Class 9 - Chapter 5 - Cell - Fundamental Unit of Life - NCERT Q & A #class9-biology #eduvictors

Fundamental Unit of Life 

NCERT Q & A

Q1: Who observed the cells the first time?
Answer: Robert Hooke. He observed a thin slice of cork cells under a simple microscope.

 

Simple Microscope made by Robert Hooke (credits: Wikipedia)

Q2: Define Cell

Answer: The cell is the structural and functional unit of life.

Q3: Who proposed the cell theory?

Answer: Schleiden (1838) and Schwann (1839).

Q4: Who expanded cell theory by suggesting that all cells arise from pre-existing cells?

Answer: Virchow (1855.

Q5: In which year the electron microscope was invented?

Answer: 1940

Q6: Name the book in which Robert Hooke published his observations about cork cells.

Answer: Micrographia.



Q7: Who discovered the nucleus in the cell?
Answer: Robert Brown (1831)

Q8: Name the two postulates of the cell theory.
Answer:

• The cell is the basic structural and functional unit of life for all living beings.
• All cells arise from pre-existing cells.

Q9: Who coined the term 'protoplasm'?

Answer: Purkinje in 1839 coined the term ‘protoplasm’ for the fluid substance of the cell.

Q10: Name the largest cell.
Answer: The egg of the ostrich is the largest cell (170 x 135 mm) which can be seen with an unaided eye.

An ostrich egg (Source: Wikipedia)

Q11: Name the world's smallest cell.

Answer: It is a type of bacteria called Mycoplasma with a diameter of 10µm (micrometre).


Q12: Name the smallest cell in the human body.

Answer: Human sperm cell with 5x3 µm.

Q13: Name the biggest cell in the human body.

Answer:  Human ovum is about 1mm in diameter.


Q14: Name the longest cell in the human body.

Answer: Human nerve cell is about 1 meter long.


Q15: Name the cell in a human body which cannot reproduce.

Answer: RBCs or Red Blood Corpuscles/cells.

Q16: Give an example of an anucleate cell i.e. cell without a nucleus.

Answer: RBCs or Red Blood Corpuscles/cells in mammals.

Q17: Give an example of cells containing two nuclei (Binucleate).

Answer: Paramecium


Q18: Give examples of cells which are muti-nucleate (i.e. having many nuclei).

Answer: Striated muscles, few types of algae and fungi.

Q19: What is the plasma membrane composed of?

Answer: Lipids and Proteins. It has a viscous bilayer of lipid with protein molecules occurring on inner and outer sides of the lipid bilayer. (Phospholipid bilayer)

Q20: Who proposed the fluid-mosaic model of cell or plasma membrane?

Answer: Singer and Nicholsan (1972)

Note: The fluid mosaic model describes the plasma membrane as a phospholipid bilayer with embedded proteins.

Q21: Is plasma membrane permeable or selectively permeable?

Answer: Selectively permeable i.e. it allows certain molecules or ions to pass through it.


Q22: What are the different types of transport of components across the cell membrane?

Answer: Two types:

• Passive Transport: e.g. Diffusion, Osmosis
• Active Transport: e.g. endocytosis, exocytosis

Q23: Define Passive Transport.

Answer: Passive transport is the net movement of materials across membranes that does not require any special source of energy.


Q24: What is diffusion?

Answer: Diffusion is the net movement of molecules from high to regions of lower concentration as a result of random molecular motion. Diffusion tends to distribute molecules uniformly.

Exchange of gases like CO₂ and O₂ in lungs, plants, blood cells, and O₂ entering stomata of leaves are examples of diffusion.

Diffusion is passive transport i.e. no external energy is provided for the movement of molecules. The natural kinetic energy of the particle supplies the energy.


Q25: Define Osmosis. What are the different types of osmosis? Give examples of osmosis.

Answer: Osmosis is a special type of diffusion i.e. passage of water (solvent) across a selectively permeable membrane,  from a region of high water concentration (dilute solution) to the region of low water concentration (concentrated solution).

Osmosis is also a passive transport i.e. no external energy is required for the passage.

There is two types of osmosis:

1. Endosmosis: The process in which the water molecules enter into the cell is known as endosmosis.
2. Exosmosis: The process in which the water molecules move out of the cell is known as exosmosis.

