Life Processes – Class 10 Science Chapter 5 Notes & NCERT PDF

Class 10ScienceChapter 5NCERT book: Science - Class 10

Notes and a simple summary of Chapter 5 of the NCERT Class 10 Science book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

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Chapter 5: Life Processes

Introduction

How do we tell whether something is alive? Visible movement is the easiest clue, but a sleeping dog or a tree is alive even when it does not move. The chapter explains that living things are highly organised structures, and this order breaks down over time unless it is constantly repaired. Repair and maintenance need energy and raw materials, which come from outside the body. The processes that together keep an organism alive are called life processes — nutrition, respiration, transportation and excretion.

Maintenance of life requires processes like nutrition, respiration, transport of materials within the body and excretion of waste products.

Key Concepts

1. Nutrition

Autotrophic nutrition — organisms such as green plants and some bacteria take in simple inorganic substances (carbon dioxide and water) and use sunlight to make carbohydrates. This is photosynthesis:

6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O (in the presence of sunlight and chlorophyll)

Photosynthesis happens in three steps:

Absorption of light energy by chlorophyll.

Conversion of light energy to chemical energy and splitting of water into hydrogen and oxygen.

Reduction of carbon dioxide to carbohydrates.

Excess carbohydrate is stored as starch. Gas exchange happens through stomata, tiny pores on leaves whose opening and closing is controlled by guard cells — they swell when water flows in (pore opens) and shrink when water is lost (pore closes). Desert plants take in CO₂ at night and store it as an intermediate, using it in the day. Plants take other raw materials such as nitrogen, phosphorus, iron and magnesium from the soil; nitrogen is taken as nitrates/nitrites or as compounds made by bacteria from atmospheric nitrogen.

Heterotrophic nutrition — organisms depend on food made by others. Some break food down outside the body and absorb it (fungi like bread moulds, yeast, mushrooms); others take food in whole and digest it inside (e.g., Amoeba engulfs food with pseudopodia into a food vacuole; Paramecium uses cilia to move food to a specific spot). Parasites such as cuscuta, ticks, lice, leeches and tapeworms feed on a host without killing it.

Nutrition in human beings follows the alimentary canal:

Mouth — teeth chew the food; saliva contains salivary amylase, which breaks starch into simple sugar.

Oesophagus — food moves by rhythmic muscle contractions called peristalsis.

Stomach — gastric glands release hydrochloric acid (creates acidic medium for pepsin, which digests protein), pepsin and mucus (protects the stomach lining from the acid).

Small intestine — the longest part; receives bile from the liver (makes the medium alkaline and emulsifies fats into small globules) and pancreatic juice containing trypsin (proteins) and lipase (emulsified fats). Intestinal juice finally converts proteins to amino acids, complex carbohydrates to glucose and fats to fatty acids and glycerol. Finger-like villi increase the surface area for absorption and are richly supplied with blood vessels.

Large intestine — absorbs more water; the rest is removed through the anus, regulated by the anal sphincter.

2. Respiration

Food is broken down in cells to release energy. The first step, in the cytoplasm, splits glucose (6-carbon) into pyruvate (3-carbon). Then:

Anaerobic respiration (yeast) — pyruvate → ethanol + carbon dioxide + energy (fermentation).

Aerobic respiration — in the mitochondria, pyruvate → carbon dioxide + water + energy. This releases much more energy.

Lack of oxygen in muscle cells — pyruvate → lactic acid + energy; build-up of lactic acid causes cramps.

The energy released is used to make ATP (adenosine triphosphate), the energy currency of the cell. When the terminal phosphate of ATP is broken using water, about 30.5 kJ/mol of energy is released.

Plants exchange gases through stomata and lenticels by diffusion. Aquatic animals get oxygen dissolved in water through gills; since the amount of dissolved oxygen is low, they breathe much faster than terrestrial animals.

