AQA A2 Biology Unit 4
- Created by: Millie
- Created on: 08-06-13 20:02
Populations & Ecosystems
Ecosystem- A self-contained system in ecology made up of both biotic (living) and abiotic (non-living) factors.
Population- The number of individuals of a species in a given area at a given time.
Community- All of the populations of different species in a given area at a given time.
Habitat- The place where a community lives.
Niche- The role a species plays in the upkeep of an ecosystem.
Investigation Populations
Quadrats, three factors to consider- size of quadrat, No of sample quadrats to use in study, Position of quadrats.
Random Sampling- e.g. draw up a grid of the area and generate coordinates randomly to sample quadrats.
Sampling along transects- tape measure places in a line and quadrats placed evenly along the transect.
Measuring Abundance- after obtaining results using quadrats or along transects, find either a frequency (likelihood of a species being found in a quadrat) or a percentage cover (estimate the area a species covers in a quadrat and then find an average over all of the quadrats).
Mark-Release-Recapture- Estimated individuals in 1st capture X individuals in 2nd capture Population Size Marked individuals recaptured
(must make sure the mark left on individuals does not disadvantage them in their ecosystem)
Variation in Population size / competition
Population Growth Curves- a natural population has three phases: 1) a period of slow growth as the initially small number of individuals reproduce slowly. 2) a period of rapid growth where the ever increasing individuals continue to reproduce. 3) a period when the population growth declines until the size remains more or less stable. decline may be due to food supply or increased predation.
Population Size- A population may grow or decrease due to limiting factors, these can be either biotic (predation) or abiotic (temperature, light, pH, water, humidity) factors.
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Intraspecific competition- Individuals of the same species competing with each other for resources, this could mean food, water or mates.
Interspecific- Individuals of different species competing for resources. Where 2 species occupy the same niche one will normally have an advantage over the other.
Predation
Predation- when one organism in consumed by another. In a natural ecosystem the area in which the predator and prey species live is so great that the prey species rarely becomes extinct.
Effect of predator-prey relationships on population size- Population of prey decreases due to predation, Fewer prey available therefore predator population decreases due to greater competition, prey population increases due to reduced number of predators, predator population increases due to increase in prey population.
Human Populations
Human Population Growth Rate- originally human growth has been kept in check by disease and famine however due to developments in technology and agriculture human populations have exploded.
Factors affecting human populations- (Births+immigration)-(deaths+emigration)= Growth Birth rate: No births per year X1000 Total population of same year (Affected by Economic conditions, religious backgrounds, society,politics and birth control.) Death rate: No Deaths per year X1000 Total population in same year (Affected by life expectancy, food supply, sanitation, medicine, war and natural disasters) emigration and immigration.
Population Structure- stable populations - where birth and death rates are in balance
increasing population - birth rate high giving a wider base at the bottom of the pyramid and very narrow at the top. countries with less economically developed
decreasing populaiton - where there is a low birth rate (narrow base) and lower mortality rate leading to more elderly people (wider apex). usually cxountries which are ecomically developed.
ATP
Energy- the ability to do work
Why do organisms need energy?- metabolism, movement, active transport,maintenance, repair and division of cells, production of substances, maintanance of body temperature.
Flow of energy through living systems- Light fro sun converted into chemical energy, chemical energy in the form of organic molecules are converted into ATP during respiration, ATP used by cells in important reactions.
How ATP stores energy- ATP + water <--> ADP + Phosphate ion + energy The forward reactions = hydrolysis reaction and the backward reaction = condensation reaction.
ATP Synthesis- can happen in 3 ways: 1) phosphorylation - takes place in chlorophyll. 2) oxidative phosphorylation - occurs in mitrocondria in electron transport. 3) substrate level phosphorylation - e.g: formation of pyruvate.
