The chapter 'Life Processes' serves as a fundamental pillar within the CBSE Class 10 Science curriculum, exploring the core physiological functions that define and sustain living organisms.1 As a significant component of the 'World of Living' unit, which carries a total weightage of 25 marks, this chapter demands a thorough and nuanced understanding of four critical processes: nutrition, respiration, transportation, and excretion.3 Mastery over these concepts is not merely about memorization but about appreciating the intricate interplay of biological systems in both plants and animals.
This compendium presents 50 meticulously selected long-answer questions, a format that constitutes a substantial portion of the board examination. The selection is not arbitrary; it is the result of a rigorous analysis of over a decade of CBSE previous year question papers, identifying high-frequency topics, recurring patterns, and concepts that require deep conceptual clarity.5 Each question is followed by a comprehensive, model solution designed to meet the highest standards of the CBSE evaluation criteria.
This guide is intended to be an active learning tool. Students are advised to use these solutions not as a means of rote learning, but as a benchmark for structuring their own answers. Pay close attention to the use of precise scientific terminology, the logical flow of explanations, the inclusion of balanced chemical equations, and the emphasis on neat, well-labelled diagrams. By engaging with this material thoughtfully, students can build the confidence and skills necessary to articulate complex biological processes clearly and accurately, thereby maximizing their performance in the board examinations.
Section I: Nutrition - The Process of Acquiring and Utilizing Food
Nutrition is the foundational life process by which an organism acquires and utilizes food, the external source of energy and raw materials required for growth, maintenance, and repair.8 This section explores the diverse strategies organisms employ, from the self-sustaining autotrophs to the dependent heterotrophs.
Questions and Solutions
1. (a) Define autotrophic nutrition and name the process by which autotrophs prepare their own food. (b) Write the balanced chemical equation for this process. (c) List the three main events that occur during this process.
Solution:
(a) Autotrophic nutrition is a mode of nutrition in which an organism synthesizes its own organic food from simple inorganic raw materials obtained from the environment.1 Green plants and some bacteria are examples of autotrophs. The process by which they prepare their food is called
photosynthesis.9
(b) The overall balanced chemical equation for photosynthesis is:
6CO2 (Carbon Dioxide)+6H2O (Water)SunlightChlorophyllC6H12O6 (Glucose)+6O2 (Oxygen)
(c) The three main events that occur during photosynthesis are 8:
Absorption of light energy by chlorophyll: The green pigment chlorophyll, located in the chloroplasts of plant cells, traps energy from sunlight.
Conversion of light energy to chemical energy and splitting of water molecules: The absorbed light energy is used to split water (H2O) molecules into hydrogen (H+) and oxygen (O2). This process is known as photolysis of water.
Reduction of carbon dioxide to carbohydrates: The hydrogen produced from the splitting of water is used to reduce carbon dioxide (CO2) into carbohydrates, primarily glucose (C6H12O6), which serves as food for the plant.
2. (a) Draw a neat, labelled diagram of a stomatal pore. (b) Explain how the opening and closing of stomata are regulated by guard cells.
Solution:
(a) Diagram of an Open Stomatal Pore:
(A diagram should be drawn showing two bean-shaped guard cells surrounding a central stomatal pore. Each guard cell should be labelled with a nucleus, chloroplasts, and a thick inner wall facing the pore and a thin outer wall.)
(b) The opening and closing of the stomatal pore are regulated by the turgor pressure within the two guard cells that surround it.11
Opening of Stomata: When water from surrounding cells flows into the guard cells, they become turgid (swollen). This causes the thin outer walls to bulge outwards, pulling the thick inner walls apart and opening the stomatal pore. This typically happens during the day when the plant needs to take in carbon dioxide for photosynthesis.
Closing of Stomata: When the guard cells lose water, they become flaccid (limp). The elastic inner walls regain their original shape, causing the stomatal pore to close. This usually occurs at night or during conditions of water scarcity to prevent excessive water loss through transpiration.
3. Describe the process of nutrition in Amoeba with the help of well-labelled diagrams.
Solution:
Amoeba exhibits a holozoic mode of nutrition, which involves the ingestion of complex solid organic matter.13 The process, known as phagocytosis, occurs in the following steps:
Ingestion: When Amoeba comes in contact with a food particle, it extends temporary finger-like projections called pseudopodia (false feet) to surround the food.
Formation of Food Vacuole: The pseudopodia fuse around the food particle, engulfing it along with a small amount of water. This forms a temporary, membrane-bound sac inside the cytoplasm called a food vacuole.
Digestion: Inside the food vacuole, digestive enzymes are secreted from the cytoplasm. These enzymes break down the complex, insoluble food substances into simple, soluble molecules.
Absorption: The digested food diffuses from the food vacuole directly into the cytoplasm and is utilized by the cell.
Assimilation: The absorbed nutrients are used for growth, repair, and obtaining energy for various life processes.
Egestion: The undigested waste material is moved to the surface of the cell, and the cell membrane ruptures at any point to expel it.
