NATIONAL 5 BIOLOGY Life on Earth

Transcription

1 NATIONAL 5 BIOLOGY Life on Earth 1

2 Biodiversity and the distribution of life The study of living things in their environment is called ecology. Living things are found living almost everywhere land, water, air and even inside us! The place where an organism lives is called its habitat. Examples of habitats include ponds, forests, rivers, deserts and the sea etc. All the plants and animals that live in a habitat is called the community. Together a habitat and its community, make up an ecosystem. The total variety of all living things on Earth is described as biodiversity_. Summary Habitat Word Meaning the place where an organism lives. Population a group of organisms which belong to the same species Ecosystem habitat and community Community all the plants and animals which live in the same habitat Biodiversity all of the different plants on animals living on Earth Niche the role an organism plays within a community Remember, an ecosystem consists of all the organisms living in a particular environment and the non-living components with which the organisms interact. 2

3 What are biomes? A biome is an environment containing plant (flora) and animal (fauna) species that live in a specific geographic region. Biomes can be on land or sea. The nature of a biome is determined primarily by its distinctive climate, including a region's annual average temperature and amount of rainfall. Below is a list of some of the major types of biome: Forest Desert Grassland Tundra Alpine Unfortunately human activities have drastically altered biomes. What is a Niche? Every organism has its own niche. A niche is the role that an organism plays within a community. This includes the use it makes of the resources in it s ecosystem, including light, temperature and nutrient availability and of course how it interacts with the other organisms in the community. These interactions might include competition, parasitism and predation. Biotic and abiotic factors 3

4 Biotic and Abiotic Factors Both biotic and abiotic factors can affect the biodiversity in an ecosystem. Biotic factors are related directly to living organisms whereas abiotic factors are without life. The table below gives some examples of each. TYPE OF FACTOR ABIOTIC (non-living) temperature humidity/moisture light intensity ph of soil / water salinity BIOTIC (living) food predation disease competition grazing Competition could be for food, shelter, space or mates. Measuring abiotic factors Abiotic factors are often related to climate and they affect the distribution of organisms in an ecosystem. An organism is only able to survive in a certain habitat and play its part in an ecosystem if a combination of these factors suited to its needs are present there. There is a range of modern instruments that can be used to measure abiotic factors. Most have some sort of probe that can be in contact with the environment and a scale which is easy to read in order to get a result. Abiotic factor soil ph light intensity temperature moisture level oxygen concentration Measurement instrument ph meter Light meter Thermometer moisture meter oxygen meter soil ph meter digital thermometer 4 light and moisture meter

5 Sampling Organisms in an Ecosystem It would be impossible to count all of the plants and animals that live in an ecosystem. For this reason a sample of the ecosystem is taken. In order to be representative, an appropriate number of samples need to be taken. This also helps to improve the reliability of the results. Sampling Techniques These techniques are used to: find out which plants and animals live in an ecosystem find out how common or rare plants and animals are in a given ecosystem investigate the reasons why the plant or animal lives there 1. Quadrats Quadrats can be used to sample low growing plants or very slow moving animals. A quadrat is used to mark off an exact area of the ground so that the organisms in that area can be identified and counted. In order to improve the reliability of the results: o quadrats should be placed randomly o multiple samples should be taken Example Counting daises in field 10 metres metres

6 Results Quadrat Number of daisy plants (per m 2) Average 7 So in this field there is estimated to be a total of 700 daises: Population of daises = Average number Total number of of daises per m X 2 m (10X10) Sampling Using a Pitfall Trap Pitfall traps can be used to sample small invertebrates living on the soil surface or in leaf litter ( dead leaves). These small invertebrates fall into the trap and are unable to climb out again. The diagram below shows a simple pitfall trap that can be made from an empty yoghurt carton. Cover Stones Alcohol Pitfall trap To improve the reliability of the results, the traps should be placed randomly. They should be checked regularly since birds might eat trapped invertebrates. Also some of the invertebrates might eat other invertebrates that have fallen into the trap. 6

