Class Angiospermae (from the Greek angeion, meaning 'small container', and sperma, meaning 'seed').
Of the more than 200 000 kinds of vascular plants in the world today over 95% flower at some time in their lives. The best-known flowers are bright and colourful but others, like those of grasses, are small and inconspicuous. Some flowers are tiny and are grouped together to look like a single large flower (as in daisies for example), and sometimes small flowers are surrounded by brightly coloured leaves (as in poinsettias). But all have an important feature in common - the seed develops inside the ovary, which then completely surrounds the seed in the ripe fruit. (Think of apples, grapes, tomatoes, and bean and pea pods.) This characteristic of having the seeds completely enclosed within the fruit distinguishes the flowering plants from all others, and gives the name to the class.
As well as a great diversity in flowers and fruits, angiosperms have less obvious differences, such as in their pollen grains. Though differences in their leaves are less significant to classification, they vary greatly in size and may be simple or divided into many leaflets. The shoot can grow into a small herb or grass, into a taller, woody shrub, into a very tall tree with a strong, woody trunk, or into a creeper or liana that needs to climb on a tree or other support. Timber from angiosperms is classed as hardwood.
It may surprise you that some angiosperm species grow on the bottom of shallow seas. Strap-weed (Posidonta) and eel-grass (Zostera) form extensive beds in bays and estuaries, and their long, thin leaves are often washed up on beaches.
Angiosperms are divided into two sub-classes:
The monocotyledons (from the Greek monos, meaning 'alone' or 'one',' referring to the one seed leaf) include grasses, lilies, irises, orchids and palms. Flower parts usually occur in threes; seeds have one seed leaf; veins run parallel in the leaves (think of a grass leaf; the vascular bundles are scattered through the young stems; and most plants do not have woody growth.
The dicotyledons (from the Greek dis, meaning 'twice', referring to the two seed leaves) include most of the flowering trees and shrubs and many non-woody plants. Flower parts are usually in fours or fives, or in multiples of four or five; seeds have two seed leaves; the veins are usually spread in net-like fashion throughout the leaves; the vascular bundles occur in a ring around both younger and older stems; and they often have woody growth.
Bacteria
Many people, on hearing the word'bacteria', immediately think of disease, but, in fact, many types of bacteria are beneficial to us. For example, some bacteria produce ammonia, using nitrogen gas from the air, and other bacteria then convert the ammonia to nitrites and finally nitrates, which can be absorbed by plants. Bacteria play an important part in the decay of dead plants and animals, leading to the recycling of many nutrients. The action of bacteria is used in the manufacture of many cheeses, yoghurt, vinegar and sauerkraut. In the digestive system of humans, bacteria feed on wastes and produce several vitamins, including vitamin K, which is necessary for the clotting of blood. People who have had large doses of antibiotics often have intestinal disturbances because the bacteria in their gut have been destroyed.
Mammals do not produce enzymes that digest cellulose, but the diet of many herbivores is mostly cellulose and it is bacteria in their guts that digest that cellulose for them. Bacteria (mostly dead ones) form the major part of faeces.
Bacteria are among the most widespread of all living things. They can be found in the depths of the oceans, in the upper layers of the atmosphere and in Antarctic ice. They are very abundant in soil and some cause diseases in both plants and animals . Many sorts of bacteria form resistant spores that survive long periods of drying and extremes of temperature.
Diseases of humans that are caused by bacteria include boils and abscesses, cholera, gonorrhea, syphilis, tetanus and tuberculosis.
A bacterium is a prokaryotic cell (ie, a cell with no internal membranes and no definite separate nucleus). Most bacterial cells are surrounded by a wall, outside the external membrane, but the chemical composition of the wall is different from that of eukaryotic cells (see Cyanophytes.)
Cyanophytes
(Cyanophyta, from the Greek kyanos, meaning 'dark blue, and phyton, meaning 'plant') Cyanophytes are prokaryotic organisms. However cyanophyte cells are generally larger than those of most bacteria, mainly because they have a system of internal photosynthetic membranes.
Some cyanophytes are chains of cells (filaments) and others are unicellular. In some species the cells surround themselves with a slimy substance and form jelly-like masses on moist surfaces that are visible to the naked eye.
About 1500 species of cyanophytes have been described. They have a world-wide distribution and are found in soil and other moist places on land, as well as in salt and fresh water. They are able to survive extreme conditions,- some live in arctic regions and others in hot springs, in temperatures up to 85'C. They often form a scum on the surface of dams and lakes, and when they die their decomposition by bacteria may use so much oxygen that the fish die from oxygen starvation. Some freshwater cyanophytes produce toxins that are harmful to organisms in the water or those that drink it.
The oldest known fossils of cyanophytes have been found in Western Australia. It is possible that oxygen released by the photosynthesis of cyanophytes, over 2000 million years ago, played a major part in increasing the free oxygen in the atmosphere.
Stromatolites are dome-shaped structures that consist of layers of carbonate built up by cyanophytes. Scientists suggest that stromatolites found today, in such places as Shark Bay, WA, are very similar to the stromatolites found in ancient rocks containing the oldest known fossils. Those scientists who suggest that some organelles of eukaryotes may have evolved from once free-living prokaryotes think that cyanophytes may have been the source of chloroplasts, particularly in red algae.
The name derives from the fact that, in addition to chlorophyll, cyanophytes contain a blue pigment and some appear blue-green. However, some species also contain other pigments and may appear yellow, green, brown or red. The Red Sea is so named because on occasions cyanophytes with a large amount of red pigment build up to sufficient numbers to affect the colour of the water.
Cyanophytes are a problem for taxonomists. Their prokaryotic nature was only discovered recently. Previously they were regarded as a group of (eukaryotic) algae. Even now many botanists regard them as plants and classify them within the algae. This is because cyanophytes carry out oxygenic photosynthesis (ie, the sort of photosynthesis common in all green plants, where oxygen is released). Accordingly, many botanists still use the common name 'blue-green algae'. However this name does not take account of their prokaryotic nature. Apart from oxygenic photosynthesis there are few differences between cyanophytes and bacteria. (There are other bacteria that are photosynthetic but do not release oxygen.) Many bacteriologists therefore regard cyanophytes as bacteria and suggest that their name should be cyanobacteria. But a problem arises when they try cyanobacteria because, according to convention, have to be held in pure culture in order to be classified, and many cyanophytes cannot be grown in culture. One way of classifying bacteria is by their shape and how they aggregate together . However studies of DNA are now making it possible to devise a more natural (evolutionary) system of classification.
Bacteria reproduce by dividing their cells into two (binary fission), with an equal sharing of the cell contents. In favourable conditions a bacterium can divide into two every 20 minutes or so, but usually such rapid growth of a population does not go on for long because they run out of food, or the mass of bacteria becomes so big that the ones inside the colony are isolated from the resources that they need for growth
KINGDOM PROTISTA
The main groups are:
Protozoa
(flagellates, ciliates, sporozoans, amoeba)
Fungus-like protists
(slime moulds, downy mildews)
Algae
(dinoflagellates, diatoms, red, green & brown algae)
Protozoans: single-celled "animals".
Phylum Protozoa (from the Greek protos, meaning 'first', and zoan, meaning 'animal'). Protozoans consist of a single cell and so they are almost all microscopic. They carry out all life functions - they move, take in food and digest it, respire, excrete and reproduce - within this one cell, which is the most complex of all cells in the biological world. We are only just beginning to appreciate its complexity through details revealed by the electron microscope. Protozoans are abundant in the oceans, fresh water and moist soil. Some also live within the bodies of other organisms. They can be sorted into classes according to the way in which they move.
Flagellates
Flagellates have one or more whip-like structures called flagella (from the Latin flagellum, meaning 'whip'). Some flagellates are green and so they are included with the single-celled algae as plants . In this group we cannot distinguish clearly between plants and animals, and in some systems of classification all single-celled organisms, including the unicellular algae, are grouped together in a separate kingdom, the Protista.
Amoebas
Another class of protozoans move by flowing along rather than swimming. Amoeba (from the Greek amoibe, meaning 'change') is the best-known. An amoeba has a different shape almost every time you look at it, as its shape changes as the fluid contents of the cell flow into finger-like extensions called pseudopodia (from the Greek, meaning 'false foot').
Ciliates
The surface of a ciliate protozoan has many fine projections, which are like short flagella and are called cilia (from the Latin for 'eyelash'). Ciliates swim by beating the cilia in coordinated waves. Many ciliates produce currents that draw food particles into a funnel-shaped groove. At the bottom of the groove these food particles enter the cell, where they are digested.
Sporozoans
Sporozoans are parasitic protozoans, and because they are adapted to the parasitic lifestyle most appear to have a similar simple cell structure. However they may have originated from several unrelated groups. Malaria is caused by the sporozoan Plasmodium.
FIGURES:
KINGDOM FUNGI
Fungi do not contain chlorophyll and are not able to make their food from simple inorganic materials. All fungi therefore depend on other living things for their food. Most fungi are saprophytic (ie, they feed on dead organic matter such as leaves or roots in soil or water). Others are parasitic (ie, they feed on a living host). Human diseases caused by parasitic fungi include monilia, ringworm, tinia and thrush. Mildews and rusts commonly infect plants., Although many fungi damage food, paper and timber, others are used in the production of foods, including yeast (for making bread and alcoholic beverages) and grey-green moulds (for making blue vein cheeses). Still other fungi are used as sources of antibiotics.
Fungi are either unicellular (eg, yeasts) or they consist of filaments called hyphae, with walls usually of chitin but sometimes of cellulose. A mass of hyphae is called a mycelium. Fungi reproduce by producing spores and they are classified by the shape of their spore-bearing bodies. These are usually formed when part of the mycelium grows up into the air and forms a much more regular shape than the tangled mass of hyphae growing on a host or on plant or animal remains. Mushrooms and toadstools are examples of these regular fruiting bodies of fungi.
Lichens
Lichens are so unusual that taxonomists cannot fit them into the classification hierarchy. A lichen is in fact two organisms, a fungus and an alga, or a cyanophyte, living together to the advantage of both of them. The algal cells five enveloped in the fungus mycelium and they obtain water and minerals from the fungus. In return the photosynthetic algae provide the fungi with carbohydrates. Perhaps because two organisms help each other in this way lichens can grow in very inhospitable places - on rocks, buildings and trees, from Arctic regions to the tropics. Reindeer moss, which is the major part of the diet of caribou and reindeer, consists of prolifically growing lichens. Each different sort of lichen consists of a particular fungus and a particular alga living together. Many different fungi and many different algae live together in this way so that there are many different shapes and sizes of lichens. These features are so characteristic that lichens are named using the binomial system. Over 15 000 species have been described and named.
VIRUSES
In 1892 a Russian biologist, Dmitri Ivanovski, showed that a disease of tobacco plants that results in light and dark patches on their leaves was transmitted in the juice of affected plants even after it had been passed through a very fine porcelain filter. In 1895 a Dutch botanist, Martinus Beijerinck, described the filtrate that carried the tobacco mosaic disease as a filterable virus because virus is the Latin word for poison. But it was not until 1935 that the virus causing the disease was isolated.
We now know that viruses cause many diseases in all kinds of living things. Viral diseases of humans include AIDS, chickenpox, the common cold, infective hepatitis, influenza and herpes.
Viruses can only reproduce inside the living cells of a host. In the inactive stage of their existence they consist of particles called virions. The structure of virions can be examined with an electron microscope. The virions show no sign of life at all - they rarely store and carry the genes of the virus. But when a virion enters a susceptible cell the virus takes over the living processes of that cell and causes the cell to produce more virions.
Among biologists a debate went on for many years about whether viruses are living or non-riving, because the virions can be crystallised like chemicals, yet inside a suitable host they can reproduce. We now realise that the life cycle of viruses is separated into two distinct phases - a seemingly non-living dispersal phase of virions, which, because of their uniform size, can form crystals, and a living phase, where they are a collection of parasite genes and proteins living inside the cells of their host.
Since viruses use their host's cell processes to reproduce, most viral infections cannot be treated with antibiotics. Any pharmaceutical that blocked virus multiplication would also damage the host's cells. If an antibiotic is prescribed for a patient suffering from a viral disease, it is done to reduce the risk of the weakened individual developing secondary, bacterial infections.