Diagrams illustrating the steps of Phagocytosis in Amoeba:
(A series of diagrams should be drawn showing: 1. Amoeba sensing food. 2. Extending pseudopodia. 3. Engulfing food to form a food vacuole. 4. Digestion within the vacuole. 5. Egestion of waste.)
4. Draw a neat, labelled diagram of the human alimentary canal. State the functions of the liver and pancreas in digestion.
Solution:
Diagram of the Human Alimentary Canal:
(A full-page diagram should be drawn showing the path of food from the mouth to the anus. Key parts to label are: Mouth (Buccal Cavity), Salivary Glands, Oesophagus, Stomach, Liver, Gall Bladder, Pancreas, Small Intestine (Duodenum, Jejunum, Ileum), Large Intestine, Appendix, Rectum, and Anus.)
Functions of Liver and Pancreas in Digestion:
The liver and pancreas are accessory digestive glands that secrete juices essential for digestion in the small intestine.10
Role of the Liver:
The liver secretes bile juice, which is stored in the gall bladder.
Bile is alkaline and serves two main functions:
It neutralizes the acidic food (chyme) coming from the stomach, creating an alkaline medium necessary for the pancreatic enzymes to act.
It contains bile salts that break down large fat globules into smaller fat droplets. This process is called emulsification, which increases the surface area for the enzyme lipase to act upon and digest fats more efficiently.9
Role of the Pancreas:
The pancreas secretes pancreatic juice, which contains several powerful digestive enzymes.
Key enzymes and their functions include:
Pancreatic Amylase: Breaks down remaining starch into simple sugars.
Trypsin: Digests proteins into smaller peptides. It is secreted in an inactive form (trypsinogen) and activated in the small intestine.
Lipase: Breaks down the emulsified fats into fatty acids and glycerol.15
5. Explain the role of the following in the human digestive system: (a) Saliva, (b) Hydrochloric acid, (c) Mucus, and (d) Villi.
Solution:
(a) Saliva: Secreted by the salivary glands in the mouth, saliva plays two key roles 15:
* It moistens and lubricates the food, making it easier to chew and swallow.
* It contains the enzyme salivary amylase (ptyalin), which begins the chemical digestion of starch (a complex carbohydrate) into simpler sugars (maltose).
(b) Hydrochloric Acid (HCl): Secreted by the gastric glands in the stomach wall, HCl has two primary functions 12:
* It creates a highly acidic medium (pH 1.5-3.5) in the stomach, which is necessary to activate the protein-digesting enzyme pepsin.
* It kills most of the harmful bacteria and other microorganisms that may enter the body along with food.
(c) Mucus: Also secreted by the gastric glands, mucus forms a thick, protective layer on the inner lining of the stomach. This layer is crucial as it prevents the stomach wall from being damaged by the corrosive action of hydrochloric acid and the digestive action of pepsin.11
(d) Villi: These are millions of tiny, finger-like projections found on the inner surface of the small intestine. Their structure is a prime example of adaptation for a specific function. The villi vastly increase the surface area available for the absorption of digested food.17 They are richly supplied with a network of blood capillaries and a lymph vessel (lacteal), which quickly absorb the nutrients and transport them to the rest of the body.
6. Give reasons for the following statements: (a) Herbivores have a longer small intestine than carnivores. (b) The inner lining of the small intestine has numerous finger-like projections. (c) Bread tastes sweet after chewing for some time.
Solution:
(a) The length of the small intestine is directly related to the diet of an organism. Herbivores, such as cows and deer, consume plant matter that is rich in cellulose, a complex carbohydrate that is difficult to digest. A longer small intestine provides a greater surface area and more time for the complete enzymatic breakdown and absorption of nutrients from cellulose.18 In contrast, carnivores eat meat, which is primarily protein and is much easier to digest. Therefore, they have a shorter small intestine. This difference in anatomy is a clear evolutionary adaptation to dietary requirements.
(b) The primary function of the small intestine is the absorption of digested food into the bloodstream. To perform this function efficiently, a very large surface area is required. The inner lining of the small intestine is folded into numerous finger-like projections called villi, which are further covered in microscopic projections called microvilli. This structural adaptation massively increases the effective surface area for absorption, ensuring that the maximum amount of nutrients can be absorbed from the digested food.17
(c) Bread is primarily composed of starch, which is a complex carbohydrate and is tasteless. When bread is chewed, it mixes with saliva in the mouth. Saliva contains the enzyme salivary amylase, which starts breaking down the complex starch molecules into simpler sugars, like maltose. Since sugars are sweet to taste, the bread begins to taste sweet after being chewed for a while.15
7. Differentiate between autotrophic and heterotrophic nutrition. Provide two examples for each.
Solution:
The primary difference between autotrophic and heterotrophic nutrition lies in the source of organic food.1
8. (a) What is the role of acid in our stomach? (b) What is emulsification of fats? (c) Name the enzyme present in pancreatic juice that digests protein.