7 Possible limitations and sources of error Using either a quadrat or a pitfall trap have their limitations and errors can sometimes be made as summarised in the table below. Technique Limitations Possible errors Ways to minimise errors Quadrat sampling Usually only suitable for low-growing, rooted plants. Quadrats may not be placed randomly. Place quadrats randomly. Pitfall trap sampling Number of samples possible limits reliability. Usually only suitable for small surface-crawling invertebrates. Number of traps set limits reliability. Too few quadrats used. Traps may not be placed randomly. Too few traps used. Birds may eat trapped invertebrates. Some invertebrates may eat others. Use many quadrats. Place traps randomly Set up many traps. Check traps regularly or disguise the opening with a lid supported on stones. Check traps regularly or put a preserving liquid e.g. alcohol in the trap. Human Influences on the Environment Human activities can also have an impact on biodiversity. These include: Pollution: When fossil fuels such as coal and gas are burned, carbon dioxide gas is released into the air which damages many plants and animals. Habitat destruction: Overexploitation: When forests are cleared, many animals lose their habitat and/or food source. Many plants and animals species are lost forever. Some animals have been hunted and killed to such an extent that they are now in danger of becoming extinct. 7

8 Energy in Ecosystems Producers and Consumers The source of energy for all living things is the sun. Only green plants can use the light energy from the sun and change it into chemical energy (in glucose) during the process of photosynthesis The energy in the plants can then be passed on to animals when they eat the plants as shown in the diagram below. LETTUCE CATERPILLAR SMALL BIRD FOX This type of diagram is called a food chain, and the arrows represent the direction of the flow of energy In the above food chain: 1. The green plant is the producer. (only green plants can be producers). 2. The rabbit and the fox are both consumers. Around 90% of the energy is lost between one level and the next. The main ways in which energy can be lost from a food chain is: movement heat undigested material (e.g. skin and hair) This means that only 10% of the energy from one level is available to the next level for growth as shown below. 8

9 Food Webs Rarely do single food chains occur in nature. We usually find many food chains which are connected as shown below. This is called a food web. Below is an example of a food web. A FOOD WEB fox hawk weasel sparrow slug rabbit caterpillar Predator and Prey lettuce General An example of a food chain from the above food web is: Lettuce fox/ hawk Many options Ecological terms Species Word Meaning organisms which can breed and produce fertile young Population a group of organisms which belong to the same species Producer an organism which can make its own food Consumer an organism which can t make its own food Herbivore an animal which only eats plants Carnivore an animal which only eats other animals Omnivore an animal which eats both plants and animals 9

10 Disrupting a food chain/web Human activities such as hunting, fishing using chemicals that cause pollution can all disrupt a food chain or a food web. The diagram below shows part of a woodland food web. If all the mice were killed by a disease, what effect would this have on the populations of greenflies and stoats? Greenflies: Decrease Reason: Since the mice feed on ladybirds, there would be more ladybirds left to eat the greenfly. Stoats: Decrease Reason: Increase Reason: Less mice for stoats to eat, so some of the stoats would starve and die. OR Less food for weasels so they decrease. Then, there would be less food for foxes so they decrease, and so less stoats would be eaten by the foxes. OR Stay the same Reason: Combination of both the reasons given for increase and decrease. *Marks come with reason, not Direction* stoat 10 weasel

11 Pyramids of number, biomass and energy 1. Pyramid of numbers Consider the following food chain: leaves caterpillar blue tit hawk In terms of numbers, the producers (in this example, the leaves), are always found to be the most numerous. This is then followed by the herbivores and so on along a food chain, with the final consumer which will be a carnivore being the least numerous. There are a couple of exceptions which do not produce true pyramid shape. Irregular Pyramids A When the producer is a tree B When a parasite is part of the food chain. So the number of organisms doesn t always decrease from the bottom to the top of the pyramid. 11

12 Predator and prey numbers The number of prey animals is always greater than the number of predator as illustrated by a pyramid of numbers. The graph below shows the relationship that exists between predator and prey over a given length of time. 1 Rabbit 2 Fox Number 2. Pyramid of biomass Time (months) The biomass of a population is the total mass of living matter in that population. This can be represented in a diagram called a pyramid of biomass like the example below. The width of each bar in this pyramid is a quantitative measure, showing how much biomass there is at each level. In a food chain, the biomass always decreases from the producer to the final consumer. This is a more reliable way to compare the organisms found at different levels in a food chain since it is based on productivity. As the pyramid on the previous page shows, this is measured as grams of dry mass per m 2 per unit of time (e.g. month / year). It can then be changed into its energy equivalent in joules (J) or kilojoules (kj), and be used to draw up a pyramid of energy. 12

