NCERT Solutions Class 10 Science Chapter 5 Life Processes

Mastering the NCERT Solutions Class 10 Science Chapter 5 Life Processes is essential for every student aiming for top scores in the CBSE Class 10 Board Examinations. Life Processes is one of the highest-weightage chapters in the Biology section, covering fundamental physiological mechanisms that keep living organisms alive: nutrition, respiration, transportation, and excretion. This comprehensive guide provides accurate, step-by-step solutions to every in-text question and chapter-end exercise in the revised NCERT textbook, complete with balanced biochemical equations, structured comparison tables, and board-level presentation techniques.

Chapter Overview: Core Concepts of Life Processes

Life processes are the basic maintenance functions performed by living organisms to sustain life and prevent bodily breakdown. The chapter is structured into four vital physiological systems:

• 1. Nutrition: The process of intake and utilization of nutrients.
  • Autotrophic Nutrition: Organisms (green plants, some bacteria) synthesize organic food from inorganic raw materials ($CO_2$ and $H_2O$) via photosynthesis using sunlight trapped by chlorophyll.
  • Heterotrophic Nutrition: Organisms derive energy by consuming other organisms. Classified into holozoic (e.g., humans, Amoeba), saprophytic (e.g., fungi, bread mould), and parasitic (e.g., Cuscuta, tapeworms, leeches).
  • Human Alimentary Canal: Sequential digestion involving mouth (salivary amylase), stomach (pepsin, $HCl$, mucus), small intestine (bile, pancreatic juice with trypsin and lipase, intestinal enzymes), and large intestine (water reabsorption).
• 2. Respiration: The biochemical process of releasing cellular energy from the breakdown of glucose molecules.
  • Glycolysis: Initial conversion of 6-carbon glucose into 3-carbon pyruvate in the cytoplasm.
  • Aerobic Pathway: Breakdown of pyruvate in mitochondria in the presence of oxygen yielding $CO_2$, $H_2O$, and 36–38 ATP.
  • Anaerobic Pathway: Fermentation in yeast producing ethanol, $CO_2$, and 2 ATP; or lactic acid pathway in human muscle cells under oxygen deficit causing muscle cramps.
• 3. Transportation: Internal movement of gases, nutrients, and metabolic wastes.
  • Human Circulatory System: Four-chambered heart facilitating complete double circulation (pulmonary and systemic loops) to prevent mixing of oxygenated and deoxygenated blood.
  • Plant Vascular System: Xylem transports water and dissolved minerals unidirectionally driven by root pressure and transpirational pull; Phloem transports soluble photosynthetic products (sucrose, amino acids) bidirectionally via active energy-driven translocation.
• 4. Excretion: Elimination of toxic nitrogenous metabolic wastes.
  • Human Excretory System: Paired kidneys containing millions of functional filtration units called nephrons. Urine formation occurs through ultrafiltration in Bowman's capsule/glomerulus, selective tubular reabsorption, and tubular secretion.
  • Plant Excretion: Gaseous wastes ($O_2, CO_2$) via stomata/lenticels, excess water via transpiration, and stored wastes in shedding leaves, gums, and resins.

Important Biochemical Equations and Summary Pathways

Memorizing and reproducing these exact chemical representations is crucial for securing full marks in CBSE board answers:

1. Photosynthesis Equation

$$6CO_2 + 12H_2O \xrightarrow[\text{Chlorophyll}]{\text{Sunlight}} C_6H_{12}O_6 + 6O_2 + 6H_2O$$

Three sequential events in photosynthesis:

1. Absorption of light energy by chlorophyll.
2. Conversion of light energy to chemical energy and splitting (photolysis) of water molecules into hydrogen and oxygen.
3. Reduction of carbon dioxide to carbohydrates (glucose).

