lahore board biology

Chapter 7: Enzymes – Class 9th Biology New Syllabus

by

Explore Chapter 7: Enzymes from the Class 9th Biology New Syllabus of the Lahore Board. This detailed post includes a thorough explanation of enzyme characteristics, the lock-and-key model vs. the induced-fit model, factors affecting enzyme activity, pH, temperature effects, competitive and non-competitive inhibition, and much more. Get exam-prepared with solved MCQs, short answers, and detailed explanations. Ideal for students looking to master this chapter for top performance in exams.”

1. Primarily, all enzymes are:

  • Options:
    a) Nucleic acids
    b) Proteins
    c) Carbohydrates
    d) Lipids
  • Answer: b) Proteins
  • Explanation: Enzymes are biological catalysts made up of proteins. They accelerate chemical reactions in the body.
  • Tip: Remember, most enzymes end in “-ase,” and they are protein-based.

2. Which best defines an enzyme?

  • Options:
    a) A chemical that breaks down food.
    b) A hormone that regulates metabolism.
    c) A protein that speeds up reactions.
    d) A molecule that stores energy.
  • Answer: c) A protein that speeds up reactions.
  • Explanation: Enzymes lower the activation energy required for a chemical reaction, thereby speeding it up without being consumed in the process.
  • Tip: Focus on the key term “speed up reactions” in the question.

3. What can happen if an enzyme is exposed to a temperature that is higher than its optimal temperature?

  • Options:
    a) Enzyme activity rate will increase.
    b) Enzyme’s shape will change, potentially reducing its activity.
    c) Enzyme will speed up the reaction and remain stable.
    d) Enzyme will become a substrate itself.
  • Answer: b) Enzyme’s shape will change, potentially reducing its activity.
  • Explanation: High temperatures can denature enzymes, causing them to lose their shape and function.
  • Tip: Recall that enzymes have an optimal temperature range for activity.

4. Enzymes are specific in their action because:

  • Options:
    a) Their active sites fit specific substrates.
    b) They are always proteins.
    c) They are consumed in reactions.
    d) They work only at high temperatures.
  • Answer: a) Their active sites fit specific substrates.
  • Explanation: Enzyme specificity arises from the “lock-and-key” model, where the active site of an enzyme binds only to specific substrates.
  • Tip: Visualize the lock-and-key analogy for enzyme specificity.

5. Prosthetic groups are:

  • Options:
    a) Required by all enzymes.
    b) Proteins in nature.
    c) Loosely attached with enzymes.
    d) Tightly bound to enzymes.
  • Answer: d) Tightly bound to enzymes.
  • Explanation: Prosthetic groups are non-protein molecules that are permanently attached to enzymes and assist in their catalytic activity.
  • Tip: Remember, “tightly bound” differentiates prosthetic groups from coenzymes.

6. How does increasing temperature affect enzyme activity?

  • Options:
    a) Increases activity to a point.
    b) Always decreases activity.
    c) Makes enzymes non-functional.
    d) No effect on enzyme.
  • Answer: a) Increases activity to a point.
  • Explanation: Enzymes work optimally within a temperature range. Beyond this range, the activity decreases due to denaturation.
  • Tip: Recall the bell-shaped curve of enzyme activity vs. temperature.

7. How does a competitive inhibitor affect enzyme action?

  • Options:
    a) Attaches with the substrate.
    b) Changes enzyme shape.
    c) Attaches and blocks the active site.
    d) Blocks the cofactors.
  • Answer: c) Attaches and blocks the active site.
  • Explanation: Competitive inhibitors compete with the substrate by binding to the enzyme’s active site, preventing substrate interaction.
  • Tip: Remember, “competitive” means direct competition for the active site.

8. An enzyme works best at a pH of 7.4. It is placed in an acidic solution with a pH of 4.0. How will this affect the enzyme?

  • Options:
    a) The active site will be modified, reducing substrate binding.
    b) Enzyme activity will increase.
    c) Enzyme will become a substrate.
    d) No change will occur.
  • Answer: a) The active site will be modified, reducing substrate binding.
  • Explanation: A pH far from the enzyme’s optimal range can alter its shape, affecting its functionality.
  • Tip: Recall that extreme pH values can denature enzymes.

9. What is TRUE according to the induced-fit model of enzyme action?

  • Options:
    a) Enzyme’s active site changes shape to bind the substrate.
    b) Substrate must fit the enzyme perfectly before binding.
    c) No shape changes occur during binding.
    d) Enzyme is inactivated during the process.
  • Answer: a) Enzyme’s active site changes shape to bind the substrate.
  • Explanation: The induced-fit model suggests that the enzyme undergoes a conformational change to better accommodate the substrate.
  • Tip: Contrast this with the rigid “lock-and-key” model.

10. What is true about the optimum pH values of the following enzymes of the digestive system?

  • Options:
    a) Pepsin works at low pH while trypsin works at high pH.
    b) Both work at high pH.
    c) Both work at low pH.
    d) Pepsin works at high pH while trypsin works at low pH.
  • Answer: a) Pepsin works at low pH while trypsin works at high pH.
  • Explanation: Pepsin operates in the acidic environment of the stomach (low pH), while trypsin functions in the alkaline environment of the small intestine (high pH).
  • Tip: Recall the specific environments where these enzymes are active.

