LIFE PROCESSES
Class 10 Science | Chapter Notes – Part 1
Concepts • Important Diagrams • Flowcharts • Quick Revision
1. Introduction to Life Processes
Earth is the only known planet to support life. Living organisms carry out certain basic activities to maintain life, whether they are moving, resting or sleeping. These maintenance activities are called life processes.
Obtaining or preparing food and using it for energy, growth and repair.
Breaking down food to release energy.
Moving materials from one part of an organism to another.
Removing waste materials from the body.
2. Nutrition
Nutrition is the process by which living organisms procure food or synthesise it and convert it into simple absorbable forms through a series of biochemical processes.
A nutrient is a substance obtained from the surroundings and used as a source of energy and raw materials for growth and repair.
Two basic modes of nutrition
Organisms meet their carbon and energy needs through photosynthesis. Carbon dioxide and water are converted into carbohydrates using light energy and chlorophyll.
Examples: Green plants.
Organisms cannot prepare their own food and depend on plants, animals or dead and decaying organic matter.
Examples: Animals and fungi.
3. Photosynthesis
Definition: Photosynthesis is the synthesis of organic compounds (carbohydrates) from carbon dioxide and water using radiant or solar energy absorbed by chlorophyll molecules.
Carbon dioxide + Water —(Sunlight and chlorophyll)→ Carbohydrates + Oxygen
Main events of photosynthesis
- Absorption of light energy by chlorophyll.
- Conversion of light energy into chemical energy and splitting of water molecules into hydrogen and oxygen.
- Reduction of carbon dioxide to carbohydrates.
These stages do not have to occur directly one after another. Some desert plants absorb carbon dioxide at night and use the energy captured by chlorophyll during the day.
4. Chloroplasts, Stomata & Starch Test
Chloroplasts are green structures inside some cells and contain chlorophyll. A large amount of gas exchange in leaves occurs through tiny openings called stomata.
Experiment: Test a leaf for starch
- Take a potted plant with variegated leaves, such as money plant or crotons.
- Keep the plant in a dark room for three days to deplete starch reserves.
- Expose the plant to sunlight for about six hours.
- Pluck a leaf, mark its green areas and trace them on a sheet of paper.
- Boil the leaf in water and then immerse it in alcohol.
- Heat the alcohol in a water bath until it boils.
- Observe colour changes in the leaf and solution.
- Dip the leaf in dilute iodine solution and compare the colours with the initial tracing.
- Draw conclusions about starch presence in different leaf areas.
5. Heterotrophic Nutrition
Heterotrophic organisms cannot prepare their own food. They depend on plants, animals or dead and decaying organic materials for food. Saprophytes derive nourishment from dead and decaying matter.
Food is obtained from dead and decaying matter. Examples mentioned in the notes include fungi such as bread mould, yeast and mushrooms.
An organism obtains food from a host. Examples: Cuscuta, ticks, lice, leeches and tapeworms.
Some organisms take in food and break it down internally, according to their body design and function.
Some organisms break down food outside the body before absorbing it, as in the examples of fungi described in the notes.
6. Holozoic Nutrition
Holozoic nutrition is a mode of nutrition that involves swallowing solid food material.
| Stage | Meaning |
|---|---|
| Ingestion | Taking food into the body. |
| Digestion | Breaking complex food into simpler substances. |
| Absorption | Passage of digested nutrients into the body fluids. |
| Assimilation | Use of absorbed food by body cells. |
| Egestion | Removal of undigested food. |
7. Nutrition in Humans – Human Digestive System
In humans, the digestive system consists of a long alimentary canal and digestive glands. The alimentary canal includes the mouth, oesophagus, stomach, small intestine and large intestine.
Journey of food through the alimentary canal
Digestion in the mouth
- Food is crushed by teeth and mixed with saliva secreted by salivary glands.
- Saliva contains salivary amylase, which breaks down starch into simple sugar.
- The swallowed food mass is called a bolus.
Peristaltic movement
Rhythmic contraction and relaxation of muscles in the wall of the alimentary canal push food forward. These movements are called peristaltic movements.
Digestion in the stomach
- The stomach is a large, J-shaped hollow organ. Its muscular walls mix food with gastric secretions.
- Gastric glands secrete hydrochloric acid (HCl), pepsin and mucus.
- HCl provides an acidic medium for pepsin and helps prevent fermentation of food and kills harmful microorganisms present in food.
- Mucus protects the inner wall of the stomach from the highly acidic HCl.
- Partially digested food, called chyme, enters the small intestine in small amounts. A sphincter muscle regulates its exit from the stomach.
8. Small Intestine – Complete Digestion & Absorption
The small intestine is the site of complete digestion of carbohydrates, proteins and fats. Its length differs among animals according to their feeding habits. Herbivores have a longer small intestine than carnivores, as plant material containing cellulose takes longer to digest than meat.
Digestive secretions and their functions
| Secretion / substance | Source or role described in the notes |
|---|---|
| Bile juice | Comes from the liver. Bile salts break large fat globules into smaller globules by emulsification, increasing the efficiency of lipase action. |
| Pancreatic juice | Secreted by the pancreas into the duodenum. It contains trypsin (proteins), lipase (fats) and amylase (carbohydrates). |
| Intestinal juice | Secreted by glands in the intestinal wall. Its enzymes convert proteins into amino acids, complex carbohydrates into glucose, and fats into fatty acids and glycerol. |
Emulsification of fats
Villi – absorption of digested food
The inner lining of the small intestine has numerous finger-like projections called villi. They increase the surface area for absorption. Villi are richly supplied with blood vessels that carry absorbed food to body cells for energy, growth and repair.
9. Large Intestine & Egestion
Undigested food passes into the large intestine, where more water is reabsorbed. The remaining undigested food material is removed from the body through the anus. The anal sphincter regulates the exit of this waste material.
10. Respiration – Overview
Food taken in during nutrition is used by cells to provide energy for various life processes. Respiration is the process in which food is broken down to release energy. It can occur with or without oxygen.
Oxygen is used for the complete breakdown of glucose in cells into carbon dioxide and water, releasing energy.
The notes introduce respiration as a process that can occur with or without oxygen. Further details are not included in this part of the notes.
11. Quick Revision – Important Points
- Life processes include nutrition, respiration, transportation and excretion.
- The two basic modes of nutrition are autotrophic and heterotrophic.
- Photosynthesis requires carbon dioxide, water, sunlight and chlorophyll.
- Stomata are tiny openings in leaves that allow gas exchange.
- Holozoic nutrition has five stages: ingestion, digestion, absorption, assimilation and egestion.
- Salivary amylase breaks down starch.
- Peristalsis moves food through the alimentary canal.
- The stomach secretes HCl, pepsin and mucus.
- Bile salts emulsify fats; pancreatic and intestinal enzymes help complete digestion.
- Villi increase the surface area for absorption in the small intestine.
- The large intestine reabsorbs more water from undigested food.
🧠 Self-check Quiz
1. Which pigment absorbs light energy during photosynthesis?
2. What are the tiny openings in leaves called?
3. Name the five stages of holozoic nutrition.
4. Which enzyme in saliva breaks down starch?
5. What is the function of villi?
6. What is emulsification?
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