Fundamental Unit Of Life Most Important Questions Of Class 9th

Exercise Questions And Answers

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

Answer:

• Cell Wall: Plant cells have a rigid cell wall; animal cells do not.
• Chloroplasts: Plant cells contain chloroplasts for photosynthesis; animal cells lack chloroplasts.
• Vacuole: Plant cells have a large central vacuole; animal cells have small, temporary vacuoles.
• Shape: Plant cells are generally rectangular; animal cells are round or irregular.

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

Answer:

• Nucleus: Prokaryotic cells lack a true nucleus; eukaryotic cells have a membrane-bound nucleus.
• Organelles: Prokaryotic cells lack membrane-bound organelles; eukaryotic cells have them.
• Size: Prokaryotic cells are generally smaller; eukaryotic cells are larger.
• Genetic Material: Prokaryotic DNA is circular and free-floating; eukaryotic DNA is linear and contained within the nucleus.

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

Answer: The cell would lose its integrity, leading to uncontrolled movement of substances in and out, and eventual cell death due to loss of essential components and inability to maintain homeostasis.

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

Answer: The cell would be unable to modify, package, and transport proteins and lipids properly, affecting cell function and secretion.

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

Answer: Mitochondria are known as the powerhouse because they produce ATP through cellular respiration, providing energy for the cell’s activities.

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

Answer:

• Lipids: Synthesized in the smooth endoplasmic reticulum.
• Proteins: Synthesized in the rough endoplasmic reticulum.

7. How does an Amoeba obtain its food?

Answer: An Amoeba engulfs food through phagocytosis, extending pseudopodia around the food particle to form a food vacuole where digestion occurs.

8. What is osmosis?

Answer: Osmosis is the movement of water across a semi-permeable membrane from an area of low solute concentration to an area of high solute concentration.

9. Carry out the following osmosis experiment:

Answer:

• (i) Explain why water gathers in the hollowed portion of B and C:
  Answer: Water gathers due to osmosis; water moves into cups B and C to equalize the solute concentration gradient.
• (ii) Why is potato A necessary for this experiment?
  Answer: Potato A acts as a control, showing the baseline scenario where no solute is present.
• (iii) Explain why water does not gather in the hollowed-out portions of A and D:
  Answer: In A, there is no solute to create an osmotic gradient. In D, boiling denatures cell membranes, preventing osmosis.

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

Answer:

• Growth and Repair: Mitosis is required.
• Formation of Gametes: Meiosis is involved.

The Fundamental Unit of Life: Questions and Answers

Introduction

Understanding the fundamental unit of life, the cell, is crucial for grasping the complexities of biological organisms. Let’s delve into some key concepts and questions from this topic.

Key Questions and Answers

1. What did Robert Hooke observe when examining a thin slice of cork?

Robert Hooke observed that the cork resembled the structure of a honeycomb consisting of many little compartments. He called these compartments “cells,” a term still used in biology today.

2. How can we observe cells from an onion peel?

To observe onion peel cells, peel off the epidermis from an onion bulb, place it in water, then transfer it to a glass slide. Add a drop of safranin solution and cover with a cover slip. Observe the slide under a microscope.

3. What are unicellular organisms, and can you name a few examples?

Unicellular organisms consist of a single cell that performs all necessary functions. Examples include Chlamydomonas, Paramecium, and bacteria.

4. What is the significance of cell division in multicellular organisms?

Cell division is crucial in multicellular organisms as it allows growth and the replacement of damaged or dead cells. Every multicellular organism originates from a single cell through repeated divisions.

5. Describe the structure and function of lysosomes.

Lysosomes are membrane-bound sacs filled with digestive enzymes. They act as the waste disposal system of the cell, digesting foreign material and worn-out cell organelles. They can break down complex substances into simpler ones.

6. What is the Golgi apparatus, and what role does it play in the cell?

The Golgi apparatus is a system of membrane-bound vesicles that stores, modifies, and packages products in vesicles. It is also involved in the formation of lysosomes and can synthesize complex sugars from simple sugars.

7. Why are mitochondria referred to as the powerhouses of the cell?

Mitochondria are known as the powerhouses of the cell because they generate ATP (adenosine triphosphate), the energy currency of the cell, through chemical reactions. They have their own DNA and ribosomes, enabling them to produce some proteins independently.

8. What are plastids, and what types are found in plant cells?

Plastids are organelles found only in plant cells. There are two main types: chromoplasts (including chloroplasts, which are crucial for photosynthesis) and leucoplasts (which store starch, oils, and proteins).