B. Short Answer Questions

  1. Define metabolism. Differentiate between catabolism and anabolism.
    • Answer: Metabolism refers to all the chemical processes in the body that maintain life.
      • Catabolism: Breakdown of molecules to release energy (e.g., digestion).
      • Anabolism: Synthesis of molecules, requiring energy (e.g., protein synthesis).
  1. Which type of metabolism demands input of energy? Give an example.
    • Answer: Anabolism requires energy input. Example: DNA synthesis.
  1. Define an enzyme. What is its role in metabolism?
    • Answer: An enzyme is a protein catalyst that speeds up chemical reactions in the body.
      • Role in metabolism: Enzymes lower the activation energy required for metabolic reactions, making them efficient.
  1. What is the active site of an enzyme? State its importance in enzyme specificity.
    • Answer: The active site is the region of an enzyme where the substrate binds and the reaction occurs.
      • Importance: It ensures that only specific substrates fit, maintaining reaction specificity.
  1. Provide an example of a specific enzyme-substrate pair.
    • Answer: Enzyme: Amylase, Substrate: Starch.
  1. How does pH affect enzyme activity?
    • Answer: Deviations from the optimal pH can denature the enzyme, altering its structure and reducing activity.
  1. Provide two examples of enzymes that operate optimally at specific pH.
    • Answer:
      • Pepsin (pH 1.5–2)
      • Trypsin (pH 8)
  1. What do you mean by optimum temperature and pH?
    • Answer: Optimum temperature and pH are the conditions where an enzyme exhibits maximum activity.
  1. Which type of enzyme inhibitors inhibit the enzymes without attaching to the active site?
    • Answer: Non-competitive inhibitors.
  1. Differentiate between competitive and non-competitive inhibition.
    • Answer:
      • Competitive inhibition: Inhibitor binds to the active site, blocking substrate binding.
      • Non-competitive inhibition: Inhibitor binds elsewhere, altering the enzyme’s shape and reducing activity.

Detailed Answer

1. Describe the characteristics of enzymes.

  • Biological Catalysts: Enzymes are proteins that catalyze biochemical reactions, increasing their speed without being consumed or permanently altered.
  • Specificity: Each enzyme is highly specific to its substrate due to the unique shape of its active site, often described using the “lock-and-key” or “induced-fit” model.
  • Reusable: Enzymes are not consumed during reactions and can be used repeatedly for the same type of reaction.
  • Temperature Sensitivity: Enzymes work best within a narrow temperature range. High temperatures can denature them, while low temperatures slow down molecular motion, reducing activity.
  • pH Sensitivity: Each enzyme has an optimal pH at which it functions most effectively. Extreme pH values can alter the enzyme’s structure and reduce its activity.
  • Regulation: Enzymes can be regulated by activators (which increase activity) or inhibitors (which decrease activity).
  • Cofactors and Coenzymes: Some enzymes require non-protein molecules (like metal ions or organic molecules) to function. These are called cofactors and coenzymes, respectively.

2. Describe how temperature extremes can inhibit enzyme activity and lead to enzyme denaturation.

  • At High Temperatures:
    • Enzymes are proteins, and high temperatures disrupt their hydrogen bonds, ionic bonds, and other interactions maintaining their structure.
    • This denaturation leads to the unfolding of the enzyme, rendering it non-functional because the active site loses its specific shape.
    • Example: Denaturation of human enzymes typically occurs above 40°C.
  • At Low Temperatures:
    • Molecular motion decreases significantly at lower temperatures, resulting in fewer collisions between enzymes and substrates.
    • The enzyme-substrate complex formation slows down, leading to reduced reaction rates.
  • Effects of Prolonged Temperature Extremes:
    • High temperatures can cause permanent denaturation, while low temperatures often cause reversible inactivation.
    • Optimal enzyme activity is observed within a specific temperature range, typically between 35°C and 40°C for most human enzymes.
  • Practical Implications:
    • Heat-sensitive enzymes are used in industries where precise temperature control is required, such as in brewing or pharmaceuticals.

3. How does pH affect enzyme activity?

  • Optimal pH:
    • Each enzyme functions best at a specific pH, called its “optimal pH.” For example, pepsin in the stomach works best at a pH of 1.5–2, while trypsin in the intestine works best at pH 8.
    • This pH aligns with the enzyme’s natural environment.
  • Effect on Ionization:
    • pH changes affect the ionization of amino acids at the enzyme’s active site and the substrate.
    • If the active site loses its correct charge distribution, it may fail to bind the substrate.
  • Denaturation at Extreme pH:
    • Both highly acidic and highly alkaline environments can disrupt the enzyme’s tertiary and quaternary structures by breaking hydrogen bonds and ionic interactions.
    • This structural alteration prevents the enzyme from functioning effectively.
  • Reversible vs. Irreversible Effects:
    • Minor pH deviations may cause reversible changes in activity, but extreme pH shifts can permanently denature the enzyme.
  • Example: Salivary amylase operates around neutral pH (7), but becomes inactive in the acidic environment of the stomach.

