CBSE Class 10 Science Life Processes Notes Set 09

These CBSE Class 10 Science notes for Chapter 5, Life Processes, cover nutrition in plants and animals, photosynthesis and the structure of stomata, the human digestive system, aerobic and anaerobic respiration, breathing, transport of blood and lymph, transport in plants through xylem and phloem, and excretion with the working of the nephron and dialysis. Key equations, comparison tables and flow diagrams are included for quick revision.

Important Notes and Formulas

Life Processes

The basic functions performed by living organisms to maintain life are called life processes. They include nutrition, respiration, transportation and excretion (together with control and coordination and reproduction). Living things need energy for these processes, and this energy comes from food. Movement, even at the molecular level, is taken as a sign of life.

In a unicellular organism, every part is in contact with the surroundings, so materials move by diffusion. In a multicellular organism like a human being, many cells are not in direct contact with the environment, so diffusion alone cannot meet the need for oxygen. That is why special organs and transport systems are needed.

Nutrition

Nutrition is the process of taking in food and using it. Nutrients are the substances that the body needs for growth, repair, work and maintenance, for example carbohydrates, fats, proteins, vitamins and minerals. Organisms get their food in two ways:

Nutrition in Plants: Photosynthesis

Green plants are autotrophs and are called producers. Photosynthesis is the process in which green plants make carbohydrates (food) from carbon dioxide and water, in the presence of sunlight and chlorophyll, and release oxygen. The sugar formed is stored as starch, the reserve food of plants.

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

Raw materials and their sources

Events during photosynthesis. The following events take place in the chloroplasts of the leaf cells:

1. Absorption of light energy by chlorophyll.
2. Conversion of light energy into chemical energy and splitting of water molecules into hydrogen and oxygen (photolysis). The oxygen released comes from water.
3. Reduction of carbon dioxide to carbohydrates using the hydrogen.

These events happen in two phases. The light reaction needs light, takes place in the grana of the chloroplast, splits water and releases oxygen. The dark reaction does not need light directly, takes place in the stroma of the chloroplast, and forms sugar from carbon dioxide.

Experiments on photosynthesis. Before each experiment the plant is kept in the dark for 2 to 3 days to remove the starch already present (destarching). After the exposure, the leaf is boiled in water, then in alcohol (in a water bath) to remove its chlorophyll, rinsed, and tested with iodine solution. Starch gives a blue-black colour with iodine.

Stomata and guard cells. Stomata are tiny pores on the surface of the leaf (mostly on the lower side), each guarded by two bean-shaped guard cells which contain chloroplasts. Gaseous exchange and loss of water vapour (transpiration) take place through the stomata. When water flows into the guard cells they swell up and the pore opens; when they lose water they shrink and the pore closes. Stomata are usually open in the day and closed at night. In desert plants the stomata stay closed in the day to save water; they take up carbon dioxide at night, form an intermediate compound, and use it in photosynthesis during the day.

Heterotrophic Nutrition

The steps of holozoic nutrition are: ingestion, digestion, absorption, assimilation and egestion. Holozoic animals may be herbivores (eat plants), carnivores (eat flesh) or omnivores (eat both).

Nutrition in Amoeba

1. Ingestion: Amoeba stretches out temporary finger-like projections called pseudopodia around the food particle and engulfs it in a bag called the food vacuole.
2. Digestion: digestive enzymes enter the food vacuole and break the complex food into simpler substances.
3. Absorption and assimilation: the digested food diffuses into the cytoplasm and is used for energy, growth and repair.
4. Egestion: the undigested food is expelled from the cell surface at any place.

Nutrition in Human Beings

The human digestive system has the alimentary canal, a long tube from the mouth to the anus, and the digestive glands (salivary glands, liver and pancreas, and the glands in the walls of the stomach and small intestine).

Teeth. Humans have two sets of teeth: 20 milk teeth and 32 permanent teeth. The 32 permanent teeth are 8 incisors (cutting), 4 canines (tearing), 8 premolars (chewing and grinding) and 12 molars (chewing and grinding). Dental caries (tooth decay): bacteria in the mouth act on sugar and food particles and produce acid, which softens the enamel when the pH falls below 5.5. A sticky layer of bacteria and food (plaque) keeps the saliva from reaching the tooth, so brushing the teeth after meals removes the plaque.

Digestive glands and enzymes

Absorption, assimilation and egestion. The digested food is absorbed through the villi of the small intestine into the blood. The blood carries it to all cells, where it is used for energy, growth and repair (assimilation). The extra glucose is stored in the liver as glycogen. The small intestine of herbivores is longer than that of carnivores because cellulose is hard to digest. The undigested food passes to the large intestine and is egested.

