Section 5- Energy and ecosystems

Question 1

How is most energy lost?

Answer 1

Lost as heat

Leaves the environment as thermal energy

Question 2

How is the energy content of organisms measured?

Answer 2

Measuring dry biomass

Question 3

Why is dry biomass used to measure the energy content of organisms?

Answer 3

There is no energy in water

Water content of an organism can vary

Question 4

What is used to measure energy content of organisms?

Answer 4

Calorimeter

Question 5

What is an autotroph?

Answer 5

Plants

Question 6

What is a heterotroph?

Answer 6

Organism that gets energy from other organsisms

Question 7

How do you calculate energy efficiency?

Answer 7

Net production of trophic level
/Total energy of previous trophic level
x100

Question 8

How is the Net production (N) calculated in heterotrophs?

Answer 8

N = I - (F + R)

I = Energy ingested 
F = Losses in faeces
R = Losses in respiration

Question 9

How is the Net Primary Product (NPP) calculated in autotrophs?

Answer 9

NPP = GPP - R

GPP = gross primary production
R = respiration losses

Question 10

Suggest how the efficiency of energy transfer in cattle could be improved?

Answer 10

Keep the cattle in sheds

Less energy used in movement

Less energy used in keeping warm

More energy available for growth

Question 11

What is the nitrogen cycle?

Answer 11

Cycling of nutrients including nitrogen involved saprobiotic micro-organisms

Question 12

What does saprobiotic mean?

Answer 12

Digesting extracellularly

Release enzymes, digestion occurs outside of the cell and the digested products are absorbed

Question 13

What is ammonification and nitrification in the nitrogen cycle?

Answer 13

Dead organic matter contains nitrogen in proteins, DNA, RNA and ATP

Nitrogen is also found in urea and faeces

Bacteria will convert nitrogen into:
Ammonia -> nitrite -> nitrate

Question 14

What is nitrogen fixation?

Answer 14

Nitrogen fixing bacteria take nitrogen gas and convert it to ammonia or nitrates

Many bacteria live in root nodules of leguminous plants

Bacteria makes nitrates for the plant which provides glucose and amino acids for the bacteria

Question 15

What do mycorrhizae do in the nitrogen cycle?

Answer 15

Fungi which grow on roots of many plants

Extend the roots further into the soil and across a wider area

Provides plants with greater surface area for absorbing nutrients and water

Fungi get a source of glucose from the plant

Question 16

What is denitrification?

Answer 16

Occurs when the soil becomes anaerobic (water-logged)

Denitrifying bacteria removes oxygen from nitrates for respiration

Releases nitrogen as nitrogen gas

-Quickly makes soil fertile

Question 17

What is assimilation in the nitrogen cycle?

Answer 17

Uptake of ammonium ions and nitrates by plant roots and their incorporation into plant protein and nucleic acids

Question 18

What are 2 reasons for the stunted growth of plants in a field?

Answer 18

Lack of nitrates due to denitrification

Little oxygen for respiration to provide energy for active transport

Question 19

Why are composts rich in cellulose likely to be poor in nitrogen-containing ions?

Answer 19

Cellulose doesn’t contain nitrogen, neither do decomposed products

Question 20

What is eutrophication?

Answer 20

When excess nitrates and phosphates are leached (washed) from soil into rivers and lakes, algal bloom occurs

Question 21

What is the problem with eutrophication?

Answer 21

Algal bloom blocks light from reaching photosynthetic aquatic organisms, leading to their death

Decomposers use up oxygen in water, leading to death of aerobic animals

Only anaerobic bacteria survives- water becomes stagnant

Question 22

What are the stages of the phosphorus cycle?

Answer 22

1. Weathering
2. Runoff
3. Assimilation
4. Decomposition
5. Uplift

Question 23

Why is the phosphorus cycle a slow process?

Answer 23

Phosphorus has no gas phase

No atmospheric cycle

Question 24

What happens during weathering and runoff in the phosphorus cycle?

Answer 24

Phosphate compounds from sedimentary rocks leach into surface water and soil

Question 25

What happens during uplift in the phosphorus cycle?

Answer 25

Sedimentary layers from oceans are brought up to land over many of years

Question 26

What are the 4 main stages of the nitrogen cycle?

Answer 26

1. Nitrogen fixation 2. Ammonification 3. Nitrification 4. Denitrification

Question 27

Why can't organisms use nitrogen directly from the atmosphere?

Answer 27

N2 is very stable due to strong covalent triple bonds

Question 28

How can the risk of eutrophication be reduced?

Answer 28

Use phosphate-free detergent Pumping nutrient-enriched sediment out of water Sewage treatment marshes on farms

Question 29

What are 2 environmental issues caused by the use of fertilisers?

Answer 29

Eutrophication- algal bloom causes water sources being putrid Leaching- nitrates dissolve in rainwater and runoff into water sources

Question 30

What are the 2 categories of fertilisers?

Answer 30

Organic- decaying organic matter & animal waster Inorganic- minerals from rocks, usually containing nitrogen, phosphorus, potassium

Question 31

What are the advantages of planting a different crop on the same field each year?