9. How do cells in multicellular organisms differ in terms of structure and function?

In multicellular organisms, cells often differ in shape, size, and function. For example, blood cells, bone cells, and muscle cells all have unique structures and specialized functions tailored to their roles in the body.

10. Explain the importance of studying cells in understanding living organisms.

Studying cells is fundamental to understanding living organisms because cells are the basic building blocks of life. They perform essential functions that sustain life, and all biological processes can be traced back to cellular activities .

The Fundamental Unit of Life: Cell Structure and Function

Introduction

Cells are the fundamental building blocks of life. This chapter delves into the intricate details of cell structure and function, exploring the differences between prokaryotic and eukaryotic cells, the various cell organelles, and the processes essential for cell survival and function.

Endoplasmic Reticulum (ER)

Structure and Function of ER

The endoplasmic reticulum (ER) is a vast network of membrane-bound tubes and sheets. It is divided into two types:

• Rough ER (RER): Studded with ribosomes, it is crucial for protein synthesis.
• Smooth ER (SER): Lacks ribosomes and is involved in lipid synthesis and detoxification processes.

Functions of ER

• Transport Channels: ER serves as pathways for transporting materials within the cell.
• Synthesis of Proteins and Lipids: RER synthesizes proteins, while SER synthesizes lipids.
• Detoxification: SER helps in detoxifying poisons and drugs.

Golgi Apparatus

Discovery and Structure

Discovered by Camillo Golgi, the Golgi apparatus consists of a series of flattened membrane-bound vesicles. These are often parallel to each other and are involved in modifying, sorting, and packaging of proteins and lipids.

Functions

• Modification and Packaging: Processes proteins synthesized in the ER.
• Formation of Lysosomes: Involves in lysosome formation.

Lysosomes

Structure

Lysosomes are membrane-bound sacs filled with digestive enzymes. They originate from the Golgi apparatus and the ER.

Functions

• Intracellular Digestion: Break down waste materials and cellular debris.
• Autolysis: Enzymes can digest the cell itself if it is damaged (suicide bags).

Mitochondria

Structure

Mitochondria are double-membraned organelles with their own DNA and ribosomes. The inner membrane is highly folded into cristae.

Functions

• Energy Production: Site of ATP (adenosine triphosphate) synthesis.
• Cellular Respiration: Involved in the energy release process.

Plastids

Types and Functions

• Chloroplasts: Contain chlorophyll for photosynthesis.
• Leucoplasts: Store starch, oils, and proteins.
• Chromoplasts: Contain pigments that give color to fruits and flowers.

Vacuoles

Structure

Vacuoles are storage sacs within cells, larger in plant cells than in animal cells.

Functions

• Storage: Store nutrients, waste products, and other materials.
• Maintaining Turgidity: Provide structural support to plant cells.

Questions and Answers

Questions from the Text

1. Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.
   • Size: Generally small (1-10 µm) | Generally large (5-100 µm)
   • Nuclear region: Not well defined, known as nucleoid | Well defined, surrounded by a nuclear membrane
   • Chromosome: Single | More than one chromosome
   • Membrane-bound cell organelles: Absent | Present
2. Can you name the two organelles we have studied that contain their own genetic material?

• Mitochondria and Plastids

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

• The cell will die as its essential functions are disrupted.

1. Why are lysosomes known as suicide bags?

• They contain digestive enzymes that can digest the cell itself if they are released into the cytoplasm.

1. Where are proteins synthesized inside the cell?

• Proteins are synthesized in the rough endoplasmic reticulum (RER).

Additional Questions

1. What are the two types of endoplasmic reticulum?

• Rough ER and Smooth ER.

1. What is the primary function of the Golgi apparatus?

• Modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles.

1. How do lysosomes help in cellular digestion?

• By breaking down waste materials and cellular debris.

1. What is the role of mitochondria in cells?

• They are the powerhouses of the cell, generating ATP through cellular respiration.

1. What is the significance of chloroplasts in plant cells?

• They conduct photosynthesis to produce food for the plant.

1. How do vacuoles contribute to plant cell structure?

• They provide turgidity and support to the plant cell.

1. What is the function of ribosomes?

• Ribosomes are the sites of protein synthesis.

1. What is the difference between chromoplasts and leucoplasts?

• Chromoplasts contain pigments for color, while leucoplasts store starch, oils, and proteins.

1. What is autolysis?

• The process where lysosomes digest their own cell.

1. What are the main components of the cell membrane?
   • Lipids and proteins.

Additional 30 Questions and Answers

1. What is the role of the cell membrane?

• Regulates the entry and exit of substances in and out of the cell.