ATP efficiency- small amounts of energy released one step reaction so very fast release of energy
Overview of Photosynthesis
Overall Equation- 6CO2 + 6H2O --> C6H12O6 + CO2 Structure of leaf- large surface area- collects as much sunlight as possible. thin - most light is absorbed in first few mm & diffusion pathway kept short. transparent cuticle and epidermis - lets light through to photosynthetic cells. long, narrow, upper epidermis cells packed with chloroplasts to collect sunlight. numerous stomata for gaseous exchange. Structure of chloroplasts- grana - stacks of up to 100 disc like structures called thylakoids where the light dependent stage of photosynthesis take place, within these are chlorophyll. stroma - a fluid filled matrix where the light independent stage takes place. within in it are other structures such as starch
Light-Dependent Reaction
ATP Production- Chlorophyll molecule absorbs light and electrons excite, electrons taken up by electron carrier and pass down transport chain(in thylakoid membrane), energy released used to produce ATP.
Photolysis- water molocule split into oxygen, protons and electrons. Electrons produced replace ones exited from chlorophyll molecule. The oxygen given off as waste product. Chlorophyll molecules go through another excitation, losing electrons, electrons leave chlorophyll molecule and join with electron acceptor (NADP) and are used along with the protons from photolysis reaction to form NADPH.
Light-independent Reactions
Calvin Cycle- CO2 joined with RuBP to produce 2xGP, 2xGP is reduced with ATP & NADPH from the light dependant reaction, to form 2xTP. 2xTP converted into amino acids, lipids, starch or glucose by plant. unused TP converted into RuP. RuP then made back into RuBP by reacting it with ATP. (RuP + ATP ---> RuBP + ADP)
Site of light-independant reaction- takes place in stroma of the chloroplasts: stroma fluid ( which contains all of the enzymes needed)surrounds the grana and so the products of the light-dependant reaction can easily diffuse into the stroma. The fluid contains DNA and ribosomes so it can quickly and easily manufacture some of the proteins needed for the light-independent reactions.
Photosynthesis summary / Limiting Factors
---------------------------------------------------------------------------------------------------------------------------------- Limiting Factors: Light- when limiting factor, rate of photosynthesis is directly proportional to light intensity. as light intensity increases the net gas exchange will decrease as O2 produced and CO2 taken in are equal. CO2- effects enzyme activity, in particular increases the enzyme that catalyse the joining of RuBP & CO2 in light-independant reactions. Temperature- photosynthesis increases as temperature increases until optimum temperature, then enzymes start to denature & rate of photosynthesis decreases.
Respiration: Glycolysis
1) Glucose + 2ATP --> Phosphorylated Glucose + 2 Phosphate ions
2) Phosphorylated Gucose --> 2 TP
3) 2TP + 2NAD --> 2 Oxidised TP + 2 Reduced NAD
4) 2 Oxidised TP + 4 ADP --> 2 Pyruvate + 4 ATP
Energy Yield-
2 molecules of ATP (4 molecules of ATP are produced but 2 were used up in the phosphorylation of glucose.
two molecules of NAD
two molecules of pryruvate
Respiration: Link Reaction & Krebs Cycle
Link Reaction: 1) pyruvate actively transported into matrix from cytoplasm. 2) pyruvate oxidised by removing a hydrogen and CO2 released to form acetyl, hydrogen then accepted by NAD to form NADH. 3) acetyl then joined with CoA to form acetylcoenzyme A
Krebs Cycle: 1) AcetylCo A joined with a 4C molecule to form a 6C molecule. 2) 6C molecule loses 2CO2 & H2 to form 4C molecule, 1 ATP molecule, NADH & FADH. 3) 4C molecule can then join with acetylCo A to restart the cycle.
Respiration: Electron Transport Chain
The Electron Transport Chain is found in the cristae of mitochondria. This is where most of the ATP is produced in respiration.
1) H2 join with NAD and FAD 2) FADH & NADH donate electrons of H2 atoms to first carrier protein in chain. 3) The H+ ions are then actively transported across the inner mitochondrial membrane. 4) electrons pass along carrier proteins gradually losing energy, this energy is then used to combine ADP and a phosphate to form ATP. 5) At the end of the chain the H+ ions and the electron combine with O2 to form water. (this means oxygen is the final acceptor in the chain)
Importance of oxygen being the final acceptor- without it the H+ and electrons would 'back up' along the chain and respiration would come to a halt.
