Amoeba engulfs food into food vacuoles where enzymes digest it inside the cell — this is intracellular digestion, typical of unicellular organisms.

Bile is produced by the liver and stored in the gall bladder; it emulsifies fats in the small intestine, aiding digestion but does not contain digestive enzymes.

Villi are finger-like projections that increase the surface area of the small intestine so digested nutrients can be absorbed more efficiently into the blood.

Salivary amylase (ptyalin) in saliva starts breaking down starch into simpler sugars in the mouth during chewing.

Food is swallowed from the mouth into the oesophagus, pushed by peristalsis to the stomach, and then passes to the small intestine for digestion and absorption.

Canines are pointed teeth used for tearing and cutting food, especially in carnivores; incisors cut, while molars grind food.

Cows are ruminants with a multi-chambered stomach; they regurgitate cud and re-chew to help break down cellulose with microbial action.

Peristalsis is the wave-like muscular contraction that moves food through the oesophagus and along the digestive tract.

The liver produces bile, stores glycogen and helps detoxify substances; filtration of urine is performed by the kidneys, not the liver.

Bile salts emulsify fats into smaller droplets; pancreatic lipase then breaks them into fatty acids and glycerol, which are absorbed via lacteals in the intestine.

Oxygen is used in aerobic respiration to release energy from food; carbon dioxide is produced as a waste product and expelled.

Insects have a network of tracheal tubes that open through spiracles and carry air directly to tissues without blood transport.

Alveoli are tiny air sacs with thin walls and capillary networks where oxygen diffuses into blood and carbon dioxide diffuses out.

Gills have filaments and lamellae providing large surface area for oxygen to diffuse from water into blood and carbon dioxide to leave.

When oxygen supply is insufficient during intense exercise, muscles perform anaerobic respiration producing lactic acid and less energy compared to aerobic respiration.

The diaphragm contracts and flattens to increase thoracic volume during inhalation and relaxes during exhalation, aiding ventilation.

Earthworms respire through moist skin; frogs can respire via skin (cutaneous) especially when in water, in addition to lungs.

In counter-current flow water and blood flow in opposite directions across gill lamellae, maximizing oxygen transfer by keeping a gradient along the entire surface.

Red blood cells contain haemoglobin, which binds oxygen in the lungs and transports it to tissues throughout the body.

Kidneys filter blood to remove nitrogenous wastes and help maintain water and electrolyte balance by forming urine.

Pulmonary veins carry oxygen-rich blood from the lungs to the left atrium of the heart; pulmonary artery carries deoxygenated blood from heart to lungs.

Blood transports digested nutrients but does not digest food; digestion is carried out by the digestive system using enzymes.

Nephrons are the functional units of kidneys where filtration, reabsorption and urine formation occur.

The excretory system, primarily kidneys in humans, removes metabolic wastes and regulates water and electrolyte balance, maintaining homeostasis.

Platelets (thrombocytes) help in blood clotting to prevent excessive bleeding when vessels are injured.

The brain receives, processes information and sends signals to effectors; it coordinates complex behaviours, movement and responses to stimuli.

Reflex actions are rapid, automatic responses (e.g., withdrawing hand from hot object) that protect the body and do not require conscious thought.

Muscles generate movement by contracting; antagonistic muscle pairs relax and contract alternately to move joints and body parts.

An axon transmits nerve impulses away from the neuron's cell body to other neurons or effectors; dendrites bring information to the cell body.

The ear detects sound vibrations and helps maintain balance; auditory receptors in the inner ear convert vibrations to nerve impulses.

Insects have an external skeleton (exoskeleton) made of chitin to which muscles attach; this provides protection and sites for muscle action.

Insects have an open circulatory system where haemolymph bathes organs in body cavities; blood is not confined entirely to vessels as in closed systems.

Frogs are amphibians using cutaneous respiration through moist skin as well as lungs for breathing air when on land.

Urea is a nitrogenous waste formed in the liver from excess amino acids and is excreted by the kidneys in urine.

Homeostasis includes processes that regulate internal conditions such as temperature and water balance, using multiple organ systems.

Leeches are parasitic annelids that suck blood from hosts using specialised mouthparts and anticoagulant secretions.

Capillaries are narrow vessels with thin walls that enable diffusion of oxygen, nutrients and wastes between blood and tissues.

Plants exchange gases (O₂ and CO₂) through stomata on leaves and lenticels on stems; they also respire like animals to obtain energy.

Many terrestrial insects can close spiracles to reduce water loss; other adaptations include excreting uric acid and having waxy cuticles.

Earthworms respire through their moist skin. Fish use gills, insects use tracheae, and humans use lungs.