CBSE Class 10 Science Life processes Sure Shot Questions Set 03

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ASSIGNMENT QUESTIONS SET - 3

CHAPTER - 6

LIFE PROCESSES

1. Which of the following statements about the autotrophs is incorrect? [1 Mark]
(A) They synthesise carbohydrates from carbon dioxide and water in the presence of sunlight and chlorophyll
(B) They store carbohydrates in the form of starch
(C) They convert carbon dioxide and water into carbohydrates in the absence of sunlight
(D) They constitute the first trophic level in food chains

Answer: (C) They convert carbon dioxide and water into carbohydrates in the absence of sunlight

1. Autotrophs require sunlight as an energy source to drive photosynthesis.
2. In the absence of sunlight, carbon dioxide and water cannot be converted into carbohydrates.
3. Hence, statement (C) is incorrect and is the correct choice.

Teacher's Note:
a) Autotrophs prepare their own food using light energy.
b) Always read options carefully to spot incorrect biological processes.

2. In which of the following groups of organisms, food material is broken down outside the body and absorbed? [1 Mark]
(A) Mushroom, green plants, Amoeba
(B) Yeast, mushroom, bread mould
(C) Paramecium, Amoeba, Cuscuta
(D) Cuscuta, lice, tapeworm

Answer: (B) Yeast, mushroom, bread mould

1. Fungi like yeast, mushrooms, and bread moulds exhibit saprophytic nutrition.
2. They secrete digestive enzymes outside their body to break down complex food material and then absorb the simpler substances.
3. Hence, the correct option is (B).

Teacher's Note:
a) Saprophytes digest food externally before absorption.
b) Green plants are autotrophic, while parasites like cuscuta feed internally on hosts.

3. Select the correct statement [1 Mark]
(A) Heterotrophs do not synthesise their own food
(B) Heterotrophs utilise solar energy for photosynthesis
(C) Heterotrophs synthesise their own food
(D) Heterotrophs are capable of converting carbon dioxide and water into carbohydrates

Answer: (A) Heterotrophs do not synthesise their own food

1. Heterotrophs depend on other organisms for their nourishment.
2. They lack chlorophyll and cannot perform photosynthesis to manufacture their own food.
3. Hence, the correct option is (A).

Teacher's Note:
a) Heterotrophic organisms rely directly or indirectly on autotrophs.
b) Options (B), (C), and (D) describe autotrophic characteristics.

4. Which is the correct sequence of parts in human alimentary canal? [1 Mark]
(A) Mouth - stomach - small intestine - oesophagus - large intestine
(B) Mouth - oesophagus - stomach - large intestine - small intestine
(C) Mouth - stomach - oesophagus - small intestine - large intestine
(D) Mouth - oesophagus - stomach - small intestine - large intestine

Answer: (D) Mouth - oesophagus - stomach - small intestine - large intestine

1. Food enters the mouth, passes down through the oesophagus into the stomach.
2. From the stomach, food moves into the small intestine and finally reaches the large intestine.
3. Hence, the correct option is (D).

Teacher's Note:
a) Trace the continuous anatomical pathway of the digestive tract.
b) Common student errors involve swapping the order of the stomach and oesophagus.

5. If salivary amylase is lacking in the saliva, which of the following events in the mouth cavity will be affected? [1 Mark]
(A) Proteins breaking down into amino acids
(B) Starch breaking down into sugars
(C) Fats breaking down into fatty acids and glycerol
(D) Absorption of vitamins

Answer: (B) Starch breaking down into sugars

1. Saliva contains the enzyme salivary amylase which digests starch.
2. It breaks down complex starch into simple sugars (maltose) inside the mouth.
3. Hence, the correct option is (B).

Teacher's Note:
a) Salivary amylase initiates carbohydrate digestion in the oral cavity.
b) Protein and fat digestion occur in the stomach and small intestine respectively.

6. The inner lining of stomach is protected by one of the following from hydrochloric acid. Choose the correct one [1 Mark]
(A) Pepsin
(B) Mucus
(C) Salivary amylase
(D) Bile

Answer: (B) Mucus

1. The gastric glands in the stomach wall secrete hydrochloric acid, pepsin, and mucus.
2. Mucus forms a protective barrier over the inner lining of the stomach against the corrosive action of hydrochloric acid.
3. Hence, the correct option is (B).

Teacher's Note:
a) Mucus secretion prevents acid erosion of the gastric mucosa.
b) Pepsin is a protein-digesting enzyme, not a protective secretion.

7. Which part of alimentary canal receives bile from the liver? [1 Mark]
(A) Stomach
(B) Small intestine
(C) Large intestine
(D) Oesophagus

Answer: (B) Small intestine

1. The liver secretes bile which is temporarily stored in the gall bladder.
2. Bile is released into the duodenum region of the small intestine to emulsify fats.
3. Hence, the correct option is (B).

Teacher's Note:
a) Bile aids in the digestion of fats by breaking large fat globules into smaller ones.
b) The small intestine receives secretions from both the liver and the pancreas.

8. A few drops of iodine solution were added to rice water. The solution turned blue-black in colour. This indicates that rice water contains [1 Mark]
(A) complex proteins
(B) simple proteins
(C) fats
(D) starch

Answer: (D) starch

1. Iodine solution is used as a standard laboratory reagent to test for the presence of starch.
2. Starch reacts with iodine to form a characteristic blue-black colored complex.
3. Since rice water turned blue-black upon adding iodine, it confirms the presence of starch.
4. Hence, the correct option is (D).

Teacher's Note:
a) Iodine test is a confirmatory chemical test for carbohydrates in the form of starch.
b) Proteins, fats, and simple sugars do not give a blue-black color with iodine.

9. In which part of the alimentary canal food is finally digested? [1 Mark]
(A) Stomach
(B) Mouth cavity
(C) Large intestine
(D) Small intestine

Answer: (D) Small intestine

1. The small intestine is the site of complete digestion of carbohydrates, proteins, and fats.
2. It receives secretions from the liver and pancreas, and intestinal juice.
3. Final breakdown products like glucose, amino acids, fatty acids, and glycerol are formed here.
4. Hence, the correct option is (D).

Teacher's Note:
a) The large intestine is primarily responsible for the absorption of water and mineral salts.
b) Digestion is fully completed in the small intestine before absorption begins.

10. Choose the function of the pancreatic juice from the following [1 Mark]
(A) trypsin digests proteins and lipase carbohydrates
(B) trypsin digests emulsified fats and lipase proteins
(C) trypsin and lipase digest fats
(D) trypsin digests proteins and lipase emulsified fats

Answer: (D) trypsin digests proteins and lipase emulsified fats

1. Pancreatic juice contains digestive enzymes such as trypsin and lipase.
2. Trypsin is a proteolytic enzyme that breaks down proteins into simpler peptides and amino acids.
3. Lipase is responsible for the breakdown of emulsified fats into fatty acids and glycerol.
4. Hence, the correct option is (D).

Teacher's Note:
a) Amylase digests carbohydrates, while trypsin targets proteins and lipase acts on fats.
b) Bile salts emulsify fats first, making them accessible for pancreatic lipase action.

