A2 Biology Unit 4 Model Answers Flashcards
(99 cards)
1
Q
Effect of low temperature
A
enzymes work slowly due to having less kinetic energy therefore less movement and less successful collisions between active site and substrate leading to decreased formation of ES complexes
2
Q
Effect of high temperature
A
enzymes are denatured - hydrogen bonds break, tertiary structure unfolds, active site changes shape and less ES complexes form.
3
Q
Effects of increased light in an ecosystem
A
rate of photosynthesis increases as light intensity increases; plants grow faster and produce more spores/seeds; animal population that feeds on producers can grow larger.
4
Q
Effects of pH
A
enzymes working in extremes of pH above and below the optimum can denature and tertiary structure unfolds leading to less ES complexes forming.
5
Q
Effects of humidity
A
affects transpiration rate in plants and rate of evaporation in animals.
6
Q
Why is it important that samples are collected at random? (1)
A
To avoid bias
7
Q
Random sampling
A
Produce a grid and select co-ordinates using a random number generator.
Place a quadrat at the intersection of each pair of co-ordinates and record the species within it.
Record a mean and the scale up to the entire area.
8
Q
How do you decide the number of quadrats to use in order to collect representative data? (4)
A
- large number of quadrats so results are more reliable (with repeats)
- enough to be able to carry out a statistical test (e.g. SR requires minimum of 7 pairs)
- not too many for the available time
- calculate a running mean which changes little when there are enough quadrats
9
Q
What are the advantages of collecting plant data as percentage cover? (2)
A
Can be collected rapidly (1); no need to define individual plants (1)
10
Q
What are the limitations of collecting plant data as percentage cover?
A
There may be “overhang” where the leaves of larger plants are outside of the quadrat area
Smaller plants may be difficult to count where overshadowed by larger plants.
11
Q
Mark-release-recapture estimate of population size
A
• Capture large sample of organisms
• Mark with non toxic paint/ not too obvious to predators/won’t wash off
• Count and release
• Allow time to disperse throughout population (eg a week)
• Recapture large sample
• Count total and how many are marked
Population equation
12
Q
Mark-Release-Recapture Population
A
N1 x N2/NM
13
Q
N1 x N2/NM
A
N1 = total 1st time N2 = total 2nd time NM = marked and recaptured
14
Q
Assumptions of mark-release-recapture techniques
A
- proportion of marked to unmarked in the second samples if equal to the proportion of marked to unmarked in the whole population
- marked individuals from first sample distribute themselves evenly with enough time to do so
- population has a boundary so no emigration/immigration
- few deaths and births
- method of marking does not make it more liable to predation
- mark is not lost during the investigation
15
Q
Pattern of population growth curves
A
- period of slow growth as small numbers reproduce slowly (lag phase)
- period of rapid growth (exponential or log phase) – population doubles per unit of time
- period where population growth remains stable with cyclic fluctuations
16
Q
Effect of predator-prey relationship on population size (6)
A
Predators eat prey and reduce the prey population (1); predators now in greater competition for food (1); predator population is reduced as some individuals cannot compete (1); fewer prey are eaten (1); prey population increases (1); more prey for food so predator population increases (1).
Remember that a predator-prey graph is often cyclical and that there is a time-lag between the pattern showed by the prey and that of the predator.
17
Q
Factors affecting birth rates
A
Economic conditions; cultural backgrounds; social conditions; birth control; political factors.
18
Q
Factors affecting death rates
A
Age profile; life expectancy at birth; food supply; effective sanitation; medical care; natural disasters; war.
19
Q
Stable population pyramid
A
birth rate and death rate in balance; no increase or decrease in population size
20
Q
Increasing population pyramid
A
high birth rate; gives a wider base to the pyramid; fewer older people; so narrower apex
21
Q
Decreasing population pyramid
A
lower birth rate; so narrower base; more older people; wider apex
22
Q
Information required to calculate growth of a population (2)
A
Births and deaths (1); numbers of emigrants and immigrants (1)
23
Q
Why organisms need energy (1)
A
Metabolism; movement (energy for muscle contraction); active transport (to change shape of carrier proteins); cell division; production of enzymes and hormones (energy needed to form lysosomes for secretion); maintenance of internal body temperatures.
