Life on Earth National 5 Course Notes. Calderglen High School National 5 Biology Life on Earth Unit

Transcription

1 Calderglen High School National 5 Biology Life on Earth Unit 1

2 Life on Earth Subtopic 1: Ecosystems A species are a group of organisms that can interbreed and produce fertile offspring. Biodiversity is a term used to describe the different species of organisms in an ecosystem. It also includes variation between the same species e.g. rabbits with black coats and rabbits with grey coats. Ecosystems with high biodiversity (a lot of different species) are healthier than ecosystems with low biodiversity (few different species) and therefore more likely to survive. Producer: - a green plant that makes its own energy by photosynthesis using energy from the sun. Consumer: - an animal that eats the plants or other animals. We can form a food chain which shows these relationships. e.g. grass rabbit fox. (producer) (primary consumer) (secondary consumer) The arrows in the food chain show the direction of energy flow. Further definitions Herbivore: - animal that eats green plants e.g. the rabbit in the above food chain Carnivore: - animal that eats other animals e.g. the fox in the above food chain. Omnivore: - animal that eats green plants and other animals e.g. bear. Food chains rarely exist in isolation e.g. in the above food chain the grass may also be eaten by deer and rabbits may also be eaten by hawks. A series of interconnecting food chains make up a food web. 2

3 A food web An ecosystem consists of all the organisms (the community) living in a particular habitat and the non-living components with which the organisms interact. e.g. a wood or a pond. A habitat is the place an organism lives and the community is made up of all the organisms in the ecosystem. A niche is the role an organism plays within an ecosystem. This relates to the resources it requires in its ecosystem, such as light and nutrient availability and its interactions with other organisms in the community. It involves competition and predation and conditions it can tolerate e.g. temperature. For example a rabbit would have predators like foxes, hawks and weasels and would feed on grass and small plants. The rabbit would also be host to many diseases and carcasses could provide food for flies and crows. Predation A predator kills and eats its prey. In cases of extreme predation the prey can be wiped out but more often a decrease in prey is followed by a decrease in predators. The prey will then increase again followed by the predators etc. 3

4 Image BBC Bitesize The predators are actually beneficial to the prey because without them they would exhaust the food supply. Competition Competition in an ecosystem occurs when resources are in short supply. Examples of resources include water, light and nutrient availability. Competition can be divided into interspecific (different species) and intraspecific (same species). Interspecific (different species) Occurs amongst individuals of different species for one or a few of the resources they require. Red squirrel and grey squirrel. Grey squirrels are stronger and more aggressive in pursuit of food so in areas where both types are present the red squirrels have been eliminated. Red squirrels still survive in coniferous woodland because they can survive on a diet of pine seeds alone whereas grey squirrels cannot. 4

5 Images scran Grey squirrel Red squirrel Intraspecific competition (same species) This occurs between members of the same species and is for all the resources they require. It is therefore more intense than interspecific competition. 5

6 Subtopic 2: Distribution of Organisms Biotic :- living factors e.g. disease, predation, food availability, grazing and competition. Abiotic :- non-living factors e.g. light intensity, temperature, mositure, ph. Both the above effect the biodiversity and distribution of organisms. Measurement of Biotic Factors Sampling techniques are designed to quantify the numbers of an organism in a habitat without having to count every individual. It is important enough samples are taken to make the results more reliable and that they are taken in a random manor i.e. if quantifying the daises on a lawn it would not be appropriate to sample only the areas where daisies were clumped. Quadrats This device can be used to estimate numbers of plants or very slow moving animals. The quadrat could be used to estimate the daisies in a field. The quadrat is divided into squares. it is placed in several random locations and each square containing daisies counted. An average is taken and used to estimate the total number of daisies in the field. N.B. quadrats must be placed randomly. Transect lines This involves placing quadrats at equal distances along a line e.g. to see the effect of increasing light intensity as the line emerges from woodland. Pitfall Traps These are used to estimate numbers of small invertebrates in a habitat such as leaf litter in woodland. 6

7 The trap must be covered to prevent predators such as birds eating the contents and to prevent excess rainwater. The trap must be level with the ground to allow animals to fall in. The trap must be checked regularly to prevent carnivorous trapped animals eating other animals. The trap should have pinholes in the base to allow water to escape. Sufficient traps should be set to give a more reliable result. Measuring Abiotic factors Temperature This is measured in degrees Celsius ( o C ) using a thermometer. There are several types including soil thermometers that have a probe to stick into the soil. Which ever type you are using you must ensure you do not hold the detecting part allow the instrument to stabilise before taking a reading. Take enough readings of the area to obtain a more reliable result. Light Measured in lux using a light meter. The detector should face the light source Avoid shading the detector 7

