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231 Cards in this Set
- Front
- Back
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Ecology |
The study of inter-relationships between organisms and its environment |
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Ecosystem |
Self-contained area where all biotic and abiotic factors interact with each other |
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Biosphere |
Layer of air, land and water surrounding Earth where organisms live |
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Microhabitat |
Smaller section within a habitat that has its own specific set of conditions creating a microclimate |
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Species |
Group of organisms that can interbreed to produce fertile offspring |
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Population |
All members of one species living in one habitat at a particular point in time. |
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Community |
Biotic part of an ecosystem consisting of all the populations of different species |
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Niche |
Specific set of biotic and abiotic factors to which an organism is adapted to live and behave. |
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Can two species occupy the same ecological niche? Why? |
No. They will out-compete each other until only one species remains. |
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What does abiotic mean? Give examples. |
Non-living factors. pH, rainfall, temperature |
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What does biotic mean? Give examples. |
Living factors. Competition, predation, disease |
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What are producers? |
Photosynthetic organisms that manufacture their own organic substances |
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State balanced photosynthesis equation |
6CO2 + 6H20 -> C6H1206 + 6O2 |
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What are consumers? |
Organisms that obtain energy by consuming other organisms |
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What do you call the group of organisms that eat secondary consumers? |
Tertiary consumers |
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What is the function of decomposers? |
Break down complex dead organisms into its simple components and by doing so release elements into the soil in a useable state for plants -> recycling of nutrients. |
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Why does competition within an ecosystem occur? |
All abiotic and biotic factors cannot be shared |
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State how most we most commonly realise that two species are not competing for the same ecological niche? |
Different feeding habits |
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Adaption |
Features that members of a species have to increase their chance of survival and reproduction. |
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What is each stage in a food chain called? |
Trophic level |
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What do arrows on food chain diagrams represent? |
Transfer of energy |
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What are the advantages of a food chain? |
Shows transfer of energy Simple and clear |
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What are the disadvantages of a food chain? |
Does not show complex feeding relationships Omits detrivores and decomposers Not quantitative |
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What are the advantages of a food web? |
Shows complex feeding relationships Shows transfer of energy
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What are disadvantages of a food web? |
Not quantitative Difficult to distinguish trophic levels Omits decomposers Population size fluctuations not taken into account Complex
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Sources of energy loss as sunlight into plants |
Light reflects off plant's transparent waxy cuticle Not all wavelengths of light can be absorbed and used for photosynthesis Light may not fall specifically onto a chlorophyll molecule |
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Gross production |
Total quantity of energy converted by plants into organic matter - energy absorbed |
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Sources of energy loss from one consumer to the next |
Heat/movement/respiratory Not all of organism is eaten Not all of organism can be digested and is thus excreted |
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Why do most food chains not have more than five trophic levels? |
Transfer of energy is so inefficient that at each successive level energy is lost. Too little energy is left at the top of the food chain to support growth and development for survival and reproduction |
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Why is the amount of energy stored/total mass of organisms less at higher trophic levels? |
At each successive level energy is lost and so decreases at each successive level. |
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Calculating efficiency of energy transfer: |
(energy available after transfer/energy available before transfer) * 100 |
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Why might a pyramid of numbers not look like a pyramid at all? |
Size dependent -one big tree can make the lowest trophic level the smallest. |
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Why might a pyramid of numbers be difficult to draw? |
Such a large range in numbers of organisms that cannot be drawn on the same scale. |
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Units of biomass for terrestrial ecosystems |
gm^-2 |