Solution:
(a) The acid in our stomach is hydrochloric acid (HCl). It performs two crucial functions 16:
Activation of Pepsin: It creates a highly acidic environment, which is required for the enzyme pepsinogen to be converted into its active form, pepsin, which then begins the digestion of proteins.
Sterilization of Food: It kills most of the harmful microorganisms that may have entered the body along with the food, thus preventing infections.
(b) Emulsification is the process of breaking down large globules of fat into much smaller, finely dispersed droplets. In the small intestine, this is carried out by bile salts, which are present in the bile juice secreted by the liver. This process is not chemical digestion but a physical breakdown that dramatically increases the surface area of fats, allowing the fat-digesting enzyme, lipase, to act on them more effectively.16
(c) The protein-digesting enzyme present in pancreatic juice is trypsin.10 It is secreted in an inactive form and becomes active in the alkaline environment of the small intestine.
9. What are the raw materials required for photosynthesis? How do plants obtain them?
Solution:
The primary raw materials required for photosynthesis are carbon dioxide, water, and sunlight.2
Carbon Dioxide (CO2): Terrestrial plants obtain carbon dioxide from the atmosphere. It enters the leaves through tiny pores called stomata, which are typically located on the underside of the leaves. Aquatic plants obtain CO2 dissolved in the surrounding water.
Water (H2O): Plants absorb water from the soil through their root systems via the process of osmosis. This water, along with dissolved minerals, is then transported upwards to the leaves through a specialized vascular tissue called xylem.
Sunlight: Sunlight is the energy source for photosynthesis. This light energy is trapped by the green pigment chlorophyll, which is present in cellular organelles called chloroplasts, found abundantly in the cells of the leaves.
10. Describe the complete process of digestion of carbohydrates, proteins, and fats in the human alimentary canal.
Solution:
The digestion of carbohydrates, proteins, and fats is a step-by-step process involving various enzymes at different locations in the alimentary canal.
Digestion of Carbohydrates:
Mouth: Digestion begins in the mouth. Salivary amylase breaks down starch into maltose.
Stomach: No carbohydrate digestion occurs in the stomach due to the acidic pH.
Small Intestine: Pancreatic amylase from the pancreas breaks down the remaining starch. Intestinal enzymes (like maltase, sucrase, lactase) then break down disaccharides into monosaccharides like glucose, which is the final absorbable form.
Digestion of Proteins:
Mouth: No protein digestion occurs here.
Stomach: In the acidic medium, pepsin breaks down large protein molecules into smaller molecules called peptones.
Small Intestine: Trypsin from the pancreas breaks down proteins and peptones into smaller peptides. Finally, intestinal enzymes (peptidases) break down these peptides into the final absorbable units, amino acids.
Digestion of Fats (Lipids):
Mouth and Stomach: Negligible fat digestion occurs.
Small Intestine: This is the primary site for fat digestion.
Emulsification: Bile from the liver breaks large fat globules into small droplets.
Enzymatic Digestion: Lipase from the pancreas and intestinal wall acts on these emulsified fats, breaking them down into fatty acids and glycerol, which are the final absorbable forms.
Key Digestive Enzymes and Their Functions
Section II: Respiration - The Biochemical Release of Energy
Respiration is the metabolic process of breaking down organic compounds, typically glucose, to release energy in the form of ATP (Adenosine Triphosphate), which fuels all cellular activities.1 This section contrasts the different respiratory pathways and details the mechanics of the human respiratory system.
Questions and Solutions
11. Differentiate between aerobic and anaerobic respiration. Name one organism that uses each type.
Solution:
Aerobic and anaerobic respiration are two distinct pathways for cellular respiration, primarily differing in their requirement for oxygen.9
12. With the help of a flowchart, explain the breakdown of glucose by various pathways in living organisms.
Solution:
The breakdown of glucose to release energy begins with a common first step in the cytoplasm for all organisms. The subsequent pathway depends on the availability of oxygen.
Flowchart of Glucose Breakdown:
Explanation of Pathways:
Step 1: Glycolysis (Common to all): In the cytoplasm of the cell, one molecule of glucose (6-carbon) is broken down into two molecules of pyruvate (3-carbon). This process releases a small amount of energy.
Pathway 1: Anaerobic Respiration in Yeast (Fermentation): In the absence of oxygen, yeast breaks down pyruvate into ethanol (a 2-carbon compound) and carbon dioxide, releasing a small amount of energy. This process is known as alcoholic fermentation.11
Pathway 2: Anaerobic Respiration in Muscle Cells: During vigorous physical activity, the demand for oxygen in muscle cells can exceed the supply. In this state of oxygen lack, pyruvate is converted into lactic acid (a 3-carbon compound), releasing a small amount of energy. The accumulation of lactic acid is what causes muscle cramps.1
Pathway 3: Aerobic Respiration in Mitochondria: In the presence of oxygen, the pyruvate enters the mitochondria. Here, it is completely oxidized to produce carbon dioxide and water, releasing a large amount of energy that is stored in ATP molecules.15
13. (a) Draw a diagram of the human respiratory system and label the following parts: Pharynx, Trachea, Bronchi, Alveoli. (b) Explain the mechanism of breathing in humans.
