Unit 4 AQA Biology

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  • Created on: 18-04-14 21:08
Define Population
All the organisms of one species in a habitat
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Define Niche
The role of a species within its habitat eg. what it eats
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What does a niche include?
Biotic (eg what a species eats) and abiotic (the oxygen the species uses) interactions
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Community All the populations of different organisms living and intercating in a particular place at the same time
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Equation of mark-release-recapture technique
(Number marked in first sample x number of individuals in second sample) / number marked in second sample
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Equation for population growth
Growth rate = (Births + immigration) - (deaths + emmigration)
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Percentage population growth rate
= (Population change / initial population) x 100
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Factors affecting birth rate
Economical conditions, war/political factors, birth control, social pressures.
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Birth rate equation
(number of births/total population in the same year) x 1000
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Factors affecting death rate
Life expectancy, availability of food, medical care, safe drinking water, war, sanitation, natural disasters.
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Death rate equation
(number of deaths per year / population the same year) x 1000
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Equation for photolysis of water
2H20 -----> 4H+ + 4e- + O2
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Where does the light dependent reaction take place?
Thylakoid membranes of chloroplast
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What happens in the light dependent reaction?
Light energy is used to add a phosphate group to ADP to make ATP and to reduce NADP so it can transfer hydrogen to the light-independent reaction. Water is also oxidised to O2
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Where does the light independent reaction take place?
The stroma
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What happens in the light independent reaction? (Calvin cycle)
ATP and reduced NADP from the light dependent reaction supply the energy and hydrogen to make glucose from carbon dioxide
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Name the photosynthetic pigments in chloroplasts
Chlorophyll a, chlorophyll b and carotene (coloured substances that absorb light energy needed for photosynthesis) The pigments are found in the thylakoid membranes
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What does the stroma contain?
enzymes, sugars and organic acids
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What are the limiting factors in photosynthesis?
1. Light intensity 2. Temperature 3. Carbon dioxide concentration
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What is energy needed for?
Metabolism, movement, active transport, maintainance, repair and division of cells, production of substances, maintainance of body temperature.
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What are the four main stages of aerobic respiration?
Glycolysis, link reaction, krebs cycle, oxidative phosphorylation
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Where does glycolysis take place?
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Is glycolysis an aerobic or anaerobic process?
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Which stages of respiration take place in the mitochondria?
Link reaction, Krebs cycle and oxidative phosphorylation
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What are the products of glycolysis?
2 x ATP, 2 x reduced NAD and 2 x pyruvate
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What is the equation for the link reaction?
Pyruvate + NAD + coA ---> acetyl coA + reduced NAD + CO2
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Where is the electron transport chain found?
In the inner mitochondrial membrane
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What happens in the electron transport chain?
reduced NAD/FAD release hydrogen, which dissociates into H+ and e-. Elctrons move along transport chain losing energy which is used to pump H+ across the membrane. H+ diffuse back via ATP synthase - regenerating ATP and forming water with O2 and e-
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Anaerobic equation for plants
pyruvate + reduced NAD ---> ethanol + CO2 + NAD
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Anaerobic equation for animals
Pyruvate + reduced NAD ---> Lactate (lactic acid)
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Why is most of the suns energy not converted to organic matter?
Most of the suns energy is reflected back into space by clouds/dust, or absorbed by the atmosphere. Not all wavelengths of light can be absorbed/used for photosynthesis, light may not fall on a chlorophyll molecule, also limiting factors
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The equation for net production (the rate at which energy is stored in plants)
Net production = gross production - respiratory losses
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What factors affect net productivity?
Efficiency of the crop at carrying out photosynthesis (can be improved by removing limiting factors), the area of ground covered by the leaves of the crop
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What is gross productivity?
The rate at which plants assimilate chemical energy
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Why is there such a low percentage of energy transferred between stages of ecosystem?
Some of the organism isn't eaten, some parts are eaten however can't be digested, some energy is lost in excretory materials, some energy losses eg heat loss
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Energy transfer equation
(energy available after transfer/energy available before transfer) x 100
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Define biomass
The total mass of plants and/or animals in a particular place
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How do agricultural ecosystems maximise growth?
Input additional energy, used to plough fields, sow crops, remove weeds, supress diseases and pests, feeding and housing animals, transporting materials etc. This energy is in 2 forms: - food (for farm workers) - fossil fuels (for machinery)
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Advantages of natural ecosystem
More species diversity, nutrients are recycled naturally, natural climax community, more genetic diversity, populations are controlled naturally (competition/climate)
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Advantage of agricultural ecosystem
increased productivity,
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are poisonous chemicals that kill pests. Herbicides kill plants, fungicides kill fungi and insecticides kill insects