Anaerobic Respiration
This is when respiration happens in the absence of oxygen, also anaerobic reactions happen in some bacteria and fungi and in some plant cells (e.g. root cells in water logged conditions).
End of Glycolysis- pyruvate + NADH --> ethanol + CO2 + NAD
In animals the reaction is slightly different:
Pyruvate + NADH --> Lactic Acid + NAD
The lactate is oxidised into glycogen when oxygen is next available. (this is what causes cramp in muscles)
Food Webs/energy transfer between trophic levels/
Food Web- systems of interlocking and interdependent food chains. ------------------------------------------------------------------------------------------------------------------------------------------Energy loss: From Producers- light reflected, not a wavelengths absorbed, limiting factors. From Consumers- don't consume all of prey, bodily waste, heat loss.
Net Production = Gross Production - Respiratory Losses
Efficiency of energy transfer - energy available after the transfer X100 energy available before the transfer
Percentage efficiency- % of energy available after transfer X100 % of energy available before transfer --------------------------------------------------------------------------------------------------------------------------------- Pyramid of Numbers- measured in numbers, no acount taken for size and some data can be to large to represent. Pyramid of Biomass- Biomass is the total mass of the plants or animals in a particular place, measured in grams per square meter, seasonal differences are not apparent Pyramid of Energy- Most accurate,difficult to collect data,results are more reliable than pyramids of biomass.
Agricultural Ecosystems / Fertilisers
Agricultural ecosystem- made up of domesticated animals used to produce food for humans, used to minimise energy loss so humans get as much energy as possible. Productivity- Rate at which something is produced net productivity = gross productivity - respiratory losses (affected by effeciency of photosynthesising crop and area of ground it covers)
Comparison of natural and agricultural ecosystems- Natural Agricultural solar energy the only input, lower productivity, solar energy + fossil fuels, higher productivity, more species diversity, more genetic diversity, less species diversity, less genetic diversity, nurients naturally recycled, population artificial fertalisers used, populaion controlled controlled by natural means, natural climax by natural and artificial (pesticides)means, community. preveted from reaching natural climax. ---------------------------------------------------------------------------------------------------------------------------------------Fertilisers are chemicals that provide crops with minerals for growth e.g. nitrates, they replace minerals lost through plant uptake so more energy from ecosystem can be used to grow, increasing the efficiency of conversion. 1. Natural fertilsers are organic matter- including mnure and sweage sludge 2. Artificial are inorganic- contain pure chemicals e.g. ammonium nitrate
Chemical & Biological control of pests
Pesticide- poisonous chemical that kills pests should be specific to pest, biodegrade, cost-affective, not accumulate in soil.
Biological control- controlling pests by the introduction og a predator species. very specific, control organism reproduced itself, no resistance.
Agricultural Pests:Integrated pest control-choosing crops/animals that are resistance to pests,provide habitats for natural predators, look for signs of pests, only use pesticides if necessary.
How pests affect productivity- Reduce productivity, Compete for resources, lacking resources may become limiting factor for, photosynthesis or growth, damaging to crops,disease causing to animals, consuming crops, competition to humans, monocultures enable rapid spread of pests or fungi.
Effect of intensive rearing on energy conversion: movement restricted (less energy lost in muscle contraction) warm environment (no heat loss to surroundings), controlled feeding (optimum diet, minimum waste), Predators excluded (no loss to other organisms in food web), selective breeding (animals that are most efficient at converting food to body mass are bred with eachother to encourage this trait).