2. Pathways of Glucose Breakdown

All cellular respiration pathways initiate in the cytoplasm with glycolysis:

$$\text{Glucose (6-carbon)} \xrightarrow{\text{In Cytoplasm}} \text{Pyruvate (3-carbon)} + \text{Energy}$$

From pyruvate, three distinct pathways diverge:

• Absence of Oxygen (in Yeast / Fermentation): $$\text{Pyruvate} \longrightarrow \text{Ethanol (2-carbon)} + CO_2 + \text{Energy (2 ATP)}$$
• Lack of Oxygen (in Human Muscle Cells): $$\text{Pyruvate} \longrightarrow \text{Lactic Acid (3-carbon)} + \text{Energy (2 ATP)}$$
• Presence of Oxygen (in Mitochondria / Aerobic Respiration): $$\text{Pyruvate} + O_2 \longrightarrow 6CO_2 + 6H_2O + \text{Energy (36--38 ATP)}$$

3. Major Digestive Enzymes and Substrates

Organ / Gland	Enzyme / Secretion	Target Substrate	End Product
Salivary Glands	Salivary Amylase (Ptyalin)	Starch (Complex carbohydrate)	Maltose (Simpler sugars)
Gastric Glands (Stomach)	Pepsin (activated by $HCl$)	Proteins	Peptones and Proteoses
Liver	Bile Juice (Bile salts)	Large fat globules	Emulsified small fat droplets
Pancreas	Pancreatic Amylase	Residual Starch	Maltose
Pancreas	Trypsin (in alkaline medium)	Proteins and Peptones	Peptides
Pancreas	Lipase	Emulsified Fats	Fatty Acids + Glycerol
Small Intestinal Glands	Intestinal Juice (Succus Entericus)	Carbohydrates, Proteins, Fats	Glucose, Amino Acids, Fatty Acids + Glycerol

NCERT In-Text Questions and Step-by-Step Solutions

In-Text Questions (Set 1 — Nutrition Concepts)

Q1. Why is diffusion insufficient to meet the oxygen requirements of multicellular organisms like humans?

Answer:

1. In large multicellular organisms like humans, body size is extensive and all individual cells are not in direct contact with the external surrounding environment.
2. Simple diffusion is a very slow physical process; calculations show that relying purely on diffusion would take approximately 3 years for an oxygen molecule to travel from human lungs to the toes.
3. Therefore, multicellular organisms require specialized respiratory surfaces (alveoli) coupled with a dedicated circulatory system containing high-affinity respiratory pigments (haemoglobin) to rapidly deliver oxygen to all tissues.

Q2. What criteria do we use to decide whether something is alive?

Answer:

• The most fundamental criterion is the presence of invisible molecular movements within cells and tissues, which are essential for cellular repair and maintenance.
• Visible characteristics include self-regulated growth, respiration, reproduction, response to external stimuli (irritability), movement or locomotion, and continuous metabolic activity.

Q3. What are outside raw materials used for by an organism?

Answer:

The primary external raw materials include:

1. Carbon-based molecules (Food/Carbohydrates): Provide energy and structural carbon skeletons for cellular growth and repair.
2. Oxygen: Required for the cellular oxidation of food substrates to liberate usable energy (ATP) in aerobic organisms.
3. Water: Essential solvent for all intracellular biochemical reactions, cellular turgidity, and thermal regulation.
4. Minerals (Nitrogen, Phosphorus, Iron, Magnesium): Essential for synthesizing vital biomolecules such as proteins, nucleic acids, and chlorophyll.

Q4. What processes would you consider essential for maintaining life?

Answer:

The fundamental life processes indispensable for the survival of any organism are:

• Nutrition: Procurement and breakdown of energy sources.
• Respiration: Cellular release of chemical energy (ATP) from digested food.
• Transportation: Internal transit of gases, nutrients, and metabolites.
• Excretion: Removal of toxic metabolic waste products.
• Control and Coordination: Regulating physiological responses to environmental changes.

In-Text Questions (Set 2 — Autotrophic & Heterotrophic Nutrition)

Q5. What are the differences between autotrophic nutrition and heterotrophic nutrition?

