Life Processes — Karnataka (SSLC) Class 10 Science Solutions (Free)

Life processes are the basic vital activities that every living organism must continuously carry out to stay alive, grow, and maintain a stable internal environment (homeostasis) — an organism that permanently stopped any one of them would die. The five major life processes: 1. Nutrition — obtaining and processing food, the raw material and energy source for every other process. 2. Respiration — breaking down that food (chiefly glucose) to release usable energy, without which no other process could run. 3. Transportation (circulation) — moving nutrients, oxygen, and waste products between the site they are produced/absorbed and the site they are needed/removed. 4. Excretion — removing the metabolic waste products these processes generate, since a build-up of waste (like urea or excess CO₂) is toxic. 5. Growth — using absorbed nutrients to increase in size and repair or replace worn-out cells and tissues. Why all five, and not fewer: they form a dependent chain — nutrition supplies material, respiration releases the energy to use it, transportation delivers both to every cell, excretion clears the resulting waste, and growth is the visible outcome of the whole cycle running successfully over time.

Nutrition is the process by which an organism obtains and uses food to get energy and the raw materials needed for growth and repair. Autotrophic nutrition: the organism makes its own food from simple inorganic substances, using an external energy source. Green plants and algae use photosynthesis (CO₂ + H₂O + light energy → glucose + O₂), while some bacteria use chemosynthesis (using energy from chemical reactions instead of light). Autotrophs are called producers, because they are the entry point of energy into every food chain. Heterotrophic nutrition: the organism cannot manufacture its own food and must consume ready-made organic matter from other organisms. This includes animals (holozoic — ingesting and digesting solid food), fungi and many bacteria (saprophytic — absorbing nutrients from dead/decaying matter), and parasites (absorbing nutrients directly from a living host, like tapeworms). Heterotrophs are called consumers or decomposers depending on their role. Why the distinction matters: because heterotrophs cannot make their own food, every heterotroph in an ecosystem is ultimately dependent on autotrophs, directly or indirectly — this is the basis of every food chain and food web.

Aerobic respiration is the oxidation of glucose in the presence of oxygen to release energy, most of which is captured and stored in ATP (adenosine triphosphate) molecules for the cell to use. Overall equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (~2,830 kJ per mole of glucose) Where each stage occurs: 1. Glycolysis — in the cytoplasm. Glucose is split into two molecules of pyruvate, producing a small net gain of 2 ATP. Notably, this stage does NOT require oxygen. 2. Krebs cycle (citric acid cycle) — in the mitochondrial matrix. Pyruvate is further oxidised, releasing CO₂ and generating high-energy electron carriers. 3. Electron transport chain — on the inner mitochondrial membrane. The electron carriers from the Krebs cycle release their energy here to synthesise the bulk of the cell's ATP. Why oxygen is essential: Oxygen acts as the final electron acceptor at the end of the electron transport chain — without it, electrons have nowhere to go, the chain backs up and stops, and ATP production collapses to only the small amount glycolysis alone can provide. This is exactly why cells starved of oxygen (as in a heart attack or stroke) rapidly run out of usable energy and begin to die.

Anaerobic respiration breaks down glucose to release energy WITHOUT using oxygen, but it is far less efficient than aerobic respiration because glucose is only partially broken down. Key differences: - Oxygen requirement: aerobic needs O₂; anaerobic does not. - Products: aerobic respiration fully breaks glucose down to CO₂ and H₂O; anaerobic respiration stops partway, leaving energy-rich by-products (like lactic acid or ethanol) that still contain most of glucose's original chemical energy. - Energy yield: aerobic respiration yields far more ATP per glucose molecule (traditionally cited as up to 36–38 ATP) than anaerobic respiration (a net of only 2 ATP), because so much energy remains locked in the incompletely broken-down by-product. Example in humans — lactic acid fermentation: during intense exercise, muscle cells cannot get oxygen fast enough to keep up with aerobic respiration, so they switch to anaerobic respiration: glucose → lactic acid + energy. The build-up of lactic acid is what causes the burning sensation and cramping felt in muscles during hard exercise. Example in yeast — alcoholic fermentation: yeast cells respire anaerobically as glucose → ethanol + CO₂ + energy. This is the exact reaction used in brewing and baking — the CO₂ produced is what makes bread dough rise.

