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CAIE IGCSE Biology 14.5 Tropic responses Question Bank

Practise tropic-response questions by interpreting seedling diagrams, clinostat controls and auxin-driven shoot growth towards light or against gravity.

Syllabus
2026–2028
Course
Biology 0610

Exam points

  • identify phototropism or gravitropism from shoot and root growth direction
  • compare clinostat and control seedlings to separate light and gravity effects
  • explain auxin made in shoot tips, diffusing to one side and stimulating elongation

Covered syllabus points

14.5.1—Gravitropism as a response in which14.5.2—Phototropism as a response in which14.5.3—Gravitropism and phototropism14.5.4—Phototropism and gravitropism14.5.5—Role of auxin in controlling shoot

14.5 Tropic responses question 1

[Maximum number: 5]

2,4-D is a synthetic plant auxin that is used as a weedkiller.
Researchers investigated the effectiveness of different treatments of 2,4-D on the control of the weed Conyza canadensis in fields of maize, Zea mays.

The results are shown in Table 5.1.

Table 5.1

Table 5.1

Question (a)

(a)

Explain how 2,4-D acts as a weedkiller.

[ 3 ]

Question (b)

(b)

Auxin causes the shoots of a plant to grow away from gravity.

State the name of this response.

[ 2 ]

14.5 Tropic responses question 2

[Maximum number: 9]

The nervous system coordinates the responses of animals to changes in their environment.

Question (a)

(a)

Fig. 2.3 shows three pots of seedlings that have been kept in different conditions.

Fig. 2.3

Fig. 2.3

[ 9 ]

Question (i)

(i)

State the conditions in which pots P and Q were kept.

P
Q

[ 1 ]

Question (ii)

(ii)

State the name of the growth response shown by the seedlings in pot R.

[ 2 ]

Question (iii)

(iii)

Explain the advantage to the seedlings of this growth response.

[ 2 ]

Question (iv)

(iv)

Auxins control the growth responses of seedlings.

Explain how auxins control the growth response of the seedlings in pot R.

[ 4 ]
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