13 3. Pyramid of energy Like a pyramid of biomass, a pyramid of energy always produces a true pyramid like the example given below. The energy at each level of the food chain is measured in units called Joules (J) Nitrogen in ecosystems Proteins (and therefore a mino acids ) contain the element nitrogen. Both plants and animals need nitrogen to make their own poteins. Despite 80% of the air being nitrogen, plants and animals cannot make use of this nitrogen gas directly. Animals need to eat food that provides them with protein (and therefore nitrogen) in order to be able make their own proteins. (The piece of cheese or chicken that you ate two weeks ago is now your hair, nails or muscles!!!!) Plants don t eat so they need to get their nitrogen from the soil so that they too can make their own proteins. Plants manufacture proteins using nitrogen from compounds present in the soil called nitrates. The nitrates are absorbed from the soil through the plant s roots. Plants do not grow well in soil that is low in nitrates. This is because the nitrates provide the plants with the elememts that they need to make proteins and proteins are needed for growth. In nature, nitrogen is recycled via the nitrogen cycle which is shown on the next page. 13

14 The Nitrogen Cycle nitrogen nitrates Dead plant and animal protein nitrites ammonium Important processes in the nitrogen cycle The nitrogen cycle is dependent on the activities of several different types of bacteria, each playing a key role in the nitrogen cycle. Decomposition: the conversion of dead plant or animal protein (and animal (1) waste e.g. faces and urea) to ammonium by bacteria and fungi (the decomposers ) Nitrification: the conversion of ammonia to ammonium, then (2 and 3) nitrites to nitrates by nitrifying bacteria. Denitrification: the conversion of nitrates to nitrogen (4) gas by denitrifying bacteria. Lightning: converts nitrogen gas to nitrates. (5) Nitorgen fixation: free-living soil bacteria absorb nitrogen gas and fix (6) it into nitrate. Other bacteria live inside swellings on the roots (called root nodules of some plants) and do the same thing. 14

15 More about Nitrogen Fixation A special group of plants called legume plants (e.g. peas, beans and cloves ), are able to absorb nitrogen gas and fix it into nitrate. This process is called nitrogen fixation and it is carried out by nitrogen-fixing bacteria. These bacteria either live freely in the soil or in swellings on a leguminous plant s roots called root nodules as shown in the diagram below. nodules Competition in Ecosystems Whenever two or more members of a community need the same resource, and that resource is in limited supply, competition occurs between them. For example green plants may compete with each other for light, water and soil nutrients (e.g. nitrate); animals may compete with each other for water, food or territory. Competition can affect an organism s chance of survival. There are two different types of competition: 1. Interspecific competition. This type of competition takes place between plants or animals that belong to a different species. An example of this is the competition that exists between grey and red squirrels. Although they are both squirrels they are different species of squirrel. 2. Intraspecific_ competition. This type of competition takes place between plants or animals that belong to the same species. An example of this is the competition that exists between two or more robins. Since members of the same species will compete for exactly the same resources in an ecosystem, intraspecific competition is much more intense than interspecific competition. (Members of a different species might compete for the same food, but compete for different mates or territory). 15

16 Summary Interspecific competition is when individuals of a different species require similar resources in an ecosystem. Intraspecific competition is when individuals of the same species require the same resources in an ecosystem. What is a species? Remember if two organisms breed to produce fertile offspring, this means that they belong to the same species. If they produce infertile offspring, this means that they do not belong to the same species. For example, a horse and donkey can still breed, but the offspring that are produced (called mules) can t breed as they are sterile + = horse donkey mule The horse and donkey are fertile, but the mule will be infertile. 16

