Living Systems AT2 MHS Year 8 2026

Levels of organisation

Cells specialise → form tissues → tissues form organs → organs form organ systems that keep the organism functioning.

Why specialisation matters

Specialised cells have structures that suit their jobs, increasing efficiency (e.g., red blood cell shape for O₂ transport).

Alimentary canal length

The human alimentary canal is about 6–7 m long — a continuous tube from mouth to anus for digestion and absorption.

Mechanical vs chemical digestion

Mechanical digestion breaks food into smaller pieces (chewing, churning); chemical digestion uses enzymes to break molecules into absorbable units.

Role of the digestive system

Breaks down food physically and chemically so nutrients (especially glucose) can be absorbed for respiration.

Small intestine function

Main site of chemical digestion and absorption of nutrients into the bloodstream.

Villi and microvilli function

Villi (and microvilli) hugely increase surface area of the small intestine so nutrients diffuse quickly into capillaries.

Pathway of absorbed nutrients

Nutrients cross epithelial cells of villi → enter capillaries → transported by blood to the liver/body tissues.

Duodenum role

The duodenum receives bile and pancreatic juice to help digest fats, proteins and carbohydrates.

Circulatory system role

Transports oxygen, nutrients, hormones and wastes; helps thermoregulation and immune transport (WBCs/antibodies).

Main circulatory components

Heart (pump), blood (transport medium), blood vessels (arteries, veins, capillaries).

Pulmonary vs systemic circulation

Pulmonary: heart→lungs→heart for gas exchange. Systemic: heart→body→heart to deliver O₂ and nutrients.

Important vessel names

Superior vena cava (from head), inferior vena cava (from body), hepatic portal vein (gut→liver), hepatic artery (to liver).

Heart chambers and flow

Atria are inflow chambers; ventricles are outflow chambers. Right side pumps to lungs, left side pumps to body.

Left vs right ventricle thickness

The left ventricle has thicker walls because it must pump blood at higher pressure around the body.

Heart valves purpose

Valves prevent backflow and ensure one-way blood flow through the chambers.

How to label a heart diagram

Label chambers, valves and major vessels; colour oxygenated vs deoxygenated flow; add one function per label.

Blood vessel structural differences

Arteries: thick muscular walls for high pressure; veins: thinner walls + valves; capillaries: one-cell thick for diffusion.

Capillary specialisation

Very thin walls and extensive networks minimise diffusion distance for O₂/CO₂ and nutrients.

Blood components & roles

Red blood cells carry O₂, white blood cells fight infection, platelets help clotting, plasma transports cells/nutrients/wastes.

Gas exchange definition

Gas exchange = diffusion of O₂ into blood and CO₂ out of blood at the lungs.

Composition change in inhaled vs exhaled air

Inhaled: higher O₂; Exhaled: lower O₂, higher CO₂ — shows gas exchange happened.

Alveoli structure for gas exchange

Numerous tiny air sacs with thin, moist walls and dense capillaries → large surface area and short diffusion distance.

Respiratory pathway

Air: nose/mouth → trachea → bronchi → bronchioles → alveoli.

Diaphragm role

The diaphragm contracts to increase chest volume for inhalation and relaxes for exhalation.

Epiglottis function

Epigottis closes the trachea during swallowing to prevent food entering the airways.

Breathing vs gas exchange

Breathing = movement of air in/out. Gas exchange = diffusion of gases between alveoli and blood.

Excretory system role

Removes metabolic wastes and regulates water & salt balance (osmoregulation).

Organs of excretion

Kidneys, lungs and skin all remove wastes (e.g., kidneys → urea; lungs → CO₂; skin → sweat).

Kidney main functions

Filter blood to remove wastes, regulate water/salt balance and produce urine.

Nephron structure basics

Each nephron has a glomerulus (filter), a tubule (reabsorption/secretion) and a collecting duct.

Three nephron processes

Filtration (glomerulus), reabsorption (useful molecules back to blood), secretion (extra wastes into tubule).

How urine concentration is adjusted

Collecting ducts reabsorb water/salt to change filtrate concentration — controls blood osmolarity.

Pathway of urine

Nephron → collecting duct → renal pelvis → ureter → bladder → urethra.

Kidney practical tip (dissection)

When dissecting kidneys, identify cortex, medulla, pelvis and trace ureter to see urine exit path.

How body systems interact (apple example)

Eating apple: digestive breaks down glucose → circulatory carries glucose + O₂ → respiratory supplies O₂ → cells respire → excretory removes CO₂/chemical wastes.

Experiment idea: exercise & rates

Exercise raises pulse and breathing rates to increase O₂ delivery and CO₂ removal for higher respiration rates.

Disease example: cystic fibrosis

Faulty CFTR protein → thick sticky mucus in lungs & pancreas → blocked airways, infections and poor digestion (less nutrient absorption).

Answer structure for “effect of disease” questions

Statement of damage → link to structural change → two consequences for organ and whole organism.

