BiologyUnit 4

AQA

Ecology DefinitionsHabitat – The place where an organism lives

Population – A group of organisms belonging to the same species

Community – All the populations of different organisms living and interacting in the same space at the same time

Ecosystem – A community of living organisms and the abiotic factors which affect them

Abiotic – The physical and chemical features of the environment

Biotic – The biological features of the environment (living)

Niche – A species role within it’s habitat

Adaptation – A feature that members of a species have to increase their chance of survival

Investigating Populations

Quadrats:- Set out 2 tape measure at right angles, forming the axes for

the chosen area- Generate 2 random numbers (using calculator) to use as co-

ordinates- Place quadrat where co-ords meet- Find mean number of species per quadrat - Multiply by size of area being sampled

Transects:- It’s a line through an area to be studied to identify changes

through an area

- Line Transects – a tape measure is placed along the transect and the species that touch the tape measure are recorded

- Belt Transects – quadrats are placed next to each other along the transect to work out species frequency & percentage cover along a transect

Measuring Abundance

Quadrats:- Have a known dimension- Used to:

- Estimate population density- Estimate % cover of an organism- Estimate the frequency of an organism

Factors:- Size of quadrat – More small quadrats = more representative

results- Number of quadrats – more quadrats = more reliable results- Position of quadrat – must be placed randomly to avoid bias

At least 20 samples taken. Eventually a sample size is big enough that the number of species doesn’t increase much more the sample is said to be representative.

Sampling StrategiesRandom Sampling:• When area is uniformed• Use random co-ordinates

Systematic:• When there’s an environmental gradient• Use a transect

Stratified:• Compare two areas• Select two areas & sample within them

Mark-Release Recapture

A known number of animals are caught and marked. They’re then released back.Later another sample are caught and the number of marked individuals is recorded

Assumptions:- No reproduction- No migration- Enough time for both marked & unmarked animals to mix- Marking doesn’t affect behaviour

Variation in Population Size

Abiotic Factors:- Affected by factors such as temperature, light, space, water

etc…- When conditions are ideal an organism will thrive and vice

versa

Biotic Factors:- Interspecific Competition:

- Competition between different species- Intraspecific Competition:

- Competition between the same species- Predation – Predator & Prey populations are linked

- Prey increases, more food, so predator increases.- Predator eats prey, prey decreases as they’re eaten- Predator decreases due to lack of food- Predator peaks after prey

Human PopulationsPopulation Growth = (BR + Immigration) – (DR + Emigration)

% Population Growth Rate = x 100

Demographic Transition Model:- Shows the change in BR, DR & population size over along period of time

Population ChangePopulation Start

Survival CurvesShow the percentage of all individuals that were born in a population that are still alive at a given age.

Life Expectancy – is the age someone is expected to live to- it’s the age at which 50% of the population are still alive

e.g. the life expectancy of this example is 81 as that is the age when 50% of the population are still alive

Age-Sex Population Pyramids

West Africa:- High BR- Short Life Expectancy- High DR- Developing Country

West Europe:- Lower BR- Long Life Expectancy- Lower DR- Developed Country

Ecosystem DefinitionsProducer – They’re photosynthetic organisms that manufacture organic substances using light energy, water and CO2

Consumer – They’re organisms that obtain their energy by feeding on other organismsDecomposers – When consumers & producers die, the energy can be used by organisms that break down the complex materials into single components againFood Chains – Describes a feeding relationship in which the producer are eaten by the primary consumers. They’re then eaten by secondary consumerTrophic Level – The level between each stage in the food chain

Food Web – More than one food chain linked together

Grass Sheep Human(Producer) (1° Consumer) (2° Consumer)

Trophic Level

Energy Transfer Between Trophic Levels

Little solar energy converted to chemical energy in PS:- Some is reflected due to wrong wavelength/frequency/colour- Doesn’t hit chlorophyll molecule- Lost as heat during evaporation

Energy is lost along a food chain:- Not all the organism is eaten- Not all organism digested – lost in faeces- Urine- Heat in respiration- Movement- Birds & Mammals – energy used to maintain a constant body

temperature (homeostasis)

