NCERT Solutions for Class 9 Science Chapter 5 - The Fundamental Unit Of Life

NCERT Solutions For Class 9 Science Chapter 5 PDF Free Download

Learn everything you need to know about the cell, through NCERT Solutions for Class 9 Science Chapter 5 – The Fundamental Unit Of Life. Solutions are carefully crafted by highly qualified teachers who are experts in their respective fields. Furthermore, we ensure that appropriate content on NCERT Solutions Class 9 is regularly updated as prescribed by the CBSE board. Besides accurate solutions, we also provide a complete breakdown of the questions, detailing all the steps and process in an easy to understand format.

Additionally, we ensure that the answers we provide are tailored to meet multiple criteria for the purpose of awarding marks. This ensures that our answers are relevant and retains its informational quotient.

Download PDF of NCERT Solutions for Class 9 Science Chapter 5 – The Fundamental Unit Of Life

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Access Answers of Science NCERT class 9 Chapter 5 – The Fundamental Unit Of Life (All in text and Excercise Questions solved)

Exercise-5.1 Questions with Answer

Q1. Who discovered cells, and how?

Solution:

in 1665, Robert Hooke discovered cells while examining a thin slice of cork through a self-designed microscope. He observed that the cork resembled the structure of a honeycomb consisting of numerous tiny compartments. The miniscule boxes are referred to as cells.

Q2. Why is the cell called the structural and functional unit of life?

Solution:

Cells form the structure of an entity. A group of cells form a tissue, further an organ and ultimately an organ system. They perform fundamental functions and life processes such as respiration, digestion, excretion etc in both unicellular and multicellular entities. They perform all the activities independently. Hence, cells are referred to as structural and fundamental units of life.

Exercise-5.2.1  page 61 Questions with Answer

Q3. How do substances like CO2 and water move in and out of the cell? Discuss.

Solution:

CO2 moves by diffusion – This 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 out 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.

Q4. Why is the plasma membrane called a selectively permeable membrane?

Solution:

The plasma membrane is called a selectively permeable membrane as it permits the movement of only a certain molecule in and out of the cells. Not all molecules are free to diffuse.

Exercise-5.2.2-5.2.4 Page 63 Questions with Answer

Q5. 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 = 10-6m

2.   Nuclear region:

______________________________

______________________________

and known as ___________________

3.  Chromosome: single

4.  Membrane-bound cell organelles absent.

1.  Size: Generally large (5-100 μm)

2.  Nuclear region: well defined and surrounded by a nuclear membrane.

 

3. More than one chromosome.

4. ______________________________

______________________________

______________________________

Solution:

Prokaryotic Cell Eukaryotic Cell
1.  Size: Generally small (1-10 μm)

1 μm = 10-6m

2.  The nuclear region is poorly defined due to the absence of a nuclear membrane and known as the nucleoid.

3. There is a single chromosome.

4. Membrane-bound cell organelles absent.

1. Size: Generally large (5-100 μm)

2. Nuclear region: well defined and surrounded by a nuclear membrane.

3. There are more than one chromosomes.

4. Membrane-bound cell organelles present.

Exercise-5.2.5 Questions with Answer

Q6. Can you name the two organelles we have studied that contain their own genetic material?

Solution:

The two organelles which have their own genetic material are:

1. Mitochondria

2. Plastids

Q7. If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?

Solution:

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’.

Q8. Why are lysosomes known as suicide bags?

Solution:

When there is damage to the cell and when revival is not possible, lysosomes may burst, and the enzymes digest their own cell. Consequently, lysosomes are known as suicide bags.

Q9. Where are proteins synthesised inside the cell?

Solution:

Protein synthesis in cells takes place in ribosomes. Hence, ribosomes are also referred to as protein factories. Ribosomes are particles that are found attached to the rough endoplasmic reticulum.

Exercise Questions with Answer

Q10. Make a comparison and write down ways in which plant cells are different from animal cells.

Solution:

The following table depicts the differences between plant cells and animal cells.

Characteristic Plant Cell Animal Cell
Cell wall Present Absent
Shape of cell Distinct edges, shape is either rectangular or square shaped. Round and irregular shape
Nucleus Present. Lies on one side of the cell Present. Lies in the center of the cell
Lysosomes Rarely present Always present
Plastids Present Absent
Structure of Vacuoles Single or a few large vacuole that is centrally located Presence of numerous and small vacuoles

Q11. How is prokaryotic cell different from a eukaryotic cell?

Solution:

The following are the differences between prokaryotic and eukaryotic cells.

Prokaryotic Cell Eukaryotic Cell
1.  Size: Generally small (1-10 μm)

1 μm = 10-6m

2.  The nuclear region is not well defined as the nuclear membrane is absent and is referred to as the nucleoid.

3. There is a single chromosome.

4. Membrane-bound cell organelles absent.

1. Size: Generally large (5-100 μm)

2. Nuclear region: well defined and girdled by a nuclear membrane.

3. There are more than one chromosomes.

4. Membrane-bound cell organelles present.

Q12. What would happen if the plasma membrane ruptures or breaks down?

Solution:

If plasma membrane ruptures or breaks down then molecules of some substances will freely move in and out of the cells. As plasma membrane acts as a mechanical barrier, exchange of material from its surroundings through osmosis or diffusion in a cell won’t take place. Consequently, the cell would die due to the disappearance of the protoplasmic material.

Q13. What would happen to the life of a cell if there was no Golgi apparatus?