Examples of Osmosis are:

• Absorption of water by plant roots.
• Absorption of water by alimentary canal.
• Re-absorption of water by tubules of the nephron in kidneys.

Q26: What happens to a cell (plant cell or animal cell) when placed in the following solutions:
(a) Hypotonic solution
(b) Isotonic solution
(c) Hypertonic solution

Answer:
(a) Hypotonic Solution: the external solution is dilute i.e. high water concentration (low solute concentration). In this case, water will rush into the cell and it will gain water.

(b) Isotonic Solution: external solution concentration is the same as the internal solution concentration of the cell. In this case, there is no net movement of water.

(c) Hypertonic Solution: the external solution is of high solute concentration i.e. low water concentration. Here water will rush out from the cell and it will shrivel/shrink.

The figure below shows red blood cell and plant cell osmotic behaviour in various types of solutions.

Q 27: What is plasmolysis?

Answer: When a living plant cell loses water placed in a hypertonic solution, the plant cell shrinks away from the cell wall. This process is called plasmolysis. Plants with plasmolysed cells wilt.


Q28: Place a de-shelled egg in water for five minutes. What do you observe?

(Note: De-shelled egg means, the shell of an egg is removed by dissolving it in dilute hydrochloric acid. The shell is mostly calcium carbonate. A thin outer skin now encloses the egg.)

Answer: The egg swells because water passes into it by osmosis. (hypotonic solution).

Q29: What will happen if a de-shelled egg is in a concentrated salt solution for 5 minutes?

Answer: The egg shrinks because water passes out of the egg into the salt solution. The salt solution is more

concentrated than the inside of the egg. (Hypertonic)

Q30 (CBSE): Put dried raisins in plain water and leave them for some time. Then place them in a concentrated solution of sugar or salt. What do you observe in both cases?

Answer: Case I:  Raisins gain water and swell when placed in pure water.

Case II: When placed in the concentrated solution, raisins lose water and hence shrink. 

Q31: What would happen if the plasma membrane ruptures or breaks down?

Answer: Plasma or Cell membrane is a selectively permeable membrane i.e. it allows movement of certain materials in and out to the cell. In case the plasma membrane ruptures (like in hypertonic solution), the cell will shrivel and eventually die. At this time, the lysosomes of the cell will come into action. Lysosomes will release digestive enzymes and eat up worn-out cell organelles and foreign material.

Q32: What do you mean by Endocytosis? How does an Amoeba obtain its food?

Answer: The process by which a cell engulfs material to bring it into the cell is called endocytosis. It is a type of active transport. Endocytosis is of two types:

• Phagocytosis: It refers to the process of engulfing large particles (or cell eating).
• Pinocytosis: refers to engulfing macromolecules. (or cell drinking)

For example, Amoeba obtains its food by endocytosis in which the flexibility of the cell membrane enables the cell to engulf food and other material from its external environment.

Q33: Define Exocytosis.

Answer: Exocytosis is a process to move material to the outside of the cell.  A vesicle fuses with the plasma membrane and discharges its contents outside.  This allows cells to secrete molecules. It is a type of active transport.

Q34: Why are lysosomes known as suicide bags?

Answer:  Lysosomes are organelles that contain digestive enzymes. They digest excess or worn-out organelles, food particles, and engulfed viruses or bacteria. Lysosomes fuse with vacuoles and dispense their enzymes into the vacuole, digesting its contents. Sometimes, lysosomes digest the cells that contain them. It happens when cells get damaged or destroyed. That's why lysosomes are called suicidal bags.

E.g. When a tadpole develops into a frog, lysosomes within the cells of the tadpole’s tail cause its digestion. Or Lysosomes help in defence by digesting germs, as in white blood cells.

Concept Map on Cell Structure

Cell Structure (concept map)

Q35: Viruses are

(a) Uni cellular micro-organisms

(b) Bi-Cellular micro-organisms

(c) Multi-cellular micro-organisms 

(d) Non-cellular micro-organisms

Answer: (d). Non-Cellular. Viruses lie on the line of division between living and non-living. They are non-living carrying RNA material. They act as living when finding a suitable host and multiply.

