1. Lack of oxygen in muscles converts pyruvate into
(A) Ethanol
(B) Lactic acid
(C) Glucose
(D) Acetic acid
Answer: B – Lactic acid
Explanation: In anaerobic respiration in muscles, pyruvate is converted to lactic acid to produce energy when oxygen is insufficient.
- (A) Ethanol – Produced in yeast and some microorganisms, not in human muscles.
- (C) Glucose – Pyruvate cannot revert to glucose directly in muscles.
- (D) Acetic acid – Not produced during human anaerobic respiration.
2. Lactic acid is a
(A) Two-carbon compound
(B) Three-carbon compound
(C) Four-carbon compound
(D) Six-carbon compound
Answer: B – Three-carbon compound
Explanation: Lactic acid has 3 carbon atoms, same as pyruvate.
- (A) Two-carbon – Ethanol is 2-carbon.
- (C) Four-carbon – Incorrect, lactic acid is not 4-carbon.
- (D) Six-carbon – Glucose is 6-carbon, not lactic acid.
3. Muscle cramps are caused due to
(A) Oxygen excess
(B) Lactic acid build-up
(C) Protein break-down
(D) Sugar loss
Answer: B – Lactic acid build-up
Explanation: Lactic acid accumulation in muscles during anaerobic exercise leads to cramps.
- (A) Oxygen excess – Opposite of cause.
- (C) Protein break-down – Not a direct cause.
- (D) Sugar loss – Does not cause cramps directly.
4. Energy released in respiration is stored in
(A) DNA
(B) Glucose
(C) ATP
(D) CO₂
Answer: C – ATP
Explanation: ATP acts as the energy currency of cells, storing energy released from glucose.
- (A) DNA – Stores genetic information, not energy.
- (B) Glucose – Source of energy, not storage.
- (D) CO₂ – Waste product, not energy storage.
5. Full form of ATP is
(A) Adenosine Triphosphate
(B) Adenine Triphosphate
(C) Adenosine Tetraphosphate
(D) Adenine Tetraphosphate
Answer: A – Adenosine Triphosphate
Explanation: Correct scientific expansion.
- (B) Adenine Triphosphate – Incorrect base name.
- (C) Adenosine Tetraphosphate – Wrong phosphate count.
- (D) Adenine Tetraphosphate – Both base and phosphate count wrong.
6. ATP is synthesised from
(A) ADP + O₂
(B) ADP + Phosphate + Energy
(C) Glucose + Oxygen
(D) Acid + Base
Answer: B – ADP + Phosphate + Energy
Explanation: ATP forms by phosphorylation of ADP using energy from respiration.
- (A) ADP + O₂ – Oxygen is used earlier in respiration but not directly in ATP formation.
- (C) Glucose + Oxygen – Used in energy production, not direct ATP formation.
- (D) Acid + Base – Not relevant.
7. Energy is released when ATP is converted into
(A) ADP
(B) Glucose
(C) Enzyme
(D) Water
Answer: A – ADP
Explanation: Hydrolysis of ATP to ADP + Pi releases energy for cellular processes.
- (B) Glucose – Not a direct product.
- (C) Enzyme – Not related.
- (D) Water – Not involved in energy release.
8. Energy released from ATP is approximately
(A) 10 kJ/mol
(B) 15 kJ/mol
(C) 30.5 kJ/mol
(D) 60 kJ/mol
Answer: C – 30.5 kJ/mol
Explanation: Standard hydrolysis of one ATP molecule releases ~30.5 kJ/mol.
- (A, B, D) – Too low or too high.
9. ATP is required for
(A) Muscle contraction
(B) Protein synthesis
(C) Nerve impulses
(D) All of these
Answer: D – All of these
Explanation: ATP is the universal energy source for all cellular activities.
- (A, B, C) – Each is correct individually but incomplete.
10. Endothermic reactions need
(A) Oxygen
(B) Energy
(C) Heat loss
(D) CO₂
Answer: B – Energy
Explanation: Endothermic reactions absorb energy from surroundings.
- (A) Oxygen – Not required for all.
- (C) Heat loss – Opposite effect.
- (D) CO₂ – Not required.
11. ATP acts like a
(A) Fuel tank
(B) Battery
(C) Enzyme
(D) Catalyst
Answer: B – Battery
Explanation: ATP stores and releases energy when needed, just like a rechargeable battery.
- (A) Fuel tank – Stores fuel but not energy in usable form directly.
- (C) Enzyme – Enzymes catalyze reactions but don’t store energy.
- (D) Catalyst – Speeds reactions but doesn’t provide energy.
12. Plants use which structures for gas exchange?
(A) Lenticels
(B) Alveoli
(C) Stomata
(D) Gills
Answer: C – Stomata
Explanation: Stomata are pores on leaves that allow CO₂ in and O₂ out.
- (A) Lenticels – Found in stems, minor role.
- (B) Alveoli – Found in animals’ lungs, not plants.
- (D) Gills – Found in aquatic animals.
13. Gas exchange in plants occurs by
(A) Filtration
(B) Conduction
(C) Diffusion
(D) Osmosis
Answer: C – Diffusion
Explanation: CO₂ and O₂ move in/out of stomata by concentration gradients.
