NCERT Class 10 Science Chapter 6: Life Processes - A Comprehensive Guide

Introduction to Life Processes

Welcome, students! In this detailed guide, we will explore Chapter 6 of the Class 10 NCERT Science syllabus, 'Life Processes'. What exactly are life processes? Imagine a living organism, whether it's a tiny bacterium, a towering tree, or a human being. To stay alive, it must perform a series of essential functions. These functions, which are necessary to maintain life and prevent damage and breakdown, are collectively known as life processes. Even when we are sleeping or sitting still, our bodies are hard at work repairing and maintaining themselves. This chapter delves into the four most crucial life processes that define living beings: Nutrition, Respiration, Transportation, and Excretion. Understanding these processes is fundamental to appreciating the complexity and beauty of biology. Let's begin our journey into the fascinating world inside every living organism.

What are Life Processes?

The fundamental functions performed by living organisms to sustain themselves are called life processes. These processes distinguish living things from non-living things. The energy required to perform these maintenance processes comes from the food that organisms consume. Let's look at the key life processes we will study:

• Nutrition: The process of taking in food (nutrients) and utilizing it to obtain energy for growth, repair, and maintenance.
• Respiration: The process of breaking down food, primarily glucose, to release energy in a form that cells can use (ATP).
• Transportation: The process by which food, oxygen, water, waste products, and other substances are carried from one part of the body to another.
• Excretion: The process of removing harmful metabolic waste products from the body.

All these processes are interconnected. For example, the food you eat (nutrition) is broken down to release energy (respiration), and the nutrients and oxygen are delivered to every cell by your circulatory system (transportation), which also carries away the waste products to be removed (excretion).

Nutrition

Nutrition is the cornerstone of all life processes. It is the mode of taking food by an organism and its utilisation by the body. The food we eat contains nutrients like carbohydrates, fats, proteins, vitamins, and minerals, which provide energy and raw materials for growth. There are two main modes of nutrition.

Autotrophic Nutrition

The term 'autotroph' comes from two Greek words: 'auto' meaning self, and 'trophe' meaning nutrition. Thus, autotrophic nutrition is a mode of nutrition in which organisms synthesize their own food from simple inorganic raw materials like carbon dioxide and water. Green plants and some bacteria are classic examples of autotrophs. They are the producers in the food chain.

The process by which green plants make their own food is called photosynthesis. Let's break it down:

• Raw Materials: The essential raw materials for photosynthesis are carbon dioxide (taken from the atmosphere through tiny pores on leaves called stomata) and water (absorbed from the soil by the roots).
• Site of Photosynthesis: The process takes place in special cell organelles called chloroplasts, which are abundant in the leaves. Chloroplasts contain a green pigment called chlorophyll, which is crucial for trapping sunlight.
• Energy Source: The energy to drive this process comes from sunlight.

The overall balanced chemical equation for photosynthesis is:

6CO₂ (Carbon Dioxide) + 6H₂O (Water) --(in the presence of Sunlight and Chlorophyll)--> C₆H₁₂O₆ (Glucose) + 6O₂ (Oxygen)

The main events that occur during photosynthesis are:

1. Absorption of light energy by chlorophyll.
2. Conversion of light energy into chemical energy and the splitting of water molecules (H₂O) into hydrogen and oxygen.
3. Reduction of carbon dioxide (CO₂) to carbohydrates (glucose).

The glucose produced is used for energy, and any excess is stored in the form of starch in various parts of the plant.

Heterotrophic Nutrition

The term 'heterotroph' comes from 'hetero' meaning other, and 'trophe' meaning nutrition. Heterotrophic nutrition is a mode of nutrition in which organisms cannot synthesize their own food and depend directly or indirectly on autotrophs for their survival. All animals, fungi, and most bacteria are heterotrophs. There are three main types of heterotrophic nutrition:

• Holozoic Nutrition: The organism takes in complex solid organic food, which is then digested, absorbed, and assimilated. Humans, amoeba, and most animals exhibit this type of nutrition.
• Saprophytic Nutrition: The organism feeds on dead and decaying organic matter. They secrete digestive enzymes onto the substrate, which breaks it down into simpler forms that can be absorbed. Fungi like bread moulds, yeast, and mushrooms are examples.
• Parasitic Nutrition: The organism (parasite) derives its nutrition from another living organism (host) without killing it, though often causing harm. Examples include Cuscuta (amar-bel) in plants and tapeworms and ticks in animals.

