Unit 4 revision

1. Unit 4 revision

2. Chapter 1 - Populations Define the following words: • Ecosystem • All the interacting biotic (living) and abiotic (non-living) features in a specific area. • Population • A group of individuals of the same species in a habitat • Community • The organisms of all species that live in the same area • Habitat • The place where an organism normally lives • Niche • All the conditions and resources required for an organism to survive and reproduce (its ‘role’)

3. Chapter 1 – Investigating Populations • List 3 factors to consider when using a quadrat • Size of quadrat, the number of quadrats to record, the position of each quadrat • How can you get a random sample? • Create a grid on the area (lay out 2 long tape measures) and obtain a series of co-ordinates using a random number generator and sample at each of those co-ordinates. • How can we measure abundance? • Frequency – if a species is in 15 out of 30 quadrats then its frequency is 50%. Percentage Cover – estimate the area within each quadrat that the species covers.

4. Chapter 1 – Investigating Populations • Explain the mark-release-recapture technique and how you can use it to calculate an estimated population size • A set of animals are caught and then marked in some way. • They’re then released back into the community. • After a specified length of time, the community is revisited and the same number or individuals is caught again. • The number of marked individuals is counted. Estimated pop. = (Total number of individuals in the first sample x size Total number of individuals in the second sample) number of marked individuals recaptured

5. Chapter 1 – Population Size Label and explain the stages of the population growth curve: Explain how the following factors affect population size: pH: light: temperature: water and humidity: Affects enzymes. Populations are larger in areas of optimum pH. Stable, no growth Slow growth Increasing light intensity increases photosynthesis, meaning faster plant growth and more food for animals. Rapid growth Slow growth – initially the small number of individuals reproduce slowly to build up numbers. Rapid growth – the ever-increasing number of individuals continue to reproduce rapidly. Stable state – factors limit the size of the population, e.g. food, predation Affects enzymes. Slow action at low temps, denaturation at high temps. Warm-blooded animals have to spend more energy keeping warm if the temp is too low, so a smaller pop size. If water is scarce then populations are small. Humidity affects transpiration and evaporation.

6. Chapter 1 – Competition and Predation • What is intraspecific competition? • Competition between members of the same species • What is interspecific competition? • Competition between members of different species • Explain the predator-prey graph • When there are higher numbers of prey the predators have more food. • This increases the numbers of predators. • As there are more predators they eat more prey. • This reduces the numbers of prey. • With less prey available the predators have less food. • This reduces predator numbers. • With less predators the prey numbers can increase again.

7. Chapter 1 – Human Populations Explain the following factors that affect human population, and how they are calculated: Migration: Birth rate: Death rate: Use the graphs to help you explain: Stable population: Increasing population: Decreasing population: Immigration – individuals join a population from outside Emigration – individuals leave a population Birth and death rates are in balance. No change in population size. Affected by economic conditions, cultural and religious backgrounds, social pressures and conditions, birth control, political factors. Birth Rate = number of births per year x 1000 total population in the same year High birth rate and fewer older people. Affected by age profile, life expectancy, food supply, safe drinking water, medical care, natural disasters, war. Death Rate = number of deaths per year x 1000 total population in the same year Lower birth rate and a lower death rate, so more elderly people.

8. Chapter 2 - ATP • Why do organisms need energy? • Metabolism, movement, active transport, maintenance, repair and division of cells, production of substances, maintenance of body temperature • How does ATP store energy? • ATP has 3 phosphate groups. The bonds between these groups are unstable and have a low activation energy. They break easily and when they do, they release energy. • How is ATP synthesised? • Adding a phosphate to ADP. Via photophosphorylation (in photosynthesis), oxidative phosphorylation (in the electron transport chain) and substrate-level phosphorylation (in glycolysis). • Why is ATP a good immediate energy source? • It cannot be stored, but is rapidly re-formed. It releases energy in small, manageable amounts. The hydrolysis of ATP is a single reaction, releasing immediate energy.