Human respiratory system: air enters through the nostrils (fine hairs and mucus filter it) → pharynx → trachea (rings of cartilage stop it from collapsing) → bronchi → bronchioles → balloon-like alveoli. Alveoli give a huge surface for gas exchange — spread out, the alveolar surface would cover about 80 m². Breathing in: ribs lift up, the diaphragm flattens and the chest cavity enlarges. Haemoglobin in red blood cells carries oxygen; carbon dioxide is carried mostly dissolved in blood.

3. Transportation

In human beings, blood is a fluid connective tissue: plasma carries food, CO₂ and nitrogenous wastes; red blood cells carry oxygen; platelets plug leaks by clotting blood.

The heart has four chambers. Oxygen-rich blood from the lungs enters the left atrium → left ventricle → pumped to the body. Deoxygenated blood returns to the right atrium → right ventricle → pumped to the lungs. Valves prevent backflow.

Blood passes through the heart twice in one cycle — double circulation — keeping oxygenated and deoxygenated blood separate, which is important for birds and mammals that need a lot of energy to maintain body temperature. Fish have a two-chambered heart; amphibians and many reptiles have three chambers.

Arteries carry blood away from the heart and have thick, elastic walls; veins bring blood back and have valves; capillaries have walls one cell thick.

Blood pressure: normal systolic is about 120 mm of Hg and diastolic about 80 mm of Hg, measured with a sphygmomanometer. High blood pressure (hypertension) can rupture arteries.

Lymph (tissue fluid) carries digested and absorbed fat from the intestine and drains excess fluid back into blood.

In plants:

Xylem moves water and minerals from roots to leaves. Root cells take up ions, creating a concentration difference that draws water in. Transpiration — loss of water vapour from aerial parts — creates a suction that pulls water up and also helps regulate temperature.

Phloem moves food (sucrose) from leaves to other parts — translocation. This uses energy from ATP; sucrose is loaded into phloem, osmotic pressure rises, and material moves to regions of lower pressure.

4. Excretion

Unicellular organisms remove wastes by diffusion. In humans, the excretory system has a pair of kidneys, a pair of ureters, a urinary bladder and a urethra. Each kidney has many filtration units called nephrons. In a nephron, a cup-shaped Bowman's capsule surrounds a cluster of capillaries (glomerulus) where blood is filtered; useful substances like glucose, amino acids, salts and a major amount of water are selectively reabsorbed in the tubule. Normally the initial filtrate is about 180 L daily, but only a litre or two is excreted as urine. When kidneys fail, an artificial kidney (haemodialysis) removes nitrogenous wastes from blood — but, unlike the kidney, it involves no reabsorption.

Plants get rid of wastes by releasing oxygen and water vapour, storing wastes in cell vacuoles or in leaves that fall off, as resins and gums in old xylem, or by releasing some wastes into the soil.

Diagrams to Draw (described in words)

Human alimentary canal: mouth → oesophagus → stomach (J-shaped) → small intestine (coiled) → large intestine → anus, with liver, gall bladder and pancreas labelled.

Section of the human heart: four chambers, with the left ventricle wall thickest; label vena cava, pulmonary artery, pulmonary veins and aorta.

Human respiratory system: nasal passage, pharynx, larynx, trachea, bronchi, lungs, alveolar sacs, diaphragm.

Human excretory system and nephron: kidneys, ureters, bladder, urethra; nephron showing Bowman's capsule, glomerulus and tubule.

Stomata: open and closed pore with two bean-shaped guard cells.

Activities in the Chapter

Activity 5.1 — A variegated leaf (money plant or croton), destarched in the dark for three days and then kept in sunlight, is boiled, decolourised in alcohol and tested with iodine. Only the areas that were green turn blue-black — chlorophyll is essential for photosynthesis.

Activity 5.2 — Two destarched potted plants are covered with bell jars; one has potassium hydroxide, which absorbs CO₂. The leaf from that plant shows no starch — CO₂ is needed for photosynthesis.