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Units of biomass for aquatic ecosystems |
gm^-3 |
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Why is dry biomass more accurate and reliable? |
Does not contain varying amounts of water which are not an energy store and so should not be taken into account |
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Biomass |
Total mass of plants/animals in a particular place |
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Disadvantages of pyramid of biomass |
Does not show seasonal fluctuations because biomass is taken at a particular time. |
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Net production |
Rate at which an organism stores energy |
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Equation for calculating net production |
gross production - respiratory losses |
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Disadvantages of pyramid of biomass |
Mass not proportional to energy content Process of dry mass kills organisms Dependent on length of life cycle Does not account for seasonal fluctuation
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Advantages of pyramid of biomass |
Uses comparable unit - quantitative Not size dependent |
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Units of pyramid of energy |
kJm^-2year^-1 |
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Advantages of pyramid of energy |
Sampled over a period of time and so seasonal fluctuations accounted for Not size/number dependent |
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Disadvantages of pyramid of energy |
Unethical process - kills organisms Complex feeding relationships not shown Omits decomposers |
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Succession |
Sequence of change within an ecosystem from a pioneer species to a climax community |
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What happens to biodiversity during succession? |
Increases |
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Primary succession |
Colonisation of new land - soil has no nutrients present |
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Examples of new land for primary succession |
Post volcanic eruption Sand dune Retreating glacier |
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Secondary succession |
Colonisation on area that has previously supported life and so soil has nutrients present already |
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Why are pioneer species typically producers? |
Autotrophs that can photosynthesise to make their own organic molecules and nutrients which the soil may lack. |
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How do pioneer species gain an advantage whilst in competition with other pioneer species? |
Germinate as quickly as possible Successful seed dispersal |
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Why might a pioneer species become out-competed by a new species? |
Abiotic and biotic factors may change to an environment not as well suited to pioneer species' adaptations. |
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State leaf adaptations for efficient photosynthesis |
Thin - short diffusion pathway for O2 out and CO2 in to reach mesophyll cells via stomata Moist - allows gases to dissolve and thus acts as a medium for faster transort Cuticle - waterproof (to conserve water by reducing evaporation) and transparent (to allow maximum light penetration reaching the palisade mesophyll layer) Good transport system - xylem, carrying water and dissolved minerals to the leaves, and phloem, carrying sugars and other organic products away maintain a steep concentration gradient Leaves have a large surface area in order to maximise the number of chlorophyll molecules exposed for light penetration required for the light dependent reaction. They are also arranged so that there is as little overlapping which could cause shade and thus less light penetration.
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Photosynthesis equation |
Carbon Dioxide + Water --> Glucose + Oxygen 6CO2 +6H20 --> C6H12O6 + 6O2 |
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Where does the light dependent reaction occur? |
Thylakoid membrane of chloroplast |
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Where does the light independent reaction occur? |
Stroma of chloroplast |
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What is the by-product of photosynthesis? |
Oxygen |
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What reaction turns ATP into ADP + Pi? |
Hydrolysis |
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What reactions turns ADP + Pi into ATP? |
Condensation |
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How does the hydrolysis reaction of ATP release energy? |
The phosphate group bonds are unstable and thus have a low activation energy. When these bonds are easily broken the terminal phosphate is removed releasing energy for cellular work and chemical synthesis |
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Why is light captured in the thylakoid membrane for use in the light dependent reaction? |
This is where photosynthetic pigments such as chlorophyll are located |
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What is a photosystem? |
Protein and photosynthetic pigment |
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Name the different photosystems used in the LDR and their working wavelengths |
PS1 - 700nm PS2 - 680nm |
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Describe the LDR |
