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Unit 4 biology

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Mark McBrien

on 31 May 2013

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Transcript of Unit 4 biology

Unit 4 Biology Population ATP Photosynthesis Respiration Energy and ecosystems Nutrient cycles Ecological succession Inheritance and selection populations and ecosystems Ecology - the study of inter-relationships between organisms and their environment Biotic- living factors Abiotic - Non-living/physical/ of an environment chemical factor/non biological;
Ecosystem - how these factors interact
Population- All organisms of one species in a habitat/area/place/at one time;
community - All the fish/all the species/all the populations/all the organisms;
Habitat- the place where an organism normally lives - subdivided into microhabitats
Ecological niche - the role an organism fits within an environment Investigating populations abundance - number of individuals in a given space three factors when using quadrats
the size of the quadrat
the number of quadrats to record
the positioning of the quadrat Random sampling - avoids bias
Lay out a long tape measure at right angles
obtain a series of coordinates from a random number generator
place a quadrat at the intersection of each pair of coordinates systematic sampling
see transition in species from a point
Line or belt transect in the line of the changing factor and place the quadrat at regular intervals measuring abundance -
frequency - number of quadrats in which the species is present - quick but doesn't show density / distribution
percentage cover - estimate the area within the quadrat that is covered (percentage of squares that are over half covered) - rapid but no use if layers overlap Mark - release- recapture for mobile organisms

caught first time, then marked and released, after a period of time they are recaptured Estimated population size = total number of individuals in first sample X total number of individuals in the second sample assumptions -
no emigration/ immigration
few deaths/ births
marking doesn't affect survival
those that are marked evenly disperse in the population
proportion marked to non marked 2nd sample = proportion marked to non marked in population statistical tests - used to calculate the strength and and direction of any correlation Variation in population size 3 stages in a growth curve
slow growth - small population to reproduce
rapid growth - exponential as no limiting factors
stable state - limiting food supply/ predation/ greater competition Abiotic factors
temperature - cold - slow metabolic rate / greater energy expenditure to stay warm - increased metabolic rate
hot - denaturation / greater energy expenditure - sweating
light - rate of photosynthesis increase with light intensity -faster growth - more seeds produced
pH - enzyme action
Water and humidity - transpiration Competition Intraspecific - individuals of the same species compete for resources - food, water, breeding sites
their availability determines population size Interspecific - individuals of different species compete for resources such as food, light water.
occurs when two species occupy the same ecological niche - one normally has a competitive advantage - it is more effective and often eliminates the other when the resources are limited - competitive exclusion principle there is a time lag for the effects of competition to be seen.
an abundance of food takes longer to affect the population than a shortage of food Predation predator - an organism that feeds on another organism (prey) predation forces adaptation - selection pressures Predators eat prey - reduce prey population
greater competition amongst predators
predator population decreases
less prey eaten - prey population increases
less competition amongst predators
predator population increases range of fluctuations less severe in natural ecosystems as more food sources

still cyclic fluctuations - disease and climatic factors play a part Human populations large increases due to development in agriculture and developing in manufacture/ trade population growth = births + immigration - deaths - emigration
individuals join a population
growth rate = population change X 100
original population individuals leave a population factors affecting birth rates
economic condition ; cultural and religious backgrounds; social pressures; birth control; political factors
birth rate = number of births per year X 1000
Total population in the same year Factors affecting death rates -
age profile; life expectancy ; food supply ; sanitation/ safe drinking water; medical care; natural disasters; war
death rate (same as birth rate but with number of deaths per year) Human populations continued Demographic transition model- shows how birth and death rates change with the development of a population and the effect this has on the population size Age and gender profile is shown by population pyramids
Stable population - Birth rate = death rate (triangle shaped pyramid)
Increasing population - high birth rate - wide base
few old people - narrow apex (top)
country is economically less stable
Decreasing population - low mirth rate - narrower base
increasing age profile as low mortality - wide apex Survival curve - percentage of people alive at different ages
life expectancy - age at which 50 % still alive
calculating life expectancy
Find age as a percentage of a maximum/find value when 50% still alive;
(Use to) calculate as a percentage of Max age energy - the ability to do work

needed for - metabolism - reactions within an organism (building molecules from monomers)
movement - muscle contraction (sliding filaments)
active transport (changes the shape of the carrier molecule)
maintenance, repair and division
production of substances (secretion - formation of lysosomes)
maintenance of body temperature
activation of molecules (phosphate added to glucose in glycolysis - lowers activation energy) Adenosine triphosphate
the bonds between phosphate groups - low activation energy - easily broken down Hydrolysis of ATP ATP + H20 ADP + P + energy i Synthesis of ATP condensation reaction Done in three ways

