NCERT Solutions For Class 9 Science Fundamental Unit Of Life

NCERT Solutions Class 9 Science Chapter 5 PDF

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The most fundamental until of life is the cell. Every organism, from the simplest microbe to the most complex organism is made up of cells. Unicellular organisms, as their name suggests, are made up of just one cell. Humans and other multicellular organisms are composed of millions of cells that work together to perform different functions.

Cells have organelles within them. Organelle performs specific functions within the cell, just like how an organ fulfils a specific function within a human body. For instance, the mitochondrion is an organelle that is responsible for the production of ATP – the energy currency of the cell. Learn more about the cell and its features by exploring Fundamental Unit Of Life Class 9 NCERT PDF For Chapter 5, right here on My NCERT.

NCERT Solutions For Class 9 Science Fundamental Unit Of Life

On-Page 59

Question 1:Who discovered cells and how?


The cell was discovered by Robert Hooke with the help of his self-designed microscope. He examined a thin slice of cork and saw that the cork resembled the structure of a honeycomb consisting of many compartments.

Question 2:Why is the cell called the structural and functional unit of life?


There are various components in the animal and plant cell known as cell organelles. Each kind of cell organelle performs a specific function, such as making new materials in the cells, release of waste, transportation, etc. Thus, a cell can perform all its functions with the help of these organelles. That is why the cells are called a structural and functional unit of life.

On-Page 61

Question 1:How do substances like CO2and water move in and out of the cell? Discuss.


Substances like CO2accumulate in high concentration inside the cell. There is CO2 concentration difference in the internal and external environment of a cell. CO2moves out of the cell, from a region of high concentration to a region of low concentration outside the cell by the process of diffusion.

Question 2:Why is the plasma membrane called a selectively permeable membrane?


The plasma membrane selectively allows the entry and exit of some materials in and out of the cell. It also prevents movement of some other materials. Therefore, it is called a selectively permeable membrane.

On-Page 65

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


Mitochondria and plastids.

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


The cell will not be able to perform its basic functions and will die after some time.

Question 3:Why are lysosomes known as suicide bags?


The lysosomes contain very powerful hydrolytic enzymes which are capable of breaking down organic matter. For example, when a cell gets damaged, then lysosomes burst and enzymes digest their own cell. Hence, the lysosomes are known as ‘suicide bags’ of cells.

Question 4:Where are proteins synthesised inside the cell?


Ribosomes are the site of protein is synthesis.


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


Comparison of plant cell and animal cell

Plant Cell

The cell wall is present outside the plasma membrane.

Generally regular in shape.

Larger in size than animal cells Plastids are present.

A permanent and large vacuole is present.

Animal Cell

The cell wall is absent.

Generally irregular in shape.

Smaller in size than animal cells.

Plastids are absent except in Euglena.

Vacuoles are many, small and temporary.

Question 2:How is prokaryotic cell different from a eukaryotic cell?


See the Ans. of Question 1 (Intext Questions Page 63).

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


ln case of plasma membrane ruptures or breaks down: All the useful substances will move out of the cell. There will be no difference between cell content and its external environment.
The cell will lose its normal shape.

Question 4:What would happen to the life of a cell if there was no Golgi apparatus?


Effect of absence of Golgi apparatus on the life of a cell

(i) The packaging and dispatching of different types of proteins to various targets inside and outside the cell will be influenced.

(ii) The products of the cell cannot be stored and modified later.

(iii) There will be an effect on lysosomes formation. This will cause accumulation of worn out and dead cell organelles within the cell which may cause cell death.

Question 5:Which organelle is known as the powerhouse of the cell? Why?


The organelle mitochondria are known as the powerhouse of the cell. Process of cellular respiration takes place in mitochondria to generate the energy required for various chemical activities in the form of ATP. This is the reason that mitochondria are known as the power house of the cell.

Question 8:What is osmosis?


The movement of solvent from a region of its high concentration to a region of its low concentration through a semipermeable membrane is called osmosis. During osmosis, the water molecules (solvent) are free to cross the plasma membrane in both directions.

Question 9:Carry out the following osmosis experiments 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 an experiment?

(iii) Explain why water does not gather in the hollowed-out portion of A and D?


(i) Osmosis is the process responsible for the gathering of water in the hollowed portion of B and C. Since, the concentration of solute (sugar in cup Band salt in cup C) is higher inside the cup as compared to the water, which is outside the cup. Hence, water from its higher concentration (outside the cup) will move towards the lower concentration (inside the cup). This process of osmosis (moving in of solvent) is called endosmosis.

(ii) Potato A acts as a control for the experiment. This is required for comparing the results of the experiment.

(iii) Water does not gather in the hollowed-out portions of A and D because of the following reasons:

• The hollowed portion of potato A is empty. So, because of no concentration difference, no osmosis can occur.

• The hollowed portion of potato D contains sugar in it but it is boiled. So, osmosis cannot occur as its semipermeable membrane is destroyed by boiling.

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