Photosystem 2 absorbs a photon of light (680nm) using photosynthetic pigments located on its thylakoid membrane and so an electron becomes excited to a higher energy level. Photosystem 2 thus has lost an electron, become oxidised whereas an electron carrier has become reduced as it gains this electron and transports it in a series of redox reactions called the electron transport chain to photosystem 1. Each electron carrier is of a successively lower energy level and so the energy released as a result is used for photophosphorylation of ADP + Pi to form ATP. Photolysis occurs whereby water splits into electrons, protons and oxygen using light. Photosystem 1 absorbs a photon of light (680nm) and this similarly excites an electron to an even higher energy level, leaving PS1 oxidised. This electrons proceeds through a second electron transport chain. The protons (hydrogen ions) released from photolysis can join with coenzyme NADP using the energy released from the second electron transport chain in order to form NADPH (reduced NADP) |
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What is the importance of photolysis in the LDR? |
Protons released (hydrogen ion) bind with NADP to form product NADPH required for the light independent reaction. Electrons released replace PS2's lost electron Oxygen is by-product |
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What is an electron transport chain? |
Series of redox reactions of successively lower energy levels which releases energy in small, controllable amounts. |
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What are the 2 major products from LDR? |
NADP and ATP |
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State the photolysis equation |
2H20 --> 4H+ + 4e- + 2O2 |
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State three ways of reduction |
Gain electron Gain hydrogen Lose oxygen |
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State three ways of oxidation |
Lose electron Lose hydrogen Gain oxygen |
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Describe LIR |
Carbon dioxide from the atmosphere enters via stomata into the leaf and diffuses into the stroma to combine with 5-carbon RuBP using the enzyme RuBisCo = carbon fixation. This 6-carbon product is unstable and so splits into two 3-carbon compounds called GP. ATP and NADPH from the light dependent reaction reduce GP into two molecules of another 3-carbon compound called TP. NADP is now reformed into its natural state to be used in the light dependent reaction. TP is used to regenerate RuBP by reduction of ATP to continue the Calvin cycle. |
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How many times does the Calvin cycle need to turn in order to make one hexose sugar? |
6 |
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How does temperature affect rate of LDR? |
No effect - no enzymes present |
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How does temperature affect rate of LIR? |
Increase in temperature will increase rate until optimum temperature because enzymes such as RuBisCo will have increased kinetic energy and so more successful collisions will occur to form enzyme-substrate complexes. More carbon fixation will occur until the temperature exceeds optimum temperature and thus will lead to enzymes denaturing so that its tertiary structure is no longer a complementary shape to the substrate. |
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How does CO2 affect rate of LDR? |
No effect - carbon dioxide not required for reaction |
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How does CO2 affect rate of LIR? |
Increase in CO2 will increase rate of carbon fixation in LIR until another limiting factor is at a less favourable value. |
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How does light intensity affect rate of LDR? |
An increase in number of photons at a useable wavelength increases rate of LDR as this wil result in more electrons from the thylakoid membrane of the chlorophyll being excited in a higher energy level which is required for the ETC. There will also be a higher rate of photolysis meaning that PS2 can be reduced to its natural state and more NADPH can be produced. |
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How does light intensity affect rate of LIR? |
No direct affect however if there is no light then the LDR will come to a halt meaning that no ATP or NADH will be produced which is essential for LIR to reduce GP into TP. |
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Under high CO2 concentration what happens to the levels of RuBP and GP? |
High levels of carbon fixation result in RuBP being used up to produce lots of GP. |
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Under low CO2 concentration what happens to levels of RuBP and GP? |
Carbon fixation rate will decrease causing RuBP to accumulate because it is not being converted to GP. |
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What is compensation point? |
Point where there is no net movement of gases because levels of CO2 produced during respiration is equal to the levels of O2 produced in photosynthesis |
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How can you determine what is the limiting factor? |
If a limiting factor is changed to a more favourable value then the rate of the reaction should increase. |
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Respiration equation |
Glucose + oxygen --> carbon dioxide + water C6H1206 + 6O2 --> 6CO2 + 6H2O |
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ATP is not energy what is it? |
Store of energy |
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Describe the structure of ATP |
adenine nitrogenous base deoxyribose sugar three inorganic phosphate groups it is a mononucleotide |
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Why is ATP and not glucose used more regularly as an immediate energy source? (BENEFITS) |
Hydrolysis of ATP into ADP is a single reaction releasing energy immediately whereas the breakdown of glucose requires several reactions which is more difficult to control, releases more energy than needed and takes longer to achieve.
