CourseCourseConceptConceptDocumentDocument

CAIE IGCSE Biology 14.5 Tropic Responses Questions

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

  • classify root and shoot phototropism or gravitropism by stimulus and direction, distinguishing tropic growth from photosynthesis or passive light absorption
  • interpret seedling or Petri-dish results and use light controls or rotating clinostats to isolate responses to light or gravity
  • trace auxin from the shoot tip to unequal distribution and explain how higher auxin drives faster elongation and shoot bending
  • explain how shoots growing upward or toward light improve access to light for photosynthesis

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

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 ]

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 ]

Question 3

[Maximum number: 7]

Question (a)

(a)

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.
- 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.
- 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.

Petri dish 1

Petri dish 1

Petri dish 2

Petri dish 2

Fig. 6.2 shows the seedlings after two days.

Fig. 6.2

Fig. 6.2

[ 7 ]

Question (i)

(i)

Describe the pattern of growth of the bean roots and shoots in Petri dish 1 shown in Fig. 6.2.

[ 1 ]

Question (ii)

(ii)

State the name of the growth responses observed in the bean roots and shoots.

[ 1 ]

Question (iii)

(iii)

Explain how auxin causes the difference in the pattern of growth shown by the shoots of seedlings B and E shown in Fig. 6.2.

[ 5 ]
All question bank results loaded