Solution:
(a) Diagram of the Human Respiratory System:
(A clear diagram should be drawn showing the pathway of air from the nasal passage to the lungs. Labels should include: Nasal Passage, Pharynx, Larynx (Voice Box), Trachea (Windpipe), Rings of Cartilage, Bronchus (plural: Bronchi), Bronchioles, Lungs, Alveoli (as a magnified inset), and Diaphragm.)
(b) Mechanism of Breathing (Inhalation and Exhalation):
Breathing is the physical process of moving air into and out of the lungs, and it involves the coordinated movement of the rib cage and the diaphragm, a large muscular sheet below the lungs.9
Inhalation (Breathing In):
The diaphragm contracts and flattens (moves downwards).
The external intercostal muscles contract, lifting the ribs upwards and outwards.
These two actions increase the volume of the thoracic (chest) cavity.
The increased volume leads to a decrease in air pressure inside the lungs compared to the atmospheric pressure outside.
To equalize the pressure, air rushes into the lungs from the outside.
Exhalation (Breathing Out):
The diaphragm relaxes and becomes dome-shaped (moves upwards).
The external intercostal muscles relax, causing the ribs to move downwards and inwards.
These actions decrease the volume of the thoracic cavity.
The decreased volume leads to an increase in air pressure inside the lungs compared to the atmospheric pressure.
Air is forced out of the lungs until the pressure inside and outside is equal.
14. Why is diffusion insufficient to meet the oxygen requirements of multicellular organisms like humans?
Solution:
Diffusion is the movement of substances from a region of higher concentration to a region of lower concentration. While it is an effective transport mechanism for single-celled organisms, it is entirely insufficient for large, multicellular organisms like humans for several key reasons.2
Large Body Size and Volume: In multicellular organisms, the body is composed of trillions of cells. Most of these cells are not in direct contact with the external environment. The distance between the outer surface and the innermost cells is vast.
Slowness of Diffusion: Diffusion is a very slow process over distances of more than a few millimeters. It would take an impractically long time for oxygen to diffuse from the lungs or skin to reach cells deep within the body, such as in the liver or brain. These cells would die from oxygen deprivation long before the oxygen could reach them.
Low Surface Area to Volume Ratio: As an organism gets larger, its volume increases much faster than its surface area. This means there is not enough surface area in direct contact with the environment to supply oxygen to the massive volume of cells inside.
The physical constraint imposed by the slowness of diffusion over large distances was a powerful selective pressure in evolution. It drove the development of specialized, complex systems to overcome this limitation. A dedicated respiratory system (like the lungs) was developed to provide a massive internal surface area for efficient gas exchange. Concurrently, a rapid circulatory system (heart, blood, and blood vessels) evolved to actively transport the oxygen from this exchange surface to every single cell in the body, ensuring their metabolic needs are met almost instantaneously.
15. How are the lungs designed to maximize the area for the exchange of gases?
Solution:
The lungs in humans are exquisitely designed to maximize the surface area for efficient gaseous exchange.11 The key structural adaptations are:
Extensive Branching: The trachea (windpipe) branches into two primary bronchi, one for each lung. These bronchi further divide into smaller secondary and tertiary bronchi, which then branch into even finer tubes called bronchioles. This extensive branching network distributes the inhaled air throughout the entire lung.
Alveoli: The bronchioles terminate in clusters of tiny, balloon-like air sacs called alveoli. There are approximately 300-500 million alveoli in a pair of human lungs. If flattened out, their total surface area would be about 80-100 square meters, roughly the size of a tennis court. This enormous surface area maximizes the space available for gas diffusion.
Thin Walls: The walls of the alveoli are extremely thin, only one cell thick. This minimizes the diffusion distance for gases (oxygen and carbon dioxide) between the air in the alveoli and the blood.
Rich Blood Supply: The surface of each alveolus is covered by a dense network of blood capillaries. This ensures that a large volume of blood is constantly flowing close to the alveolar surface, maintaining a steep concentration gradient that facilitates rapid and continuous diffusion of gases.
16. What would be the consequences of a deficiency of haemoglobin in our bodies?
Solution:
Haemoglobin is the red-coloured, iron-containing respiratory pigment found in red blood cells (RBCs). Its primary function is to bind with oxygen in the lungs and transport it to all the body tissues for cellular respiration.16
A deficiency of haemoglobin in the blood leads to a condition called anaemia. The consequences of this deficiency are significant:
Reduced Oxygen-Carrying Capacity: The most direct consequence is a drastic reduction in the blood's ability to transport oxygen. Even if the lungs are functioning perfectly, there aren't enough "carriers" to deliver the oxygen to the cells.