Of the more than 200 000 kinds of vascular plants in the world today over 95% flower at some time in their lives. The best-known flowers are bright and colourful but others, like those of grasses, are small and inconspicuous. Some flowers are tiny and are grouped together to look like a single large flower (as in daisies for example), and sometimes small flowers are surrounded by brightly coloured leaves (as in poinsettias). But all have an important feature in common - the seed develops inside the ovary, which then completely surrounds the seed in the ripe fruit. (Think of apples, grapes, tomatoes, and bean and pea pods.) This characteristic of having the seeds completely enclosed within the fruit distinguishes the flowering plants from all others, and gives the name to the class.
As well as a great diversity in flowers and fruits, angiosperms have less obvious differences, such as in their pollen grains. Though differences in their leaves are less significant to classification, they vary greatly in size and may be simple or divided into many leaflets. The shoot can grow into a small herb or grass, into a taller, woody shrub, into a very tall tree with a strong, woody trunk, or into a creeper or liana that needs to climb on a tree or other support. Timber from angiosperms is classed as hardwood.
It may surprise you that some angiosperm species grow on the bottom of shallow seas. Strap-weed (Posidonta) and eel-grass (Zostera) form extensive beds in bays and estuaries, and their long, thin leaves are often washed up on beaches.
Angiosperms are divided into two sub-classes:
The monocotyledons (from the Greek monos, meaning 'alone' or 'one',' referring to the one seed leaf) include grasses, lilies, irises, orchids and palms. Flower parts usually occur in threes; seeds have one seed leaf; veins run parallel in the leaves (think of a grass leaf; the vascular bundles are scattered through the young stems; and most plants do not have woody growth.
The dicotyledons (from the Greek dis, meaning 'twice', referring to the two seed leaves) include most of the flowering trees and shrubs and many non-woody plants. Flower parts are usually in fours or fives, or in multiples of four or five; seeds have two seed leaves; the veins are usually spread in net-like fashion throughout the leaves; the vascular bundles occur in a ring around both younger and older stems; and they often have woody growth.
NOT PLANT, NOT ANIMAL
KINGDOM MONERABacteria
Many people, on hearing the word'bacteria', immediately think of disease, but, in fact, many types of bacteria are beneficial to us. For example, some bacteria produce ammonia, using nitrogen gas from the air, and other bacteria then convert the ammonia to nitrites and finally nitrates, which can be absorbed by plants. Bacteria play an important part in the decay of dead plants and animals, leading to the recycling of many nutrients. The action of bacteria is used in the manufacture of many cheeses, yoghurt, vinegar and sauerkraut. In the digestive system of humans, bacteria feed on wastes and produce several vitamins, including vitamin K, which is necessary for the clotting of blood. People who have had large doses of antibiotics often have intestinal disturbances because the bacteria in their gut have been destroyed.
Mammals do not produce enzymes that digest cellulose, but the diet of many herbivores is mostly cellulose and it is bacteria in their guts that digest that cellulose for them. Bacteria (mostly dead ones) form the major part of faeces.
Bacteria are among the most widespread of all living things. They can be found in the depths of the oceans, in the upper layers of the atmosphere and in Antarctic ice. They are very abundant in soil and some cause diseases in both plants and animals . Many sorts of bacteria form resistant spores that survive long periods of drying and extremes of temperature.
Diseases of humans that are caused by bacteria include boils and abscesses, cholera, gonorrhea, syphilis, tetanus and tuberculosis.
A bacterium is a prokaryotic cell (ie, a cell with no internal membranes and no definite separate nucleus). Most bacterial cells are surrounded by a wall, outside the external membrane, but the chemical composition of the wall is different from that of eukaryotic cells (see Cyanophytes.)
Cyanophytes
(Cyanophyta, from the Greek kyanos, meaning 'dark blue, and phyton, meaning 'plant') Cyanophytes are prokaryotic organisms. However cyanophyte cells are generally larger than those of most bacteria, mainly because they have a system of internal photosynthetic membranes.
Some cyanophytes are chains of cells (filaments) and others are unicellular. In some species the cells surround themselves with a slimy substance and form jelly-like masses on moist surfaces that are visible to the naked eye.
