v4 033380368X.Text.qxd 2/19/09 2:00 PM Page 1 1 The variety of living organisms By the end of this chapter you should be able to: understand why there exists a range of living organisms on Earth; list and define the characteristics of life; describe the major groups of organisms; understand how a classification system is used to group all living organisms; observe and classify living organisms according to visible similarities and differences; understand the meaning of the term species. Concept map range of living organisms characteristics of life growth respiration irritability movement nutrition excretion reproduction Prokaryota Protoctista Fungi Plantae Animalia classified according to common features Kingdom Phylum Class Order Family Genus Species species can interbreed with each other breeds varieties races ITQ1 List three characteristics of the planet Earth that enables it to sustain life. The planet Earth, the third planet from the Sun, has all the conditions necessary to support life as we know it. Our planet is positioned at such a distance from the Sun that living organisms can survive in the range of temperatures on its surface (although it is a fairly wide range). The presence of water in all its forms (solid, liquid and gas), and the combination of gases which make up the atmosphere (including nitrogen, oxygen and carbon dioxide), are all conditions that are essential to life on Earth. A huge variety of living forms exist on the planet Earth. They can inhabit most of the Earth s surface, land, air and water. They show an enormous range in size and complexity from the microscopic, which cannot be seen by the naked eye and are as simple as one cell, to giant-like whales which must live in water since they are too heavy to support themselves and move on land. 1
v4 033380368X.Text.qxd 2/19/09 2:00 PM Page 2 characteristics of life ITQ2 Animals and plants are able to carry out certain processes which distinguish them from non-living things. Describe briefly how a plant (i) feeds, (ii) responds. Characteristics of life Biology is the study of life and how living things stay alive. All living organisms, microscopic to gigantic, possess certain characteristics. These are the characteristics of life that distinguish living things from non-living things. There are seven of these characteristics. 1 Growth Living organisms increase in mass, size and numbers. 2 Respiration The energy released during respiration is needed to carry out all life processes. 3 Irritability Living organisms can respond to changes in their internal environment and the world around them. These responses usually increase their chances of survival. 4 Movement Most living organisms can move. Plants show growth movements. Most animals can move from place to place to find or a mate. 5 Nutrition All living organisms need which is used as a source of energy. Plants make their during photosynthesis. Animals get their by eating plants or other animals. 6 Excretion All living things make waste products during metabolism. These must be removed from the body. 7 Reproduction This is the production of new organisms. Living organisms are able to carry out all these processes on Earth. Most organisms are adapted to live on land or in water, more or less close to sea level. Some survive in extreme places such as: in hot sulphur springs where chemical conditions are toxic to most living things; in extreme cold, such as at the North and South Pole; in deep parts of the ocean where no light can reach, such as the Marianas Trench; in the upper atmosphere; in extremely hot deserts, such as the Gobi desert; inside other living organisms. Wherever they live, as long as they are able to carry out the processes of life living organisms survive and produce offspring. Most places on Earth can support life. The major groups of organisms virus All organisms used to be classified or placed in two kingdoms or main groups animals and plants, depending on whether they get their from other organisms or make their own. However, living things are more diverse than this and a classification system of five kingdoms is now used. These kingdoms are the Prokaryotes, Protoctists, Fungi, Plants and Animals. Viruses do not fit into this classification. They are the smallest organisms, though it is difficult to think of them as living because they can only live inside The kingdoms have scientific names that are slightly different from their common names: Prokaryota; Eukaryota; Protoctista; Fungi; Plantae; Animalia. Prokaryotes (chromosomes not enclosed in a nucleus) Living organisms Eukaryotes (chromosomes enclosed in a nucleus) Viruses Protoctists Fungi Plantae Animalia ITQ3 What are the five major groups of life-forms or organisms? 2 unicellular multicellular Figure 1.1 Living organisms are placed in five major kingdoms (shown in colour).