11. When air is blown from mouth into a test-tube containing lime water, the lime water turned milky due to the presence of [1 Mark]
(A) oxygen
(B) carbon dioxide
(C) nitrogen
(D) water vapour

Answer: (B) carbon dioxide

1. Exhaled air contains a high concentration of carbon dioxide produced during cellular respiration.
2. When carbon dioxide is passed through lime water (calcium hydroxide solution), it reacts to form insoluble calcium carbonate.
3. The formation of insoluble calcium carbonate creates a milky white precipitate.
4. Hence, the correct option is (B).

Teacher's Note:
a) Lime water turns milky specifically in the presence of carbon dioxide gas.
b) Prolonged bubbling can redissolve the precipitate due to the formation of soluble calcium bicarbonate.

12. The correct sequence of anaerobic reactions in yeast is [1 Mark]
(A) Glucose → cytoplasm → Pyruvate → mitochondria → Ethanol + Carbondioxide
(B) Glucose → cytoplasm → Pyruvate → cytoplasm → Lactic acid
(C) Glucose → cytoplasm → Pyruvate → mitochondria → Lactic acid
(D) Glucose → cytoplasm → Pyruvate → cytoplasm → Ethanol + Carbondioxide

Answer: (D) Glucose → cytoplasm → Pyruvate → cytoplasm → Ethanol + Carbondioxide

1. The first step for all metabolic pathways of glucose breakdown is the conversion into pyruvate in the cytoplasm.
2. In yeast, anaerobic respiration (fermentation) takes place entirely in the absence of oxygen.
3. This breakdown of pyruvate into ethanol and carbon dioxide occurs within the cytoplasm, not mitochondria.
4. Hence, the correct option is (D).

Teacher's Note:
a) Lactic acid formation occurs in human muscle cells during vigorous exercise due to lack of oxygen.
b) Mitochondria are exclusively involved in aerobic respiration steps.

13. Which of the following is most appropriate for aerobic respiration? [1 Mark]
(A) Glucose → mitochondria → Pyruvate → cytoplasm → CO₂ + H₂O + Energy
(B) Glucose → cytoplasm → Pyruvate → mitochondria → CO₂ + H₂O + Energy
(C) Glucose → cytoplasm → Pyruvate + Energy → mitochondria → CO₂ + H₂O
(D) Glucose → cytoplasm → Pyruvate → mitochondria → CO₂ + H₂O + Energy

Answer: (D) Glucose → cytoplasm → Pyruvate → mitochondria → CO₂ + H₂O + Energy

1. Glycolysis takes place in the cytoplasm where glucose is broken down into pyruvate.
2. Pyruvate then enters the mitochondria for the aerobic phase of respiration.
3. Inside the mitochondria, pyruvate is completely broken down into carbon dioxide, water, and a large amount of energy.
4. Hence, the correct option is (D).

Teacher's Note:
a) Aerobic respiration yields significantly more energy than anaerobic pathways.
b) Option (D) correctly identifies the locations and end products of both glycolysis and the Krebs cycle/electron transport chain.

14. Which of the following statement(s) is (are) true about respiration? [1 Mark]
(i) During inhalation, ribs move inward and diaphragm is raised
(ii) In the alveoli, exchange of gases takes place i.e., oxygen from alveolar air diffuses into blood and carbon dioxide from blood into alveolar air
(iii) Haemoglobin has greater affinity for carbon dioxide than oxygen
(iv) Alveoli increase surface area for exchange of gases
(A) (i) and (iv)
(B) (ii) and (iii)
(C) (i) and (iii)
(D) (ii) and (iv)

Answer: (D) (ii) and (iv)

1. During inhalation, ribs move outward and the diaphragm is flattened/lowered, making statement (i) incorrect.
2. Alveoli provide a very large surface area for efficient gaseous exchange in the lungs, making statement (iv) correct.
3. Oxygen diffuses into blood and carbon dioxide diffuses out into alveoli, making statement (ii) correct.
4. Haemoglobin has a much greater affinity for oxygen than carbon dioxide, making statement (iii) incorrect; hence the correct option is (D).

Teacher's Note:
a) Alveoli are richly supplied with blood capillaries to facilitate rapid diffusion of gases.
b) Carbon dioxide is mostly transported dissolved in blood plasma.

15. Which is the correct sequence of air passage during inhalation? [1 Mark]
(A) Nostrils → larynx → pharynx → trachea → lungs
(B) Nasal passage → trachea → pharynx → larynx → alveoli
(C) Nostrils → pharynx → larynx → trachea → alveoli
(D) Larynx → nostrils → pharynx → lungs

Answer: (C) Nostrils → pharynx → larynx → trachea → alveoli

1. Air enters through the nostrils into the nasal cavity, then passes into the pharynx.
2. From the pharynx, air moves through the larynx (voice box) into the trachea (windpipe).
3. The trachea branches into bronchi, bronchioles, and finally reaches the alveoli in the lungs.
4. Hence, the correct option is (C).

Teacher's Note:
a) The correct anatomical sequence of the respiratory tract must be memorized thoroughly.
b) Cilia and mucus in the passage trap dust particles to clean the incoming air.

16. During respiration exchange of gases take place in [1 Mark]
(A) trachea and larynx
(B) alveoli of lungs
(C) alveoli and throat
(D) throat and larynx

Answer: (B) alveoli of lungs

1. Alveoli provide a very large surface area for gas exchange.
2. The walls of the alveoli contain an extensive network of blood vessels.
3. Oxygen diffuses into the blood and carbon dioxide diffuses out of the blood in the alveoli.
4. Hence, the correct option is (B).

Teacher's Note:
a) Alveoli act as the primary structural site for respiratory gas exchange in human lungs.
b) Students often confuse the site of exchange with the conducting tubes like the trachea or bronchi.

17. Which of the following statement (s) is (are) true about heart? [1 Mark]
(i) Left atrium receives oxygenated blood from different parts of body while right atrium receives deoxygenated blood from lungs
(ii) Left ventricle pumps oxygenated blood to different body parts while right ventricle pumps deoxygenated blood to lungs
(iii) Left atrium transfers oxygenated blood to right ventricle which sends it to different body parts
(iv) Right atrium receives deoxygenated blood from different parts of the body while left ventricle pumps oxygenated blood to different parts of the body
(A) (i) (B) (ii)
(C) (ii) and (iv) (D) (i) and (iii)

Answer: (C) (ii) and (iv)

1. Statement (i) is false because the left atrium receives oxygenated blood from the lungs, not from different parts of the body.
2. Statement (ii) is true as the left ventricle pumps oxygenated blood to the body and the right ventricle pumps deoxygenated blood to the lungs.
3. Statement (iii) is false because the left atrium transfers blood to the left ventricle.
4. Statement (iv) is true as the right atrium receives deoxygenated blood from the body and the left ventricle pumps oxygenated blood to the body.
5. Hence, the correct option is (C).

Teacher's Note:
a) Statement analysis questions require checking each Roman numeral statement independently for factual accuracy.
b) Remember that the right side of the heart deals with deoxygenated blood and the left side with oxygenated blood.
c) Tracing the exact path of blood circulation helps eliminate incorrect statements quickly.