24
Q
Flow of energy through an ecosystem (3)
A
Light energy converted to chemical energy during photosynthesis (1); organic molecules converted to ATP during respiration (1); ATP used by cells to perform useful work (1)
25
Roles of ATP (2
Energy released in smaller more manageable quantities (1); hydrolysis of ATP to ADP is a single-step reaction so releases immediate energy (1)
26
Adaptations of the leaf
Large surface area to absorb light (1); arrangement of leaves that avoids shadowing (1); thin so short diffusion pathway (1); transparent cuticle and epidermis to allow light through to mesophyll (1); lots of chloroplasts in upper mesophyll cells (1); numerous stomata for gas exchange (1); air spaces in lower mesophyll for rapid diffusion (1); network of xylem and phloem (1)
27
How NADP is reduced (2)
NADP accepts a hydrogen ion and electron (1) from photolysis/breakdown of water using light energy (1)
28
Describe how the light-dependent reactions produce ATP and reduced NADP
• chlorophyll absorbs light energy
• Electrons in chlorophyll are excited/energised by light energy/photons
• This increases the energy levels in the electrons
• Electrons move to an electron acceptor
• Electrons lose energy as they are passed from one electron carrier to the next along the electron transfer/transport chain (ETC)
• As electrons are passed along the ETC, ATP is formed from ADP+Pi using energy from electrons (PHOTOPHOSPHORYLATION)
• NADPH is formed when the electrons from the electron transfer chain and H+ from photolysis combine with NADP
• NADP+H+ + e- →NADPH
• The H+ and electron come from photolysis( to reduce NADP to NADPH)
• O2 is given off and the electrons (e-) replace those lost from chlorophyll
• Photolysis – the break down of water using light energy
H2O →2H+ + ½O2 +2e-
29
Adaptations of the chloroplast to the light-dependent reaction (4)
Thylakoid membrane provide a large surface area for the attachment of chlorophyll, enzymes and electron carriers (1); network of proteins hold chlorophyll in a position to absorb maximum amount of light (1); granal membranes have enzymes that help make ATP (1); chloroplasts have their own DNA and ribosomes to make proteins quickly (1).
30
Light-independent reaction
* Carbon dioxide joins with ribulose bisphosphate (RuBP) a 5 carbon compound. (This gives a unstable 6 carbon compound.)
* This quickly breaks down to 2 molecules of a 3 carbon compound glycerate 3-phosphate (GP)
* This reaction is catalysed by the enzyme ribulose bisphosphate carboxylase (RUBISCO)
* ATP from the light dependent reaction is used to provide energy for the reduction of GP into TP (Triose Phosphate)
* The reduction reaction needs H+/reducing power
* H+ are provided by reduced NADP (NADPH ) from the light dependent stage
* Two TP’s join to form hexose, whIch can combine to form starch and cellulose, 1 in every 6 TP molecules is used to make hexose
* TP regenerates RuBP and so the cycle continues, 5 in every 6 TP molecules form RuBP
* TP also forms amino acids, fatty acids, glycerol, DNA, RNA, glucose and starch
31
Describe how carbon in carbon dioxide becomes carbon in triose phosphate (5).
Carbon dioxide combines with RuBP (1); to make 2 x G3P (1); this is reduced to TP (1); which requires NADPH to provide the hydrogen for reduction (1); and energy from the breakdown of ATP (1)
32
Adaptations of the chloroplast to the light-independent reaction (3)
Fluid of stroma contains enzymes needed to carry out reduction of carbon dioxide (1); stroma fluid allows easy diffusion of products of light-dependent reaction into the stroma (1); contains DNA and ribosomes to make proteins quickly (1).
