NCERT Solutions For Class 9 Science Chapter 5 The Fundamental Unit of Life

Class 9 Science Chapter 5:- Class 9 Science Chapter 5, The Fundamental Unit of Life, introduces students to the concept of cells, the building blocks of all living organisms. This chapter explores how cells were discovered and their important roles in plants and animals. Students will gain an understanding of cell structure, including the cell membrane, nucleus, and cytoplasm, along with the key differences between plant and animal cells. Through clear explanations and diagrams, the chapter helps students understand the essential functions of organelles, contributing to a deeper understanding of how living organisms grow and function.

Check out: Class 9th Books

NCERT Solutions Class 9 Science Chapter 5 PDF

You can find the PDF link for NCERT Solutions Class 9 Science Chapter 5 “The Fundamental Unit of Life” below.

This PDF provides detailed solutions and explanations to help you understand the concepts covered in the chapter.

NCERT Solutions Class 9 Science Chapter 5 PDF

Class 9 Science Chapter 5 Question Answer

Go through the fundamental unit of life class 9 questions and answers below:-

1. Who discovered cells, and how?

Solution: In 1665, Robert Hooke discovered cells while examining a thin slice of cork through a self-designed microscope. He observed that the cork resembled the structure of a honeycomb consisting of numerous tiny compartments. The minuscule boxes are referred to as cells.

2. Why is the cell called the structural and functional unit of life?

Solution: Cells form the structure of an entity. A group of cells form a tissue, further an organ and ultimately an organ system. They perform fundamental functions and life processes such as respiration, digestion, excretion etc., in both unicellular and multicellular entities. They perform all the activities independently. Hence, cells are referred to as structural and fundamental units of life.

Read More: NCERT Solutions for Class 9 Science Chapter 1 Matter in Our Surroundings

3. How do substances like CO2 and water move in and out of the cell? Discuss.

Solution: CO2 moves by diffusion. The cellular waste accumulates in high concentrations in the cell, whereas the concentration of CO2 in the external surroundings is comparatively lower. This difference in the concentration level inside and outside of the cell causes the CO2 to diffuse from a region of higher (within the cell) to a lower concentration.

H2O diffuses by osmosis through the cell membrane. It moves from a region of higher concentration to a lower concentrated region through a selectively permeable membrane until equilibrium is reached.

Read More: NCERT Solutions for Class 9 Science Chapter 2

4. Why is the plasma membrane called a selectively permeable membrane?

Solution: The plasma membrane is called as a selectively permeable membrane as it permits the movement of only certain molecules in and out of the cells. Not all molecules are free to diffuse.

NCERT Solutions for Class 9 Science Chapter 5 Exercise 5.2

5. Fill in the gaps in the following table, illustrating the differences between prokaryotic and eukaryotic cells.

Solution:

NCERT Solutions for Class 9 Science Chapter 5 Exercise 5.3

6. Can you name the two organelles we have studied that contain their own genetic material?

Solution: The two organelles which have their own genetic material are

1. Mitochondria

2. Plastids

7. If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?

Solution: In the event of any damage to cells and when the revival of cells is not possible, Lysosomes burst, and enzymes digest such cells. This is why lysosomes are often referred to as ‘suicide bags’.

Check out: Class 9th Revision Books

8. Why are lysosomes known as suicide bags?

Solution: When there is damage to the cell and when revival is not possible, lysosomes may burst, and the enzymes digest their own cell. Consequently, lysosomes are known as suicide bags.

9. Where are proteins synthesised inside the cell?

Solution: Protein synthesis in cells takes place in ribosomes. Hence, ribosomes are also referred to as protein factories. Ribosomes are particles that are found attached to the rough endoplasmic reticulum.

NCERT Solutions for Class 9 Science Chapter 5 Exercise 5.4

1. Make a comparison and write down ways in which plant cells are different from animal cells.

Solution:

The following table depicts the differences between plant cells and animal cells.

2. How is a prokaryotic cell different from a eukaryotic cell?

Solution:

The following are the differences between prokaryotic and eukaryotic cells.

3. What would happen if the plasma membrane ruptures or breaks down?

Solution: If the plasma membrane ruptures or breaks down, molecules of some substances will freely move in and out of the cell. Normally, the plasma membrane acts as a barrier that controls the exchange of materials through processes like osmosis and diffusion. If this barrier is compromised, the cell can’t maintain its internal environment properly.