Carbon Cycle
- CO2 is absorbed by plants when they carry out photosynthesis- it becomes organic compounds in plant tissues. - Carbon is passed on to primary consumers when they eat plants. It's passed on through the food chain. - Carbon compounds in dead organisms digested by microorganisms called decomposers e.g. bacteria and fungi. Feeding on dead organic matter is called saprobiontic nutrition. - Carbon is returned to the air (and water) as all living organisms (including decomposers) carry out respiration, which produces CO2. - If dead organic matter in places where there aren't any decomposers e.g. deep oceans,carbon compounds are turned into fossil fuels. - The carbon in fossil fuels is released when they're burnt- called combustion.
Nitrogen Cycle
Ammonification- Nitrogen compounds found in dead organisms and bodily waste are broken down by saprobiotic microorgamisms. NH4+ --> NH3
Nitrogen Fixation- Nitrogen is converted into NH3. This can happen when lightning passes through the atmosphere, by bacteria living in soil, or bacteria living in root nodules of plants.
Nitrification- This is the conversion of ammonium ions to nitrate ions by nitrifying bacteria, to be used by the plant. Firstly nitrfying bacteria oxidise ammonium ions to nitrite ions (N02-) and Secondly other nitrifying bacteria oxidise nitrite ions to nitrate ions (N03-).
Denitrification- Nitrates in soil converted to N2 by denitrifying bacteria, they use nitrates in soil to carry out respiration and produce N2. Happens under anaerobic conditions.
Leaching and Eutrophication
Leaching- Rain water dissolves and washes nutrients through of the soil so they are so deep, they cant be reached by plant roots. From here they can be washed into ground water and eventually pollute bodies of water like streams and fresh water lakes.
Eutrophication-1. Nitrates leached from fertilised fields stimulate growth of algae in ponds etc. 2. Large amounts of algae block light from reaching plants below 3. Plants die as they are unable to photosynthesise 4. Bacteria feed on the dead plant matter 5. Increased numbers of bacteria reduce the oxygen concentration in water by carrying out aerobic respiration 6. Fish etc. die as there isn't enough dissolved oxygen
Succession
Succession- the name given to the process of a ecosystem as it changes through out time. 1) Where there is bare land a pioneer species will colonise the area e.g. lichens, this could be by the lichens dying and when they decompose release nutrients into the soil. 2) The pioneer species will then change the area so it becomes habitable for other species. 3) This will carry on until a climax community has been reached. During succession you will see: A greater number and variety of habitats, Increases biodiversity, More complex food web, Increased biomass Conservation of Habitats- conservation is the management of the earths natural resources so that maximum use of them can be made in the future. Done for ethical, economic, cultural and aesthetic purposes.
Inheritance
Gene- length of DNA which codes for a poly peptide, a gene may also code for a characteristic.
Allele- one from of a gene, of which their may be many.
Homologous Chromosomes- pair of chromosomes that have the same gene loci and so determine the same features.
Sex Linkage- A Gene which is carried on the X or Y chromosomes, however due to the X chromosome being longer many genes are only seen on the X and there is no equivalent gene on the Y.
Haemophilia- The blood clots slowly. Although some females have haemophilia it mostly occurs in males as it is a recessive allele on a sex-linked gene.
Pedegree chart- A way to trace sex-linked genes across generations.
Co-dominance- where 2 alleles share dominance over a characteristic.theresult could be that both alleles are expressed or a mix of them is expressed.
Population Genetics / Selection
Hardy-Weinberg Principle: P + 2PQ + Q = 1 and P + Q = 1 Provided that: no mutation, isolated population, no selection, large population, random mating. -------------------------------------------------------------------------------------------------------------------------------------------Directional Selection - favours individuals that vary one side of the mean
Stabalising Selection- favors individuals about the mean
Speciation
Occurs when populations of the same species are seperated, and due to different environmental conditions, over time become different species altogether.
speciation: The eveolution of two or more species from an existing species. 1) Due to climate change, a population living in an area is seperated to become two separate populations. 2) The climates are different and so favour different phenotypes that are survival advantages in these conditions. 3) Over time, the type and frequency of alleles of the gene pool in each population is so different that they become different species.
The two populations could be isolated by either sympatric (breeding seasons) or allopatric means (geographical).
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