Tropic Responses
Overview
Plants cannot walk towards the sunshine, but they can grow towards it. Put a seedling on a windowsill and within days its shoot bends to face the light. Plant roots, meanwhile, grow downwards no matter which way you plant the seed. These growth responses to direction are called tropisms.
In this lesson you will learn what phototropism and gravitropism are, how to investigate them in shoots and roots, and (for the extended curriculum) how the chemical auxin controls them by making one side of a shoot grow faster than the other.
Objectives
- Describe gravitropism as a response in which parts of a plant grow towards or away from gravity
- Describe phototropism as a response in which parts of a plant grow towards or away from the direction of the light source
- Investigate and describe gravitropism and phototropism in shoots and roots
- [Supplement] Explain phototropism and gravitropism of a shoot as examples of the chemical control of plant growth
- [Supplement] Explain the role of auxin in controlling shoot growth, limited to: (a) auxin is made in the shoot tip (b) auxin diffuses through the plant from the shoot tip (c) auxin is unequally distributed in response to light and gravity (d) auxin stimulates cell elongation
Audio Lesson
Listen to this lesson in the app
Mind map
This topic is mapped out so you can see how the ideas connect.
Open the mind map in the app
Flashcards
Quick recall practice on the facts this topic is tested on.
Practise these cards in the app
Lesson Note
Complete Note Available on the Green Bridge App
Get the Green Bridge CBT app on your phone or computer for the complete IGCSE library: past papers, mark schemes, mind maps, flashcards and audio lessons.
Lesson Evaluation
Congratulations on completing the lesson on Tropic Responses. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- A plant shoot growing towards light shows: A. positive gravitropism B. negative gravitropism C. positive phototropism D. negative phototropism Answer: C
- A root growing downwards towards gravity shows: A. positive gravitropism B. negative gravitropism C. positive phototropism D. negative phototropism Answer: A
- Auxin is made in the: A. root tip only B. shoot tip C. leaves D. flowers Answer: B
- When a shoot is lit from one side, auxin collects on the: A. lit side B. shaded side C. top D. roots Answer: B
- Auxin stimulates shoot cells to: A. divide only B. elongate C. die D. shrink Answer: B
Work through these questions in the app
Work through these questions in the app
Recommended Books
Practice Mock Questions
Want to practice mock questions on Tropic Responses? Download the Green Bridge CBT app to access mock questions and full practice assessments for this topic.
Download The App On Google Playstore
Everything you need to excel in your exams