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When and why does activation of a molecule using a phosphate molecule occur? |
Hexose sugar in glycolysis is activated so as to make the molecule more reactive and by doing so reduce its activation energy so that reactions can occur more easily. |
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Where does glycolysis occur? |
Cytoplasm |
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Describe glycolysis |
Hexose sugar is activated via substrate-level phosphorylation (using the hydrolysis of 2 ATP molecules as a source of the phosphate molecules). This phosphorylated hexose sugar intermediate splits into two 3-carbon TP molecules. These TP molecules undergo oxidation causing NAD to become reduced and 2 ATP molecules to form. The end product is 2 3-carbon pyruvate molecules. |
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What is reduced in glycolysis? |
1 NAD is converted into NADH as TP is converted into pyruvate |
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What is oxidised in glycolysis? |
TP as it is converted into pyruvate |
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What is the net product of glycolysis from one hexose sugar? |
2ATP, 2NADH and 2 pyruvate |
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What is a coenzyme? Give examples |
A non-protein compound necessary for the functioning of an enzyme NAD/FAD |
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Where does the link reaction occur? |
Mitochondrial matrix |
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State overview of aerobic respiration |
Glycolysis Link reaction Krebs Cycle Electron Transport Chain |
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Describe the link reaction |
3-carbon pyruvate undergoes oxidative decarboxylation as carbon dioxide forms and NAD becomes reduced forming 2 carbon acetate. Coenzyme A binds to acetate to form acetyl coenzyme A. |
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State the link reaction equation |
pyruvate + NAD --> NADH + CO2 + CoA |
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What is the name of the 2 carbon intemediate compound in the link reaction? |
Acetate |
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What is the name of the 3 carbon intermediate compound in glycolysis? |
TP |
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What does TP stand for? |
Triose Phosphate |
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Where does the Krebs Cycle occur? |
Mitochondrial matrix |
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Describe the Krebs Cycle |
The coenzyme A on the CoA is recycled to form more CoA leaving the two carbon to bind with 4-carbon oxoloacetate to form 6-carbon citrate. The 6-carbon molecule undergoes oxidative decarboxylation whereby CO2 is removed along with hydrogen to reduce NAD into NADH thus forming a 5-carbon compound. This 5-carbon compound similarly undergoes oxidative decarboxylation forming 2NADH and 1 reduced FAD as well as ATP to reform the 4-carbon oxoloacetate.
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How many oxidative decarboxylation reactions occur in the Krebs cycle? |
twice: 6carbon citrate to 5carbon (releases CO2 and NADH) 5carbon to 4carbon oxoloacetate (releases 2NADH, 1 reduced FAD and ATP) |
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How many times does the Krebs Cycle occur per hexose sugar? |
Twice |
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Describe the electron transport chain |
Pairs of electrons donated by coenzymes NAD and FAD are passed via electron carrier proteins in a series of redox reactions. As the electrons pass down electron carrier proteins of successively lower energies releasing the energy required for ATP to form. Hydrogen ions (protons) are actively pumped across the inner mitochondrial membrane into the inter membrane space. The protons then diffuse back into the mitochondrial matrix down the gradient via chemiosmosis through ATP synthase membrane channel protein. The electrons are finally removed once accepted by the terminal electron acceptor oxygen, forming water.
