A student investigated plant growth responses in roots and shoots. They used this method: - Damp cotton wool was placed in two Petri dishes. - Three bean seedlings were attached to the cotton wool in each Petri dish. - $$$\quad$$$ Each seedling was orientated so that the roots pointed in a different direction in each Petri dish. - Petri dish 1 was kept on its side in a fixed position. - Petri dish 2 was kept on its side and rotated constantly. - $$$\quad$$$ Both Petri dishes were kept in the dark. - Both Petri dishes were kept in these conditions for two days. - After two days the seedlings were observed. Fig. 6.1 is a diagram of the apparatus. Fig. 6.2 shows the seedlings after two days. Explain how auxin causes the difference in the pattern of growth shown by the shoots of seedlings $$$\mathbf{B}$$$ and $$$\mathbf{E}$$$ shown in Fig. 6.2.

Biology

IGCSE&ALevel

CAIE

Exam No：0610_s23_qp_42 Year：2023 Question No：6(a)(iii)

Answer:

Knowledge points:

14.5.1 Define gravitropism as a response in which parts of a plant grow towards or away from gravity

14.5.2 Define phototropism as a response in which parts of a plant grow towards or away from the direction from which light is coming

14.5.3 Investigate gravitropism and phototropism in shoots and roots

14.5.4 Explain phototropism and gravitropism of a shoot as examples of the chemical control of plant growth

14.5.5 Explain the role of auxin in controlling shoot growth, limited to: – auxin made in shoot tip (only) – auxin spreads through the plant from the shoot tip – auxin is unequally distributed in response to light and gravity – auxin stimulates cell elongation

Answer:

Knowledge points:

Solution:

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