Annotating diagrams (exam trick)

Always label, indicate flow direction, give one short function per label and add arrows/colours if asked.

Levels of organisation in multicellular organisms

Cells specialise → form tissues → tissues form organs → organs work together in organ systems → organism functions efficiently.

Why cell specialisation is important

Specialised cells perform specific functions, making processes like respiration and transport more efficient.

Role of the digestive system

The digestive system breaks food down so nutrients like glucose can be absorbed for respiration.

Mechanical vs chemical digestion

Mechanical digestion increases surface area; chemical digestion uses enzymes to break molecules into absorbable forms.

Function of the small intestine

The small intestine is the main site of nutrient absorption into the bloodstream.

Why villi increase absorption

Villi and microvilli increase surface area, allowing faster diffusion of nutrients into capillaries.

Role of the circulatory system

The circulatory system transports oxygen, nutrients, hormones and wastes around the body.

Pulmonary vs systemic circulation

Pulmonary circulation exchanges gases in the lungs; systemic circulation delivers oxygenated blood to the body.

Why arteries have thick walls

Arteries have thick, muscular walls to withstand high pressure blood flow from the heart.

Why capillaries are one cell thick

Thin walls reduce diffusion distance, allowing rapid exchange of gases and nutrients.

Role of the respiratory system

The respiratory system supplies oxygen and removes carbon dioxide for cellular respiration.

Gas exchange definition

Gas exchange is the diffusion of oxygen into blood and carbon dioxide out of blood in the lungs.

Why alveoli are efficient

Alveoli have a large surface area, thin moist walls and a rich blood supply for rapid diffusion.

Role of the excretory system

The excretory system removes metabolic wastes and maintains water and salt balance.

Difference between excretion and elimination

Excretion removes metabolic wastes; elimination removes undigested food as faeces.

Function of the kidneys

Kidneys filter blood, remove wastes and regulate water and salt concentration.

Structure of a nephron

Nephrons contain a glomerulus for filtration and a tubule for reabsorption and secretion.

How nephrons enable function

Filtration removes small molecules; reabsorption returns useful substances; secretion removes extra wastes.

How body systems work together

Digestive provides glucose, respiratory provides oxygen, circulatory transports both, excretory removes wastes.

Why no body system works alone

All systems depend on each other to maintain respiration, growth and survival.

How disease affects organisms

Damage to one organ reduces system efficiency and impacts the whole organism.

Example of system disruption

Blockage in airways reduces oxygen uptake, lowering energy production in cells.

Characteristics of plants

Plants are multicellular, autotrophic, photosynthetic and have specialised tissues.

Plant organ systems

Vascular plants have a shoot system for photosynthesis and a root system for absorption and anchorage.

Role of leaves

Leaves are the main site of photosynthesis.

Why leaves are thin

Thin leaves shorten diffusion distance for carbon dioxide and oxygen.

Function of stomata

Stomata allow gas exchange and water loss through transpiration.

How guard cells work

Guard cells open stomata when turgid and close them during water stress.

Role of xylem

Xylem transports water and minerals upward from roots to leaves.

How water moves in xylem

Transpiration pull and cohesion-tension move water passively up the plant.

Role of phloem

Phloem transports glucose from sources to sinks in the plant.

How glucose moves in phloem

Pressure-flow uses active loading and unloading to move sugars.

Definition of ecology

Ecology is the study of interactions between organisms and their environment.

Levels of organisation in ecosystems

Organism → population → community → ecosystem → biosphere.

Biotic factors

Biotic factors are living components like plants, animals and bacteria.

Abiotic factors

Abiotic factors are non-living components such as temperature, water and light.

Ecological niche

A niche is the role of a species and how it uses resources in its environment.

Why species can coexist

Species avoid competition by occupying different niches.

Energy source of ecosystems

The Sun is the primary source of energy in most ecosystems.

Energy flow in ecosystems

Energy flows one way through food chains and is lost as heat.

Matter cycling in ecosystems

Matter is recycled by decomposers and reused by producers.

Producers definition

Producers make their own glucose using photosynthesis.

Consumers definition

Consumers obtain glucose by eating other organisms.

Decomposers definition

Decomposers break down dead organisms and recycle nutrients.

Purpose of food chains

Food chains show who eats whom and the direction of energy flow.

Meaning of arrows in food chains

Arrows show the flow of energy from one organism to another.

Trophic levels

Trophic levels describe an organism’s position in a food web.

Why energy pyramids narrow

Only about 10% of energy is transferred to the next trophic level.

Why energy is lost between levels

Energy is lost through respiration, heat and undigested material.

Definition of biodiversity

Biodiversity is the variety of living things on Earth.

Levels of biodiversity

Biodiversity includes genetic, species and ecosystem diversity.

Why biodiversity is important

High biodiversity increases ecosystem stability and resilience.

Factors that change populations

Habitat loss, introduced species, disease and climate change alter population sizes.

Why Australia has high extinction rates

Introduced species, habitat destruction and specialised native species increase extinction risk.