Tissue Hypoxia: This leads to a lack of sufficient oxygen supply to the body tissues (hypoxia). As a result, the rate of aerobic respiration in cells decreases, leading to reduced energy (ATP) production.
Symptoms: A person suffering from anaemia will experience symptoms such as:
Persistent fatigue, weakness, and lethargy.
Shortness of breath, especially upon exertion.
Pale skin, lips, and nail beds.
Dizziness and headaches.
In severe cases, it can lead to complications affecting the heart and other organs.
17. Give reasons for the following: (a) Rings of cartilage are present in the throat. (b) Lungs always contain a residual volume of air. (c) The wall of the trachea is lined with cilia and mucus.
Solution:
(a) The throat contains the trachea, or windpipe, which is the main passage for air to the lungs. This passage is supported by C-shaped rings of cartilage. Their function is to provide structural support and ensure that the airway does not collapse when there is low air pressure inside, such as during forceful exhalation. This guarantees that the air passage remains open and unobstructed at all times.12
(b) After a complete exhalation, a certain amount of air, known as the residual volume, always remains in the lungs and alveoli.12 This is crucial for two reasons:
It prevents the delicate alveoli from collapsing completely.
It allows for continuous gaseous exchange to occur between breaths. Even when we are not actively inhaling or exhaling, some oxygen can still diffuse into the blood and carbon dioxide can diffuse out, ensuring a more stable level of blood gases.
(c) The inner wall of the trachea is lined with specialized cells that secrete mucus and have hair-like projections called cilia. This system acts as a protective filter. The sticky mucus traps inhaled dust, pollen, and other foreign particles. The cilia then beat in a coordinated upward motion, sweeping this mucus-laden debris up towards the pharynx, where it can be swallowed or coughed out. This mechanism helps to clean the inhaled air and protect the delicate lungs from infection and damage.
Section III: Transportation - The Body's Internal Logistics Network
Transportation systems are vital for delivering essential substances like oxygen and nutrients to all cells and for removing waste products. This section examines the highly efficient double circulatory system in humans and the distinct vascular systems in plants.
Questions and Solutions
18. (a) Draw a schematic diagram showing double circulation in humans. (b) Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?
Solution:
(a) Schematic Diagram of Double Circulation:
(A block diagram should be drawn. It should show the four chambers of the heart at the center. A loop on one side, labelled "Pulmonary Circulation," should show the right ventricle pumping deoxygenated blood via the pulmonary artery to the lungs, and the pulmonary vein returning oxygenated blood to the left atrium. A larger loop on the other side, labelled "Systemic Circulation," should show the left ventricle pumping oxygenated blood via the aorta to the body tissues, and the vena cava returning deoxygenated blood to the right atrium.)
(b) The separation of oxygenated and deoxygenated blood is a key feature of the four-chambered heart in mammals and birds, and it is necessary for maintaining their high metabolic rate.15
High Energy Needs: Mammals and birds are warm-blooded (endothermic), meaning they maintain a constant high body temperature irrespective of the external environment. This process of thermoregulation is energetically very expensive and requires a high and continuous rate of cellular respiration.
Efficient Oxygen Supply: To support this high metabolic rate, their body tissues require a constant and efficient supply of oxygen. The separation of oxygenated and deoxygenated blood ensures that the blood delivered to the body tissues via the aorta is fully saturated with oxygen.
Prevention of Mixing: If the blood were to mix (as it does in three-chambered hearts of amphibians), the oxygen content of the blood supplied to the body would be lower. This would not be sufficient to meet the high energy demands of a warm-blooded animal. Therefore, the four-chambered heart and the resulting double circulation represent a highly efficient system that was a critical evolutionary adaptation for an active, endothermic lifestyle.
19. What is meant by 'double circulation'? Explain its significance.
Solution:
Double circulation is a circulatory system in which the blood flows through the heart twice for each complete circuit of the body.16 This system consists of two distinct pathways:
Pulmonary Circulation: This circuit moves blood between the heart and the lungs. Deoxygenated blood from the right ventricle is pumped to the lungs to get oxygenated. This oxygenated blood then returns to the left atrium of the heart.
Systemic Circulation: This circuit moves blood between the heart and the rest of the body. Oxygenated blood from the left ventricle is pumped to all body tissues and organs. After delivering oxygen and picking up carbon dioxide, the deoxygenated blood returns to the right atrium of the heart.
Significance of Double Circulation:
Efficient Transport: It ensures a highly efficient supply of oxygen to the body's cells by preventing the mixing of oxygenated and deoxygenated blood.
High-Pressure System: It allows blood to be pumped to the rest of the body at a much higher pressure. After returning from the lungs, the blood is sent back to the heart's powerful left ventricle to be re-pressurized before being sent on the longer systemic journey. This high pressure ensures rapid delivery of blood to all tissues, which is essential for organisms with high energy needs.
