Unit Synthesis + Working Scientifically Depth Study
In 2019, CSIRO scientists ran more than 500 controlled plant-growth experiments, each one changing just one variable at a time, and confirmed that sunlight increases duckweed growth by up to 400%.
Printable Worksheets
Print or save as PDF, or build a custom worksheet from any module's questions.
Q1 · Without looking back, write everything you can remember about MRS GREN, classification and cells in 2 minutes. Just a brain dump, don't worry about being neat.
Q2 · A student claims plants grow taller with classical music playing. What's WRONG with that statement as a starting point for a science experiment? List two problems.
● Know
- The big ideas of Unit 1: MRS GREN, classification, cell theory, and cells → tissues → organs
- The six steps of a scientific investigation: Q → H → M → R → D → C
- The three types of variable (independent, dependent, controlled)
● Understand
- Why a fair test changes only one variable at a time
- Why replicates and controls make results trustworthy
- How to write a testable hypothesis using "If… then…"
● Can do
- Identify IV, DV and controlled variables in an investigation
- Write a testable hypothesis
- Plan your own simple investigation using the Q-H-M-R-D-C structure
- Hypothesis
- Independent variable
- Dependent variable
- Controlled variable
- Replicate
- A repeat of the same condition
- The one thing you deliberately change
- A testable prediction ("If… then…")
- Something kept the same across all groups
- What you measure to see the effect
Picture a single duckweed plant floating on the surface of a pond: it is alive (it shows MRS GREN), it can be classified (a tiny flowering plant), and like every living thing it is built from cells. Those three ideas, life, classification and cells, are the whole of Unit 1 in one tiny floating leaf. Here's the big map.
| Idea | Where it sat in the unit | How it connects |
|---|---|---|
| Characteristics of life MRS GREN | L01 | The test for what counts as living. Only living things get classified, and only living things are made of cells. |
| Classification kingdoms, domains, keys | L02–L05 | Sorting life by shared features: kingdoms and domains, vertebrates vs invertebrates, the plant groups, and the microorganisms (bacteria, fungi, protists, and the virus "grey area"). |
| Cell theory the smallest unit of life | L06 | Every living thing is made of one or more cells, and all cells come from existing cells. |
| Plant vs animal cells organelles | L07–L08 | Shared parts (nucleus, membrane, cytoplasm, mitochondria) plus the plant-only cell wall, chloroplasts and large vacuole. |
| Specialised cells → tissues → organs | L09–L10 | The same building blocks specialise and organise into the bigger working parts of an organism. |
A single example to tie it together: a koala is alive, it shows all seven MRS GREN signs, so it can be classified. It belongs to the animal kingdom, is a vertebrate (a mammal), and sits on the same branch of life as other Australian marsupials. Like every animal it is built from cells: specialised cells (nerve, muscle, blood) group into tissues, tissues into organs, and organs into the body systems that keep it alive. Characteristics, classification and cells, every Unit 1 idea shows up in one animal.
Every formal science investigation in NSW uses the same backbone. Memorise the six letters.
| Letter | Step | What you do |
|---|---|---|
| Q | Question | A clear, testable scientific question. Usually starts "How does …?" or "What is the effect of …?" |
| H | Hypothesis | A predicted answer in "If … then … because …" form. |
| M | Method | The steps anyone could follow to repeat your experiment. Include variables, equipment, replicates and safety. |
| R | Results | Tables and graphs of what you measured. Numbers, not feelings. |
| D | Discussion | What patterns do the results show? Were there any errors? Compare with the hypothesis. |
| C | Conclusion | One or two sentences answering the original question, based on the results. |
This structure isn't a school invention, published scientific papers use the same skeleton.
A formal investigation runs Q (Question), , , , Discussion, Conclusion. The independent variable is the one thing you ; the dependent variable is what you .
You can't run a fair test until you know your variables. There are three jobs to label.
- Independent variable (IV) the ONE thing you deliberately change. Usually goes on the x-axis of a graph.
- Dependent variable (DV) the thing you measure. Usually goes on the y-axis.
- Controlled variables everything else, kept the same. Often called the "controls" of the experiment.
The fair-test rule: change one IV, keep everything else the same, and measure the DV. If you changed two things at once, you wouldn't know which one caused the result.
Example to ground it. "Does light intensity affect how fast duckweed grows in a pond microcosm?" → IV = light intensity (lux). DV = number of new leaves per week. Controlled: water type, water volume, container size, temperature, starting number of duckweed, time of day measured.