9. Chapter 3 – The Light Dependent Reaction What do plants capture light energy for? • Making ATP • Chlorophyll absorbs light energy and excites a pair of e-s • e-s leave the chlorophyll and are passed along a series of carriers (redox reactions) in the membrane of the thylakoids • e-s lose energy at each stage • This energy is used to combine ADP + Pi  ATP • Photolysis of water • Chlorophyll is now short of e-s • Water provides replacement e-s from water molecules that are split using light energy • 2H2O  4H+ + 4e- + O2 • H+ ions are taken up by NADP, which becomes reduced NADP

10. Chapter 3 - The Light Independent Reaction Explain the Calvin Cycle = a product from the light dependent reaction CO2 RuBP 2x GP ATP ATP Glucose etc. 2x TP ADP + Pi ADP + Pi Reduced NADP NADP

11. Chapter 3 - Factors Affecting Photosynthesis What is a limiting factor? • The rate of a process is limited by the factor that is at its least favourable value Limiting factors in photosynthesis? • Light intensity • CO2 concentration • Temperature

12. Chapter 3 - Limiting Factor Graphs – What is happening here? High [CO2] High Temp High [CO2] Low Temp Rate of Photosynthesis Low [CO2] Low Temp Light Intensity

13. Chapter 4 - Glycolysis • Where does glycolysis take place? • In the cytoplasm of cells • Describe the process of glycolysis Glucose is phosphorylated (USES 2 ATP) Glucose splits into 2x Triose Phosphate (TP) NAD NAD 2x ADP + Pi 2x ADP + Pi Hydrogen is removed from TP and given to NAD to form reduced NAD 2x ATP 2x ATP Reduced NAD Reduced NAD P P TP is converted into pyruvate. This generates 4x ATP P P

14. Chapter 4 – The Link Reaction • What are the products of glycolysis? • 2x ATP, 2x reduced NAD, 2x pyruvate • Where does the link reaction take place? • In the matrix of the mitochondria • What is the overall equation for the link reaction? • Pyruvate + NAD + CoA  acetyl CoA + reduced NAD + CO2

15. Chapter 4 - The Krebs Cycle Describe the Krebs Cycle Acetyl CoA 4 carbon molecule Combines with a 4C molecule 6 carbon molecule ATP NAD Reduced FAD 2H 2H Reduced NAD FAD Carbon Dioxide Carbon Dioxide

16. Chapter 4 – The Electron Transport Chain • Using the diagram, explain the stages of the ETC and how ATP is generated 1 2 3 4 5 6

17. Chapter 4 – Anaerobic Respiration • If no oxygen is present which part(s) of respiration can take place? • Glycolysis only (only generates small amounts of ATP) • What products does this leave you with? • Pyruvate and reduced NAD • What is the equation for how plants deal with these products? • Pyruvate + reduced NAD  Ethanol + CO2 + NAD • What is the equation for how animals deal with these products? • Pyruvate + reduced NAD Lactate + NAD

18. Chapter 5 – Energy and Ecosystems Explain the following terms: Trophic level: Food chain: Food web: Producer: Consumer: Decomposer: Describe how energy enters an ecosystem: Energy from the Sun is trapped by producers. Plants only convert 1-3% of the Sun’s energy into organic matter. Each stage in a food chain Describe how energy is lost from the food chain: Showing feeding relationships and transfer of energy Not all the organism is eaten, some parts cannot be digested easily (e.g. cellulose), loss by excretion, loss by heat from respiration. Linking together all the food chains in an area The efficiency of energy transfers is calculated using the following equation: Calculate the energy efficiency for this example: Energy available after the transfer = 50kJm-2year-1 Energy available before the transfer = 250kJm-2year-1 An organism that manufactures organic substances by photosynthesis An organism that obtains its energy by feeding on other organisms (50/250) x 100 = 20% An organism that breaks down dead plant/animal matter to release nutrients

19. Chapter 5 - Pyramids Explain what a pyramid of numbers is: Explain the advantages of using a pyramid of numbers: Explain the disadvantages of using a pyramid of numbers: Explain what a pyramid of energy is: Explain the advantages of using a pyramid of energy: Explain the disadvantages of using a pyramid of energy: Explain what a pyramid of biomass is: Explain the advantages of using a pyramid of biomass: Explain the disadvantages of using a pyramid of biomass: A pyramid drawn with bar lengths proportional to the numbers of organisms present A pyramid drawn with bar lengths proportional to the mass of plants/animals A pyramid drawn with bar lengths proportional to the energy stored in organisms Can be easy to be accurate in some food chains, simple to construct More reliable than using numbers, fresh mass is easy to assess Most accurate representation, much more reliable No account is taken of size, some food chains are hard to represent accurately (e.g. if millions of insects living on one tree) To get dry mass the organisms need to be killed and a sample may not be representative of the population, does not show seasonal differences Collecting data for pyramids of energy can be difficult