20. Differentiate between arteries and veins based on four distinct features.
Solution:
Arteries and veins are the two main types of blood vessels in the circulatory system, differing significantly in their structure and function.9
21. List the components of blood and write one major function for each component.
Solution:
Blood is a fluid connective tissue composed of a liquid matrix, plasma, in which three types of cells are suspended.15
Plasma:
Composition: The pale yellow, liquid component of blood, consisting mainly of water (about 90%) with dissolved proteins, salts, hormones, digested food, and waste products.
Function: It acts as the transport medium for blood cells, nutrients (like glucose and amino acids), carbon dioxide, nitrogenous wastes (like urea), and hormones.
Red Blood Cells (RBCs or Erythrocytes):
Composition: Biconcave, disc-shaped cells that lack a nucleus at maturity. They are packed with the red pigment haemoglobin.
Function: Their primary function is the transport of oxygen. Haemoglobin binds with oxygen in the lungs and releases it in the tissues.
White Blood Cells (WBCs or Leucocytes):
Composition: Irregularly shaped cells that are larger than RBCs and contain a nucleus. There are several types (e.g., neutrophils, lymphocytes).
Function: They are the soldiers of the body's immune system. They fight infection and protect the body from diseases by engulfing pathogens or producing antibodies.
Platelets (Thrombocytes):
Composition: Tiny, irregular cell fragments that lack a nucleus.
Function: They play a crucial role in blood clotting. When a blood vessel is injured, platelets accumulate at the site and help form a clot to plug the leak, preventing excessive blood loss.
22. What is lymph? Explain its formation and state two of its important functions.
Solution:
Lymph, also known as tissue fluid, is a light-yellow fluid that is similar in composition to blood plasma but contains fewer proteins and more lymphocytes.21
Formation of Lymph:
As blood flows through the capillaries in the tissues, the high pressure forces some of the water, dissolved salts, and small proteins from the plasma to leak out through the thin capillary walls into the spaces between the cells. This leaked fluid is the tissue fluid, or lymph. It bathes the cells, facilitating the exchange of materials. This fluid is then collected by a network of tiny vessels called lymph capillaries, which join to form larger lymph vessels. The lymph eventually returns to the bloodstream via the subclavian veins.
Functions of Lymph:
Transportation: Lymph carries digested and absorbed fats from the small intestine (via lacteals in the villi) to the blood. It also transports waste products and carbon dioxide from the tissue cells back to the blood.
Immunity: Lymph plays a vital role in the body's defense system. It contains specialized white blood cells called lymphocytes, which fight against infection. As lymph passes through structures called lymph nodes, pathogens and foreign particles are filtered out and destroyed.
23. Explain the mechanism of transport of water and minerals in a plant.
Solution:
The transport of water and minerals in a plant from the roots to the leaves is carried out by the xylem tissue. This upward movement is primarily driven by a process called transpiration pull.15
The mechanism involves several steps:
Absorption by Roots: The cells of the root hairs are in contact with soil water. They actively take up mineral ions from the soil, creating a difference in concentration between the root cells and the soil. To balance this, water moves from the soil into the root cells by osmosis.
Root Pressure: The continuous entry of water into the root xylem generates a hydrostatic pressure known as root pressure. This pressure can push the water column up to a certain height in the stem.
Transpiration Pull (Cohesion-Tension Theory): This is the main driving force for water movement over long distances in tall plants.
Transpiration: Water is constantly lost from the surfaces of leaves in the form of water vapour through the stomata.
Creation of Suction Force: This loss of water from the leaf cells creates a suction or tension, known as the transpiration pull.
Cohesion and Adhesion: This pull is transmitted down the continuous column of water in the xylem vessels all the way to the roots. The water column does not break due to the cohesive forces between water molecules and the adhesive forces between water and the xylem walls.
Upward Movement: This pull effectively draws more water from the soil into the roots and up through the plant to replace the water lost from the leaves.
24. What is translocation? How is food transported in plants?
Solution:
Translocation is the process of transporting the soluble products of photosynthesis (mainly sucrose) from the leaves (the source) to other parts of the plant, such as roots, fruits, and growing points (the sinks), for use or storage.21 This process occurs through a specialized vascular tissue called the
phloem.
Mechanism of Food Transport:
Unlike water transport in the xylem, which is a passive process, translocation in the phloem is an active process that requires energy in the form of ATP.
Loading at the Source (Leaves): Sucrose produced during photosynthesis in the leaf cells is actively loaded into the sieve tubes of the phloem. This process requires energy (ATP).
Creation of Osmotic Pressure: The loading of sugar into the phloem increases the solute concentration, causing water to move from the adjacent xylem into the phloem by osmosis. This influx of water creates a high turgor pressure at the source.
Movement to the Sink: This high pressure forces the phloem sap (sugar solution) to move along the sieve tubes towards regions of lower pressure, which are the 'sink' areas (e.g., roots, fruits).
Unloading at the Sink: At the sink, the sugar is actively unloaded from the phloem and moved into the cells where it is needed for respiration or stored as starch. This removal of sugar lowers the solute concentration in the phloem.
Return of Water: As sugar is removed, water also moves out of the phloem and back into the xylem, reducing the pressure at the sink. This pressure gradient between the source and the sink drives the continuous flow of sap through the phloem.
Comparative Overview of Transport Vessels
Table 1: Arteries vs. Veins vs. Capillaries
Table 2: Xylem vs. Phloem
Section IV: Excretion - The Essential Process of Waste Management
Excretion is the biological process of removing harmful metabolic wastes from the body to maintain a stable internal environment (homeostasis).9 This section focuses on the sophisticated human excretory system, particularly the function of the nephron, and the simpler excretory methods of plants.
Questions and Solutions
25. (a) Define excretion. (b) Draw a well-labelled diagram of the human excretory system. (c) Name the basic filtration unit of the kidney.
Solution:
(a) Excretion is the process by which metabolic waste products, which can be toxic if allowed to accumulate, are removed from the body of an organism.9 In humans, the primary nitrogenous waste product is urea.
(b) Diagram of the Human Excretory System:
(A diagram should be drawn showing a pair of bean-shaped kidneys, one on either side of the backbone. From each kidney, a ureter should be shown emerging and connecting to a muscular urinary bladder. The urethra should be shown extending from the bladder. The renal artery (entering the kidney) and renal vein (leaving the kidney) should also be labelled.)
(c) The basic filtration unit of the kidney is the nephron.18 Each kidney contains approximately one million of these microscopic tubules.
26. (a) Draw a neat, labelled diagram of a nephron. (b) Describe the process of urine formation in the kidneys.
Solution:
(a) Diagram of a Nephron:
(A detailed diagram of a single nephron should be drawn. It must include the Bowman's capsule enclosing the glomerulus (a bundle of capillaries), the proximal convoluted tubule (PCT), the loop of Henle, the distal convoluted tubule (DCT), and the collecting duct. The afferent arteriole (entering the glomerulus) and efferent arteriole (leaving it), along with the network of peritubular capillaries surrounding the tubule, should also be shown and labelled.)
(b) The process of urine formation occurs in the nephrons and involves three main steps:
Glomerular Filtration (Ultrafiltration): Blood enters the glomerulus under high pressure through the wider afferent arteriole. This pressure forces water, urea, glucose, amino acids, salts, and other small molecules from the blood into the Bowman's capsule. Large molecules like proteins and blood cells are retained in the blood. The fluid that enters the Bowman's capsule is called the glomerular filtrate.
Selective Reabsorption: As the filtrate passes through the long, tubular part of the nephron (PCT, Loop of Henle, DCT), the body reclaims essential substances that it needs. This is a highly efficient conservation mechanism. Nearly all the glucose and amino acids, and most of the water and salts, are selectively reabsorbed back into the blood in the surrounding peritubular capillaries. This process is "selective" because the amount of water and salts reabsorbed depends on the body's needs, regulated by hormones.
Tubular Secretion: Some waste products, such as excess potassium ions, hydrogen ions, and certain drugs, that were not filtered in the glomerulus are actively secreted from the blood into the filtrate in the distal tubule. This final step helps in maintaining the pH and ionic balance of the blood.
The fluid remaining in the tubule after these three processes is urine. It is primarily composed of water, urea, and some excess salts. The urine from all nephrons is collected in the collecting ducts, passes through the ureters, is stored in the urinary bladder, and is finally expelled from the body through the urethra.
27. What is the purpose of making urine? What would be the consequence if selective reabsorption did not occur in the nephrons?
Solution:
The primary purpose of making urine is to filter metabolic waste products, especially nitrogenous wastes like urea, from the blood and expel them from the body.18 This process is vital for maintaining
homeostasis—a stable internal environment. By regulating the amount of water and salts excreted, the kidneys also play a crucial role in controlling the body's water balance and blood pressure.
The process of urine formation is a clever two-stage strategy: first, filter almost everything small out of the blood, and then take back only what is needed. The second stage, selective reabsorption, is therefore critically important.
If selective reabsorption did not occur in the nephrons:
Massive Loss of Water and Nutrients: The glomerular filtrate contains large amounts of water, glucose, amino acids, and essential salts. Without reabsorption, all these vital substances would be lost from the body along with the urine.
Rapid Dehydration and Starvation: An average adult produces about 180 litres of glomerular filtrate per day. If this were all excreted as urine, the body would dehydrate and die within a very short time. Similarly, the loss of all glucose and amino acids would lead to rapid starvation and a complete shutdown of cellular functions.
Failure of Homeostasis: The body would be unable to regulate its internal water, salt, and nutrient balance, leading to a catastrophic failure of all physiological systems.
Thus, selective reabsorption is an essential conservation mechanism that allows the body to efficiently remove waste without losing vital resources.
28. Describe the various methods used by plants to get rid of their excretory products.
Solution:
Unlike animals, plants do not have a specialized excretory system. They use a variety of simpler strategies to get rid of their waste products 9:
Gaseous Waste Removal:
Oxygen, a byproduct of photosynthesis, is a waste product for the plant. It is released into the atmosphere through the stomata on the leaves.
