Energy Transfer Of Organisms - Energy And Ecosystems

Question 1

What are the three groups of organisms according to how they obtain their energy?

Answer 1

Producers, consumers, saprobionts

Question 2

What are producers?

Answer 2

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

Question 3

What are consumers?

Answer 3

Organisms that obtain energy by consuming other organisms in a lower tropic level than them

Question 4

What are saprobionts

Answer 4

Organisms that break down dead organisms by releasing enzymes so feed of dead matter. Majority are fungi and bacteria

Question 5

What are food chains?

Answer 5

They describe a feeding relationship between producers and consumers to show energy transfers in an ecosystem

Question 6

What are tropic levels?

Answer 6

The stages of the food chain

Question 7

What are food webs?

Answer 7

Many food chains linked together due to many organisms having multiple food sources so show feeding relationships within a community

Question 8

What is biomass?

Answer 8

The total dry mass of an organism in a specific area at a given time

Question 9

In biomass, why is it the dry mass and not the fresh mass that’s measured?

Answer 9

Because the varying volume of water would make the mass not comparative as well as unreliable

Question 10

What is the issue with biomass measuring?

Answer 10

The organism has to be killed and so it’s usually only measured in a small sample however this in itself is an issue as it may not be representative of the whole population

Question 11

How does energy first enter an ecosystem?

Answer 11

Through sunlight which is used for photosynthesis by the producer

Question 12

Why is only a small amount of energy from light, transferred to the producer’s biomass?

Answer 12

• most of the sun’s light energy is reflected back into space or absorbed by the atmosphere
• not all wavelengths of light can be absorbed by each plant to be used for photosynthesis
• light may not fall on a chlorophyll molecule so isn’t used in photosynthesis
• a limiting factor may slow the rate of photosynthesis e.g. low temperatures

Question 13

How do you calculate the Net Primary Productivity? (NPP) (producers)

Answer 13

Gross primary production (GPP) - respiratory losses (R)

Question 14

What is the gross primary productivity? What is the net primary productivity?

Answer 14

• GPP=The total amount of chemical energy stored in the plants biomass
• NPP = the chemical energy store that is left when the losses in reparation have been taken into account hence telling you the energy available to be passed on to the next tropic level in the food chain

Question 15

Give 5 reasons only a low percentage of energy is transferred between each tropic level in the food chain

Answer 15

• some parts of the organism are not eaten e.g. bones, wood
• some parts of the organism can’t be digested so are lost in faeces e.g. connective tissue in animals, cellulose in laments
• some energy is lost in excretory materials e.g. urine and co2
• energy lost as heat in respiration especially in mammals as they maintain a constant body te
• energy lost in movement e.g. during hunting

Question 16

How can you calculate the net production of consumers?

Answer 16

N = I - (F + R)

Where:

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

Question 17

What does the inefficiency of energy transfer between trophies levels explain in the food chain?

Answer 17

• most food chains only have 4-5 tropic levels as insufficient energy is available to support a large enough breeding population at a tropic level higher than this
• the total mass of organisms in a certain biomass is less at higher trophic levels
• the total amount of energy available is less at each trophic level as you go up the food chain

Question 18

How do you calculate percentage efficiency?

Answer 18

% efficiency = ( energy available after transfer / energy available before transfer ) x 100

Question 19

How do farmers intensively rear livestock to produce the max quantity of meat, eggs, and milk at the lowest possible cost? Why does this work?

Answer 19

By keeping animals in enclosed spaces as this:

• restricts movement so less energy is used in muscle contraction
• environment is kept warm so energy isn’t used to maintain body heat
• feeding is being controlled so animals receive optimum amount and type of food for max growth an minimal wastage
• predators are excluded so no loss to organisms in the food web

Question 20

Summarise the common sequence of nutrient cycles

Answer 20

1. Producers take up nutrients as simple, inorganic molecules/ ions
2. The producer incorporates and converts the nutrients into complex organic molecules
3. When the producer is eaten, the nutrient is passed onto the consumer as organic molecules
4. When producers and consumers die, saprobiontic organisms feed off of the organic complex molecules like amino acids so they release the nutrient in its original simple form so the cycle can repeat

Question 21

Why is the nitrogen cycle necessary?