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Why is it important that the electrons be removed from the final electron carrier protein during the electron transport chain in aerobic respiration? |
To allow the final electron carrier protein to accept electrons from further up the chain otherwise the electrons would "back up" causing respiration to come to a halt. |
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Where does substrate level phosphorylation occur? |
Glycolysis- when TP is converted into pyruvate Krebs cycle - breakdown of 5carbon to 4carbon |
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Where does oxidative phosphorylation occur? |
Electron transport chain |
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Number of reduced NAD produced per hexose in: Glycolysis Link Krebs |
2 2 (2x1) 6 (2x3)
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Number of reduced FAD produced per hexose in: Glycolysis Link Krebs |
0 0 2 (2x1) |
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Number of CO2 produced per hexose in: Glycolysis Link Krebs
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0 2(2x1) 4(2x2) |
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Number of ATP produced per hexose in: Glycolysis Link Krebs |
4 (net = 2) 0 2 |
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Number of ATP used per hexose in: Glycolysis Link Krebs |
2 0 0 |
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Describe anaerobic respiration in animals and state equation |
Pyruvate formed from glycolysis converts into lactate causing cramp in muscles using NADH to transfer its two excess hydrogen atoms. NADH must be removed otherwise if it accumulates glycolysis cannot continue without the NAD it requires for TP to be oxidised into pyruvate. pyruvate + NADH --> lactate + NAD |
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Describe aerobic respiration in plants and state equation |
Pyruvate formed from glycolysis ferments and thus converts into ethanol and carbon dioxide. pruvate +NADH --> ethanol + CO2 + NAD |
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What is oxygen debt and how is it remedied? |
Occurs during exercise when oxygen is used up more rapidly than it is being taken in causing anaerobic respiration to occur, producing toxic lactate. Lactate must be oxidised back into pyruvate once oxygen is present so that the pyruvate can be utilised in the link,krebs and finally ETC. |
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What is reduced during anaerobic respiration? |
pyruvate gains hydrogen from NADH to convert pyruvate into lactate. |
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What is oxidised during anaerobic respiration? |
NADH donates a hydrogen atom to pyruvate and by doing so converts back into its normal form NAD which can be utilised in glycolysis. |
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What are the advantages of anaerobic respiration? |
Permits ATP synthesis in the period immediately after birth when oxygen is yet to fill the lungs Allows animals to adapt to environments with low oxygen. Allows prey to escape predators through extended periods of muscle contraction when the supply of oxygen cannot match its consumption |
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Describe and explain the variations in carbon dioxide concentration varying on the time of day. |
During the day when sunlight is available the light dependent reaction of photosynthesis can occur leading to lower levels of carbon dioxide as this is absorbed in the process. At night sunlight is not available and so photosynthesis cannot take place. However, respiration is continuously occurring and so the levels of carbon dioxide are higher. |
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By what process do organisms release carbon dioxide into the atmosphere? |
Respiration |
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What is the difference between energy and nutrients? |
Energy is transferred whereas nutrients are recycled |
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Scavenger |
Consumer which feeds on dead organic matter |
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Detritivore |
Organism that feeds on partly broken down organic matter through internal digestion. |
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Decomposer |
Organism that completes break down of organic molecules through saprophitic digestion where enzymes are secreted outside of the body before the broken down remains are then fully absorbed. |
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What is the difference between a decomposer and a detritivore? |
Decomposers fully absorb all material they feed on whereas detritivores only partly absorb their food. |
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What are the bacteria called that decompose organic matter? |
Saprobionts |
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Fossilation |
Reduction in the rate of demposition due to anaerobic conditions (deep water/marshland) |
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What is global warming? |
Term for the global increase in temperature |
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Describe and explain how human activity has caused global warming? |
Human activity has enhanced the greenhouse effect by disrupting (increasing) the carbon dioxide concentration in the atmosphere. The consequence of this is an increased rate of global warming. |
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Describe and explain the greenhouse effect |
Greenhouse gases such as methane and carbon dioxide absorb the reflected waves of infrared electromagnetic radiation off of the Earth's surface meaning that less is lost to space and so is trapped, warming up the Earth's surface. |
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Give examples of human activities which have resulted in the greenhouse effect |
Destruction of natural carbon sinks: combustion of fossil fuels releases carbon dioxide previously locked up and deforestation reduces the amount of photosynthesis occurring meaning that less carbon dioxide is being absorbed from the atmosphere. |
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How do saprobionts absorb the food which they have just secreted enzymes onto? |
Diffusion - the enzymes have broken down these complex starting organic materials into smaller, soluble moleules. |
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How does an increase in carbon dioxide concentration affect the ocean and its inhabitants? |
As carbon dioxide is dissolved carbonic acid forms and so the ocean's pH lowers. This results in the thinning/corroding affect on aquatic life which have shells made out of calcium carbonate. |
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Name some examples of methane emissions |
Metabollic processes by decomposers/consumers digest and thus break down their food. Fossil fuel extraction Cattle flatulence Natural stores e.g. frozen ground - as global warming occurs the frozen ground melts releasing methane |
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How may global warming affect crop yield? |
An increase in temperature increases rate of enzyme activity and thus increases the rate of photosynthesis (especially LIR) meaning that crop yield could increase. An increase in temperature, however, also increases the rate of transpiration and evaporation which could decrease crop yield. The increased carbon dioxide concentration will also favour photosynthesis as it is required for the light independent reaction to occur - increasing crop yield. A rise of sea level due to thermal expansion could result in fertile land. |
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How may global warming affect animals? (higher temperature all year round) |
Higher temperatures melt the polar ice caps reducing the amount of ice for polar bears to live on. Plus, this could lead to flooding which could devastate even more habitats. Insects are poikilothermic and so their life cycle is quickened as temperature increases. As a result they reach sexual maturity faster and so can establish a higher number of generations. Warmer winters will increase the chance of survival meaning that population numbers could increase. As areas previously too cold may become warm enough for a species to thrive and so the animals may distribute via migration.
