Plant Hormones | GCSE Biology

Homeostasis and response

Lesson overview

This lesson introduces the core biology idea, the useful equipment and the calculation or data skills used on this page.

Focusplant hormones, tropisms and growth responses

Time45-60 minutes

EquipmentNotebook, calculator and a pen for labelled diagrams.

Practical linkseedling growth and plant-response evidence

Maths tagslength, rate, concentration and comparison

What you will learn

Describe the key biology ideas behind plant hormones and tropisms.
Use precise GCSE command-word language in explanations.
Apply the idea to unfamiliar cells, organisms, data or practical contexts.
Check answers using units, labelled diagrams, observations, calculations or biological evidence where relevant.

Core knowledge

Big idea: Plant growth responses happen because auxin changes growth rate on different sides of shoots or roots.
This lesson focuses on plant hormones, tropisms and growth responses. A strong answer explains the biology and points to evidence such as feedback graphs, receptor-effector pathways, hormone levels and response data.
Auxin: a plant hormone that affects growth direction and cell elongation.
Phototropism: growth response to light.
Gravitropism: growth response to gravity.
Use the model as a thinking route: Plant shoots and roots detect a stimulus -> Auxin distribution changes growth rate -> Unequal growth bends the plant organ.
Likely question evidence: seedling diagrams, light direction, gravity responses, growth measurements and hormone concentration data. Use it to justify the explanation, not as decoration.
When numbers or graphs appear, show working with length, rate, concentration and comparison and finish by saying what the result means biologically.

Plant hormones and tropisms infographic

Infographic explaining GCSE Biology plant hormones and tropisms, including auxin, phototropism, gravitropism, unequal growth, evidence and hormone uses. — Use this visual to connect auxin redistribution with unequal growth, tropism responses, growth evidence and plant-hormone uses.Download visual

Plant Hormones practice set

Use the worked examples and practice questions on this page as a complete study task: learn the definitions of auxin and phototropism, summarise the infographic in your own words, then answer the questions using the data, equations and observations given here. Check every answer for length, rate, concentration and comparison.

Clear explanation

First secure the anchor idea: plant hormones, tropisms and growth responses. In ordinary language, this means using auxin, phototropism and gravitropism to explain what is happening, not just spotting those words in the question.

Next look for the evidence. In this lesson it is likely to come from seedling diagrams, light direction, gravity responses, growth measurements and hormone concentration data.

Then build the answer in order: Plant shoots and roots detect a stimulus then auxin distribution changes growth rate then unequal growth bends the plant organ. This stops the answer becoming a list of disconnected facts.

If the question includes data, use length, rate, concentration and comparison. Keep the unit or comparison visible, then link the result back to auxin or phototropism.

Exam-ready model sentence: Unequal auxin distribution causes unequal growth, so the shoot or root bends in response to the stimulus.

Worked examples

Plant Hormones: from idea to explanation

Question: Explain plant hormones, tropisms and growth responses using the model.

Start with the idea: Plant shoots and roots detect a stimulus.

Add the mechanism: auxin distribution changes growth rate.

Finish with the consequence: unequal growth bends the plant organ.

Reveal worked answer

Answer: A good answer uses auxin (a plant hormone that affects growth direction and cell elongation), phototropism (growth response to light) and gravitropism (growth response to gravity) in one connected explanation. For example: Unequal auxin distribution causes unequal growth, so the shoot or root bends in response to the stimulus.

Plant Hormones: from evidence to marks

Question: A student has evidence from seedling diagrams, light direction, gravity responses, growth measurements and hormone concentration data. What should their answer include?

Step 1: name the useful evidence rather than writing a general fact about the topic.

Step 2: process any data with length, rate, concentration and comparison.

Step 3: explain what the evidence shows about auxin and phototropism.

Reveal worked answer

Answer: The answer earns marks by joining evidence, method or data to a biological reason. Avoid describing a change without showing how feedback or a response returns conditions towards normal.

Quick checks

Choose an answer, then check your thinking.

1. Which answer would make plant hormones clearer?

Plant shoots and roots detect a stimulus and explain it using auxin Repeat the topic title without explaining it Ignore the evidence and write a memorised paragraph

2. What should you check before finishing an answer on this lesson?

Whether the answer sounds long enough Whether length, rate, concentration and comparison and evidence such as seedling diagrams, light direction, gravity responses, growth measurements and hormone concentration data have been used where needed Whether every keyword from the page has been copied

Practice questions

Question 1

Define auxin and use it in a complete sentence about plant hormones and tropisms.

Reveal answer and marking guidance

Answer: Auxin means a plant hormone that affects growth direction and cell elongation. In plant hormones and tropisms, it helps explain plant shoots and roots detect a stimulus.

Marking: Credit the definition and a sentence that uses the term in the lesson context.

Question 2

Explain the main sequence in Plant Hormones using the infographic.

Reveal answer and marking guidance

Answer: Plant shoots and roots detect a stimulus -> Auxin distribution changes growth rate -> Unequal growth bends the plant organ. A strong answer says why the final step follows from the first two steps.

Marking: Credit the correct order plus a biological link between the steps.

Question 3

A question gives evidence such as seedling diagrams, light direction, gravity responses, growth measurements and hormone concentration data. What should you do with that evidence?

Reveal answer and marking guidance

Answer: Identify the useful observation, method detail or data first. Then use length, rate, concentration and comparison where relevant and explain what it shows about auxin, phototropism or gravitropism.

Marking: Credit evidence use, relevant data handling and a clear biology explanation.

Question 4

A student writes: 'auxin is involved, so the answer is correct.' What detail is missing?

Reveal answer and marking guidance

Answer: Auxin means a plant hormone that affects growth direction and cell elongation. A better answer also uses phototropism (growth response to light) and explains the evidence route: Plant shoots and roots detect a stimulus then auxin distribution changes growth rate. An exam-ready version could be: Unequal auxin distribution causes unequal growth, so the shoot or root bends in response to the stimulus.

Marking: Credit a precise definition, a second linked term and use of evidence or model steps.

Practice ladder

FluencyRecall the key definition, symbol, structure, equation or observation.

ApplicationApply plant hormones and tropisms to unfamiliar organisms, cells, systems, practicals or data.

Practical interpretationUse evidence, method quality, uncertainty or conclusion wording where asked to evaluate.

Maths skillUse units, ratios, graphs and significant figures accurately.

Answers and marking guidance

The exact practice answers are hidden under each question so you can try first. Marks come from using the correct biology model, choosing the right calculation where needed, keeping units with values, labelling diagrams clearly, and explaining changes with precise words such as cells, enzymes, hormones, genes, adaptation, rate, evidence and uncertainty.

Common mistakes

Using auxin, phototropism or gravitropism as labels without explaining what they mean.
Forgetting to connect the answer to likely evidence, such as seedling diagrams, light direction, gravity responses, growth measurements and hormone concentration data.
Missing the maths or data habit: length, rate, concentration and comparison.
Falling into the common trap of describing a change without showing how feedback or a response returns conditions towards normal.

Extension challenge

Create a focused revision card for plant hormones and tropisms: three exact definitions, one model sequence, one evidence detail such as seedling diagrams, light direction, gravity responses, growth measurements and hormone concentration data, one data check using length, rate, concentration and comparison, one common misconception, and one exam-ready explanation sentence: Unequal auxin distribution causes unequal growth, so the shoot or root bends in response to the stimulus.

Reveal answer

Example answer: A complete response names the biology model, uses accurate units or observations, and explains why the evidence supports the conclusion.