18. What prevents backflow of blood inside the heart during contraction? [1 Mark]
(A) Valves in heart
(B) Thick muscular walls of ventricles
(C) Thin walls of atria
(D) All of the above

Answer: (A) Valves in heart

1. Valves ensure that blood flows in only one direction during contraction of the heart chambers.
2. They prevent the backward flow of blood when atria or ventricles contract.
3. Thick walls provide pumping pressure, not prevention of backflow.
4. Hence, the correct option is (A).

Teacher's Note:
a) Heart valves function like one-way check valves to maintain unidirectional blood flow.
b) Confusing muscular wall thickness with valve function is a common error.

19. Single circulation i.e., blood flows through the heart only once during one cycle of passage through the body, is exhibited by [1 Mark]
(A) Labeo, Chameleon, Salamander
(B) Hippocampus, Exocoetus, Anabas
(C) Hyla, Rana, Draco
(D) Whale, Dolphin, Turtle

Answer: (B) Hippocampus, Exocoetus, Anabas

1. Single circulation is characteristic of fishes.
2. Hippocampus (seahorse), Exocoetus (flying fish), and Anabas (climbing perch) are all bony fishes.
3. Amphibians and reptiles exhibit incomplete double circulation, and mammals exhibit double circulation.
4. Hence, the correct option is (B).

Teacher's Note:
a) Know your biological classifications; Pisces show single circulation while higher vertebrates show double circulation.
b) Watch out for common names and scientific names of fishes in matching questions.

20. In which of the following vertebrate group/groups, heart does not pump oxygenated blood to different parts of the body? [1 Mark]
(A) Pisces and amphibians
(B) Amphibians and reptiles
(C) Amphibians only
(D) Pisces only

Answer: (D) Pisces only

1. In fishes (Pisces), the heart pumps deoxygenated blood to the gills where it gets oxygenated and then passes directly to the rest of the body.
2. Amphibians and reptiles have mixed or partially oxygenated blood pumped to the body from their three-chambered or incompletely four-chambered hearts.
3. Hence, the correct option is (D).

Teacher's Note:
a) Fish hearts are two-chambered and exclusively handle deoxygenated blood.
b) Amphibians and reptiles pump mixed blood due to incomplete separation of ventricles.

21. Choose the correct statement that describes arteries. [1 Mark]
(A) They have thick elastic walls, blood flows under high pressure; collect blood from different organs and bring it back to the heart
(B) They have thin walls with valves inside, blood flows under low pressure and carry blood away from the heart to various organs of the body
(C) They have thick elastic walls, blood flows under low pressure; carry blood from the heart to various organs of the body
(D) They have thick elastic walls without valves inside, blood flows under high pressure and carry blood away from the heart to different parts of the body.

Answer: (D) They have thick elastic walls without valves inside, blood flows under high pressure and carry blood away from the heart to different parts of the body.

1. Arteries carry blood away from the heart under high pressure generated by ventricular contraction.
2. They possess thick, elastic walls to withstand this high pressure.
3. They do not have internal valves because the high pressure prevents backflow.
4. Hence, the correct option is (D).

Teacher's Note:
a) Arteries transport blood away from the heart, whereas veins carry blood toward the heart.
b) Valves are exclusive to veins to assist low-pressure return flow against gravity.

22. The filtration units of kidneys are called [1 Mark]

Answer: Nephrons

1. Each kidney contains a large number of filtering units known as nephrons.
2. Nephrons filter waste products and excess water from the blood to form urine.

Teacher's Note:
a) Nephrons are the structural and functional units of the human excretory system.
b) Do not confuse nephrons with neurons, which are the functional units of the nervous system.

22. [Remaining options from previous page]
(a) ureter
(b) urethra
(c) neurons
(d) nephrons

Answer: (d) nephrons

1. The structural and functional unit of the kidney is the nephron.
2. Nephrons are responsible for filtering blood and forming urine.
3. Hence, the correct option is (d).

Teacher's Note:
a) Nephrons contain glomeruli and renal tubules for filtration and reabsorption.
b) Neurons are the basic units of the nervous system.

23. Oxygen liberated during photosynthesis comes from [1 Mark]
(a) water
(b) chlorophyll
(c) carbon dioxide
(d) glucose

Answer: (a) water

1. During the light reaction of photosynthesis, photolysis of water takes place.
2. Water molecules are split into hydrogen ions, electrons, and oxygen.
3. The oxygen released as a byproduct originates from water molecules.
4. Hence, the correct option is (a).

Teacher's Note:
a) Van Niel first proved that oxygen comes from water in green sulfur bacteria experiments.
b) Carbon dioxide is reduced to form glucose, not oxygen gas.

24. The blood leaving the tissues becomes richer in [1 Mark]
(a) carbon dioxide
(b) water
(c) heamoglobin
(d) oxygen

Answer: (a) carbon dioxide

1. Active tissues continuously perform cellular respiration, consuming oxygen and producing carbon dioxide.
2. Oxygen from the blood diffuses into the tissues, while carbon dioxide from the tissues diffuses into the blood.
3. Consequently, the deoxygenated blood leaving the tissues has a higher concentration of carbon dioxide.
4. Hence, the correct option is (a).

Teacher's Note:
a) Blood entering tissues is oxygen-rich, and blood leaving is carbon dioxide-rich.
b) Hemoglobin is a carrier protein, not a waste gas.

25. Which of the following is an incorrect statement? [1 Mark]
(a) Organisms grow with time
(b) Organisms must repair and maintain their structure
(c) Movement of molecules does not take place among cells
(d) Energy is essential for life processes

Answer: (c) Movement of molecules does not take place among cells

1. Living organisms are continuously exchanging substances and molecules within and between cells.
2. Molecular movement is essential for maintaining life processes and cellular organization.
3. Therefore, stating that molecular movement does not take place among cells is factually incorrect.
4. Hence, the correct option is (c).

Teacher's Note:
a) Diffusion and active transport facilitate the movement of molecules between cells.
b) Growth, repair, and energy requirement are fundamental characteristics of living beings.

26. The internal (cellular) energy reserve in autotrophs is [1 Mark]
(a) glycogen
(b) protein
(c) starch
(d) fatty acid

Answer: (c) starch

1. Plants synthesize glucose during photosynthesis and store the excess food as starch.
2. Starch acts as the internal carbohydrate energy reserve in plants.
3. Glycogen serves as the energy reserve in animals and fungi.
4. Hence, the correct option is (c).

Teacher's Note:
a) Autotrophs store energy as starch granules inside their chloroplasts or storage organs.
b) Do not confuse plant storage (starch) with animal storage (glycogen).

27. Which of the following equations is the summary of photosynthesis? [1 Mark]
(a) 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O
(b) 6CO₂ + H₂O + Sunlight → C₆H₁₂O₆ + O₂ + 6H₂O
(c) 6CO₂ + 12H₂O + Chlorophyll + Sunlight → C₆H₁₂O₆ + 6O₂ + 6H₂O
(d) 6CO₂ + 12H₂O + Chlorophyll + Sunlight → C₆H₁₂O₆ + 6CO₂ + 6H₂O

Answer: (c) 6CO₂ + 12H₂O + Chlorophyll + Sunlight → C₆H₁₂O₆ + 6O₂ + 6H₂O

1. Photosynthesis uses carbon dioxide and water in the presence of sunlight and chlorophyll.
2. It produces glucose, oxygen gas, and water molecules as byproducts.
3. Equation (c) is balanced stoichiometrically and includes all necessary conditions and products.
4. Hence, the correct option is (c).

