unit 4 revision
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Unit 4 revision. 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 - PowerPoint PPT PresentationTRANSCRIPT
UNIT 4 REVISION
Chapter 1 - PopulationsDefine 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’)
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.
Chapter 1 – Investigating Populations• Explain the mark-release-recapture technique and how you
can use it to calculate an estimated population size1. A set of animals are caught and then marked in some
way.2. They’re then released back into the community.3. After a specified length of time, the community is revisited
and the same number or individuals is caught again. 4. 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
Chapter 1 – Population SizeExplain how the following factors affect population size:pH:
light:
temperature:
water and humidity:
Label and explain the stages of the population growth curve:
Slow growth
Rapid growth
Stable, no 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. Populations are larger in areas of optimum pH.
Increasing light intensity increases photosynthesis, meaning faster plant growth and more food for animals.
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.
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.
Chapter 1 – Human PopulationsUse the graphs to helpyou explain:Stable population:
Increasing population:
Decreasing population:
Explain the following factors that affect human population, and how they are calculated:Migration:
Birth rate:
Death rate:
Immigration – individuals join a population from outsideEmigration – individuals leave a population
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
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
Birth and death rates are in balance. No change in population size.
High birth rate and fewer older people.
Lower birth rate and a lower death rate, so more elderly people.
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.
Chapter 3 – The Light Dependent ReactionWhat do plants capture light energy for?1. 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
2. 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
Chapter 3 - The Light Independent Reaction
CO2
RuBP
2x TP
2x GP
ATP
ADP + Pi
Reduced NADPNADP
ATP
ADP + Pi
Glucose etc.
= a product from the light dependent reaction
Explain the Calvin Cycle
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
Chapter 3 - Limiting Factor Graphs – What is happening here?
Light Intensity
Rate of Photosynthesis
Low [CO2]Low Temp
High [CO2]Low Temp
High [CO2]High Temp
Chapter 4 - Glycolysis• Where does glycolysis take place?• In the cytoplasm of cells• Describe the process of glycolysis
P P
P P
Glucose is phosphorylated (USES 2 ATP)
Glucose splits into 2x Triose Phosphate (TP)
NAD
Reduced NAD
2x ADP + Pi
2x ATP
2x ADP + Pi
2x ATP
NAD
Reduced NAD
Hydrogen is removed from TP and given to NAD to form reduced NAD
TP is converted into pyruvate. This generates 4x ATP
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
Chapter 4 - The Krebs Cycle
Acetyl CoA
6 carbon molecule
Combines with a 4C molecule4 carbon molecule
NAD
Reduced NAD
Carbon DioxideCarbon Dioxide
FAD
Reduced FAD
ATP
2H2H
Describe the Krebs Cycle
Chapter 4 – The Electron Transport Chain• Using the diagram, explain the stages of the ETC and
how ATP is generated
1 23
4
5
6
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
Chapter 5 – Energy and EcosystemsExplain the following terms:Trophic level:
Food chain:
Food web:
Producer:
Consumer:
Decomposer:
Describe how energy enters an ecosystem:
Describe how energy is lost from the food chain:
Each stage in a food chain
Showing feeding relationships and transfer of energy
Linking together all the food chains in an area
An organism that manufactures organic substances by photosynthesis
An organism that obtains its energy by feeding on other organisms
An organism that breaks down dead plant/animal matter to release nutrients
Energy from the Sun is trapped by producers. Plants only convert 1-3% of the Sun’s energy into organic matter.
Not all the organism is eaten, some parts cannot be digested easily (e.g. cellulose), loss by excretion, loss by heat from respiration.
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
(50/250) x 100 = 20%
Chapter 5 - PyramidsExplain 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 biomass is:
Explain the advantages of using a pyramid of biomass:
Explain the disadvantages of using a pyramid of biomass:
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:
A pyramid drawn with bar lengths proportional to the numbers of organisms present
Can be easy to be accurate in some food chains, simple to construct
No account is taken of size, some food chains are hard to represent accurately (e.g. if millions of insects living on one tree)
A pyramid drawn with bar lengths proportional to the mass of plants/animals
More reliable than using numbers, fresh mass is easy to assess
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
A pyramid drawn with bar lengths proportional to the energy stored in organisms
Most accurate representation, much more reliable
Collecting data for pyramids of energy can be difficult
Chapter 5 – Agricultural EcosystemsDescribe what an agricultural ecosystem is:
Describe what is meant by productivity and give the formula:
Complete the table to show how natural and agricultural ecosystems differ:
An ecosystem made up of domesticated animals/plants to produce food for human consumption. Attempts are made to keep energy losses low.