Activity 5.4 — Air breathed out turns lime water milky faster than air pumped with a syringe — exhaled air has more CO₂.

Activity 5.5 — Yeast in sugar solution produces a gas that turns lime water milky — fermentation releases CO₂.

Activity 5.8 — A pot with a plant and a pot with a stick are covered with plastic; droplets appear only with the plant — transpiration.

Board Exam Focus

Differences between aerobic and anaerobic respiration; the three pathways of breaking down glucose.

Role of HCl, bile, trypsin and lipase; function of villi.

Double circulation and why it is needed.

Structure and working of a nephron; why urine volume is far less than filtrate.

Xylem vs phloem transport.

Key Terms

Autotroph (स्वपोषी) — makes its own food

Heterotroph (परपोषी) — depends on others for food

Stomata (रंध्र) — pores on leaves for gas exchange

Peristalsis (क्रमाकुंचन) — wave-like muscle contractions moving food

Emulsification (पायसीकरण) — breaking fat into tiny droplets

Villi (दीर्घरोम) — finger-like projections in small intestine

Fermentation (किण्वन) — anaerobic respiration in yeast

Alveoli (कूपिकाएँ) — air sacs in lungs

Haemoglobin (हीमोग्लोबिन) — oxygen-carrying pigment

Double circulation (दोहरा परिसंचरण) — blood passes through heart twice per cycle

Transpiration (वाष्पोत्सर्जन) — loss of water vapour from leaves

Translocation (स्थानांतरण) — transport of food in phloem

Nephron (वृक्काणु) — filtration unit of kidney

Haemodialysis (अपोहन) — artificial filtering of blood

Common Mistakes

Saying the first step of respiration happens in mitochondria — glucose → pyruvate happens in the cytoplasm.

Thinking bile is an enzyme — bile has no enzyme; it emulsifies fats and makes the medium alkaline.

Mixing up arteries and veins — arteries carry blood away from the heart (pulmonary artery carries deoxygenated blood).

Writing that all the filtrate becomes urine — most of the ~180 L is reabsorbed.

Confusing transpiration (water movement, xylem) with translocation (food movement, phloem).

💡 Key Learning Points

✓Nutrition, respiration, transportation and excretion together maintain life by supplying energy and raw materials and removing wastes.
✓Photosynthesis needs chlorophyll, sunlight, CO₂ and water; plants exchange gases through stomata controlled by guard cells.
✓Glucose is first broken into pyruvate in the cytoplasm; aerobic respiration in mitochondria releases far more energy than anaerobic pathways.
✓The four-chambered human heart gives double circulation; xylem carries water and minerals while phloem translocates food.
✓Nephrons filter about 180 L of blood filtrate daily but reabsorb most of it, so only 1–2 L of urine is excreted.

👨‍🏫 Teaching Tips

→Do Activity 5.1 with a croton leaf and let students compare the iodine-stained leaf with their tracing of the green areas.
→Use a flow chart on the board for the three pathways of breakdown of glucose (yeast, muscle, mitochondria) and have students fill in products.
→Draw the heart as a simple four-box diagram first, then trace a single drop of blood through double circulation with coloured chalk.
→Set up the plant-and-stick transpiration pots in the morning and check for droplets after lunch.
→Give each group one part of the alimentary canal to present: what enters, which juice acts, what leaves.
→Use the 180 L versus 1–2 L figure to start a discussion on why reabsorption is essential.
→Practise the five board diagrams with timed labelling drills.

📋 Assessment Questions

Why is chlorophyll essential for photosynthesis? Describe an activity to prove it.
Compare aerobic respiration, anaerobic respiration in yeast and respiration in muscle cells during lack of oxygen.
Explain double circulation and why it is important for mammals and birds.
Describe the structure of a nephron and explain how urine is formed.
How are water and food transported in plants?

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