About 1500 species of cyanophytes have been described. They have a world-wide distribution and are found in soil and other moist places on land, as well as in salt and fresh water. They are able to survive extreme conditions,- some live in arctic regions and others in hot springs, in temperatures up to 85'C. They often form a scum on the surface of dams and lakes, and when they die their decomposition by bacteria may use so much oxygen that the fish die from oxygen starvation. Some freshwater cyanophytes produce toxins that are harmful to organisms in the water or those that drink it.
The oldest known fossils of cyanophytes have been found in Western Australia. It is possible that oxygen released by the photosynthesis of cyanophytes, over 2000 million years ago, played a major part in increasing the free oxygen in the atmosphere.
Stromatolites are dome-shaped structures that consist of layers of carbonate built up by cyanophytes. Scientists suggest that stromatolites found today, in such places as Shark Bay, WA, are very similar to the stromatolites found in ancient rocks containing the oldest known fossils. Those scientists who suggest that some organelles of eukaryotes may have evolved from once free-living prokaryotes think that cyanophytes may have been the source of chloroplasts, particularly in red algae.
The name derives from the fact that, in addition to chlorophyll, cyanophytes contain a blue pigment and some appear blue-green. However, some species also contain other pigments and may appear yellow, green, brown or red. The Red Sea is so named because on occasions cyanophytes with a large amount of red pigment build up to sufficient numbers to affect the colour of the water.
Cyanophytes are a problem for taxonomists. Their prokaryotic nature was only discovered recently. Previously they were regarded as a group of (eukaryotic) algae. Even now many botanists regard them as plants and classify them within the algae. This is because cyanophytes carry out oxygenic photosynthesis (ie, the sort of photosynthesis common in all green plants, where oxygen is released). Accordingly, many botanists still use the common name 'blue-green algae'. However this name does not take account of their prokaryotic nature. Apart from oxygenic photosynthesis there are few differences between cyanophytes and bacteria. (There are other bacteria that are photosynthetic but do not release oxygen.) Many bacteriologists therefore regard cyanophytes as bacteria and suggest that their name should be cyanobacteria. But a problem arises when they try cyanobacteria because, according to convention, have to be held in pure culture in order to be classified, and many cyanophytes cannot be grown in culture. One way of classifying bacteria is by their shape and how they aggregate together . However studies of DNA are now making it possible to devise a more natural (evolutionary) system of classification.
Bacteria reproduce by dividing their cells into two (binary fission), with an equal sharing of the cell contents. In favourable conditions a bacterium can divide into two every 20 minutes or so, but usually such rapid growth of a population does not go on for long because they run out of food, or the mass of bacteria becomes so big that the ones inside the colony are isolated from the resources that they need for growth
KINGDOM PROTISTA
The main groups are:
Protozoa
(flagellates, ciliates, sporozoans, amoeba)
Fungus-like protists
(slime moulds, downy mildews)
Algae
(dinoflagellates, diatoms, red, green & brown algae)
Protozoans: single-celled "animals".
Phylum Protozoa (from the Greek protos, meaning 'first', and zoan, meaning 'animal'). Protozoans consist of a single cell and so they are almost all microscopic. They carry out all life functions - they move, take in food and digest it, respire, excrete and reproduce - within this one cell, which is the most complex of all cells in the biological world. We are only just beginning to appreciate its complexity through details revealed by the electron microscope. Protozoans are abundant in the oceans, fresh water and moist soil. Some also live within the bodies of other organisms. They can be sorted into classes according to the way in which they move.
Flagellates
Flagellates have one or more whip-like structures called flagella (from the Latin flagellum, meaning 'whip'). Some flagellates are green and so they are included with the single-celled algae as plants . In this group we cannot distinguish clearly between plants and animals, and in some systems of classification all single-celled organisms, including the unicellular algae, are grouped together in a separate kingdom, the Protista.
Amoebas
Another class of protozoans move by flowing along rather than swimming. Amoeba (from the Greek amoibe, meaning 'change') is the best-known. An amoeba has a different shape almost every time you look at it, as its shape changes as the fluid contents of the cell flow into finger-like extensions called pseudopodia (from the Greek, meaning 'false foot').