Photophosphorylation - occurs in plant cells
Oxidative phosphorylation - electron transport chain in mitochondria
energy is provided which combines and ADP and an inorganic phophate to produce ATP
Substrate level phosphorylation - Phosphate from donor molecule to an ADP - e.g formation of pyruvate Roles of ATP Immediate energy source cannot be stored for a long period of time

Suited to its purpose
Energy released in smaller, more manageable quantities (than glucose)
Hydrolysis ATP to ADP is a single step reaction - releases immediate energy overview structure of the leaf -
large surface area;
arrangement of leaves avoids overlapping;
thin (short diffusion distance);
transparent cuticle and upper epidermis (to allow passage of light); long, narrow chloroplasts full of chloroplasts);
many stomata (for gas exchange);
stomata that open and close as with changing light intensity;
air spaces to allow for diffusion;
xylem and phloem vessels C H O + 6CO 6H 0 + 6O 6 6 2 2 2 12 Structure and role of chloroplasts The grana - stacks of thylakoids - place where light dependent stage of photosynthesis - contains chlorophyll in the membrane. Intergranal lamellae join grana
The stroma - fluid filled matrix - light independent stage occurs - Light - dependent reaction oxidation - loss of electrons/ hydrogen OR gain of oxygen
Reduction - gain of electrons/hydrogen OR loss of oxygen chlorophyll in thylakoid membrane absorbs light - this excites an electron which leaves the chlorophyll (so it is oxidised) and passes down the electron transfer chain- taken up by an electron carrier (so it is reduced)

photolysis - light causes the splitting of water

2H O 4H + 4e + O 2 + - 2 the electrons produced are taken up by the chlorophyll to replace those that were lost electrons move down the electron carriers in a series of Redox reactions - losing energy - provides energy to transport protons into the thylakoid compartment
The electron then combines with (in the stroma) a proton and NADP to form reduced NADP The protons that were moved into the thylakoid then move back into the stroma through ATP synthase - losing energy - provides energy for ADP and a P to combine to form ATP i The oxygen bi-product is either used for respiration or diffuses out of the leaf -Thylakoids provide a large surface area for this process to take place
-proteins hold chlorophyll in position to maximise light absorption
- enzymes on the surface of the grana
- chloroplasts contain DNA and ribosomes for quick synthesis of proteins the light-independent reaction (the Calvin cycle) -CO2 diffuses from the atmosphere into the leaf through the stomata into stroma of chloroplast
- It then combines with ribulose bisphosphate (5 carbons)
- the 6C chain then breaks down into 2 Glycerate 3- phosphate molecules (3C)
- ATP and reduced NADP are then used to reduce this to triose phosphate (3C)
-NADP moves back towards the sight of the light dependent reaction
-1/6 of the triose phosphate are used for useful organic substances such as glucose
- The rest are used to regenerate ribulose bisphosphate using the ATP http://www.biologymad.com/master.html?http://www.biologymad.com/a2biology.htm -carbon dioxide fixation catalysed by the enzyme rubisco the site of the light independent reaction is adapted to its function as the stroma contains all the required enzymes; the stroma surrounds the grana so the products of the light dependent reaction have only a short diffusion pathway; the chloroplast contains DNA and ribosomes so that it can manufacture proteins easily Factors affecting photosynthesis limiting factor - a variable which limits the rate of a chemical reaction as the limiting factor increases , the rate of reaction increases until it is no longer the limiting factor - the rate therefore depends on another variable
the rate is directly proportional to the factor when it is limiting
The law of limiting factors - at any given moment, the rate of a physiological process is limited by the factor that is at its least favourable value rate is affected by light intensity, CO2 concentration (more enzyme substrate complexes with rubisco), temperature(enzyme activity)- measured by volume of O2 given out or CO2 taken up. compensation point - O2 given out = CO2 taken in it is the limiting factor there is a different limiting factor Glycolysis - cytoplasm activation of glucose by phosphorylation - Phosphate comes from hydrolysis of ATP - lowers the activation energy of the reaction 2 ATP
2ADP Splitting of phosphorylated glucose - produces two triose phosphates Oxidation of triose phosphate - a hydrogen is removed and and accepted by NAD forming reduced NAD (NADH ) 2 Triose phosphate is converted to pyruvate - produces 2 molecules ATP NAD



2 Pyruvate 2 The Link reaction The pyruvate is actively transported into the matrix of the mitochondrion 2 X Pyruvate is oxidised -loss of H - produces NADH i 2 Carbon dioxide is formed 2 carbon acetyl group formed -
combines with coenzyme A Acetylcoenzyme A NAD
NADH 2 CO 2 overall yield 2 NADH 2 2 CO 2 2 Acetylcoenzyme A Krebs cycle 4C 6C 5C CO 2 CO ATP

