IGCSE Biology Extended 14.5.1—Gravitropism as a response in which Topic Practice

Plants also make hormones.

State the name of one hormone made by plants.

Two identical potted plants were used to investigate plant responses.
Plant A was placed on a clinostat that continually rotated. Plant B was not rotated.
Both plants were then placed on their sides and kept in the dark.
Fig. 4.1 shows the two plants at the start of the experiment and after seven days.

State the name of the response shown by the shoot of plant B.

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.

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

State the name of this response.

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.

Fig. 6.2 shows the seedlings after two days.

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

Fig. 5.1 is an image of a germinating seed showing the growing root.

The root shown in Fig. 5.1 is growing downward into the soil.

Name this response seen in roots.