Ciliates
The surface of a ciliate protozoan has many fine projections, which are like short flagella and are called cilia (from the Latin for 'eyelash'). Ciliates swim by beating the cilia in coordinated waves. Many ciliates produce currents that draw food particles into a funnel-shaped groove. At the bottom of the groove these food particles enter the cell, where they are digested.
Sporozoans
Sporozoans are parasitic protozoans, and because they are adapted to the parasitic lifestyle most appear to have a similar simple cell structure. However they may have originated from several unrelated groups. Malaria is caused by the sporozoan Plasmodium.
FIGURES:
KINGDOM FUNGI
Fungi do not contain chlorophyll and are not able to make their food from simple inorganic materials. All fungi therefore depend on other living things for their food. Most fungi are saprophytic (ie, they feed on dead organic matter such as leaves or roots in soil or water). Others are parasitic (ie, they feed on a living host). Human diseases caused by parasitic fungi include monilia, ringworm, tinia and thrush. Mildews and rusts commonly infect plants., Although many fungi damage food, paper and timber, others are used in the production of foods, including yeast (for making bread and alcoholic beverages) and grey-green moulds (for making blue vein cheeses). Still other fungi are used as sources of antibiotics.
Fungi are either unicellular (eg, yeasts) or they consist of filaments called hyphae, with walls usually of chitin but sometimes of cellulose. A mass of hyphae is called a mycelium. Fungi reproduce by producing spores and they are classified by the shape of their spore-bearing bodies. These are usually formed when part of the mycelium grows up into the air and forms a much more regular shape than the tangled mass of hyphae growing on a host or on plant or animal remains. Mushrooms and toadstools are examples of these regular fruiting bodies of fungi.
Lichens
Lichens are so unusual that taxonomists cannot fit them into the classification hierarchy. A lichen is in fact two organisms, a fungus and an alga, or a cyanophyte, living together to the advantage of both of them. The algal cells five enveloped in the fungus mycelium and they obtain water and minerals from the fungus. In return the photosynthetic algae provide the fungi with carbohydrates. Perhaps because two organisms help each other in this way lichens can grow in very inhospitable places - on rocks, buildings and trees, from Arctic regions to the tropics. Reindeer moss, which is the major part of the diet of caribou and reindeer, consists of prolifically growing lichens. Each different sort of lichen consists of a particular fungus and a particular alga living together. Many different fungi and many different algae live together in this way so that there are many different shapes and sizes of lichens. These features are so characteristic that lichens are named using the binomial system. Over 15 000 species have been described and named.
VIRUSES
In 1892 a Russian biologist, Dmitri Ivanovski, showed that a disease of tobacco plants that results in light and dark patches on their leaves was transmitted in the juice of affected plants even after it had been passed through a very fine porcelain filter. In 1895 a Dutch botanist, Martinus Beijerinck, described the filtrate that carried the tobacco mosaic disease as a filterable virus because virus is the Latin word for poison. But it was not until 1935 that the virus causing the disease was isolated.
We now know that viruses cause many diseases in all kinds of living things. Viral diseases of humans include AIDS, chickenpox, the common cold, infective hepatitis, influenza and herpes.
Viruses can only reproduce inside the living cells of a host. In the inactive stage of their existence they consist of particles called virions. The structure of virions can be examined with an electron microscope. The virions show no sign of life at all - they rarely store and carry the genes of the virus. But when a virion enters a susceptible cell the virus takes over the living processes of that cell and causes the cell to produce more virions.
Among biologists a debate went on for many years about whether viruses are living or non-riving, because the virions can be crystallised like chemicals, yet inside a suitable host they can reproduce. We now realise that the life cycle of viruses is separated into two distinct phases - a seemingly non-living dispersal phase of virions, which, because of their uniform size, can form crystals, and a living phase, where they are a collection of parasite genes and proteins living inside the cells of their host.
Since viruses use their host's cell processes to reproduce, most viral infections cannot be treated with antibiotics. Any pharmaceutical that blocked virus multiplication would also damage the host's cells. If an antibiotic is prescribed for a patient suffering from a viral disease, it is done to reduce the risk of the weakened individual developing secondary, bacterial infections.
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