4. Briefly describe the factors that affect enzyme activity.

  • Temperature:
    • Enzyme activity increases with temperature until it reaches the optimum point, beyond which activity decreases due to denaturation.
    • Example: Human enzymes have an optimal temperature around 37°C.
  • pH:
    • Each enzyme has a specific pH range for optimal activity. Deviations from this range reduce enzyme efficiency or lead to denaturation.
    • Example: Digestive enzymes like pepsin (acidic) and trypsin (alkaline) have different pH optima.
  • Substrate Concentration:
    • Enzyme activity increases with substrate concentration until all active sites are saturated. Beyond this point, increasing substrate concentration has no further effect.
  • Enzyme Concentration:
    • Increasing enzyme concentration increases the rate of reaction, provided the substrate is in excess.
  • Inhibitors:
    • Competitive inhibitors: Bind to the active site, blocking substrate access.
    • Non-competitive inhibitors: Bind elsewhere on the enzyme, altering its shape and reducing functionality.
  • Cofactors and Coenzymes:
    • These molecules are essential for the activity of some enzymes.
    • Example: Metal ions like Mg²⁺ are cofactors, while vitamins like B6 act as coenzymes.
  • Environmental Conditions:
    • Factors like ionic strength, salinity, and pressure can also influence enzyme activity.

5. Compare the Lock-and-Key model and Induced-Fit model of enzyme action.

  • Lock-and-Key Model:
    • Proposed by Emil Fischer, it suggests that the enzyme’s active site is rigid and fits only specific substrates, like a key fits into a lock.
    • Strength: Explains enzyme specificity well.
    • Limitation: Fails to explain flexibility and conformational changes in enzymes.
  • Induced-Fit Model:
    • Proposed by Daniel Koshland, this model suggests that the enzyme’s active site is flexible and molds itself to fit the substrate.
    • Strength: Explains the dynamic nature of enzyme-substrate interactions and the formation of the enzyme-substrate complex.
    • Limitation: Slightly more complex to conceptualize compared to the lock-and-key model.
  • Comparison:
    • The lock-and-key model emphasizes rigidity and specificity, while the induced-fit model accounts for enzyme flexibility and adaptability.
    • Induced-fit is considered more accurate and widely accepted today due to evidence from structural biology.

Let me know if you’d like to explore further concepts or have more questions!

Chapter 6: Molecular Biology – Solved Exercise for 9th

by

MCQ 1

Statement: What is the primary function of carbohydrates?
Options:
a) Provide energy
b) Act as enzymes
c) Regulate processes
d) Make membranes

Answer: a) Provide energy

Explanation: Carbohydrates are the body’s main source of energy. They are broken down into glucose, which is used by cells for metabolic activities.

Tips and Tricks:

  • Remember: “Carbs = Energy.”
  • Enzymes are proteins, not carbohydrates.

MCQ 2

Statement: How will you differentiate between monosaccharides and polysaccharides?
Options:
a) Monosaccharides are single sugars.
b) Polysaccharides are sweet in taste.
c) Monosaccharides are present in plant cell walls.
d) Polysaccharides dissolve easily.

Answer: a) Monosaccharides are single sugars.

Explanation: Monosaccharides (like glucose) are simple sugars, while polysaccharides (like starch) are complex carbohydrates made of many monosaccharide units.

Tips and Tricks:

  • Mono = one (single sugar); Poly = many (complex sugars).
  • Polysaccharides are not usually sweet.

MCQ 3

Statement: What is true about cellulose?
Options:
a) It is sweet in taste.
b) It is digestible by the human digestive system.
c) It provides structural support in plants.
d) It is soluble in water.

Answer: c) It provides structural support in plants.

Explanation: Cellulose is a polysaccharide that forms the cell walls in plants, providing structural strength. Humans cannot digest cellulose due to a lack of the enzyme cellulase.

Tips and Tricks:

  • Remember cellulose as the “building block” of plant cell walls.
  • It is insoluble in water and not sweet.

MCQ 4

Statement: Which of the following proteins is involved in oxygen transport?
Options:
a) Collagen
b) Hemoglobin
c) Keratin
d) Myosin

Answer: b) Hemoglobin

Explanation: Hemoglobin is a protein found in red blood cells responsible for transporting oxygen from the lungs to body tissues and carrying carbon dioxide back to the lungs.

Tips and Tricks:

  • Think of “Hemoglobin = Oxygen transporter.”
  • Collagen supports structure, keratin strengthens skin and hair, and myosin aids in muscle contraction.

MCQ 5

Statement: Which component of an amino acid determines its unique properties?
Options:
a) Amino group
b) Carboxyl group
c) R group (side chain)
d) Hydrogen group

Answer: c) R group (side chain)

Explanation: The R group (side chain) varies among amino acids and determines their unique chemical properties, such as polarity, charge, and hydrophobicity.

Tips and Tricks:

  • Remember: “R group = unique.” The amino and carboxyl groups are the same in all amino acids.

MCQ 6

Statement: Which proteins are involved in defense against pathogens?
Options:
a) Myosin
b) Hemoglobin
c) Antibodies
d) Fibrinogen

Answer: c) Antibodies

Explanation: Antibodies are proteins produced by the immune system that recognize and neutralize pathogens like bacteria and viruses.

Tips and Tricks:

  • Antibodies = “Defenders” in the immune system.
  • Myosin aids in movement, hemoglobin in oxygen transport, and fibrinogen in blood clotting.

MCQ 7

Statement: Which of the following is the basic structural unit of most lipids?
Options:
a) Nucleotides
b) Fatty acids and glycerol
c) Simple sugars
d) Amino acids

Answer: b) Fatty acids and glycerol

Explanation: Lipids are composed of glycerol and fatty acids. Glycerol serves as the backbone, while fatty acids provide hydrophobic tails.

Tips and Tricks:

  • Lipids = “Fatty acids + Glycerol.”
  • Nucleotides form DNA/RNA, amino acids make proteins, and simple sugars form carbohydrates.

