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Biology Unit 4:
Ecosystems and practical techniques:
Ecosystems – A natural unit consisting of producer’s consumers and decomposers together
with non-living components
...

Community – All of the organisms of all species within an ecosystem
...

Microhabitat – A small organisms immediate surroundings
...
Defined by what
an organism eats, what eats it and what conditions it lives in
...

Producer – An organism which produces its own organic molecules
...

Consumer – An organism which consumes organic molecules
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Biotic – Living factors which affect the ecosystem
...

Quadrats provide accurate data and also take a small amount of time
...

Transects – sample organisms along a line to show a change from one area to another
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Continuous belt transect – quadrats placed without intervals
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Qualitative – what species are present
...


Hypothesis – a testable idea
...

Chi squared – statistical test used to decide whether results are significant or due to chance
...

Degree of freedom is one less than the number of categories
...
They are the
first to establish themselves e
...
lichen, moss
...
The existing species
change the biotic or abiotic environment so that new species can establish
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Climax community – Stable ecosystem when succession stops
...

Clearing a patch of land – Remove all plants, fence of the area from grazing animals and
observe the changes
...
The soil must have low humus content
and there must be no grazing animals
...
They have a rapid life cycle, then they die and increase the humus content of the soil
e
...
grass
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They out compete the colonisers
...
The
greater diversity of plants attracts more insects, birds and small mammals
...

Establishment of climax community – Small woody plants begin to dominate
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Eventually large, slow growing trees begin to dominate
until the climax community is established and there is no further succession
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Mutualism – A mutually beneficial relationship between different organisms
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The fungus builds a protective structure that the
algae can live in and photosynthesise
...
The fungus is a decomposer so provides nutrients for the both by
decomposing organic material
...
It also maximises biodiversity, which is greatest
during succession
...

In some places succession is controlled for aesthetic value e
...
Lake District
...

Human activity reduces the number of ponds that can form
...
Saving a valuable habitat and maintaining
biodiversity
...

Chemoautotrophs – Something that makes organic molecules using chemical reactions
...

Parasites - an organism which lives in or on another organism and benefits by deriving
nutrients at the other's expense
...

Detritivore - an animal which feeds on dead organic material, especially plant detritus
...

Trophic level – A stage in a food chain
...

Main components of soil: Water, dead plants and animals (humus), sand, air and bacteria
and fungi
...
coli), undigested food and gut lining cells
...
Enzymes hydrolyse food material
...

Energy flow through ecosystems: The elements that form the molecules in living things are
finite
...
Recycling needs energy, mostly
provided by the sun
...
If the sun stopped shining recycling would stop so would eventually end life on
earth
...

All organisms are interdependent
...

Food webs are better than food chains as it shows an animal’s varied diet
...

Gross primary production – The total amount of chemical energy converted from light
energy by plants in a given area at a given time
...

Much of the energy in absorbed compounds is lost as heat when an animal respires
...

Pyramid of biomass – The mass of the population within the ecosystem
...

Plankton - All organisms that drift
...

Nitrogen cycle:


Plants absorb nitrogen as nitrate
...




Plant combines nitrate with the carbohydrate made in photosynthesis
making amino acids and nucleotides
...




All nitrogen ends up in dead organic material
...
They obtain nutrients by
extracellular digestion
...

Deamination occurs, the removal of an amino group, producing ammonia
which is ammonification
...
This is nitrification
...
The nitrite is further oxidised to nitrate ions by
the bacteria genus nitrobacter
...


Nitrogen gas is unavailable to living things as the triple bond requires a lot of energy to
break, it is inert
...

Nitrogen can be fixed by lightning or by nitrogen fixing bacteria that have the enzyme
nitrogenase
...
Nitrate/
ammon/ium are made into nitrogen gas losing it from the cycle
...




Carbon locked up in organic molecules is eaten by animals and passes up the
food chain or leaves drop off and die
...




Animals excrete or die and the carbon is trapped in dead organic matter
...


Populations:
Typical stages of a growth curve:


Lag phase – Slow growth and further maturing is needed
...




Logarithmic or exponential phase – No limiting factors
...
Competition for food, waste accumulates,
etc…



The population stabilises at its carrying capacity – the size of a population that can
be supported in any particular situation
...

Density-dependent factors – factors that change with the size of the population e
...
food supply
...

Intraspecific competition – competition between individuals of the same species
...

Demographic transition means change in the population structure
...

Stage 2 expanding – High birth rate, fall in death rate as more surviving to middle age and a slightly
longer life expectancy
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Stage 4 contracting – Low birth rate, low death rate, higher dependency ratio and a longer life
expectancy
...