1. What is cytoplasm?

• The jelly-like substance within the cell that contains organelles.

1. How does the nucleus control cell activities?

• It contains DNA which controls the synthesis of proteins and cell functions.

1. What are ribosomes made of?

• RNA and proteins.

1. What is the function of the cell wall in plant cells?

• Provides structural support and protection.

1. What is the significance of ATP in cellular processes?

• ATP acts as an energy currency for cellular activities.

1. How do peroxisomes detoxify the cell?

• By breaking down toxic substances using enzymes.

1. What are the main types of plastids found in plant cells?

• Chloroplasts, chromoplasts, and leucoplasts.

1. What is the difference between active and passive transport?

• Active transport requires energy, while passive transport does not.

1. What is the function of the nucleolus?
   • Synthesizes ribosomal RNA (rRNA).
2. How do centrioles contribute to cell division?
   • They help in the formation of the spindle fibers that separate chromosomes.
3. What is the role of smooth endoplasmic reticulum in muscle cells?
   • Stores and releases calcium ions during muscle contraction.
4. How do chloroplasts capture light energy?
   • Using chlorophyll pigments.
5. What is the function of microtubules in the cell?
   • Provide structural support and help in cell division and intracellular transport.
6. What is exocytosis?
   • The process by which cells expel materials using vesicles.
7. What are glycoproteins?
   • Proteins with carbohydrate groups attached, involved in cell recognition.
8. How do cells communicate with each other?
   • Through chemical signals and receptors on their surfaces.
9. What is the function of the Golgi apparatus in plants?
   • Involved in the synthesis of polysaccharides used in cell walls.
10. How do lysosomes protect the cell from bacteria?
    • By digesting invading bacteria.
11. What is the significance of the fluid mosaic model?
    • Describes the dynamic nature of the cell membrane structure.
12. How are new mitochondria formed?
    • By the division of existing mitochondria.
13. What is the function of the endoplasmic reticulum in liver cells?
    • Detoxifies drugs and poisons.
14. How does the cytoskeleton support cellular movement?
    • Through microfilaments and microtubules.
15. What is the role of vacuoles in single-celled organisms?
    • Involved in digestion and expulsion of excess water.
16. What is the function of the central vacuole in plant cells?
    • Maintains pressure against the cell wall.
17. How do plant cells differ from animal cells in terms of energy storage?
    • Plant cells store energy in the form of starch, while animal cells store it as glycogen.
18. What are the main types of cell junctions?
    • Tight junctions, desmosomes, and gap junctions.
19. How do mitochondria generate energy?
    • Through the process of oxidative phosphorylation.
20. What is the role of the cytoplasm in cellular metabolism?
    • It contains enzymes that facilitate metabolic reactions.
21. What is the importance of the semi-permeable nature of the cell membrane?
    • It allows selective transport of substances, maintaining homeostasis.

Additional Questions and Answers

11. What are the basic components of a cell?

The basic components of a cell include the plasma membrane, cytoplasm, and nucleus. These parts are essential for the cell’s structure and function.

12. How do plant cells differ from animal cells?

Plant cells have a cell wall, chloroplasts, and a large central vacuole, which are not present in animal cells. Animal cells have centrioles, which are typically not found in plant cells.

13. What is the role of the plasma membrane?

The plasma membrane regulates the entry and exit of substances, maintaining the cell’s internal environment.

14. Describe the structure and function of the nucleus.

The nucleus is a membrane-bound structure that contains the cell’s genetic material (DNA). It controls cell growth, metabolism, and reproduction.

15. What is cytoplasm, and why is it important?

Cytoplasm is a jelly-like substance within the cell, containing organelles. It is essential for maintaining cell shape and providing a medium for biochemical activities.

16. How do chloroplasts function in photosynthesis?

Chloroplasts contain chlorophyll, which captures light energy and converts it into chemical energy during photosynthesis.

17. What is the endoplasmic reticulum, and what are its types?

The endoplasmic reticulum (ER) is a network of membranes involved in protein and lipid synthesis. There are two types: rough ER (with ribosomes) and smooth ER (without ribosomes).

18. What are ribosomes, and what do they do?

Ribosomes are molecular machines that synthesize proteins by translating genetic information from mRNA.

19. Explain the function of vacuoles in plant cells.

Vacuoles store nutrients, waste products, and help maintain turgor pressure, which is crucial for plant structure.

20. What is the role of centrioles in animal cells?

Centrioles are involved in cell division, helping to organize the mitotic spindle and ensuring proper chromosome separation.