Q36: Who is known as the Father of Biology?

Answer: Aristotle.

Q37: Who discovered the Golgi apparatus?

Answer: Camillo Golgi

Q38: Which cell organelle is known as the "protein factory"?

Answer: Ribosomes

Q39: What is the energy currency of the cell called?

Answer: ATP (Adenosine triphosphate)

Q40: When chromosomes are visible in the nucleus?

Answer: During cell division.

Q41: Which of the following is NOT involved in the synthesis of proteins?
(a) rough ER
(b) smooth ER
(c) Golgi body
(d) ribosomes

Answer: (b) smooth ER. 

Rough ER is the site for protein synthesis and has ribosomes embedded. Ribosomes on the rough ER produce
proteins that are passed from the cell; the Golgi body then packages them for this purpose. Smooth ER is used mainly in the making of lipids and detoxifying enzymes.

Q42: Which of the following often distinguishes plant cells from animal cells?
(a) centrioles
(b) nucleus
(c) chromatin
(d) rough ER

Answer: (a) Centrioles

Q43: Are plastids present in all cells? What are its types?

Answer: Plastids are present only in plant cells. Based on colour pigments,  there are three types of plastids:

• Leucoplasts: White or colourless.
• Chromoplast: Coloured like blue, red, and yellow.
• Chloroplast: Green in colour.

Q44: Name the sac-like structure which forms the grana.      

Answer: Sac-like structures in chloroplasts are called thylakoids.

Q45: What are the conditions for osmosis?
Answer: Conditions for osmosis are:

1. There should be two solutions of different concentrations.
2. The membrane separating these two solutions should be semi-permeable.

Q46: Will the temperature have any effect on the process of osmosis?

 Answer: Yes the higher temperature will increase the rate of water entering the cell as it increases the kinetic energy of the solution.

Q47: What is osmoregulation?

Answer: The regulation of the water content of the cell is called osmoregulation.


Q48: Which organ of the plant body helps in osmoregulation?

Answer: Leaves


Q49: Which organelle of the cell in animals helps in osmoregulation?

Answer: Contractile Vacuole.

Q50 What are centrosomes? What functions do they perform?

Centrosomes during cell division

Answer:  Centrosome is a small, star-shaped protoplasmic organelle and is present near to the nucleus. Animal cells, it consists of two small granules called centrioles. These centrioles are orthogonally arranged i.e. lie at right angles to each other.  In plant cells, centrioles are absent.

Functions of Centrosomes:

1. Initiate cell division
2. During cell division, centrioles move to opposite poles of the cell and help in spindle formation.
3. They form basal bodies (microtubules-like structures)  which form cilia or flagella.

Click on the image below to see the video showing cell division in pig kidney cells. Hamamatsu.com, a Japanese company, that sells microscopy-related cameras has a nice collection of cell images.

Cell Division
(source: http://learn.hamamatsu.com)

Q51: Who is known as the 'Father of Microscopy'?

Answer: Antony van Leeuwenhoek

Q52: Are Viruses Prokaryotic or Eukaryotic?

Answer: Neither of the two. Viruses are smaller than prokaryotic cells. A virus is considered as a simple nucleic acid surrounded by a protein coat. They act as non-living and become living after finding a suitable host.

Q53: Which cell organelle is called the "kitchen of plant"?

Answer: Plastids

Q54: Which cell organelle is called the 'control centre'?

Answer: Nucleus.

Q55: Which cell organelle is called the 'transport system'?

Answer: Endoplasmic Reticulum

Q55: What is the Endoplasmic Reticulum(ER)? Name its types.

Answer: The cell organelle, Endoplasmic reticulum (ER) is an extensive, interconnected, membrane-bound network of tubes and sheets. It consists of various channels like cisternae, vesicles and tubules. ER carries materials throughout the cell. There is two types of ERs:

• The rough Endoplasmic Reticulum (RER) - bears ribosomes, involved in protein synthesis.
• Smooth Endoplasmic Reticulum (SER) - Does not bear ribosomes, involved in lipid synthesis.

Q56: What are the functions of the Endoplasmic Reticulum (ER)?