MCQ 8

Statement: How do unsaturated fatty acids differ from saturated fatty acids?
Options:
a) They have more hydrogen atoms.
b) They contain double bonds in their hydrocarbon chains.
c) They are solid at room temperature.
d) They are found only in animal fats.

Answer: b) They contain double bonds in their hydrocarbon chains.

Explanation: Unsaturated fatty acids have one or more double bonds in their carbon chain, making them liquid at room temperature (e.g., oils). Saturated fatty acids lack double bonds and are solid at room temperature (e.g., butter).

Tips and Tricks:

  • Unsaturated = Double bonds = Liquid (Oils).
  • Saturated = Single bonds = Solid (Butter).

MCQ 9:

Statement: Which of the following is NOT a function of proteins?
Options:
a) Transport oxygen in the blood
b) Carry genetic information
c) Help in digesting food
d) Fight against infections

Answer: b) Carry genetic information

Explanation: Proteins are responsible for functions like oxygen transport (e.g., hemoglobin), digestion (e.g., enzymes), and immunity (e.g., antibodies). Genetic information is carried by nucleic acids (DNA and RNA), not proteins.

Tips and Tricks:

  • Remember: “Proteins = Functional workers” and “DNA/RNA = Genetic storage.”

MCQ 10:

Statement: Which component makes up a nucleotide?
Options:
a) Amino acid, phosphate, nitrogenous base
b) Sugar, phosphate, nitrogenous base
c) Fatty acid, nitrogenous base, sugar
d) Protein, sugar, phosphate

Answer: b) Sugar, phosphate, nitrogenous base

Explanation: A nucleotide, the building block of DNA/RNA, consists of a pentose sugar (deoxyribose or ribose), a phosphate group, and a nitrogenous base (A, T, C, G, or U).

Tips and Tricks:

  • Remember the “S-P-B” structure: Sugar-Phosphate-Base.

MCQ 11:

Statement: Which nitrogenous base is found in RNA but not in DNA?
Options:
a) Adenine
b) Uracil
c) Thymine
d) Guanine

Answer: b) Uracil

Explanation: RNA contains uracil instead of thymine, which is found in DNA. Both uracil and thymine pair with adenine during transcription or replication.

Tips and Tricks:

  • Remember: “DNA = Thymine (T),” “RNA = Uracil (U).”

Short Questions with Answers

  1. What are the main functions of carbohydrates in the body?
    Answer:
    • Provide energy (e.g., glucose for cellular respiration).
    • Serve as storage (e.g., glycogen in animals, starch in plants).
    • Form structural components (e.g., cellulose in plants).
  2. Write the general formula of carbohydrates and give two examples of monosaccharides.
    Answer:
    • General formula: Cn(H2O)nC_n(H_2O)_n
    • Examples: Glucose and fructose.
  3. Name one polysaccharide found in plants and one in animals.
    Answer:
    • Plants: Starch
    • Animals: Glycogen
  4. What is the difference between a nucleotide and a nucleoside?
    Answer:
    • Nucleotide: Composed of a sugar, phosphate, and nitrogenous base.
    • Nucleoside: Composed of a sugar and nitrogenous base only (no phosphate).
  5. Name the two types of nucleic acids and describe their functions.
    Answer:
    • DNA (Deoxyribonucleic acid): Stores genetic information.
    • RNA (Ribonucleic acid): Assists in protein synthesis and carries genetic messages.
  6. Differentiate between saturated and unsaturated fatty acids.
    Answer:
    • Saturated fatty acids: Contain no double bonds, solid at room temperature (e.g., butter).
    • Unsaturated fatty acids: Contain one or more double bonds, liquid at room temperature (e.g., olive oil).

Long Questions with Answers

1. Discuss the levels of molecular biology.

Answer:

  • Nucleotides and nucleic acids:
    • Nucleotides form nucleic acids like DNA and RNA, which store and transmit genetic information.
  • Proteins:
    • Made up of amino acids, proteins perform diverse biological functions like catalysis (enzymes), structure (collagen), and transport (hemoglobin).
  • Carbohydrates and lipids:
    • Carbohydrates provide energy, while lipids are essential for energy storage, insulation, and forming cell membranes.

2. Differentiate between DNA and RNA.

Answer:

FeatureDNARNA
SugarDeoxyriboseRibose
StrandsDouble-strandedSingle-stranded
BasesA, T, G, CA, U, G, C
FunctionStores genetic informationHelps in protein synthesis

3. What are saturated and unsaturated fatty acids? Give their functions.

Answer:

  • Saturated fatty acids:
    • No double bonds between carbon atoms.
    • Solid at room temperature (e.g., animal fats).
    • Function: Provide long-term energy storage.
  • Unsaturated fatty acids:
    • Contain one or more double bonds.
    • Liquid at room temperature (e.g., vegetable oils).
    • Function: Maintain membrane fluidity and support heart health.

4. Write a note on lipids.

Answer:

  • Definition: Lipids are hydrophobic molecules that include fats, oils, and steroids.
  • Structure: Composed of glycerol and fatty acids.
  • Functions:
    • Long-term energy storage.
    • Insulation and protection.
    • Forming cell membranes (phospholipids).