Answer:

Parameter	Autotrophic Nutrition	Heterotrophic Nutrition
Food Source	Synthesizes organic food from inorganic substances ($CO_2$, $H_2O$) using external energy.	Obtains readymade organic food directly or indirectly from autotrophs.
Chlorophyll	Essential for trapping solar radiation.	Absent; organisms cannot trap solar energy.
Energy Transformation	Converts light energy into chemical energy.	Utilizes chemical energy stored within ingested organic food.
Examples	Green plants, cyanobacteria, autotrophic algae.	All animals, fungi, non-photosynthetic bacteria.

Q6. Where do plants get each of the raw materials required for photosynthesis?

Answer:

• Carbon dioxide ($CO_2$): Absorbed from the atmospheric air through microscopic pore complexes called stomata present on leaves.
• Water ($H_2O$): Absorbed from soil moisture by roots through osmosis and transported upward via xylem vessels.
• Solar Energy: Trapped directly from sunlight by the photosynthetic green pigment chlorophyll located within chloroplast thylakoids.
• Inorganic Minerals (N, P, Fe, Mg): Dissolved in soil water and absorbed actively and passively through root hair systems.

Q7. What is the role of the acid in our stomach?

Answer:

Hydrochloric acid ($HCl$) secreted by the oxyntic (parietal) cells of gastric glands performs three vital functions:

1. Activation of Enzymes: Creates a strongly acidic medium ($pH \approx 1.5\text{--}2.5$) necessary to convert the inactive proenzyme pepsinogen into active proteolytic pepsin.
2. Antimicrobial Action: Kills swallowed pathogenic microorganisms, bacteria, and germs ingested with food.
3. Food Softening: Softens fibrous food components, aiding mechanical churning and digestion.

Q8. What is the function of digestive enzymes?

Answer:

Digestive enzymes are specialized biological catalysts that hydrolyze complex, insoluble macromolecules (starches, proteins, lipids) into simple, soluble, and diffusible micromolecules (glucose, amino acids, fatty acids, and glycerol) that can be easily absorbed across the intestinal epithelium into blood and lymph capillaries.

Q9. How is the small intestine designed to absorb digested food?

Answer:

The small intestine features several structural adaptations maximizing absorption efficiency:

1. Extensive Surface Area: The inner mucosal wall possesses millions of tiny, finger-like projections called villi, and each epithelial cell possesses microscopic microvilli (brush-border), increasing the absorptive surface area exponentially.
2. Rich Vascular Supply: Each villus is supplied with an extensive network of blood capillaries that immediately carry absorbed monosaccharides and amino acids to the liver and systemic circulation.
3. Lacteal System: Each villus contains a central lymphatic capillary (lacteal) specifically designed to absorb fatty acids and glycerol packaged into chylomicrons.
4. Thin Epithelial Barrier: A single-celled thin epithelial layer ensures rapid, minimal diffusion distance.

In-Text Questions (Set 3 — Respiration)

Q10. What advantage over an aquatic organism does a terrestrial organism have with regard to obtaining oxygen for respiration?

Answer:

1. Higher Oxygen Availability: Terrestrial organisms breathe atmospheric air, which contains a high and stable oxygen concentration (approx. $21\% = 210,000\text{ ppm}$), whereas aquatic organisms extract dissolved oxygen from water, which is remarkably low (approx. $<10\text{ ppm}$).
2. Lower Energy Expenditure: Air has a much lower density and viscosity than water; hence, terrestrial organisms expend significantly less energy ventilating respiratory surfaces compared to aquatic organisms, which must continuously pump large volumes of water over gills at rapid breathing rates.

Q11. What are the different ways in which glucose is oxidized to provide energy in various organisms?