Productivity is the rate at which something is produced.Net productivity = gross productivity – respiratory losses
Natural Agricultural
Input of Energy
Rate of Productivity
Amount of Species Diversity
Amount of genetic diversity within a
species
Nutrient Recycling
Control of Populations
Point in Succession
Solar energy only
Solar energy + energy from food
Lower Higher
More Less
More Less
Natural recycling of nutrients
Limited recycling of nutrients, fertilisers used
Natural means e.g. climate, competition
Natural means and use of pesticides etc.
Natural climax community
Artificial community prevented from reaching climax
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.
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
Chapter 6 – The Carbon Cycle• Describe the carbon cycle
CO2 in the atmosphere
AnimalsPlants
Photosynthesis
Feeding
Respiration
Decomposers
Death
Decay
Fossil Fuels
Decay Prevented
Combustion
Chapter 6 – The Greenhouse EffectDescribe what the greenhouse effect is:
State the main greenhouse gasses and describe where they come from:
Describe what global warming is:
Explain the consequences of global warming: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.
CO2 – comes from human activities mainlyMethane – from decomposers or the intestines of primary consumers such as cattle
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.
Melting of polar ice capsRise in sea level, causing floodingHigher temperatures and less rainfall could lead to crops failing and changes in the distribution of plantsGreater 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
Chapter 6 – The Nitrogen Cycle
N2 in the atmosphere
Plants
Nitrogen fixation by mutualistic bacteria
AnimalsFeeding
Decomposers
Death
Ammonium ions Ammonification
Nitrite ions
Nitrate ions
Nitrification
Nitrification
Absorption
Denitrification
Nitrogen fixation by free-living bacteria
Describe the Nitrogen Cycle
Chapter 6 - FertilisersExplain why fertilisers are needed in agricultural ecosystems:
Explain how natural and artificial fertilisers differ:
Explain how fertilisers increase productivity
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.
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).
Minerals are needed for growth e.g. Nitrogen is needed for proteins. Plants that have sufficient minerals grow quicker, taller and have bigger leaves.
Explain Eutrophication:
1. Leaching of fertilisers increases nitrate concentrations in lakes and rivers2. Nitrate is no longer limiting and so algae and plants grow very quickly3. Results in an ‘algal bloom’ across the top of the water4. This prevents light reaching the lower depths5. Plants below the surface die6. Decomposers grow quickly with lots of dead plants for food7. Decomposers use up the oxygen for respiration8. Fish etc die due to lack of oxygen9. With less competition anaerobic organisms increase quickly10. These anaerobic organisms further decompose dead material releasing toxic wastes, making the
water putrid.
Chapter 7 - Succession
Explain what changes occur in the variety of species that occupy an area over time:
Explain what is meant by the terms:succession:
climax community:
conservation: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.
The changes in an ecosystem, over time, of the species that occupy it
The stable, final, community that exists in a balanced equilibrium
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.
Chapter 8 - InheritanceExplain 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
One form of a gene
When the alleles are the same for a particular gene
When the alleles are different for a particular gene
An allele that is always expressed in the phenotype
An allele that is only expressed in the phenotype when there is another identical allele
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?
G g
G
g
GG
Gg
Gg
gg
Probability of yellow offspring = ¼ or 25%
Chapter 8 – Sex Linkage and Co-dominanceSex LinkageWhat 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-dominanceWhat 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
If recessive, males only need 1 copy of the allele to suffer the disease, females need 2.
XH Xh
XH
Y
XHXH XHXh
XHY XhY
25% of children suffer, but 50% of sons suffer
Both alleles are equally dominant and are both expressed in a phenotype
CR CR
CR
CW
CRCR CRCR
CRCW CRCW
50% of offspring are red, 50% are pink
Chapter 8 – Multiple Alleles and Hardy-Weinberg
Multiple AllelesWhat 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-WeinbergWhat 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
IA IB
IO
IO
IAIO IBIO
IAIO IBIO
50% blood group A, 50% blood group B
p2 + 2pq + q2 = 1
The frequencies of alleles in a population
No mutations, isolated population, no selection, large population, mating is random.
Recessive, so the frequency of tt = 1/15000So, q2 = 1/15000 = 0.000067So, q = square root of 0.000067 = 0.0082p + q = 1.0So, 1.0 – q = pp = 1.0 – 0.0082 = 0.9918 (This is the frequency of allele T)
Chapter 8 – Selection and SpeciationExplain directional selection
Explain stabilising selection
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.
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.
What is speciation?
Explain how geographical isolation leads to speciation.
The evolution of new species from existing species
1. Populations become separated2. Therefore they stop interbreeding3. Selection pressures will be different in
different areas4. Allele frequencies will change in the
different populations5. Over time they become so different
that they can no longer interbreed