Energy and ecosystems

Question 1

What is the ultimate source of energy in an ecosystem?

Answer 1

sunlight - converted as chemical energy by plants during photosynthesis

Question 2

What is biomass?

Answer 2

• the total dry mass of an organism or ecosystem, measured once water has been removed from a sample
• measured in grams/m^2
• measured in terms of dry mass of carbon or dry mass of tissue

Question 3

What is an autotroph?

Answer 3

another name for a producer - an organism that is able to synthesise its own organic material

Question 4

What is a heterotroph?

Answer 4

Another name for a consumer - an organism that obtains its organic material by eating other living organisms

Question 5

What is calorimetry?

Answer 5

An experimental method used to assess the chemical energy content of a sample in dry biomass, by heating a known mass and comparing the temp change of water

Question 6

Why is bomb calorimetry better?

Answer 6

less energy lost as heat to the surroundings

Question 7

What are saprobionts?

Answer 7

Also known as decomposers - they are a group of organisms that break down the complex materials in dead organisms into simple ones. This releases nutrients and minerals which can be absorbed by plants so contribute to mineral recycling. This can be fungi or bacteria

Question 8

What is a food chain?

Answer 8

• a feeding relationship in which producers are eaten by primary consumers
• these are in turn eaten by secondary consumers, which are eaten by tertiary consumers
• each stage is called a trophic level, and the arrows between trophic levels represent the direction of energy transfer

Question 9

What are food webs?

Answer 9

• within a single habitat, many food chains are linked together to form a food web, all organisms are linked to others in a food web

Question 10

Why is a lot of the suns energy not converted to organic matter by photosynthesis?

Answer 10

• a lot of the sunlight is reflected by clouds or dust back into space
• not all wavelengths of light can be absorbed and used for photosynthesis
• light may not fall on a chlorophyll molecule
• other factors may limit the rate of photosynthesis

Question 11

What is gross primary production? (GPP)

Answer 11

the total quantity of the chemical energy store in plant biomass in a given volume

Question 12

What is net primary production? (NPP)

Answer 12

• total energy available for plant growth, plant reproduction and energy transfer to other trophic levels after respiratory losses

therefore: NPP = GPP - R
(R = respiratory losses)

Question 13

What can NPP energy be used for?

Answer 13

• plant growth
• reproduction
• transferred to other trophic levels in an ecosystem such as herbivores or decomposers

Question 14

Why is only a low percentage of energy transferred across trophic levels?

Answer 14

• some of the organism cannot be consumed eg. bones
• some parts are consumed but cannot be digested, and are therefore lost in faeces
• some of the energy is lost in excretory materials eg. urine
• energy loss through heat eg. through respiration or maintaining body temperature

Question 15

How is net production of consumers calculated?

Answer 15

N = I - (F + R)

N = net production
I = chemical energy store of ingested food
F = energy lost in faeces and urine
R = energy lost in respiration

Question 16

Energy transfer between trophic levels is very inefficient, this explains why..

Answer 16

• most food chains only have 4-5 trophic levels because insufficient energy is available to support a large enough breeding population
• biomass is less at higher trophic levels
• total energy available is less at each level as you move up a food chain

Question 17

Why does keeping animals in confined spaces increase the energy conversion rate?

Answer 17

• movement is restricted so less energy used for muscle contraction

Question 18

What other strategies are used in intensive farming and why?

Answer 18

• environment is kept warm - reduces energy lost as heat
• control feeding - animal receives the optimum amount and type of food needed for maximum growth with no wastage
• predators are excluded (simplifying food webs) - no loss to other organisms in the food web

Question 19

What is leaf area index and how does a greater index reduce productivity?

Answer 19

Proportion of ground covered by leaves

• greater index means that there is more overlap between leaves - leaves beneath can get no sunlight for photosynthesis so productivity decreases

Question 20

How can pesticides and biological control be used to increase productivity?

Answer 20

• pesticides = introduction of chemicals to kill pest organisms
• biological control = introducing predators/pathogens to kill pest species

Question 21

What are sugars synthesised by plants used for?

Answer 21

• used as respiratory substrates
• the rest are used to make biological molecules, which form the biomass of the plant