NAD substrate
level phosphorylation NAD, FAD, NADP are all coenzymes - so with dehydrogenase remove a hydrogen from molecules Yield from Krebs 4 CO 6 NADH


2 ATP 2X 2 2 2 2 2 2 2 2 YIELD from Glycolysis, link and Krebs 6 CO



4 ATP 2 2 2 Significance of the Krebs cycle Breaks down macromolecules into smaller ones

Produces Hydrogen atoms for use in the electron transport chain

Regenerates the the 4C molecule

It is a source of intermediate compounds - used to manufacture other substances - i.e fatty acids and chlorophyll Methylene blue accepts hydrogen like a coenzyme

shows when the coenzymes are being reduced as when it accepts a hydrogen it turns colourless The electron transport chain occurs on the inner membrane of the mitochondria (on the cristae)

NADH and FADH donate a proton to the matrix and an electron to the electron transport chain
The electrons move down the electron transport chain (along the carriers) in a series of Redox reactions - They lose energy - this moves the protons into the intermembrane space
the protons then move back down the chemical gradient back into the matrix - providing energy for ATP synthase to combine and ADP and an inorganic phosphate to form ATP (oxidative phosphorylation)
Oxygen is the terminal acceptor of electrons and protons forming water Yield of the electron transport chain 34 ATP - Each NADH produces 3 ATP
FADH produces 2 ATP

6 H2O Cyanide prevents the enzyme which combines Oxygen, electrons and the protons
protons build up in the electron transport chain- so it stops

sequencing the chain - if the enzyme specific to a carrier is inhibited then the carrier cannot be reduced so remains oxidised Anaerobic respiration NAD has to be regenerated to allow glycolysis to continue Yeast and some plant tissues Ethanol and CO Animals

Lactate glycolysis 2 ADP + 2 P

NADH transported to liver where it is converted to glycogen Less ATP is produced per glucose molecule Food chains and food webs producers - photosynthetic organisms
consumers - feed on other organisms (primary, secondary , tertiary)
Decomposers - break down larger molecules
Detritivores - worms -eat and secrete
Saprobiotic microorganisms - extracellularly digest food chains - shows feeding relationships in an ecosystem - arrows show energy flow
each stage - a trophic level

Food webs - combination of many food chains Energy transfer between trophic levels Energy is lost at each trophic level

sun to plant - energy is reflected by upper atmosphere; plant can only use some wavelengths; light may not fall on chlorophyll; there may be another limiting factor 2 2 2 i Net production = gross production - respiratory losses to the next consumer - not all of the organism is eaten; some parts cannot be digested so are egested; energy is lost through respiration (heat, movement) With large energy losses only a few trophic levels can be sustained percentage efficiency = Energy available after the transfer X 100 Energy available before the transfer units for energy - kj m year -2 -1 ecological pyramids Agricultural ecosystem Chemical and biological control of agricultural pests Intensive rearing of domestic livestock bars showing trophic level
consumers being higher up

length proportional to numbers present

limitations- no account taken of size - 1 oak - many aphids biomass
dry all above ground material in an oven just below 100 degrees Celsius
organisms must be killed
only shows organisms present at single time energy
difficult and complex tries to ensure maximum transfer of energy productivity - rate at which something is produced
the rate at which plants assimilate chemical energy - gross productivity
same units as energy (slide on energy transfer)

net productivity = gross productivity - respiratory losses tries to reduce competition- pesticides Natural ecosystem
only solar energy
low productivity
greater species and genetic diversity
nutrients recycled

population controlled by competition and climate
it has reached climax community Agricultural ecosystem
energy from sun, labour, fossil fuels
high productivity
low species and genetic diversity
natural recycling is supplemented by fertilisers
populations controlled by pesticides

climax community is prevented Pesticides - chemicals that kill pests (herb-, insect-, fung-)
have to
- be specific - doesn't harm humans or other useful organisms in an ecosystem
- be biodegrade yet chemically stable- long shelf life but eventually becomes harmless
- be cost effective - before resistance develops
- not bioaccumulate biological control- introducing a predator biological
- specific
- pest doesn't develop resistance
- only applied once as it reproduces
- takes longer to be effective
- can become a pest itself - eat alternative food sources must not eradicate as the controller will die without food source and pest returns chemical
- can affect other species - by bioaccumulation, disrupting food chains, directly affecting other non pests
- pests can develop resistance
- has to be reapplied at intervals
- fast acting integrated pest control system
choosing plant/animal varieties suited to the conditions/pests
managing the environments to provide habitats for natural predators of the pests
regular monitoring of crops - early action
hand picking pests off crops
biological agents
pesticide as last resort controlling pests reduces competition from weeds, yield being reduced by pests

as crops are monoculture (1 species) pests spread rapidly

demand for food Vs conservation and sustainability trying to minimise energy losses - so as to increase productivty

kept in confined spaces
- less energy lost to movement
- less energy lost to heat as surroundings warmer
- feeding controlled - maximum growth
- predation prevented also increased by selective breeding efficient varieties
use of hormones to increase growth rate ethics
greater chance of disease transmission
animal welfare is compromised
antibiotic resistance develops
loss of genetic diversity carbon cycle CO2 in the atmosphere Plants consumers decomposers
(saprobiotic bacteria secrete enzymes to extracellulary digest molecules into smaller soluble ones which it then uses to respire
Detritivores) Fossilisation incorporates CO2 into organic molecules photosynthesis respiration death combustion consumption dissolved in oceans CO2 reservoirs- carbonates (react with acid rain) , ice bergs melt, deforestation Global warming greenhouse gases allow short wavelength waves to pass through
absorbed by earth
re-emitted as long wave radiation which is reflected back off the greenhouse gases
earth warms greenhouse gases are CO2 , methane rapidly rising temperature - no chance to adapt
- failure of crops, rising sea levels (thermal expansion and melting ice caps)
- life cycle of insects affected
- disease spreads towards poles
- new areas to harvest
- change precipitation
- extreme events Nitrogen cycle Nitrogen in the atmosphere Ammonium ions Nitrite ions Nitrate ions nitrogen fixation free living bacteria bacteria in root nodules of leguminous plants Nitrification Nitrosomonas Nitobacter Cyanobacteria Azotaobacter
Rhizobium N in plants N in animals urea Ammonia containing molecules which saprobiotic microorganisms feed on releasing ammonia death ammonification absorption
assimilation Denitrifying bacteria in waterlogged soil
(anaerobic) Atmospheric N fixation (lightning) Use of fertilisers Crops are removed - taking away mineral ions from the soil - these have to be replaced - not returned by the death of the organism

natural - dead/ decaying plant material, animal manure
artificial - mined and blended NPK
Nitrogen needed for proteins - growth

not enough fertiliser - minerals limit growth
too much fertiliser the yield decreases Environmental consequences of using fertilisers Nitrogen rich soils favour some species - reduced species diversity

Leaching - nutrients dissolve in the rain - flow into watercourses - can harm humans if in the drinking water

Eutrophication -
as leaching occurs - nitrates no longer limiting growth - algal bloom
light can no longer penetrate deeper depths - plants at bottom cannot photosynthesise - die
algae dies - rapid growth of saprobiotic bacteria
these respire aerobically- reducing oxygen concentration in the water
aerobic organism in the water such as fish die
Anaerobic organism numbers increase - release toxins - makes water putrid Succession the changes over time of the species that occupy an area

Inititially a pioneer species colonises an inhospitable environment (exposed by glacier retreat; area around a volcano after an eruption; lakes created by land subsidence; silt deposited by estuaries)
Adaptations of pioneer species - large amount of spores; rapid germination of spores; can photosynthesise; can fix nitrogen; tolerant to extreme conditions

Pioneer species fix nitrogen which is returned to the soil when they decompose + rock is weathered producing soil - soil is less hostile
Abiotic conditions change over time
soil becomes thicker
later species better adapted so out compete previous species
as more plant species present- more habitats - more animal species present - biodiversity increases - food webs more complex - increased biomass
this continues until a climax community is reached.

if climax community damaged (e.g deforestation) it returns to the climax community quicker)
if factors altered (climate change) a different climax community shall be reached. conservation of habitats managing of the earth's resources with the hope to maximise their usage in the future - maintaining the ecosystem and hence biodiversity
reasons are ethical; economic; cultural and aesthetic

managing succession - prevent loss of species as they are outcompeted - succession prevented by either mowing , grazing , burning Studying inheritance Genotype - the genetic constitution of an organism - the alleles that it contains
Phenotype- observable characteristics
mutation is inherited if it occurs in the formation of the gametes
Modification - change in phenotype without a change in the genotype Gene - section of DNA - determines a single characteristic - codes for polypeptides - enzymes
locus - position of a gene on a chromosome
Allele - variation of a gene Sexually reproducing organisms - homologous chromosomes - 2 alleles for each gene
if they are the same - homozygous
different - heterozygous

