[Maximum number: 2]

Cultivated rice, Oryza sativa, is often grown in fields flooded with water.

(a)

Some varieties of cultivated rice are able to grow long internodes when they are submerged in water, keeping the leaves and flowers above water level (an internode is a length of stem between leaves). These varieties are known as deepwater rice.

The snorkel genes SK1 and SK2, thought to be responsible for this response, were identified in a variety of deepwater rice, C9285. A non-deepwater variety, T65, did not have these genes.

When submerged, rice plants produce the gaseous plant hormone ethene. This has a very low solubility in water, so it accumulates in the aerenchyma tissue in the rice stems.

Fig. 4.1 shows the concentration of ethene in the aerenchyma of T65 and C9285 when the plants are submerged in water for 18 hours.

Fig. 4.1

Fig. 4.2 shows the results of exposing T65 and C9285 to different concentrations of ethene in dry conditions.

Fig. 4.2

[ 2 ]

(i)

With reference to Fig. 4.1, describe the effect of submergence in water on the production of ethene in rice.

[ 2 ]

(a)

The Venus fly trap is a plant that is able to capture and digest insects. It has modified leaves, which have sensory hairs that respond to touch. When an insect comes into contact with the hairs, receptor potentials are generated.

[ 1 ]

(i)

If two or more of these hairs are stimulated within a period of 20-35 seconds, action potentials are generated, causing the leaf to close quickly and trap the insect.

Suggest why it is beneficial to the plant for stimulation of two or more hairs to be necessary before the leaf will close.

[ 1 ]

[Maximum number: 9]

The Venus fly trap, Dionaea muscipula, is a carnivorous plant, native to wetlands of the East Coast of the USA. Mineral ions from decayed organisms are often washed away in these wetlands.

Fig. 7.1 shows a Venus fly trap leaf.

Fig. 7.1

(a)

Suggest why a Venus fly trap benefits from catching insects in these wetlands.

[ 2 ]

(b)

(i)

The leaves of the Venus fly trap will close if stimulated by an insect.

State which part of the leaf detects the stimulus.

[ 1 ]

(ii)

Explain how the plant does not waste energy by closing when it does not need to, such as when a large drop of rain touches the receptor.
Question 7 continues on page 20.

[ 1 ]

(c)

Describe how the production of action potentials in the leaf cells of the Venus fly trap can result in the leaves closing and trapping an insect.

[ 5 ]

[Maximum number: 5]

The Venus fly trap, Dionaea muscipula, is a carnivorous plant. It has traps which catch insects.
Each trap consists of a pair of modified leaves joined by a midrib of hinge cells. The modified leaves have touch-sensitive hairs. If two hairs are touched within 20 seconds, or the same hair is touched twice in rapid succession, the trap closes.

(a)

Explain how touching the hairs results in closure of the trap.

[ 5 ]

(a)

Describe the response of the Venus fly trap to touch.

[ 8 ]