AQA A-level Biology Unit 4 Intensive farming and Eutrophication

Brief important points on Unit 3 topics: intensive farming, food chains, energy transfer eutrophication, speciation, nitrogen cycle, carbon cycle, succession, conservation, researching population methods photosynthesis, respiration, brief genetic definitions. Enjoy :)

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Intensive Farming

Purposes; Increase efficiency of energy conversion,

Increase energy input - more added to ecosystem

Ensure growth is not a limiting factor

1) Killing pest species; Biological control/ Chemical Pesticides /Integrated system

2) Fertilisers

3) Rearing livestock intensively

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Killing Pest Species

Pests are organisms that inhibit crop productivity, so there is less energy for growth, so less biomass, and less profit.

Chemical pesticide; Insecticide ensures less biomass is lost

Herbicide reduces competition

Fungicide ensures less energy is wasted on fighting infections


Directly damage non-pest species (butterfly)

Indirectly affect non-pest by accumalating in tissue of pest and pass in to consumer

Economically Expensive

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Biological control

Introduce natural predators into ecosystem to eat pests

use parasites to linve in/lay eggs on pest and reduce ability to function

Introduce pathogens to cause disease and kill pests


Natural predators become pests

parasites/ pathogens Affects Non-pests

Productivity short term so less cost effective

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integrated System

Combining Chemical and Biological

Reduces cost, because more expensive method is reduced

Reduces enviromental impact, because less pesticide used

Killing Pest Species needs to be:

Specific Bio-degradable Cost effective Not Accumalate Easy & Safe to use

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Intensive Farming - Fertilisers

Artificial/ inorganic - pure chemicals containing ammonium nitrate in the form of powders/pellets

Natural/organic matter - Sewage, manure.

Provide Crops with minerals and nitrates for growth

No longer limiting factor

replaces lost minerals -more energy to grow - Increased efficiency of energy conversion

Disadvantages; Changes balance of nutrients in soil and cause other species to die

Causes leaching, ( chemicals washed into rivers) Eutrophication kills fish/plants,

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Intensive Farming - Rearing Livestock Intensively

Controlling conditions that the livestock live in

Warmth, movement restricted, feed higher in energy

Less energy wasted to maintain body temperature, or for movement

More energy used for growth - Efficiency of energy conversion increased - more biomass - productivity increased - less time wasted - more profit

Disadvantages; Ethics - Pain, Distress, Effects natural behaviour


Advantages for consumer - People in poverty can afford to eat.

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leaching - Water soluble compounds (fertilisers) in soil washed by rain or irrigation systems into rivers.

Nitrates/phosphates in water - Increased ion available for plants - Algae grows on surface and reduces light intensity - Increase of inter/intra-specific competition - Death - Saprobiotic nutrition (bacteria feeding on dead)- bacteria respire more (take in oxygen) - Increased BioChemical Demand (BOD) - 02 supply reduced - Death - more food for decomposers

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Energy transfer and productivity

Ecosystem - All organisms living in an area inc. Abiotic conditions

Gross productivity - Remaining energy available

Respiratory losses - lost energy through movement/heat

Net Productivity - Amount of energy available to next trophic level

Energy Transfer Efficiency - Net Productivity / Energy received (Gross productivity)

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Food chains

Pyramid of number

Pyramid of Biomass (Dry mass) ( kgm-2) Nearly always pyramid shaped

Pyramid of Energy (kjm-2yr-1) net productivity of each trophic level, Always pyramid.

Tertiary consumer

Secondary Consumer

Primary Consumer


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Ecosystem terms

Habitat - the place where an organism lives

Population - All the organisms of 1 species in a habitat

Community - Populations of different species in a habitat

Ecosystem - All Abiotic conditions and organisms living in a particular area

Abiotic conditions - Non living

Biotic - Living

Niche - the role of a species within it's habitat

Adaptation - A feature that increases a member of a species chance of survival and reproduction

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Species- similar organisms with similarthat can breed and produce fertile offspring

Speciation - The evolution of 2 or more species from existing species

Isolation; Behavioural- no longer recognise courtship displays

Geographical- separated by a physical barrier (e.g river/ road)

Speciation: Single population- split due to isolation - different selection pressures - allele frequency differs - reproductively isolated (cannot interbreed) - become 2 separate species

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Speciation, Selection

Differential reproductive success - individuals with beneficial alleles have selective advantage - thrive and reproduce - allele frequency increases.

