NCERT Solutions for Class 9th Science
Chapter 5 – THE FUNDAMENTAL UNIT OF LIFE
(Complete Downloadable Chapter Solution PDF file is at the bottom of the page)
Q.1 Who discovered cells, and how?
Ans Robert Hooke discovered cells in 1665 while examining a thin slice of cork (substance which comes from the bark of a tree) through a self designed microscope.
Q.2 Why is the cell called the structural and functional unit of life?
Ans The cell in a living organism is the basic structural & functional unit as it is the smallest living part of an organism i.e. an organ (group of which makes an organism) is made up of tissues which in turn, are made up of cells and each living cell perform certain basic functions like respiration, obtaining nutrition, clearing of waste material etc that are characteristic of all living forms. In other words, cells are the building blocks of life. The shape and size of cells varies and are related to the specific function they perform.
Q.3 How do substances like CO2 and water move in and out of the cell? Discuss.
Ans The movement of substances in and out of the cell is regulated by the selectively permeable membrane called cell membrane or plasma membrane.
Movement of CO2: CO2 movement takes place due to diffusion i.e. from a region of high concentration to a region of low concentration. CO2 (which is cellular waste and requires to be excreted out by the cell) accumulates in high concentrations inside the cell. In the cell’s external environment, the concentration of CO2 is low as compared to that inside the cell. As soon as there is a difference of concentration of CO2 inside and outside a cell, CO2 moves out of the cell by the process of diffusion.
Movement of water: The movement of water takes place by the process of osmosis i.e. movement of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration. The movement of water across the plasma membrane is affected by the amount of substance dissolved in water.
Q.4 Why is the plasma membrane called a selectively permeable membrane?
Q.5 Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.
Q.6 Can you name the two organelles we have studied that contain their own genetic material?
Ans Mitochondria and plastids
Q.7 If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?
Q.8 Why are lysosomes known as suicide bags?
Q.9 Where are proteins synthesised inside the cell?
EXERCISES
Q.1 Make a comparison and write down ways in which plant cells are different from animal cells.
Q.2 How is a prokaryotic cell different from a eukaryotic cell?
Q.3 What would happen if the plasma membrane ruptures or breaks down?
Ans Plasma membrane also called selectively permeable membrane is the outermost covering of the cell that separates and protects cell’s contents from its external environment. If it ruptures, its contents will get exposed to the external environemnt and ultimately the cell will die.
Q.4 What would happen to the life of a cell if there was no Golgi apparatus?
Ans Golgi apparatus is responsible for storage, modification and packaging of products in vesicles. Hence if it is not available, the following things will happen:
1) material synthesised in the cell will not be packaged and dispatched to various targets inside and outside the cell.
2) No formation of complex sugars from simple sugars.
3) No formation of lysosomes
Q.5 Which organelle is known as the powerhouse of the cell? Why?
Q.6 Where do the lipids and proteins constituting the cell membrane get synthesised?
Q.7 How does an Amoeba obtain its food?
Q.8 What is osmosis?
Q.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.