Zusammenfassung der Ressource
Pack 17 - Energy,
Ecosystems and
Nutrient cycles
- Food chains and
energy
transfer:
- Most plants convert energy from
sunlight into chemical energy in
organic comounds
- Nitrates and
phosphates are
required to make
these organic
compounds
- Food chains:
- Producers:
- Photosynthetic organisms
manufacture organic
substances
- Consumers:
- Consume other organisms
to obtain their energy
- Primary consumers
eat producers
- Secondary consumers eat
primary consumers
- Saprobionts
- Extracellular
digestion
- Break down things to
absorbable parts
- Assimilated
- Trophic levels
- Energy flows from primary
producers to consumers. Each
group is said to be at a certain
trophic level
- e.g. grass-->rabbit-->fox
- There are usually only 4 or
5 trophic levels due to the
inefficiency of energy
transfer
- Food webs:
- In any habitat, many food chains are
inter-linked to form food webs
- Some organisms will be in
more than one trophic
level
- The greater the number of
interactions, the more stable the food
web is
- Biomass
- Total mass of living material in a
specific material in a specific area at a
given time
- All organisms
contain a variable
volume of water
- Dry mass is measured by drying the
sample in an oven at 100 degrees until a
constant mass is reached.
- Issues:
- Organisms must be dead
- Only small samples
can be taken
- Sample may not be representative
- Measured in dry mass per
given area in a given time
- Calorimetry can be used to
estimate the chemical energy
store in dry mass
- 1. Sample of dry material weighed
- 2. Burnt in pure oxygen in a sealed chamber
- 3. Bomb is surrounded by water bath
- 4. Heat of combustion causes temp. of the water to rise
- Energy transfer
and Productivity
- 90% of energy from the sun is lost,
even more is lost of the energy
hitting a leaf:
- Some energy
used for
evaporation
- Some energy is
reflected by
cuticle
- Not all light hits
the cuticle
- Not all wavelengths
used in photosynthesis
- Low CO2 Conc. may
limit photosynthesis
- Gross primary production (GPP) and
net primary production (NPP)
- GPP = The chemical energy store
in a plant biomass, in a given
area volume at a given time
- NPP = Chemical energy store in
plant biomass after respiratory
losses to the environment
- NPP = GPP - R
- Less than 10% NPP in plants available to consumers
- Not all plant eaten
- Some used in respiration
for ATP production
- Some lost in egestion
and excretion
- Plant material is
difficult to digest
- Less than 20% available from secondary to tertiary
- Not all consumed
- Some parts are lost in faeces
- Lost in excretion
- Net production of consumers
- N = I - (F+R)
- I = Chemical energy
- F = chemical energy lost to environment
- R = Respiratory loss
- Productivity and
farming practices
- Increasing the
efficiency of energy
transfer leads to
higher yields
- Intensive farming techniques:
- Restrict movement - less
energy used in muscle
contraction
- Environment kept warm -
reduce heat loss from the
body
- Optimum amount of
food for max growth
- Predators excluded
so no loss to other
organisms
- Chemical and biological
control of agricultural pests
- Pesticides
- Effective ones should:
- Be specific to only
one organism
- Biodegrade
- Not accumulate
- Development of
genetic resistance
- Mutation confers resistance
- Pests without mutant
allele are killed by
pesticide
- Organisms with allele for resistance survive
- Breed to pass on allele
- Biological Control
- Eradicating pests may
mean that other pests
can multiply
- Very specific, once introduced
the organisms reproduce
themselves
- Pests can't become resistant
- Integrated control systems
- Aim to keep pests
are acceptable levels
- Choose varieties of
animals/plants that are
resistance to pest
- Providing habitats close to crops for
natural predators
- Monitor crops for signs of pests
- Remove pests mechanically
- Use biological agents
- Use pesticides
- Nutrient cycles
- Saprobiotic organisms:
- Activate a gene that makes
digestive enzymes
- Enzymes are secreted and hydrolyse
surrounding material into soluble compounds
- Compounds are absorbed by
cells and assimilated
- Nitrogen cycle
- Ammonification
- Production of ammonia
from organic nitrogen
containing compounds
- Carried out by
saprobiotic
organisms
- Nitrification
- Oxidation of
ammonium ions
to nitrate ions
- Then oxidation of nitrite
ions to nitrate ions
- Nitrogen Fixation
- Reduce gaseous
nitrogen to
ammonia
- Denitrification
- Denitrifying bacteria
convert soil nitrates
into gaseous
nitrogen in anaerobic
conditions
- Phosphorus cycle
- Role of
Mycorrhizae
- This is the
association between
certain types of fungi
and most plants
- Fungi act as extension of
plants to increase surface
area
- Plants provide
organic compounds
- Mycorrhizae provide
water and minerals and
resist drought
- Fertilisers
- Natural fertilisers
- Dead and
decaying remains
of animals and
plants
- Animal waste
- More expensive
- Artificial fertilisers
- Mined from
rocks and
deposits
- Convert into different
forms and blended to give
balance of minerals
- Agricultural ecosystems
- Intensive food production
means minerals are taken away
- Nitrogen is
needed for
growth (amino
acids)
- Environmental issues:
- Leeching occurs:
- This is the process by
which nutrients are
removed from the soil
- Rainwater dissolves soluble
nutrients, this is carried
into watercourses
- This can lead to
eutrophication
- 1) Nitrate ion concentration increases due to leaching
- 2) Algae bloom - upper layers become densely populated
- 3) Algae absorb light - light cannot penetrate lower levels
- 4) Light becomes the limiting factor for plants below - they die
- 5) Lack of dead plants no longer the limiting factor for saprobionts, so they grow
- 6) Saprobionts require oxygen for respiration, increased oxygen demand
- 7) Oxygen concentration in water reduces, nitrates released from decaying organisms
- 8) Oxygen now limiting factor for fish - they die
- 9) Less competition for anaerobic respiration, so anaerobic organisms increase
- 10) Anaerobic organisms continue to
decompose material and release nitrate
and toxic waste