33
The true rate of photosynthesis is greater than simply the plant’s uptake of carbon dioxide, why? (1)
Some of the carbon dioxide produced in respiration is used in photosynthesis
34
How does an increase in carbon dioxide levels in the atmosphere affect yield of grain? (3)
Causes in increase in rate of photosynthesis (1); therefore increases the amount of glucose (1) made, which increases growth rate (due to an increased rate of respiration and there ATP production) and yield; increase in carbon dioxide levels usually causes in increase in climate temperature, which would cause faster reaction rate (1) hence higher yield
35
How does the concentration of carbon dioxide in a forest change over time? (5)
* low carbon dioxide during day
* as plants are photosynthesizing and taking in carbon dioxide
* plants respire all the time but do not photosynthesise at night so carbon dioxide concentrations increase at night
* carbon dioxide levels are increased at the forest floor
* because ground level has less photosynthesizing tissue, less light and more respiring animals
36
Concept of limiting factors
refer to the graph showing rate of photosynthesis (y axis) plotted against carbon dioxide or light (x axis).
Don’t forget that limiting factors also apply to ecology
37
Limiting factors in ecology
(competition for food etc) and respiration. Limiting factors can include: carbon dioxide, oxygen, light, nitrates, ions, water, food, glucose.
38
Glycolysis
* Glucose is activated (PHOSPHORYLATED) by the addition of inorganic phosphorus
* Produced by the breakdown of ATP into ADP + Pi
* Glucose splits into 2 molecules of triose phosphate
* NAD co-enzyme accepts hydrogen from triose phosphate
* And becomes reduced
* Inorganic phosphorus is removed from triose phosphate to make pyruvate
* 4 molecules of ATP are produced by substrate level phosphorylation to give a net gain of 2 ATP per glucose molecule
39
Link Cycle
* pyruvate is oxidised to the 2C compound acetyl coA
* CO2 is released
* NAD accepts hydrogen from pyruvate and so is reduced
40
Kreb's Cycle
* pyruvate is oxidised to the 2C compound acetyl coA
* CO2 is released
* NAD accepts hydrogen from pyruvate and so is reduced
* 2C acetyl coA combines with 4C compound
* 6C compound loses CO2
* 5C compound loses CO2
* one molecule of ATP is produced by substrate-level phosphorylation
* FAD and NAD accept hydrogen (AND ELECTRONS)
* And become reduced (FADH and NADH)
* 4C compound combines with another 2C compound and the cycle begins again
41
Decarboxylation in respiration
Pyruvate (a 3 carbon compound) loses a carbon atom with co- enzyme A, to produce a 2-carbon compound of Acetyl co-enzyme A.
• During this conversion decarboxylation occurs and CO2 is released
• Acetyl co-enzyme A then enters the Kreb’s cycle and combines with a 4- carbon compound to produce a 6-carbon compound.
• The 6-carbon compound is then converted to a 5-carbon compound, decarboxylation occurs
• This 5- carbon compound is then converted to a 4- carbon compound and decarboxylation occurs again releasing CO2. NAD and FAD are reduced to give NADH and FADH2.
42
Significance of Kreb's cycle
* breaks down macromolecules into smaller ones
* produces hydrogen atoms that are carried by NAD to the ETC for oxidative phosphorylation (and the subsequent production of ATP)
* regenerates the 4C compound, which would otherwise accumulate
* source of intermediate compounds used in the manufacture of other substances
43
Synthesis of ATP during the electron transport chain (oxidative phosphorylation)
Takes place on inner mitochondrial membrane/cristae
• Reduced NAD and FAD ARE OXIDISED
• Electrons passed from one carrier to another in an electron transport chain ETC
• As electrons pass down the chain, they lose energy, which is dissipated as heat
• Hydrogen ions are pumped into the inter-membrane space
• Hydrogen ions diffuse back into the matrix down an electrochemical gradient
• Via ATP synthase
• ATP is made from ADP and Pi
• Electrons at the end of the transport chain bind with H+ ion and are accepted by oxygen, the final acceptor, to make water.
