Ecosystems, Cells and Human Body Systems

MYP Unit Framework

Key Concept: SYSTEMS Related Concepts: Balance. Interaction. Function. Global Context: Globalisation and Sustainability (How do living systems maintain BALANCE — and what happens when that balance is DISRUPTED?) Statement of Inquiry: Living organisms are ORGANISED into interacting SYSTEMS — from cells to ecosystems — that maintain BALANCE through complex FEEDBACK mechanisms, and human actions can DISRUPT these systems with far-reaching consequences.

Inquiry Questions

1. The Cell — The Basic Unit of Life

Cell Theory

1. All living things are made of CELLS. 2. The cell is the BASIC UNIT of structure and function. 3. All cells arise from PRE-EXISTING cells.

Plant vs. Animal Cells

Key Organelles

Specialised Cells

'All cells in your body have the SAME DNA. But they LOOK and ACT differently because different GENES are "switched on" in each type.' Red blood cells: no nucleus, biconcave (more surface area for oxygen). Nerve cells: long axons (transmit signals). Root hair cells: long extensions (absorb water).

2. Ecosystems — The Web of Life

Levels of Organisation

Organism → Population → Community → Ecosystem → Biome → Biosphere.

Ecosystem Components

• BIOTIC (living): Producers (plants). Consumers (herbivores, carnivores, omnivores). Decomposers (bacteria, fungi).
• ABIOTIC (non-living): Sunlight. Water. Temperature. Soil. Air.

Food Chains and Webs

Sun → Grass → Grasshopper → Frog → Snake → Hawk. 'A food chain shows a SINGLE path of energy. A food web shows ALL the interconnected paths. Real ecosystems are WEBS — not chains.'

Energy Flow and the 10% Rule

'Only about 10% of the energy at one trophic level passes to the NEXT level. The rest is LOST as heat (metabolism). This is why: there are FEWER predators than prey. Food chains are SHORT (rarely more than 4-5 levels). The pyramid of ENERGY is ALWAYS upright.'

Disruption — What Happens When We Remove a Species?

Trophic Cascade: 'When wolves were removed from Yellowstone National Park, ELK populations exploded. Elk ate young trees. Beavers lost their food and building material. Rivers changed course. Wolves were reintroduced in 1995 — the ecosystem began to RECOVER. ONE species. Enormous CONSEQUENCES.'

3. Photosynthesis and Respiration — The Carbon Cycle

Photosynthesis (Plants, Algae, Cyanobacteria)

6CO₂ + 6H₂O + Light → C₆H₁₂O₆ + 6O₂. 'Plants TAKE IN carbon dioxide and water. Using SUNLIGHT, they produce GLUCOSE (food) and release OXYGEN. Photosynthesis is the FOUNDATION of almost every food chain on Earth.'

Cellular Respiration (ALL Living Things)

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ENERGY (ATP). 'Respiration is the OPPOSITE of photosynthesis. It BURNS glucose using oxygen to RELEASE energy. ALL living things — plants AND animals — respire. Plants photosynthesise in the DAY (light) and respire ALL THE TIME.'

The Carbon Connection

'Photosynthesis and respiration form a CYCLE — plants take in CO₂, animals release it. This is part of the global CARBON CYCLE. Human activity — burning fossil fuels — has DISRUPTED this cycle, adding MORE CO₂ than natural processes can absorb. That's climate change.'

4. Human Body Systems — Integrated and Interdependent

The Circulatory System

Heart → Arteries → Capillaries → Veins → Heart. Function: Transports OXYGEN, NUTRIENTS, HORMONES. Removes WASTE (CO₂, urea). 'The heart is a PUMP. It beats ~100,000 times a day. ~35 million times a year. The blood vessels in your body, if laid end to end, would circle the Earth TWICE.'

The Respiratory System

Nose → Trachea → Bronchi → Lungs (Alveoli). Gas exchange at the ALVEOLI: O₂ diffuses INTO blood. CO₂ diffuses OUT.

The Digestive System — From Food to Fuel

Mouth (mechanical + amylase) → Oesophagus → Stomach (HCl, pepsin) → Small Intestine (enzymes from pancreas, bile from liver — absorption through VILLI) → Large Intestine (water) → Excretion.

HOMEOSTASIS — The Body's Balancing Act

'Your body maintains a CONSTANT INTERNAL ENVIRONMENT — temperature (~37°C), blood sugar, water balance, pH. This is HOMEOSTASIS — and it's maintained through FEEDBACK MECHANISMS.'

Example — Temperature Regulation:

• Too HOT → Sweat (evaporative cooling). Blood vessels DILATE (vasodilation — heat lost).
• Too COLD → Shiver (muscles generate heat). Blood vessels CONSTRICT (vasoconstriction — heat conserved).

Your Summative Assessment

Option A — Ecosystem in a Bottle : Build a sealed ECOSYSTEM (terrarium/aquarium). Observe for 4 weeks. Document: energy flow. Nutrient cycling. Population changes. What keeps it in BALANCE? What could DISRUPT it?

Option B — Human Body Systems Poster : Choose TWO body systems. Explain: their STRUCTURES and FUNCTIONS. HOW they INTERACT. What happens when ONE system FAILS.

ATL Skills