Carbon dioxide, produced during respiration, is released through stomata at night. During the day, it is often reused for photosynthesis.
Water Removal: Plants get rid of excess water through the process of transpiration, where water evaporates from the leaf surfaces through the stomata.
Storing Waste in Tissues:
Many solid and liquid waste products are stored in the vacuoles of cells.
Some wastes are stored in old leaves, bark, or heartwood. These parts are eventually shed from the plant, thereby removing the stored waste. The yellowing and falling of leaves in autumn is one such method.
Secretion of Gums and Resins: Plants like pine and acacia excrete waste products in the form of resins and gums. These substances are often stored in old xylem tissue and can be seen oozing out from the stem.
Excretion into the Soil: Some plants excrete certain waste substances into the soil around their roots.
29. What is haemodialysis? Explain the principle and procedure of using an artificial kidney.
Solution:
Haemodialysis is a medical procedure used to remove waste products like urea and excess salts from the blood of a person whose kidneys have failed. The device used for this process is called a dialyzer or an artificial kidney.13
Principle:
The principle of haemodialysis is diffusion across a semi-permeable membrane. Blood from the patient is passed through tubes made of a semi-permeable material. These tubes are bathed in a special fluid called dialysate. The composition of the dialysate is similar to that of normal blood plasma but is completely free of nitrogenous wastes like urea. This creates a steep concentration gradient, causing waste products from the blood to diffuse out into the dialysate, while essential substances like glucose and salts (which are present at normal concentrations in the dialysate) are retained in the blood.
Procedure:
Blood is drawn from an artery in the patient's arm and is cooled and mixed with an anticoagulant like heparin to prevent clotting.
The blood is then pumped into the dialyzer.
Inside the dialyzer, the blood flows through a network of long tubes made of a selectively permeable membrane (e.g., cellophane).
These tubes are immersed in a tank filled with the dialysing solution (dialysate), which flows in the opposite direction to the blood flow (counter-current flow) to maximize the efficiency of waste removal.
As blood passes through the tubes, waste products like urea and excess salts diffuse out into the dialysate.
The purified blood is then warmed to body temperature, the anticoagulant is neutralized, and the blood is returned to the patient's body through a vein.
This process is different from the natural process in kidneys as there is no provision for selective reabsorption in an artificial kidney. Therefore, the composition of the dialysate must be carefully controlled to prevent the loss of essential substances from the blood.
Conclusion: Strategic Insights for Exam Success
This compendium has traversed the four essential life processes, providing model answers to questions that frequently appear in the CBSE board examinations. A deeper analysis of these topics reveals several overarching biological principles that, when understood, can elevate a student's answers from simple descriptions to insightful explanations.
Key Takeaways for Deeper Understanding
The Structure-Function Paradigm: A recurring theme is how the structure of a biological component is perfectly tailored for its function. The long intestine of herbivores, the vast surface area of alveoli and villi, and the thick walls of arteries are all prime examples. When answering, always try to link the "what" (structure) with the "why" (function).
Physical Constraints as Evolutionary Drivers: The insufficiency of diffusion in large organisms is not just a fact; it is the fundamental reason for the existence of complex respiratory and circulatory systems. Understanding this helps explain the very necessity of lungs and the heart.
Energy Needs and System Complexity: The evolution of a four-chambered heart and double circulation is directly linked to the high energy demands of warm-blooded animals. This connection explains why different animals have different types of hearts and circulatory efficiencies.
Homeostasis and Conservation: Biological systems, like the nephron in the kidney, are not just about waste removal but also about maintaining internal balance (homeostasis). The process of selective reabsorption demonstrates a powerful principle of conservation, where the body efficiently discards waste while meticulously reclaiming vital resources.
Answering Techniques for Maximizing Scores
To excel in the board examination, knowledge must be paired with effective presentation. Adhere to the following checklist when writing your answers:
Underline Keywords: Make it easy for the examiner to spot key biological terms (e.g., photosynthesis, double circulation, nephron, transpiration). This highlights your command of the subject.
Practice Diagrams: A neat, large, and accurately labelled diagram can often convey more information than a paragraph of text and can secure full marks. Practice drawing the human alimentary canal, respiratory system, heart, and nephron repeatedly.
Use Structured Answers: For long answers, break down your explanation into points using bullets or numbers. This makes the information clear, logical, and easy to evaluate.
Address "Reasoning" Questions Logically: For questions that ask "Why?" or "Give a reason," structure your answer by stating the principle, explaining the mechanism, and concluding with the consequence. For example: "Rings of cartilage are present (structure) to prevent the trachea from collapsing (function), thereby ensuring an unobstructed passage for air at all times (consequence)."
By internalizing the core concepts and adopting these strategic answering techniques, you will be well-equipped to tackle any question on 'Life Processes' with confidence and precision.