44
How reactions occurring in the mitochondrion generate ATP (7) NB no credit for glycolysis, as this occurs in the cytoplasm
* pyruvate is actively transport into the matrix
* pyruvate is decarboxylated to produce acetyl coA and CO2
* NADH is also produced, as pyruvate loses hydrogen
* acetyl coA combines with 4C compound to produce 6C compound, which is then decarboxylated
* NADH is produced in the Kreb’s cycle
* One molecule of ATP is produced by substrate level phosphorlyation
* NADH carries hydrogen and electrons to the cristae
* Electrons are passed along a series of carrier proteins in the membrane
* Electrons lose energy, which is dissipated as heat
* Electron transport chain answer
45
Fermentation in yeast
* C6H12O6 ==> 2CH3CH2OH + CO2 (glucose -> ethanol and carbon dioxide)
* Anaerobic conditions
* Optimum temperature/pH
* Only glycolysis can take place
* glucose ==> pyruvate (NAD==>NADH)
* Pyruvate ==> Ethanol CO2 (NADH==>NAD)
* NAD recycled/regenerated
46
What happens to pyruvate in anaerobic conditions and why this type of respiration is advantageous to skeletal muscle (4)
* pyruvate takes up hydrogen ions from the reduced NAD
* to produce lactate and NAD
* this ensures that glucose can still be respired
* even in the absence of oxygen
47
Advantage of mitochondria having more cristae (2)
Larger surface area (1); to carry out oxidative phosphorylation producing more ATP (1)
48
Describe the part played by the inner membrane of a mitochondrion in producing ATP (4).
Cristae contain electron transport proteins that transfer electrons from the carriers NADH and FADH (1)
H+ ions from the carriers are pumped into the intermembrane space using energy lost by electrons (1)
H+ ions move back into the matrix along a concentration gradient by ATPase (1)
energy from the H+ ion gradient is used to combine ADP and Pi to make ATP (1)
49
Role of co-enzymes and carrier proteins in synthesis of ATP (5)
NAD accepts hydrogen during glycolysis, link reaction and Kreb’s cycle (1)
NAD is reduced (1)
NADH releases hydrogen ions during the electron transport chain, which are pumped across the mitochondrial membrane (1)
electrons released from the co-enzymes are passed along a series of carrier proteins in the membrane (1)
energy lost from the electrons is used to make ATP from ADP + Pi (1)
50
Explain how carbon dioxide is produced during aerobic respiration (4)
One CO2 is released during the link reaction (1) when pyruvate 3C is converted to acetyl coA 2C (1)
2 molecules of CO2 are released during the Kreb’s cycle (1) when the 6C compound is decarboxylated to regenerate the 4C compound (1)
51
Why does a reduction in temperature decrease the amount of carbon dioxide produced in respiration? (4)
Enzymes catalyse respiration reactions (1)
rate of reaction decreases as particles have less kinetic energy (1)
so fewer collisions between enzyme active site and substrate (1)
so fewer ES complexes form (1)
52
Explain why an increase in temperature leads to a decrease in the rate of respiration (4)
Respiration is catalysed by enzymes, which are proteins (1)
hydrogen bonds in the tertiary structure break (1)
active site is denatured (1)
substrate can no longer bind the active site (1)
so fewer ES complexes form (1)
53
Why does anaerobic respiration produce more carbon dioxide then aerobic respiration?