Answer:

Glucose is first cleaved in the cytoplasm into two molecules of 3-carbon pyruvate along with 2 ATP molecules. This pyruvate is subsequently oxidized through three alternative metabolic pathways:

1. Aerobic Respiration (In Mitochondria): In the presence of oxygen, pyruvate is completely broken down into carbon dioxide, water, and a high yield of energy ($36\text{--}38\text{ ATP}$). Occurs in higher plants and animals.
2. Alcoholic Fermentation (In Yeast): Under anaerobic conditions, pyruvate is converted into ethanol, carbon dioxide, and a low yield of energy ($2\text{ ATP}$).
3. Lactic Acid Fermentation (In Human Striated Muscle Cells): Under anaerobic conditions during strenuous exercise, pyruvate is converted directly into lactic acid and $2\text{ ATP}$. Accumulation of lactic acid leads to muscular fatigue and cramps.

Q12. How are oxygen and carbon dioxide transported in human beings?

Answer:

• Transport of Oxygen ($O_2$): Oxygen has low solubility in aqueous blood plasma. About $97\text{--}98\%$ is bound chemically to the iron-containing pigment haemoglobin inside Red Blood Cells (RBCs) forming oxyhaemoglobin. Only $2\text{--}3\%$ dissolves directly in plasma.
• Transport of Carbon Dioxide ($CO_2$): $CO_2$ is significantly more soluble in water than $O_2$. Approximately $70\%$ is transported as dissolved bicarbonate ions ($HCO_3^-$) in blood plasma, $20\text{--}23\%$ bound to haemoglobin as carbaminohaemoglobin, and $7\%$ physically dissolved in plasma.

Q13. How are the lungs designed in human beings to maximize the area for exchange of gases?

Answer:

1. Branching Tree Architecture: Within the lungs, the primary bronchi repeatedly subdivide into secondary bronchi, tertiary bronchi, and microscopic terminal bronchioles.
2. Alveolar Sacs: The bronchioles terminate in balloon-like structures called alveoli. A pair of human lungs contains approximately $300\text{--}400\text{ million}$ alveoli, providing a massive surface area of roughly $80\text{ m}^2$ (equivalent to a tennis court).
3. Extensive Capillary Plexus: The alveolar walls are exceptionally thin (single-cell squamous epithelium) and enveloped by an intricate mesh of capillary blood vessels, minimizing diffusion distance and maximizing instantaneous gas exchange.

In-Text Questions (Set 4 — Transportation & Excretion)

Q14. What are the components of the transport system in human beings? What are the functions of these components?

Answer:

The human circulatory system consists of three main components:

1. The Heart: A muscular pumping organ. It maintains blood pressure gradients, keeps oxygenated and deoxygenated blood streams completely separate across four chambers, and drives systemic and pulmonary circulation.
2. Blood Vessels:
   • Arteries: Thick-walled, elastic vessels carrying oxygenated blood away from the heart under high pressure (except the pulmonary artery).
   • Veins: Thin-walled vessels carrying deoxygenated blood toward the heart under low pressure, equipped with internal semilunar valves to prevent backflow (except the pulmonary vein).
   • Capillaries: Microscopic, single-cell-thick vessels facilitating nutrient, gas, and waste exchange between blood and interstitial fluid.
3. Circulating Fluids:
   • Blood: Composed of plasma (transports nutrients, gases, hormones, urea), RBCs (carry oxygen via haemoglobin), WBCs (immunity/defense), and platelets (hemostasis and blood clotting).
   • Lymph (Tissue Fluid): Colorless fluid draining interstitial space; carries digested fats from lacteals and returns excess fluid and proteins back into venous circulation.

Q15. Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?

Answer:

Mammals and birds are warm-blooded (homeothermic) animals that continuously expend large amounts of energy to maintain a constant internal body temperature regardless of ambient environmental temperatures. Complete anatomical separation of oxygenated and deoxygenated blood ensures highly efficient, high-pressure oxygen delivery to metabolically active tissues, supporting rapid cellular respiration rates.

Q16. What are the components of the transport system in highly organised plants?