Teacher's Note:
a) Always check for balanced carbon, hydrogen, and oxygen atoms in chemical equations.
b) Chlorophyll and sunlight are essential catalysts and energy sources written above/below the arrow or as reactants.

28. Choose the event that does not occur in photosynthesis [1 Mark]
(a) Absorption of light energy by chlorophyll
(b) Reduction of carbon dioxide to carbohydrates
(c) Oxidation of carbon to carbon dioxide
(d) Conversion of light energy to chemical energy

Answer: (c) Oxidation of carbon to carbon dioxide

1. Photosynthesis involves the reduction of carbon dioxide into carbohydrates, not the oxidation of carbon to carbon dioxide.
2. Chlorophyll absorbs light energy, which is subsequently converted into chemical energy.
3. Water molecules are oxidized to release oxygen, but carbon is not oxidized to carbon dioxide.
4. Hence, the correct option is (c).

Teacher's Note:
a) Know the three main phases of photosynthesis: absorption, conversion, and reduction.
b) Carbon dioxide gains hydrogen and electrons, which is a reduction process.

29. The opening and closing of the stomatal pore depends upon [1 Mark]
(a) oxygen
(b) temperature
(c) water in guard cells
(d) concentration of CO₂ in stomata

Answer: (c) water in guard cells

1. Guard cells swell when water flows into them, causing the stomatal pore to open.
2. When guard cells lose water, they shrink and become flaccid, closing the pore.
3. Turgor pressure driven by water content regulates the stomatal aperture.
4. Hence, the correct option is (c).

Teacher's Note:
a) Potassium ion influx and efflux drive the osmotic movement of water into guard cells.
b) Stomata close in dry conditions to prevent excessive transpirational water loss.

30. Choose the forms in which most plants absorb nitrogen [1 Mark]
(i) Proteins
(ii) Nitrates and Nitrites
(iii) Urea
(iv) Atmospheric nitrogen
(a) (i) and (ii)
(b) (ii) and (iii)

Answer: (b) (ii) and (iii)

1. Plants absorb nitrogen mainly in inorganic forms such as nitrates and nitrites from the soil.
2. Certain fertilizers and organic manures also provide nitrogen in the form of urea.
3. Atmospheric nitrogen cannot be utilized directly by most plants without fixation.
4. Hence, the correct option is (b).

Teacher's Note:
a) Rhizobium bacteria fix atmospheric nitrogen into usable nitrogenous compounds for legumes.
b) Proteins are complex organic molecules that plants synthesize rather than absorb directly from soil.

31. Which is the first enzyme to mix with food in the digestive tract? [1 Mark]
(a) Pepsin
(b) Cellulase
(c) Amylase
(d) Trypsin

Answer: (c) Amylase

1. Digestion begins in the mouth with the secretion of saliva.
2. Saliva contains the enzyme salivary amylase.
3. Salivary amylase breaks down starch into simple sugars.
4. Hence, the correct option is (c).

Teacher's Note:
a) Salivary amylase initiates carbohydrate digestion in the oral cavity.
b) Pepsin acts in the stomach, while trypsin functions in the small intestine.

32. Which of the following statement(s) is (are) correct? [1 Mark]
(i) Pyruvate can be converted into ethanol and carbon dioxide by yeast
(ii) Fermentation takes place in aerobic bacteria
(iii) Fermentation takes place in mitochondria
(iv) Fermentation is a form of anaerobic respiration
(a) (i) and (iii)
(b) (ii) and (iv)
(c) (i) and (iv)
(d) (ii) and (iii)

Answer: (c) (i) and (iv)

1. Yeast converts pyruvate into ethanol and carbon dioxide during anaerobic respiration, making statement (i) correct.
2. Fermentation is a type of anaerobic respiration that occurs in the absence of oxygen, making statement (iv) correct.
3. Statements (ii) and (iii) are incorrect because fermentation occurs in anaerobic conditions and takes place in the cytoplasm, not mitochondria.
4. Hence, the correct option is (c).

Teacher's Note:
a) Anaerobic breakdown of glucose without oxygen is termed fermentation.
b) Cellular respiration in mitochondria is strictly aerobic.

33. Lack of oxygen in muscles often leads to cramps among cricketers. This results due to [1 Mark]
(a) conversion of pyruvate to ethanol
(b) conversion of pyruvate to glucose
(c) non conversion of glucose to pyruvate
(d) conversion of pyruvate to lactic acid

Answer: (d) conversion of pyruvate to lactic acid

1. During vigorous physical activity, oxygen supply in muscle cells becomes insufficient.
2. Under this anaerobic condition, pyruvate is converted into lactic acid.
3. The accumulation of lactic acid causes painful muscle cramps.
4. Hence, the correct option is (d).

Teacher's Note:
a) Lactic acid buildup is a classic response to oxygen debt in skeletal muscles.
b) Ethanol conversion happens in yeast, not in human muscle tissue.

34. Choose the correct path of urine in our body [1 Mark]
(a) kidney -> ureter -> urethra -> urinary bladder
(b) kidney -> urinary bladder -> urethra -> ureter
(c) kidney -> ureters -> urinary bladder -> urethra
(d) urinary bladder -> kidney -> ureter -> urethra

Answer: (c) kidney -> ureters -> urinary bladder -> urethra

1. Urine is produced by filtration in the kidneys.
2. It travels through the ureters into the urinary bladder for temporary storage.
3. Finally, it is released from the body through the urethra.
4. Hence, the correct option is (c).

Teacher's Note:
a) The human excretory system consists of a pair of kidneys, ureters, bladder, and urethra.
b) Ensure proper sequence from production site to expulsion site.

35. During deficiency of oxygen in tissues of human beings, pyruvic acid is converted into lactic acid in the [1 Mark]
(a) cytoplasm
(b) chloroplast
(c) mitochondria
(d) golgi body

Answer: (a) cytoplasm

1. Breakdown of glucose into pyruvate takes place in the cytoplasm.
2. When oxygen is deficient, further conversion of pyruvate into lactic acid also occurs in the cytoplasm of muscle cells.
3. Mitochondria are the sites for complete aerobic oxidation.
4. Hence, the correct option is (a).

Teacher's Note:
a) Glycolysis and anaerobic fermentation steps happen in the cytoplasm.
b) Chloroplasts are found in plant cells, not human tissues.

36. Name the process in plants that links light energy with chemical energy [1 Mark]

Answer: Photosynthesis.

Teacher's Note:
a) Photosynthesis traps solar energy and converts it into chemical energy stored in glucose.

37. Name the Organisms that can prepare their own food [1 Mark]

Answer: Autotrophs (or Plants / Producers).

Teacher's Note:
a) Autotrophs synthesize complex organic food from simple inorganic substances using light or chemical energy.

38. Name the cell organelle where photosynthesis occurs [1 Mark]

Answer: Chloroplast.

Teacher's Note:
a) Chloroplasts contain the green pigment chlorophyll necessary for trapping sunlight.

39. Name the Cells that surround a stomatal pore [1 Mark]

Answer: Guard cells.