20. Chapter 5 – Agricultural Ecosystems Complete the table to show how natural and agricultural ecosystems differ: Describe what an agricultural ecosystem is: An ecosystem made up of domesticated animals/plants to produce food for human consumption. Attempts are made to keep energy losses low. Solar energy + energy from food Solar energy only Lower Higher More Less Describe what is meant by productivity and give the formula: More Less Productivity is the rate at which something is produced. Net productivity = gross productivity – respiratory losses Limited recycling of nutrients, fertilisers used Natural recycling of nutrients Natural means and use of pesticides etc. Natural means e.g. climate, competition Artificial community prevented from reaching climax Natural climax community

21. Chapter 5 - Pests • What are pests and pesticides? • Pests are organisms that compete with humans for food/space. Pesticides are poisonous chemicals that kill pests. • State 4 features of an effective pesticide • Specific, biodegradable, cost-effective, will not accumulate • What is a biological control? • Using predators of a pest to control its numbers. It is specific but slower and the predator may become a pest itself. • Explain what an integrated pest-control system is • A system that integrate all forms of pest control to try and keep the pest at an acceptable level. It does not eradicate the pest. • How does controlling pests affect productivity? • Removing pests increases productivity e.g. weeds take nutrients from crops, slowing growth, so removing these increases growth of crops.

22. Chapter 5 – Intensive Farming • Explain how rearing animals intensively increases the efficiency of energy conservation • Movement is restricted so less energy used in muscle contraction • The environment is kept warm, so less heat lost from the body • Feeding is controlled to give animals the optimum nutrients for growth • Predators are kept out so energy is not lost to another organism • Selective breeding has produced varieties of animal that are better at converting food eaten into body mass

23. Chapter 6 – The Carbon Cycle • Describe the carbon cycle CO2 in the atmosphere Combustion Fossil Fuels Photosynthesis Respiration Plants Animals Feeding Death Decay Decay Prevented Decomposers

24. Chapter 6 – The Greenhouse Effect Explain the consequences of global warming: Describe what the greenhouse effect is: A natural process. Some radiation from the Sun reaches the Earth’s surface and is reflected back as heat. Greenhouse gases trap this heat and keep it close to the Earth’s surface, keeping us warm. Melting of polar ice caps Rise in sea level, causing flooding Higher temperatures and less rainfall could lead to crops failing and changes in the distribution of plants Greater rainfall and storms in some areas would alter the distribution of plants and animals Life cycles of insects would alter, insects carrying diseases could spread northwards State the main greenhouse gasses and describe where they come from: CO2 – comes from human activities mainly Methane – from decomposers or the intestines of primary consumers such as cattle Describe what global warming is: The rising of the Earth’s average temperature. Human activities have increased the CO2 levels in the atmosphere from 270ppm before the industrial revolution to 370ppm today, trapping more heat.

25. Chapter 6 – The Nitrogen Cycle Describe the Nitrogen Cycle N2 in the atmosphere Nitrogen fixation by free-living bacteria Denitrification Nitrogen fixation by mutualistic bacteria Nitrate ions Absorption Plants Animals Nitrification Feeding Nitrite ions Death Nitrification Ammonium ions Decomposers Ammonification

26. Chapter 6 - Fertilisers Explain how natural and artificial fertilisers differ: Explain how fertilisers increase productivity Explain why fertilisers are needed in agricultural ecosystems: Minerals are needed for growth e.g. Nitrogen is needed for proteins. Plants that have sufficient minerals grow quicker, taller and have bigger leaves. Natural = Dead and decaying remains of organisms and waste materials. Artificial = Mined from rock deposits and blended together to give the best balance of minerals (NPK). All plants need mineral ions from the soil. Repeatedly using the same land for crops will remove these minerals from the soil. Fertilisers can replace them. Explain Eutrophication: Leaching of fertilisers increases nitrate concentrations in lakes and rivers Nitrate is no longer limiting and so algae and plants grow very quickly Results in an ‘algal bloom’ across the top of the water This prevents light reaching the lower depths Plants below the surface die Decomposers grow quickly with lots of dead plants for food Decomposers use up the oxygen for respiration Fish etc die due to lack of oxygen With less competition anaerobic organisms increase quickly These anaerobic organisms further decompose dead material releasing toxic wastes, making the water putrid.

