Required Practical: Plant Growth (AQA GCSE Biology)

Revision Note

Lára Marie McIvor

Written by: Lára Marie McIvor

Reviewed by: Lucy Kirkham

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Effect of Light or Gravity

  • Aim: To investigate the effect of light or gravity on the growth of newly germinated seedlings

  • In order to investigate the effect of gravity on germinated seedlings you will:

    • Set up two petri dishes with 3 mustard seeds and allow them to germinate

    • Place one dish on a clinostat and the other to a support on its side

    • Record the direction of growth of both the shoots and the roots for each seed

Method

Investigating the gravitropic response (set-up), IGCSE & GCSE Biology revision notes

Investigating the gravitropic response (set-up)

  • Add some damp cotton wool to two petri dishes

  • Place 3 bean seedlings in the cotton wool in each petri dish

    • A - radicle facing downwards

    • B - horizontally

    • C - radicle (root grows from here) facing upwards

  • Cover each dish with a lid

  • Attach one petri dish to a support so that it’s on its side

  • Attach the second petri dish to a clinostat (as shown in the diagrams above).

  • Place both in a light-proof box (so that the seedlings are in complete darkness), leave for two days and then observe growth of the seedlings

Analysis of results

Investigating the gravitropic response (results), IGCSE & GCSE Biology revision notes

Investigating the gravitropic response (results)

  • In the first petri dish all radicles (roots) have grown downwards (positive gravitropic response) regardless of which way they were initially facing (horizontal, up or down) and all plumules (shoots) have grown upwards (negative gravitropic response)

  • In the second petri dish, all radicles and all plumules have all grown neither up nor down but straight outwards in whichever direction they were placed as the effect of gravity has been cancelled out by the revolving of the clinostat - they have shown no gravitropic response at all

  • The experiment needs to be done in a lightproof box in order to control the effect of light on the growth of the seedlings

    • Light is a control variable when investigating gravity

Examiner Tip

Make sure you know what a clinostat is and what it does (it cancels out the effect of gravity).

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Lára Marie McIvor

Author: Lára Marie McIvor

Expertise: Biology Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.

Lucy Kirkham

Author: Lucy Kirkham

Expertise: Head of STEM

Lucy has been a passionate Maths teacher for over 12 years, teaching maths across the UK and abroad helping to engage, interest and develop confidence in the subject at all levels.Working as a Head of Department and then Director of Maths, Lucy has advised schools and academy trusts in both Scotland and the East Midlands, where her role was to support and coach teachers to improve Maths teaching for all.