Answer:

Plants possess two complex conducting tissues known as vascular bundles:

1. Xylem Tissue: Composed of non-living, lignified conducting cells (tracheids and xylem vessels), along with xylem parenchyma and xylem fibres. Transports water and inorganic mineral ions unidirectionally from roots to aerial parts.
2. Phloem Tissue: Composed of living conducting units (sieve tubes with perforated sieve plates and adjacent nucleated companion cells), phloem parenchyma, and phloem fibres. Conducts synthesized sucrose, hormones, and amino acids bidirectionally (translocation).

Q17. How are water and minerals transported in plants?

Answer:

1. Active Ion Uptake at Roots: Root epidermal cells actively pump mineral ions from soil water into root cells, establishing an osmotic concentration gradient.
2. Osmotic Inflow (Root Pressure): Water follows ions into root xylem cells via osmosis, creating a positive hydrostatic pressure (root pressure) effective for short-distance transport and nocturnal sap ascent.
3. Transpiration Pull (Cohesion-Tension Theory): During the daytime, evaporation of water molecules through open leaf stomata creates a severe negative suction pressure (tension) in the mesophyll cells. Due to strong cohesive forces (attraction between water molecules) and adhesive forces (attraction between water and xylem walls), an unbroken, continuous column of water is pulled upward from roots to the highest canopy.

Q18. How is food transported in plants?

Answer:

The transport of soluble photosynthetic products (primarily sucrose) is termed translocation:

1. Sucrose is actively loaded into sieve tubes of phloem tissue using metabolic energy derived from ATP.
2. This increases the osmotic pressure inside the sieve tubes, causing water from adjacent xylem vessels to enter the phloem via osmosis.
3. The resulting high hydrostatic pressure drives the phloem sap toward physiological sinks (storage organs, roots, developing buds, and fruits) where hydrostatic pressure is lower.
4. At the sink, sucrose is actively unloaded, and water leaves the sieve tube osmotically.

Q19. Describe the structure and functioning of nephrons.

Answer:

Structure: A nephron is the microscopic structural and functional unit of the kidney, consisting of:

• Malpighian Body: Composed of a cup-shaped Bowman's capsule enclosing a tuft of high-pressure capillaries called the glomerulus fed by the afferent arteriole.
• Renal Tubule: Composed sequentially of the Proximal Convoluted Tubule (PCT), hairpin-shaped Loop of Henle (descending and ascending limbs), and Distal Convoluted Tubule (DCT), which opens into a Collecting Duct.
• Peritubular Capillary Network: Blood capillaries surrounding the tubular elements to facilitate substance exchange.

Functioning (Urine Formation):

1. Glomerular Ultrafiltration: High hydrostatic blood pressure forces water, glucose, amino acids, urea, uric acid, and inorganic salts through the fenestrated glomerular membrane into Bowman's space, forming primary filtrate (approx. 180 litres/day in adults).
2. Selective Tubular Reabsorption: As the filtrate flows through the PCT and Loop of Henle, essential substances ($100\%$ glucose, $100\%$ amino acids, major fractions of $Na^+, Cl^-$, and water) are selectively reabsorbed back into the peritubular capillaries.
3. Tubular Secretion: Excess ions ($K^+, H^+, NH_4^+$) and certain metabolic residues are actively secreted from peritubular blood directly into the tubular lumen, forming final hypertonic urine (approx. 1.5 to 2 litres/day).

Q20. What are the methods used by plants to get rid of excretory products?

Answer:

• Gaseous By-products: Excess photosynthetic oxygen and respiratory carbon dioxide diffuse out directly into the atmosphere through open stomata on leaves and lenticels on woody stems.
• Excess Water: Transpired into the atmosphere as water vapor through stomatal transpiration.
• Stored Solid/Liquid Wastes: Stored within cellular vacuoles of aging leaves, bark, and fruit walls, which periodically die and shed from the plant body.
• Resins and Gums: Toxic metabolic wastes stored permanently in old, non-functional xylem tissue.
• Root Exudation: Some metabolic waste compounds are actively excreted directly into the surrounding soil.

Q21. How is the amount of urine produced regulated?