Anaerobic respiration produces less ATP (1)
| so more glucose is respired to generate same amount of ATP (1)
54
Why most of Sun’s energy is not converted to organic matter (4)
Not all wavelengths can be absorbed (1)
light may not fall on a chlorophyll molecule (1)
other factors may limit the rate (1)
most light is reflected back by clouds (1)
55
Why a low percentage of energy is transferred along the food chain (4)
Some of the organism is not eaten (1)
some parts are not digested (faeces) (1)
some energy is lost in excretory material e.g. urine (1)
energy lost as heat from the organism (1)
energy lost in respiration (1)
56
Impact of inefficiency of energy transfer (3)
Most food chains only have 4-5 trophic levels because insufficient energy is available to support a large breeding population at the top level (1)
biomass is less at higher trophic levels (1)
total amount of energy stored in each level is less at higher trophic levels (1).
57
Limitations of using pyramids of numbers (2)
No account is taken of size of the organism (1)
| number of individuals may be so great as to not be able to represent them accurately (1)
58
Why are animals that are more active less likely to survive in winter? (2)
Activity increases rate of respiration (1)
| which uses glucose and depletes food reserves (1)
59
Describe how and explain why the efficiency of energy transfer is different at different stages in the transfer (6).
* some light is reflected off the plant or is the wrong wavelength to be absorbed by chlorophyll
* efficiency of photosynthesis is low (less than 2%)
* energy lost during respiration / excretion or some parts of the plant / animal are not eaten
* heat loss
* efficiency of transfer increases with increasing trophic level (along the food chain) so efficiency of consumers is greater than efficiency of producers
* efficiency is lower in: older animals, primary consumers, warm blooded animals (endotherms)
* carnivores use more their food than herbivores
60
The factors that affect net productivity (2)
The efficiency of the crop (1)
| the area of ground covered by the leaves of the crop (1)
61
Comparison of natural and agricultural ecosystems
Natural – lower productivity; higher species diversity; more genetic diversity within a species
nutrients recycled naturally
populations controlled by competition or climate
solar energy only
reaches a natural climax community
Artificial – higher productivity
lower species diversity
less genetic diversity within a species
nutrient cycling supplemented by use of fertilizers
populations controlled by pesticides an cultivation
energy from food and fossil fuels as well as solar
prevented from reaching a natural climax community.
62
Effective pesticides should be… (4)
Specific (1)
biodegradable (1)
cost-effective (1)
will not accumulate in the food chain (1)
63
Why intensive rearing increases energy conversion rate
Movement is restricted therefore less energy used in muscle contraction
Warm environment to reduce heat loss from the body
No wastage as animals fed only the optimum amount
Predators are excluded
64
non-intensive ways of increasing the energy conversion rate
Selectively breeding animals more efficient at converting food into body mass
Using hormones to increase growth rates
65
How does intensive rearing of domestic livestock increase net productivity?
slaughtered when young so more energy transferred to biomass
fed on a controlled diet so higher proportion of nutrients are absorbed
genetically selected for high productivity
66
What are nutrient cycles?
nutrients taken up by producers as simple, inorganic molecules
producer incorporates nutrients into complex organic molecules
when producer is eaten nutrient is passed into consumers
nutrients pass along the food chain
when producers and consumers die their complex molecules are broken down by saprobiotic microorganisms that release the nutrient in its original simple form
67
Reasons for CO2 increase globally
Combustion of fossil fuels release carbon dioxide
| Large-scale deforestation has caused there to be fewer plants to take in CO2 during photosynthesis
68
Carbon Cycle
* Plant takes in carbon dioxide
* This is used for photosynthesis
* sugars/starch (carbon compounds) synthesised
* Carbon compounds then passed along food chain when primary consumer eats producer, secondary consumer eats primary consumer etc
* Organism dies
* Decomposers, use extra-cellular enzymes to digest and break down organism and use their carbon compounds in respiration
* All the living organisms (plants, animals, and the decomposers) give off CO2 from respiration and CO2 is returned into the atmosphere this way
* Plants take in CO2 again for photosynthesis
* Burning trees and fossil fuels releases CO2 also.
* Burning coal also releases sulphur dioxide (SO2)
69
How do microorganisms make carbon available to plants?
