CBSE Class 10 Science Life Processes Notes

1.  Nutrition

Nutrition is the process by which organisms obtain and utilise food for energy, growth, and repair. There are two main modes:

•         Autotrophic nutrition: Organisms make their own food using inorganic raw materials (CO2, water) and an energy source (sunlight or chemicals). Example: Plants, algae, cyanobacteria.

•         Heterotrophic nutrition: Organisms cannot make their own food and depend on other organisms. Example: Animals, fungi, most bacteria.

Autotrophic Nutrition: Photosynthesis

Photosynthesis is the process by which green plants use sunlight, carbon dioxide, and water to prepare their own food (glucose) in the presence of chlorophyll.

6CO2 + 6H2O  --(Sunlight, Chlorophyll)-->  C6H12O6 + 6O2

Photosynthesis occurs in two stages:

1.       Light reaction (in thylakoids of chloroplast): Light energy splits water molecules (photolysis) into H+ ions, electrons, and O2. ATP and NADPH are produced. O2 is released as a byproduct.

2.       Dark reaction / Calvin cycle (in stroma): CO2 is fixed using ATP and NADPH to produce glucose. Does not require direct light.

•         Raw materials: CO2 (from air via stomata), water (from soil via roots), sunlight, chlorophyll.

•         Site: Chloroplasts (mainly in mesophyll cells of leaves).

•         Chlorophyll: The green pigment that absorbs sunlight (mainly red and blue wavelengths, reflects green).

•         Stomata: Tiny pores on leaf surface for gas exchange (CO2 in, O2 out). Opened and closed by guard cells.

Photosynthesis produces glucose which is later converted to starch for storage. The O2 released comes from water (H2O), not from CO2. This was proved by isotope experiments.

Heterotrophic Nutrition in Animals

Animals cannot make their own food. They depend on plants or other animals. Heterotrophic nutrition involves ingestion, digestion, absorption, assimilation, and egestion.

•         Holozoic nutrition: Solid food is ingested and digested internally (e.g., humans, amoeba).

•         Saprophytic nutrition: Organisms feed on dead and decaying matter (e.g., fungi, some bacteria).

•         Parasitic nutrition: Organisms feed on a living host organism (e.g., tapeworm, Cuscuta plant).

Nutrition in Amoeba

• Amoeba is a unicellular organism that shows holozoic nutrition using a process called phagocytosis.

• Amoeba detects food (bacteria or algae) and extends pseudopodia (false feet) around it.

• Pseudopodia engulf the food particle, forming a food vacuole around it.

• Digestive enzymes secreted into the food vacuole break down the food into simpler molecules.

• Digested nutrients are absorbed into the cytoplasm. Undigested waste is expelled by exocytosis.

Human Digestive System

The human digestive system processes food through a series of organs, breaking it down into absorbable nutrients using mechanical and chemical digestion.

The small intestine is the main site of digestion and absorption. Its inner surface has finger-like projections called villi that increase surface area for absorption. Each villus has blood capillaries and lymph vessels.

The path of food: Mouth -> Oesophagus -> Stomach -> Small Intestine -> Large Intestine -> Rectum -> Anus

Starch: Salivary amylase -> Maltose -> Maltase -> Glucose

Proteins: Pepsin (stomach) -> Peptides -> Trypsin + Peptidase -> Amino acids

Fats: Bile (emulsification) -> Lipase -> Fatty acids + Glycerol

2.  Respiration

Respiration is the biochemical process by which cells break down organic molecules (glucose) to release energy in the form of ATP. The energy is used for all cellular activities. Respiration occurs in all living cells.

Glucose + O2  ->  CO2 + H2O + Energy (ATP)   [Aerobic]

Types of Respiration

Aerobic:   C6H12O6 + 6O2  ->  6CO2 + 6H2O + 38 ATP

Anaerobic (yeast): C6H12O6  ->  2C2H5OH + 2CO2 + 2 ATP

Anaerobic (muscle): C6H12O6  ->  2C3H6O3 (Lactic acid) + 2 ATP

Muscle cramps during intense exercise occur because lactic acid accumulates in muscles (anaerobic respiration). Resting and deep breathing help clear the lactic acid debt.

Glycolysis

Glycolysis is the first step of both aerobic and anaerobic respiration. It occurs in the cytoplasm and does not require oxygen.

