9th Class Biology Chapter # 3 Exercise Solutions – Punjab Board
The Cell
9th Class Biology Chapter 3 Solution (MCQs)
1. The process of cellular respiration occurs in:
Options:
a) Nucleus
✅ b) Mitochondria
c) Ribosomes
d) Golgi apparatus
Explanation:
Cellular respiration, which produces energy (ATP), takes place in the mitochondria, also called the “powerhouse of the cell.”
2. The smooth endoplasmic reticulum (SER) is primarily involved in the synthesis of:
Options:
a) Proteins
✅ b) Lipids
c) Carbohydrates
d) Nucleic acids
Explanation:
The smooth ER is responsible for lipid synthesis and detoxification, while the rough ER (with ribosomes) synthesizes proteins.
3. Ribosomes are composed of:
Options:
✅ a) RNA and protein
b) Lipids and protein
c) Carbohydrates and lipids
d) DNA and carbohydrates
Explanation:
Ribosomes are made up of ribosomal RNA (rRNA) and proteins. They are involved in protein synthesis.
4. What is the primary function of ribosomes?
Options:
a) Energy production
b) Lipid synthesis
✅ c) Protein synthesis
d) DNA synthesis
Explanation:
Ribosomes are the site of protein synthesis where amino acids are linked to form proteins.
5. Which cell organelle is involved in packaging and modifying proteins?
Options:
a) Nucleus
b) Mitochondria
✅ c) Golgi apparatus
d) Endoplasmic reticulum
Explanation:
The Golgi apparatus modifies, sorts, and packages proteins and lipids for secretion or use within the cell.
6. Which cell organelle is responsible for breaking down waste materials?
Options:
a) Golgi apparatus
b) Nucleus
c) Mitochondria
✅ d) Lysosome
Explanation:
Lysosomes contain digestive enzymes that break down waste, old cell parts, and invading pathogens.
7. Which of the following cell structures is involved in maintaining cell shape?
Options:
a) Nucleus
✅ b) Centrioles
c) Nucleolus
d) Lysosome
Explanation:
Centrioles are involved in cell structure, shape, and cell division. Microtubules in centrioles support the cytoskeleton.
8. Which specialized region of the nucleus is responsible for ribosome assembly?
Options:
a) Nucleoplasm
✅ b) Nucleolus
c) Chromatin
d) Nuclear envelope
Explanation:
The nucleolus is the dense region within the nucleus where ribosomal RNA is produced and ribosome assembly begins.
9. What is the main function of the nuclear pores?
Options:
a) Regulation of cell division
b) Control of pH of the cell
c) Protein synthesis
✅ d) Control of transport of molecules
Explanation:
Nuclear pores control the movement of molecules (like RNA and proteins) between the nucleus and the cytoplasm.
10. Which of the following cellular structures is found in animal cells and helps in cell division?
Options:
a) Cell membrane
✅ b) Centriole
c) Plasmodesma
d) Vacuole
Explanation:
Centrioles help in organizing the spindle fibers during cell division in animal cells. Plant cells usually lack centrioles.
11. Which sub-cellular organelle plays a crucial role in energy production within the cell?
Options:
a) Endoplasmic reticulum
b) Golgi apparatus
✅ c) Mitochondria
d) Lysosomes
Explanation:
Mitochondria are known as the powerhouses of the cell because they produce energy (ATP) through cellular respiration.
12. In a multicellular plant, which cell type is responsible for the production of glucose?
Options:
a) Xylem
b) Phloem
c) Epidermal
✅ d) Mesophyll
Explanation:
Mesophyll cells in plant leaves contain chloroplasts and perform photosynthesis, producing glucose.
13. Which organelle can double its number by self-replication?
Options:
a) Ribosomes
b) Lysosomes
✅ c) Mitochondria
d) Golgi apparatus
Explanation:
Mitochondria contain their own DNA and can replicate independently, similar to bacteria.
14. Which of these are present on the surface of rough endoplasmic reticulum?
Options:
✅ a) Ribosomes
b) Lysosomes
c) Mitochondria
d) Vacuoles
Explanation:
The rough endoplasmic reticulum is called “rough” because it is studded with ribosomes, which synthesize proteins.
9th Class Biology Chapter 3 Solution Mcqs.
9th Class Biology Chapter 3 Solution Short Answer Questions
1. What are the main functions of the cell membrane?
Answer:
Regulates entry and exit of substances.
Provides protection and support.
Maintains cell’s internal environment.
2. What key role does the Golgi apparatus play in eukaryotic cells?
Answer:
It modifies, sorts, and packages proteins and lipids for storage or transport outside the cell.
3. How do ribosomes contribute to the cell’s functioning?
Answer:
Ribosomes synthesize proteins, which are essential for growth, repair, and enzyme production.
4. Which organelle detoxifies harmful substances and breaks down lipids?
Answer:
The smooth endoplasmic reticulum (SER) detoxifies drugs and toxins, and also synthesizes and breaks down lipids.