Nutrition in Human Beings

Humans have a highly specialized system for holozoic nutrition called the human digestive system. It consists of the alimentary canal and associated digestive glands. The alimentary canal is a long tube extending from the mouth to the anus.

1. Mouth (Oral Cavity): Digestion begins here. The teeth physically break down the food (mastication). The salivary glands secrete saliva, which contains the enzyme salivary amylase. This enzyme starts the chemical digestion of starch into simpler sugars. The tongue helps in mixing the food with saliva and pushing it down.
2. Oesophagus (Food Pipe): The swallowed food passes into the oesophagus. The walls of the oesophagus have muscles that contract and relax rhythmically to push the food forward. This wave-like movement is called peristalsis.
3. Stomach: This J-shaped organ receives food from the oesophagus. The stomach walls contain gastric glands that secrete gastric juice. Gastric juice contains three main components:
   • Hydrochloric Acid (HCl): Creates an acidic medium which facilitates the action of the enzyme pepsin. It also kills any harmful bacteria that enter with the food.
   • Pepsin: A protein-digesting enzyme that begins the breakdown of proteins into smaller fragments called peptones.
   • Mucus: Protects the inner lining of the stomach from the corrosive action of HCl.
4. Small Intestine: This is the longest part of the alimentary canal and the site of complete digestion of carbohydrates, proteins, and fats. It receives secretions from two glands: the liver and the pancreas.
   • From the Liver: The liver secretes bile juice, which is stored in the gall bladder. Bile does not contain any enzymes but performs two crucial functions: it makes the acidic food coming from the stomach alkaline (for pancreatic enzymes to act) and it breaks down large fat globules into smaller ones (emulsification), increasing the efficiency of fat-digesting enzymes.
   • From the Pancreas: The pancreas secretes pancreatic juice containing enzymes like pancreatic amylase (for digesting starch), trypsin (for digesting proteins), and lipase (for digesting emulsified fats).
   • Intestinal Juice: The walls of the small intestine secrete intestinal juice, whose enzymes finally convert proteins into amino acids, complex carbohydrates into glucose, and fats into fatty acids and glycerol.
   Absorption: The inner lining of the small intestine has numerous finger-like projections called villi. These villi vastly increase the surface area for absorption. The digested food is absorbed into the blood vessels within the villi.
5. Large Intestine: The unabsorbed food is sent to the large intestine. Its main function is to absorb excess water from this material. The rest of the material is stored in the rectum and removed from the body via the anus. This removal of faecal matter is called egestion.

Respiration

After food is digested and absorbed, the body needs to extract energy from it. This is the role of respiration. Respiration is the biochemical process in which the cells of an organism obtain energy by combining oxygen and glucose, resulting in the release of carbon dioxide, water, and ATP (Adenosine Triphosphate), the energy currency of the cell. It's important not to confuse respiration with breathing, which is just the physical process of inhaling and exhaling air.

The first step in cellular respiration is the breakdown of glucose, a six-carbon molecule, into a three-carbon molecule called pyruvate. This process happens in the cytoplasm and is common to all types of respiration.

The fate of pyruvate depends on the presence or absence of oxygen:

The accumulation of lactic acid in muscle cells during vigorous physical activity is the reason we experience muscle cramps.