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Why can't nitrogen gas easily be absorbed? |
Strongly held by a triple bond Inert gas |
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Which is soluble and thus more easily taken up roots: nitrate or nitrite ions? |
Nitrate |
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Chemical formula of nitrate ion |
NO3- |
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Chemical formula of nitrite ion |
NO2- |
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Why do producers need nitrogen? |
Make proteins such as photosynthetic enzymes synthesise DNA and NAD
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Why do farmed soils contain too little nitrogen? |
Crops assimilate nitrogen found in soil and when they are harvested the nitrogen is therefore not recycled back into the soil. Grazers consume the crops Soluble nitrates are leached out of the fields after rainfall Increased levels of denitrification due to anaerobic conditions. |
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Why are ammonium ions less prone to leaching? |
Ammonium ions are positively charged and so adhere to the negatively charged soil particles. |
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Describe and explain the process of denitrification |
In anaerobic conditions oxygen is not present to act as the terminal electron acceptor for the electron transport chain to occur and so denitrifying bacteria pass electrons onto nitrate/nitrite ions instead in order to synthesise ATP. |
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Ways of increasing nitrogen concentration in soil |
Increase nitrogen fixation Reduce denitrification Apply fertilisers |
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What occurs if the niches of two different species are similar? |
Interspecific competition |
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Describe the process of nitrification |
Ammonium ions are first oxidised to nitrite ions and then to nitrate ions. |
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Name the three ways in which nitrogen fixation can occur |
Lightning Free-living nitrogen fixing bacteria reduce nitrogen to ammonia which they use to manufacture amino acids. When these bacteria die their decay releases nitrogen containing compounds |
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Primary productivity |
Rate at which producers transfer sunlight to chemical energy in the form of organic material (biomass) |
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Secondary productivity |
Rate at which energy is built up (assimilated) into the tissues of a consumer. |
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Primary productivity equation |
Net productivity = gross productivity - respiratory losses |
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Compare energy input in natural vs. agricultural ecosystems |
Natural: just sunlight Agricultural: sunlight, fossil fuels for tractors and chemical energy for us |
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What is phosphorus required for? |
ATP DNA |
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Ways of maximising primary productivity |
Remove factors that inhibit plant growth such as predators and disease Increase ground coverage to maximise amount of available sunlight energy to be used. Improve conditions for photosynthesis to occur |
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Ways of maximising secondary productivity |
Reduce respiratory losses by restricting movement and controlling temperature. Exclude predators by containing animals in enclosures Antibiotics reduce spread of disease, enforce herd immunity and avoid unnecessary losses to pathogens. Selective breeding uses livestock with faster growing rates. |
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Pest |
an organism that has an undesirable effect (often competes with humans) |
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Advantages of biological pest management |
Specific to the pest and so does not affect other organisms in the ecosystem Cheaper because the organism reproduces and so only one implementation is required No risk of bioaccumulation means that organisms higher up in the food chain are not affected No development of resistance makes it an effective long term strategy |
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How do fertilisers increase productivity? |
Plants which have a good supply of nitrogen are more likely to develop stronger, taller and have broader leaves and these features make it more fit for photosynthesis. By increasing the rate of photosynthesis its productivity is also increased. |
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Advantages of organic fertilisers |
Contains a mix of compounds which have a reduced chance of leaching because some are more soluble than others. Improves soil structure by encouraging soil microorganisms Recycles waste products |
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Disadvantages of organic fertilisers |
Unspecific contents could potentially be harmful - may contain toxic compounds (metals) or be contaminated with disease Bulky to store and not for long periods of time Difficult to apply easily
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Advantages of inorganic fertilisers |
Contains nutrients in specific amounts which match a plant's requirements Nutrients are readily soluble and so are quickly absorbed Clean to handle - in the form of pellets Easy to store - for extended periods of time |
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Disadvantages of inorganic fertilisers |
Expensive Nutrients are easily leached which can lead to eutrophication |
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2 major effects of nitrogen fertilisers |
Leaching Eutrophication |
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Describe leaching and its consequences |