5. What is the smooth endoplasmic reticulum responsible for?
Answer:
Lipid and steroid hormone synthesis
Detoxification of harmful substances
Metabolism of carbohydrates
6. How do the vacuoles in plant cells differ from vacuoles in animal cells?
Answer:
Plant vacuoles are large and central, storing water and maintaining turgor pressure.
Animal vacuoles are smaller and more numerous, mainly for waste storage.
7. What could happen if lysosomal enzymes stop working properly?
Answer:
Damaged or unneeded materials won’t be broken down, leading to waste accumulation, which can cause cell damage or death.
8. Why are the cristae important for cellular respiration?
Answer:
Cristae are folds in the inner membrane of mitochondria that increase surface area for energy (ATP) production.
9. How are chromatin and chromosomes related?
Answer:
Chromatin is the uncoiled form of DNA. During cell division, it condenses into chromosomes to ensure proper DNA distribution.
10. Which type of cell is responsible for sending nerve signals?
Answer:
Neuron (nerve cell) — it transmits electrical and chemical signals in the nervous system.
11. What do mesophyll cells do in plant leaves?
Answer:
Mesophyll cells contain chloroplasts and carry out photosynthesis, converting sunlight, water, and CO₂ into glucose and oxygen.
12. How would you define a stem cell?
Answer:
A stem cell is an undifferentiated cell capable of dividing and developing into various types of specialized cells in the body.
13. Name the chemical compounds that make up:
a. Cell membrane: → Phospholipids and proteins
b. Fungal cell wall: → Chitin
c. Plant cell wall: → Cellulose
d. Bacterial cell wall: → Peptidoglycan
e. Ribosomes: → rRNA and proteins
f. Chromosomes: → DNA and proteins (histones)
- 9th Class Biology Chapter 3 Solution Short question Complete.
9th Class Biology Chapter 3 Solution in Detail
1. Explain the fluid mosaic model of the cell membrane.
Answer:
The Fluid Mosaic Model, proposed by Singer and Nicolson in 1972, explains the structure of the plasma membrane in eukaryotic cells. It is called fluid because the components are flexible and mosaic due to the pattern of proteins embedded in the lipid bilayer.
The membrane consists of a phospholipid bilayer where hydrophilic (water-loving) heads face outward and hydrophobic (water-repelling) tails face inward.
Proteins are scattered throughout the membrane like a mosaic:
Integral proteins span the entire bilayer.
Peripheral proteins are attached to either surface.
Cholesterol molecules are also embedded, providing stability and maintaining fluidity of the membrane.
This model explains how the membrane is selectively permeable, allowing some substances to pass while blocking others.
2. Describe the structure and functions of the cell wall.
Answer:
The cell wall is a rigid, non-living structure found in plant cells, fungi, and bacteria. It is absent in animal cells.
Composition:
Plants: Made of cellulose.
Fungi: Made of chitin.
Bacteria: Made of peptidoglycan.
Functions:
Provides mechanical support and protection.
Maintains cell shape.
Prevents the cell from bursting due to excess water.
Allows free movement of water and solutes due to its porous nature.
3. Discuss the components of the nucleus.
Answer:
The nucleus is the control center of the cell, containing the genetic material (DNA). Its components include:
Nuclear Envelope: A double membrane with pores that regulate material exchange between the nucleus and cytoplasm.
Nucleoplasm: A jelly-like fluid that suspends the contents of the nucleus.
Nucleolus: A dense region that produces ribosomal RNA (rRNA) and assembles ribosomes.
Chromatin: A thread-like structure of DNA and proteins (histones), which condenses into chromosomes during cell division.
4. Describe the structure and function of lysosome and endoplasmic reticulum.
Answer:
Lysosome:
Membrane-bound vesicles containing digestive enzymes.
Functions:
Break down worn-out organelles, food particles, and foreign invaders.
Involved in autolysis (self-destruction of cells).
Endoplasmic Reticulum (ER):
Rough ER: Has ribosomes on its surface; responsible for protein synthesis and transport.
Smooth ER: Lacks ribosomes; involved in lipid synthesis, detoxification, and calcium ion storage.
5. Describe the structure and function of the Golgi complex.
Answer:
The Golgi complex (or Golgi apparatus) is a stack of flattened, membrane-bound sacs called cisternae.
Functions:
Modifies, sorts, and packages proteins and lipids received from the ER.
Forms lysosomes and transport vesicles.
Involved in secretion of materials outside the cell.
6. Describe the structure and functions of the chloroplast.
Answer:
Chloroplasts are green, double-membraned organelles found in plant cells and some algae.
Contain thylakoids, which are disc-like structures stacked into grana.
The fluid part surrounding the grana is called stroma.
Contain chlorophyll, the pigment that absorbs sunlight.
Functions:
Site of photosynthesis, where sunlight is converted into chemical energy (glucose).
Release oxygen as a by-product.