8 Take enough samples to give a more reliable result This is a measure of acidity or alkalinity. The range is 0-14 with ph 7 being neutral. Acids become stronger as they move away from 7 towards 0 and alkalis become stronger as they move away from 7 towards 14. Soil Moisture This has a probe to measure moisture levels in the soil. With this meter and the ph meter it is important to clean the probe between each use to remove any moisture from the previous reading. Paired-statement keys These can be used to identify organisms. Statement 1. Does the animal have four legs Yes go to statement 2 No go to statement 4 2. Does the animal have a curly tail? Yes pig No go to statement 3 BBC Bitesize 3. Does the animal have a hoof divided into two parts? Yes cow No - horse 4. Does the animal have webbed feet? Yes duck No - human 8

9 .The effect of abiotic factors on biodiversity ph Most aquatic environments have a ph range between 6-8. Acidification due to pollution e.g. pollution from factories causing acid rain. Temperature The north sea temperature is rising due to climate change forcing cold water species such as sardines and anchovies to move further north. At the same time warm water species like red mullet are beginning to inhabit the north sea. Indicator Species An Indicator species is a species that can show the levels of pollution of an environment by being absent or in some cases present. For example, the Stonefly nymph shown in the diagram is only found in water which does not have any sewage pollution. Stonefly Nymph Lichens are found on the bark of trees and indicate imagebbc Bitesize the levels of air pollution (particularly sulphur dioxide). Crusty lichen is found at all levels of pollution, whereas lung Lichen is only found in unpolluted air. 9

10 Subtopic 3: Photosynthesis Photosynthesis Photosynthesis is the process in green plants involving the manufacture of glucose sugar from Carbon dioxide gas and water, producing Oxygen gas as a by-product. Leaves contain a special pigment known as CHLOROPHYLL that allows plants to capture the energy of light to drive the process. The sugar can be used by the plant cells themselves during respiration, stored in the leaves as starch or built up into cellulose, a chemical that makes up cell walls. Summary: Carbon dioxide + Water Light energy Chlorophyll Glucose + Oxygen The process of photosynthesis takes place in the chloroplast and occurs in two stages: the light reaction and the carbon fixation stage. Stage 1 The light reactions The light energy from the sun is trapped by chlorophyll in the chloroplasts and is converted into chemical energy in the form of ATP. Water is split to produce hydrogen and oxygen. The oxygen diffuses from the cell. Sunlight energy is absorbed by the chlorophyll inside the chloroplast. Light energy is used to split water (H 2O) Energy is used to join ADP + Pi Oxygen diffuses out of the leaf Hydrogen 10 is formed This forms ATP

11 Stage 2 Carbon Fixation Hydrogen and ATP produced by the light reaction is used with carbon dioxide to produce glucose in an enzyme controlled process. ATP hydrogen Carbon fixation stage Carbon dioxide Glucose The glucose can be used for respiration or converted into starch or cellulose. Factors affecting Photosynthesis We might expect an increase in the following to have an increase in the rate of photosynthesis: Concentration (availability) of Carbon dioxide Light intensity Temperature Aquatic plants such as elodea can be used to investigate these hypotheses either by observing the rate of production of oxygen bubbles or by using colour changes in bicarbonate indicator solution as measures of the rate of photosynthesis: 11

12 Limiting Factors Graph The graph below shows the effect of increasing carbon dioxide concentration on the rate of photosynthesis at different light intensities and temperatures. D Light intensity 20 kilolux 0.5 Temperature 16 o C C Rate of photosynthesis (cm 3 CO2 used per minute) A B Light intensity 20 kilolux Temperature 10 o C Light intensity 10 kilolux Temperature 10 o C Carbon dioxide concentration (%) The limiting factor at A, B and C on the graph above Area of graph being limited A Limiting factor Carbon dioxide concentration. Explanation As the concentration of carbon dioxide increases to 1% the rate of photosynthesis increases. B Light intensity By comparing points B and C on the graphthe only difference between these to points is light intensity. Point B has a lower light intensity therefore the rate of photosynthesis is lower. C temperature By comparing points C and D on the graphthe only difference between these to points is temperature. Point C has a lower temperature therefore the rate of photosynthesis is lower. Apparatus to investigate the rate of Photosynthesis by production of Oxygen: 12

13 Oxygen Aquatic plant Action Move the lamp closer to the plant Substitute warmer water Add Sodium bicarbonate Adjusted variable The light intensity increases Temperature increases Increases the concentration of dissolved Carbon dioxide The rich biodiversity of the rain forests is depleted by this human activity and when deforestation occurs on hillsides this can cause landslip which causes the loss of vegetation and increases the chance of flooding. 13

14 Subtopic 4: Energy in Ecosystems Image BBC BiteSize In transfer of energy from 1 level of a food chain to the next. The majority of the energy is lost as heat, movement or undigested material. Only a very small quantity is used for growth and can then be passed on to the next level of the food chain. Pyramids A pyramid of numbers is used to represent the numbers of different organisms in a food chain. The wider the bar the greater the number of organisms. Pyramid of numbers fox rabbits Grass Normally the bars get smaller going up the pyramid (remember energy is lost at each stage). However this is not always the case. For example suppose there is one big producer. Or small secondary consumers (e.g. oak tree, midge) 14