v4 033380368X.Text.qxd 2/19/09 2:00 PM Page 3 Viruses that attack humans Influenza virus HIV or human immunodeficiency virus protein/ lipid coat virus RNA Viruses that attack bacteria are called bacteriophages or simply phages Phage 2 bacteriophage phage DNA ITQ4 Bacteria are described as being microscopic and unicellular organisms. What do these terms mean? Figure 1.2 Phage DNA is injected into the bacterium where it makes copies of itself (20-1000) which are released to infect further bacteria. The structure of some viruses. surface of bacterium Figure 1.3 Escherichia coli is a rodshaped bacterium which is part of the normal gut flora of humans and other vertebrates. Figure 1.4 Anabaena is a bacterium where the cells stick together in long chains. strand of DNA cell wall cell membrane Figure 1.5 Structure of a typical bacterium, e.g. Escherichia coli. The chromosomes are not enclosed in a nucleus and there is little structure in the. another living cell. They also do not have a true cellular structure like other organisms. Billions of viruses exist around us and it is only when they enter the cells of an organism that they show some of the characteristics of life. There they can reproduce and grow in numbers. Viruses have a great impact on life on Earth, since they can live inside every type of living organism, from bacteria to plants and animals. It is believed that they have changed the course of human history because of diseases like smallpox, measles and now AIDS. Prokaryotes The prokaryotes are organisms that are commonly called bacteria. They occupy many environments such as soil, dust, water, air, in or on animals and plants. Some are found in hot springs where temperatures may be higher than 78 C. Some can survive freezing in ice. Some have been found in deep cracks in the ocean floor, at very high pressures and temperatures of 360 C. They can be found in every part of the living world. They are the most ancient group of organisms. They are also the smallest organisms that have a cellular structure. Many exist as single cells, others are found in groups (figure 1.4). Their cells have a much simpler structure than those of the eukaryotes (figure 1.5). Prokaryotes are vital to all other organisms since they cause decay of dead plant and animal material which releases nutrients back into the environment. They are essential to the nitrogen cycle. They are also important to humans because they cause disease (such as cholera and TB chapter 24) and are used in biotechnology (for example in insulin production chapter 23). Protoctists Most protoctists are unicellular, that is made of one cell. This cell shows all the characteristics of life. Algae and protozoa are two kinds of protoctists. Algae live in both marine and fresh water, and some live on land where the surface is damp. They make their own by photosynthesis. Some live as single cells, others are found in groups or colonies. A few, such as the seaweeds, 3
v4 033380368X.Text.qxd 2/19/09 2:00 PM Page 4 nucleus vacuoles cell membrane pseudopodia Figure 1.6 Amoeba proteus ( 200). Figure 1.7 contractile vacuole The structure of Amoeba. light-sensitive spot chloroplast flagella nucleus starch storage Figure 1.8 Chlorella, a photosynthetic alga. Note the presence of the chloroplast, where photosynthesis takes place. ITQ5 Using one named example of each, describe one similarity and one difference between algae and protozoans. spore body can grow extremely large. These have structures that look like stems, roots and leaves, but they are much simpler than true plants. Rapid growth (blooms) of algae can form scums on the surface of ponds, lakes and rivers, turning them green. Protozoa are unicellular and feed on other organisms (heterotrophically). They are found in all environments, especially in water, and examples include Amoeba and Paramecium. They are important to humans because diseases such as malaria and sleeping sickness are caused by protozoan parasites. Malaria infects millions of people each year and it is estimated that 2.7 million people worldwide die from this disease each year. Fungi Fungi range in size from unicellular yeasts to large toadstools. Some are used by humans for medicinal and dietary purposes. They are heterotrophic organisms (see chapter 7) and obtain their from the environment. However, they do not take in large particles of that need to be broken down. They digest their outside the body using enzymes which make it soluble. Then they absorb the. So they are usually found living in or on their, which can be a dead or living organism. Fungi reproduce by producing spores asexually or sexually. These are dispersed by the wind and water and some rely on animals to take them to new environments. Common fungi are: moulds; yeasts; mushrooms and toadstools. hypha of fungus mycelium absorbed into fungus vesicles release enzyme and is digested Figure 1.9 the body. 4 soluble enzymes insoluble The hyphae of fungi extend into their. Digestion occurs outside Figure 1.10 Penicillin spores are made in sexual reproduction ( 600).
v4 033380368X.Text.qxd 2/19/09 2:00 PM Page 5 Figure 1.11 Yeast cells bud to make new cells in asexual reproduction. Importance of fungi to Man Important in the making of the antibiotic penicillin. Essential to many fermentation processes, such as bread, wine, beer and other alcoholic beverages. Used to make a range of chemical products, such as anaesthetics, birth control pills and meat tenderiser. Moulds and rusts are fungi that are important in damaging growing crops. Cause of spoilage of. Used to make, such as sufu of East Asia. Plants (Plantae) The plant kingdom includes mosses, liverworts, ferns, conifers and flowering plants. Almost all plants are photosynthetic. Some plants can be used as medicines. Bidens is a weed which has a small daisy-like flower. The leaves and flowers are steeped and used to cool the blood (prickly heat) and to relieve a sick stomach. Sometimes it is given to children to cure worms. Figure 1.12 Mushrooms are the spore bodies of some fungi. ITQ6 Name three kinds of fungi and a possible use of each. Flowering plants The flowering plants have true flowers and so make seeds. They are also called angiosperms and are divided into two groups: the monocotyledons; the dicotyledons. Table 1.1 shows the distinguishing features of monocotyledons and dicotyledons. ITQ7 (i) Plants range in size from unicellular to giant. Put these plants in order of size starting with the smallest. Fern, mango tree, croton, moss and lettuce. (ii) List five reasons why plants are important. Feature Monocotyledons Dicotyledons seed has one cotyledon or seed leaf has two cotyledons or seed leaves leaf has parallel veins has net-like or branching veins angiosperms example corn (Zea mays) Hibiscus Table 1.1 Distinguishing features of monocotyledons and dicotyledons. Figure 1.13 Bananas Figure 1.14 Mangroves Figure 1.15 Bidens Shepherds needle, Spanish needle, Beggar-ticks, sticktight. 5