- (A) Filtration – Not involved.
- (B) Conduction – Transport within plant, not gas exchange.
- (D) Osmosis – Movement of water, not gases.
14. At night, plants mainly release
(A) Oxygen
(B) Nitrogen
(C) Carbon dioxide
(D) Hydrogen
Answer: C – Carbon dioxide
Explanation: Photosynthesis stops without light; respiration dominates, releasing CO₂.
- (A) Oxygen – Produced mainly during daytime photosynthesis.
- (B) Nitrogen – Not released by plants.
- (D) Hydrogen – Not released.
15. During the daytime, plants mainly release
(A) CO₂
(B) Oxygen
(C) Nitrogen
(D) Methane
Answer: B – Oxygen
Explanation: Photosynthesis during daylight produces O₂ as a byproduct.
- (A) CO₂ – Consumed, not released.
- (C) Nitrogen – Not a product.
- (D) Methane – Not produced by plants.
16. Aquatic animals breathe using
(A) Lungs
(B) Gills
(C) Skin only
(D) Nostrils
Answer: B – Gills
Explanation: Gills extract dissolved oxygen from water.
- (A) Lungs – Terrestrial animals.
- (C) Skin only – Minor in some species.
- (D) Nostrils – Not for respiration in aquatic animals.
17. Oxygen in water is
(A) Equal to air
(B) Greater than air
(C) Less than air
(D) Same as air
Answer: C – Less than air
Explanation: Water contains less free oxygen than air, making aquatic respiration challenging.
- (A, D) – Incorrect, oxygen solubility in water is lower.
- (B) – Incorrect, water never has more O₂ than air.
18. Rate of breathing in aquatic animals is
(A) Slower
(B) Same
(C) Faster
(D) Zero
Answer: C – Faster
Explanation: Less O₂ in water requires faster breathing to meet oxygen needs.
- (A, B, D) – Slower or zero would not supply enough O₂.
19. Fishes obtain oxygen from
(A) Water
(B) Air
(C) Food
(D) Skin
Answer: A – Water
Explanation: Fish gills extract oxygen dissolved in water.
- (B) Air – Only some surface-dwelling fish.
- (C) Food – Not a source of O₂.
- (D) Skin – Minor in amphibians, not fish.
20. Organ protecting gills is called
(A) Operculum
(B) Rib
(C) Diaphragm
(D) Trachea
Answer: A – Operculum
Explanation: The operculum covers and protects the delicate gills.
- (B) Rib – Skeleton, not related to gills.
- (C) Diaphragm – Muscle in mammals.
- (D) Trachea – Part of terrestrial respiratory system.
21. Terrestrial animals take oxygen from
(A) Water
(B) Air
(C) Soil
(D) Food
Answer: B – Air
Explanation: Lungs extract oxygen from air in terrestrial animals.
- (A) Water – Aquatic respiration.
- (C) Soil – Not used directly.
- (D) Food – Not a source of O₂.
22. Respiratory surfaces are always
(A) Thick
(B) Dry
(C) Fine and moist
(D) Hard
Answer: C – Fine and moist
Explanation: Thin, moist surfaces allow efficient gas diffusion.
- (A) Thick – Reduces diffusion efficiency.
- (B) Dry – Hinders gas exchange.
- (D) Hard – Not permeable to gases.
23. Human air enters through
(A) Mouth only
(B) Nose
(C) Skin
(D) Ears
Answer: B – Nose
Explanation: Nose filters, warms, and humidifies incoming air.
- (A) Mouth – Secondary route.
- (C) Skin – Not respiratory surface.
- (D) Ears – Not involved.
24. Fine hairs in nose help in
(A) Breathing
(B) Removing CO₂
(C) Filtering dust
(D) Producing oxygen
Answer: C – Filtering dust
Explanation: Nasal hairs trap dust particles and microbes.
- (A) Breathing – Supported by structures, not hairs.
- (B) Removing CO₂ – Blood carries CO₂, not hairs.
- (D) Producing oxygen – Not possible.
25. Cartilage rings are found in
(A) Lungs
(B) Throat
(C) Nose
(D) Alveoli
Answer: B – Throat
Explanation: Rings in trachea prevent collapse during inhalation/exhalation.
- (A) Lungs – Do not contain cartilage.
- (C) Nose – No rings.
- (D) Alveoli – Thin, for diffusion, not cartilage.
26. Cartilage prevents air passage from
(A) Widening
(B) Hardening
(C) Collapsing
(D) Expanding
Answer: C – Collapsing
Explanation: Cartilage rings in the trachea keep it open and prevent it from collapsing during inhalation and exhalation.
- (A) Widening – Not the primary function.
- (B) Hardening – Cartilage is flexible, not for hardening.
- (D) Expanding – Rings allow slight expansion but mainly prevent collapse.
27. In lungs, air tubes end in
(A) Bronchi
(B) Trachea
(C) Alveoli
(D) Capillaries
Answer: C – Alveoli
Explanation: Bronchioles terminate in alveoli, the site of gas exchange.
