Living Systems Powerpoint Based Year 8 MHS AT2 2026

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.