Teacher's Note:
a) Guard cells control the opening and closing of stomatal pores by changing their turgor pressure.

40. Name the Organisms that cannot prepare their own food [1 Mark]

Answer: Heterotrophs (or Animals / Consumers).

Teacher's Note:
a) Heterotrophs depend directly or indirectly on autotrophs for their nutrition.

41. Name an enzyme secreted from gastric glands in stomach that acts on proteins. [1 Mark]

Answer: Pepsin.

Teacher's Note:
a) Pepsin is secreted in an inactive form called pepsinogen, which is activated by hydrochloric acid.

42. “All plants give out oxygen during day and carbon dioxide during night”. Do you agree with this statement? Give reason. [2 Marks]

Answer:
1. No, we do not completely agree with this statement.
2. During the day, plants undergo photosynthesis producing oxygen, but they also respire continuously, taking in oxygen and releasing carbon dioxide.
3. However, the net gas exchange during the day shows release of oxygen because the rate of photosynthesis is much higher than respiration.
4. During the night, photosynthesis stops in the absence of sunlight, so only respiration occurs, releasing carbon dioxide.

Teacher's Note:
a) Cellular respiration happens 24 hours a day in all living plant cells.
b) Distinguish clearly between net gas exchange and ongoing metabolic processes.

43. How do the guard cells regulate opening and closing of stomatal pores? [3 Marks]

Answer:
1. Water flows into the guard cells when water enters them, causing them to swell and bulge outward.
2. This turgor pressure leads to the opening of the stomatal pore.
3. When the guard cells lose water, they shrink and become flaccid, causing the pore to close.
4. This mechanism regulates transpiration and gaseous exchange in plants.

Teacher's Note:
a) Turgor pressure changes driven by water movement dictate stomatal aperture.
b) Mention the role of potassium ions and osmotic potential for advanced clarity.
c) Guard cells are uniquely kidney shaped in dicots and dumbbell shaped in monocots.

44. Two green plants are kept separately in oxygen free containers, one in the dark and the other in continuous light. Which one will live longer? Give reasons. [3 Marks]

Answer:
1. The plant kept in continuous light will live longer.
2. In continuous light, the plant carries out photosynthesis, producing oxygen inside the container.
3. The oxygen produced can be utilized by the plant for respiration, whereas the plant in the dark cannot perform photosynthesis and will quickly run out of oxygen and energy.

Teacher's Note:
a) Photosynthesis requires sunlight to produce glucose and oxygen from carbon dioxide and water.
b) Respiration occurs continuously in both light and dark conditions, consuming oxygen and releasing carbon dioxide.
c) The plant in darkness exhausts its limited oxygen supply due to respiration without any replenishment.

45. If a plant is releasing carbon dioxide and taking in oxygen during the day, does it mean that there is no photosynthesis occurring? Justify your answer. [3 Marks]

Answer:
1. No, it does not mean that photosynthesis is not occurring.
2. During the day, both respiration and photosynthesis take place simultaneously in plants.
3. If the rate of respiration is higher than the rate of photosynthesis, the net result is the release of carbon dioxide and uptake of oxygen.

Teacher's Note:
a) Respiration is an ongoing cellular process that releases energy and carbon dioxide in all living cells.
b) A common misconception is that plants only respire at night and only photosynthesize during daytime.
c) Net gas exchange depends on the prevailing light intensity and metabolic rates.

46. Why do fishes die when taken out of water? [2 Marks]

Answer:
1. Fishes take in dissolved oxygen from water using their specialized respiratory organs called gills.
2. When taken out of water, the gills collapse and cannot absorb oxygen from the air, leading to suffocation and death.

Teacher's Note:
a) Aquatic organisms are specially adapted to extract oxygen dissolved in water.
b) Atmospheric air has a much higher oxygen concentration, but gill structures require aqueous suspension to remain functional and prevent sticking together.

47. Differentiate between an autotroph and a heterotroph. [3 Marks]

Answer:
1. Autotrophs synthesize their own food from simple inorganic substances like carbon dioxide and water using light energy, whereas heterotrophs depend on other organisms for food.
2. Autotrophs possess chlorophyll and perform photosynthesis, while heterotrophs lack chlorophyll and cannot synthesize complex organic molecules.
3. Examples of autotrophs include green plants and algae, while examples of heterotrophs include animals and fungi.

Teacher's Note:
a) Autotrophs represent the primary producers in any ecosystem trophic structure.
b) Heterotrophs are classified as consumers or decomposers depending on their feeding habits.
c) A tabular comparison highlighting energy source, presence of chlorophyll, and examples is ideal for scoring full marks.

48. Is ‘nutrition’ a necessity for an organism? Discuss. [3 Marks]

Answer:
1. Yes, nutrition is an absolute necessity for all living organisms.
2. It provides the essential energy required to carry out various metabolic and life processes.
3. Nutrients are also vital for the growth, repair of damaged tissues, and maintenance of body structures.

Teacher's Note:
a) Life processes require a continuous supply of molecular building blocks and energy.
b) Absence of proper nutrition leads to metabolic failure, stunted growth, and eventual death.
c) Nutrition bridges the external environment and internal cellular requirements.

49. What would happen if green plants disappear from earth? [3 Marks]

Answer:
1. The collapse of green plants would eliminate the primary source of food for all herbivores and omnivores.
2. Oxygen levels in the atmosphere would gradually deplete as photosynthesis stops, making aerobic respiration impossible.
3. The entire terrestrial and aquatic food webs would collapse, leading to the extinction of most life forms on earth.

Teacher's Note:
a) Green plants occupy the foundational producer level in ecological pyramids.
b) They maintain the balance of oxygen and carbon dioxide in the biosphere.
c) Without plants, heterotrophic organisms would starve and suffocate within a short geological timeframe.

50. Leaves of a healthy potted plant were coated with vaseline. Will this plant remain healthy for long? Give reasons for your answer. [3 Marks]

Answer:
1. No, the plant will not remain healthy for long and will eventually die.
2. Coating the leaves with vaseline blocks the stomata, preventing gaseous exchange necessary for respiration and photosynthesis.
3. It also prevents transpiration, which disrupts the upward transport of water and dissolved minerals from the roots.

Teacher's Note:
a) Stomata are microscopic pores on leaves responsible for gas exchange and transpiration.
b) Vaseline creates an impermeable oily layer that seals these pores completely.
c) Disruption of transpiration halts the cooling mechanism and mineral distribution in plants.

51. How does aerobic respiration differ from anaerobic respiration? [3 Marks]

Answer:
1. Aerobic respiration takes place in the presence of oxygen, whereas anaerobic respiration takes place in the absence of oxygen.
2. Complete breakdown of glucose occurs in aerobic respiration, yielding carbon dioxide, water, and a large amount of energy.
3. Anaerobic respiration results in the partial breakdown of glucose into ethanol or lactic acid along with a relatively small amount of energy.

Teacher's Note:
a) Aerobic respiration yields 38 ATP molecules per glucose, whereas anaerobic yields only 2 ATP.
b) Mitochondria are essential sites for the later stages of aerobic respiration.
c) Mentioning end products clearly ensures full credit in board examinations.

