7 - Ecological energetics and Nutrient cycling

CCEA GCE Biology - A2 1 - 4.4 (c + d) - Ecological energetics and Nutrient Cycling

What are producers?

Organisms that manufacture organic substances from inorganic substances. This uses energy.

What are photoautotrophs?

Producers which use light energy to make organic molecules

What are chemautotrophs?

Producers which use chemical energy to produce organic molecules.

What organisms are photoautotrophs?

Green plants

What organisms are chemoautotrophs?

Nitrifying bacteria

What are consumers?

Organisms that obtain their energy by feeding on other organisms

What are heterotrophs?

Organisms that cannot make their own food

What are decomposers or detritivores?

Organisms which live on decay and decomposition.

What organisms are detritivores?

Earthworms, springtails and woodlice

What is lysotrophic nutrition?

Secretion of enzymes on dead material. The enzymes hydrolyse the larger molecules into smaller molecules which can then be absorbed by decomposers.

What organisms are decomposers?

bacteria and fungi

What is a trophic level?

Each link in a food chain

What is a food web?

Several food chains linked together

What is the source of energy for most ecosystems?

The sun

Why is most solar radiation reaching earth unavailable for photosynthesis?

• Light is reflected back into space by dust particles

• It is absorbed by water vapour or dust in the atmosphere and then redistributed as heat energy

• It falls on bare ground and therefore misses the leaves of plants

How is solar energy that reaches the leaf lost?

• Reflection due to the waxy cuticle

• Used in water evaporation

• Light transmits through the leaf without striking a chloroplast

• The light is the wrong wavelength

• Energy is lost as heat

What is gross primary production (GPP)?

The rate at which plants convert sunlight into chemical energy

What is net primary production? (NPP)

The rate at which plants accumulate products of photosynthesis

How is NPP calculated?

NPP = GPP - Respiratory losses (R)

What are typical units for net production?

KJ m^-2 year ^-1

Why is only 10% of the chemical energy in plants used by primary consumers for growth?

• Much of the plant is not eaten

• Plant material may be difficult to digest (e.g. few species possess cellulase which is needed to hydrolyse cellulose)

• Energy is lost to excretory products

• Energy is used in respiration pt lost as heat energy

• Plant parts may enter the decomposer food chain

How is percentage efficiency calculated?

Energy available after transfer / energy available before transfer x 100

How can quantitative relationships between trophic levels be illustrated?

Pyramids

What are the main drawbacks when drawing pyramids of numbers?

• The size of an organism is not taken into account

• It can be difficult to represent number accurately to scale

What is biomass?

The total mass of organisms present on. aparticular trophic level in a habitat

What are the main drawbacks when drawing pyramids of biomass?

• It is almost impossible to measure the biomass of all individuals on a trophic level

• time of sampling may effect biomass

What do pyramids of energy show?

The amount of energy stored on each trophic level in a habitat over a given period of time

How is agricultural productivity increased?

• Increasing primary productivity in plants

• intensive farming of domestic livestock

What factors affect NPP?

• How effectively a crop carries out photosynthesis.

• The area of the ground covered by leaves

What additional energy input may agricultural ecosystems recieve?

• Food energy

• Energy from fossil fuels

Describe a natural ecosystem

In a natural ecosystem solar energy is the only source of energy as there s no additional input. Any limiting factors affecting photosynthesis cannot be removed or reduced so there is lower primary productivity. There is no control over the spacing of plants but there is higher species diversity as well as greater genetic diversity within species. Mineral ions are naturally recycled and population size is controlled by natural means so a natural climax community is reached.

Describe an agricultural ecosystem

Solar energy, as well as energy from food or fossil fuels are used. Crops are grown in a greenhouse so any limiting factors affecting the rate of photosynthesis can be removed or reduced meaning there is a higher primary productivity. Productivity can also be enhanced by appropriate crop spacing. There is, however, lower species diversity and lower genetic diversity within species. As crops are harvested there is limited recycling and the mineral concentration is supplemented by fertilisers. The population size is controlled by natural means but also by artificial methods such as pesticides and cultivation The ecosystem is prevented from reaching a natural climax community.

How does factory farming increase the efficiency of energy conversion?

• Movement is restricted so less used for muscle contraction

• Kept in warm conditions so less energy lost due to heat

• Animals can be fed high energy or protein foods

• Only the most productive varieties of animals are kept.

What are the problems associated with factory farming?

• Ethical issues

• Fast spread of disease

• Overuse of antibiotics

• Reduced genetic diversity

• Increased pollution

Hoe could energy floe through an ecosystem be described?

Linear

How can flow of nutrients through. anecosystem be described?

Cyclic

What are the basic principles of nutrient cycles?

• Producers take in the nutrient as simple inorganic molecules

• Producers build the nutrient into complex organic molecules

• The producer is eaten and passes the nutrient onto the primary consumer etc.

• The organisms eventually die

• The complex organic molecules are broken down by saprobiotic microorganisms into simple inorganic molecules

What happens in carbon foxing?

Producers make use of carbon dioxide in photosynthesis. The carbon from carbon dioxide becomes incorporated into complex organic molecules that make up the structure of the plant.

What happens when consumers feed on producers as part. ofthe carbon cycle?

The complex organic molecules are digested, absorbed and used by the consumer

What happens in the carbon cycle when plants or animals die?

Their organic molecules become available for saprobiotic organisms who feed lysotrophically. When the microorganisms respire they release carbon dioxide.

What are carbon sinks?

Materials where carbon is stored for long periods of time

What happens when fossil fuels are combusted?

Carbon dioxide is released into the atmosphere

How do living organisms contain nitrogen?

So they can make nitrogenous molecules (proteins, nucleic acids)

How do plants obtain nitrogen?

Absorbing nitrate ions from soil/water via active transport

How do animals obtain nitrogen?

Consuming plants or animals

What is ammonification?

Release of ammonium or ammonia when saprobiotic microorganisms break down nitrogenous molecules

What is nitrification?

The conversion of ammonia/ammonium ions into nitrate ions by nitrifying bacteria

What is denitrification?

Conversion of nitrates into nitrogen gas by denitrifying bacteria.