5. Explain the double-helix structure of DNA and discuss the base pairing in DNA.

Answer:

  • Double-helix structure: DNA is a spiral-shaped molecule made of two strands twisted around each other, held together by hydrogen bonds.
  • Base pairing:
    • Adenine (A) pairs with Thymine (T).
    • Cytosine (C) pairs with Guanine (G).
    • Base pairing follows the complementary rule (A-T, C-G).
  • Significance: Base pairing ensures accurate replication and transcription of genetic information.

9th Class Biology Chapter 3: The Cell – New Syllabus

by

1. The process of cellular respiration occurs in:

  • Options:
    a) Nucleus
    b) Mitochondria
    c) Ribosomes
    d) Golgi apparatus
  • Answer: b) Mitochondria
  • Explanation: Mitochondria are known as the “powerhouse of the cell” because they produce energy (ATP) through cellular respiration.
  • Tip: Associate “mitochondria” with “energy production.”

2. The smooth endoplasmic reticulum (SER) is primarily involved in the synthesis of:

  • Options:
    a) Proteins
    b) Lipids
    c) Carbohydrates
    d) Nucleic acids
  • Answer: b) Lipids
  • Explanation: The SER is specialized in lipid synthesis and detoxification of harmful substances in cells.
  • Tip: Think of “smooth” as “soft,” linked to fats (lipids).

3. Ribosomes are composed of:

  • Options:
    a) RNA and protein
    b) DNA and protein
    c) Carbohydrates and lipids
    d) RNA and carbohydrates
  • Answer: a) RNA and protein
  • Explanation: Ribosomes are made up of rRNA (ribosomal RNA) and proteins, enabling them to synthesize proteins.
  • Tip: Remember “R” in ribosomes for “RNA.”

4. What is the primary function of ribosomes?

  • Options:
    a) Energy production
    b) Protein synthesis
    c) Lipid synthesis
    d) DNA synthesis
  • Answer: b) Protein synthesis
  • Explanation: Ribosomes assemble amino acids into proteins.
  • Tip: Ribosomes are like “factories” for making proteins.

5. Which cell organelle is involved in packaging and modifying proteins?

  • Options:
    a) Nucleus
    b) Mitochondria
    c) Golgi apparatus
    d) Endoplasmic reticulum
  • Answer: c) Golgi apparatus
  • Explanation: The Golgi apparatus processes, modifies, and packages proteins for transport.
  • Tip: Link “Golgi” with “gift wrap” for packaging.

6. Which cell organelle is responsible for breaking down waste materials?

  • Options:
    a) Golgi apparatus
    b) Nucleus
    c) Mitochondria
    d) Lysosome
  • Answer: d) Lysosome
  • Explanation: Lysosomes contain digestive enzymes to break down cellular waste and debris.
  • Tip: Think “lyso-” as in “lysis” (breaking down).

7. Which of the following cell structures is involved in maintaining cell shape?

  • Options:
    a) Cytoskeleton
    b) Centrioles
    c) Nucleus
    d) Lysosome
  • Answer: a) Cytoskeleton
  • Explanation: The cytoskeleton provides structural support and maintains the shape of the cell.
  • Tip: “Skeleton” in cytoskeleton helps recall “support.”

8. What is the main function of the smooth endoplasmic reticulum in a cell?

  • Options:
    a) Synthesis of proteins
    b) Synthesis of lipids
    c) Digestion of cellular waste
    d) Storage of genetic material
  • Answer: b) Synthesis of lipids
  • Explanation: The smooth ER specializes in lipid and steroid hormone synthesis.
  • Tip: Recall that smooth ER handles “fats” (lipids), unlike rough ER, which synthesizes proteins.

9. Which specialized region of the nucleus is responsible for ribosome assembly?

  • Options:
    a) Nucleoplasm
    b) Nucleolus
    c) Chromatin
    d) Chromatid
  • Answer: b) Nucleolus
  • Explanation: The nucleolus is the site where ribosomal RNA (rRNA) is synthesized and ribosome assembly begins.
  • Tip: Think “nucleolus” for “ribosome production hub.”

10. 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
  • Answer: d) Control of transport of molecules
  • Explanation: Nuclear pores allow selective transport of molecules (e.g., RNA and proteins) between the nucleus and cytoplasm.
  • Tip: “Pores” indicate passage or transport.

11. Which of the following cellular structures is found in animal cells and helps in cell division?

  • Options:
    a) Cell membrane
    b) Plasmodesma
    c) Centriole
    d) Vacuole
  • Answer: c) Centriole
  • Explanation: Centrioles play a key role in the organization of spindle fibers during mitosis and meiosis in animal cells.
  • Tip: Centrioles are specific to animal cells for cell division.

12. 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
  • Answer: c) Mitochondria
  • Explanation: Mitochondria are the site of ATP production via cellular respiration.
  • Tip: Recall “powerhouse of the cell.”

13. In a multicellular plant, which cell type is responsible for the production of glucose?

  • Options:
    a) Xylem
    b) Phloem
    c) Epidermal
    d) Mesophyll
  • Answer: d) Mesophyll
  • Explanation: Mesophyll cells contain chloroplasts, where photosynthesis occurs to produce glucose.
  • Tip: Link “mesophyll” with “middle” (the leaf tissue performing photosynthesis).

14. Which organelle can double its number by itself?

  • Options:
    a) Ribosomes
    b) Lysosomes
    c) Mitochondria
    d) Golgi apparatus
  • Answer: c) Mitochondria
  • Explanation: Mitochondria have their own DNA and replicate independently through binary fission.
  • Tip: Mitochondria behave like “semi-autonomous” organelles.