Phenotype – The observable characteristics an organism has
...

Chromosome – Tightly coiled DNA molecule
...

Allele – A version of a gene
Dominant – The allele which if present is expressed in the phenotype
...


Homozygous – Both alleles are the same
Heterozygous – Both alleles are different
...


Human blood groups:
Humans can be classified according to the proteins they carry on their cells – tissue typing
...
You can give o to anybody
...

AB – The universal recipient
...

In a large population, with a large gene pool, lots of unrelated individuals mate
...
Faulty recessive alleles do exist
but are rarely matched up and expressed
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In a small population with a small gene pool, lots of related individuals mate
...
Faulty recessive alleles are often
matched up and expressed
...

Sex linked inheritance concerns genes found of the sex chromosomes
...

A karyotype is prepared by inducing mitosis and inhibiting the spindle
...

With sex linked inheritance males cannot be carriers
...

Allele frequency – The frequency of an allele relative to that of other alleles of the same gene in a
population
...

Assumptions made with the Hardy-Weinberg equation:


No migration in or out



No mutation making new alleles



The population is large



All are equally fertile



No natural selection



No cross generational mating



More offspring are created than can possibly survive
...


Darwin:

The source of variation is mutation
...

Variation within populations is vital as it helps populations survive in unfavourable conditions
...

Stabilising selection – A mechanism that favours mid-range values
...

Directional selection – A force for change
...

Species – A population that can interbreed to produce fertile offspring
...




Natural selection acts differently on the two populations
...




Over many generations, genetic differences accumulate
...
The 2 populations can no longer mate to produce
fertile offspring
...

Sympatric speciation – The populations are not physically separated
...

ATP, Respiration and Photosynthesis:
Photosynthesis:
Carbon dioxide + Water -----------> Oxygen + glucose
Sunlight and chlorophyll located above the arrow
...
Photosynthesis
is the reduction of carbon dioxide to form organic molecules
...

Reduction – The gaining of electrons
...

ATP provides instant energy in small, usable amounts
...

ATP – Adenosine tri-phosphate
...

ATP is a nucleotide consisting of a sugar, a base and three phosphates
...
It carries energy from the site of respiration to
areas where energy is needed
...

In respiration the energy contained in organic molecules is released in a series of steps
...
Respiration is a process which replenishes ATP stocks
...
When all
the phosphate exists as ATP the battery is fully charged
...

Uses of ATP:


Muscular contraction



Active transport



Translation: Protein synthesis

ATP and energy is not the same thing
...

ATP has a high free energy of hydrolysis
...
These are used to make
ATP and NADPH
...

NADPH:
A coenzyme, it is an electron carrier
...




A triple membrane, the third membrane is the thylakoid membrane
...




The place between the in the inner membrane and the thylakoid is the stroma
...


Chloroplasts are adapted for photosynthesis as:


Lots of thylakoids so a lot of membranes
...




Flat shape for rapid diffusion
...


Chlorophyll absorbs certain wavelengths
...
Green is
reflected
...

The light independent reaction:


Happens on the thylakoid, where the chlorophyll molecules are housed
...




Chlorophyll emits 2 high energy electrons which pass along an electron transport
chain
...




Water is split – photolysis
...


The light independent reaction:
This process happens in the stroma in the centre of the chloroplast
...
Triose phosphate is converted into useful
organic molecules 1 in 6 times
...

Respiration:
The release of energy from organic molecules
...
These electrons are picked up by NAD so NADH is an electron being carried
...
FADH2 made in the Krebs cycle is similar to NADH and does the same
electron carrying function
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Produced by anaerobic respiration
...
This is ATP from stages 2,3 and 4 of respiration which
is aerobic respiration
...


The link reaction:


Links the anaerobic and aerobic part of respiration
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

Production of acetate and carbon dioxide from pyruvate
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

Makes no ATP but 2 NADH



Takes place in the matrix of the mitochondria

The Krebs cycle:


A series of reactions which oxidises acetate, stripping the electrons off it creating
large amounts of NADH and FADH
...




Turns twice producing 2 ATP, 6 NADH, 2 FADH 2 and 4 CO2
...


The electron transport chain:



A series of proteins on the inner mitochondrial membrane (cristae) which is folded
to provide a large surface area
...




The electrons pass from one protein to the next along the chain
...




This creates a diffusion gradient of H+ ions which diffuse back into the matrix
through the middle of the ATPase enzymes
...




The by—products of this process and the low energy electrons and protons combine
with oxygen to form water
...


Phosphorylation – Making ATP from ADP
Substrate level phosphorylation – ATP made in glycolysis and the Krebs cycle
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