Revision notes

Feel free to use the notes but don't take them as gospel; they were all done by a student studying for exams, NOT a teacher/ exam official. DON'T rely on my notes, and be aware that they are specific to the exam boards for the exams I am taking. The information mostly comes from my own school notes and official specifications from exam boards. Sources can be found on the “Sources” page.

[iamrevisinghonest]

Managed ecosystems such as wheat fields are prone to pest infestations. Describe the advantages and disadvantages of using biological agents to control pests.

Advantages

Specific (to one pest);

Only needs one application / reproduces;

Keeps/maintains low population;

Pests do not develop resistance;

Does not leave chemical in environment/on crop / no bioaccumulation;

Can be used in organic farming;

Disadvantages

Does not get rid of pest completely;

May become a pest itself;

Slow acting / lag phase / takes time to reduce pest population.

5 max

[iamrevisinghonest]

Succession occurs in natural ecosystems. Describe and explain how succession occurs.

(Colonisation b) pioneer (species);

Change in environment / example of change caused by organisms present;

Enables other species to colonise/survive;

Change in diversity/biodiversity;

Stability increases / less hostile environment;

Climax community.

5 max

[iamrevisinghonest]

Scientists have developed a standard procedure for comparing RFI in cattle. They control two factors. These are type of food and environmental temperature. Explain why each of these factors needs to be controlled.

Type of food (not a mark)

May vary in protein/fat/carbohydrate/fibre/roughage/vitamins/minerals;

May affect absorption / digestibility / energy value / tastiness / growth / overall food intake;

Temperature (not a mark)

Will affect heat loss/gain/respiration/metabolism;

(Need) to maintain/regulate body temperature;

More food/energy can be used for growth.

4 max

[iamrevisinghonest]

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.

Less/no proton/H+ movement so less/no ATP produced;

Heat released from electron transport/redox reactions / energy not used to produce ATP is released as heat;

Oxygen used as final electron acceptor/combines with electrons (and protons).

3

[iamrevisinghonest]

Scientists predict that in a mountain area the mean summer temperature is likely to rise from 20°C to 23°C. It is also likely to become much cloudier. Describe and explain how these changes are likely to affect the growth of plants that live there.

Growth will decrease (at higher temperature);

Rate of respiration will increase at higher temperature;

Photosynthesis decreases as limited by light/ as there is less light.

3

[iamrevisinghonest]

Suggest how the addition of NBPT to urea fertiliser could result in increased growth of crop plants.

Less urea/ammonia lost (from soil) / less urea broken down;

Urea/ammonia converted to nitrite/nitrate;

Used to produce protein/amino acids/DNA/bases/nucleotides.

3

[iamrevisinghonest]

Micro-organisms make the carbon in polymers in a dead worm available to cells in a leaf. Describe how.

Micro-organisms are saprobionts/saprophytes;

Secrete enzymes (onto dead tissue) / extracellular digestion;

Absorb products of digestion/smaller molecules/named relevant substance;

Respiration (by micro-organisms) produces carbon dioxide;

Carbon dioxide taken into leaves;

Through stomata.

5 max

[iamrevisinghonest]

In the light-independent reaction of photosynthesis, the carbon in carbon dioxide becomes carbon in triose phosphate. Describe how.

Carbon dioxide combines with ribulose bisphosphate/RuBP;

To produce two molecules of glycerate 3-phosphate/GP;

Reduced to triose phosphate/TP;

Requires reduced NADP;

Energy from ATP.

5

[iamrevisinghonest]

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.

High concentration of carbon dioxide linked with night/darkness;

No photosynthesis in dark/night / light required for photosynthesis/light-dependent reaction;

(In dark) plants (and other organisms) respire;

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;

Decrease in carbon dioxide concentration with height;

At ground level fewer leaves/less photosynthesising tissue/more animals/less light.

5 max

[iamrevisinghonest]

Describe the part played by the inner membrane of a mitochondrion in producing ATP.

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.

3 max

[iamrevisinghonest]

What does the Hardy-Weinberg principle predict?

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.

3 max

[iamrevisinghonest]

Explain how the intensive rearing of domestic livestock increases net productivity.

Slaughtered when still growing/before maturity/while young so more energy transferred to biomass/tissue/production;

Fed on concentrate/controlled diet/controlled conditions so higher proportion of (digested) food absorbed/lower proportion lost in faeces / valid reason for addition;

Movement restricted so less respiratory loss/less energy used;

Kept inside/heating/shelter/confined so less heat loss / no predators;

Genetically selected for high productivity.

4 max

[iamrevisinghonest]

Energy is transferred through an ecosystem. Describe how and explain why the efficiency of energy transfer is different at different stages in the transfer.

Some light energy fails to strike/is reflected/not of appropriate wavelength;

Efficiency of photosynthesis in plants is low/approximately 2% efficient;

Respiratory loss / excretion / faeces / not eaten;

Loss as heat;

Efficiency of transfer to consumers greater than transfer to producers/approximately 10%;

Efficiency lower in older animals/herbivores/primary consumers/warm blooded animals/homoiotherms;

Carnivores use more of their food than herbivores.

