The Fundamental Unit of Life Solution: Class 9 Science Chapter 5
In-text questions page 59
1. Who discovered cells and how?
In 15 century 1665, Robert Hooke, an English scientist, observed a cross section of a cork cell. Here he found a tiny compartment like structure. He used the term ‘Cell’ for these compartments.
Note: Compound microscope was discovered by Galileo at the beginning of the 15th century. During those days a compound microscope was very costly and available only to selected people. Robert Hooke was a wealthy scientist with many inventions. He was among the few people who had a compound microscope at that time.
2. Why is the cell called the structural and functional unit of life?
Cells are the building block of every living organism. Cells of similar nature combine to form tissue; tissues form organs and organs combine to form the body.
All the function in the body mediates through the cells. Different proteins form in the cell and change the function of cells and therefore, the body. So, we call cells as the structural and functional unit of life.
In-text questions page 61
1. How do substances like CO2 and water move in and out of the cell?
Carbon dioxide is a waste produced by the cells. It diffuses from the cell to the extracellular space through the concentration gradient by simple diffusion. Water also diffuses due to its concentration gradient by the process termed osmosis.
2. Why is the plasma membrane called a selectively permeable membrane?
The plasma membrane is the outer covering of a cell which separates one cell from another. It has pores and channels which allow only specific materials to pass in and out. So, we call them selectively permeable.
Note: A cell wall is a semi-permeable structure as a cell wall allows particles to pass through it depending on the size of the particles and not on the nature.
3. Differences between prokaryotic and eukaryotic cells.
4. Name of organelles which have their genetic material.
Answer: Mitochondria and plastids are the two organelles which have their genetic materials and ribosome.
2. If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?
Cells of an organism contain numerous lysosome. Lysosomes are single membrane organelles with digestive enzymes. Lysosome ruptures in a damaged cell and releases the digestive enzymes inside the cell. Digestive enzymes kill the cell and nutrients present in them are distributed to other cells. For this reason, we also call lysosomes as a suicidal bag of the cell.
3. Why are lysosomes known as suicide bags?
See question 2.
4. Where are proteins synthesised inside the cell?
The rough endoplasmic reticulum is the sites for protein synthesis. Here ribosomes attach to the outer membrane of the organelle and form the new proteins from amino acids.
The Fundamental Unit of Life Solution
Exercises question solution
1. Make a comparison and write down ways in which plant cells are different from animal cells.
Cell wall: A plant cell contains a cell wall which provided the plant rigidity. Animal cells do not contain a cell wall.
Vacuole: A plant cell has a large vacuole. A vacuole is a large space in the cell. In plants, it keeps air for buoyancy or stores fluid and foods. In animals, vacuoles are smaller and perform digestion of food materials.
Organelles: Some organelles like chloroplast, plastids etc. are present only in a plant cell.
2. How is a prokaryotic cell different from a eukaryotic cell?
See answer for question 3 of page 61.
3. What would happen if the plasma membrane ruptures or breaks down?
The plasma membrane of a cell separate on a cell from another and maintains the integrity of the cell. If plasma membrane ruptures, the organelles, cytoplasm and nucleus of the cell will move out of the cell and will be destroyed. As a result, the cell will die.
4. What would happen to the life of a cell if there was no Golgi apparatus?
Golgi bodies are the flat sac-like vesicles arranged parallel like a cistern. Rough endoplasmic reticulum attaches to a Golgi body and transfers newly formed protein. Goldi body modifies this newly formed protein into a usable form. A cell requires numerous protein molecules to function. So, if there is no Golgi body, a cell will cease to work and will eventually die.
5. Which organelle is known as the powerhouse of the cell? Why?
Mitochondria produces ATP on its inner membrane. Various chemical and the mechanical process use ATP as energy currency. So, we call mitochondria as the powerhouse of the cell.
6. Where do the lipids and proteins constituting the cell membrane get synthesised?
Rough Endoplasmic Reticulum (RER) produces protein while Smooth Endoplasmic Reticulum produces lipid molecules.
7. How does an Amoeba obtain its food?
Amoeba is a unicellular organism. It has pseudopodia ( false feet) on its surface. Whenever a food comes in contact with the body, pseudopodia forms and engulfs the food. Food inside the cell forms a food vacuole. Amoeba secretes digestive enzymes in the food vacuole and digests the food.
8. What is osmosis?
When a membrane separates two solutions with different tonicity, if the membrane permits the only solvent but not the solute, then solvent molecule moves from its high concentration to low concentration. We call this process osmosis.
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.
10. Which type of cell division is required for growth and repair of the body, and which type is involved in the formation of gametes?
A cell undergoes mitosis to grow and repair the body; to form gametes germ cell undergoes meiosis.
Ref: Chapter 5.