Ncert Solutions for Class 9 Science Chapter 5: The fundamental unit of life class 9 questions and answers
| Textbook | Ncert |
| Class | Class 9 |
| Subject | Science |
| Chapter | Chapter 5 |
| Chapter Name | The fundamental unit of life class 9 ncert solutions |
| Category | Ncert Solutions |
| Medium | English |
Are you looking for Class 9 Science Chapter 5 question answer ? Now you can download The fundamental unit of life class 9 questions and answers pdf from here.
In Text Questions Page No: 51
Question 1: Who discovered cells, and how?
Answer 1: Cells were discovered by Robert Hooke in 1665. He used a microscope to examine a thin slice of cork and saw tiny, box-like structures, which he called “cells” because they looked like small rooms in a monastery.
Question 2: Why is the cell called the structural and functional unit of life?
Answer 2: A cell is capable of independently carrying out all necessary activities of life. So, they are called basic or functional unit of life.
In Text Questions Page No: 53
Question 1: How do substances like CO2 and water move in and out of the cell? Discuss.
Answer 1: 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.
Question 2: Why is the plasma membrane called a selectively permeable membrane?
Answer 2: Plasma membrane called a selectively permeable membrane because it regulates the movement of substances in and out of the cell. This means that the plasma membrane allows the entry of only some substances and prevents the movement of some other materials.
In Text Questions Page No: 55
Question 1: Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.
| Prokaryotic cell | Eukaryotic cell | ||
| 1. | Size: generally small (1–10 µm) 1 µm = 10-6 m | 1. | Size: generally large (5-100 µm) |
| 2. | Nuclear region: ____________ ____________ and is known as _____. | 2. | Nuclear region: well defined and surrounded by a nuclear membrane. |
| 3. | Chromosome: single | 3. | More than one chromosome |
| 4. | Membrane-bound cell organelles absent | 4. | ____________ ____________ ____________ |
Answer 1:
| Prokaryotic cell | Eukaryotic cell | ||
| 1. | Size: generally small (1-10 µm) 1µ | 1. | Size: generally large (5-100 µm) |
| 2. | Nuclear region: Poorly defined due to the absence of a nuclear membrane and known as nucleoid. | 2. | Nuclear region: Well-defined and surrounded by a nuclear membrane. |
| 3. | Chromosome: single | 3. | More than one chromosome. |
| 4. | Membrane-bound cell organelles are absent. | 4. | Membrane-bound cell organelles, such as mitochondria, lysosomes, endoplasmic reticulum, Golgi complexes, etc., are present. |
In Text Questions Page No: 57
Question 1: Can you name the two organelles we have studied that contain their own genetic material?
Answer 1: The two organelles we have studied that contain their own genetic material are mitochondria and plastids. Mitochondria help in respiration in the cell while plastids are responsible for the process of photosynthesis in leaves.
Question 2: If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?
Answer 2: 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’.
Question 3: Why are lysosomes known as suicide bags?
Answer 3: When the cell gets damaged, lysosomes may burst, and the enzymes digest their own cell. Therefore lysosomes are known as suicide bags.
Question 4: Where are proteins synthesised inside the cell?
Answer 4: Ribosomes are the site for protein synthesis. Ribosomes are very small structures found either in a free state, suspended in the cytoplasm, or attached to the surface of the endoplasmic reticulum. They are composed of ribonucleic acids and proteins.
Exercises
Question 1: Make a comparison and write down ways in which plant cells are different from animal cells.
Answer 1: differences between plant and animal cells:
| Feature | Plant Cells | Animal Cells |
|---|---|---|
| Cell Wall | Present (made of cellulose) | Absent |
| Chloroplasts | Present (for photosynthesis) | Absent |
| Vacuole | One large central vacuole | Small or absent |
| Shape | Usually rectangular or box-like | Usually round or irregular |
| Energy Storage | Stores energy as starch | Stores energy as glycogen |
| Centrioles | Absent (in most plant cells) | Present |
| Lysosomes | Rare | Common |
Question 2: How is a prokaryotic cell different from a eukaryotic cell?
Answer 2: Prokaryotic cell is generally smaller in size (1-10 pm), nuclear region is poorly defined, the cell organelles are not membrane-bound and has a single chromosome.
Eukaryotic cell is generally larger in size (5-100 pm), nuclear region is well defined with nuclear membrane. Membrane-bound cell organelles are present and has more than one chromosome.
Question 3: . What would happen if the plasma membrane ruptures or breaks down?
Answer 3: If the plasma membrane ruptures or breakdown then the cell will not be able to exchange material from its surrounding by diffusion or osmosis. Thereafter the protoplasmic material will be disappeared and the cell will die.
Question 4: What would happen to the life of a cell if there was no Golgi apparatus?
Answer 4: The function of the Golgi apparatus is packaging and transferring substances from one part of the cell to another. If the Golgi apparatus is absent in a cell then packaging of the proteins or the arrangement of the structural protein will not take place inside a cell. Proteins are essential for cells to perform various metabolic functions and if the proteins fail to reach the cell then this metabolism in the cell will not take place and eventually this will cause the cell to die.
Question 5: Which organelle is known as the powerhouse of the cell? Why?
Answer 5: Mitochondria are known as the powerhouse of the cell. It is because it releases the energy required for different activities of life. Mitochondria releases energy in the form of ATP (Adenosine triphosphate) molecules, essential for numerous chemical activities of life. Hence, ATP is often referred to as the ‘energy currency of the cell’.
Question 6: Where do the lipids and proteins constituting the cell membrane get synthesised?
Answer 6: Lipids and proteins are synthesised in the ER (Endoplasmic Reticulum).
Question 7: How does an Amoeba obtain its food?
Answer 7: 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.
Question 8: What is osmosis?
Answer 8: The movement of water molecules from a region of high concentration to a region of low concentration through a selectively permeable membrane is called osmosis. It is a special case of diffusion, where the medium is water.
Question 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,
Keep cup A empty
Put one teaspoon of sugar in cup B
Put one teaspoon salt in cup C
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:
Explain why water gathers in the hollowed portion of B and C.
Why is potato A necessary for this experiment?
Explain why water does not gather in the hollowed-out portions of A and D.
Answer 9: (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.
Question 10: Which type of cell division is required for growth and repair of body and which type is involved in formation of gametes?
Answer 10: Mitosis is used for the growth and repair of the body and produces diploid cells identical to each other and the parent cell.
Meiosis is used for sexual reproduction, and haploid cells are different to each other and the parent cell. Thus, meiosis results in the formation of gametes.