- Light intensity (lux)
- New leaves per week
- Water temperature
- Volume of water in each cup
- Container size
- Controlled variable
- Independent variable
- Controlled variable
- Dependent variable
- Controlled variable
Let's walk through a full investigation using the Q-H-M-R-D-C structure on a real pond plant.
| Step | What it looks like |
|---|---|
| Q (Question) | "How does light intensity affect the growth of duckweed in a pond microcosm?" |
| H (Hypothesis) | "If light intensity increases, then the rate of duckweed leaf growth will increase, because duckweed is a green plant and uses light for photosynthesis." |
| M (Method) | (1) Fill 12 clear cups with the SAME 300 mL of pond water. (2) Add exactly 10 starting duckweed plants to each cup. (3) Place 3 cups in each of 4 light conditions: dark cupboard, low (one weak lamp), medium (room window), high (under bright lamp). (4) Keep temperature, water volume, water source, container size and time the same. (5) Count new leaves every 3 days for 3 weeks. |
| R (Results) | Table of leaf counts at each light level, averaged across 3 replicates. Bar graph: Light level (x-axis) vs Average new leaves per week (y-axis). |
| D (Discussion) | Duckweed in higher light grew faster, supporting the hypothesis. Possible sources of error: leaves stuck together, some cups slightly warmer. Replicates reduce the impact of one stray cup. |
| C (Conclusion) | "As light intensity increased, duckweed leaf growth increased. The data supports the hypothesis that photosynthesis-driven growth depends on light intensity." |
Notice the three things that make this a fair test: one IV (light), measured DV (new leaves), and everything else controlled. The three replicates per condition are what make the conclusion trustworthy.
Wrong: "My hypothesis is: plants are amazing." Not testable, there's no way to measure "amazing", and no way to prove the statement wrong.
Right: A hypothesis must be testable and falsifiable. Use the "If … then … because …" form.
Wrong: "I changed the amount of light AND the temperature, so the plants grew differently because of one of those." If you change two variables, you can't tell which caused the effect.
Right: Change ONLY one IV at a time. Keep all other variables constant.
Wrong: "I tested it once and got a result, so it's proved." One trial could be a fluke. You need replicates and ideally repeats across different days.
Right: Use multiple replicates per condition and report an average. More repeats = more trust in the result.
In the duckweed investigation, what do you predict will happen at VERY high light (e.g. directly under a strong lamp 24 hours a day) compared to high but normal light? Will growth keep increasing forever? Explain in 1–2 sentences, then reveal.
How close was your prediction?
Excellent, you grasped that biological responses usually plateau.
Good, the "upside-down U" is one of biology's most important patterns.
At the start of the lesson you were asked how you would actually prove that plants grow better in sunlight, what would you change and what would you keep the same?
Now that you've worked through the full scientific method, revisit your original idea. Did you include a control? Did you think about repeating the experiment? Write your improved experimental design.
Q1. Name the six steps of a scientific investigation (Q-H-M-R-D-C) and briefly describe what each step does. (3 marks)
Q2. A student asks: "Does water temperature affect how many mosquito larvae hatch?" Write a testable hypothesis, then identify the IV, DV, and three controlled variables. (4 marks)
Q3. Choose ONE concept from Unit 1 (MRS GREN, classification, cell theory, plant vs animal cells, or specialised cells/tissues/organs). Explain how it links to the other concepts in the unit, using a real Australian example. Show that you understand the unit as a connected system, not isolated topics. (4 marks)
Answers
▾MCQ 1
B The IV is what the experimenter deliberately changes. A describes the DV. C describes controlled variables.
MCQ 2
C Only the "If light intensity increases, then duckweed growth will increase" option is testable and falsifiable. The others are vague feelings or simple facts, not predictions.
MCQ 3
A Number of new leaves per week is what's being measured (the DV). Light intensity is the IV; the others are controlled.
MCQ 4
D Three cups at each light level are replicates. Running multiple replicates lets you average and trust the result.
MCQ 5
B MRS GREN defines life → classification sorts that life by shared features → and every living thing is built from cells that specialise into tissues and organs. That is the unit's main story arc. The other options miss that connection.
Short Answer 1
Model answer: Q = Question (a clear, testable scientific question). H = Hypothesis (a predicted answer in "If … then … because …" form). M = Method (the repeatable steps you'll follow, including variables and replicates). R = Results (your measured data in tables and graphs). D = Discussion (interpret the patterns, mention errors and compare with hypothesis). C = Conclusion (one or two sentences answering the original question using your results).
Short Answer 2
Model answer: Hypothesis: "If water temperature increases from 10 °C to 30 °C, then the number of mosquito larvae hatching from a fixed batch of eggs will increase, because warmer water speeds up the embryo's development." IV = water temperature. DV = number of larvae hatched per 100 eggs in 48 hours. Controlled = type of water (rainwater), volume of water in each container (200 mL), number of eggs per container (100), light conditions, container size. Run 3 replicates at each temperature and graph average hatch rate vs temperature.
Short Answer 3
Model answer (classification): Classification is how we sort the variety of life, and it connects every Unit 1 idea. It only applies to living things, which we recognise because they meet MRS GREN (Lesson 1). We group organisms by shared features into kingdoms and domains, separate vertebrates from invertebrates, sort the plant groups, and place the microorganisms (Lessons 2–5). All of those groups share one deeper feature: every member is built from cells (cell theory, Lesson 6), whether plant or animal cells (Lessons 7–8), and in larger organisms those cells specialise into tissues and organs (Lessons 9–10). Take a Tasmanian devil: it shows MRS GREN, so it can be classified, it is in the animal kingdom, a vertebrate, a mammal, in fact a marsupial, and like every animal its body is built from specialised cells that form tissues, organs and organ systems. Every concept from the unit shows up in classifying one species.