* These organisms are saprobiotic
* Release (secrete) enzymes
* Hydrolyse starch to glucose; products are ABSORBED by the microorganisms
* Respire
* Release carbon dioxide, which is taken into leaves by stomata
70
Consequences of global warming
-Melting of ice caps could cause extinction of some species
-Rise in sea level could flood low-lying land
higher temperatures
-Less rainfall could lead to the failure of crops
-Intense storms would be prevalent in some areas leading to changes in wildlife distribution
-Life-cycles and populations of insect pests would alter and increase spread of tropical diseases towards the poles
71
Nitrogen Cycle
* Plants take up nitrate ions (NO3-) from the soil
* The nitrates then form amino acids which are used to synthesise PROTEINS, WHICH ARE ORGANIC N-CONTAINING COMPOUNDS IN PLANTS AND ANIMALS
* The plants are eaten by animals and the proteins are digested
* Both plants and animals die, leaving a collection of dead materials (detritus) which contain nitrogen containing compounds
* Decomposers decay the excretory products and detritus, releasing ammonia (NH3) and ammonium ions (NH4+) into the soil
* Nitrifying bacteria oxidise the ammonia into nitrites (NO2-)
* Then the nitrites are oxidised into nitrates (NO3-) which are taken up by the plants
* Lightning and nitrogen-fixing bacteria in the soil and in nodules on the roots of legumes ‘fix’ nitrogen gas (N2) into ammonia (NH3)
* Denitrifying bacteria reduce nitrate to nitrogen, in anaerobic soil conditions that escapes from the soil AND RETURNS TO THE ATMOSPHERE
72
Eutrophication (3-6)
Leaching of fertilizers causes algae to grow exponentially at the surface of the water.
This absorbs light and prevents it penetrating to lower depths.
Light is limiting factor for plant growth at lower depths and so aquatic plants die. Saprobiotic bacteria feed on dead plant matter and use up oxygen for respiration.
Oxygen becomes limiting factor for aerobic organisms e.g. fish and so they die.
73
Nitrogen Fixation
Mutualistic bacteria in the root nodules of leguminous plants fix nitrogen to ammonium.
The plant uses this to create amino acids, proteins, DNA etc
74
Nitrogen Organic Compounds are:
```
DNA/RNA
ATP
Proteins
Amino acids
Urea/Uric acid
```
75
Nitrogen inorganic Compounds are:
nitrates
nitrites
ammonium
76
Why does denitrification not happen in sandy soils?
Sandy soils contain lots of oxygen
| Denitrifying bacteria are anaerobic (use nitrates for respiration)
77
Features of pioneer species for successful colonization
```
Produce lots of wind-dispersed seeds/spores
Rapid germination
Ability to photosynthesise
Ability to fix nitrogen
Tolerance to extreme conditions
```
78
Sequences involved in succession
•Pioneer species with appropriate adaptations colonise bare land and interact with the environment.
•Members of pioneer species die and are decomposed by bacteria and fungi
•This adds humus to the soil which improves water holding capacity of the soil
•Changes in the soil make environment less hostile
•Larger plants replace smaller plants (competition)
•New niches/habitats produced for new species to form new communities
•Increased biodiversity
•New communities will form and be replaced by later communities until a climax community is established.
Biotic factors are more important than abiotic factors, biodiversity remains constant due to competition making a stable climax community.
79
Outcomes of succession (5)
```
Environment becomes less hostile
greater number and variety of habitats
increased biodiversity
more complex food webs
increased biomass
```
80
Importance of conswervation
Ethical - We should preserve for future generations
Economic -
Cultural/Heritage -
Aesthetic - Don't ruin the countrysides
81
Deforestation
Loss of trees means less photosynthesis
Therefore less CO2 removed from atmosphere
Unwanted trees often burned releasing CO2 into the atmosphere
The concentration of CO2 in the atmosphere increases leading to increased global warming
Reduced input to nitrogen cycle as less recycling of nitrate ions occurs
Increased loss of nitrates by leaching
Roots of trees hold fertile part of soil = topsoil together. With no trees, wind erosion occurs causing removal of topsoil
Soil loses fertility so can only support lower numbers and fewer species of plants, giving lower biodiversity.