Glucose (6C)  ->  2 Pyruvate (3C each)  +  2 ATP  +  2 NADH

Pyruvate then enters either aerobic pathway (mitochondria) or anaerobic pathway (cytoplasm) depending on oxygen availability.

Human Respiratory System

In humans, breathing (inhalation and exhalation) brings oxygen into the lungs and removes carbon dioxide. Gas exchange occurs in the alveoli.

•         Nasal cavity: Filters, warms, and moistens incoming air. Hairs trap dust and bacteria.

•         Trachea (windpipe): Carries air to lungs. Lined with cilia and mucus to trap particles.

•         Bronchi and bronchioles: Trachea branches into two bronchi, then further into bronchioles, ending in alveoli.

•         Alveoli: Tiny air sacs with very thin walls (one cell thick) and rich blood supply. Site of gas exchange.

•         Diaphragm: Muscular partition below lungs. Contracts during inhalation (dome flattens, volume increases).

Alveoli are the functional units of lungs. They have extremely thin walls, moist surface, and rich capillary network — all adaptations for efficient gas exchange by diffusion.

Respiration in Plants

Plants respire continuously (24 hours). During the day, the CO2 released in respiration is used in photosynthesis, so net gas exchange appears to only release O2.

•         Gas exchange in plants: Through stomata in leaves, lenticels in stems, and root hair cells.

•         No specialised respiratory organ: Each plant cell exchanges gas directly with its environment. Diffusion distances are short.

3.  Transportation

Transportation in Plants

Plants have two conducting tissues for transportation: xylem for water and minerals, and phloem for food (sucrose and amino acids).

Water Movement in Plants

1.       Absorption: Root hair cells absorb water from soil by osmosis. Minerals are absorbed by active transport.

2.       Root pressure: Water moves from root hair cells into xylem by osmosis, creating a pressure that pushes water upward.

3.       Transpiration pull: Water evaporating from leaves (transpiration) creates a suction force that pulls water up from roots through xylem. This is the main force for water transport in tall trees.

4.       Translocation: Food made in leaves (source) is transported to all growing parts and storage organs (sinks) through phloem.

Transpiration pull is the main driving force for upward movement of water in plants. Water molecules form a continuous column in xylem due to cohesion (water-water attraction) and adhesion (water-xylem wall attraction).

Human Circulatory System

The human circulatory system consists of the heart, blood vessels (arteries, veins, capillaries), and blood. It transports oxygen, nutrients, hormones, and waste products.

•         Heart: A muscular four-chambered pump (2 atria + 2 ventricles). Right side pumps deoxygenated blood to lungs; left side pumps oxygenated blood to body.

•         Arteries: Carry blood away from the heart. Thick, elastic walls. Carry oxygenated blood (except pulmonary artery).

•         Veins: Carry blood towards the heart. Thinner walls; have valves to prevent backflow. Carry deoxygenated blood (except pulmonary vein).

•         Capillaries: Extremely thin walls (one cell thick). Site of exchange of gases, nutrients, and waste between blood and tissues.

Double Circulation: Pulmonary circulation (heart <-> lungs) + Systemic circulation (heart <-> body)

Double circulation means blood passes through the heart twice per complete circuit of the body. This keeps oxygenated and deoxygenated blood completely separate, allowing high-pressure delivery of oxygen to all body tissues.

Blood and Its Components

Lymphatic System

The lymphatic system returns tissue fluid (lymph) back to the bloodstream. Lymph is similar to plasma but contains fewer proteins and no RBCs. Lymph nodes filter lymph and contain white blood cells that fight infection.

4.  Excretion

Excretion is the process of removing metabolic waste products from the body. The main nitrogenous waste product in humans is urea (formed in the liver from ammonia). Ammonia (fish), Urea (mammals), Uric acid (birds, reptiles, insects).

Human Excretory System

The human excretory system consists of two kidneys, two ureters, a urinary bladder, and the urethra.

•         Kidneys: Bean-shaped organs that filter blood and produce urine. Each kidney contains about 1 million nephrons.

•         Ureters: Carry urine from kidneys to the urinary bladder.

•         Urinary bladder: Stores urine until it is expelled.

•         Urethra: Tube through which urine is expelled from the body.