Not enough energy to support further trophic levels, so rarely more than 4 trophic levels present in a food chain

Gross Primary Productivity (GPP) – Amount of light energy that plants convert to chemical energy

Net Primary Productivity (NPP) – Total amount of energy stored in a plant that is available to the next trophic level

NPP = GPP - Respiration

Measured in kJ m-2 Year -1

Energy Energy after TransferTransfer (%) Energy before Transfer

Net Primary Productivity

= 100X

Ecological PyramidsPyramids of Numbers:

Pyramids of Biomass:• Fresh Biomass less accurate as different amounts of H2O present in organism• Dry Biomass better but organism has to be killed

Fox

RabbitGrass

LadybirdAphid

Oak Tree Oak Tree

Caterpillar

ParasiteCaterpillar

Large Fish

Small FishZooplankton

Phytoplankton

This happens as zoo plankton is rapidly reproducing

Pyramids of Energy:• Always pyramid shaped• Amount of energy stored in organisms at each trophic level

Agricultural EcosystemsNatural Ecosystem:• Haven’t been changed by human activities

Agricultural Ecosystem:• Have changed by controlling abiotic & biotic conditions to make

it more favourable for crops or livestock

Natural Ecosystem• Solar Energy only• Lower Productivity• More Species & Genetic Diversity• Nutrients Recycled• Populations controlled naturally• Natural Climax Community

Agricultural Ecosystem• Solar Energy + Food• Higher Productivity• Less Species & Genetic Diversity• Nutrients Supplemented by Fertilisers• Population Controlled by Pesticides Too• Prevented From Reaching Natural Climax

Intensive Rearing Of Livestock:• Increases efficiency of energy conversion – movement restricted & warmth

provided to reduce respiration – more energy available for growth• Increase energy input – more energy available for growth (optimum

amount/type of food provided)• Animal produces more growth in a shorter period of time earning more money

Biological & Chemical Controls

Herbicide:- Chemicals that kill plantsFungicide:- Chemicals that kill fungiInsecticide:- Chemicals that kill insectsPesticide:- Chemicals that kill pests

Features of effective chemical pesticide:• Specific – Only toxic to specific organism not to

humans• Biodegrade – Breakdown into harmless

compounds in soil and chemically stable• Cost Effective – Only useful until pest becomes

resistant or needs reapplying• Bioaccumulation – No build up of chemicals in the

cropBiological Control

Chemical Control

Control using organisms that are the pest’s parasite or predatorDisadvantages:

Not as quick Doesn’t completely remove pestControl organism may become pest

Biological Control Chemical Control

Specific Always Effect Non-Target Species

Control Organism Reproduces

Chemicals Must Be Reapplied

Pests Don’t Become Resistant

Pests Develop Resistant (New Pesticide Need To Be

Developed)

Integrated Pest-Control Systems:- Combines Bio & Chem

Carbon CycleIn Carbohydrates, Lipids, Proteins & Nucleic Acids

Stages:• Photosynthesis:

• CO2 from atmosphere & dissolved in oceans is absorbed by producers• This produces carbon-containing compounds e.g. sugar

• Feeding:• Carbon-containing compounds pass along food chain

• Death:• Dead remains digested by saprobiotic microorganisms

• Decay:• Saprobiotic organisms secrete enzymes that breakdown large carbon-

containing compounds into smaller ones• When the microorganisms respire they release CO2

• Respiration:• All organism respire and release CO2

• Fossilisation:• When organisms don’t decay fully due to conditions in the soil• Fossil fuels form (Oil, Coal, Gas)

• Combustion:• Fossil fuels are burnt & CO2 is released into the atmosphere

Carbon Cycle

Carbon Containing Compounds In Producers

Carbon Containing Compounds In Primary Consumers

Carbon Containing Compounds

In Secondary Consumers

Feeding Feeding

Carbon Containing Compounds

In Dead Remains

Death

Saprobiotic Microorganis

ms

Decay

Death Death

Fossil Fuels

CO2 In Atmosphere & Dissolved In

Oceans Combustion Fossilisation

Respiration

Photosynthesis

Respiration

[CO2]Short-Term Fluctuations:• Day:

• Plants respire & photosynthesise• Usually photosynthesis > respiration• More CO2 taken up• [CO2] falls

• Night:• Plants respire• More CO2 released• [CO2] rises

• Winter:• Cold temp, short days, leaf loss means photosynthesis rate decreases• Less CO2 taken up• [CO2] rises

• Summer:• Warm temp, long days means photosynthesis rate increases• More CO2 taken up• [CO2] falls

[CO2]

Long-Term Fluctuations:• Burning Fossil Fuels:

• Releases CO2 into atmosphere from locked up sources

• [CO2] rises• Deforestation:

• Trees remove carbon from atmosphere (Carbon Sinks)

• Less trees – less PS – less CO2 taken up• Forests cleared by burning – releasing CO2

• Forests cleared by chopping down – leaving the stumps – stumps are decomposed releasing CO2 by respiration

Global WarmingGreenhouse Effect:

Trapping of the sun’s warmth, increasing the global temperature

Main Greenhouse Gases:CO2 Burning FF’s, respiration…..

CH4 Livestock, rice farming, landfill…..

CFC’s Aerosols, refrigerants…..

H2O

Consequences:- Rising Sea Levels- Extreme Weather- More Disease- Distribution of Species

Nitrogen CycleIn DNA, RNA, Proteins

Nitrogen Fixation:• Lightening

• N2(g) NO3-

• Free-Living Nitrogen Fixing Bacteria (azotobacter)• N2(g) NH4

+

• Symbiotic Nitrogen Fixing Bacteria (rhizobium)• Found in root nodules of legumes (peas, clover…)• N2(g) NH4

+

Nitrification:• Carried out aerobically by nitrifying bacteria

• NH4+ NO2

- (nitrosomonas)• NO2

2- NO3- (nitrobacter)

Ammonification:• Dead remains/waste NH3

• Saprobiotic Microorganisms breakdown the nitrogen containing compounds

Denitrification:• NO3

- NO2(g) Anaerobically (waterlogged soil)• Denitrifying bacteria

Nitrogen CycleN2(g) in

Atmosphere

Symbiotic N2 fixing

bacteria in rootsFree-living

N2 fixing bacteria in

soil

NH4+

NO2-

NO3-

N2 in dead remains,

waste

N2 in Produce

rs

N2 in Primary

Consumers

N2 in Secondary Consumers

Lightening

Nitrogen Fixation

Nitrification

Nitrification

Denitrification

Absorption

DeathDeath Death

Ammonification

Nitrogen Fixation in Roots

N2(g) NH4+ NO3

-

Nitrogen to Ammonium ions requires nitrogenase (anaerobic)

This requires ATP & rNAD

Sugar used by bacteria to produce ATP & rNAD

Plants supply bacteria with sugar

Symbiotic relationship

Plant then gets NO3- from soil

Catalyst

Deforestation & Nitrogen Cycle

Trees cut down & burnt:• Ash provides temporary high of N2

• This is rapidly leached from the soil

Trees are removed:• More rain hits soil• More leaching• Soil is waterlogged allowing denitrifying bacteria to work• No decomposition so no N2 returned to soil• [NO2] falls

FertilisersChemicals that provide crops with minerals for growth

More N2 provided More growth more PS more productivity

Natural Fertilisers:• Organic• Dead and decaying remains of plants & animals• e.g. manure

Artificial Fertilisers:• Inorganic (e.g. NH4NO3)• Mined from rocks• Converted into different forms to provide correct mineral

balance for particular crop• More easily leached from soil

Artificial fertiliser use can lead to eutrophication & bioaccumulation Build up of

chemical in body

Eutrophication• In most water sources nitrate levels are low so it limits algal/plant growth

• Added nitrates mean the growth of plants is not limited

• Algal blooms appear on water’s surface

• This ‘bloom’ absorbs light and prevents it reaching the bottom

• Light becomes a limiting factor, so plants at a lower depth die

• Lots of dead organisms, saprobiotic organisms grow exponentially

• Saprobiotic organisms require O2

• [O2] reduced as more [NO3-] is released from decaying organisms

• O2 is now a limiting factor so aerobic organisms die (e.g. fish)

