13- Energy and ecosystems

What three groups can organisms be divided into based on how they obtain their energy and nutrients?

• Producers

• Consumers

• Saprobionts

What are producers?

Photosynthetic organisms that manufacture organic substances using light energy, water, carbon dioxide, and mineral ions

What are consumers (in general)?

Organisms that obtain their energy by feeding on (consuming) other organisms, rather than using energy from sunlight directly

What are primary consumers?

Organisms that eat producers

What are secondary consumers?

Organisms that eat primary consumers

What are tertiary consumers?

Organisms that eat secondary consumers

What are two general examples of secondary and tertiary consumers?

• Predators

• Parasites

What are saprobionts?

• A group of organisms/ decomposers

• That break down complex materials in dead organisms into simple ones

• This releases valuable minerals and elements that can be absorbed by plants

• This means they contribute to recycling

What are two general examples of saprobionts?

• Fungi

• Bacteria

What is a food chain?

• A diagram showing feeding relationships

• Producers are eaten by primary consumers, which are eaten by secondary consumers, which are eaten by tertiary consumers which may be eaten by quaternary consumers

• Each stage in the food chain is called a trophic level

• The arrows represent the direction of energy flow

What is a food web?

• A diagram where many food chains are linked together

What is biomass?

The total mass of living material in a specific area at a given time

Why may biomass be difficult to calculate?

• Fresh mass is easy to assess, but the presence of varying amounts of water makes it unreliable

• Measuring dry mass requires the organism to be killed so is usually only made on a small sample, but this sample may not be representative

What are the potential units for biomass?

• g m^-2 - this is for when an area is being sampled, such as grassland or a seashore

• g m^-3 - this is for when a volume is being sampled, such as a pond or ocean

What method is used to calculate the chemical energy store in dry mass?

Calorimetry

What are the stages in using bomb calorimetry to calculate the chemical energy store in dry mass?

• A sample of dry material is weighed

• It is burnt in pure oxygen within a sealed chamber called a bomb

• The bomb is surrounded by a water bath

• Combustion of dry material causes a temperature rise in the water

• Calculate the energy released from the dry material using the specific heat capacity of water, the volume of water, and the temperature rise

• Typical units would be kJ kg^-1

What percentage of the Sun’s energy is typically converted to organic matter by plants?

1-3%

Why is most of the Sun’s energy not converted to organic matter by photosynthesis?

• Over 90% of the Sun’s energy is reflected back into space by clouds and dust or absorbed by the atmosphere

• Not all wavelengths of light can be absorbed and used for photosynthesis

• Light may not fall on a chlorophyll molecule/ photosynthetic pigment

• Another factor, such as low carbon dioxide levels, may limit the rate of photosynthesis

What is GPP

• Gross primary production

• The total quantity of the chemical energy store in plant biomass

• In a given area or volume

• At a given time

What is NPP?

• Net primary production

• Plants use 20-50% of GPP in respiration

• NPP is the gross primary production minus respiratory losses

Write out a word equation involving GPP and NPP.

Net primary production = gross primary production - respiratory losses

Write out a symbol equation involving GPP and NPP.

NPP = GPP - R

What can the net primary production be available for?

• Plant growth and reproduction

• Other trophic levels in the food chain, such as consumers and decomposers

What proportion of net primary production in plants can be used by primary consumers?

Usually less than 10%

What proportion of the energy available in prey can be used by secondary and tertiary consumers?

Up to 20%

Why is a low percentage of energy transferred between trophic levels?

• Some of the organism is not consumed

• Some parts of the organism are consumed but cannot be digested and are therefore lost in faeces

• Some of the energy is lost in excretory materials, such as urine

• Some energy losses occur as heat from respiration lost to the environment

Explain which organisms have high respiratory losses.

• Mammals and birds

• They have high body temperatures

• Lots of energy is needed to maintain their body temperature when heat is being lost to the environment

What is a symbol equation representing the net production of consumers?

N = I - (F + R)

In the equation N = I - (F + R), what does N stand for?

The net production

In the equation N = I - (F + R), what does I stand for?

The chemical energy store of ingested food

In the equation N = I - (F + R), what does F stand for?

Energy lost in faeces and urine

In the equation N = I - (F + R), what does R stand for?

Energy lost in respiration

How can you tell energy transfer between trophic levels is inefficient from looking at a food chain?

• Most food chains only have four or five trophic levels- not enough energy available to support more levels

• Biomass decreases at higher trophic levels

• The total amount of energy available decreases as you move further up the food chain