The Leaf: The Smallest Cleaning Tool

The Leaf: The Smallest Cleaning Tool

About a thousand square meters of plane trees can trap 3.5 tons, and pine trees 2.5 tons of pollutants!

The services that plants carry out for other living things are not restricted to giving off oxygen and water. Leaves at the same time carry out the most highly developed cleansing and purification functions. The cleaning tools we regularly use in our daily lives are produced and set in operation as the result of long studies by experts and after the expenditure of a lot of effort and money. These need considerable technical support and maintenance both during and after use. In addition, problems or defects that can arise on a daily basis, and the necessary staff and the need for other tools and renewals where necessary can all mean a great many more processes.
There are hundreds of details to consider even in a small piece of cleaning equipment, whereas plants do the same job as these tools in return for just sunlight and water, and perform the same cleaning service with the guarantee of greater efficiency. They also give rise to no waste product problem, because the waste product they give off after cleaning the air is oxygen, which all living creatures need!

Leaves Catch Air Pollutants

Tree leaves possess tiny filters that catch pollutants in the air. There are thousands of tiny hairs and pores, invisible to the naked eye, on the surface of a leaf. The individual pores trap pollutants in the air and send them to other parts of the plant to be absorbed. When it rains, these substances are washed to the ground. These structures on the surfaces of leaves are only of the thickness of a film; but when one considers that there are millions of leaves in the world, it becomes clear that the amount of pollutants trapped by leaves is not to be underestimated. A 100-year-old beech tree, for example, has about 500,000 leaves. The amount of pollutants caught by these leaves is more than one might guess. About a thousand square metres of plane trees can trap 3.5 tons, and pine trees 2.5 tons of pollutants! These materials then fall to the ground with the first rain. The air in a forest two kilometers from a settlement area is some 70 percent cleaner than that in the settlement area. Even in winter when trees lose their leaves, they still filter out 60 percent of the dust in the air.

Trees can trap dust weighing 5 to 10 times more than their leaves: bacteria levels in an area with trees is considerably less than in one with no trees [1]. These are very important figures.

As a food resource and cleaning tool scientists showed that leaves are protected by another perfectly planned mechanism. With the approach of winter the air grows colder and the days shorter, and less light reaches the Earth from the Sun. This reduction causes changes in plants, and the aging process in leaves, or leaf fall, begins.

Before trees lose their leaves, they begin to absorb all the nourishing substances in the leaves. Their aim is to prevent substances such as potassium, phosphate, and nitrate from disappearing with the falling leaves. These substances are directed through the pipelines that run through the layers of bark and the centre of the trunk. The collection of these substances in the xylem makes it easier for them to be digested by the tree.

The Leaf Fall Process


Trees must shed their leaves because in cold weather the water in the soil increasingly solidifies and becomes more difficult to absorb. But the perspiration in the leaves continues, despite the cold weather. A leaf that continues to perspire at a time when there is less water starts to become a burden on the plant. In any case, the cells in the leaf would freeze and break up in the cold days of winter, for which reason the tree acts early and frees itself of its leaves before winter arrives, and in this way its limited water reserves will not be wasted [2].

This leaf fall, which looks like a purely physical process, actually comes about as the result of a sequence of chemical events.

In the cells in the palm of the leaf are pigments called phytochromes that are sensitive to light and give color to plants. It is these molecules that allow the tree to realize that the nights are growing longer and that less light is reaching the leaves. When phytochromes sense this change they cause various changes within the leaf, and begin the leaf's aging program.

One of the first signs of leaf aging is that the cells in the palm of the leaf begin to produce ethylene. The gas ethylene begins to destroy the chlorophyll that gives the leaf its green color, in other words the tree withdraws the chlorophyll from the leaves. Ethylene gas also prevents the production of auxine, a growth hormone that delays the falling of the leaf. Together with the loss of chlorophyll, the leaf also starts to receive less energy from the sun and produces less sugar. Furthermore, carotenoids, which have hitherto been suppressed and that give the leaf its rich color, reveal themselves and in this way the leaf begins to change color[3].

A short while later, ethylene has spread to every part of the leaf, and when it reaches the leaf stalk, small cells there start to swell up and give rise to an increase in tension in the stalk. The number of cells in that part of the stalk that join onto the trunk increases, and they begin to produce special enzymes. First, cellulose enzymes tear apart the membranes formed from cellulose, and then pectinase enzymes tear apart the pectin layer that binds the cells to one another. The leaf can no longer bear this rising tension and starts to split from the outer part of the stalk in.

The processes we have been describing so far may be described as the cessation of food production and the first stages of the leaf's split from the stalk. Rapid changes go on around the developing split, and the cells immediately begin to produce suberin. This substance slowly settles over the cellulose wall and strengthens it. All these cells leave behind them a large gap replacing the fungus layer and die [4].


What has been described so far shows that a string of interlinked events is necessary for just one leaf to fall. Phytochromes determining that there is a reduction in sunlight, all the enzymes necessary to the falling of the leaf moving into action at the appropriate time, the cells beginning to produce suberin just at the place where the stalk will break off: it is clear what an extraordinary chain of events it takes for a leaf to detach itself. "Chance" cannot be offered as the explanation of this series of processes, all planned and following one another in perfect order. The leaf fall plan functions in a perfect manner.

Before the leaf is completely separated from the trunk, it no longer receives any water from the transport tubes, for which reason its grip on the place it is attached to grows progressively weaker. A moderate wind becomes all that is needed to break off the leaf stalk.

Contained in the dead leaf that falls to the soil are food substances that fungi and bacteria can make use of. These food substances undergo changes brought about by micro-organisms and become mixed with the soil. Trees can take these substances up again from the soil by their roots as nutriments.

Each and every process that occurs in leaves can be described as an individual miracle. These systems in green leaves, in the superb planning as in a microscopic factory, are proof of the creation of God, the Lord of all the worlds, and have come down to our day after hundreds of thousands of years in the same perfect state with no changes and no defects.

That's a very beautiful post, RiDDLe. May Allah reward you in heaps of good. Aameen.