Respiration

Respiration is the process by which the food (mainly glucose) is broken down in the cells with the release of energy. The energy is stored in the molecule ATP (adenosine triphosphate), the energy currency of the cell. When the cell needs energy, the ATP is broken down and gives a fixed amount of energy. Respiration is an enzyme-controlled process, and it takes place in the cytoplasm and the mitochondria.

Aerobic respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy

Examples of anaerobic respiration are fermentation by yeast (glucose → ethanol + carbon dioxide + energy) and the formation of lactic acid in our muscles during sudden or heavy exercise, when the oxygen supply is low. The build-up of lactic acid in the muscles causes cramps.

Respiration and breathing.

Respiration in plants. Plants exchange gases by simple diffusion. Leaves and green stems have stomata, woody stems have lenticels, and young roots absorb oxygen from the soil air through the root hairs. In the day, the carbon dioxide released by respiration is used in photosynthesis and the extra oxygen is given out. At night, only respiration takes place, so oxygen is taken in and carbon dioxide is given out.

Respiration in animals. Different animals use different respiratory organs, but each has a large surface area, thin walls and a rich blood supply.

Aquatic animals breathe faster than land animals because the amount of oxygen dissolved in water is much less than the amount in air.

Human respiratory system. The path of air is: Nostrils → Nasal cavity → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli.

1. The nasal cavity has hairs and mucus that filter dust and warm and moisten the air.
2. The trachea (windpipe) is held open by C-shaped rings of cartilage, so it does not collapse when there is less air in it.
3. The epiglottis closes the opening of the windpipe when we swallow food.
4. The lungs are spongy organs; the bronchioles end in millions of balloon-like alveoli with thin walls and a network of blood capillaries. Alveoli are the sites of gas exchange and give a very large surface area.
5. The lungs always keep some air (residual volume), so there is enough time for oxygen to be absorbed and carbon dioxide to be released.

Mechanism of breathing

Gas exchange and transport. Oxygen from the alveolar air diffuses into the blood and combines with haemoglobin, the red iron-containing respiratory pigment in red blood cells, which carries it to the tissues. Carbon dioxide released by the cells is more soluble in water than oxygen, so it is carried mostly in dissolved form in the blood to the lungs and diffuses into the alveoli to be breathed out.

Transportation in Human Beings

In human beings the transport system consists of blood, blood vessels and the heart (the blood circulatory system) and the lymphatic system.

Blood is a fluid connective tissue. It has a fluid part, the plasma, in which the blood cells are suspended.

Blood vessels

The heart is a muscular organ of about the size of one’s fist, enclosed in a sac called the pericardium. It has four chambers: two upper chambers, the right and left atria (thin-walled, receiving chambers), and two lower chambers, the right and left ventricles (thick-walled, pumping chambers). A wall (septum) separates the right and left sides, and valves ensure that the blood flows in one direction only.

1. The right atrium receives deoxygenated blood from the body through the vena cava and passes it to the right ventricle.
2. The right ventricle pumps it to the lungs through the pulmonary artery.
3. The left atrium receives oxygenated blood from the lungs through the pulmonary veins and passes it to the left ventricle.
4. The left ventricle has the thickest wall and pumps the oxygenated blood to the whole body through the aorta.

Double circulation. The blood passes twice through the heart in one complete round of the body. In pulmonary circulation the blood goes from the heart to the lungs and back to the heart; in systemic circulation it goes from the heart to the body and back to the heart. The separation of oxygenated and deoxygenated blood gives an efficient supply of oxygen, which is useful for birds and mammals that need a lot of energy to keep their body temperature constant. Amphibians and many reptiles have three-chambered hearts, in which some mixing of blood is tolerated. Fish have a two-chambered heart, and the blood goes through the heart only once in a cycle.

Blood pressure is the force that the blood exerts on the walls of the blood vessels. The pressure during the contraction of the ventricles is the systolic pressure (about 120 mm of Hg) and the pressure during their relaxation is the diastolic pressure (about 80 mm of Hg). It is measured with a sphygmomanometer. High blood pressure (hypertension) is caused by the narrowing of the arterioles and can lead to the rupture of an artery and internal bleeding.

Lymph. Through the pores in the walls of the capillaries, some plasma, proteins and blood cells escape into the spaces between the cells. This fluid is called lymph or tissue fluid. It is colourless and has fewer proteins than blood. It carries digested and absorbed fat from the intestine and drains the excess fluid from the tissues back into the blood.