15. Which of these are present on the surface of rough endoplasmic reticulum?

  • Options:
    a) Ribosomes
    b) Lysosomes
    c) Mitochondria
    d) Vacuoles
  • Answer: a) Ribosomes
  • Explanation: Ribosomes attached to the rough ER synthesize proteins, giving it a “rough” appearance.
  • Tip: Remember “Rough ER” is rough due to ribosomes.

Section B: Short Answers

1. What are the main functions of the cell membrane?

  • Answer:
    • Regulates the entry and exit of substances (selective permeability).
    • Protects the cell by providing structural support.
    • Facilitates communication and signaling between cells.

2. What key role does the Golgi apparatus play in eukaryotic cells?

  • Answer:
    • Modifies, sorts, and packages proteins and lipids for secretion or use within the cell.
    • Forms lysosomes and transports cellular materials.

3. How do lysosomes contribute to the cell’s functioning?

  • Answer:
    • Break down cellular waste and debris using digestive enzymes.
    • Play a role in recycling cellular components (autophagy).

4. Which organelle detoxifies harmful substances and breaks down lipids?

  • Answer: Smooth Endoplasmic Reticulum (SER).
  • Explanation: SER is involved in lipid synthesis, detoxification of drugs, and storage of calcium ions.

5. What is the smooth endoplasmic reticulum responsible for?

  • Answer:
    • Synthesis of lipids and steroid hormones.
    • Detoxification of harmful substances.
    • Storage and release of calcium ions in muscle cells.

6. How do the vacuoles in plant cells differ from vacuoles in animal cells?

  • Answer:
    • Plant cells have large central vacuoles for storage of water, nutrients, and waste.
    • Animal cells have smaller, temporary vacuoles, mainly for storage and transport.

7. What could happen if lysosomal enzymes stop working properly?

  • Answer:
    • Accumulation of waste materials and toxins within the cell.
    • Possible cell death due to impaired autophagy and digestion.

8. Why are the cristae important for cellular respiration?

  • Answer:
    • Cristae increase the surface area of the inner mitochondrial membrane, allowing more space for the enzymes and proteins involved in ATP production during cellular respiration.

Here’s the detailed solution to the questions in the uploaded image:

Section B: Short Answers

9. How are chromatin and chromosomes related?

  • Answer:
    Chromatin is the uncoiled and relaxed form of DNA, combined with proteins (histones), found in the nucleus during interphase. During cell division, chromatin condenses and organizes into tightly coiled structures called chromosomes.

10. Which type of cell is responsible for sending nerve signals?

  • Answer:
    Neurons (nerve cells) are specialized cells that transmit electrical and chemical signals throughout the body.

11. What do mesophyll cells do in plant leaves?

  • Answer:
    Mesophyll cells in plant leaves perform photosynthesis. They contain chloroplasts that use sunlight, carbon dioxide, and water to produce glucose and oxygen.

12. How would you define a stem cell?

  • Answer:
    A stem cell is an undifferentiated cell capable of dividing and differentiating into specialized cell types. Stem cells also have the ability to self-renew.

13. Name the chemical compounds that make up:

  • a) Cell membrane: Phospholipids, proteins, carbohydrates, and cholesterol.
  • b) Fungal cell wall: Chitin and glucans.
  • c) Plant cell wall: Cellulose, hemicellulose, and pectin.
  • d) Bacterial cell wall: Peptidoglycan (murein).
  • e) Ribosomes: rRNA (ribosomal RNA) and proteins.
  • f) Chromosomes: DNA and proteins (histones).

14. Label the parts of these cell diagrams.

For the provided cell diagrams, the labels typically represent major cell organelles. Based on general diagrams:

  • A: Nucleus
  • B: Mitochondria
  • C: Endoplasmic reticulum
  • D: Golgi apparatus
  • E: Cell membrane
  • F: Lysosome
  • G: Ribosome

Section C: Detailed Answers

1. Explain the fluid mosaic model of the cell membrane.

  • The cell membrane is a phospholipid bilayer with embedded proteins.
  • The “fluid” aspect refers to the flexible and dynamic nature of the bilayer, allowing lateral movement of lipids and proteins.
  • The “mosaic” aspect describes the patchwork of proteins interspersed within the bilayer, performing various functions such as transport, signaling, and enzymatic activity.

2. Describe the structure and functions of the cell wall.

  • Structure:
    • Found in plants, fungi, and bacteria.
    • Composed of cellulose (plants), chitin (fungi), or peptidoglycan (bacteria).
  • Functions:
    • Provides structural support and protection.
    • Maintains cell shape.
    • Prevents excessive water uptake (osmotic regulation).

3. Discuss the components of the nucleus.

  • Nuclear envelope: Double membrane with pores for transport.
  • Nucleoplasm: Fluid containing ions, enzymes, and nucleotides.
  • Nucleolus: Site of ribosome assembly.
  • Chromatin: DNA and protein that form chromosomes during cell division.

4. Describe the structure and function of lysosomes and the endoplasmic reticulum.

  • Lysosomes:
    • Membrane-bound organelles containing digestive enzymes.
    • Function: Breakdown of waste materials, cellular debris, and pathogens.
  • Endoplasmic Reticulum (ER):
    • Rough ER: Ribosomes on its surface; synthesizes proteins.
    • Smooth ER: Synthesizes lipids and detoxifies harmful substances.