dominant allele is always expressed if it is present in the genotype
recessive allele - only expressed if homozygous
If both alleles are expressed when heterozygous - so-dominant
When more than 2 alleles for a gene - multiple alleles Monohybrid inheritance Use a single letter for each characteristic
often the first letter of the characteristic
needs distinguishable higher and lower case forms
Higher case is dominant allele
show parent genotypes and phenotypes
State the gametes and circle them
draw a punnett square and label gametes
state all the offspring genotypes and phenotypes Mother Father
blue (eyes) brown
bb Bb
b b B b mother father B b b b Bb Bb bb bb First filial (generation)
offspring Bb bb
Brown blue plants that keep giving rise to plants with the same phenotype - pure breeding - organisms homozygous Genotypes can be determined whether homozygous or heterozygous dominant by doing a test cross with an organism which is homozygous recessive - if any offspring homozygous recessive then the genotype is heterozygous Sex inheritance and sex linkage Co-dominance and multiple alleles Allelic frequencies and population genetics Selection Speciation Two sex chromosomes are X and Y
XX - female XY- male
there is no allele for a gene on the Y as a section of DNA is missing.
The recessive allele is therefore more likely to be expressed - occurs more frequently in males
e.g haemophilia (blood doesn't clot) as most most die at an early age they never pass on their allele so a daughter is unlikely to be homozygous recessive Alleles are shown as X X H h Heterozygous parents are said to be carriers Pedigree charts
square = male circle = female
shading = allele expressed in phenotype dot = a carrier co-dominance - both alleles expressed when heterozygous. Different letters used for each allele - put as superscripts + upper case
Red and White colour flowers shown as

C C R W Blood groups

I and I are co-dominant
I is recessive
Only two alleles can be present in the genotype A B O Gene pool - all the alleles of all the genes of all the individuals in a population at any one time Number of times an allele occurs within a gene pool - allelic frequency - (between 0 and 1)
when considering 1 gene there is twice as many alleles as there are people Hardy- Weinberg is based on the following assumptions
No mutations arise; the population is isolated so there is no flow of alleles into or out of the population; there is no selections so alleles are equally likely to be passed on; the population is large; mating is random within the population frequency of dominant allele A = p
frequency of recessive allele a = q

p+q = 1 as there are no other alleles

possible combinations are AA , Aa , aa
so the sum of the frequencies of the phenotypes is one

p + 2pq + q = 1

p + 2pq = the frequency of the dominant phenotype 2 2 2 As more offspring produced than can be sustained there is competition
within the gene pool there is a variety of different alleles
Some alleles are better suited to the environment
they are more likely to attain available resources
better chance of successful breeding
alleles more likely to be passed on to the next generation
frequency of advantageous allele increases a the expense of the other What is advantageous depends on the environment - which changes if the environment changes - individuals on one side of the mean may be favoured - selection occurs towards one side - directional selection advantageous environmental conditions stable then the individuals close to the mean are favoured - extremities selected against - stabilising selection range becomes narrower over time mean shifts to the right over time the evolution of a new species from an existing species a species X can freely interbreed
(geographical) isolation separates 2 groups of species X
The two groups experience different selection pressures as the environment is different
they adapt to the new environment
Over enough time the alleles become so different that when they are reunited they can no longer interbreed - new species Ethics and fieldwork
the organism should be studied in situ
organisms remove should be returned to their original habitat
sufficient time should be left between studies
disturbance and damage to the habitat should be minimised

This prevents damage to the communtities present most energy enter the food chain through photosynthesis assumes allelic frequency remains constant down generations Snow lying longer/melts slower further north/at greater latitudes;
White geese better camouflaged (further north);
Predation linked to survival/reproductive success; Stabilising;
Few geese survive at the extremes/most survive from the middle
of the range; How starch in dead leaves is made available to plants
Extracellular digestion / releases enzymes;
Starch to monosaccharides /glucose/sugars/smaller molecules ;
Respire product of digestion;
Produce carbon dioxide from respiration; More disease/poor food supplies/poor sanitation/poor medicalcare;
High death rate among the young/in childhood / curve drops
steeply at first/in first 40; placing quadrats at random
Method of positioning quadrats,
E.g. Find direction and distance from specified point/
find coordinates on a grid / split area into squares;
Method of generating random numbers;
E.g. From calculator/telephone directory/numbers drawn from a
Ensure enough samples taken
Calculate running mean/description of running mean;
When enough quadrats, this shows little change/levels out (if
plotted as a graph);
Enough to carry out a statistical test;
A large number to make sure results are reliable;
Need to make sure work can be carried out in the time available; Role of reduced NAD in convertung pyruvic acid to ethanol
Requires hydrogen/electrons / is reduction;
Hydrogens from reduced NAD/reduced NAD reduces (pyruvic acid) / reduced NAD oxidised; more CO2 produced without oxygen
Respiring anaerobically;
(Anaerobic respiration/respiration with nitrogen) less
efficient/produces less ATP;
More anaerobic respiration/ more glucose/substrate must be
respired to produce same amount of ATP (so more carbon dioxide
produced); random sampling 1. Avoids bias;
2. Data representative/choice of nest not influencing results;
3. Allows use of statistical tests/named statistical test; How ATP is generated