Structure and Function of Nephron

The nephron is the structural and functional unit of the kidney. Urine formation involves three processes:

1. Glomerular filtration: Blood is filtered under high pressure in the glomerulus (a network of capillaries). Small molecules (water, glucose, amino acids, urea, salts) pass into the Bowman's capsule as glomerular filtrate. Blood cells and large proteins stay in blood.

2. Tubular reabsorption: As the filtrate flows through the renal tubule, useful substances (glucose, amino acids, salts, water) are selectively reabsorbed back into the blood. This is mostly active transport.

3. Secretion: Some additional waste substances (H+ ions, potassium ions, certain drugs) are secreted from the blood into the tubule to be eliminated.

4. 
   

Blood -> Glomerulus -> Filtration -> Bowman's capsule -> Tubule -> Reabsorption -> Collecting duct -> Ureter -> Bladder -> Urine

Glomerulus filters about 180 litres of blood per day, but only about 1.5 litres of urine is produced. The remaining ~178.5 litres is reabsorbed back into the blood — showing how efficient tubular reabsorption is.

Excretion in Plants

Plants do not have a specialised excretory system. They get rid of waste products by the following methods:

•         CO2 and O2 exchange: CO2 (waste of respiration) exits through stomata and lenticels. O2 (waste of photosynthesis) exits through stomata.

•         Excess water: Released as water vapour through transpiration from stomata.

•         Stored wastes: Some waste products are stored in leaves, bark, and old xylem (resin, gum, latex, tannins). When leaves fall in autumn, stored wastes are removed.

•         Excreted into soil: Some plants excrete waste into the surrounding soil (e.g., allelopathic chemicals).

Plants are much more efficient than animals at converting waste into useful products. CO2 is reused in photosynthesis, and many stored waste products (resins, gums, latex) have commercial value.

5.  Quick Comparison: Life Processes in Plants vs Humans

6.  Key Definitions and Terms

•         Autotrophic nutrition: Organisms that prepare their own food using simple inorganic substances and an external energy source.

•         Heterotrophic nutrition: Organisms that obtain food by consuming other organisms or organic matter.

•         Photosynthesis: Process by which green plants convert light energy into chemical energy (glucose) using CO2 and water.

•         Stomata: Pores on leaf surface for gas exchange; controlled by guard cells.

•         Transpiration: Evaporation of water from aerial parts of plants (mainly through stomata).

•         Aerobic respiration: Breakdown of glucose in presence of O2 to release maximum energy (38 ATP).

•         Anaerobic respiration: Breakdown of glucose without O2; produces less energy (2 ATP); products are ethanol/lactic acid.

•         Translocation: Transport of food (sucrose) from leaves (source) to other plant parts (sink) through phloem.

•         Double circulation: Blood passes through the heart twice per circuit: once for pulmonary and once for systemic circulation.

•         Nephron: The structural and functional unit of the kidney; responsible for filtration, reabsorption, and secretion.

•         Glomerulus: Tuft of capillaries in the Bowman's capsule where blood filtration under pressure occurs.

•         Osmoregulation: Regulation of water and salt balance in the body (function of kidneys).

7.  Board Exam Practice Questions

These questions cover all types from CBSE Class 10 Science (Chapter 6) board examinations.

1 Mark Questions

1.       Name the raw materials required for photosynthesis.

2.       What is the structural and functional unit of the kidney?

3.       What is the role of HCl in the stomach?

4.       Name the tissue responsible for transport of food in plants.

5.       What is double circulation? Name one animal that shows it.

3 Mark Questions

1.       Explain the process of photosynthesis. Write the overall chemical equation and name the two stages.

2.       Compare aerobic and anaerobic respiration under four headings: oxygen requirement, end products, energy released, and example organisms.

3.       Describe the role of xylem and phloem in transportation in plants. What is the driving force for each?

4.       Explain the structure of the nephron and describe the three processes involved in urine formation.

5 Mark Questions

1.       Draw a labelled diagram of the human digestive system. Name the enzyme secreted at each stage and state the substrate and product of each enzyme action.

2.       Explain double circulation in humans. Why is it necessary? Describe the path of blood through the pulmonary and systemic circulation separately.

3.       Compare life processes (nutrition, respiration, transportation, excretion) in plants and humans under separate headings for each process.