Answer:

1. Helps in transporting materials from one part to another inside cells.
2. Acts as a skeletal framework and provides mechanical strength to the cytoplasmic matrix.
3. Provides a larger surface area for the synthesis of various metabolic activities.
4. It contains various enzymes which act as a catalyst in the synthesis of lipids and proteins.
5. SER is also involved in the process of detoxification of drugs and poison.

Q57: What are the components nucleus?

Answer:

1. nucleolus
2. nuclear membrane
3. chromatin network (forms in chromosomes and carries genes).
4. nucleoplasm

Q58: What is the function of nucleoplasm?

Answer:  Nucleoplasm is a semi-fluid which contains a number of enzymes which help in the synthesis and functioning of DNA and RNA (genetic material).

Q59: How chromatic network is related to chromosomes?

Answer: Chromatin network is a tangled fibrous mass inside the nucleus. The chromatin threads condense and turn into chromosomes during cell division.

Q60: What are chromosomes?

Answer: Chromosomes are compact rod-like bodies, which are formed at the time of cell division from chromatin material. They are made up of DNA and carry genes (unit of inheritance).

Q61: What is the full form of DNA and RNA?

Answer: DNA - Deoxyribose Nucleic Acid

                RNA - Ribonucleic acid

Q62: Who discovered Virus?

Answer: Virus was discovered by Ivanowsky, a Russian Botanist in 1892.

Q63: What are the functions of the nucleus?

Answer:

1. The nucleus controls all the cellular activities of the cell.
2. The nucleolus is involved in the synthesis of ribosomes.
3. The nucleus contains the hereditary information of a cell. 
4. It is responsible for cell division (reproduction) and transmission of genetic information from parents to offspring.

Surface Area to Volume Ratio

Surface Area of a cube (SA) =  (Length x Width) x 6 Faces
Volume of cube (V) = length x length length
Surface Area to Volume Ratio = SA/V
SA/V ratio of cube of 1 cm length =  6:1
SA/V ratio of cube of 2 cm length =  24/8 = 3:1
SA/V ratio of cube of 4 cm length = 96/64 = 1.5: 1
⇒ SA/V ratio decreases as the sizes of the cube increases

Q64: Why can't single cells grow very large? Or  Big organisms like human beings are multi-cellular? Why can't such big organisms be a single large cell?

Answer: The cell is the fundamental unit of life. All metabolic activities (necessary for life) take place inside the cell. All raw materials required for these metabolic activities enter through the cell surface via the cell membrane. The greater the surface is, a large amount of raw material can enter (this is the case of unicellular micro-organisms). As the size of the cell grows larger, the Surface Area to Volume (SA/V) ratio decreases, it means the raw material required for the cell to survive will not be sufficient. Thus, the SA/V ratio limits the size of the cell. Therefore big organisms like human beings are mulch-cellular.

Q65(NTSE Stage2): Which of the following is an example of a single cell that does not function as a full-fledged organism?

(a) White blood cells (WBC)
(b) Amoeba
(c) WBC and Amoeba
(d) Paramecium

Answer:  (a) WBC


Q66: Why do vegetable vendors (sabzi-walla) regularly sprinkle water on the vegetables in their baskets?

Answer: Water makes a hypotonic environment for the plant cells and they take up water to avoid the plasmolysed condition. Therefore the vegetables look crisp and fresh.


Q67: Why do we stain cells while observing under a microscope? List commonly used stains.

Answer: Stains help us visualize specific organelles of cells in a better way. Otherwise, these organelles are not easily recognizable via microscope. Stains or dyes are basic or acidic in nature and have an affinity to certain organelles.  For example, methylene blue is a basic dye which has an affinity to nucleic acid and hence it can stain the nucleus. Methylene blue is commonly used to stain animal cells. Similarly, iodine dye is used to detect starch and used to stain plant cells. Eosin is used to identify RBCs, cell membrane and cytoplasm. Safranin is another nuclear stain and is also used to stain Rheo leaves to visualize stomata.
(Read a nice article on Cell Stain)


Q68: Are there any exceptions to cell theory proposed by  Schleiden & Schwann and Virchow? If yes, what are those?

