24 Substances transported in plants

Plants obtain the substances they need to flourish in a completely different way to animals.

We are learning how to:

• identify substances transported in plants

• Animals eat complex chemicals that are broken down to provide those substances

• Plants absorb and use simple chemicals to create those substances themselves

Consequently substances are transported in different ways.

Transport of gases

You learned in the previous unit that:

• all organisms carry out respiration to obtain energy; this process requires oxygen and produces carbon dioxide

• green plants carry out photosynthesis to make food; this process requires carbon dioxide and produces oxygen

ProcessGas neededGas produced respirationoxygencarbon dioxide photosynthesiscarbon dioxideoxygen

TABLE B 3.24.1

Plants have no organ corresponding to the lungs or gills of an animal. They rely on diffusion for transport of gases. Oxygen and carbon dioxide pass into and out of the plant through tiny pores. Many of these pores, or stomata, are located on the underside of leaves.

This is not an active method of transport so gases take much longer to move through a plant than through an animal.

Transport of substances in solution

Plants cannot ingest solids in the same way that animals can, so all of the chemicals they need must be absorbed in solution from the soil.

Soil water containing dissolved minerals is absorbed into root hair cells by osmosis. The solution passes from cell to cell in the root by the same process until it reaches the stem.

Inside a plant stem there are two types of vessels called the xylem and the phloem. You will learn more about these vessels later in this unit.

• The solution of minerals passes up from the roots to the rest of the plant through the xylem.

• Solutions of substance pass from one part of a plant to another through the phloem.

Plants have no organ corresponding to the heart of an animal. Solutions of substances are not pumped around a plant in the same way as blood circulates in an animal and consequently transport takes much longer.

Check your understanding

1. a) How are gases transported in and out of plants?

b) Why does the movement of gases in plants take much longer than it does in animals?

2. a) How are nutrients transported from the soil through the roots of a plant?

b) Through which vessels are substances transported in a plant?

Key terms diffusion net movement of particles spreading from an area where they are in high concentration to one where they are in low concentration osmosis net movement of water from an area of high concentration to one of low concentration through a partially permeable membrane