52. Differentiate between an artery and a vein. [3 Marks]

Answer:
1. Arteries carry oxygenated blood away from the heart to various body organs, whereas veins carry deoxygenated blood from organs back to the heart.
2. Arteries possess thick, elastic walls to withstand high blood pressure, while veins have thin walls with valves to prevent backflow of blood.
3. Blood flows under high pressure in arteries and under low pressure in veins.

Teacher's Note:
a) Pulmonary artery and pulmonary vein are important exceptions to the general rule of blood oxygenation.
b) Valves are a key structural feature present exclusively in veins.
c) Wall thickness is directly proportional to the internal fluid pressure handled by the vessel.

53. What are the adaptations of leaf for photosynthesis? [3 Marks]

Answer:
1. Leaves are broad and flat to provide a large surface area for maximum sunlight absorption.
2. They contain numerous chloroplasts packed in mesophyll cells to capture solar energy efficiently.
3. Stomata present on the surface facilitate the rapid exchange of carbon dioxide and oxygen gases.

Teacher's Note:
a) Leaf structure is optimized for light capture and gas diffusion.
b) The arrangement of veins ensures a continuous supply of water and removal of synthesized food.
c) Waxy cuticle minimizes excessive water loss while permitting light penetration.

54. Why is small intestine in herbivores longer than in carnivores? [3 Marks]

Answer:
1. Herbivores feed on grass and plant material which contain complex cellulose that is difficult to digest.
2. A longer small intestine provides more time and surface area for the complete digestion and absorption of plant matter.
3. Carnivores eat meat, which is much easier to digest, and hence have a shorter small intestine.

Teacher's Note:
a) Cellulose digestion requires prolonged enzymatic and microbial action.
b) Diet type dictates the morphological length of the alimentary canal across animal species.
c) Carnivorous guts are shorter because protein breakdown requires less transit time.

55. What will happen if mucus is not secreted by the gastric glands? [2 Marks]

Answer:
1. Mucus protects the inner lining of the stomach from the corrosive action of hydrochloric acid.
2. If mucus is not secreted, the acid will damage the stomach wall, leading to inflammation, severe pain, and gastric ulcers.

Teacher's Note:
a) Hydrochloric acid maintains an acidic pH necessary for activating pepsin.
b) The mucosal barrier is vital for preventing self-digestion of the gastric epithelium.

56. What is the significance of emulsification of fats? [2 Marks]

Answer:
1. Emulsification breaks down large fat globules into smaller droplets, significantly increasing the surface area for enzyme action.
2. This allows pancreatic lipase to efficiently digest fats into fatty acids and glycerol.

Teacher's Note:
a) Bile salts secreted by the liver are responsible for the emulsification process.
b) Fats are insoluble in water, making surface area expansion critical for enzymatic hydrolysis.

57. What causes movement of food inside the alimentary canal? [2 Marks]

Answer:
1. The walls of the alimentary canal possess muscles that rhythmically contract and relax.
2. This wave-like muscular movement is known as peristalsis, which pushes food forward systematically through the digestive tract.

Teacher's Note:
a) Peristalsis occurs all along the gut from the esophagus to the rectum.
b) It ensures smooth, unidirectional transit of food regardless of body orientation.

58. Why does absorption of digested food occur mainly in the small intestine? [3 Marks]

Answer:
1. The small intestine is very long and provides a large surface area for absorption.
2. Its inner lining has numerous finger-like projections called villi, which are richly supplied with blood vessels.
3. These villi greatly increase the surface area available for the efficient transfer of digested food into the bloodstream.

Teacher's Note:
a) Villi contain microvilli to further enhance absorptive efficiency.
b) Extensive capillary networks ensure rapid transport of nutrients away from the gut.
c) Chemical digestion is fully completed within the small intestine before absorption begins.

59. Why is the rate of breathing in aquatic organisms much faster than in terrestrial organisms? [3 Marks]

Answer:
1. Aquatic organisms take in oxygen dissolved in water.
2. The amount of dissolved oxygen in water is fairly low compared to the amount of oxygen in the atmosphere.
3. Therefore, aquatic organisms must breathe much faster to obtain adequate oxygen required for their metabolic needs.

Teacher's Note:
a) Oxygen availability in aquatic habitats varies with temperature and turbulence.
b) Rapid gill ventilation compensates for low oxygen concentration in aqueous media.
c) Terrestrial animals have direct access to air with high oxygen content, requiring lower breathing rates.

60. Why is blood circulation in human heart called double circulation? [2 Marks]

Answer:
1. Blood passes through the human heart twice during each complete circuit of the body.
2. This involves pulmonary circulation between the heart and lungs, and systemic circulation between the heart and the rest of the body.

Teacher's Note:
a) Double circulation prevents the mixing of oxygenated and deoxygenated blood.
b) It ensures a highly efficient supply of oxygen to body tissues to maintain high metabolic rates.

61. What is the advantage of having four chambered heart? [2 Marks]

Answer:
1. A four-chambered heart completely separates oxygenated and deoxygenated blood.
2. This efficient separation ensures a high supply of oxygenated blood to all body parts, supporting high energy needs for warm-blooded animals.

Teacher's Note:
a) Essential for endothermic animals like birds and mammals that maintain constant body temperature.
b) Prevents mixing of blood streams, maximizing metabolic efficiency.

62. Mention the major events during photosynthesis [3 Marks]

Answer:
1. Absorption of light energy by chlorophyll.
2. Conversion of light energy into chemical energy and splitting of water molecules into hydrogen and oxygen.
3. Reduction of carbon dioxide into carbohydrates.

Teacher's Note:
a) These steps may not take place one after the other immediately, such as in desert plants where carbon dioxide is taken up at night.
b) Chloroplast stroma and grana are the cellular sites for these reactions.
c) Listing the exact three biochemical milestones is standard for full marks.

63. In each of the following situations what happens to the rate of photosynthesis?
(a) Cloudy days
(b) No rainfall in the area
(c) Good manuring in the area
(d) Stomata get blocked due to dust [4 Marks]

Answer:
1. (a) Cloudy days: Rate of photosynthesis decreases due to reduced sunlight intensity.
2. (b) No rainfall in the area: Rate of photosynthesis decreases because water stress causes stomata to close, restricting carbon dioxide intake.
3. (c) Good manuring in the area: Rate of photosynthesis increases due to adequate supply of essential minerals like nitrogen for chlorophyll synthesis.
4. (d) Stomata get blocked due to dust: Rate of photosynthesis decreases as carbon dioxide entry is obstructed.

Teacher's Note:
a) Photosynthesis rate depends on environmental factors including light, water, carbon dioxide, and nutrients.
b) Stomatal closure acts as a defense against water loss but halts gas exchange.
c) Mineral availability directly affects pigment synthesis and enzymatic activity.
d) Each sub-part tests a distinct limiting factor principle in plant physiology.

64. Name the energy currency in the living organisms. When and where is it produced? [3 Marks]

Answer:
1. Adenosine triphosphate (ATP) is the energy currency in living organisms.
2. It is produced during cellular respiration whenever energy is released in the cell.
3. It is produced inside the mitochondria of cells.