Stabilising Selection - When environmental conditions are constant organisms within a species with phenotypes (medium length fur) towards middle of range have selective advantage - reduces phenotype range

Directional Selection - Extreme enviromental conditions, so organisms within a species with extreme phenotype (long fur) have selective advantage - causes genetic change

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1) Pioneer (lichen/mosses) Harsh Abiotic Conditions (no soil) -Lichens colonise & fix nitrogen - Lichens decompose - humus forms

2) Dryas (grass/small plants) Simple soil developed through more nutrients - inter-specific competition so Pioneers die off

3) Alder (shrubs) Nutrients increased by animal faeces and nitrogen fixing plants

4) Spruce (big trees) - Soil deep enough for root growth of big trees - climax community*

* Growth, but no more Succession

Species diversity increases - more niches - more humus - more food

Stability increases -if one species dies off there are still other resources to feed on

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Conservation Methods - seed banks/ fishing quotas

Conservation - Method of maintaining ecosystems and the organisms that occupy them

1)Seed Banks - Storing seeds with different characteristics

Pros: Needs little space

Cons: Expensive/ Time consuming, Need regular tests to prove viable

2)Fishing Quotas - International agreements that limit the amount a fisherman can catch

Pros: Reduces Number caught and killed

Cons: job losses

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Conservation methods continued - Captive breeding

3) Capive Breeding Programmes


Breeding in controlled enviroments increases number

Cons: When re-introduced into wild, can spread new diseases

Hard for animals to reproduce in unnatural habitat

4) Relocation - transfer organism to a location that is not under threat


May be outcompeted in new location

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Conservation - general pros/cons

Pros: Cons:

Without it resources may be lost (e.g drugs) Prevents Economic growth

Organisms have a right to exist time = money

Aesthetics - tourist attraction

Prevents disruption of food chains

Prevents climate change

(e.g less deforestation less C02 released)

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Conservation methods of Succession


A climax community may cause loss of habitats


Less species diversity

Managed fires used, so Secondary Succession (not starting from rock) can occur, so larger species take longer to grow.

Animals Graze/ mowing keeps vegetation low

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Investigating populations

Pitfall Traps

Steep containers in a hole underground

Lid partially open so curious insects can fall in, but have protection from predators


Jars with rubber bungs, a long tube partially covered, and a short tube

**** through short tube to vacuum up insects - time consuming :(

Beating Tray

Tray/sheet held under vegetation to catch insects when you shake the plant

Large samples/good estimates :) Not random

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Investigating Populations cont.

Quadrats [|||||||] are Random so eliminate Bias

placed on ground at different sections of ground

calculate species frequency or Number of individuals recorded

Percentage Cover - How much is covered by species (quick method)

Line Transects are Systematic to study a gradual change in precentage cover etc

Tape measure or Quadrats placed next to each other in a line

Evaluating methods

Reliability - Random sampling eliminates bias / Repetitions reduces affect of anomeles

Accuracy+precision - larger sample size

Control experiment shows whether result is due to another factor

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Investigating populations cont. 2 Mark release rec

To measure the abundance of a more mobile species

Total Population size =

(Number caught in 1st sample X Number caught in 2nd sample) / (Number marked from 2nd sample)

Capture a sample (pitfall/pooter/beating tray)

Mark with paint & Release & redistribute

take 2nd sample and count the amount marked with paint

Requirements to be Accurate:

Marked sample has oppurtunity to mix

Marking hasn't affected chance of survival

No changes to population due to births/deaths/migration

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Nitrogen cycle

[ Nitrogen gas ]--Nitrogen fixation--> [Nitrogen compounds in producers]--Digestion-->

[Nitrogen compounds in consumers]--death-->[Nitrogen compounds in decomposers]

Ammonification-->[Ammonium Ions]-Nitrification-->[Nitrites]--Nitrification>[Nitrates in soil]

-->Denitrification-->[Nitrogen in atmosphere]

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Nitrogen cycle cont

Nitrogen fixation = Nitrogen gas into nitrogen compounds by nitrogen fixing bacteria on roots of leguminous plants. Bacteria gets sugars from plants to respire

Ammonia = nitrogen + hydrogen

Ammonification = decomposers turn nitrogen compounds in dead organisms and urea turned into ammonium compounds

Nitrification = Ammonium compounds changed into nitrogen compounds to be used by plants. so ammonia - nitrites - nitrates

Denitrification - only in anerobic conditions (waterlogged soil) Nitrates in soil converted to nitrogen gas by denitrifying bacteria which respire.

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Carbon Cycle

Carbon cycle - how carbon moves through Biotic organisms and Abiotic environment

[Carbon Dioxide in air] --Photosynthesis-->[Carbon compounds in producer]--Digestion-->

[C-compounds in Consumer]--Death-->[C-compounds in Decomposers]--Respiration-->

[Carbon dioxide in air]...