Answer:

The total volume of urine produced is dynamically regulated based on two primary physiological factors:

1. Hydration Status: The amount of excess water present in bodily fluids. When the body is dehydrated, Antidiuretic Hormone (ADH / Vasopressin) increases the water permeability of the collecting ducts, maximizing water reabsorption and producing concentrated, low-volume urine.
2. Concentration of Dissolved Nitrogenous Wastes: Higher concentrations of circulating urea and metabolic salts necessitate a higher mandatory volume of water for safe urinary excretion.

NCERT Chapter End Exercises: Detailed Solutions

Q1. The kidneys in human beings are a part of the system for:

(a) nutrition
(b) respiration
(c) excretion
(d) transportation

Answer: (c) excretion
Explanation: The kidneys filter metabolic nitrogenous waste products (urea, uric acid, excess salts) from the circulating blood to form urine.

Q2. The xylem in plants are responsible for:

(a) transport of water
(b) transport of food
(c) transport of amino acids
(d) transport of oxygen

Answer: (a) transport of water
Explanation: Tracheids and vessels of xylem tissue transport water and dissolved mineral ions upward from roots to the aerial parts of the plant.

Q3. The autotrophic mode of nutrition requires:

(a) carbon dioxide and water
(b) chlorophyll
(c) sunlight
(d) all of the above

Answer: (d) all of the above
Explanation: Autotrophs require carbon dioxide and water as inorganic raw materials, chlorophyll to absorb solar radiation, and sunlight as the prime thermodynamic energy source.

Q4. The breakdown of pyruvate to give carbon dioxide, water and energy takes place in:

(a) cytoplasm
(b) mitochondria
(c) chloroplast
(d) nucleus

Answer: (b) mitochondria
Explanation: While the initial conversion of glucose to pyruvate occurs in the cytoplasm, the subsequent complete oxidative decarboxylation (Krebs cycle and oxidative phosphorylation) takes place exclusively inside the mitochondria.

Q5. How are fats digested in our bodies? Where does this process take place?

Answer:

Fat digestion takes place primarily in the small intestine (duodenum and ileum) through two sequential stages:

1. Emulsification by Bile Salts: Fats enter the duodenum as large, hydrophobic globules, making enzymatic access difficult. Bile juice (secreted by the liver, stored in gallbladder) contains bile salts that break large fat globules down into fine, suspended droplets. This physical process is called emulsification and dramatically increases the total surface area for enzymatic attack.
2. Enzymatic Hydrolysis by Lipase: The pancreas secretes pancreatic lipase into the alkaline duodenal fluid. Lipase catalyzes the hydrolysis of emulsified triglycerides into diglycerides, monoglycerides, and ultimately into absorbable fatty acids and glycerol. Intestinal lipases complete the breakdown before absorption into lacteals.

Q6. What is the role of saliva in the digestion of food?

Answer:

• Chemical Digestion of Starch: Saliva contains the enzyme salivary amylase (ptyalin), which hydrolyzes complex insoluble starch molecules into soluble disaccharides (maltose) at a neutral to slightly acidic $pH$ of $6.8$: $$\text{Starch} \xrightarrow[\text{pH 6.8}]{\text{Salivary Amylase}} \text{Maltose}$$
• Mechanical Lubrication: Saliva contains mucus, which wets, softens, and lubricates dry food particles, binding them into a cohesive mass called a bolus for smooth deglutition (swallowing) through the esophagus.
• Oral Hygiene: Saliva contains lysozyme, an antibacterial enzyme that destroys bacterial cell walls, protecting the oral cavity from infection.

Q7. What are the necessary conditions for autotrophic nutrition and what are its by-products?

Answer:

Necessary Conditions:

1. Continuous availability of Carbon Dioxide ($CO_2$) from the atmosphere.
2. Adequate absorption of Water ($H_2O$) from the soil through roots.
3. Presence of functional Chlorophyll pigments in chloroplasts.
4. Sufficient intensity and duration of Sunlight (Photons).
5. Optimum ambient temperature for photosynthetic enzymes ($20^\circ\text{C}\text{--}35^\circ\text{C}$).