Teacher's Note:
a) ATP stores energy in the form of high-energy phosphate bonds.
b) Mitochondria are widely known as the powerhouse of the cell.
c) Energy from ATP is utilized for various metabolic activities and mechanical work in cells.

65. What is common for cuscuta, ticks and leeches? [2 Marks]

Answer:
1. Cuscuta, ticks, and leeches all follow a parasitic mode of nutrition.
2. They derive their nutrition from other living organisms (hosts) without killing them directly.

Teacher's Note:
a) Parasites depend entirely on host organisms for nourishment.
b) Cuscuta is a plant parasite, while ticks and leeches are ectoparasites in animals.

66. Explain the role of mouth in digestion of food. [3 Marks]

Answer:
1. Food is ingested through the mouth where teeth chew, crush, and grind it into smaller particles.
2. Salivary glands secrete saliva which moistens the food and contains salivary amylase.
3. Salivary amylase breaks down complex starch into simple sugars (maltose).

Teacher's Note:
a) Mechanical digestion in the mouth increases surface area for enzyme action.
b) Chemical digestion begins right in the oral cavity through salivary action.
c) The tongue helps in thorough mixing of food with saliva and swallowing.

67. What are the functions of gastric glands present in the wall of the stomach? [2 Marks]

Answer:
1. They release hydrochloric acid which creates an acidic medium to facilitate the action of pepsin and kills harmful bacteria.
2. They secrete mucus which protects the inner lining of the stomach from the action of the acid.
3. They secrete the enzyme pepsin which digests proteins into simpler forms.

Teacher's Note:
a) Gastric glands contain three main types of secretory cells.
b) The mucus barrier prevents self-digestion of the stomach wall.

68. Name the correct substrates for the following enzymes
(a) Trypsin (b) Amylase (c) Pepsin (d) Lipase [2 Marks]

Answer:
1. (a) Trypsin - Proteins and peptones
2. (b) Amylase - Starch or carbohydrates
3. (c) Pepsin - Proteins
4. (d) Lipase - Emulsified fats

Teacher's Note:
a) Each digestive enzyme is specific to a particular substrate.
b) Trypsin acts in the small intestine while pepsin acts in the stomach.

69. Why do veins have thin walls as compared to arteries? [2 Marks]

Answer:
1. Arteries carry blood away from the heart under high pressure, requiring thick and elastic walls.
2. Veins collect blood from different organs and bring it back to the heart, where the blood is no longer under high pressure.
3. Therefore, veins do not need thick muscular walls and have valves to ensure blood flows only in one direction.

Teacher's Note:
a) Pressure drops significantly as blood flows through capillaries.
b) Veins appear wider and have thinner walls than corresponding arteries.

70. What will happen if platelets were absent in the blood? [2 Marks]

Answer:
1. Blood platelets are responsible for the clotting of blood at the site of an injury.
2. If platelets were absent, clotting would not occur, leading to excessive loss of blood from cuts or wounds.
3. This uncontrolled hemorrhage could prove fatal due to a massive drop in blood volume and pressure.

Teacher's Note:
a) Platelets release thromboplastin initiating the coagulation cascade.
b) A lack of platelets is a medical condition known as thrombocytopenia.

71. Plants have low energy needs as compared to animals. Explain. [2 Marks]

Answer:
1. Plants are stationary and do not move from place to place, which eliminates the energy requirement for locomotion.
2. A large proportion of plant tissue consists of dead cells such as cork and sclerenchyma, which require little or no maintenance energy.

Teacher's Note:
a) Animals spend substantial energy searching for food and escaping predators.
b) Plant metabolic rate is significantly lower than mammalian metabolic rate.

72. Why and how does water enter continuously into the root xylem? [3 Marks]

Answer:
1. Root cells actively take up ions from the soil, creating a concentration difference between the root and soil.
2. Water moves into the root xylem from the soil by osmosis to eliminate this concentration difference.
3. This continuous intake creates a root pressure that pushes water upward into the plant stem.

Teacher's Note:
a) Transpiration pull is the major driving force in tall trees during the day.
b) Active transport of ions establishes the osmotic gradient.

73. Why is transpiration important for plants? [2 Marks]

Answer:
1. It helps in the absorption and upward movement of water and dissolved minerals from roots to leaves.
2. It helps in temperature regulation of the plant by preventing overheating through evaporative cooling.

Teacher's Note:
a) Transpiration creates a suction pull responsible for water transport.
b) It is often called a necessary evil because of water loss.

74. How do leaves of plants help in excretion? [2 Marks]

Answer:
1. Waste products such as oxygen and carbon dioxide are excreted through stomata in leaves during photosynthesis and respiration.
2. Excess water is eliminated from leaves through transpiration.
3. Plants also store some waste products in leaf cells that eventually fall off.

Teacher's Note:
a) Unlike animals, plants lack specialized excretory organs.
b) Leaf abscission is an effective method of waste elimination.

75. Explain the process of nutrition in Amoeba. [3 Marks]

Answer:
1. Ingestion: Amoeba engulfs food particles using temporary finger-like extensions of its cell surface called pseudopodia to form a food vacuole.
2. Digestion: Digestive enzymes are secreted into the food vacuole to break down complex food into simpler soluble substances.
3. Absorption and Assimilation: The digested food is absorbed into the cytoplasm and utilized for growth and energy.
4. Egestion: Undigested waste is moved to the cell surface and thrown out of the body.

Teacher's Note:
a) Amoeba exhibits holozoic nutrition.
b) Phagocytosis is the specific mechanism for solid particle ingestion.

76. Describe the alimentary canal of man. [5 Marks]

Answer:
1. The human alimentary canal is a long muscular tube extending from the mouth to the anus.
2. Mouth and Buccal Cavity: Ingestion of food begins here, where teeth chew food and saliva mixes with it.
3. Oesophagus: Food travels down the food pipe through rhythmic peristaltic movements.
4. Stomach: A muscular bag where food is mixed with gastric juices, hydrochloric acid, and enzymes for protein digestion.
5. Small Intestine: A highly coiled tube where complete digestion of carbohydrates, proteins, and fats takes place, followed by absorption of nutrients.
6. Large Intestine: Absorbs excess water from unabsorbed food, and the remaining waste is expelled through the anus.

Teacher's Note:
a) The total length of the alimentary canal is about 9 meters.
b) Peristalsis is an involuntary wave-like muscular contraction.

77. Explain the process of breathing in man. [3 Marks]

Answer:
1. Inhalation: The ribs move up and flat diaphragm muscles contract, increasing the chest cavity volume and drawing air into the lungs.
2. Exchange of Gases: Oxygen from alveolar air diffuses into blood capillaries while carbon dioxide from blood diffuses into alveoli.
3. Exhalation: Ribs move down and diaphragm relaxes, decreasing the chest cavity volume and forcing air out of the lungs.

Teacher's Note:
a) Breathing is a mechanical process driven by pressure gradients.
b) Gaseous exchange occurs across the thin membrane of alveoli.

78. Explain the importance of soil for plant growth. [2 Marks]

Answer:
1. Soil provides anchorage and physical support to the plant roots.
2. It acts as a reservoir of essential mineral nutrients and water required for plant metabolic activities.

Teacher's Note:
a) Air spaces in soil supply oxygen for root respiration.
b) Soil microbes help in nitrogen fixation and nutrient cycling.