Carbon compounds in Producers can also be converted to carbon dioxide in air by burning fossil fuels (combustion)

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Carbon dioxide in atmosphere / Affects of Global w

Least carbon dioxide in air mid-day in summer, because increase in light intensity - increase in photosynthesis

more fossil fuels burnt = more Carbon dioxide + methane

More decomposers - more respiration - more Carbon dioxide

more cattle - more farting - more methane

higher temperature - frozen ground thaws - natural stores of methane released

Wild animals/plants less abundant - when ice melts polar bear loses surface to hunt on

more abundant - Boarfish , organisms with extreme phenotypes

Crop yield - Carbon Dioxide no longer limiting factor - increases rate

Insect Pests - Warmth speeds up larvae process so reach adulthood quicker

Warm/wet increases mosquitoes

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Photosynthesis key words

Photosynthesis 6C02 + 6H20 --->C6H1206 + 602

Carbon dioxide + water ----> Glucose + Oxygen

Metabolic pathway - A series of small reactions controlled by enzymes

Photophosphorylation - Adding Phosphate using Light

Photolysis - Splitting of a molecule using light energy

Hydrolysis - Splitting of a molecule using water

Decarboxylation - Removal of Carbon Dioxide

Dehydrogenation - removal of Hydrogen

Redox reactions - involve oxidation (loss of electrions/hydrogens) & reduction (gain of e- & H+)

Thylakoid - site of dependent reaction Stroma - site of independent reaction

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Photosynthesis Light Dependent

Light dependent - in Thylakoid which absorbs light energy

light energy excites electrons in cholorophyll

electrons move along electron carriers

energy released generates ATP from ADP + Pi

Electrons accepted by another chorophyl molecule and is excited by light

electrons move along and are accepted by NADP

Light energy splits water (photolysis) into electrons (restore chlorophyl) hydrogens ( reduce NADP) and Oxygen

Products: reduced NADP (NADPH), ATP, Oxygen

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Photosynthesis - light independent (A.K.A calvin c

Light Independant occurs in the stroma which is within the inner membrane of chloroplast (contains enzymes, sugars and organic acids)

Ribulose Bisphosphate (RuBP) ( 5 Carbon)

combines with Carbon dioxide to make Glycerate 3 Phosphate (GP) (2 X 3C)

GP is reduced from the addition of electrons/hydrogens by Reduced Nadp (from Light dependent) converting to Nadp (returns to light dependent), and ATP ( from Light Dependent) converting into ADP+Pi (returns to light dependent)

Triose Phosphate is formed (TP/ GALP)

makes organice substances, amino acids, fatty acids, Glucose-starch/cellulose

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Respiration Glycolysis

Aerobic - oxygen present Anerobic - Oxygen is not present

Anaerobic Glycolysis takes place in the Cytoplasm of a mitochondria

Glucose (6Carbon sugar)

energy released from splitting of 2ATP into 2ADP+Pi

Makes PG (unstable)

Converts into Triose Phosphate (TP/ GALP) (2 X 3C)

Oxidised by loss of hydrogens/electrons to reduce coenzyme NAD into NADH (goes to electron transport chain) and converts 4ADP+Pi into 4ATP

Pyruvate (2 X 3C) Net Gain 2ATP molecules

Products: Pyruvate, ATP, Reduced NADP (NADPH)

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Respiration The Link reaction (aerobic)

2 link reactions take place: addition of Coenzyme A to Pyruvate (3C)

NAD reduced to NADH and Carbon Dioxide is released

Acetyl Coenzyme A (2C) is formed!

Krebs Cycle ( in Matrix)

Acetyl Coenzyme A combines with 4-carbon molecule = 6 Carbon molecule

NAD is reduced to NADH

2Carbon dioxides released

FAD reduced to FADH

ATP formed by Substrate- level Phosphorylation (formation of ATP by direct transfer of phosphate group)

Products: Acetyl CoenzymeA, NADH, FADH, Carbon dioxide

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Respiration - Oxidative phosphorylation - electron

Oxidative Phosphorylation

NADH to NAD supplies Electron transport chain with electrons off hydrogen atom

Electrons decrease in energy making 3 ATP from 3 ADP+Pi

energy from electron transport chain pumps protons off Hydrogen atoms into inner membrane of Cristae in mitochondria

Protons diffuse out of ATP Synthase molecule on membrane into matrix and ATP from ADP+Pi is created

finally, when protons and electrons at end of electron transport chain combine and are accepted by oxygen to make water (H20)

Products: 3 ATP, water

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Genetics terms

Gene - A sequence of bases on a DNA molecule that codes for a protein

Allele - A version of a gene. The order of bases are slightly different

Genotype - Genetic constitution BB

Phenotype - Expression of gene and interaction with enviroment

Co-dominant - neither is recessive or dominant (e.g. sickle-cell anaemia)

Locus - position of a gene on a chromosome

Homozygote - organism carries 2 copies of the same allele BB

test cross - When a plant or animal is crossed with homozygous/recessive to determine if an organism is homozygous or heterozygous for a particular allele

Sex-linked - gene carried on the X or Y chromosome. Y chromosome is shorter than X so alleles will be expressed in phenotype whether recessive or not

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