17 Adaptation, natural selection and the evolution of species Mutations A mutation is said to occur when an organism s genetic material has been altered. They can affect single genes or whole chromosomes. These changes occur spontaneously (they just happen) and randomly, but mutations are rare. If a change in an organism s genotype produces a change in their phenotype, the organism is called a mutant. Mutations can be neutral and have little or no effect on an organism. Mutations can be harmful_ and this gives the organism a disadvantage and so this will decrease its chance of survival. Mutations might be useful as they might give the organism an advantage and so this will increase its chance of survival. Without mutations, organisms would never change in other words evolution would not occur. This is because mutations are the only source of new alleles in a population. Mutations therefore increase variation within members of the same species. Variation within a population makes it possible for a population to evolve over time in response to changing environmental conditions. Mutagenic agents The rate of mutations can be increased by environmental factors such as radiation (e.g. X-rays), UV light (from the Sun), and some chemicals e.g. mustard gas. These are all examples of mutagenic agents. 17

18 Natural Selection Species produce more offspring than the environment can support due to the limited resources available. A struggle for survival then takes place as they compete for these limited resources. Differences exist between members of a population this is called variation. Those organisms which are best suited or adapted to their environment will survive and reproduce. This means that favourable alleles will be passed on to their offspring. These favourable alleles might give these organism an advantage over others of the same species and so increase their chance of survival. This process is called natural selection or survival of the fittest. The diagram below shows how natural selection might have occurred in giraffes. 1. Variation exists between members of the same population. In this example some giraffes have a longer neck than others. 2. If there is a shortage of food on the ground (the selection pressure here), the giraffes will have to eat the leaves of trees. The giraffes with the longer necks will be able to reach the leaves at the top of the tree whilst those with shorter necks won t. 3. Due to natural selection (or survival of the fittest), only those giraffes with the long necks survive and so they would be able to pass on the gene that caused this characteristic to the next generation. So, natural selection results in the survival of those organisms whose variation makes them best suited to their environment (which constantly changes). Some individuals survive, but others don t this is why it is called survival of the fittest. 18

19 Natural selection or survival of the fittest occurs when there are selection pressures. Selection pressures are factors that act on members of a population and results in the death of some members of the population and the survival of others. Selection pressures include: predation disease temperature food availability Another example of natural selection can be seen in moths. In polluted areas, tree trunks are covered in soot particles and turn black. In non-polluted areas the tree trunks remain a silvery-grey colour. There are two different varieties of the same species of this moth: 1. light moth 2. dark moth (the mutant) Tree trunk in nonpolluted environment Tree trunk in polluted environment The population of light moths would increase in a non-polluted environment, whilst the population of dark moths in this environment would decrease. This is because the light moths are well camouflaged and are therefore not as easily seen by predators. So in this environment, the light moths enjoy a selective advantage and so more of them survive. In a polluted environment, the population of dark moths would increase, whilst the population of light moths in this environment would decrease. 19

20 Speciation Speciation is the term used to describe the formation of two or more new species from one original species. This process takes millions of years. The diagram below shows how all these different species had the same common ancestor i.e. they all came from one original species. Another example of speciation is demonstrated by the ostrich, rhea and kiwi. They have the same common ancestor, but have evolved to become three different species, but they are quite similar. ostrich rhea kiwi Speciation occurs after part of a population (sub-population) becomes isolated (separated from the remainder of the population). An isolating mechanism might be sea, mountains, ravines etc. They act as barriers to gene exchange as they prevent sub-populations from interbreeding. 20

21 Mutations then occur in each of the isolated sub-populations. Natural selection then selects for different mutations in each group. This is due to different selection pressures. As long as the sub-populations are prevented from interbreeding, each sub population eventually becomes a different species, but this takes millions of years. This is because the mutations that have occurred over this time make them so genetically different that they would no longer be able to interbreed and produce fertile offspring. Speciation has occurred. Speciation in action - Darwin s Finches The Galapagos islands are isolated in the Pacific ocean 600 kilometres from the coast of South America. It is thought that a species of finch-like bird (the founder species) left the mainland and arrived on these islands hundreds of thousands of years ago. The birds spread out over these islands and a lack of competition allowed their populations to increase. Groups became isolated from each other and this prevented them from interbreeding. Different mutations occurred within the populations on the different islands and selection pressures varied between the islands because of habitat differences. Over the years, they became so genetically different that they no longer belonged to the same species - so speciation had taken place. Today there are about 13 different species of finch that inhabit these islands, but they all have a common ancestor (the founder species ). The diagram below shows some of these new species of finch. 21