Respiration in Human Beings

The human respiratory system is designed for efficient gas exchange. Let's trace the path of air:

1. Nostrils: Air enters the body through the nostrils, where it is filtered by fine hairs and mucus.
2. Pharynx and Larynx: The air then passes through the pharynx (throat) and the larynx (voice box) into the trachea.
3. Trachea (Windpipe): The trachea is supported by rings of cartilage which prevent it from collapsing. It branches into two smaller tubes.
4. Bronchi: These two tubes, called bronchi (singular: bronchus), enter each lung.
5. Bronchioles and Alveoli: Inside the lungs, the bronchi divide into smaller and smaller tubes called bronchioles, which finally terminate in balloon-like structures called alveoli.

The alveoli are the primary sites of gas exchange. They have very thin walls and are surrounded by a dense network of blood capillaries. Oxygen from the inhaled air diffuses across the alveolar and capillary walls into the blood. In the blood, oxygen binds to a respiratory pigment called haemoglobin in red blood cells and is transported to all the cells of the body. Simultaneously, carbon dioxide, a waste product from the body's cells, is transported by the blood back to the lungs. It diffuses from the capillaries into the alveoli and is then exhaled.

Transportation

In complex multicellular organisms like humans, simple diffusion is not sufficient to meet the requirements of all cells for food, oxygen, and waste removal. A specialized transport system is required. This process is called transportation or circulation.

Transportation in Human Beings

The human circulatory system is responsible for this vital task. It consists of the heart, blood, and blood vessels.

Blood

Blood is a fluid connective tissue. It has two main components:

• Plasma: A pale-yellow fluid matrix that transports food, carbon dioxide, and nitrogenous wastes in dissolved form.
• Blood Cells: Suspended in the plasma are three types of cells:
  • Red Blood Cells (RBCs): These contain haemoglobin and are responsible for transporting oxygen.
  • White Blood Cells (WBCs): These are the soldiers of the body, fighting against infection and disease.
  • Platelets: These cell fragments are responsible for blood clotting, which prevents excessive blood loss during injury.

The Heart

The heart is a muscular organ, about the size of a fist, that acts as a pump. The human heart has four chambers to prevent the mixing of oxygen-rich and carbon dioxide-rich blood:

• Two upper chambers called atria (singular: atrium).
• Two lower chambers called ventricles.

This separation allows for a highly efficient supply of oxygen to the body. This is particularly important for warm-blooded animals like humans, who need more energy to maintain their body temperature.

Path of Blood Flow (Double Circulation):

Blood passes through the human heart twice for each complete circuit of the body. This is known as double circulation.

1. Pulmonary Circulation (To the lungs): Deoxygenated (CO₂-rich) blood from the body enters the right atrium. It is then pumped into the right ventricle, which pumps it to the lungs via the pulmonary artery for oxygenation.
2. Systemic Circulation (To the body): Oxygenated blood from the lungs returns to the left atrium via the pulmonary vein. It is then pumped into the left ventricle, the strongest chamber, which pumps it through the aorta to the rest of the body.

Valves between the atria and ventricles, and between the ventricles and major arteries, ensure that blood flows in only one direction.

Blood Vessels

There are three main types of blood vessels:

• Arteries: Carry blood away from the heart. They have thick, elastic walls because the blood here is under high pressure. They carry oxygenated blood (except for the pulmonary artery).
• Veins: Carry blood towards the heart. They have thinner walls as the blood pressure is lower. They also have valves to prevent the backflow of blood. They carry deoxygenated blood (except for the pulmonary vein).
• Capillaries: These are extremely narrow, thin-walled vessels that form a network throughout the body tissues. They are the sites where the exchange of materials (oxygen, nutrients, CO₂) between the blood and the cells takes place.

Transportation in Plants

Plants also have a transport system, but it is less elaborate than in animals. They need to transport water and minerals from the roots to the leaves, and food (glucose) from the leaves to other parts. This is done by two types of conducting tissues:

• Xylem: This tissue transports water and dissolved minerals from the roots to all other parts of the plant. The movement is always upwards. This upward movement of water is driven by a process called transpiration. Transpiration is the loss of water in the form of vapour from the aerial parts of the plant (mainly stomata). This creates a suction pull, known as transpiration pull, which draws water up the xylem vessels.
• Phloem: This tissue transports the food (sugars) produced during photosynthesis from the leaves to other parts of the plant, such as roots, fruits, and seeds, for use or storage. This process is called translocation, and it requires energy (in the form of ATP). The transport in phloem can be in any direction, depending on the plant's needs.