1 Light (energy) excites/raises energy level of electrons in
2 Electrons pass down electron transfer chain;
3 (Electrons) reduce carriers/passage involves redox
4 Electron transfer chain / role of chain associated with
chloroplast membranes / in thylakoids / grana;
5 Energy released / carriers at decreasing energy levels;
6 ATP generated from ADP and phosphate/Pi /
phosphorylation of ATP; Efficiency changes through the ecosystem
1 Some light energy fails to strike/is reflected/not of
appropriate wavelength;
2 Efficiency of photosynthesis in plants is low/approximately
2% efficient;
3 Respiratory loss / excretion / faeces / not eaten;
4 Loss as heat;
5 Efficiency of transfer to consumers greater than transfer
producers/approximately 10%;
6 Efficiency lower in older animals/herbivores/ primary
consumers/warm blooded animals/homoiotherms;
7 Carnivores use more of their food than herbivores; how intensive farming affects productivity
1 Slaughtered when still growing/before maturity/while young
so more energy transferred to biomass/tissue/production;
2 Fed on concentrate /controlled diet /controlled
conditions/so higher proportion of (digested) food
absorbed/lower proportion lost in faeces / valid reason for
3 Movement restricted so less respiratory loss / less energy
4 Kept inside/heating/shelter / confined so less heat loss / no
5 Genetically selected for high productivity; Not always reliable as
Population changes;
As young birds leave nest/join population;

(Would be likely to) catch all birds (again) in second sample / sample sizes are the same;
Birds (in territories and) not mixing with population;
Only estimates number of birds in territories sampled / territory sample not representative (of population); What does Hardy Weinberg predicts
The frequency/proportion of alleles (of a particular gene);
Will stay constant from one generation to the next/over generations / no genetic change over time;
Providing no mutation/no selection/population large/population genetically isolated/mating at random/no migration; How the energy transfer in ingested food is affected by intensive farming
Increase because fed concentrates/food with high nutritive value/food with high digestibility/food with little waste/because less egested;

How it affects respiration
Decrease because movement restricted/heat loss reduced; Nitrate concentration increase over time as
Increase in) dead organisms/humus/decomposition;
Leading to (increase in) nitrification/ammonia to nitrate/activity of nitrifying bacteria;
Nitrogen fixation; Why managing succession is necessary
(Grassland consists of) small/annual plants;
Will be replaced by/outcompeted by woody plants;
So these (woody plants) must be removed/have growth checked/grazed; role inner membrane mitochondrion
Electrons transferred down electron transport chain;
Provide energy to take protons/H+ into space between membranes;
Protons/H+ pass back, through membrane/into matrix/through ATPase;
Energy used to combine ADP and phosphate/to produce ATP; role of oxygen
Terminal/final acceptor (in electron transport chain) / used to make water; if results are significant
There was a probability of less than 0.05/ 5 in a hundred/5%;
That the difference was due to chance; Drying at too high a temperature
Combustion/ would burn/cause loss of substances (other than water)/named substance/cause loss of dry mass;; energy in animals less than in plants
Seaweeds/plants are producers/lower/first trophic level / animals are consumers/higher trophic level/feed on seaweeds;
Loss of energy between trophic levels;
As a result of respiration/ as heat; The concentrations of carbon dioxide in the air at different heights above ground in a
forest changes over a period of 24 hours. Use your knowledge of photosynthesis to
describe these changes and explain why they occur.
1. High concentration of carbon dioxide linked with night/darkness;
2. No photosynthesis in dark/night / light required for photosynthesis/light-dependent reaction;
3. (In dark) plants (and other organisms) respire;
4. In light net uptake of carbon dioxide by plants/plants use more carbon dioxide than they produce/ rate of photosynthesis greater than rate of respiration;
5. Decrease in carbon dioxide concentration with height;
6. At ground level fewer leaves/less photosynthesising tissue/more animals/less light; How CO2 becomes triose phosphate
1. Carbon dioxide combines with ribulose bisphosphate/RuBP;
2. To produce two molecules of glycerate 3-phosphate/GP;
3. Reduced to triose phosphate/TP;
4. Requires reduced NADP;
5. Energy from ATP; 1. Microorganisms are saprobionts/saprophytes;
2. Secrete enzymes (onto dead tissue) / extracellular digestion;
3. Absorb products of digestion/smaller molecules/named relevant substance;
4. Respiration (by microorganisms) produces carbon dioxide;
5. Carbon dioxide taken into leaves;
6. Through stomata; Improved medical care / improved nutrition / improved sanitation/water treatment / lower infection rates / less disease; a recessive allele
Only expressed/shown (in the phenotype) when homozygous / two (alleles) are present / when no dominant allele / is not expressed when heterozygous;

