CHAP. 3.3 – KINGDOM: FUNGI
I. WHAT ARE FUNGI?
You have seen fungi when you observed mold on bread or decaying fruit, mushrooms sprouting out of the grass, and in the grout of bathroom tiles.
Characteristics of Fungi:
1. Fungi are eukaryotes (they have a nucleus).
2. Fungi reproduce by spores.
3. Fungi are Heterotrophs (does not make their own food).
4. Grow when the environment is moist, warm, and damp.
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II. CELL STRUCTURE
Fungi cells are arranged in structures called hyphae
(the exception to this is yeast cells).
Hyphae are branching, threadlike tubes made of cytoplasm.
Hyphae are arranged in two ways and the arrangement will decide the appearance of the fungi:
1. Loosely – tangled: Hyphae will spread across a surface like a web. This structure is the fuzz growing on top of old food.
2. Tightly – packed: Hyphae that is tightly wound together that it forms a solid mass. It forms the stalk and cap of mushrooms.
III. HOW DO FUNGI OBTAIN FOOD?
First, the fungus grows hyphae unto a food source.
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Second, digestive chemicals ooze from the tips of the hyphae into the food.
Third, the digestive chemicals break down the food into small substances.
Fourth, the small substances are absorbed through hyphae.
Fungi feed off of dead organisms (such as fallen leaves) and living organisms (such as human skin in athlete’s foot).
IV. REPRODUCTION IN FUNGI
A. ASEXUAL REPRODUCTION
Fungi can asexually reproduce in two ways: making spores or budding.
1. Spores
The usual way fungi reproduce is making thousands of spores.
The spores are lightweight and surrounded by a protective covering.
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Being lightweight, spores are easily carried by air and water.
If the spore lands in a place that is moist, warm, and damp, it will grow.
The spores are produced in a fungi structure called a fruiting body. The fruiting body is nothing more than a reproductive hyphae.
2. Budding
Only unicellular fungi like yeast reproduce by budding.
In budding, a new cell forms inside a parent cell. The new cell eventually makes it way out of the parent cell and lives on its own. The new cell is identical to the parent cell.
B. SEXUAL REPRODUCTION
Fungi only undergo sexual reproduction when growing conditions become unfavorable.
In sexual reproduction, hyphae of two different fungi meet and exchange genetic material.
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A new spore-producing structure grows from the joined hyphae. This new spore-producing structure makes spores that will develop into fungi.
V. CLASSIFICATION OF FUNGI
Fungi are classified according to 1) shape of their spore-producing structure and 2) on their ability to reproduce.
There are four groups of fungi:
1. threadlike fungi – Fungi are produced by spores in their threadlike hyphae (ex. Bread mold).
2. sac fungi – Fungi produce spores in structures that look like sacs (ex. Yeast).
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3. club fungi – Fungi produce spores that look like clubs
(ex. Mushrooms).
4. imperfect fungi – Fungi in this group will not reproduce sexually (ex. Penicillium).
VI. FUNGI AND THE LIVING WORLD
A. ENVIRONMENTAL RECYCLING
Fungi are great decomposers. As decomposers, they break down the chemicals in dead organisms and return the important nutrients in the chemicals back to the soil.
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B. FOOD & FUNGI
Yeast helps bread rise and makes wine.
In bread, the yeast is added to the bread dough. The yeast eats the sugar in the dough and produces carbon dioxide gas bubbles. The bubbles causes the bread to rise (you see the bubbles in bread).
Blue cheese is made from a fungus (Penicillium
roqueforti).
C. DISEASE – CAUSING FUNGI
There are many fungi that destroy crops, plants, and trees. The most famous one is Dutch Elm disease.
The fungi can also attack human skin in the form of
Athlete’s foot and Ringworm.
D. DISEASE – FIGHTING FUNGI
The most important fungus that kills bacteria is penicillium. It was discovered in 1928 by a Scottish biologist Alexander Fleming.
Fleming was growing bacteria in Petri dishes and noticed that a mold grew on some of the dishes. Where the mold grew, it killed the bacteria and the bacteria refused to grow near it.
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E. FUNGUS – PLANT ROOT ASSOCIATIONS
Some fungi help plants grow healthier and stronger such as orchids.
The hyphae of a fungus grow with a plant’s root system. The hyphae spread out to absorb water and nutrients for the plant. In return, the fungus eats the extra food the plant makes.
F. LICHENS
Lichen is a symbiotic relationship between a fungus and either algae or bacteria. The fungus eats the food produced from the algae or bacteria. The algae or bacteria get water and minerals from the fungus.
Lichen is important because:
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1. They are the first organisms to grow on bare rock after a volcano or fire has occurred. The lichen will break down the rock into soil for organisms to grow in.
2. They are very sensitive to pollution and will die if it is present.
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