The Blueprint of Multicellular Life
Complex organisms are built upon a universal hierarchical framework, from a single specialised cell to a fully functioning organism. This organisation allows for specialisation and the emergence of complex functions. Click the cards to explore each level.
Cells
Tissues
Organs
Systems
Organism
Select a level to learn more.
How Plants Function
Vascular plants have evolved sophisticated systems to thrive on land, centered on harnessing sunlight, absorbing resources, and transporting them. Explore their specialised structures and the critical balance they must maintain between gas exchange and water conservation.
Cellular Specialists
Root Hair Cells
Long extensions increase surface area for absorbing water (osmosis) and minerals (active transport).
Palisade Mesophyll Cells
Packed with chloroplasts and arranged in columns to maximise light absorption for photosynthesis.
Guard Cells & Stomata
Paired cells that change shape to open or close stomata, regulating gas exchange and water loss.
The Vascular Highway
Xylem Transport
Moves water and minerals from roots to leaves. A passive process driven by the Transpiration-Cohesion-Tension Theory.
Structure: Hollow, dead cells (vessels) reinforced with lignin.
Phloem Transport
Moves sugars (food) from source to sink. An active process described by the Pressure-Flow Hypothesis.
Structure: Living sieve-tube cells supported by companion cells.
How Animals Function
Animal bodies consist of multiple organ systems working in concert to process food, manage waste, and transport essential substances. These systems are highly interdependent, with the circulatory and respiratory systems providing critical support for all others.
Digestive System: Fuel Processing
This system breaks down food into absorbable nutrients. Villi and microvilli in the small intestine vastly increase surface area for efficient absorption.
Excretory System: Waste Management
Removes metabolic wastes (like urea) from blood and regulates water balance (osmoregulation). The functional unit is the nephron in the kidney, which performs filtration, reabsorption, and secretion.
Circulatory & Respiratory Systems
These two systems are tightly linked. The respiratory system (lungs, alveoli) performs gas exchange, while the circulatory system (heart, blood vessels) transports O₂ to cells and CO₂ away. Mammals have a double-circuit system to ensure efficient oxygen delivery.
Homeostasis & Feedback
All organisms must maintain a stable internal environment—a process called homeostasis. This is achieved through stimulus-response pathways and feedback loops. Explore the key concepts below.
Feedback Loops
Negative feedback counteracts a stimulus to maintain stability, while positive feedback amplifies it to completion.
Stimulus-Response Model
This model describes how an organism responds to change. Click the buttons to see it in action with thermoregulation.
When Systems Fail
Disease can be understood as a disruption of homeostasis. When feedback loops fail, the body’s internal environment can shift outside the narrow range required for normal function. Explore the case studies below.
Key Science Skills
A key part of biology is applying scientific thinking. Use this module to practice designing an investigation into phototropism.
Design an Experiment
Your research question is: “How does the colour of light affect the direction of shoot growth in seedlings?”
Your hypothesis: Seedlings will bend most towards blue light.
Identify the variables for your experiment:
