notes!
Why Study Class 9 Science Chapter 5?
Before we start, let’s see why this chapter is essential. Cells are the foundation of all living things—plants, animals, and even you! Understanding their structure and functions is key to excelling in Biology, a subject worth around 25-30 marks in the CBSE Class 9 Science syllabus. Mastering this chapter in 2025 will not only boost your exam scores but also prepare you for advanced topics in higher classes and competitive exams like NEET.
Let’s break this down into three sections: Notes, In-Text Questions and Answers, and Exercise Solutions.
Class 9 Science Chapter 5 Notes
1. Cell Discovery
- Robert Hooke (1665): Discovered cells in cork using a primitive microscope, calling them “cells” due to their box-like appearance.
- Leeuwenhoek: Observed living cells (e.g., bacteria) with improved microscopes.
- Cell Theory (1839): By Schleiden and Schwann, states:
- All living organisms are made of cells.
- Cells are the basic unit of life.
- (Later added by Virchow) Cells arise from pre-existing cells.
2. Types of Organisms
- Unicellular: Single-celled organisms (e.g., Amoeba, Paramecium).
- Multicellular: Many-celled organisms (e.g., humans, plants).
3. Cell Structure
- Plasma Membrane: Thin, flexible boundary; controls what enters/exits the cell (selective permeability).
- Cell Wall: In plants, made of cellulose; provides rigidity and support.
- Cytoplasm: Jelly-like substance where organelles reside.
- Nucleus: Control center with DNA; regulates cell activities.
4. Cell Organelles
- Mitochondria: Powerhouse; produces energy (ATP) via respiration.
- Endoplasmic Reticulum (ER):
- Rough ER: Has ribosomes, synthesizes proteins.
- Smooth ER: Synthesizes lipids.
- Golgi Apparatus: Modifies, packs, and ships proteins.
- Lysosomes: “Suicide bags”; digest waste and damaged parts.
- Vacuoles: Storage sacs; large in plant cells, small in animal cells.
- Plastids (Plants):
- Chloroplasts: Contain chlorophyll for photosynthesis.
- Leucoplasts: Store starch.
- Chromoplasts: Give color to fruits/flowers.
5. Prokaryotes vs. Eukaryotes
- Prokaryotes: No true nucleus (e.g., bacteria).
- Eukaryotes: True nucleus and organelles (e.g., plant and animal cells).
6. Cell Processes
- Diffusion: Movement of substances from high to low concentration (e.g., oxygen into cells).
- Osmosis: Water movement across a semi-permeable membrane (e.g., in plant roots).
- Active Transport: Energy-requiring movement against concentration gradient.
7. Plant vs. Animal Cells
- Plant Cells: Have cell wall, chloroplasts, large vacuole.
- Animal Cells: No cell wall or chloroplasts, small vacuoles.
These notes cover the chapter’s essentials—use them for quick revision!
In-Text Questions and Answers: Page 58
Question 1: Who discovered cells, and how?
Answer:
Cells were discovered by Robert Hooke in 1665. He observed thin slices of cork under a self-made microscope and saw tiny, box-like structures, which he named “cells” because they resembled the cells of a honeycomb.
Question 2: Why is the cell called the structural and functional unit of life?
Answer:
The cell is the structural unit because all living organisms are made of cells, forming their basic framework. It’s the functional unit because all life processes (e.g., respiration, digestion) occur within cells, making them essential for survival.
In-Text Questions and Answers: Page 61
Question 1: Why is the plasma membrane called a selectively permeable membrane?
Answer:
The plasma membrane is called selectively permeable because it allows only certain substances to pass through while blocking others. For example, it permits oxygen and nutrients to enter but restricts harmful substances, maintaining cell balance.
Question 2: What would happen to the life of a cell if there was no Golgi apparatus?
Answer:
Without the Golgi apparatus, the cell couldn’t modify, package, or transport proteins and lipids. This would disrupt secretion (e.g., hormones), waste removal, and organelle formation, ultimately leading to cell dysfunction and death.
In-Text Questions and Answers: Page 67
Question 1: Where do the lipids and proteins constituting the cell membrane get synthesized?
Answer:
- Lipids: Synthesized in the smooth endoplasmic reticulum (smooth ER).
- Proteins: Synthesized by ribosomes on the rough endoplasmic reticulum (rough ER).
Question 2: What is the difference between plant and animal cells?
Answer:
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell Wall | Present (cellulose) | Absent |
| Chloroplasts | Present (photosynthesis) | Absent |
| Vacuole | Large, central | Small, scattered |
| Shape | Fixed (rectangular) | Irregular |
Exercise Questions and Answers: Page 70
Question 1: Make a comparison and write down ways in which plant cells are different from animal cells.
Answer:
See the table above for a detailed comparison. Key differences:
- Plant cells have a cell wall, chloroplasts, and a large vacuole; animal cells do not.
- Plant cells are rigid due to the wall; animal cells are flexible.
Question 2: How is a prokaryotic cell different from a eukaryotic cell?
Answer:
| Feature | Prokaryotic Cell | Eukaryotic Cell |
|---|---|---|
| Nucleus | No true nucleus (nucleoid) | True nucleus with membrane |
| Organelles | Few, no membrane-bound | Many, membrane-bound |
| Size | Smaller (1-10 µm) | Larger (10-100 µm) |
| Examples | Bacteria, blue-green algae | Plants, animals, fungi |
Question 3: What would happen if the plasma membrane ruptures or breaks down?
Answer:
If the plasma membrane ruptures, the cell loses its selective permeability. Uncontrolled entry of substances (e.g., toxins) and leakage of cytoplasm would occur, disrupting cell functions and leading to cell death.
Question 4: Why are lysosomes known as suicide bags?
Answer:
Lysosomes are called suicide bags because they contain digestive enzymes that can break down waste or damaged cell parts. If they burst, these enzymes digest the entire cell, causing its death—acting like a self-destruct mechanism.
Question 5: Which organelle is known as the powerhouse of the cell? Why?
Answer:
The mitochondrion is the powerhouse of the cell. It produces energy (ATP) through cellular respiration by breaking down glucose, fueling all cell activities.
Tips to Master Chapter 5
- Learn Cell Parts: Memorize organelles and their functions with diagrams.
- Practice Comparisons: Focus on plant vs. animal and prokaryotic vs. eukaryotic cells.
- Understand Processes: Grasp diffusion, osmosis, and organelle roles.
- Draw Diagrams: Sketch plant and animal cells for better retention.
Class 9 Science Chapter 5: The Fundamental Unit of Life opens the door to Biology by exploring cells—the essence of all living organisms. With these notes, questions, and solutions, you’re well-prepared to ace your 2025 CBSE exams. This chapter blends theory with practical understanding, making it both engaging and high-scoring.
For extra practice, explore NCERT solutions and sample papers online. Have questions? Drop them in the comments—we’re here to help! Keep studying and stay curious!
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