By-Products Formed:

• Molecular Oxygen ($O_2$): Released as a gaseous by-product into the atmosphere due to photolysis of water.
• Water ($H_2O$): Formed as a metabolic by-product during chemical reorganization.

Q8. What are the differences between aerobic and anaerobic respiration? Name some organisms that use the anaerobic mode of respiration.

Answer:

Parameter	Aerobic Respiration	Anaerobic Respiration
Oxygen Requirement	Requires molecular oxygen ($O_2$).	Occurs in total absence or strict deficit of oxygen.
Subcellular Location	Starts in cytoplasm; completes inside mitochondria.	Confined entirely to the cytoplasm.
Substrate Breakdown	Complete oxidation of glucose into $CO_2$ and $H_2O$.	Incomplete oxidation into ethanol $+ CO_2$, or lactic acid.
Energy Yield per Glucose	High net yield: $36\text{ to }38\text{ ATP}$ molecules ($2870\text{ kJ}$).	Low net yield: Only $2\text{ ATP}$ molecules ($150\text{ kJ}$).
End Products	$CO_2 + H_2O + \text{Energy}$	$\text{Ethanol} + CO_2 + \text{Energy}$ OR $\text{Lactic Acid} + \text{Energy}$

Organisms utilizing anaerobic respiration: Yeast (Saccharomyces cerevisiae), anaerobic bacteria (such as Clostridium botulinum, Lactobacillus), and internal parasitic worms like tapeworms (Taenia solium) and Ascaris.

Q9. How are the alveoli designed to maximise the exchange of gases?

Answer:

1. Immense Surface Area: The lungs contain roughly 300 to 400 million individual alveoli, providing a combined respiratory surface area of approximately $80\text{ m}^2$.
2. Extremely Thin Diffusion Barrier: The alveolar wall is lined by a delicate, single-cell layer of squamous epithelial cells supported by an ultra-thin basement membrane, keeping diffusion thickness under $0.5\text{ }\mu\text{m}$.
3. Dense Capillary Meshwork: Every alveolus is enveloped by a fine network of pulmonary capillaries, allowing maximum blood volume to come into proximity with alveolar air.
4. Moist Inner Surface: A thin fluid film lines the inner surface of the alveolus, enabling oxygen gas to dissolve rapidly before diffusing into the blood.

Q10. What would be the consequences of a deficiency of haemoglobin in our bodies?

Answer:

A deficiency of haemoglobin leads to a clinical condition called anaemia, causing severe systemic consequences:

1. Reduced Oxygen-Carrying Capacity: Less haemoglobin means the blood cannot transport sufficient quantities of oxygen from lungs to systemic tissues.
2. Diminished Cellular Respiration: Inadequate oxygen supply reduces mitochondrial ATP production in body cells.
3. Chronic Fatigue and Lethargy: The individual feels constantly tired, weak, drowsy, and experiences muscular exhaustion even after minimal exertion.
4. Shortness of Breath (Breathlessness): The brain stimulates rapid ventilation rates to compensate for cellular hypoxia, causing breathlessness and elevated heart rate (palpitations).
5. Pallor: The skin, nail beds, and inner conjunctiva become visibly pale due to reduced oxyhaemoglobin pigmentation.

Q11. Describe double circulation of blood in human beings. Why is it necessary?

Answer:

Description: In the human cardiovascular system, blood passes through the heart twice during one complete circuit around the body. Double circulation consists of two distinct loops:

1. Pulmonary Circulation: Deoxygenated blood collected from body tissues enters the right atrium $\rightarrow$ right ventricle $\rightarrow$ pumped via pulmonary artery to lungs for oxygenation $\rightarrow$ returns as oxygenated blood via pulmonary veins into the left atrium.
2. Systemic Circulation: Oxygenated blood passes from left atrium $\rightarrow$ left ventricle $\rightarrow$ pumped under high pressure via the aorta to all systemic body organs and tissues $\rightarrow$ deoxygenated blood is collected by superior and inferior vena cava $\rightarrow$ returns to right atrium.