Answer 31

Different crops use different proportions of certain ions Different crops have different pathogens Nitrogen-fixing crops make soil more fertile

Question 32

How do plants use the sugars from photosynthesis?

Answer 32

Primarily as respiratory substrates To synthesise other biological molecules

Question 33

What is biomass?

Answer 33

Total dry mass of tissue or mass of carbon measured over a given time in a specific area

Question 34

What is gross primary production?

Answer 34

Total chemical energy in plant biomass within a given volume or area

Question 35

What is net primary productivity?

Answer 35

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

Question 36

Why is most of the suns energy not converted to organic matter?

Answer 36

Most absorbed by atmosphere or reflected by clouds Photosynthetic pigments cannot absorb some wavelengths of light Not all light falls directly on a chlorophyll molecule Lost as heat during respiration/ photosynthesis

Question 37

Why does biomass decrease along a food chain?

Answer 37

Energy lost in nitrogenous waste and faeces Some of organisms not consumes Energy lost to surroundings as heat

Question 38

What are some common farming practices used to increase efficiency of energy transfer?

Answer 38

Exclusion of predators Artificial heating Restriction of movement Feeding is controlled at the optimum

Question 39

What are 2 nitrogen-containing molecules that are found in plants and animals?

Answer 39

DNA ATP

Question 40

What is the role of microorganisms in nitrogen fixation?

Answer 40

Converts nitrogen gas to ammonia ions

Question 41

What is the role of microorganisms in denitrification?

Answer 41

Converts ammonia ions into Nitrogen gas

Question 42

What are 2 advantages of using treated sewage sludge on farmland, rather than inorganic fertilisers?

Answer 42

Improves soil quality Ensures it is anaerobic Cheaper for farmers to use it

Question 43

Why is there no build-up of phosphate ions when they enter chloroplasts?

Answer 43

Used in phosphorylation of ATP in the light-dependent reaction Catalysed by ATP synthase

Question 44

What do the arrows in a food web show?

Answer 44

The direction of energy flow

Question 45

What is the general name to describe the bacteria and fungi that will break down death matter?

Answer 45

Saprobionts/ decomposers

Question 46

What are 3 reasons for the small percentage of energy transferred at each trophic level?

Answer 46

Some of the organism is not eaten Some parts are not digested and so are lost as faeces Some energy is lost as excretory materials Some energy is lost as heat

Question 47

Why do most food chains rarely have more than four trophic levels?

Answer 47

After 4 trophic levels there is insufficient energy to support a large enough breeding population

Question 48

Why does biomass show little increase after 100 years?

Answer 48

Net productivity = gross productivity - respiratory loss Decrease in gross productivity

Question 49

Why does gross productivity decrease as woodland matures?

Answer 49

Less light = more competition for light Reduced photosynthesis

Question 50

How do nitrogen-containing substances get into a lake from a field?

Answer 50

Runoff

Question 51

How is nitrogen taken up by plant roots?

Answer 51

Uptake by roots involves active transport Requires ATP

Question 52

How does the presence of nitrates in a lake eventually lead to the death of fish? [4]

Answer 52

Algal bloom Blocks light = less photosynthesis Plants die Less oxygen for fish

Question 53

What is the role of microorganisms in producing nitrates from the remains of dead organsisms?

Answer 53

Saprobiotic break down dead material Ammonium -> nitrite -> nitrate By nitrifying bacteria

Question 54

What is leaching?

Answer 54

Fertiliser dissolves in soil water

Question 55

What are mycorrhizae and how do they benefit many plants?

Answer 55

Fungi that live in close association with plant roots Increase water uptake

Question 56

How does hedge removal result in the removal of nitrogen-containing compounds?

Answer 56

Leaching of nitrates

Question 57

Why are leguminous plants important in succession?

Answer 57

Able to grow in nitrate poor soil It will provide more nitrate when it dies - these can be used by other species

Question 58

What happens to the energy reaching producers that is not converted to growth?

Answer 58

Lost to surroundings as heat Reflected off the plant

Question 59

Why would percentage energy transfer between producers and primary consumers be less than the transfer between primary consumers and secondary consumers?

Answer 59

Producers have cell walls Difficult to digest Much cannot be eaten

Question 60

What are 2 disadvantages of using biological pest control?

Answer 60

Risk of migration Slow to work May eat crop

Question 61

What is a way in which nitrogen in the air can be converted directly into nitrate ions?

Answer 61

Lightning

Question 62

Why might farmers grow plants containing root nodules on fields during periods when crop plants are not growing?

Answer 62

Nodules contain nitrogen-fixing bacteria Increase amount of nitrogen containing compounds, increases amount of nitrogen available for next crop to use

Question 63

What is one source of phosphate in a lake?

Answer 63

Fertilisers, detergents, sewage, faeces

Question 64

Explain how a change in the phosphate concentration in a lake may have resulted in a decrease in fish population? [6]

Answer 64

Increased phosphate causes algal bloom Plants cover surface, blocking light so plants underneath die - causes increase in decomposers Decomposers use up oxygen in respiration Plants unable to photosynthesise so less oxygen produced