79. Draw the diagram of alimentary canal of man and label the following parts.
Mouth, Oesophagus, Stomach, Intestine [3 Marks]

Answer:
1. Draw a clean diagram showing the human digestive system.
2. Label Mouth at the upper anterior opening.
3. Label Oesophagus as the tube connecting mouth to stomach.
4. Label Stomach as the J-shaped expanded organ below the diaphragm.
5. Label Intestine as the coiled tube comprising the small and large intestines.

[Figure: Diagram of human alimentary canal showing Mouth, Oesophagus, Stomach, and Intestine]

Teacher's Note:
a) Diagrams must be neat, clean, and properly labeled with arrows pointing precisely to the required organs.
b) Relative proportions of organs should be maintained.

80. How do carbohydrates, proteins and fats get digested in human beings? [5 Marks]

Answer:
1. Carbohydrates: Digestion begins in the mouth with salivary amylase breaking starch into sugar, and is completed in the small intestine by pancreatic and intestinal amylase into glucose.
2. Proteins: Digestion starts in the stomach via pepsin, and is completed in the small intestine by trypsin and chymotrypsin breaking proteins into amino acids.
3. Fats: Bile juice emulsifies large fat globules in the small intestine, and lipase breaks them down into fatty acids and glycerol.

Teacher's Note:
a) The small intestine is the site of complete digestion for all major food components.
b) Digestive enzymes function optimally in specific pH environments.

81. Explain the mechanism of photosynthesis. [3 Marks]

Answer:
1. Absorption of light energy by chlorophyll pigments.
2. Conversion of light energy into chemical energy and splitting of water molecules into hydrogen and oxygen.
3. Reduction of carbon dioxide into carbohydrates using the energy produced in the light reaction.

Teacher's Note:
a) Photosynthesis takes place in chloroplasts.
b) Oxygen is released as a byproduct from water photolysis.

82. Explain the three pathways of breakdown in living organisms. [3 Marks]

Answer:
1. Absence of oxygen (anaerobic respiration in yeast): Glucose is broken down into ethanol, carbon dioxide, and energy.
2. Lack of oxygen (in human muscle cells during vigorous exercise): Glucose is converted into lactic acid and energy, causing muscle cramps.
3. Presence of oxygen (aerobic respiration in mitochondria): Glucose is broken down completely into carbon dioxide, water, and a large amount of energy.

Teacher's Note:
a) All three pathways start with the breakdown of glucose into pyruvate in the cytoplasm.
b) Aerobic respiration yields much more ATP than anaerobic pathways.

83. Describe the flow of blood through the heart of human beings. [4 Marks]

Answer:
1. Deoxygenated blood from the body enters the right atrium through vena cava.
2. From the right atrium, blood passes into the right ventricle, which pumps it to the lungs through the pulmonary artery for oxygenation.
3. Oxygenated blood from the lungs returns to the left atrium via pulmonary veins.
4. From the left atrium, blood flows into the left ventricle, which pumps it out to the rest of the body through the aorta.

Teacher's Note:
a) Valves prevent the backward flow of blood during contraction.
b) The left ventricle has thicker walls because it pumps blood to the entire body.

84. Describe the process of urine formation in kidneys. [4 Marks]

Answer:
1. Glomerular Filtration: Blood enters the glomerulus under high pressure, and water, salts, glucose, and urea are filtered into Bowman's capsule.
2. Tubular Reabsorption: As the filtrate flows along the tubule, useful substances like glucose, amino acids, and major amounts of water are reabsorbed into the blood.
3. Secretion: Additional waste products like potassium and hydrogen ions are actively secreted into the tubule.
4. Urine Collection: The remaining fluid rich in urea and excess water forms urine, which is collected in the urinary bladder via ureters.

Teacher's Note:
a) Nephrons are the structural and functional units of the kidney.
b) Selective reabsorption ensures essential nutrients are not lost in urine.

85. Why is the process of diffusion insufficient to meet the oxygen requirement of human beings? [2 Marks]

Answer:
1. The human body is large and complex, and most cells are not in direct contact with the external environment.
2. Simple diffusion is a very slow process that cannot transport oxygen efficiently over long distances within the human body.

Teacher's Note:
a) Multicellular organisms rely on circulatory systems for transport.
b) Diffusion is sufficient only in unicellular organisms.

86. Draw a diagram of human alimentary canal showing duodenum, small intestine, liver and pancreas. [3 Marks]

Answer:
1. Draw the outline of the human digestive tract from mouth to large intestine.
2. Clearly draw and label the liver on the right upper abdomen and pancreas beneath the stomach.
3. Label the C-shaped duodenum at the beginning of the small intestine.
4. Label the coiled small intestine.

[Figure: Diagram of human alimentary canal showing duodenum, small intestine, liver, and pancreas]

Teacher's Note:
a) Labeling must be accurate and clearly indicate organ positions.
b) The liver and pancreas must be shown connected via ducts to the duodenum.

87. Draw a diagram of the human urinary system and label in it. [3 Marks]

Answer:
1. Draw a pair of bean-shaped kidneys on the dorsal wall.
2. Draw ureters emerging from each kidney leading down to the urinary bladder.
3. Draw the urinary bladder and urethra.
4. Label Kidneys, Ureters, Urinary Bladder, and Urethra clearly.

[Figure: Diagram of the human urinary system showing kidneys, ureters, urinary bladder, and urethra]

Teacher's Note:
a) Symmetry and appropriate proportions are important in anatomical sketches.
b) Renal artery and vein connections can be included for completeness.

88. What do you mean by double circulation of blood? [2 Marks]

Answer:
1. It is a circulatory system in which blood passes through the heart twice during each complete circuit of the body.
2. This involves pulmonary circulation between heart and lungs, and systemic circulation between heart and the rest of the body.

Teacher's Note:
a) Double circulation prevents mixing of oxygenated and deoxygenated blood.
b) It ensures efficient oxygen supply to support high energy needs in mammals and birds.

89. “If there were no algae there would be no fish in the sea”. Comment. [3 Marks]

Answer:
1. Algae are primary producers in aquatic ecosystems that perform photosynthesis and form the base of aquatic food chains.
2. Herbivorous aquatic animals feed directly on algae.
3. Small fish feed on these herbivores, and larger carnivorous fish feed on smaller fish, so the entire aquatic food web collapses without algae.

Teacher's Note:
a) Energy flow in ecosystems begins with producers.
b) Disruption at the trophic base affects all higher consumer levels.

90. Write the functions of the following in the digestive process :
(i) Bile (ii) Bicarbonate secreted by the duodenal wall. (iii) Pancreatic amylase. [3 Marks]

Answer:
1. (i) Bile: Emulsifies large fat globules into smaller droplets to increase the surface area for lipase action, and makes the acidic food alkaline.
2. (ii) Bicarbonate secreted by the duodenal wall: Neutralizes the acidic chime coming from the stomach and creates an alkaline medium for pancreatic enzymes to function.
3. (iii) Pancreatic amylase: Digests remaining carbohydrates by breaking down starch into maltose.

Teacher's Note:
a) Enzymes secreted by pancreas and intestinal walls require alkaline conditions.
b) Bile does not contain any digestive enzymes.