22 These finch species have many different features, but the most striking difference is the shape and size of their beak. Having a different shaped beak meant that they could eat different things - so their beak allowed them to inhabit a different island and this helped them to survive as it reduced competition for food. Human Impact of the Environment The Human Population Year on year, the human population is increasing. In 2011, it was estimated to be 7,021,836,029. Today it is even higher. Tomorrow it will be higher still. In order to provide enough food to meet the needs of our ever increasing population, methods to increase food yield are needed. The main way in which humans guarantee food is via farming, and farmers are always looking for new ways to increase food production. Unfortunately, some of the methods that farmers have used to increase food yield (known as intensive farming) have had a negative effect on biodiversity. Intensive Farming Intensive farming usually involves growing a specific crop species e.g. only growing wheat or only growing barley etc. in huge fields. The main drawback is that harmful chemicals (fertilisers and pesticides) are used in order to increase plant growth (and therefore yield). Fertilisers Fertilisers are used to add nutrients to the soil, and this helps to improve plant growth, and therefore helps to increase yield. Unfortunately fertilisers can cause problems. The main problem is that fertilisers can be leached into fresh water (e.g. ponds, streams, rivers and lochs) when it rains heavily. The fertilisers greatly increase the growth of plants called algae which live in the fresh water, and leads to something called an algal bloom forming. These algal blooms cause the levels of oxygen in the water to decrease and many of the animals that live there die as a result. Algal blooms can therefore affect the biodiversity of a freshwater ecosystem. 22

23 Pesticides These chemicals are used to deter a variety of different pests that affect plant growth. They too therefore help to increase yield and so increases the amount of crops that can be harvested. Unfortunately, like fertilisers, pesticides can also cause problems. The main problem with pesticides that are sprayed onto crop plants is that, over time, they can accumulate in the bodies of organisms. They are passed on from one organisms to the next via a food chain, and as they are passed along food chains, toxicity increases and can reach levels that are lethal to many animals - especially the ones at the top of a food chain. This is called biomagnification an example of which is shown in the diagram below. Increasing toxicity DDT is an example of a pesticide that was used to kill the mosquitos that were responsible for causing malaria. Although it undoubtedly saved many lives it killed other insects and it accumulated in the food chain. Every molecule of DDT that was ever used is still somewhere in the world s ecosystems!!!! 23

24 Biological controls Instead of using pesticides to kill the pests that affect plant growth, natural predators of these pests could be used - this is what is meant by biological control. This works well in enclosed spaces like greenhouses but is more difficult in open fields. Ladybirds are used as biological controls as they are the natural predators of aphids which are pests. GM crops (Genetically Modified) Another alternative to using fertilisers and pesticides is to grow crop plants that have been genetically modified (changed). Plants can be genetically modified by genetically engineering them. This of course now means that their genetic information has been changed usually by the addition of a useful gene from another organism. Common GM foods include tomatoes, rice cabbage and potato. These crop plants are genetically modified to: increase yield. reduce the need to use fertilisers and pesticides. 24

25 Indicator species An indicator species is a species that by their presence or absence gives us information about: the quality of it s environment levels of pollution in it s environment. Animal indicator species All the water invertebrates shown below are examples of indicator species. They all give information about the levels of pollution in a river 25

26 So, if the water is very clean (is not polluted), then we would expect group 1 to be present in the river, however, group 3 would be absent as they are only found in a river that is heavily polluted. Plant indicator species Lichen are simple plants. Different species of lichen can tolerate different levels of a gas called sulphur dioxide (SO2) which is produced when fossil fuels (e.g. coal, oil and gas) are burned. The presence or absence of such species indicate the levels of pollution by this gas. Crusty lichen Leafy lichen Hairy lichen can tolerate high levels of sulphur dioxide can tolerate moderate levels of sulphur dioxide cannot tolerate sulphur dioxide at all So, only crusty lichen would be present in an environment that is highly polluted with sulphur dioxide. The other two species of lichen (leafy and hairy) would be absent 26