Transportation in Plants

In plants, the conducting tissues are the xylem and the phloem. Plants have low energy needs and many of their cells are dead, so they can use relatively slow transport systems.

Transport of water. Root hairs absorb water from the soil. The water moves from cell to cell into the xylem of the root, which is connected to the xylem of the stem and leaves, forming a continuous channel. Water evaporating from the leaves creates a suction, the transpiration pull, which draws the water column up. In the day this is the main driving force. At night, when the stomata are closed, root pressure moves the water upward.

Transpiration is the loss of water in the form of vapour from the aerial parts of the plant, mainly through the stomata. It helps in the upward movement of water and minerals, cools the plant and removes the extra water.

Translocation is the transport of food from the leaves to the other parts of the plant through the phloem. The sugar is loaded into the sieve tubes using energy from ATP; water follows by osmosis and the pressure rises, which moves the food to the parts where the pressure is lower, according to the needs of the plant.

Excretion

Excretion is the removal of harmful metabolic wastes, mainly nitrogenous wastes, from the body. Unicellular organisms remove wastes by diffusion through the cell surface (Amoeba also uses a contractile vacuole).

Human excretory system. It has a pair of kidneys, a pair of ureters, a urinary bladder and a urethra. The kidneys are bean-shaped organs on either side of the backbone. Each kidney has about a million filtering units called nephrons, the structural and functional units of the kidney. A nephron has a cup-shaped Bowman’s capsule that contains a bunch of capillaries called the glomerulus, and a long tubule that opens into a collecting duct. A network of capillaries surrounds the tubule.

Formation of urine takes place in three steps:

1. Ultrafiltration: blood is filtered under pressure in the glomerulus and the filtrate collects in the Bowman’s capsule. The filtrate contains water, glucose, amino acids, salts and urea.
2. Selective reabsorption: as the filtrate flows along the tubule, useful substances such as glucose, amino acids, salts and a major amount of water are taken back into the blood.
3. Tubular secretion: some extra wastes are passed from the blood into the tubule. The fluid that remains is urine.

The amount of water reabsorbed depends on how much excess water is in the body and how much dissolved waste has to be excreted, so the amount of urine changes. In an adult about 180 litres of filtrate is formed in a day, but only about 1.8 litres leaves the body as urine, because the rest is reabsorbed. The urine is collected in the collecting duct, flows through the ureter to the urinary bladder, where it is stored, and is passed out through the urethra. Urea is formed in the liver from ammonia, which is more toxic.

Artificial kidney (haemodialysis). When the kidneys fail, wastes such as urea build up in the blood. An artificial kidney has many tubes with a semipermeable lining placed in a tank of dialysing fluid, which has the same osmotic pressure as blood but no nitrogenous wastes. The patient’s blood is passed through the tubes, the waste products pass into the dialysing fluid by diffusion, and the cleaned blood is pumped back into the patient. There is no reabsorption in an artificial kidney. A kidney transplant is a long-term solution.

Excretion in plants. Plants have no special excretory organs. They get rid of oxygen (from photosynthesis) and carbon dioxide (from respiration) through the stomata and lenticels, lose extra water by transpiration, store wastes in the cell vacuoles, and shed them in the old leaves, bark and old xylem. Some wastes are lost as gums, resins and latex, and some pass into the soil around the roots.

Quick Revision Points

1. Life processes: nutrition, respiration, transportation and excretion keep an organism alive.
2. Autotrophs make food by photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (sunlight, chlorophyll).
3. Stomata are opened and closed by the guard cells; they allow gas exchange and transpiration.
4. Saliva digests starch, the stomach digests proteins, and the small intestine completes the digestion of carbohydrates, proteins and fats.
5. Bile has no enzyme but it makes the food alkaline and emulsifies fats.
6. Aerobic respiration releases much more energy than anaerobic respiration; ATP is the energy currency.
7. Alveoli are the sites of gas exchange in the lungs; haemoglobin carries oxygen.
8. The human heart has four chambers and double circulation; arteries carry blood away from the heart and veins bring it back.
9. Xylem carries water and minerals (upward); phloem carries food (up and down, using ATP).
10. Transpiration pull and root pressure move water in the xylem.
11. The nephron is the unit of the kidney: ultrafiltration, selective reabsorption and tubular secretion form urine.
12. Dialysis cleans the blood of patients whose kidneys have failed.