Answer 21

Because the N2 in the atmosphere has the triple bond making the nitrogen on its own inert hence it can’t be used by plants and animals

Question 22

Give the sequence of the nitrogen cycle

Answer 22

1. Nitrogen fixation is carried out by nitrogen fixing bacteria in the soil converting N2 into NH3
2. Nitrification is carried out by nitrifying bacteria where NH4+ is oxidised to NO2- which is oxidised to NO3-.
3. Producers can now absorb NO3- ions which are fed on by consumers and saprobionts which also feed on the faeces and dead organism material from the consumers so release ammonia by breaking down proteins back into the soil in ammonification
4. When the soil has low o2 concentration as a result of it e.g. being waterlogged , Denitrification occurs as anaerobic nitrifying bacteria convert NO3- ions in the soil back into gaseous N2

Question 23

What are the two types of nitrogen fixing bacteria in the nitrogen cycle?

Answer 23

• free living nitrogen fixing bacteria which reduce gaseous nitrogen in the atmosphere into ammonia
• mutualistic nitrogen fixing bacteria - these live in nodules of roots in plants like peas and beans. They have a mutualistic relationship as the bacteria obtain carbohydrates from the plant and the plant gets amino acids from the bacteria

Question 24

Why do farmers need to keep their soil light and aerated?

Answer 24

To maintain o2 concentration for aerobic nitrifying bacteria and prevent too much denitrification as otherwise less of the NO3- will be absorbed by the plant and instead will be converted back into N2 by the anaerobic denitrifying bacteria

Question 25

What steps of the phosphorus cycle?

Answer 25

1. Rock stores phosphate ions
2. Weathering and erosion releases the phosphate ions into the soil
3. These are then absorbed by the producers for e.g. formation of phospholipids and ATP
4. Consumers feed on producers
5. The consumers and producers waste and their dead organic matter is broken down by saprobionts which release the phosphate ions back into the soil
6. Phosphate ions in the soil may also leach into water bodies
7. Sedimentation then causes the creation of new rock and the cycle repeats

Question 26

Why are fertilisers needed in agricultural ecosystems?

Answer 26

They are added to soil in order to replace the nitrate and phosphate ions lost when plants are harvested and removed from the nutrient cycle as crops

Question 27

What are the two types of fertilisers and give a description of each

Answer 27

• natural fertilisers which consist of dead plants and animals as well as manure
• artificial fertilisers which are mined from rocks and then chemically converted into different forms and quantities of the ions required

Question 28

Give an advantage and a disadvantage of natural fertilisers

Answer 28

• Advantage: they are cheaper and free if the farmer owns animals
• disadvantage: they are extract minerals so proportions can’t be controlled

Question 29

Give an advantage and a disadvantage of artificial fertilisers

Answer 29

Advantage: contains the exact proportions of minerals so more likely to be effective
Disadvantage: inorganic substances are more water soluble hence dissolve in water surrounding the soil meaning larger quantities are washed away with rainfall into water sources so greater impacting the environment

Question 30

Give the three environmental impacts of nitrogen containing fertilisers

Answer 30

• leaching (when water soluble substances are washed away into rivers/ ponds)
• eutrophication (the process by which nutrient concentrations increase in bodies of water which can be caused by leaching)
• reduced species diversity (nitrogen rich soils favour rapidly growing species which may outcompete other species)

Question 31

How do fertilisers increase productivity?

Answer 31

As nitrate ions used for ATP become readily available to the plant allowing it to grow taller and have greater leaf area which increases the rate of photosynthesis and hence productivity

Question 32

What is nitrogen essential for in plants and animals?

Answer 32

• ATP synthesis
• amino acid structure
• DNA nucleotide structure

Question 33

What are the steps of eutrophication?

Answer 33

1. Nitrates leach from fertilised fields into ponds where they stimulate algae growth
2. Excessive algae growth creates a blanket on the surface blocking out light (algal bloom)
3. Plants below can’t photosynthesis so due as light becomes a limiting factor of growth
4. Saprobiontic bacteria feed and respire on dead plant matter hence using up o2
5. O2 conc in the water is reduced and nitrates are released from the decaying organisms
6. Population of aerobic organisms die which means less competition for anaerobic organisms so their population increases
7. Anaerobic organisms then further decompose dead material releasing nitrates and toxic wastes and so having a negative impact on the environment