The Fundamental Unit of Life Class 9 is one of the most important biology chapters in the Class 9 Science syllabus. It introduces students to the concept of the cell as the basic structural and functional unit of life.
NCERT Solutions Class 9 Science Chapter 5 are prepared strictly according to the CBSE syllabus and NCERT textbook. These solutions explain complex biological concepts in simple language, helping students grasp ideas easily and perform well in exams.
NCERT Solutions Class 9 Science Chapter 5 Overview
Class 9 Science Chapter The Fundamental Unit of Life focuses on the discovery of cells, types of cells, and their structure. The chapter explains how cells differ in shape, size, and function, and how various cell organelles work together to maintain life.
The Fundamental Unit of Life Class 9 Questions And Answers include detailed explanations, labelled diagrams, and step-by-step answers to textbook questions. These solutions help students understand key topics such as cell membrane, nucleus, cytoplasm, and cell organelles clearly.
The Fundamental Unit of Life Class 9 Questions And Answers
The Fundamental Unit of Life Class 9 Questions and Answers cover all important topics from the chapter in a clear way. This content also includes the fundamental unit of life class 9 MCQ to help students practice objective questions and revise key concepts effectively.
Class 9 Science Chapter 5 Exercise 5.1
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.Class 9 Science Exercise 5.2
3. How do substances like CO 2 and water move in and out of the cell? Discuss.
Solution: CO 2 moves by diffusion. The cellular waste accumulates in high concentrations in the cell, whereas the concentration of CO 2 in the external surroundings is comparatively lower. This difference in the concentration level inside and outside of the cell causes the CO 2 to diffuse from a region of higher (within the cell) to a lower concentration. H 2 O 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.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.5. Fill in the gaps in the following table, illustrating the differences between prokaryotic and eukaryotic cells.
| Prokaryotic Cell | Eukaryotic Cell |
| 1. Size: Generally small (1-10 μm) 1 μm = 10 -6 m 2. Nuclear region: ______________________________ ______________________________ and known as ___________________ 3. Chromosome: single 4. Membrane-bound cell organelles absent. | 1. Size: Generally large (5-100 μm) 2. Nuclear region: well-defined and surrounded by a nuclear membrane. 3. More than one chromosome. 4. ______________________________ ______________________________ ______________________________ |
| Prokaryotic Cell | Eukaryotic Cell |
| 1. Size: Generally small (1-10 μm) 1 μm = 10 -6 m 2. The nuclear region is poorly defined due to the absence of a nuclear membrane and is known as the nucleoid. 3. There is a single chromosome. 4. Membrane-bound cell organelles absent. | 1. Size: Generally large (5-100 μm) 2. Nuclear region: well-defined and surrounded by a nuclear membrane. 3. There is more than one chromosome. 4. Membrane-bound cell organelles present. |
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. Plastids7. 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’.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.Class 9 Science Chapter 5 Exercise Questions
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.| Characteristic | Plant Cell | Animal Cell |
| Cell Wall | Present | Absent |
| Shape of Cell | With distinct edges, the shape is either rectangular or square-shaped. | Round and irregular shape |
| Nucleus | Present. It lies on one side of the cell | Present. It lies in the centre of the cell |
| Lysosomes | Rarely present | Always present |
| Plastids | Present | Absent |
| Structure of Vacuoles | Single or a few large vacuoles that are centrally located | Presence of numerous and small vacuoles |
2. How is a prokaryotic cell different from a eukaryotic cell?
Solution: The following are the differences between prokaryotic and eukaryotic cells.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:- Storage of Substances: It stores and accumulates various molecules and substances synthesized by the cell.
- 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.
- 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.
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.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: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.