Soluble nutrients are washed away by heavy rainfall into watercourses which may be harmful if consumed by humans Can lead to eutrophication |
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Describe eutrophication |
Soluble nitrates are leached into enclosed slow moving bodies of water. An algal bloom occurs since there is a higher concentration of nitrogen available for mitosis to occur Aquatic vegetation dies due to reduced levels of sunlight reaching the river floor and so photosynthesis is also reduced Saprophitic bacteria decompose this dead vegetation and as a result they acquire the nitrogen containing compounds they need for mitosis. As a result the population of saprophitic bacteria increases. As these saprobionts aerobically respire they deplete the oxygen concentration of the water. Other aquatic organisms will due to the lack of oxygen making them unable to respire. |
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What statistical test do you use to look for associations between different measurements from the same sample? |
Spearman's Rank correlation |
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What does Spearman's Rank look for? |
Association between two factors |
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What statistical test do you use to look for differences between mean values? |
Standard error and 95% confidence limits |
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What does standard error and 95% confidence limits look for? |
Differences between mean values |
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What statistical test do you use to find the number of individuals in particular categories? |
Chi-squared |
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What does chi-squared find out? |
Frequency Difference between observed and expected values |
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Genotype |
Genetic composition of an organism |
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Phenotype |
Physical characteristics of an organism resulting from its genotype and environment |
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Gene |
Length of DNA that codes for a polypeptide |
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Allele |
Form of a gene |
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Homologous chromosomes |
Pair of chromosomes that have the same gene loci and determine the same features |
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Dominant |
A type of allele that is always expressed in its phenotype |
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Recessive |
A type of allele that is only expressed in the phenotype when there is an identical recessive allele |
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Heterozygous |
Alleles are different for a particular gene |
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Homozygous |
Alleles are the same for a particular gene |
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What is a change in genotype? |
Mutation |
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What is a change in phenotype? |
Modification |
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Multiple alleles |
More than two alleles present in the gene pool for a particular gene |
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Co-dominance |
Two alleles in a heterozygous gene are both fully expressed in the phenotype simultaneously |
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What determines sex-linked inheritance? |
Genes present on the 23rd chromosome pair (sex) |
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Basic genotype for a girl |
XX |
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Basic genotype for a boy |
XY |
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How many copies if each allele are present in a diploid cell? |
2 - one from the mother and one from the father |
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How many copies of each allele are present in a haploid cell? |
1 - gamete so only from mother's egg/father's sperm |
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What is the difference between a mutation and a modification |
Mutation is a change to a person's genotype and so can be passed on to future generations whereas a modification is only a change to a person's phenotype and so is not inherited by future generations |
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Representing genetic crosses |
Parental phenotype Parental genotype (dom = capital; rec = lower) MEIOSIS Gametes (circled individual allele) Punnett square |
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What does a punnett square reveal? |
F1 genotype possibilities |
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What is the difference between female and male gametes? |
Female gametes are always X chromosome Male gametes are 50/50 X or Y chromosome |
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What are the consequences of the X chromosome being bigger than the Y chromosome? |
X chromosome carries more genetic information Areas where there is no equivalent homologous portion for the Y chromosome and so whatever is on the X chromosome will be expressed most frequently for men. |
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What is haemophilia? |
Condition where an individual is unable to produce a vital protein required for clotting and so may result in persistent internal bleeding |
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Monohybrid |
Inheritance of one feature/trait |
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How many genes are present in determining blood type and which ones are dominant? |
alleles A, B and i each lead to the production of an antigen on a red blood cell's surface A and B are dominant whereas i is recessive |
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How many different blood types are there?
