NCERT Solutions Class 9 Science Chapter 5 The Fundamental Unit of Life
NCERT Solutions Class 9 Science Chapter 5 The Fundamental Unit of Life: National Council of Educational Research and Training Class 9 Science Chapter 5 Solutions – The Fundamental Unit of Life. NCERT Solutions Class 9 Science Chapter 5 PDF Download.
NCERT Solutions Class 9 Science Chapter 5: Overview
Board |
NCERT |
Class |
9 |
Subject |
Science |
Chapter |
5 |
Chapter Name |
The Fundamental Unit of Life |
Topic |
Exercise Solutions |
NCERT Solutions Class 9 Science Chapter 5 – The Fundamental Unit of Life
- Intext Questions:
1.) Who discovered cells, and how?
Ans. Cells were first discovered is the year 1665. Robert hook discovered tiny box like structures when he was observing a thin layer of cork tissue under a rudimentary microscope. It was later understood that cork cells were dead tissue cells observed at that time.
2.) Why is the cell called the structural and functional unit of life?
Ans. Cells perform all metabolic activities and functions necessary for life. Apart from this cell come together to form tissues, organs etc. forming structural and functional unit of life.
3.) How do substances like CO2 and water move in and out of the cell? Discuss.
Ans. Plasma membrane is a selectively permeable membrane. CO2 moves inside and outside the cell by diffusion. After metabolic activities, CO2 is generated in the cell. As CO2 concentration is higher inside the cell in this stage, CO2 will diffuse out of the cell.
Water moves inside and outside the cell through the passage of semipermeable membrane from the higher water concentration to lower water concentration.
4.) Why is the plasma membrane called selectively permeable membrane?
Ans. The plasma membrane is selectively permeable as it does not allow the passage of all ions, molecules inside the cells.
5.) Can you name the two organelles we have studied that contain their own genetic material?
Ans. The two cell organelles which have their own genetic material are mitochondria and plastids.
6.) If the organization of a cell is destroyed due to some physical or chemical influence, what will happen?
Ans. In case of damage to cell due to any physical or chemical activity, the cells will die. The damaged cell contents can be reutilized by the action of lysosomal enzymes.
7.) Why are lysosomes known as suicide bags?
Ans. Lysosomes are responsible for digestion of self-cells which may be damaged due to some physical or chemical activity. Hence, they are called suicide bags.
8.) Where are proteins synthesized inside the cell?
Ans. Proteins are synthesized on the ribosomes. These ribosomes are found attached to the endoplasmic reticulum known as the rough endoplasmic reticulum.
- Textbook exercise questions:
1.) Make a comparison and write down ways in which plant cells are different from animal cells.
Ans: There are large number of differences in animals and plant cells.
Parameter | Animal cell | Plant cell |
Cell wall | Animal cells do not have cell wall | Plant cells have cell wall |
Nucleus | A small central nucleus is present | A large nucleus is present towards the periphery near the cell wall |
Plastids | They are absent in animal cells as they are mainly involved in photosynthesis | They are present in plant cells and are involved in photosynthesis |
Vacuoles | A large number of small vacuoles are present. | A single central large vacuole is present |
Shape | Small, irregularly shaped, many other varied shapes are present | Rectangular or square shaped cells are present in plants |
Rigidity | Due to absence of cell wall cells are less rigid as compared to plant cell. | Cell wall provides rigidity to the plant cell. |
Lysosomes | They are present in animal cells | They are absent in plant cells. |
2.) How is a prokaryotic cell different from a eukaryotic cell?
Sr.No. | Prokaryotic cells | Eukaryotic cells |
1. | They are small in size usually 1 – 10 µm | These cells have a size of about 5-100 µm |
2. | Nuclear membrane is absent so genetic material is present in the nucleus | A well-defined nucleus is present |
3. | A single circular chromosome is present | More than one chromosome is present. |
4. | Membrane bound cell organelles are absent | Membrane bound cell organelles are present |
5. | Most of the prokaryotic organisms are unicellular | Eukaryotic cells are multicellular |
6. | Examples include bacteria, blue green algae | Most of funguses, animals and plants are multicellular eukaryotes |
3.) What would happen if the plasma membrane ruptures or breaks down?
Ans. Plasma membrane is the selective barrier between cell and the environment. It separates content of the cells from the surroundings. If the cell membrane breaks down or ruptures all the contents of the cell spill out in the surroundings. Processes like diffusion and osmosis are affected. This may lead to cell death.
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4.) What would happen to the life of a cell if there was no Golgi apparatus?
Ans. The functions of Golgi apparatus include storage, modification and packaging of products generated in vesicles. Hence Golgi apparatus is not present all the above functions will be impaired. Apart from this lysosome synthesis is also affected if Golgi apparatus is not present.
5.) Which organelle is known as the powerhouse of the cell? Why?
Ans. The mitochondria are rightfully called the power house of the cell as it is the site of generation of ATP (Adenosine triphosphate). ATP is the source of energy for making new chemical compounds and formechanical work in a cell.
6.) Where do the lipids and proteins constituting the cell membrane get synthesized?
Ans. Lipids and proteins are important constituents of the cell membrane. The site of synthesis of lipids and proteins in a cell is the endoplasmic reticulum in the process of membrane biogenesis.
7.) How does an Amoeba obtain its food?
Ans. Endocytosis is a unique process by which amoeba acquire their food. The cell membrane is dynamic structure. In amoeba the pseudopodia (false feet) help in enclosing the food particles, and engulfing the food material from the surrounding environment. The food material is digested with the help of vacuoles. This is called as endocytosis.
8.) What is osmosis?
Ans. Osmosis is the movement of water from a region of high-water concentration to low water concentration through a selectively permeable membrane till equilibrium is achieved.
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.
Ans. I) Osmosis occurs when there is difference in concentration. Water flows from higher water concentration to lower water concentration hence water accumulates in the hollow parts of B and C.
II) As the cup A is empty it serves as a control as there will be no osmosis or diffusion. It can be used to compare if movement of water is taking place in potato cups in other experiment setup
III) For osmosis to take place a concentration gradient is essential. As there is no difference in concentration gradient in cup A movement of water is not seen. Apart from concentration gradient semi permeable membrane is also essential. As the cup is boiled there is no semipermeable membrane present, so osmosis does not occur in Cup D.
10.) Which type of cell division is required for growth and repair of body and which type is involved in formation of gametes?
Ans. A process in which cell division is required for growth and repair of body is called mitosis, whereas meiosis is the cell division required for formation of gametes.
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