Respiration and photosynthesis are, in a real sense, opposite processes that together keep atmospheric oxygen and carbon dioxide in balance. Respiration: breaks DOWN glucose using oxygen to RELEASE energy (a catabolic, energy-releasing process). It occurs in the cells of ALL living organisms, all the time, day and night. Photosynthesis: builds UP glucose from carbon dioxide and water using light energy, STORING that energy in the glucose formed (an anabolic, energy-storing process). It occurs only in cells containing chlorophyll — green plants, algae, and certain bacteria — and only when light is available. The key connection: photosynthesis releases oxygen as a by-product, which respiration then consumes; respiration releases carbon dioxide as a by-product, which photosynthesis then consumes. This is why green plants are said to do both processes (photosynthesis during daylight, respiration continuously), while animals can only respire — they depend entirely on plants to replenish the oxygen and food they use up.

The human circulatory system consists of the heart (a muscular pump), blood vessels (arteries carrying blood away from the heart, veins carrying it back, and capillaries where actual exchange with tissues happens), and blood itself. Humans have DOUBLE circulation: blood passes through the heart twice in one complete circuit — once through the pulmonary circulation (heart → lungs → heart, to pick up oxygen) and once through the systemic circulation (heart → rest of the body → heart, to deliver that oxygen). This is more efficient than the single circulation of fish, since it lets oxygenated and deoxygenated blood be kept separate and pumped at higher pressure to the body. Three main roles of blood: 1. Transport — carries oxygen from the lungs to every cell in the body, and carbon dioxide from cells back to the lungs to be exhaled; also carries digested nutrients from the intestine to cells. 2. Excretion support — carries metabolic waste products like urea from the cells that produce them to the kidneys, where they are filtered out. 3. Defence and repair — white blood cells fight infection, and platelets trigger clotting to seal wounds and prevent both blood loss and the entry of pathogens. Blood also helps regulate body temperature, by redistributing heat generated in active tissues around the body.

Kidneys are a pair of bean-shaped organs that filter the blood to remove nitrogenous waste (chiefly urea) and excess substances, forming urine. The three stages of urine formation, occurring in the nephron (the kidney's basic filtering unit): 1. Ultrafiltration — blood enters the glomerulus (a knot of capillaries) at high pressure. This pressure forces small molecules — water, glucose, amino acids, salts, and urea — out through the capillary walls into the surrounding Bowman's capsule. Large molecules like proteins and blood cells are too big to pass through and stay in the blood. 2. Selective reabsorption — as this filtrate flows along the tubule, useful substances the body still needs (essentially all the glucose, most of the water, and most of the salts) are actively reabsorbed back into the surrounding blood capillaries. 3. Secretion and concentration — the remaining fluid, now concentrated waste (mainly urea, excess water and salts), passes on as urine, which collects in the bladder before being expelled from the body. By adjusting exactly how much water and salt gets reabsorbed in stage 2, the kidneys also keep the body's internal water and salt balance (osmoregulation) stable, regardless of how much water or salty food a person has consumed.

Plants obtain the raw materials for their nutrition from three sources: 1. Carbon dioxide — absorbed from the air through pores (stomata) on the leaves, used in photosynthesis to build glucose. 2. Water — absorbed from the soil through root hairs, also used in photosynthesis and to transport dissolved minerals. 3. Mineral nutrients — nitrogen, phosphorus, potassium, magnesium, iron and others, absorbed from the soil in dissolved form through the roots; these are needed to build proteins, chlorophyll, and other essential compounds that photosynthesis alone cannot supply. The nitrogen cycle — how plants get nitrogen: Plants cannot use atmospheric nitrogen gas (N₂) directly, even though it makes up about 78% of the air, because the triple bond holding N₂ together is too strong for plant cells to break. 1. Nitrogen fixation — certain bacteria (notably Rhizobium, which lives in root nodules of legume plants like beans and peas, in a mutually beneficial relationship with the plant) convert atmospheric N₂ into ammonia (NH₃), a form plants CAN use. 2. Nitrification — other soil bacteria (nitrifying bacteria) convert this ammonia into nitrites and then nitrates (NO₃⁻). 3. Absorption — plant roots absorb these nitrates and use them to build amino acids and proteins. 4. Return to the cycle — animals obtain nitrogen by eating plants (or other animals); when organisms die, decomposers break down their proteins back into ammonia, which nitrifying bacteria convert to nitrates again, continuing the cycle. This is exactly why crop rotation with legumes, and Rhizobium-based biofertilisers, are recommended in sustainable agriculture — they replenish soil nitrogen naturally instead of relying solely on manufactured fertiliser.