biomass and energy transfer through ecosystems pt1

what do arrows in a food chain show?

show the flow of energy

what 3 ecological pyramids are there?

• pyramids of number

• pyramids of biomass

• pyramids of energy

what do pyramids of numbers show?

they represent numbers of organisms in each trophic level in a food chain

are pyramids of numbers always pyramid shaped?

no

why are pyramids of numbers not always pyramid shaped?

they only show the number of organisms in each trophic level, and don’t take into account the size of organisms

what are some advantages of pyramids of numbers?

• Simple method of giving an overview

• Good at comparing changed in population numbers with time or season

what are some disadvantages of pyramids of numbers?

• The size of the organism isn't taken into account i.e. an oak tree producer would lead to an inverted pyramid

• Do not allow for juveniles or immature forms

• Numbers can be too large to represent accurately

what do pyramids of biomass show?

the total mass of organisms in each trophic level of a food chain

are they usually pyramid shaped?

• yes

• as energy and material are lost at each stage of the chain

why do we measure organisms dried for pyramids of biomass?

measuring them dry makes sure water mass isn’t taken into account as water in organisms vary

what units is the biomass at each trophic level measured in?

• grams per square meter for land  (gm-²)

• grams per cubic meter for water (gm-³)

what is an advantage of pyramids of biomass?

• Overcomes the problems of pyramids of number to give a more representative picture of the feeding relationships in an ecosystem

what are some disadvantage of pyramids of biomass?

• Only uses samples from populations - impossible to measure biomass exactly

• Time of year biomass is measured can affect the result - standing crop does not take into account changes over time

• To obtain dry mass calculations, organisms must be killed so samples are small

what is biomass?

total dry mass of organic matter in organisms or ecosystems which can be equated to energy content

what is the method for measuring biomass? (5 steps)

1. representative samples are collected

2. organisms are sorted into trophic levels

3. organisms are dried (due to varying amounts of water) in an oven at 80°C until all water has evaporated

4. mass is measured with an electronic balance

5. drying and measuring may be repeated

what is a disadvantage of the method of measuring biomass?

• samples must be killed to be dried

• can only used small samples (and so may not be represented)

what do pyramids of energy show?

these show the energy contained in the organisms in each trophic level of a food chain

are pyramids of energy always pyramid shaped?

• yes

• they are always pyramid shaped as energy and material are lost at each stage of the chain

• also takes into account time of year

what are pyramids of energy measured in?

Kilojoules per meter squared per year (kJm-²yr-1)

or

Kilojoules per meter cubed per year (kJm-³yr-1)

hat are some advantages of pyramids of energy?

• Most accurate representation of the feeding relationships between the organisms at different trophic levels

• It takes into account the energy gains and losses over a period of time

what is a disadvantage of pyramids of energy?

Very difficult and complex to collect energy data

how do you use a bomb calorimeter to construct a pyramid of energy?

• the energy content of samples of organisms from each trophic level is measured

• each sample is dried in an oven

• the samples are weighed

• samples are burned in a bomb calorimeter in oxygen

• energy produced passes to a known mass of water and the temp rise of the water is measured

• how much energy is released per gram is calculated and converted to kJ