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An effective pesticide should...
be specific (only toxic to the pest), biodegrade(should have a long shelf life but also break down into harmless substances), be cost effective and not accumulate (or it would pass along food chain)
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Disadvantages of pesticides
They must be reapplied at regular intervals - making them expensive, always have some effect on non-pest species, pests can become resistant to pesticides meaning new ones must constantly be developed
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Biological Agents...
using predators or parasites of the pest species to control pest numbers
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Advantages of biological agents
very specific to pest, pests cannot become resistant, no need for reapplication
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Disadvantages of biological agents
slow acting, control organism may become a pest eg - if population rises too high,
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Integrated systems are designed to have minimal impact on the environment and involve...
choosing suitable plant or animal species (eg pest resistant), managing environment to provide habitats for natural predators, regularly monitoring crops for pests, removing pests if population becomes too high, using pesticides as a last resort
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Intensive rearing increases energy conversion by:
restricting movement (less energy lost), warmer environment (less heat loss), controlled feeding (optimum amount of food for maximum growth), predators excluded
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Dangers of intensive rearing
Concentrated populations are more suceptable to disease and infection can spread more easily, overuse of antibiotics to prevent this has lead to increase antibiotic resistance. Pollution (large amounts of waste), restricted gene pools= less diversity
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Production of ammonium by releasing organic nitrogen in the breakdown of dead or waste matter.
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Nitrogen fixation (eg lightening)
The conversion of nitrogen gas in the atmosphere to nitrogen containing compounds
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Conversion of ammonium compounds to nitrites, which are then converted to nitrates which can be absorbed by plants directly from the soil
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Conversion of nitrates to nitrogen gas which is released into the atmosphere under anaerobic conditions
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Negative effects of nitrogen-containing fertilisers
reduced species diversity (nitrogen-rich soils favour certain species), leaching and eutrophication
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Water dissolves soluble nutrients in soil (eg nitrates). The leached nutrients then make their way into streams/rivers. This can lead to eutrophication, prevent efficient oxygen transport in babies and has been linked to cancer.
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- High nitrate levels causes algal bloom -algae prevent light reaching photosynthesising plants which die -saprobionts decompose dead plants - bacteria respire releasing CO2 and reducing O2 concentration - aerobic organisms die due to lack of O2
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Explain why CO2 concentration is often less during summer than winter
During summer: light intensity is greater / longer periods of light, temperature is usually higher, these factors both affect the rate of photosynthesis so during summer more CO2 is removed from the atmosphere so concentrations fall.
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Consequences of global warming
melting of polar ice caps, rise in sea level (could flood low-lying land), disruption of weather patterns (droughts/flooding more common), life cycles of insect pests altered
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Define succession
Succession describes the changes in the ecosystem over time in the species that occupy that particular area
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Common features of succession
Abiotic conditions - less hostile, more varied habitats, increased biodiversity, more complex food webs, increased biomass
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Features of a pioneer species
Rapid germination of seeds, ability to photosynthesise (to provide food), tolerance to extreme conditions, ability to fix nitrogen (no soil/few nutrients)
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What is conservation?
Management of the earths natural resources, requiring human intervention to maintain ecosystems and biodiversity
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What is phenotype?
The expression/actual appearance of a gene. This is also affected by environment.
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What is genotype?
the genetic constitution of an organism
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What is a gene
A portion of DNA
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What is a dominant allele?
An allele which is always expressed
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What is a recessive allele?
An allele which is only expressed in the presence of another identical allele.
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What is codominance?
Where both alleles contribute to the phenotype
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What are the five conditions of Hardy Weinberg?
1. No mutations 2. Large population 2. No selection 4. Random mating 5. Isolated population
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What does Hardy Weinberg predict?
That the proportion of dominant/recessive alleles of any gene in a population with remain the same from one generation to the next assuming the conditions are met.
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The Hardy Weinberg equations:
p + q = 1 p^2 + q^2 + 2pq = 1
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What are the two types of selection?
Directional selection and stabilising selection
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Directional selection
favours individuals that vary in one direction from the mean as they are more suited to the altered conditions. Over time the mean will shift in the direction of these individuals
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Stabilising selection
Preserves the characteristics of a population and favours average individuals
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What is speciation?
Evolution of a new species from existing species
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Geographical isolation
When a physical barrier prevents 2 populations from interbreeding.
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Define Niche


The role of a species within its habitat eg. what it eats

Card 3


What does a niche include?


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Equation of mark-release-recapture technique


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