Rice is a semi-aquatic plant. In true aquatic plants air spaces (aerenchyma tissue) help to support the leaves near to the surface of the water. Locate the air spaces on the picture of the pond weed below. Click on the picture to see if you are right.

The term anaerobic means;

excess oxygen present
no oxygen present
an aquatic environment
a muddy habitat

In rice the main function of the air spaces (aerenchyma) is;

supply carbon dioxide to the roots
support the stem
help to cool the stem
supply oxygen to the roots

Complete the equation for anaerobic respiration in plants.

sugar ----> carbon dioxide + ?

Plants adapted to aquatic conditions are called;

mesophytes
hydrophytes
halophytes
xerophytes

Two advantages rice gain from growing in a semi-aquatic habitat are;

increased supply of nutrients
easy to harvest
increased supply of carbon dioxide
less competition with other species

 

Want to find out more about Rice? Follow this link to rice web.

 

 

Rice

The text below is adapted from material supplied by AQA.

Rice is one of the most important tropical food crops and forms the main source of food for nearly half of the world's human population. There are many varieties of rice and they differ in height, in the amount of time they take to mature and in their water requirements. In various parts of its range, rice is grown in different ways but most of the rice in south-cast Asia is grown in unusual conditions for a cereal plant. It is grown partly submerged in water in paddy fields. The fields are flooded and then ploughed. Young rice plants are planted in the rich mud formed in these paddy fields. The oxygen concentration of this mud fails rapidly after the paddy field has been flooded. The top ten centimetres or so retains some oxygen because it is able to diffuse in but below this depth anaerobic conditions exist and there is little or no oxygen present.

Rice plants have a number of adaptations which enable them to grow well in these conditions.

Rice stems contain a large number of air spaces. These spaces allow oxygen to penetrate through to the cells of roots growing in the absence of oxygen. These cells continue to get oxygen and are able to respire aerobically. Another adaptation shown by rice plants is that many of their roots are very shallow. These roots are able to make use of the oxygen which diffuses into the surface layer.

Rice stem showing its hollow middle and aerenchyma tissue.

When fields in which a cereal such as wheat is growing are flooded for any length of time, the plants die. The oxygen concentration of the waterlogged soil falls rapidly. The root cells are unable to get the oxygen they need in order to respire. In these conditions they can carry on respiring without oxygen. This is called anaerobic respiration and results in ethanol being formed as a waste product. Unfortunately, this substance is poisonous so a plant can only respire in this way for a short time before the ethanol concentration builds up and kills it. Cells in the roots of rice plants have been shown to be extremely tolerant of ethanol, much more so than cells from the roots of other cereals. They can therefore respire anaerobically for longer periods. There are two advantages of growing rice in paddy fields. Flooding brings about chemical changes in the soil which increases the supply of soil nutrients required by the rice plants. It also reduces weeds. Rice does not grow well when it has to compete with weeds for the resources that it needs.