Codominant alleles
Both alleles are expressed/shown (in the phenotype); learn how to interpret pedigree charts
e.g 3 and 4 / two Rhesus positives produce Rhesus negative child/children / 7 / 9;
Rhesus positives/3 and 4 carry recessive (allele)/ are heterozygous / if Rhesus positive was recessive, all children (of 3 and 4) would be Rhesus positive/recessive; Evidence (not a mark)
3 would not be/is Rhesus positive / would be Rhesus negative;
Explanation (not a mark)
3 would receive Rhesus negative (allele) on X (chromosome) from mother / 3 could not receive Rhesus positive (allele) from mother / 3 would not receive Rhesus positive (allele)/X (chromosome) from father/1 / 3 will receive Y (chromosome) from father/1;
Evidence (not a mark)
9 would be Rhesus positive / would not be/is Rhesus negative / 8 and 9/all daughters of 3 and 4 would be Rhesus positive;
Explanation (not a mark)
As 9 would receive X chromosome/dominant allele from father/3; effect of a woodlouse with potassium hydroxide
1. Oxygen taken up/used (by woodlouse);
2. Carbon dioxide (given out) is absorbed by solution/potassium hydroxide;
3. Decrease/change in pressure; DNP inhibits respiration by preventing a proton gradient being maintained across
membranes. When DNP was added to isolated mitochondria the following changes
were observed
less ATP was produced
more heat was produced
the uptake of oxygen remained constant.
Explain how DNP caused these changes.

1. Less/no proton/H+ movement so less/no ATP produced;
2. Heat released from electron transport/redox reactions /
/ energy not used to produce ATP is released as heat;
3. Oxygen used as final electron acceptor/combines with electrons (and protons); why control type of food
1. May vary in protein/fat/carbohydrate/fibre/roughage/ vitamins/minerals;
2. May affect absorption / digestibility / energy value / tastiness / growth / overall food intake;