• Less aerobic organisms, so less competition for anaerobic organisms, so there population rises exponentially

• Anaerobic organisms further decay dead remains releasing toxic waste, making the water putrid

Leaching

• Rain dissolves soluble nutrients (e.g. nitrates) • They’re carried deep into the soil• Dissolved nutrients may find there way into water sources• May cause harm if the water is consumed• Leached nitrates can cause eutrophication

Reduces Species Diversity:

• N2 rich soils favour growth of grasses etc…• These species out compete other species • Other species die out• Reducing the species diversity

SuccessionSuccession – describes the change of ecosystems over time

Seres – various stages of succession

Pioneer Species – 1st species to bring about colonisation in an area

Climax Community – ultimate stable community that is in equilibrium with the abiotic conditions

Primary Succession – when succession starts from bare, previously uncolonised ground or water with no life

Secondary Succession – when succession starts again in an area where communities have been destroyed – it occurs more quickly

Lithosere/Halosere/Hydrosere – succession from rocks/seawater/freshwater

Plagioclimax – when succession is stopped

Succession

- 1. Originally hostile – only pioneer species can live here

- 2. Pioneer species die – increases organic content of soil e.g. mineral, humus

- 3. Gradually environment changes & becomes less hostile

- 4. More nutrients present

- 5. Other species now grow, with more habitats present

- 6. Climax Community eventually reached (usually oak trees)

Conservation

Conservation – protection & management of species & habitats

Methods:

- Seed Banks- Fishing Quotas- Captive Breeding Programmes- Relocation- Protecting Areas/National Parks

Conservation Moorland:

- Sheep graze & controlled burning prevents climax community from being reached

- Preventing loss of habitat for many species

Production of ATP• ATP- Adenine TriPhosphate

• Made from ADP + Pi

• Energy stored in the phosphate bond

• ATPase catalyses the breakdown of ATP into ADP + Pi

• ATP synthase catalyses the production of ATP

• The ADP + Pi is recycled and the process starts again

Properties:• Small compound – easily transported around

the cell• Easily broken down (Hydrolysed)• Cell has instant energy supply

Photosynthesis

Inner & Outer membrane

GranumContains Chlorophyll

Thylakoid StromaStarch Grain

Loop of DNA

2 Photo Systems capture light in a chloroplast PSI (best at 700nm) & PSII (best at 680nm)

Lamellae (Membrane joining Thylakoids)

6CO2 + 6H2O + Energy = C6H12O6 + 6O2

Number of Chloroplasts

Substomatal Cavity

Lower EpidermisSpongy Mesophyll

Airy Cells, lots of space

Palisade Layer

Upper Epidermis

Waxy Cuticle

Absorption Spectrum

Plants absorb red & blue wavelengths only reflecting green. It’s why they’re green

LDS (Non-Cyclic Photophosphorylation)

Photolysis Of Water:

2H2O = 4H+ + 4e- + O2

Requires a photon to split water

Occurs in the Thylakoids of chloroplasts

Thylakoids adapted for their function:• Large SA, large area for attachment of chlorophyll, electron carriers and enzymes• Proteins in grana hold chlorophyll to allow max light intake• Granal membranes contain enzymes that help make ATP• Chloroplast contain DNA & Ribosomes to manufacture proteins for LDS quickly

Electron CarrierElectron Acceptor

Cyclic Photophosphorylation

Happens when lack of NADP

No light wasted

Only uses Photo System 1

Only ATP produced

LIS (Calvin Cycle)

In Stroma

RuBp – Ribulose BisphosphateTP – Triose Phosphate (GALP)GP – Glycerate 3-PhosphateRUBISCO – Enzyme used in CO2 Fixation

