Fungi: The scavengers of the natural world

Fungi are a group of organisms that play a vital role in the natural world. Fungi are the scavengers of the natural world. They (fungi) range in complexity from simple single-celled organisms like yeast to complex multi-cellular organisms like mushrooms.

The fungus is abundant and omnipresent in the natural world. The air we breathe, the water we drink and the soil, all contain fungus. Apart from being natural scavengers, the fungus is also important in medicine. Fungus cause many diseases. The most common infections caused by fungus include skin and hair infections. However, the fungus can also cause serious infections like pneumonia and bloodstream infections, especially in persons with compromised immunity.

What is unique about fungus?

Till 1969, fungi were considered to be a part of the plant kingdom. However, research showed that fungi are different from other animals and plants. The cell walls of fungi contain a substance- chitin. The cell wall or membrane of plants and animals does not contain chitin. Therefore, fungi are now a separate kingdom.

How do fungi derive their nutrition?

Like other animals, fungi are also heterotrophs. That means that they (fungi) derive their nutrition from the natural world. As discussed before, a fungus is the first scavengers of the natural world. Therefore, you are likely to see them near rotting organic matter, like waste dumps or even in your garden.

What are the types of fungi?

There are three major types:-

  1. Single-celled yeasts

  2. Filamentous Multicellular moulds like Aspergillus or Rhizopus: – The basic unit of moulds is the hyphae. The hypha is a long filament that grows and repeatedly divides, forming a bunch of intervened filaments- the mycelium.

  3. Mushrooms- multicellular, filamentous fungus that form large fruiting bodies: – Mushrooms are also made up of hyphae. The body of the mushrooms contains many hyphae that are tightly packed to form the umbrella-like structure that grows overground.

Most of the medically important fungus belong to the category of yeasts or moulds. On the other hand, the commercially important fungus belongs to the class of mushrooms (not in the strictest sense, fungi like yeast are also important commercially, like in bakeries and breweries).


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How do fungi reproduce?

Fungus reproduces by spore formation. Spore formation is a method of asexual reproduction. Spores are specialised structures that are resistant to sunlight and drying. Therefore, they can persist in the environment for many days or even months. These spores can germinate when the condition is favourable to produce a daughter fungus. You must have seen a powdery substance that sticks to all surfaces during the rainy season. The powdery substance is a fungus. During rains, the atmosphere is high in moisture. Therefore, this is a favourable time for fungal spores to germinate. The fungal spores that are present in the air settle on moist surfaces and then germinate, thus forming the powdery substance. The same principle is true for mushrooms as well.

Thus, the fungus is a ubiquitous organism that play a vital role in the natural world. The fungus has many important roles in medicine, everyday life and many commercial applications. Mycology is the study of fungus.

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Movement in Plants

We have all seen trees swaying in the wind. Is it an example of movement in plants? In the strictest sense, yes. However, this action is not indicative of life. Even a dead tree or plant can sway in the wind. The movement of plants here is caused by the wind and is not intrinsic to the tree or plant. So, what movements are essential to a tree or plant?

There are two such movements in plants that are indicative of life. One is the immediate response to stimuli and the other is in response to growth.

Prof. Jagdish Chandra Bose, an Indian physician, biologist and scientist was the first to demonstrate movement in plants. He invented the crescograph, an instrument that can be used to measure movement in plants.

Have you seen or touched the ?touch-me-not? plant (Mimosa pudica)? As soon as you reach the leaves, they droop and curl up. How does this happen?

Plants do not have specialised structures like nerves or neurones to control their movement. They instead rely on electromechanical signals to control movement in plants. In the above example, when we touch the leaves, the leaves sense the pressure, and this is transmitted as electric signals to the cells adjoining the leaves. These then quickly lose water, leading to drooping of the leaves. In fact, most of the movement in plants is due to ingress and egress of water from the cells.

Another movement in plants is in response to growth. We have all eaten sprouts. Have you noted how your mother makes these? Sprouts are made from a class of plants called lentils. There are different varieties of lentils, and the seeds of these plants are soaked and allowed to germinate to produce the sprouts.

When these seeds are soaked in water and left in air, they germinate, and you can see the roots and shoots coming out. If you leave them long enough, one can see them grow in length. This movement in plants is a manifestation of growth. If we take this germinating seed and plant it in the soil, in a few days you will note that the shoot starts growing upwards, and a new plant is born.

What would happen if we suspend this germinating seed in the air? Will the root grow upwards or the shoot grow downwards? ?No, irrespective of where a seed is planted, the roots will always grow in the direction of gravity, and the shoots will grow against gravity.

Now let us set up another experiment. Take two potted plants and keep them inside a cardboard box. In one box, make a hole on one side to let in sunlight. Maintain the plants for a few days inside these boxes. What would you notice?

You would see that the plant in the box with the hole has grown in the direction of the hole. Movement is plants in influenced by the direction of sunlight. Gravity also affects movement in plants. This movement in plants is called as tropism or more accurately called heliotropism and geotropism respectively.

Plants can also move in response to chemical stimuli. In the above experiment, the plant grows in the direction of sunlight by the action of a chemical called Auxin. This chemical diffuses to the shady side of the shoot and stimulates growth on that side. Therefore, the shoots grow towards the sunlight.

Thus, we have learnt that movement in plants can be a manifestation of growth, or it can be in response to environmental changes. Even though plants do not have a nervous system, they can move using electromechanical or chemical signals.

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