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CAIE IGCSE Biology 14.5.4 Chemical Control of Shoot Tropisms

Practise explaining phototropism and gravitropism in shoots as chemically controlled, directional growth responses.

Syllabus
2026–2028
Course
Biology 0610

Exam points

  • identify auxin as the chemical controlling unequal shoot growth in a tropic response
  • link greater cell elongation on one side of a shoot to bending towards or away from a stimulus
  • explain how upward or light-directed shoot growth improves access to light for photosynthesis

14.5.4—Phototropism and gravitropism question 1

[Maximum number: 4]

Fig. 6.1 shows some cells from the shoot tip of an onion, Allium cepa.

Fig. 6.1

Fig. 6.1

Cells just behind a shoot tip absorb water and grow in length. A plant hormone stimulates cell elongation and controls the response of stems to gravity.

Explain how the response of stems to gravity is controlled.

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