Excretion

During various metabolic activities, organisms produce waste products that can be toxic if allowed to accumulate. Excretion is the biological process involved in the removal of these harmful metabolic wastes from the body.

Excretion in Human Beings

The main nitrogenous waste product in humans is urea. The human excretory system consists of:

• A pair of kidneys
• A pair of ureters
• A urinary bladder
• A urethra

The kidneys are bean-shaped organs located in the abdomen. They are the primary filtration units. Each kidney is made up of millions of tiny filtration units called nephrons. The nephron is the structural and functional unit of the kidney.

Structure and Function of a Nephron

A nephron consists of a cup-shaped structure called Bowman's capsule at its upper end, which contains a bundle of blood capillaries called the glomerulus. The Bowman's capsule extends into a long, coiled tubule.

Urine Formation involves three steps:

1. Glomerular Filtration (Ultrafiltration): Blood enters the glomerulus under high pressure. This pressure forces water, glucose, amino acids, salts, and urea from the blood into the Bowman's capsule. This filtrate is called the glomerular filtrate.
2. Tubular Reabsorption (Selective Reabsorption): As the filtrate passes through the long tubule, useful substances like glucose, amino acids, most salts, and a major amount of water are selectively reabsorbed back into the blood.
3. Tubular Secretion: Certain waste products like potassium ions, ammonia, and creatinine, which were not filtered earlier, are actively secreted from the blood into the filtrate in the tubule.

The fluid remaining after these processes is urine. The urine from all nephrons is collected in the collecting duct, passed through the ureters into the urinary bladder where it is stored, and finally expelled from the body through the urethra.

Excretion in Plants

Plants use different strategies for excretion compared to animals:

• Oxygen, a by-product of photosynthesis, is removed through stomata.
• Excess water is removed by transpiration.
• Many plant waste products are stored in cellular vacuoles.
• Waste products may be stored in leaves that later fall off.
• Other waste products are stored as resins and gums, especially in old xylem.
• Plants also excrete some waste substances into the soil around them.

Important Questions and Answers

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

Answer: The key differences are:

2. Describe the structure and functioning of nephrons.

Answer: The nephron is the structural and functional unit of the kidney. Each kidney contains about a million nephrons.

Structure: A nephron has two main parts: the renal corpuscle and the renal tubule.

• Renal Corpuscle: This consists of a cup-shaped structure called the Bowman's capsule which encloses a dense network of blood capillaries known as the glomerulus.
• Renal Tubule: This is a long, convoluted tubule that emerges from the Bowman's capsule. It has three parts: the proximal convoluted tubule (PCT), the loop of Henle, and the distal convoluted tubule (DCT), which finally opens into a collecting duct.

Functioning (Urine Formation):

1. Ultrafiltration: Blood enters the glomerulus under high pressure, forcing water and small solutes (glucose, salts, urea, amino acids) through the capillary walls into the Bowman's capsule. This initial fluid is called the glomerular filtrate.
2. Selective Reabsorption: As this filtrate passes through the renal tubule, the body reclaims useful substances. Glucose, amino acids, most salts, and a significant amount of water are reabsorbed back into the blood in the surrounding capillaries. The amount of water reabsorbed depends on the body's hydration level.
3. Tubular Secretion: The walls of the tubule actively secrete certain waste products like potassium ions and ammonia from the blood into the filtrate. This final fluid is urine.

The urine is then passed into the collecting duct, which leads to the ureter and subsequently to the urinary bladder.

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

Answer: The breakdown of glucose to provide energy occurs in several steps. The first step is the breakdown of glucose (a 6-carbon molecule) into pyruvate (a 3-carbon molecule). This process, called glycolysis, occurs in the cytoplasm.

