Class 10 Science Notes Chapter 5 — Life Processes#

Life processes are the basic functions that keep an organism alive: nutrition, respiration, transportation and excretion. Multicellular organisms need specialised tissues for these, since diffusion alone is too slow.

Nutrition#

Heterotrophs take food in different ways: breaking it down outside the body and absorbing it (fungi like bread mould, yeast, mushrooms), taking in whole food and digesting it inside (most animals), or living on a host (parasites like cuscuta, ticks, lice, tapeworms).

Photosynthesis#

Three events:

1. Absorption of light energy by chlorophyll (in chloroplasts).
2. Conversion of light energy to chemical energy, and splitting of water into hydrogen and oxygen.
3. Reduction of CO₂ to carbohydrates.

• These need not happen one right after another. Desert plants take in CO₂ at night, store it as an intermediate, and use it in the day.
• Carbohydrates not used immediately are stored as starch.
• Stomata — tiny pores on the leaf for gas exchange and water loss. Guard cells open the pore when they swell with water and close it when they shrink.
• Plants get nitrogen, phosphorus, iron and magnesium from the soil. Nitrogen is taken as nitrates or nitrites, or as organic compounds made by bacteria.

Nutrition in single-celled organisms#

• Amoeba takes in food with temporary finger-like pseudopodia, which form a food vacuole. Food is digested in it and absorbed.
• Paramoecium has a fixed shape; food enters at a specific spot, moved by cilia.

Human digestion#

• Bile (from the liver, stored in the gall bladder) makes the food alkaline and emulsifies fats (breaks large fat globules into smaller ones).
• Pancreatic juice: trypsin digests proteins, lipase digests emulsified fats.
• Intestinal juice finally converts proteins to amino acids, carbohydrates to glucose, and fats to fatty acids and glycerol.
• Villi — finger-like projections in the small intestine wall that increase the surface area for absorption. They have many blood vessels.
• Herbivores eating grass have a longer small intestine than carnivores, to digest cellulose.

Respiration#

Breaking down glucose to release energy, stored as ATP (the energy currency of the cell).

• Aquatic animals breathe faster than land animals, because water has much less dissolved oxygen than air.
• Plants exchange gases by diffusion through stomata and the surface of stems and roots. At night only CO₂ is released; in the day the CO₂ of respiration is used for photosynthesis.

Human respiratory system#

Nostrils → pharynx → larynx → trachea → bronchi → bronchioles → alveoli

• Hairs and mucus in the nose filter the air.
• The trachea has rings of cartilage so it does not collapse.
• Alveoli — balloon-like sacs with thin walls and a dense network of blood vessels. They give a huge surface for gas exchange (about 80 m² if spread out).
• Breathing in: ribs lift and the diaphragm flattens, so the chest cavity gets larger and air is sucked in.
• Haemoglobin (red pigment in red blood cells) carries oxygen. CO₂ is carried mostly dissolved in blood.

Transportation#

In humans#

• Blood = fluid plasma (carries food, CO₂, nitrogen wastes) + RBCs (carry oxygen) + WBCs + platelets (help blood clot at a cut).

• The heart has four chambers. The right side carries deoxygenated blood, the left side oxygenated blood. A partition keeps them apart.

  • Body → vena cava → right atrium → right ventricle → pulmonary artery → lungs.
  • Lungs → pulmonary vein → left atrium → left ventricle → aorta → body.

• Valves stop blood flowing backwards.

• Double circulation — blood passes through the heart twice in one cycle of the body. It keeps oxygenated and deoxygenated blood separate and gives an efficient oxygen supply, which warm-blooded animals need.

• Fish have a 2-chambered heart (single circulation). Amphibians and many reptiles have a 3-chambered heart and tolerate some mixing.

• Lymph (tissue fluid) — colourless fluid that leaks from capillaries into spaces between cells. It carries digested fat from the intestine and drains back into veins.
• Blood pressure: normal is about 120/80 mm Hg (systolic/diastolic), measured with a sphygmomanometer. High pressure is hypertension.

In plants#

• Transpiration — loss of water vapour from the leaves through stomata. It helps pull water up, absorb minerals, and cool the plant.

Excretion#

In humans#

• The kidneys remove nitrogen wastes such as urea from the blood. The nephron is the filtering unit of a kidney.
• In each nephron, blood is filtered at the glomerulus (a cluster of capillaries) into Bowman’s capsule. Useful substances (glucose, amino acids, salts, much of the water) are reabsorbed in the tubule.
• Urine flows down the ureters to the urinary bladder and leaves through the urethra. Bladder emptying is under nervous control.
• Artificial kidney (haemodialysis) — removes wastes when kidneys fail, by passing blood through tubes in a dialysing fluid. There is no reabsorption.

In plants#

• Oxygen (from photosynthesis) and CO₂ leave through stomata. Extra water is lost by transpiration.
• Wastes are stored in cell vacuoles, in leaves that fall off, as resins and gums in old xylem, or released into the soil.

Common mistakes#

• Saying bile has enzymes. Bile has no enzymes; it emulsifies fats.
• Saying anaerobic respiration happens in mitochondria. It happens in the cytoplasm.
• Mixing up the pulmonary artery (deoxygenated blood, to the lungs) and the pulmonary vein (oxygenated blood, from the lungs).
• Saying xylem carries food. Xylem carries water and minerals; phloem carries food.