University of Crete Biology
University of Crete Biology
Text 3: THE PLANT KINGDOM
ALGAE: Algae are very simple plants with no stems, roots or leaves. They grow in very wet or damp places. Seaweed and pondweed are types of algae.
FUNGI: Fungi are unlike other plants as they are not green, and cannot make their own food. Instead they feed off dead or decaying plants and animals. Many fungi are made up of tiny threads called hyphae. Mushrooms, mildews and moulds are all types of fungi.
MOSSES: Mosses are slightly more complex plants with very thin leaves and no proper roots. They reproduce by spores. They grow close to the ground in wet or damp areas. They are made up of hundreds of tiny separate plants.
FERNS: Ferns are plants which have stems, leaves and roots, but no flowers. They grow in moist shady places, such as woods. At the backs of the leaves are dark spots called spores from which they reproduce.
SEED-BEARING PLANTS: Seed-bearing plants have roots, stems and leaves and reproduce by means of seeds. Unlike a spore, a seed is made up of many cells. There are two classes of seed-bearing plants.
COFINERS: Conifers are a class of seed-bearing plants. They have needle-shaped leaves and their seeds are produced in cones.
FLOWERING PLANTS: Flowering plants are also seed-bearing plants. They include trees as well as flowers. Their seeds are produced inside a fruit, which develops from a flower.
THE PLANT KINGDOM
Anatomy of a flower
A flower consists of several kinds of highly modified leaves that are arranged in concentric rings and are attached to the receptacle. The sepals, which form the outermost ring, are frequently green. They enclose the flower before it opens. Next are the petals, which are often large and colourful. Their colour often helps attract the pollinators. Within the petals, the stamens form a whorl around the pistil. Stamens are the pollen-producing portion of the flower. Each stamen has a slender filament with an anther at the tip. The pistil of most flowers has three parts the stigma, style and ovary.
How do plants reproduce?
Flowering plants reproduce themselves from seeds which form inside the ovary of the flower after fertilization.
Flowers produce a fine dust called pollen (known as pollen grains) in the anther. Pollination takes place when pollen is carried from an anther to a stigma. When the anther ripens, the pollen sacs split open and release the pollen grains. Pollen can be carried to a stigma in the same flower. This is called self-pollination. Insects such as bees, butterflies, wasps, dragonflies, carry pollen from flower to flower. The wind also often carries pollen from plant to plant. This process is known as cross-pollination.
Insect-pollinated flowers have large, coloured scented petals and nectar, with which to attract insects. They have large pollen grains that stick to the insects' body. They also have anthers and stigmas inside the flower, so that the insect can brush against them when it is drinking nectar. The presence of nectar, a sweet sugary substance, is also very attractive to insects and even small birds, in some areas of the world. In addition, flowers pollinated by night-flying insects often have a strong scent.
Wind-pollinated flowers do not have large scented petals, or nectar, because they do not need to attract insects. Their anthers hang outside the flower, in order to catch the wind. They produce large amounts of very small light pollen grains which blow away easily in a slight breeze. They also have large feathery stigmas to catch pollen grains which are blown by the wind.
Fertilization takes place when a rnale sex cell joins up with a female sex cell, and this occurs in the following manner, after a pollen grain lands on a stigma. First a tube grows out of the pollen grain and grows towards the female sex cell. The male sex cell moves down the tube which then enters the female sex cell, the tip of the tube bursts open and the male sex cell joins up with the female sex cell. The ovule becomes a seed. The ovary becomes a fruit with the seed inside it.
How do plant diseases spread?
Micro-organisms can cause diseases in plants as well as in humans and animals. Diseases are often infectious, which means that they can be passed on from plant to plant, usually by carriers such as insects, which may drink juices from a diseased plant and then inject them into a healthy one. What are parasites and how are they controlled?
Plants are also attacked by parasites which can harm or even kill them. A parasite is an organism which lives on or in, another organism. Parasites are never helpful, and are often harmful, to the host organism.
Chemical sprays and disinfectants enable farmers to kill parasites and to control plant diseases. These substances can be sprayed over wide areas from aeroplanes and helicopters. Many farmers depend on this form of crop protection to save their harvest of grain, fruit or vegetables. Without it, many people all over the world would die of hunger.
Why do many people object to crop-spraying?
The problem of the American robin is an example of the hidden dangers involved in the use of insecticides. Elm trees in United States, like those in Europe, are being attacked by Dutch Elm Disease. This fungal disease is spread by the elm bark beetle.
American scientists have attacked the disease by attacking the carrier. But the substance they use sticks to the leaves of the trees. These leaves are the basic food of a certain type of earthworm which is not affected by the insecticide. The worms can store up huge amounts of this poison in their systems. The robin eats these worms and is thus being poisoned by its normal food. The bird is already in danger of dying out in some areas.
It is sometimes difficult to foresee side effects like these, which is why many people object to the use of chemical sprays. They fear that man may be poisoning himself in the same way as he has poisoned the American robin and other higher organisms at the top of the food chain.
English 1 Department of Biology
Text3: The Plant Kingdom
Find the derivatives of the following words and make sure you know what they mean.
ovulum, ovulase, ovulation, ovule, ovum
infectible, infective, infecting, infectious
Can you guess how many types of injections there are?
Translation into Greek
An injection can be:
Find the following defined technical terms of a flower:
1. How do you call the upper part of the pistil of a flower on which pollen is deposited?
2. What is that part of the flower that occurs at the base of the carpel and contains one or more ovules?
3. How do you call that part of a flower that is like a leaf and lies under and supports the petals?
4. How do you call that small, thin male part in the middle of a flower that produces pollen and is made of a stalk supporting an anther? The center of each flower usually has several of those.