- (A) Bronchi – Branch into smaller bronchioles.
- (B) Trachea – Branches into bronchi.
- (D) Capillaries – Surround alveoli but are blood vessels, not air tubes.
28. Alveoli look like
(A) Sacs
(B) Bubbles
(C) Balloons
(D) Cubes
Answer: C – Balloons
Explanation: Alveoli are balloon-shaped sacs to maximize surface area for gas exchange.
- (A, B) – Partially correct but less precise.
- (D) Cubes – Incorrect, alveoli are spherical, not cubic.
29. Exchange of gases occurs in
(A) Windpipe
(B) Nose
(C) Alveoli
(D) Mouth
Answer: C – Alveoli
Explanation: Alveoli provide thin, moist surfaces for O₂ and CO₂ exchange between air and blood.
- (A) Windpipe – Only conducts air.
- (B) Nose – Filters, warms air.
- (D) Mouth – Entry point, not site of exchange.
30. Walls of alveoli contain
(A) Nerves
(B) Veins only
(C) Blood vessels
(D) Cartilage
Answer: C – Blood vessels
Explanation: Alveoli are surrounded by capillaries for rapid gas exchange.
- (A) Nerves – Not directly for gas exchange.
- (B) Veins only – Capillaries are mixed arterial and venous.
- (D) Cartilage – Only in trachea/bronchi, not alveoli.
31. Oxygen enters blood from
(A) Muscles
(B) Lungs
(C) Heart
(D) Liver
Answer: B – Lungs
Explanation: Oxygen diffuses from alveoli into pulmonary capillaries.
- (A) Muscles – Use O₂, do not supply it.
- (C) Heart – Pumps blood, does not oxygenate it.
- (D) Liver – Not involved in gas exchange.
32. Carbon dioxide is given to alveoli by
(A) Heart
(B) Blood
(C) Lungs
(D) Muscles
Answer: B – Blood
Explanation: Blood transports CO₂ from tissues to alveoli for exhalation.
- (A) Heart – Pumps blood but doesn’t carry CO₂ directly.
- (C) Lungs – Receive CO₂ for exhalation.
- (D) Muscles – Produce CO₂ but blood transports it.
33. Rib movement during inhalation is
(A) Down
(B) Inward
(C) Up and outward
(D) Fixed
Answer: C – Up and outward
Explanation: Ribcage expansion increases thoracic volume, reducing pressure to draw air in.
- (A, B) – Opposite movement occurs during exhalation.
- (D) Fixed – Ribs move; not fixed.
34. Diaphragm movement during inhalation is
(A) Curved
(B) Flattened
(C) Raised
(D) Tightened
Answer: B – Flattened
Explanation: Flattening diaphragm increases thoracic cavity volume, allowing lungs to fill with air.
- (A) Curved – Normal position, not during inhalation.
- (C) Raised – Exhalation.
- (D) Tightened – Not precise description.
35. Residual air in lungs helps in
(A) Cooling air
(B) Continuous oxygen absorption
(C) Holding breath
(D) Removing dust
Answer: B – Continuous oxygen absorption
Explanation: Residual air prevents lung collapse and maintains gas exchange even between breaths.
- (A) Cooling – Not a function.
- (C) Holding breath – Secondary.
- (D) Removing dust – Done by cilia, not residual air.
36. Diffusion alone is insufficient for
(A) Small animals
(B) Large animals
(C) Plants
(D) Bacteria
Answer: B – Large animals
Explanation: Large animals need circulatory systems for rapid O₂ and CO₂ transport; diffusion is too slow.
- (A, C, D) – Small organisms can rely on diffusion.
37. Respiratory pigment in humans is
(A) Melanin
(B) Chlorophyll
(C) Hemoglobin
(D) Insulin
Answer: C – Hemoglobin
Explanation: Hemoglobin binds O₂ in red blood cells and transports it.
- (A) Melanin – Pigment, not for O₂ transport.
- (B) Chlorophyll – Photosynthesis pigment.
- (D) Insulin – Hormone, not respiratory pigment.
38. Hemoglobin is found in
(A) Plasma
(B) WBC
(C) RBC
(D) Platelets
Answer: C – RBC
Explanation: Hemoglobin is contained in red blood cells to carry oxygen.
- (A) Plasma – Transports dissolved substances, not hemoglobin.
- (B) WBC – Immune cells.
- (D) Platelets – Involved in clotting.
39. Hemoglobin has high affinity for
(A) Nitrogen
(B) CO₂
(C) Oxygen
(D) Hydrogen
Answer: C – Oxygen
Explanation: Hemoglobin binds O₂ strongly for transport.
- (A) Nitrogen – Not carried.
- (B) CO₂ – Carried in small amounts as bicarbonate.
- (D) Hydrogen – Not transported.
40. CO₂ is transported mainly
(A) As gas
(B) In dissolved form
(C) As solid
(D) As vapor
Answer: B – In dissolved form
Explanation: Most CO₂ is carried in blood as bicarbonate ions, a dissolved form.
- (A, C, D) – Not primary forms in blood