6 max

[iamrevisinghonest]

In the light-dependent reaction of photosynthesis, light energy generates ATP. Describe how.

Light (energy excites/raises energy level of electrons in chlorphyll;

Electrons pass down electron transfer chain;

(Electrons) reduce carriers / passage involves redox reactions;

Electron transfer chain / role of chain associated with chloroplast membranes, in thylakoids/grana;

Energy released / carriers at decreasing energy levels;

ATP generated from ADP and phosphate/Pi / phosphorylation of ATP.

5 max

[iamrevisinghonest]

The rate of carbon dioxide production was higher when plants were in nitrogen than when they were in the air. Explain why.

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.

3 max

[iamrevisinghonest]

Biol 1 exam spec: 1.1 Disease may be caused by infectious pathogens or may reflect the effects of lifestyle.

From the official AQA exam specification for A level Biology

Pathogens

Pathogens include bacteria, viruses and fungi.

Disease can result from pathogenic micro-organisms penetrating any of an organism’s interfaces with the environment. These interfaces include the digestive and gas-exchange systems.

Pathogens cause disease by damaging the cells of the host and by producing toxins.

Lifestyle

Lifestyle can affect human health.

Specific risk factors are associated with cancer and coronary heart disease.

Changes in lifestyle may also be associated with a reduced risk of contracting these conditions.

Analyse and interpret data associated with specific risk factors and the incidence of disease

Recognise correlations and causal relationships

[iamrevisinghonest]

Electron arrangement

Electron configurations

We describe elements’ electron arrangements in terms of the number of electrons and their positions in sub-shells and orbitals.

There are four types of electron shell you need to know for AS level chemistry:

s (sharp) -- this has 1 s orbital

p (principle) -- this has 3 p orbitals

d (diffuse) -- this has 5 d orbitals

f (fundamental) -- this has 7 f orbitals

Each orbital can hold a maximum of two electrons.

Each row in the periodic table represents a new major shell, and within the major shells there are sub-shells:

N=1 sub-shells contain only an s orbital; they can hold a total of 2 electrons

N=2 sub-shells contain one s and three p orbitals; they can hold a total of 8 electrons (2+(3×2))

N=3 sub-shells contain one s, three p, and five d orbitals; they can hold a total of 18 electrons (2+(3×2)+(5×2))

N=4 sub-shells contain one s, three p, five d, and seven f orbitals; they can hold a total of 32 electrons (2+(3×2)+(5×2)+(7×2))

We label electrons as follows:

Nxy

N = energy level

x = orbital name (s, p, d, or f)

y = number of electrons in orbital

e.g. Cl

1s2 2s2 2p6 3s2 3p5

1s ↿⇂  2s ↿⇂  2p ↿⇂↿⇂↿⇂  3s ↿⇂  3p↿⇂↿⇂↿

The up and down arrows represent paired and unpaired electrons. Electrons pair up in orbitals. However, if there is more than one orbital available, electrons will go into empty orbitals before they pair up; this is because electrons “prefer” to be alone in orbitals, rather than paired up.

e.g. P

1s2 2s2 2p6 3s2 3p3

1s ↿⇂  2s ↿⇂  2p ↿⇂↿⇂↿⇂  3s ↿⇂  3p ↿↿↿

Ionisation energies

Ionisation energy: the minimum energy required to remove an electron from each atom/ion in one mole of free gaseous atoms/ions

First ionisation energy: the minimum energy required to remove one electron from each atom in one mole of free gaseous atoms, to form one mole of free gaseous ions

Ionisation energy increases if:

there are more protons in the nucleus

there is more nuclear attraction for the outer electrons

the shielding (from other electron shells) remains the same

Ionisation energy decreases if:

there are outer electrons that are further away from the nucleus

there is less nuclear attraction for the outer electrons

there are more shells so there is more shielding

The ionisation energies of the elements across Period 3 show a pattern that links to their electron arrangement

The general trend in first ionisation energy is that it is increasing; however, some of the elements have a lower first ionisation energy than the one before.

e.g. Mg → Al

The first ionisation energy of aluminium is lower than that of magnesium because aluminium has one electron in a higher outer shell. This electron is further away from the nucleus than the outer electrons of magnesium, so requires less energy to remove because it is not as strongly attracted to the nucleus and there is more shielding between it and the nucleus.

e.g. P → S

The first ionisation energy of sulphur is lower than the first ionisation of phosphorus because sulphur has one electron that is in a pair in a p orbital. As electrons repel each other, a paired electron requires less energy to remove than an unpaired electron.

The first ionisation decreases down the group because with each extra shell, there is more shielding between the outer electrons and the nucleus and the electrons are further away from the nucleus so less nuclear attraction is acting on them.