Answer: Yes there are exceptions to the cell theory. These are:

1. Cell theory does not explain the nature of the Virus. They become live and multiply though they are made up of non-living material.
2. How come the first living cell originated or how life began on the earth? (Scientists J.B.S. Haldane, Stanley L. Miller and Harold C. Urey did experiments on this.).
3. Mitochondria and chloroplasts have their own genetic material and can reproduce independently.

Q69: What is the thickness of the cell membrane?

Answer: 7-10 nanometers.

Q70: Why are mitochondria absent in red blood cells?

Answer: RBCs are the oxygen and food transporters to different body cells. If they have mitochondria, they will consume the carrying oxygen for themselves.


Q71: Name the cell organelles which their own DNA and Ribosomes.

Answer: Mitochondria and Plastids.


Q72: What is the cytoskeleton?

Answer: It is a dynamic network of protein fibres which provide structural support and shape to the cell.


Q73: Name the cell organelles involved in the synthesis, packaging and movement of protein (or other macromolecules) inside a cell.

Answer: Ribosomes, Golgi Bodies and Endoplasmic Reticulum (Smooth and Rough ER)

Watch the youtube video on The Wacky History of Cell Theory by TED.com

Q74: Name the cell type that has internal membranes which compartmentalize their functions.

Answer: Eukaryotes.

Q75: Name the cell organelles which change energy from one form to another.

Answer: Mitochondria (breaks glucose to obtain energy) and chloroplast (converts sunlight energy to food).



Q76(HOTS): Which of the following cell is a better candidate to study lysosomes?

⒜ White Blood Cell ⒝ Muscle Cell

Answer: White Blood Cell. It acts as a soldier cell and kills germs and foreign bodies.

Q77: What kind of plastids is more common in
   a. root of the plant?
   b. leaves of the plant.
   c. flowers and fruits

Answer:
a. Leucoplasts in roots (for storage)
b. Chloroplasts in leaves (for photosynthesis)
c. Chromoplasts in flowers and fruits (to provide colour)



Q78: Why do plant cells possess largely sized vacuoles?

Answer: Vacuoles are large-sized in plants because it carries out the following activities:
1. It stores salts, sugar, amino acids, organic acids and some proteins.
2. Metabolic wastes of the cell are dumped in the vacuole.
3. Lysosomal enzymes occur in the vacuole of a plant cell.
4. It stores cell sap that helps in maintaining the turgidity of the cell.
5. It contains osmotic concentration which facilitates the osmosis process through the plasma membrane


Q79: Why does the skin of your fingers shrink when you wash clothes for a long time?

Answer: Clothes are washed with soaps and detergent solutions which are hypertonic. It results in exosmosis in skin cells ( loses water)  results in the shrinking of cells.


Q80: Why is endocytosis is found in animals only?

Answer: In animal cells cell wall is absent. Hence the plasma membrane is in direct contact with the external environment. The plasma membrane is flexible in nature and helps in swallowing up food and foreign particles (virus, bacteria etc.) by active transport. Plants have a rigid cell wall and cannot perform endocytosis.


Q81: A person takes a concentrated solution of salt, and after some time, he starts vomiting. What is the phenomenon responsible for such a situation? Explain. 

Answer: The Concentrated salt solution is hypertonic which causes dehydration the in alimentary canal due to exosmosis. It causes vomiting.


Q82: Name any cell organelle which is non-membranous.

Answer: Ribosomes


Q83: What type of processes generally occur in a cell?

Answer: Common processes occur in cells:
- cell metabolism (respiration, photosynthesis etc.)
- transport of substances,
- communication, and
- cell reproduction.


Q84: What is cell metabolism?

Answer: The chemical reactions that a cell carries out to maintain life are known collectively as cell metabolism.


Q85: Name the types of cell metabolic reactions.

Answer: There are three types of metabolic activities that occur inside a cell:
1. Anabolic reactions
2. Catabolic reactions.
3. Oxidation-reduction reactions


Q86: State the differences between mitosis and meiosis.

Answer:

	Mitosis	Meiosis
1	Two daughter cells are produced.	It is equational division i.e. the number of chromosomes in the daughter remains the same.
2	Four daughter cells are produced.	It is reductional division i.e. the number of chromosomes is reduced to half in the daughter cells.

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