why control temperature
3. Will affect heat loss/gain/respiration/metabolism;
4. (Need) to maintain/regulate body temperature;
5. More food/energy can be used for growth; Not flooded aerobic conditions/more oxygen / with flooding anaerobic conditions/less oxygen;
Not flooded fewer/less active anaerobic microorganisms/respiration / not flooded more/more active aerobic microorganisms/respiration; How succession occurs
1. (Colonisation by) pioneer (species);
2. Change in environment / example of change caused by organisms present;
3. Enables other species to colonise/survive;
4. Change in diversity/biodiversity;
5. Stability increases / less hostile environment;
6. Climax community; Advantages and disadvantages of biological agents
1. Specific (to one pest);
2. Only needs one application/ reproduces;
3. Keeps/maintains low population;
4. Pests do not develop resistance;
5. Does not leave chemical in environment/on crop / no bioaccumulation;
6. Can be used in organic farming;
7. Does not get rid of pest completely;
8. May become a pest itself;
9. Slow acting/ lag phase/ takes time to reduce pest population; How does a lake separating lead to new species
1. Geographical isolation;
2. Separate gene pools / no interbreeding (between populations);
3. Variation due to mutation;
4. Different environmental/abiotic/biotic conditions / selection pressures;
5. Selection for different/advantageous, features/characteristics/mutation/ /allele;
6. Differential reproductive success / (selected) organisms survive and reproduce;
7. Leads to change in allele frequency;
8. Occurs over a long period of time; 1. Energy released in small/suitable amounts;
2. Soluble;
3. Involves a single/simple reaction; Why do organisms synthesise so much ATP
1. ATP is unstable;
2. ATP cannot be stored / is an immediate source of energy;
3. Named process uses ATP ;
4. ATP only releases a small amount of energy at a time; Consequence of leaching
1. Increase algae/algal bloom;
2. Light blocked out;
3. Plants can’t photosynthesise / plants and/or algae die;
4. Bacteria/saprobionts/EW feed off/breakdown dead organisms;
5. Bacteria/saprobionts/EW use up oxygen/bacteria respire/BOD rises; Benefit of natural fertiliser
1. Acts as soil conditioner/improves drainage/ aerates soil/increases organic content of soil;
2. Contains other elements/named element/wider range of elements;
3. Production of artificial fertiliser energy-consuming;
4. Less leaching / slow release (of nutrient); birth rate is
Births per thousand/given number of the population and per year/given period of time; why women have longer life expectancy than men. Why UK has higher life expectancy than Sudan
1. Females tend to outlive males linked to reason e.g.
male risk of CVD
more males smoke/drink to excess
males involved in fighting / war;
2. Medical care/vaccination programmes better in UK/infectious disease common in Sudan;
3. More food/better diet in UK;
4. Food preservation/sanitation/clean water supply better in UK; Parental phenotypes
Chocolate male Black female
1. Parental genotypes
bbi Bbi;
2. Parental gametes
b bi B bi;
3. Offspring genotypes
Bb, Bbi bbi bibi;
Offspring phenotypes
Black Chocolate cinnamon role of bacteria
1. Saprobionts/saprophytes;
2. Digest/break down proteins/DNA/nitrogen-containing substances;
3. Extracellular digestion/release of enzymes;
4. Ammonia/ammonium produced;
5. Ammonia converted to nitrite to nitrate/ammonia to nitrate;
6. Nitrifying (bacteria)/ nitrification;
7. Oxidation; effect of clearing and burning
1. Carbon dioxide concentration increases;
2. No/Less vegetation so no/less photosynthesis / photosynthetic organisms;
3. No/Less carbon dioxide removed (from the atmosphere);
4. Burning/combustion releases / produces carbon dioxide; CO2 to other organic substances
1. Carbon dioxide combines with ribulose bisphosphate/RuBP;
2. Produces two molecules of glycerate (3-)phosphate/GP;
3. Reduced to triose phosphate/TP;
4. Using reduced NADP;
5. Using energy from ATP;
6. Triose phosphate converted to other organic substances/ named organic substances/ribulose bisphosphate;
7. In light independent reaction/Calvin cycle; 1. Capture sample, mark and release;
2. Appropriate method of marking suggested / method of marking does not harm fish;
3. Take second sample and count marked organisms;
4. No in No in
Population = sample1 × sample2
Number marked in sample2; 1. Transect/lay line/tape measure (from one side of the dune to the other);
2. Place quadrats at regular intervals along the line;
3. Count plants/percentage cover/abundance scale (in quadrats)
Count plants and record where they touch line/transect; pioneer species
1. Stabilises sand / stops sand shifting;
2. Forms/improves soil / makes conditions less hostile; 1. Variation in original colonisers / mutations took place;
2. Some better (adapted for) survival (in mountains);
3. Greater reproductive success;
4. Allele frequencies change; fish die from lack of oxygen 1. Same breed so similar alleles;
2. Controls/removes variable/so genes not a factor / only temperature affects results / rate of growth affected by genes; Why is ATP used
1. Releases energy in small / manageable amounts;
2. (Broken down) in a one step / single bond broken;
3. Immediate energy compound/makes energy available rapidly;
4. Phosphorylates/adds phosphate;
5. Makes (phosphorylated substances) more reactive / lowers activation energy;
6. Reformed/made again; How is ATP produced in mitochondrion
1. Substrate level phosphorylation / ATP produced in Krebs cycle;
2. Krebs cycle/link reaction produces reduced coenzyme/reduced NAD/reduced FAD;
3. Electrons released from reduced /coenzymes/ NAD/FAD;
4. (Electrons) pass along carriers/through electron transport chain/through series of redox reactions;
5. Energy released;
6. ADP/ADP + Pi;
7. Protons move into intermembrane space;
8. ATP synthase; Why do plants need to respire if ATP is produced during photosynthesis
1. In the dark no ATP production in photosynthesis;
2. Some tissues unable to photosynthesise/produce ATP;
3. ATP cannot be moved from cell to cell/stored;
4. Plant uses more ATP than produced in photosynthesis;
5. ATP for active transport;
6. ATP for synthesis (of named substance); Why do species change
1. Species/plants/animals change the environment/conditions/add humus/nutrients etc.;
2. Less hostile (habitat);
3. Species/plants better competitors; dominant allele
Is always expressed/shown (in the phenotype); Without reduced NADP and ATP
1. (Less) GP converted to TP;
2. (Less) TP converted to RuBP; How do farming practices affect productivity
1. Fertilisers/minerals/named ion (added to soil);
2. Role of named nutrient or element e.g. nitrate/nitrogen for proteins / phosphate/phosphorus for ATP/DNA;
3. Pesticides/biological control prevents damage/consumption of crop;
4. Pesticides/weed killers /herbicides/weeding remove competition;
5. Selective breeding / genetic modification (of crops);
6. Glass/greenhouses enhance temp/CO2/ light;
7. Ploughing aerates soil/improves drainage;
8. Ploughing/aeration allows nitrification/decreases denitrification;
9. Benefit of crop rotation in terms of soil nutrients/fertility/pest reduction;
10. Irrigation/watering to remove limiting factor;
11. Protection of crops from birds/pests/frost by covers/netting etc.; How microorganisms produce nitrates
1. Protein/amino acids/DNA into ammonium compounds / ammonia;
2. By saprobionts;
3. Ammonium/ammonia into nitrite;
4. Nitrite into nitrate;
5. By nitrifying bacteria/microorganisms;
6. Nitrogen to ammonia/ammonium;
7. By nitrogen-fixing bacteria/microorganisms in soil; how does resistance develop form pesticides
1. Variation/variety in pest population;
2. Due to mutation;
3. Allele for resistance;
4. Reference to selection;
5. Pests with resistance (survive and) breed / differential reproductive success;
6. Increase in frequency of allele;
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