7. How does turgor pressure develop in a plant cell?
Answer:
Turgor pressure is the pressure exerted by the central vacuole against the cell wall in plant cells.
When a plant cell absorbs water via osmosis, the vacuole fills and swells.
This causes the plasma membrane and cytoplasm to push against the rigid cell wall.
The resulting pressure, called turgor pressure, helps maintain the rigidity and structure of the plant.
It keeps plants upright and supports growth.
8. Write a note on differences between a plant cell and an animal cell.
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell Wall | Present (made of cellulose) | Absent |
| Vacuole | Large, central vacuole | Small or absent |
| Chloroplast | Present (for photosynthesis) | Absent |
| Shape | Regular, rectangular | Irregular or round |
| Centrioles | Usually absent | Present (important for division) |
9. Describe the concept of division of labour and how it applies in multicellular organisms.
Answer:
In multicellular organisms, cells are specialized to perform specific functions — this is called division of labour.
It improves efficiency and survival.
Instead of all cells doing all tasks, specific cells or tissues take up dedicated roles.
Examples:
Red blood cells transport oxygen.
Muscle cells contract to enable movement.
Nerve cells (neurons) conduct impulses for communication.
This allows organisms to function smoothly, grow larger, and adapt better to complex environments.
10. Write a note on cell specialization.
Answer:
Cell specialization (also called differentiation) is the process by which unspecialized cells (like stem cells) become specialized in structure and function.
Specialized cells perform unique roles in the body.
This is necessary for the complex functioning of multicellular organisms.
Examples:
Root hair cells absorb water and minerals in plants.
Mesophyll cells in leaves perform photosynthesis.
Sperm and egg cells are specialized for reproduction.
Specialization helps organisms work efficiently, repair themselves, and respond to changing environments.
9th Class Biology Chapter 3 Solution Detail Complete.
9th Class Biology Chapter 3 Solution Inquisitive Questions
1. What impact might mitochondrial dysfunction or absence have on other organelles’ ability to operate in a cell?
Detailed Answer:
Mitochondria are often called the “powerhouses of the cell” because they produce adenosine triphosphate (ATP), which is the primary source of energy for all cellular activities. Every organelle in the cell relies on ATP to carry out its specific functions. If mitochondria are absent or not functioning properly, it has serious consequences for the entire cell.
Effects on other organelles:
Golgi Apparatus:
Without ATP, the Golgi cannot modify, sort, or package proteins and lipids, which are vital for secretion and internal use. Protein trafficking and hormone release would be disrupted.Ribosomes:
Ribosomes need energy to assemble amino acids into proteins. Without ATP, protein synthesis slows down or stops, affecting growth and repair.Endoplasmic Reticulum (ER):
The ER depends on energy for transporting proteins and lipids, especially in secretory cells. Energy shortage results in accumulated unfolded proteins and ER stress.Lysosomes:
Digestive enzymes in lysosomes require energy to be synthesized and transported. Without it, waste and damaged organelles accumulate, leading to cellular toxicity.Overall Cell Survival:
Mitochondrial failure causes:Low energy availability.
Oxidative stress due to reactive oxygen species.
Cell death (apoptosis) in extreme cases.
Conclusion:
Mitochondria are central to the functioning of every cell. Their dysfunction directly disrupts the operation of other organelles, making them essential for cell health and survival.
2. What may happen if the coordination between the ribosomes and the nucleus were to fail, and why is it so important?
Detailed Answer:
In a healthy cell, the nucleus controls all cellular activities by sending genetic instructions (mRNA) to ribosomes, which then use this information to synthesize proteins. This coordination is critical for life.
If coordination fails:
Disrupted mRNA transmission:
If the nucleus cannot send proper mRNA to ribosomes, the ribosomes will not receive the correct instructions to build proteins.Protein Synthesis Stops or Malfunctions:
Proteins are essential for:Enzyme production
Hormone signaling
Cell repair and growth
Defense mechanisms (antibodies)
Without proper coordination, these proteins are either not made, or made incorrectly, leading to cellular malfunction.
Loss of Gene Expression Control:
Gene expression is how a cell “reads” and “executes” its DNA code. Miscommunication between the nucleus and ribosomes leads to failed gene expression, making the cell non-functional.Effect on Other Organelles:
Many organelles depend on specific proteins for their structure and function. If those proteins aren’t made properly:ER can’t process proteins.
Golgi can’t package them.
Cell membrane won’t receive transport proteins.
Consequences:
Slowed cell growth
Cell aging or death
Developmental defects in multicellular organisms
Increased chance of disease (e.g., cancer, genetic disorders)
Conclusion:
The coordination between the nucleus and ribosomes is like the relationship between a software programmer and a computer. Without proper instructions, the computer (ribosome) can’t function correctly. This harmony is essential for life, repair, defense, and reproduction at the cellular level.
9th Class Biology Chapter 3 Solution Inquisitive Question Complete.
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