21. How do prokaryotic cells differ from eukaryotic cells?

Prokaryotic cells lack a true nucleus and membrane-bound organelles, whereas eukaryotic cells have both.

22. What is the function of the cell wall in plant cells?

The cell wall provides structural support, protection, and helps maintain cell shape.

23. Describe the role of mitochondria in cellular respiration.

Mitochondria convert glucose and oxygen into ATP, carbon dioxide, and water through cellular respiration.

24. What are peroxisomes, and what is their function?

Peroxisomes are organelles that contain enzymes for breaking down fatty acids and detoxifying harmful substances.

25. How does the structure of a cell relate to its function?

The structure of a cell is closely related to its function. For example, nerve cells have long extensions to transmit signals, while red blood cells are disc-shaped to transport oxygen efficiently.

26. Explain the process of osmosis in cells.

Osmosis is the movement of water molecules across a semi-permeable membrane from a region of lower solute concentration to higher solute concentration.

27. What is the significance of the Golgi apparatus in secretion?

The Golgi apparatus modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

28. Describe the role of the cytoskeleton in cells.

The cytoskeleton provides structural support, facilitates cell movement, and aids in intracellular transport.

29. How do cells communicate with each other?

Cells communicate through chemical signals (hormones, neurotransmitters) and direct contact (gap junctions, plasmodesmata).

30. What is apoptosis, and why is it important?

Apoptosis is programmed cell death, essential for removing damaged cells and maintaining tissue homeostasis.

31. How do lysosomes contribute to intracellular digestion?

Lysosomes contain hydrolytic enzymes that break down macromolecules, damaged organelles, and pathogens.

32. What are the different types of plastids found in plant cells?

Plastids include chloroplasts (photosynthesis), chromoplasts (pigment synthesis), and leucoplasts (storage of starch, oils, and proteins).

33. Describe the process of endocytosis and exocytosis.

Endocytosis involves the engulfing of external substances into the cell, while exocytosis is the release of substances from the cell.

34. How does the nucleolus contribute to ribosome production?

The nucleolus is the site of ribosomal RNA (rRNA) synthesis and assembly of ribosomal subunits.

35. What is the role of microfilaments in cells?

Microfilaments are part of the cytoskeleton, involved in cell movement, shape, and division.

36. Explain the function of intermediate filaments.

Intermediate filaments provide mechanical strength and stability to cells and tissues.

37. How do cells maintain their shape?

Cells maintain their shape through the cytoskeleton, cell wall (in plants), and turgor pressure.

38. What is the significance of cell differentiation?

Cell differentiation allows cells to specialize and perform specific functions, essential for the development and function of multicellular organisms.

39. How do viruses differ from cells?

Viruses are acellular, lack cellular machinery, and can only replicate inside a host cell.

40. What are the stages of the cell cycle?

The cell cycle consists of interphase (G1, S, G2 phases) and mitotic phase (mitosis and cytokinesis).

41. How do antibiotics affect bacterial cells?

Antibiotics target specific structures or functions in bacterial cells, inhibiting growth or causing cell death.

42. Describe the process of mitosis.

Mitosis is the division of a parent cell into two genetically identical daughter cells, involving prophase, metaphase, anaphase, and telophase.

43. What is the function of the smooth endoplasmic reticulum?

The smooth endoplasmic reticulum synthesizes lipids, detoxifies drugs, and stores calcium ions.

44. How do cells adapt to changes in their environment?

Cells adapt through mechanisms like gene expression

changes, structural modifications, and metabolic adjustments.

45. What is the significance of membrane fluidity?

Membrane fluidity is crucial for membrane function, allowing movement of proteins, lipids, and facilitating cell signaling and transport.

46. How do plant cells perform photosynthesis?

Plant cells perform photosynthesis in chloroplasts, converting light energy into chemical energy stored in glucose.

47. What is the difference between passive and active transport?

Passive transport requires no energy and moves substances down their concentration gradient, while active transport requires energy to move substances against their concentration gradient.

48. Describe the structure and function of microtubules.

Microtubules are part of the cytoskeleton, providing structural support, and are involved in cell division and intracellular transport.

49. How do cells regulate their internal environment?

Cells regulate their internal environment through homeostasis, maintaining conditions like pH, temperature, and ion concentration.

50. What is the role of cell surface receptors?

Cell surface receptors bind to signaling molecules, triggering cellular responses and facilitating communication with the external environment.

By exploring these questions and answers, we gain a deeper appreciation for the intricate world of cells and their vital roles in the life of all organisms. Understanding cells not only enhances our knowledge of biology but also provides insights into the functioning and maintenance of life itself.