27. Chapter 7 - Succession Explain what is meant by the terms: succession: climax community: conservation: The changes in an ecosystem, over time, of the species that occupy it The stable, final, community that exists in a balanced equilibrium Explain what changes occur in the variety of species that occupy an area over time: To start with there are very few species, and only those that can survive the hostile conditions (pioneer species). Gradually more species will colonise the area and conditions improve (plants die and nutrients added to the soil). These will gradually be larger plants and trees until the stable state is reached. Management of the Earth’s natural resources in such a way that maximum use can be made of them in the future Explain how you can conserve habitats by managing succession: You can help to keep a community at a stage before the climax community. This will keep different species present that would be lost in the climax community. E.g. the moorland in the UK is kept from becoming deciduous woodland by burning heather and sheep grazing.

28. Chapter 8 - Inheritance Monohybrid Crosses. Complete the cross for green and yellow plants. Green is dominant. Both parents are heterozygous. What is the probability of a yellow offspring? Explain what is meant by the following key terms: Genotype: Phenotype: Allele: Homozygous: Heterozygous: Dominant: Recessive: The genetic composition of an organism The characteristics of an organism (often visible), resulting from its genotype and the environment G g One form of a gene G GG Gg When the alleles are the same for a particular gene g Gg gg When the alleles are different for a particular gene An allele that is always expressed in the phenotype Probability of yellow offspring = ¼ or 25% An allele that is only expressed in the phenotype when there is another identical allele

29. Chapter 8 – Sex Linkage and Co-dominance Sex Linkage What do we mean by sex linkage? Why are sex-linked diseases more common in males? Complete a cross to show the chances of a child having haemophilia from a female carrier and a normal male. Co-dominance What is co-dominance? An example of co-dominance is in the snapdragon flower, which can be red, white or pink. Complete a cross for a red flower and a pink flower. A gene carried on the X or Y chromosome Both alleles are equally dominant and are both expressed in a phenotype If recessive, males only need 1 copy of the allele to suffer the disease, females need 2. CR CR 50% of offspring are red, 50% are pink CR XH Xh CRCR CRCR 25% of children suffer, but 50% of sons suffer XH XHXH XHXh CW CRCW CRCW XHY Y XhY

30. Chapter 8 – Multiple Alleles and Hardy-Weinberg Multiple Alleles What are multiple alleles? An example of multiple alleles are blood groups in humans. Alleles = IA, IB, IO. IA and IB are co-dominant whilst IO is recessive to both. Complete a cross to show the offspring of a female with blood group O and a male who is blood group AB. Hardy-Weinberg What is the Hardy-Weinberg equation? What can it calculate? State the assumptions of H-W Work out, using the Hardy-Weinberg equation, the allele frequencies of cystic fibrosis, a recessive condition affecting the lungs. In a population of 15,000 people, 1 person suffers from the disease. More than 2 possible alleles for a particular gene p2 + 2pq + q2 = 1 The frequencies of alleles in a population No mutations, isolated population, no selection, large population, mating is random. IA IB 50% blood group A, 50% blood group B Recessive, so the frequency of tt = 1/15000 So, q2 = 1/15000 = 0.000067 So, q = square root of 0.000067 = 0.0082 p + q = 1.0 So, 1.0 – q = p p = 1.0 – 0.0082 = 0.9918 (This is the frequency of allele T) IO IAIO IBIO IAIO IO IBIO

31. Chapter 8 – Selection and Speciation Explain directional selection Explain stabilising selection What is speciation? Explain how geographical isolation leads to speciation. Selection that favours individuals at one extreme. Often occurs when environmental conditions change. Phenotypes at one extreme may be more suited to the conditions and so survive and breed more, passing on their genes. Over time the mean will move in the direction of these individuals. The evolution of new species from existing species Populations become separated Therefore they stop interbreeding Selection pressures will be different in different areas Allele frequencies will change in the different populations Over time they become so different that they can no longer interbreed Selection that favours average individuals. Occurs if the environmental conditions are stable. Those individuals closest to the mean survive and breed more, passing on their genes. Phenotypes at the extremes will be eliminated.