The subsequent pathway depends on the availability of oxygen:

• Aerobic Respiration (Presence of Oxygen): In organisms like humans, the pyruvate enters the mitochondria. Here, it is completely broken down into carbon dioxide and water, releasing a large amount of energy (around 38 ATP molecules).
  Equation: Pyruvate --(In mitochondria, in presence of O₂)--> CO₂ + H₂O + Energy
• Anaerobic Respiration (Absence of Oxygen):
  • In Yeast (Fermentation): Pyruvate is converted into ethanol (a 2-carbon compound) and carbon dioxide. This process releases a small amount of energy (2 ATP).
    Equation: Pyruvate --(In cytoplasm, in absence of O₂)--> Ethanol + CO₂ + Energy
  • In Human Muscle Cells (During intense exercise): When there is a lack of oxygen, pyruvate is converted into lactic acid (a 3-carbon compound). This also releases a small amount of energy (2 ATP) and the buildup of lactic acid causes muscle cramps.
    Equation: Pyruvate --(In cytoplasm, lack of O₂)--> Lactic Acid + Energy

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

Answer: The transport system in human beings is the circulatory system. Its main components are the heart, blood, and blood vessels.

Functions of the Components:

• Heart: The heart is a muscular pumping organ. Its function is to pump blood to all parts of the body. It pumps deoxygenated blood to the lungs for oxygenation and pumps oxygenated blood from the lungs to the rest of the body. Its four-chambered structure ensures the separation of oxygenated and deoxygenated blood for efficient oxygen supply.
• Blood: Blood is the medium of transport. It is a fluid connective tissue with several functions:
  • Transports Oxygen: Red blood cells (RBCs) with haemoglobin transport oxygen from the lungs to the body tissues.
  • Transports Carbon Dioxide: It carries CO₂ from the tissues back to the lungs.
  • Transports Nutrients: It carries digested food from the small intestine to all cells.
  • Transports Waste: It transports excretory products like urea from the liver to the kidneys.
  • Defence: White blood cells (WBCs) fight infection and protect the body from diseases.
  • Clotting: Platelets help in clotting blood at the site of an injury to prevent excessive bleeding.
  • Regulation: It helps regulate body temperature and pH.
• Blood Vessels (Arteries, Veins, Capillaries): These are a network of tubes through which blood flows.
  • Arteries: Carry high-pressure blood away from the heart to various organs.
  • Veins: Collect low-pressure blood from various organs and bring it back to the heart.
  • Capillaries: These are the finest vessels that connect arteries and veins. Their thin walls allow for the exchange of gases, nutrients, and waste products between the blood and body cells.

Chapter Summary

Here are the key takeaways from our exploration of Life Processes:

• Life Processes are the essential functions that maintain life, including nutrition, respiration, transportation, and excretion.
• Nutrition is the process of obtaining and utilizing food. It can be autotrophic (organisms make their own food, e.g., plants via photosynthesis) or heterotrophic (organisms depend on others for food, e.g., animals).
• The human digestive system breaks down complex food into simple, absorbable substances through the action of various enzymes in the alimentary canal.
• Respiration is the process of releasing energy from food. It can be aerobic (with oxygen, releasing more energy) or anaerobic (without oxygen, releasing less energy).
• The human respiratory system facilitates the exchange of oxygen and carbon dioxide in the lungs, specifically in the alveoli.
• Transportation in humans is carried out by the circulatory system, which consists of the heart (a four-chambered pump), blood (the transport medium), and blood vessels (arteries, veins, capillaries).
• Humans have double circulation, ensuring efficient oxygen supply to the body.
• In plants, xylem transports water and minerals, while phloem translocates food.
• Excretion is the removal of metabolic waste. In humans, the main excretory organs are the kidneys, whose functional units are the nephrons.
• Urine is formed in the nephrons through the processes of ultrafiltration, selective reabsorption, and tubular secretion.