Solution:

The Golgi apparatus consists of stacks of membrane-bound vesicles whose functions are as follows:

  • storage of substances
  • packaging of substances
  • manufacture of substances

Without the golgi apparatus, the cells will be disabled from packing and dispatching materials that were produced by the cells. The golgi apparatus is also involved in the formation of cells. Hence, in the absence of golgi apparatus, cells will not be produced.

Q14. Which organelle is known as the powerhouse of the cell? Why?

Solution:

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 ‘energy currency of the cell’.

Q15. Where do the lipids and proteins constituting the cell membrane get synthesised?

Solution:

Lipids and proteins are synthesised in the ER [Endoplasmic Reticulum].

Q16. How does an Amoeba obtain its food?

Solution:

Through the process of endocytosis, an Amoeba obtains its food. As its cell membrane is flexible enough, food particles are engulfed forming a food vacuole girdling it which is assisted by the pseudopodia. Amoeba secretes digestive enzymes to bring about digestion of the engulfed particle once food is trapped.

ncert solution class 9 chapter 5 fig 1

Q17. What is osmosis?

Solution:

The process of movement of a water molecule from a region of higher concentration to a region of lower concentration through a semipermeable membrane is known as osmosis.

Q18. 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.

Solution:

(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. The 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 the 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.

Q19. Which type of cell division is required for growth and repair of body and which type is involved in formation of gametes?

Solution:

There are two ways in which a cell divides:

  • Mitosis
  • Meiosis

Mitosis is the type of cell division that is involved in the growth and repair of body whereas meiosis is a type of cell division which results in the formation of gametes.

NCERT Solutions for Class 9 Science Chapter 5 – The Fundamental Unit Of Life

NCERT Solutions of class 9 Science Chapter 5 – The Fundamental Unit Of Life is a part of Unit 2 – Organisation in the Living World, and is expected to fetch around 20 marks. Therefore, this is quite an important chapter and it becomes imperative that it is thoroughly learnt before attempting the exam.

The topics and Subtopics of  NCERT Solutions of class 9 Science Chapter 5 – The Fundamental Unit Of Life:

  • What are Living Organisms Made Up of ?
  • What is a Cell Made Up of ? What is the Structural Organisation of a Cell?
    • Plasma Membrane Or Cell Membrane
    • Cell Wall
    • Nucleus
    • Cytoplasm
    • Cell Organelles.

Exercises with Question count covered in NCERT Solutions for Class 9 Chapter 5:

Exercise 5.1, Page number 59 – Solution of 2 Questions
Exercise 5.3, Page number 63 – Solution of 4 Questions
Exercise 5.4, Page number 63 – Solution of 2 Questions
Exercise 5.5, Page number 65 – Solution of 4 Questions
Chapter Exercise, Page number 67 – Solution of 10 Questions

NCERT Solutions for Class 9 Science Chapter 5 – The Fundamental Unit Of Life

Life is all around us, from microscopic microbes to gargantuan whales. But if we were to take a look at all these organisms under a microscope, we would find the cell – the basic and fundamental unit of life.

A cell and be an individual organism – such as a bacteria, or it could amass and form a multicellular organism, like humans. Discover everything you need to know about the cell and learn its definition, types, characteristics and more by exploring our NCERT Solutions. Additionally, these solutions are very helpful for last-minute revisions during exams.

Key Features of NCERT Solutions for Class 9 Science Chapter 5 – The Fundamental Unit Of Life

  1. Content delivered in an easy-to-learn format.
  2. Solutions are crafted in-house by knowledgable teachers
  3. Updated questions and solutions according to the latest prescribed syllabus
  4. Breakdown of the toughest exam questions from previous years
  5. Discover other additional resources like previous year question papers and sample papers.

Also Read: NCERT Solutions Class 9 Science

Frequently Asked Questions on The Fundamental Unit Of Life

Who discovered cells, and how?

In 1665, Robert Hooke discovered cells while examining a thin slice of cork through a self-designed microscope. He observed that the cork resembled the structure of a honeycomb consisting of numerous tiny compartments. The miniscule boxes are referred to as cells.

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

Cells form the structure of an entity. A group of cells form a tissue, further an organ and ultimately an organ system. They perform fundamental functions and life processes such as respiration, digestion, excretion etc in both unicellular and multicellular entities. They perform all the activities independently. Hence, cells are referred to as structural and fundamental units of life.

Why is the plasma membrane called a selectively permeable membrane?

The plasma membrane is called a selectively permeable membrane as it permits the movement of only a certain molecule in and out of the cells. Not all molecules are free to diffuse.

Why are lysosomes known as suicide bags?

When there is damage to the cell and when revival is not possible, lysosomes may burst, and the enzymes digest their own cell. Consequently, lysosomes are known as suicide bags.

Where are proteins synthesised inside the cell?

Protein synthesis in cells takes place in ribosomes. Hence, ribosomes are also referred to as protein factories. Ribosomes are particles that are found attached to the rough endoplasmic reticulum.

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

If plasma membrane ruptures or breaks down then molecules of some substances will freely move in and out of the cells. As plasma membrane acts as a mechanical barrier, exchange of material from its surroundings through osmosis or diffusion in a cell won’t take place. Consequently, the cell would die due to the disappearance of the protoplasmic material.

What is osmosis?

The process of movement of a water molecule from a region of higher concentration to a region of lower concentration through a semipermeable membrane is known as osmosis.

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