5. Describe the formation and function of the Golgi apparatus.

  • Formation: Derived from vesicles from the ER.
  • Function: Modifies, sorts, and packages proteins and lipids for secretion or delivery within the cell.

6. Describe the structure and functions of the chloroplast.

  • Structure:
    • Double membrane.
    • Contains thylakoids stacked into grana, surrounded by stroma.
    • Contains chlorophyll for capturing light energy.
  • Function: Photosynthesis to convert light energy into glucose and oxygen.

7. How does turgor pressure develop in a plant cell?

  • Turgor pressure develops due to water entering the cell via osmosis. The vacuole swells, pressing the plasma membrane against the cell wall, providing rigidity to the plant.

8. Write any four differences between a plant cell and an animal cell.

FeaturePlant CellAnimal Cell
Cell wallPresent (cellulose)Absent
ChloroplastsPresent (photosynthesis)Absent
VacuolesLarge central vacuoleSmall, temporary vacuoles
CentriolesAbsentPresent

9. Describe the concept of division of labor and how it applies in multicellular organisms.

  • Concept: Division of labor refers to specialization of cells, tissues, or organs to perform specific functions.
  • Examples:
    • Red blood cells transport oxygen.
    • Neurons transmit nerve signals.
    • Muscle cells contract to enable movement.

10. Write a note on cell specialization.

  • Cell specialization is the process where generic cells develop into specific cell types to perform unique functions. For example:
    • Muscle cells specialize in contraction.
    • Xylem cells specialize in water transport.
    • Specialized cells increase efficiency and allow multicellular organisms to perform complex tasks.

The science of biology-9th class solved Exercise

by

Biology 9th is a foundational subject under the Lahore Board and Punjab Board syllabus. The science of biology explores the study of life, organisms, and their interactions, helping students build essential knowledge for higher studies in medicine, agriculture, and environmental sciences.

1. Which branch of Biology focuses on the study of the structure and function of cells?

  • Options:
    a) Cytology
    b) Microbiology
    c) Histology
    d) Ecology
  • Answer: a) Cytology
  • Tip/Trick: The prefix “cyto-” means “cell,” so Cytology is the study of cells.

2. The study of the processes of heredity and variation in living organisms is known as:

  • Options:
    a) Ecology
    b) Genetics
    c) Anatomy
    d) Proteomics
  • Answer: b) Genetics
  • Tip/Trick: Genetics deals with genes and inheritance, which govern heredity and variation.

3. Insulin made through bacteria is an example of the technique of:

  • Options:
    a) Parasitology
    b) Biotechnology
    c) Biochemistry
    d) Histology
  • Answer: b) Biotechnology
  • Tip/Trick: Biotechnology involves using organisms or biological processes to create useful products like insulin.

4. Heart pumps, the brain memorizes, kidneys excrete. The statement comes from:

  • Options:
    a) Physiology
    b) Anatomy
    c) Morphology
    d) Cardiology
  • Answer: a) Physiology
  • Tip/Trick: Physiology focuses on the functions and processes of living organisms and their parts.

5. Which branch of Biology involves the study of the classification of organisms?

  • Options:
    a) Taxonomy
    b) Physiology
    c) Palaeontology
    d) Biogeography
  • Answer: a) Taxonomy
  • Tip/Trick: Taxonomy is about naming, classifying, and organizing organisms into groups.

6. Which step comes between making a hypothesis and doing experiments?

  • Options:
    a) Making deductions
    b) Making observations
    c) Summarizing results
    d) Analyzing data
  • Answer: b) Making observations
  • Tip/Trick: Observations help refine hypotheses and guide experimental design.

7. Which of the following is NOT a characteristic of the scientific method?

  • Options:
    a) It relies on evidence
    b) It involves formulating hypotheses
    c) Hypotheses will always be correct
    d) It requires rigorous testing
  • Answer: c) Hypotheses will always be correct
  • Explanation: Hypotheses are tentative explanations and can be disproven.
  • Tip/Trick: Remember that in science, hypotheses are tested and may be rejected or refined.

8. Choose the correct sequence of steps of the scientific method.

  • Options:
    a) Observations → hypothesis → deduction → experiments
    b) Observations → hypothesis → law → theory
    c) Hypothesis → observations → deduction → experiments
    d) Law → theory → deduction → observations
  • Answer: a) Observations → hypothesis → deduction → experiments
  • Explanation: The scientific method begins with observations, followed by forming a hypothesis, making deductions, and performing experiments.
  • Tip/Trick: Think of it as “observe first, then hypothesize, test, and conclude.”

9. People who slept near smoky fire had less chance to suffer from malaria. Why?

  • Options:
    a) Smoke kills Plasmodium in their blood
    b) Fire increases temperature and Plasmodium are killed in air
    c) Mosquitoes cannot tolerate smoke and are repelled
    d) Smoke kills Plasmodium present in mosquitoes
  • Answer: c) Mosquitoes cannot tolerate smoke and are repelled
  • Explanation: Smoke repels mosquitoes, reducing their bites and preventing the spread of malaria.
  • Tip/Trick: Remember that mosquitoes are the carriers of malaria, and repelling them is effective.

10. Experiments are very important in the scientific method because a researcher:

  • Options:
    a) Always gets correct results
    b) Disproves many hypotheses and gets some hypotheses proved
    c) Is sure that he will prove the hypotheses
    d) Gets a chance to work in the laboratory
  • Answer: b) Disproves many hypotheses and gets some hypotheses proved
  • Explanation: Experiments validate or refute hypotheses, advancing scientific understanding.
  • Tip/Trick: Science progresses by eliminating incorrect hypotheses and validating correct ones.