82
What does the H-W principle predict?(3)
The frequency of alleles will stay constant over time providing the conditions are met.
83
What are the conditions of the H-W principle?
* no mutations arise
* population is isolated
* no selection – all alleles are equally likely to be passed on
* large population
* mating within the population is random
84
Reproductive success and allele frequency (natural selection)
* Variation within the original population
* Spontaneous mutation
* Adaptation coded by mutated allele may give survival advantage/disadvantage
* Survival to reproduce (differential reproductive success)
* Pass on alleles for favourable characteristic/adaptation to offspring
* Allele frequency increases in population
* More of the new variants in population
85
How geographical isolation leads to the formation of a new species
* individuals of one species can freely interbreed and have a single gene pool
* climate change over time causes a split in the area with different conditions – GEOGRAPHICAL ISOLATION
* [insert selection model answer]
* type of alleles and their frequency in each area/each gene pool changes
* and becomes so different that they become a separate species
* if species are reunited, they will not be able to interbreed to produce fertile offspring – REPRODUCTIVE ISOLATION
86
reproductive isolation is...
When gametes are incompatible (different number of chromosomes so fusion cannot occur)
OR
When members of the species no longer recognize each other (different physical characteristics)
OR
When courtship behavior is different.
87
What is the difference between accuracy and reliability? (2)
Accuracy is being free from error, making no mistakes with instruments
Reliability means that there is little variation from the true value i.e. results are concordant when repeated
88
Describe ways you could show whether there is correlation between 2 variables.
1) Plot a scatter graph (1); draw a line of best fit (1)
| 2) Conduct Spearman Rank correlation test (1); look for figures close to +1 or -1 (1)
89
Why is it important to check repeatability of measurements? (2)
```
Identifies anomalies
Increases reliability (because differences less likely to be due to personal error)
```
90
Correlation and cause (2)
Correlation does not establish a cause
There may be another factor
NOTE: Spen Viger, spurious correlations
91
Use the words probability and chance to explain the meaning of ‘differed significantly’ (p < 0.05) (2)
There is a probability of less than 0.05 (5%) that the difference was due to chance.
OR
There is a probability of more than 0.95 (95%) that the difference was not due to chance i.e. was biological.
92
Explain why a statistical test is necessary (2).
Determines the probability of results being due to chance
Determines whether result is biologically significant
Enables Null to be accepted or rejected
93
How could you use a scatter diagram to check the repeatability of measurements made by two observers?
Plot a scatter graph of X versus Y
Look for overlying points - i.e. points should lie close to a line of best fit in both cases
If results are less reliable then many points may not lie on or close to the line of best fit.
94
Reasons for the effect of halting succession on animal diversity (4)
Prevents growth of woody plants
Decreases plant diversity
Less habitats and niches for animals
Lower variety of food sources
95
How increasing plant biodiversity causes increased animal biodiversity (3)
Increased variety of food sources
Increased number of niches
Increased number of habitatS
96
How do IPC's work?
- choosing animal/plant varieties that suit the local area and are as pest-resistant as possible
- managing the environment to provide suitable habitats for natural predators
- regularly monitoring for signs of pests so early action can be taken
- removing the pest mechanically
- using biological agents
- using pesticides as a last resort if pest populations become out of control
97
Disadvantages of chemical pesticides (3)
Always have some effect on non-target species (1)
must be re-applied therefore expensive (1)
pests may develop resistance (1)
98
Advantages of biological control (3)
Specific (1)
control organism reproduces itself and does not need to be re-applied (1)
pests do not become resistant (1)
99
Disadvantages of biological control (2)
Time lag as control does not act quickly (1)
| control organism itself may become a pest - i.e. Cane Toads
