⭐ BONUS – 🧬 Science – Biology: Cells, Ecology & Evolution – Not on Level 1 Exam
ACER Level 1 · Bonus early-prep content – advantage for future levels
📋 What You’ll Learn in This Lesson
- Cell organelles and their functions – the 5 you must know
- Photosynthesis and respiration – word equations and where they occur
- Food chains, food webs, and what happens when a species is removed
- Natural selection and the 3 conditions required for evolution
- 3 worked ACER-style biology questions with strategies
⭐ BONUS – Not on ACER Level 1 Exam. Science appears from ACER Level 2 onwards (our L3-L5). Starting early gives you a measurable advantage. Work through this at your own pace – no timer pressure for now.
🔬 Cell Structure – The 5 Key Organelles
| Organelle |
Found in |
Function |
| Cell membrane |
All cells |
Controls what enters and exits the cell (selective permeability) |
| Nucleus |
All cells (eukaryotes) |
Contains DNA – the genetic instructions. Controls cell activity. |
| Mitochondria |
All cells |
Site of cellular respiration. Converts glucose to usable energy (ATP). ‘Powerhouse of the cell.’ |
| Chloroplasts |
Plant cells only |
Site of photosynthesis. Contain chlorophyll (green pigment) that captures sunlight. |
| Cell wall |
Plant cells only |
Rigid outer layer (cellulose). Provides structural support. |
🌿 Photosynthesis vs Cellular Respiration
Photosynthesis: CO2 + H2O + light energy → glucose + O2
Occurs in chloroplasts. Plants, algae, some bacteria. Stores energy.
Cellular Respiration: glucose + O2 → CO2 + H2O + energy (ATP)
Occurs in mitochondria. ALL living cells. Releases energy for life processes.
| Feature |
Photosynthesis |
Cellular Respiration |
| Reactants (inputs) |
CO2 and H2O (+ light) |
Glucose and O2 |
| Products (outputs) |
Glucose and O2 |
CO2 and H2O (+ energy/ATP) |
| Energy |
Stored (light energy → chemical energy) |
Released (chemical energy → ATP) |
| Location |
Chloroplasts (plants only) |
Mitochondria (all cells) |
| When |
During daylight |
Continuously, day and night |
🌐 Ecology – Food Chains & Webs
🌱 Producer
Makes own food via photosynthesis. Always at the base of the food chain. Examples: grass, algae, trees.
🐇 Primary consumer (herbivore)
Eats producers. Examples: rabbit, caterpillar, grasshopper.
🦊 Secondary consumer (carnivore/omnivore)
Eats primary consumers. Examples: fox, frog, small fish.
🦅 Tertiary consumer (top predator)
Eats secondary consumers. Examples: eagle, shark, tiger.
🍄 Decomposer
Breaks down dead organic matter. Returns nutrients to soil. Examples: fungi, bacteria.
📝 Worked Example — ACER Food Web – Species Removal
Question
In a food web: Grass → Rabbit → Fox → Eagle. Grass → Grasshopper → Frog → Eagle. If foxes are removed, what happens to the rabbit population?
Step 1
Foxes eat rabbits. Remove foxes = less predation on rabbits.
Step 2
Rabbit population INCREASES (no predator controlling it).
Step 3
Consequence: more rabbits eat more grass, so grass decreases.
Key insight
Removing a predator causes the prey population to overshoot, which then depletes the producers.
✅ Answer: Rabbit population increases (over-populated); grass population decreases
🧬 Natural Selection and Evolution
1 – Variation
Individuals in a population are not identical. Some have traits that are advantageous.
2 – Heredity
Advantageous traits can be passed from parents to offspring (genetic inheritance).
3 – Selection pressure
The environment favours certain traits. Individuals with the advantageous trait survive and reproduce more.
4 – Over generations
The proportion of individuals with the advantageous trait increases in the population. This is evolution by natural selection.
| Evidence for Evolution |
What it shows |
| Fossil record |
Preserved remains show organisms that existed in the past and how species changed over time |
| Homologous structures |
Similar bone structures in different species (e.g. human arm, whale flipper, bird wing) suggest common ancestry |
| DNA similarity |
Species that share more DNA are more closely related (modern molecular evidence) |
| Comparative embryology |
Early embryos of many vertebrates look remarkably similar, suggesting shared ancestry |
⭐ ACER Examiner’s Trick: ACER biology questions about food webs almost always involve removing one species and asking about the effect on others. Trace EVERY chain that includes that species. Some effects are indirect and two steps away.
📌 Quick Reference Card — Biology
| Photosynthesis |
CO2 + H2O + light → glucose + O2. Chloroplasts. Plants only. |
| Respiration |
Glucose + O2 → CO2 + H2O + energy. Mitochondria. All cells. |
| Mitochondria |
Energy (ATP) production. All cells. |
| Chloroplasts |
Photosynthesis. Plant cells only. |
| Food chain direction |
Energy flows from producers to consumers (→). Never backwards. |
| Remove predator |
Prey increases → producers decrease (overpopulation then crash). |
