Life Processes

Diffusion is fine for tiny, single-celled organisms — every cell touches the environment directly. But a human body is huge and multi-layered: cells deep inside (like heart cells) are far from the body surface. Diffusion alone is too slow and too limited in range to deliver O₂ quickly to trillions of cells, so we need a specialised system — breathing + blood transport.

We check for signs of life — visible movements (breathing, growth, locomotion) OR invisible molecular activities. Living organisms are those in which life processes (nutrition, respiration, etc.) are continuously running, even when no movement is visible. If even molecular processes stop — it is no longer alive.

Raw materials (food, water, minerals, oxygen) taken from outside are used for two jobs: (1) building & repairing the body (growth, replacing worn-out cells) and (2) providing energy to drive all life processes. Since the body keeps wearing out, the supply must be continuous.

The essential maintenance processes are: nutrition (getting food), respiration (releasing energy from food), transportation (carrying substances around the body) and excretion (removal of waste).

Autotrophic: organisms make their OWN food from inorganic raw materials (CO₂, water, minerals) using sunlight + chlorophyll — e.g., green plants.
Heterotrophic: organisms CANNOT make food; they depend directly or indirectly on autotrophs for their nutrition — e.g., animals, humans, fungi.

• Carbon dioxide — from the air, entering leaves through the stomata (tiny leaf pores).
• Water — absorbed from the soil by the roots and carried up via xylem.
• Sunlight — from the Sun.
• Chlorophyll — already present inside green leaves (it is not taken from outside).

Hydrochloric acid (HCl) does two big jobs: (1) it creates an acidic medium in which the enzyme pepsin can properly digest proteins; (2) it kills most bacteria/germs that sneak in with food, protecting us from infection.

Food molecules (proteins, starch, fats) are big, complex and insoluble — blood can’t carry them. Digestive enzymes break these large molecules into small, simple, water-soluble molecules (glucose, amino acids, fatty acids + glycerol) that can be easily absorbed into the blood.

It is custom-built for absorption: (1) it is the longest part of the alimentary canal — digestion is completed here with all juices acting. (2) Its inner lining has millions of finger-like villi, hugely increasing the surface area. (3) Each villus is packed with blood capillaries that quickly carry absorbed nutrients to every body cell.

Air holds much more oxygen than the amount dissolved in water. So a terrestrial (land) organism gets O₂ easily and with less effort/slower breathing, while aquatic organisms must breathe much faster to extract enough oxygen from water.

Step 1 is common — 6-C glucose breaks into 3-C pyruvate in the cytoplasm. Then: (i) Aerobic (with O₂, in mitochondria) → CO₂ + H₂O + large energy; (ii) Anaerobic in yeast → ethanol + CO₂ + little energy; (iii) Anaerobic in muscle cells (O₂ shortage) → lactic acid + little energy.

Oxygen birds onto haemoglobin in red blood cells and travels as oxyhaemoglobin to the tissues. Carbon dioxide, being more water-soluble, is mostly transported dissolved in the blood plasma (some as bicarbonate) from tissues back to the lungs.

The bronchi branch repeatedly into tiny bronchioles that end in millions of alveoli. These balloon-like sacs give a huge total surface area, have paper-thin walls for easy diffusion, and are wrapped in a dense network of blood capillaries — the perfect geometry for maximum gas exchange.

(i) Heart — the muscular pump that circulates blood; (ii) arteries — carry blood AWAY from the heart to organs; (iii) veins — bring blood from organs BACK to the heart; (iv) capillaries — one-cell-thick exchange points between blood and tissues; (v) blood itself (plasma + cells) that carries food, O₂, CO₂ and wastes.

Mammals and birds are warm-blooded — they must maintain a constant body temperature, which needs a continuous, high-energy output from respiration. Mixing oxygen-rich and oxygen-poor blood would dilute the O₂ supply. Complete separation (4-chambered heart + septum) guarantees a high-efficiency oxygen delivery to every cell.

Two pipelines: xylem (vessels & tracheids of root, stem, leaves connected into one pipe — carries water + dissolved minerals) and phloem (sieve tubes + companion cells — transports food like sugars and amino acids made mostly in leaves).

Roots actively absorb minerals, and water follows (osmosis), entering xylem. Root pressure helps push it up a bit, and tall trees rely chiefly on transpiration pull: water evaporating from leaf stomata creates a suction that drags the continuous xylem water column upwards to the highest leaves. Adhesion between water molecules keeps the column unbroken.

Through the phloem by a process called translocation. Sugars produced in leaves are actively loaded into sieve tubes using ATP energy; water follows by osmosis, building pressure that drives the sugary sap to wherever it’s needed — roots, fruits, seeds, growing tips. It can go both up and down.

Structure: A nephron has a cup-shaped Bowman’s capsule enclosing a tuft of thin-walled capillaries called the glomerulus, connected to a long coiled tubule ringed by more capillaries.
Function: (i) Blood pressure forces a filtrate (water, glucose, amino acids, salts, urea) from blood into the capsule. (ii) As the filtrate crawls through the tubule, glucose, amino acids, salts and most water are reabsorbed into the capillaries as needed. (iii) The leftover – urea + excess water & salts – is collected as urine.

Plants use four quiet routes: (i) oxygen and excess water escape through stomata (transpiration); (ii) wastes are stored in cell vacuoles and, in some plants, in the old xylem as resins and gums; (iii) some waste products are released into the soil; (iv) wastes are loaded into old leaves which then fall off — nature’s litter removal!

It depends mainly on how much water the body holds. If there is MORE water in the body → less is reabsorbed in the nephron tubule → a larger, more dilute urine is produced. If the body is short of water (hot day, dehydration) → more water is reabsorbed → smaller, concentrated urine. The amount of dissolved waste needing exit also counts.