As a result, essential protoplasmic material can leak out or harmful substances can enter unchecked. This disruption can lead to the death of the cell due to the loss of its vital components and inability to function properly.

4. What would happen to the life of a cell if there was no Golgi apparatus?

Solution: The Golgi apparatus consists of stacks of membrane-bound vesicles with several key functions:

1. Storage of Substances: It stores and accumulates various molecules and substances synthesized by the cell.

2. Packaging of Substances: It modifies, sorts, and packages proteins and other molecules into vesicles for transport to different parts of the cell or for secretion outside the cell.

3. Manufacture of Substances: While the Golgi apparatus primarily processes and modifies substances rather than directly manufacturing them, it plays a crucial role in modifying proteins and lipids synthesized in the endoplasmic reticulum.

Without the Golgi apparatus, cells would be unable to properly package and transport materials essential for their functioning. This would impair processes such as secretion, cell signaling, and the maintenance of cellular structure. The Golgi apparatus is involved in the formation of lysosomes, which are essential for cellular digestion and recycling. Therefore, the absence of a functional Golgi apparatus would severely compromise the cell’s ability to function and survive.

5. Which organelle is known as the powerhouse of the cell? Why?

Solution: Mitochondria are referred to as the powerhouse of the cell because they generate energy required for various life activities. They achieve this by releasing energy in the form of ATP (Adenosine triphosphate) molecules. ATP is essential for numerous chemical processes that sustain life, including muscle contraction, protein synthesis, and cellular metabolism. This ability to produce ATP makes mitochondria crucial for providing the energy necessary for cells to function effectively, earning ATP the nickname ‘energy currency of the cell’.

6. Where do the lipids and proteins constituting the cell membrane get synthesised?

Solution: Lipids and proteins are synthesised in the ER (Endoplasmic Reticulum).

7. How does an Amoeba obtain its food?

Solution: Through the process of endocytosis, an Amoeba obtains its food. The Amoeba’s flexible cell membrane allows it to engulf food particles, forming a food vacuole around them with the help of pseudopodia, which are extensions of its cell membrane. Once the food is trapped inside the food vacuole, Amoeba secretes digestive enzymes into the vacuole.

These enzymes break down the engulfed food particles through digestion, allowing the Amoeba to absorb nutrients and sustain itself. This process of endocytosis and digestion is essential for the Amoeba’s nutrition and survival.

8. What is osmosis?

Solution: Osmosis is the process where water molecules move across a semipermeable membrane from an area of higher water concentration to an area of lower water concentration. This movement occurs until equilibrium is reached, balancing the concentration of water on both sides of the membrane. Osmosis plays a crucial role in biological systems, helping regulate the balance of water and solutes inside cells and organisms.

Check out: Class 9 Sample Papers

9. Carry out the following osmosis experiment:

Take four peeled potato halves and scoop each one out to make potato cups. One of these potato cups should be made from a boiled potato. Put each potato cup in a trough containing water. Now,

(a) Keep cup A empty

(b) Put one teaspoon sugar in cup B

(c) Put one teaspoon salt in cup C

(d) Put one teaspoon sugar in the boiled potato cup D.

Keep these for two hours. Then observe the four potato cups and answer the following:

(i) Explain why water gathers in the hollowed portion of B and C.

(ii) Why is potato A necessary for this experiment?

(iii) Explain why water does not gather in the hollowed-out portions of A and D.

Solution: (i) Water accumulates in the hollowed portions of B and C as a difference in the water concentration is observed. Thereby, endosmosis occurs as the cells act as a semipermeable membrane.

(ii) Potato A is essential in this experiment as it is significant to compare different scenarios seen in potato cups B, C and D. Potato A in this experiment clearly shows that the potato cavity on its own cannot bring about water movement.

(iii) Cup in A does not show any change in the water flow concentration for osmosis to occur, which requires concentration to be higher than the other. Cells in cup D are dead; thus, there is no existence of a semipermeable membrane for water flow. Consequently, osmosis does not occur.

10. Which type of cell division is required for the growth and repair of the body, and which type is involved in the formation of gametes?