15 Bird of prey Small bird Caterpillar Oak tree Pyramid of energy This gives the energy each species produces per metre squared per year (kj/ m 2 / year). This is calculated using dry mass and should always give the correct pyramid shape. Image BBC Bitesize 15

16 Subtopic5: Food Production Human Population growth curve Image BBC Bitesize An increasing population requires an increased food yield. This can involve the use of fertiliser and pesticides. Fertilisers provide chemicals such as nitrates which increase crop yield. Plants and animals which reduce crop yields can be reduced by pesticides. Fertilisers Nitrates occur naturally in the soil but are removed by growing plants. Fertilisers can be added to the soil to increase the nitrate content. The nitrates in the fertiliser dissolves in water ad is absorbed into the plant. These nitrates are used by the plant to produce amino acids which can be synthesised into plant proteins. Animals can then consume these plants or other animals to obtain amino acids for protein production. 16

17 Problems with fertilisers Leaching (washing out) of fertiliser into rivers and lochs adds extra unwanted nitrates to the water. This a source of food for algae which rapidly increase in population causing an algal bloom. Algal blooms reduce light levels, killing aquatic plants. Both the dead plants and dead algae are a food source for bacteria which rapidly increase in number. These bacteria use up oxygen reducing its availability to other organisms e.g. fish, which will therefore decrease in numbers. Diagram BBC Bitesize Pesticides and Bioaccumulation As pesticides are toxic and a predator will usually eat many pests the quantity of pesticide in organisms tends to increase as they are passed along the food 17

18 chain. This has led to problems with animals at the top of a food chain e.g. birds of prey have been found to produce soft shelled eggs. DDT was a chemical used to spray crops in the 1970 s. It was found to have such harmful effects that it is now banned in many countries although not all. Alternatives to pesticides and fertilisers Biological Control Biological control is the use of one species to control numbers of another. Myxomatosis Used in 1950 s to control rabbit population (95% of Britain s rabbits killed in 1955) this virus is still present in rabbit populations today. Ladybirds These can be bread in large numbers to feed on aphids which are a plant pest. Genetically Modified (GM) crops E.g. a gene that enables plants to be unaffected by a higher pesticide levels could be inserted to the plant by genetic engineering. The plant could then be sprayed with higher levels of pesticide eliminating the pests while growing normally itself. 18

19 Subtopic 6: Evolution of the Species A mutation is a random change to genetic material. Mutations may be disadvantageous, neutral or advantageous to survival. Mutations are spontaneous and are the only source of new alleles. However, certain environmental factors increase the rate of mutations. These include radiation and some chemicals e.g. mustard gas. Disadvantageous These mutations give rise to proteins that may not function normally. e.g. haemophilia is a blood clotting disorder 33% of cases are caused by spontaneous mutation other cases are inherited. Neutral These have neither an advantage or disadvantage to survival e.g. some different DNA sequences code for the same amino acid if one is altered other sequences can code for the same amino acid. Advantageous These mutations are rare but individuals who inherit them are more likely to increase in numbers because they have an advantage over other individuals to survival. E.g. a mutation to a protein that helps remove cholesterol from arteries making it more effective. New alleles (forms of a gene) produced by a mutation can result in plants and animals becoming better adapted to their environment. Variation within a population makes it possible for a population to evolve over time in response to changing environmental conditions. Some members of a species will be more suited to survive and reproduce in the present environment or in a changed environment than other members of its species. Examples of adaptations Kangaroo rat : - this desert mammal has several adaptations making it suited to a very hot environment. It produces large volumes of a hormone (ADH) causing reabsorption of water from the kidneys. Feeds at night staying in cool burrows during daytime. Produces very dry faeces. Has no sweat glands. Reduce water loss 19

20 Bee Orchid: - this plant has adapted to look like a female bee. This attracts male bees for pollination. Natural Selection and Speciation Natural selection is often referred to as survival of the fittest. In normal conditions a species will produce more offspring than the environment can support. Variation will be present among the species and some will be better suited to the environment than others. The best adapted individuals in a population survive and pass on their favourable genes to their offspring. E.g. If a rabbit has a gene (that has arisen through mutation) giving it stronger leg muscles it is more likely to escape predators because it can run faster than rabbits without the gene. Speciation occurs after part of a population becomes isolated by an isolation barrier which can be geographical, ecological or behavioural. E.g. a geographical barrier could occur to a river changing course and isolating some of the population. Mutations occur within each sub-population and natural selection will select different mutations in each sub-population due to the different selection pressures that suit their environment. The sub-populations evolve into genetically different species. Galapagos Finches Beak for seed and nut eating Charles Darwin s drawings of the different beaks shapes found on finches in the Galapagos islands Image BBC Bitesize Beak for insect eating 20

21 Finches from the South American mainland colonised these islands. Natural selection enabled finches with different variations to occupy separate ecological niches. Beak shape is related to diet. This had not been possible on the mainland as other species already occupied these niches. Arctic Char These are related to salmon and would have naturally migrated out to sea as young fish. During the ice age populations of these fish were trapped in some of Scotland s freshwater lochs where they have evolved into a true freshwater species. 21