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A, B, AB , O = 4 |
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Which alleles are co-dominant for blood type? |
A and B to produce blood type AB |
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Allelic frequency |
Number of times an allele appears in a gene pool |
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Gene pool |
All the alleles present of all individuals in a population at any one time |
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What does the Hardy-Weinberg principle tell us? |
Frequencies of alleles of a particular monohybrid gene in a population at one time |
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What 5 conditions must be met for Hardy-Weinberg to be correct? |
No genetic drift : large population No emigration/immigration = isolated No natural selection = all alleles equally likely to be passed on Random mating No mutations |
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How do you work out allele frequency? |
p + q = 1.0
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In Hardy-Weinberg what does p stand for? |
Dominant allele |
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In Hardy-Weinberg what does q stand for? |
Recessive allele |
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How do you work out genotype frequency? |
p^2 + q^2 + 2pq = 1.0 |
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What does p^2 stand for in Hardy-Weinberg? |
Homozygous dominant |
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What does q^2 stand for in Hardy-Weinberg? |
Homozygous recessive |
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What does 2pq stand for in Hardy-Weinberg? |
Heterozygous |
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Which genotype frequency do you calculate first in Hardy-Weinberg and why? |
q^2 = homozygous recessive Phenotype for heterozygous and homozygous dominant are the same |
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What does a pedigree chart show? |
Phenotypes of family members |
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What are the different types of selection? |
Directional Stabilising Destructive - synoptic |
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What is directional selection? |
Distribution of alleles in a population shifted to one extreme trait because it becomes the most advantageous. Natural selection favours one particular phenotype to a certain trigger (environmental) and so these will survive to be able to reproduce successfully. This may result in the less common phenotype being lost altogether. |
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What is stabilising selection? |
No environmental change occurs and so alleles closest to the mean are favoured. This phenotype is selected for whereas alleles at the extremes of the normal distribution will be selected against, eliminating their phenotypes |
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Speciation |
Genetic divergence of a species resulting in the formation of a new species |
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Postzygotic |
Reproductive isolating mechanism preventing gene flow after fertilisation has taken place |
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Prezygotic |
Reproductive isolating mechanism preventing gene flow from taking place before fertilisation |
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Allopatric |
Type of speciation as a result of a geographical barrier |
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Sympatric |
Type of speciation as a result of reproductive isolation |
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Stages of speciation |
Isolation Seperate gene pools/no interbreeding between populations Genetic variation due to mutation Trigger - selection pressure Selection for advantageous features Advantageous features have higher reproductive success Change in allele frequency Over a long period of time
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Features of a stable population |
Birth rate equal to death rate so net population stays same |
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Features of increasing population |
Birth rate exceeds death rate (wider base, narrower apex) |
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Features of decreasing population |
Death rate exceeds birth rate (broader apex, narrower base) |
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Demographic transition |
Change in population size over time |
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How to work out life expectancy |
point on survival curve where 50% of population are alive |
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Reasons for low birth rate |
Birth control/ contraception Social pressure not to have large family Empowering of women = having children later in life
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Reasons for high birth rate |
Lack of contraception/birth control Lack of education Cultural/social Need manpower High fatality rate
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Reasons for change in death rate |
Medical care - healthcare, vaccinations Sanitation Nutrition - food supply Disease spread Natural disasters
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