– DISTRIBUTION OF NUTRIENTS IN PLANTS –
It is generally believed by scientists that millions of years ago plant life originated in the water, and that new forms of plant life that could live on land developed gradually. This would not have been possible if an effective transport system had not evolved inside the plant to distribute food, water, and minerals.
Plants use both their leaves and roots to obtain food. The leaves, for example, capture the energy from the sunlight and hold it for future use in molecules of sugar. This sugar is later transported to the various other growing parts – the young branches, the growing fruit, the stem, and the roots.
The roots, on the other hand, pick up water and minerals from the soil. The sap, the liquid in a plant, transports them to the leaves and the other growing parts. Since nutrients often have to be distributed over long distances, an efficient transport system is necessary.
One of the best examples of this transport system can be seen in the giant sequoia tree, in California. ( 2000 years old tree )This tree sends down to the ends of its roots sugars that are made in the leaves hundreds of feet up in the air. And the ends of the roots may be a hundred feet away from the base of the tree.
Plants have three systems that make possible the interchange of substances among various parts of the plant body. These are the food transport system, the water transport system and the air transport system. The food transport system is the most delicate of the three. It can be easily damaged because it is alive.
Wounds, heat and exposure of the plant to toxic chemicals all damage the system that transports food. If you cut a branch and put it in water, it may seem alive for many days or even weeks; yet the food transport system stops functioning soon after the branch is cut from the tree. The water transport system is much less delicate than the food transport system. Water transport takes place in long strong tubes called capillaries. These consist of dead cells.
A German scientist once cut down a tree and then placed the base in a tub containing picric acid. The yellow, poisonous acid moved up to the top of the tree. There it killed the leaves, but the water transport system itself was not affected by the poison. When you cut through a tree trunk or branch, you notice two different tissues: the bark and the wood. The food transport system flows through the bark and the water transport system through the wood. These transport tissues wear out as the tree grows, so they are continually replaced. Every year new water- transporting tubes appear in new bark. The tissue responsible for this rejuvenation is a very thin layer of cells.
These cells form a tissue called the cambium. Being conveniently located between the wood and the bark, the cambium can easily receive the water, minerals and food necessary for producing fresh bark and wood tissue. The air transport system consists of air spaces between cells. Unlike desert plants, marsh plants have especially well developed air transport systems. This is mainly because marsh plants live on soft, wet land. So their roots are not exposed to much oxygen. The leaves of marsh plants can transport oxygen from the stomata, which are small openings on the surface of a leaf, through the stem to the roots. It is because of these transport systems that a plant can function as the whole organism that it is.
A. What do the following refer to?
1. “if (line 7):
2. ‘them’ (line 11):
3. ‘these’ (line 29):
4. ‘there’ (line 32):
B. Mark the best choice.
1. Line 21, ‘delicate’ probably means something that .
a) can be easily damaged b) is alive c) is damaged d) is toxic
2. Line 39, ‘rejuvenation’ probably means the .
a) production of new cells
b) destruction of live cells
c) transportation of water
d) wearing out of the bark and wood tissue
3. The function of the transport system is to .
a) evolve inside the plant
b) distribute food, water and minerals
c) develop land plants
d) obtain sugar from the green leaves