ATP and rNADP from LDS

6 Cycles = 1 Glucose Molecule

Respiration

C6H12O6 + 6O2 = 6CO2 + 6H2O + Energy

1. Glycolysis:• Makes Pyruvate from Glucose• In cytoplasm• Anaerobic Process• Net Yield of 2ATP

Dehydrogenation – Removal of H2

- Using dehydrogenase enzyme

Substrate Level Phosphorylation- ADP + Pi ATP

2. Link Reaction:• Pyruvate oxidised by removing H• Acetyl CoEnzyme A produced• Per Pyruvate a CO2 molecule produced

Pyruvate + NAD + CoA = Acetyl CoA + rNAD + CO2

Decarboxylation – Removal of CO2

- Using Decarboxylase enzyme

3. Krebs Cycle:• Acetyl CoA + oxaloacetate (4C) = Citrate• Citrate converted to 5C compound ( 2H+ & CO2 removed)• 5C to 4C Produces:

• 2 x rNAD• ATP• rFAD• CO2

NAD – Nicotinamide Adenine DinucleotideFAD – Flavine Adenine Dinucleotide

In Mitochondrion

Electron Transfer Chain

When rFAD & rNAD are oxidised they release 2H & 2e-

Electrons used in transfer chain

Energy/ATP produced in ETC is used to power chemiosmosis

Hydrogen used in chemiosmosis

Oxygen is the last electron acceptor.O2 + 2e- + 2H H2O

ChemiosmosisIn Photosynthesis & RespirationEnergy (ATP) from ETC used to power Chemiosmosis

Active Transport

If ATP synthase not present energy lost in the form of Heat instead of forming ATP

Electro – Chemical Gradient

Respiration

Anaerobic Respiration

Instead of pyruvate being converted into Acetyl CoA it’s converted into ethanol (in plants and yeast) and lactic acid (in animals and some bacteria)

Allows

glycolysis

to occur

GeneticsAllele: Variant of a gene

Phenotype: Characteristics of an organism, often visible, resulting from both it’s genotype and the effects of the environment

Genotype: Genetic composition of an organism

Poly-genetic Inheritance: More than one gene to produce a characteristic

Gene: Section of DNA that codes for a protein

Gamete: Reproductive cell that fuses with another gamete during fertilisation

Trait: A characteristic

Multiple Allele: Many forms of a gene (e.g. Blood group)

Heterozygous: One Dominant & One Recessive e.g. Rr

Homozygous: Both recessive or dominant e.g. RR or rr

Codominant: Both dominant or recessive contribute to final trait

Monohybrid Genetics

Red x WhiteRR rr

OR OR Or Or

R R

r Rr Rr

r Rr Rr

All Rr

Red x RedRr Rr

OR OROr Or

R r

R RR Rr

r Rr rr

1RR : 2Rr : 1rr

Sex Linked Diseases

Carrier Girl x Well Boy XHXh XHY XH Y

XH XHXH XHY

Xh XHXh XhY

1 Carrier Girl XHXh

1 Well Girl XHXh

1 Well Boy XHY1 Ill Boy XhY

Male = XYFemale = XX

Dihybrid Crosses

Yellow Smooth Green Wrinkled YYSS yyss

x

All YySs

Yellow Smooth Yellow Smooth YySs YySs

x

9YYSS : 3YySS : 3YYSs : 1yyss

F1 Generation

F2 Generation

Hardy-Weinberg Equation

Assumptions:No mutationsNo migration/Population IsolatedLarge populationsRandom MatingNo natural selection

P2 + 2PQ + Q2 = 1P + Q = 1

1RR : 2Rr : 1rr

e.g. 1 in 10,000 Albino (Recessive) Population = 10,000

Q2 = 1/10,000Q = 0.01P = 1 – QP = 0.99

(2 x P x Q) x 10,000 = 198 Heterozygotes

P2 x 10,000 = 9801 Homozygous Dominants

Speciation

• Development of a new species

• Population separated – e.g. geographical isolation

• Abiotic conditions in each location is different, so there are different selection pressures

• In colder climates polar bears with longer fur are more likely to survive, reproduce & pass allele to offspring

• Eventually the polar bears become so different that a new species develops – so they’re no longer able to breed with the other group

Polar Bears

Variation in Fur Length

Stabilising

Directional