NCERT Solutions for Class 9 Science, Chapter 5: The Fundamental Unit of Life

Class 9 is the first stepping stone for a student in the competitive world. With the introduction of the CBSE Board Exam for class 10 a few years back, this has become an important gateway for a student. Based on the results of class 9th a student selects his future stream of Science, Commerce or Arts suiting his interest.

Takshila Learning is providing NCERT Solutions for Class 9 Science as per the latest syllabus by CBSE. Class 9 is the building block for the CBSE Class 10 Board Exams, not only for your exams but also for your higher studies and career. Science is the most essential subject and the knowledge in this field opens up wider career opportunities for the students.

Below you can find the NCERT solution for Class 9th Science. You can get a Solution for the all-important question of “The Fundamental Unit of Life”

Q1. Who discovered cells, and how?

Answer: In 1665, Robert Hooke discovered cells by examining a thin slice of cork through a self-designed microscope. He observed that Cork formed a hive structure consisting of several small compartments. Miniscule boxes are referred to as cells.

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

Answer: Cells form the structure of a unit. A group of cells forms a tissue, further an organ and eventually 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 activities independently. Therefore, cells are known as structural and fundamental units of life.

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Q3. How do substances like CO₂ and H₂O move in and out of the cell? Discuss.

Answer: CO₂ moves by diffusion – it accumulates in high concentrations in the cellular waste cell, while the concentrations of CO₂ in the external environment are comparatively low. This difference in concentration levels inside and outside the cell causes CO₂ to diffuse from a region of high (within the cell) to a low concentration.

H₂O is transmitted through the cell membrane by osmosis. It moves from a region of high concentration through a selectively permeable membrane to a less concentrated region until equilibrium is reached.

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

Answer: The plasma membrane is called a selectively permeable membrane because it allows the movement of only a certain molecule in cells. Not all molecules are free to disperse.

Q5. Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.

Answer:

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Q1. Can you name the two organelles we have studied that contain their own genetic material?

Answer: The two organelles which have their own genetic material are:

1. Mitochondria
2. Plastids

Q2. If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?

Answer: In the event of any damage to cells and when cells are not regenerated, the lysosome bursts and enzymes digest such cells. This is why lysosomes are often referred to as ‘suicide bags’.

Q3. Why are lysosomes known as suicide bags?

Answer: Lysosomes can burst when damage occurs to the cell and when revival is not possible, and enzymes digest their own cell. As a result, lysosomes are known as suicide bags.

Q4. Where are proteins synthesised inside the cell?

Answer: Protein synthesis in cells occurs in ribosomes. Therefore, ribosomes are also known as protein factories. Ribosomes are particles that are found to be attached to some endoplasmic reticulum.

Exercises:

Q1. Make a comparison and write down ways in which plant cells are different from animal cells.

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

Q2. How is prokaryotic cell different from a eukaryotic cell?

Answer: The following are the differences between prokaryotic and eukaryotic cells.

Q3. What would happen if the plasma membrane ruptures or breaks down?

Answer: If the plasma membrane breaks or breaks, molecules of some substances will move freely in and out of cells. Since the plasma membrane acts as a mechanical barrier, materials are not exchanged from the surrounding environment via osmosis or diffusion into the cell. As a result, the cell will die due to the disappearance of protoplasmic material.

Q4. What would happen to the life of a cell if there was no Golgi apparatus?

Answer: The Golgi system consists of membrane-bound vesicles whose functions are as follows:

•       Storage of substances•       packaging of substances•       manufacture of substances Without the Golgi apparatus, cells would be disabled by packing and dispatching materials that were produced by the cells. The Golgi apparatus is also involved in the formation of cells. Therefore, in the absence of the Golgi apparatus, cells will not be produced.

Q5. Which organelle is known as the powerhouse of the cell? Why?

Answer: Mitochondria are known as the cell’s powerhouse. This is because it releases the energy required for various activities of life. Mitochondria release energy in the form of ATP (adenosine triphosphate) molecules, which are essential for many chemical activities of life. Therefore ATP is often called the ‘energy posture of the cell’.

Q6. Where do the lipids and proteins constituting the cell membrane get synthesized?

Answer: Lipids and proteins are synthesized in the ER [Endoplasmic Reticulum].

Q7. How does an Amoeba obtain its food?

Answer: Through the process of endocytosis, an amoeba receives its food. Since its cell membrane is quite flexible, food particles are attached to form a food vacuole, which is assisted by pseudopodia. The amoeba secretes digestive enzymes once the food is trapped.

Q8. What is osmosis?

Answer: The process of moving the motion of a water molecule from a region of high concentration to a region of low concentration through a low concentration is known as osmosis.

Q9. 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,

1. Keep cup A empty
2. Put one teaspoon sugar in cup B
3. Put one teaspoon salt in cup C
4. 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:

1. Explain why water gathers in the hollowed portion of B and C.
2. Why is potato A necessary for this experiment?

• Explain why water does not gather in the hollowed out portions of A and D.

Answer:

       i.          Water collects water in hollow parts of B and C as difference of concentration is seen. Because of this, endosmosis occurs when cells act as a semiconductor membrane.      ii.          Potato A is essential in this experiment because it is important to compare the different scenarios seen in it. Potato Cup B, C and D. Potato A in this experiment clearly shows that the potato cavity cannot move water on its own.

   iii.          It shows no change in water flow concentration for cup osmosis in A, whichConcentration should be higher than the other. The cells in cup D are dead, thus none of the existence of a semiconductor membrane for water flow. Consequently, osmosis does not occur.

Q10. Which type of cell division is required for growth and repair of body and which type is involved in formation of gametes?

Answer: There are two methods of cell:

• Mitosis
• Meiosis

Mitosis is the type of cell division involved in the development and repair of the body while meiosis is a type of cell division that results in gametes.

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