5. The Fundamental Unit of Life

Assam Class 9 Science Class 9 Science Chapter 5. The Fundamental Unit of Life

Chapter 5. The Fundamental Unit of Life

Class 9 Science Chapter 5 The Fundamental Unit of Life Internal Questions and Answers :

Internal Questions :

1. Who discovered cells, and how ?

Answer: Cells were discovered by Robert Hooke in 1665. He used a compound microscope to examine a thin slice of cork and observed tiny compartments that he called "cells," resembling the cells of a honeycomb.
2. Why is the cell called the structural and functional unit of life ?

Answer: The cell is called the structural and functional unit of life because it is the basic building block of all living organisms. Cells perform essential functions, such as metabolism, reproduction, and responding to stimuli, and collectively, they form the foundation of biological structure and function.

Internal Questions :

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

Answer: Substances like and water move in and out of cells through diffusion. They pass through the cell membrane, from areas of high concentration to low concentration, to maintain balance inside and outside the cell.

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

Answer: The plasma membrane is called selectively permeable because it allows certain substances to pass through while blocking others. It selectively regulates the entry and exit of molecules to maintain cell function.

Internal Questions :

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

Answer: The two organelles that contain their own genetic material are:

(i) Mitochondria

(ii) Plastids

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

Answer: If the organisation of a cell is disrupted, lysosomes may release their enzymes, causing cellular self-digestion and cell death. This breakdown can harm the cell and surrounding tissues, contributing to disease or injury.

3. Why are lysosomes known as suicide bags?

Answer: Lysosomes are known as "suicide bags" because they contain powerful digestive enzymes capable of breaking down all organic material. When cells get damaged or disrupted, lysosomes may burst, causing these enzymes to digest their own cell, leading to cell self-destruction.
4. Where are proteins synthesized inside the cell?

Answer: Proteins are synthesized inside the cell on ribosomes, which can be found in the cytoplasm and attached to the endoplasmic reticulum.

Class 9 Science Chapter 5 The Fundamental Unit of Life Exercise Questions and Answers :

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

Answer : The differences between plant cells and animals cells are :

Characteristic	Plant Cells	Animal Cells
Cell Wall	Present	Absent
Chloroplasts	Present	Absent
Vacuole	Large central vacuole	Small or multiple vacuoles
Shape and Size	Often rigid and fixed	Usually flexible and varied
Locomotion	Lacks mobility	May have mobility structures
Food Storage	Store starch	Store glycogen
Nucleus Location	Periphery	Center
Centrioles	Generally absent	Present (in some)
Lysosomes	Rarely present	Commonly present

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

Answer: The difference between prokaryotic cells and eukaryotic cells are :

Characteristic	Prokaryotic Cell	Eukaryotic Cell
Nucleus	No true nucleus	True nucleus present
Membrane-bou Organelles	Few or none	Numerous organelles
DNA Location	In the nucleoid region	Enclosed in the nucleus
Size	Usually smaller	Usually larger
Complexity	Simple	Complex
Example	Bacteria, Archaea	Animals, Plants, Fungi

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

Answer: If the plasma membrane ruptures or breaks down, the cell loses its structure and control over what enters and exits. This can lead to cell death and potentially harm neighboring cells.
4. What would happen to the life of a cell if there was no Golgi apparatus?

Answer: Without a Golgi apparatus, the cell would have difficulty processing, modifying, and packaging proteins and other molecules for transport. This could disrupt essential cellular functions and affect the cell's survival.
5. Which organelle is known as the powerhouse of the cell? Why?

Answer: Mitochondria are known as the powerhouses of the cell because they release the energy required for various chemical activities needed for life in the form of ATP (Adenosine triphosphate) molecules. ATP is known as the energy currency of the cell. The body uses energy stored in ATP to make new chemical compounds and for mechanical work.
6. Where do the lipids and proteins constituting the cell membrane get synthesised?

Answer: The lipids and proteins that make up the cell membrane are primarily synthesized in the endoplasmic reticulum (ER).
7. How does an Amoeba obtain its food?

Answer: An amoeba obtains food through a process called endocytosis. It surrounds its food with its cell membrane, creating a small food vacuole. Then, it digests the engulfed food inside the vacuole to extract nutrients and energy for its survival and growth.

8. What is osmosis ?

Answer: Osmosis is a process in which solvent molecules move from an area of lower solute concentration to an area of higher solute concentration through a semipermeable membrane to equalize the concentrations.
9. Carry out the following osmosis experiment:
Take four peeled potato halves and scoos 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.

Answer: (i) Water gathers in the hollowed portions of B (sugar) and C (salt) because of osmosis. Water moves from areas of lower solute concentration (inside the potato cups) to areas of higher solute concentration (the sugar and salt in the cups), causing the cups to fill with water.

(ii) Potato A is necessary as a control to show the natural state of a potato cup without any added substances. It helps us compare the effects of sugar and salt on water movement.

(iii) Water does not gather in the hollowed portions of A because there are no added solutes to create a concentration difference. In D, the boiled potato likely has damaged cell membranes, preventing osmosis, so water doesn't gather there either.

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

Answer: Cell division for growth and repair of the body is called "mitosis." Mitosis creates identical daughter cells with the same number of chromosomes as the parent cell. Cell division for the formation of gametes (sperm and egg) is called "meiosis," which produces haploid cells with half the chromosome number .