Short Questions

1. Define the following branches of Biology:

  • Genetics: The study of heredity and the variation of inherited traits.
  • Anatomy: The study of the structure of organisms and their parts.
  • Palaeontology: The study of fossils to understand past life and evolution.
  • Marine Biology: The study of organisms in the ocean and other saltwater environments.
  • Pathology: The study of diseases, their causes, and effects.

2. Which branch of Biology involves the study of the development and growth of organisms from fertilization to adulthood?

  • Answer: Embryology.
  • Explanation: Embryology focuses on the development of organisms from a single cell to maturity.

3. How is the profession of medicine and surgery different from animal husbandry?

  • Answer: Medicine and surgery deal with diagnosing and treating human diseases, while animal husbandry involves breeding, feeding, and caring for animals for agricultural purposes.

4. Differentiate between Morphology and Physiology.

  • Answer:
    • Morphology: The study of the structure, shape, and form of organisms.
    • Physiology: The study of the functions and processes of living organisms.

5. What is Computational Biology?

  • Answer: Computational Biology is the application of data analysis, mathematical models, and algorithms to study biological systems.

6. What is the role of observation and experimentation in the scientific method?

  • Answer: Observation helps identify patterns and formulate hypotheses, while experimentation tests these hypotheses to validate or refute them.

Detailed Answers for Section C

1. Link the study of Biology with that of Physics, Chemistry, Statistics, Geography, Economics, and Computer Science.

  • Biology is interconnected with many disciplines:
    • Physics: Explains biological phenomena like fluid dynamics in blood flow and biomechanics in movement.
    • Chemistry: Essential for understanding biochemical reactions like photosynthesis, respiration, and digestion.
    • Statistics: Helps in analyzing experimental data, such as population genetics or epidemiological studies.
    • Geography: Influences ecosystems, biodiversity, and environmental studies.
    • Economics: Impacts resource management, agricultural biology, and biotechnology industries.
    • Computer Science: Supports bioinformatics, genetic sequencing, and computational biology for data analysis and modeling.

2. Explain how the study of Biology can lead to different professional studies.

  • Biology serves as a foundation for numerous professions:
    • Medicine and Surgery: Diagnosis and treatment of diseases.
    • Agriculture and Horticulture: Crop production and pest management.
    • Environmental Science: Ecosystem conservation and pollution control.
    • Biotechnology: Development of medicines, vaccines, and genetically modified crops.
    • Pharmaceuticals: Drug design and clinical research.
    • Research: Advancing knowledge in genetics, microbiology, and molecular biology.

3. Science is a collaborative field in which scientists work together to share knowledge. Prove this statement by giving examples.

  • Collaboration is vital for scientific progress:
    • Human Genome Project: Involved scientists from various countries to map all human genes.
    • COVID-19 Vaccine Development: Teams across the globe shared data to develop effective vaccines quickly.
    • Discovery of DNA Structure: James Watson, Francis Crick, Rosalind Franklin, and Maurice Wilkins worked together to elucidate DNA’s double helix.
    • Climate Change Research: Requires collaboration between biologists, geographers, and meteorologists.

4. How is a hypothesis converted to theory, law, and principle?

  • Hypothesis: A testable statement based on observations.
    • Example: “Plants grow faster with more sunlight.”
  • Theory: When a hypothesis is repeatedly tested and supported by evidence.
    • Example: The Theory of Evolution explains biodiversity through natural selection.
  • Law: A universal statement that describes a consistent natural phenomenon.
    • Example: Mendel’s Laws of Inheritance explain genetic traits.
  • Principle: A fundamental truth that serves as a basis for other scientific concepts.
    • Example: The Principle of Homeostasis explains the stability of internal environments.

5. What are the basic steps a scientist adopts in order to solve scientific problems?

  • Steps in the Scientific Method:
    1. Observation: Identify a phenomenon or problem.
    2. Hypothesis: Propose a possible explanation.
    3. Experimentation: Design and conduct tests to validate the hypothesis.
    4. Data Analysis: Interpret experimental results.
    5. Conclusion: Accept, reject, or refine the hypothesis.
    6. Publication: Share findings for peer review.

6. Describe the work of different scientists in discovering the cause of malaria.

  • Charles Laveran: First observed the malaria parasite in a patient’s blood in 1880.
  • Patrick Manson: Demonstrated the transmission of parasites through mosquitoes.
  • Ronald Ross: Proved that the Anopheles mosquito is the vector for malaria by showing parasites in the mosquito’s stomach.
  • Giovanni Battista Grassi: Confirmed Ross’s findings and identified the lifecycle of the parasite.

7. Write a descriptive note on the experiments performed by Ross.

  • Ronald Ross’s experiments:
    1. In 1897, Ross dissected mosquitoes fed on malaria-infected patients and found Plasmodium parasites in their stomachs.
    2. He demonstrated the lifecycle of Plasmodium in mosquitoes, showing that mosquitoes were the vector for malaria.
    3. His experiments took place in India, where he meticulously studied mosquito behavior and malaria transmission.
    4. His work earned him the Nobel Prize in 1902, revolutionizing the understanding and prevention of malaria.

©2024. Everexams.com. All Rights Reserved.