Solution: Mitosis: Mitosis is a type of cell division involved in the growth, development, and repair of the body. It produces two identical daughter cells, each with the same number of chromosomes as the parent cell. This process ensures that the body’s cells can replace damaged or worn-out cells and maintain proper function.

Meiosis: Meiosis is a type of cell division that occurs in specialized cells called germ cells, which are involved in sexual reproduction. It results in the formation of gametes (sperm and egg cells) with half the number of chromosomes as the parent cell. During fertilization, these gametes combine to form a new organism with a full set of chromosomes.

These two processes, mitosis and meiosis, play crucial roles in maintaining the genetic stability of organisms and ensuring successful reproduction.

Check out: Science Experiment Kit For Class 9th

Class 9 Science Chapter 5 Summary

Discovery of Cells:

• Cells were first discovered by Robert Hooke in 1665 when he observed a thin slice of cork under a microscope.

• Later, the development of better microscopes allowed scientists to explore cells more thoroughly, leading to the formulation of the Cell Theory.

Cell Theory:

• Proposed by Schleiden and Schwann, this theory states:

• All living organisms are composed of cells.

• Cells are the basic structural and functional units of life.

• New cells arise from pre-existing cells (added by Rudolf Virchow).

Structure of a Cell:

• Cell Membrane (Plasma Membrane): A thin, flexible layer that surrounds the cell and controls the movement of substances in and out of the cell.

• Cytoplasm: The jelly-like fluid inside the cell where various organelles are suspended and metabolic activities occur.

• Nucleus: The control center of the cell, containing genetic material (DNA) that regulates cell growth, reproduction, and function.

Organelles and Their Functions:

• Mitochondria: Known as the powerhouse of the cell, mitochondria are responsible for producing energy through cellular respiration.

• Endoplasmic Reticulum (ER): A network of membranes involved in the synthesis of proteins (rough ER) and lipids (smooth ER).

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for storage or transport out of the cell.

• Lysosomes: Known as the cell’s waste disposal system, they contain enzymes that break down waste materials and cellular debris.

Differences Between Plant and Animal Cells:

• Plant Cells:

• Have a rigid cell wall made of cellulose, providing structural support.

• Contain chloroplasts with chlorophyll, enabling photosynthesis.

• Usually have a larger central vacuole that stores nutrients and waste products.

• Animal Cells:

• Lack a cell wall and chloroplasts.

• Have smaller, more numerous vacuoles.

• Often contain centrioles, involved in cell division.

Functions of Cells:

• Cells perform various functions essential for life, such as metabolism, growth, reproduction, and response to environmental changes.

• Different cells in multicellular organisms have specialized functions (e.g., nerve cells for transmitting signals, muscle cells for movement).

Cell Division:

• Cells reproduce through processes like mitosis (for growth and repair) and meiosis (for the production of gametes).

• Cell division is critical for growth, maintenance, and repair in organisms.

Importance of Studying Cells:

• Understanding cells helps us grasp the fundamental processes of life, including how organisms grow, respond to their environment, and maintain homeostasis.

• It also provides insights into health and disease, as many medical conditions result from abnormalities at the cellular level.

Check out: PW School Books

Class 9 Science Chapter 5 FAQs

Q1. What is the cell and why is it called the fundamental unit of life?

Ans. A cell is the smallest structural and functional unit of life. It is called the fundamental unit because all living organisms are made up of cells, and the cell is the basic unit that performs essential life processes.

Q2. Who discovered cells, and how were they discovered?

Ans. Cells were discovered by Robert Hooke in 1665 when he observed a thin slice of cork under a microscope and noted small, box-like structures, which he named "cells."

Q3. What is the cell theory, and who proposed it?

Ans. The cell theory, proposed by Schleiden and Schwann, states that all living organisms are made of cells, cells are the basic units of life, and all cells arise from pre-existing cells (Virchow added this later).

Q4. What are the main differences between plant cells and animal cells?

Ans. Plant cells have a cell wall, chloroplasts, and a large central vacuole, while animal cells lack a cell wall and chloroplasts but have smaller vacuoles and centrioles.

Q5. What is the function of the nucleus in a cell?

Ans. The nucleus acts as the control center of the cell, regulating growth, metabolism, and reproduction. It contains genetic material (DNA), which controls cell activities and passes hereditary information to offspring.