Why it is necessary:

• It completely prevents the mixing of oxygen-rich blood with oxygen-poor blood through the interventricular and interatrial septa.
• It ensures the systemic delivery of blood at optimal, high pressure while maintaining lower, delicate filtration pressures in pulmonary capillary beds.
• It provides the high metabolic efficiency required by endothermic humans to maintain a stable core body temperature ($37^\circ\text{C}$).

Q12. What are the differences between the transport of materials in xylem and phloem?

Answer:

Feature	Transport in Xylem	Transport in Phloem (Translocation)
Substances Transported	Water and dissolved inorganic mineral salts.	Soluble organic food (sucrose), amino acids, and plant hormones.
Direction of Transport	Strictly unidirectional (upward from roots to leaves).	Bidirectional or multidirectional (from source leaves to sinks and storage tissues).
Nature of Conducting Cells	Composed of dead, hollow, lignified cells (tracheids and vessels).	Composed of living cells (sieve tube elements and companion cells).
Driving Mechanism	Physical forces: Transpiration pull and root pressure (no direct ATP expenditure).	Active transport: Requires metabolic energy (ATP) to generate osmotic pressure gradients.

Q13. Compare the functioning of alveoli in the lungs and nephrons in the kidneys with respect to their structure and functioning.

Answer:

Comparative Feature	Alveoli (Lungs)	Nephrons (Kidneys)
Primary Organ	Lungs (Respiratory System).	Kidneys (Excretory System).
Structural Shape	Tiny, thin-walled, sac-like balloon structures.	Long, convoluted tubular structures with a cup-shaped Bowman's capsule.
Capillary Network	Surrounded by an extensive superficial capillary meshwork.	Contains two capillary networks: internal glomerulus and surrounding peritubular capillaries.
Primary Function	Exchange of respiratory gases ($O_2$ intake and $CO_2$ removal).	Filtration of blood, selective reabsorption of nutrients, and excretion of nitrogenous wastes.
Basic Mechanism	Passive physical diffusion across a partial pressure gradient.	Ultrafiltration under pressure, selective active and passive reabsorption, and active secretion.
End Output	Expired air enriched with $CO_2$ and water vapor.	Concentrated liquid urine enriched with urea, uric acid, and excess salts.

Common Mistakes and Tips

Board Exam Relevance and Marks Weightage

In the CBSE Class 10 Science Board Exam, the chapter Life Processes consistently carries a substantial weightage of 8 to 10 marks within the Biology unit (Total Biology unit weightage is 25 marks). The question types distributed across sections typically include:

• Section A (1 Mark): Multiple Choice Questions (MCQs) and Assertion-Reason questions focusing on enzyme substrates, photosynthetic raw materials, respiratory pathways, and blood vessel structural differences.
• Section B & C (2 & 3 Marks): Structured difference questions (Aerobic vs Anaerobic, Xylem vs Phloem, Arteries vs Veins) and mechanistic questions on transpirational pull, emulsification, and gastric secretions.
• Section D (5 Marks): High-weightage descriptive questions, typically paired with mandatory, well-labelled diagrams:
  • Schematic diagram of the Human Alimentary Canal and digestive physiology.
  • Sectional view of the Human Heart showing double circulation pathways.
  • Structure and functioning of a Nephron with ultrafiltration stages.
  • Schematic representation of Glucose Breakdown Pathways.
• Section E (4 Marks): Case-based / Data-based questions evaluating experimental setups (e.g., starch test in destarched leaves with KOH bell jar, anaerobic fermentation setups with limewater).

More NCERT Solutions and Practice

To score a perfect 100 in your CBSE Class 10 Science Board Examination, conceptual understanding must be paired with consistent exam-style writing practice. Access chapter-wise NCERT question banks, past 10 years solved CBSE board papers, and customized mock test series designed by senior CBSE examiners at qptool.theorify.in.