Energy Transfer and Nutrient Cycle

Question 1

Define biomass

Answer 1

Chemical energy stored in plants

Question 2

Define dry mass and outline how you measure it

Answer 2

• Mass of the organism w/ water removed
• Sample of organism is dried in oven. Sample is weighed at regular intervals. Once mass is constant, water is fully removed
• Unit: kg m^-2
• Mass of C present usually takes 50% of dry mass

Question 3

Outline how you can estimate the amount of chemical energy stored in biomass

Answer 3

• Sample of dry biomass is burnt + energy released is used to heat known vol of water (calorimeter)
• Change in temp of water is used to calculate chemical energy of dry mass

Question 4

Define gross primary production (GPP)

Answer 4

Total amount of chemical energy converted from light energy by plants

Question 5

Define respiratory loss (R)

Answer 5

50% of GPP is lost to env as heat when plants respire

Question 6

Define net primary production (NPP)

Answer 6

• Energy available to plant for growth + reproduction
• Energy available to organisms at next stage of food chain

Question 7

What is it called when primary production is expressed as a rate?

Answer 7

Primary productivity

Question 8

Net primary production equation

Answer 8

NPP = GPP - Respiratory loss

Question 9

What percentage of chemical energy stored in consumers’ food is not transferred to the next trophic level?

Answer 9

90% of total available energy is lost

Question 10

Give examples of how energy is lost

Answer 10

• Not all the food is eaten eg. bones
• Egested as faeces
• Respiration
• Excretion of urine

Question 11

Net production of consumer equation

Answer 11

N = I - (F+R)

• N = Net production
• I = chem energy in ingested food
• F = chem energy lost in faces + urine
• R = energy lost during respiration

Question 12

What does food chains and food webs show

Answer 12

• How energy is transferred through an ecosystem
• Food chain: simple lines, each stage = trophic level
• Food web: Lots of food chains that overlap

Question 13

Define decomposers

Answer 13

Break down dead or undigested material, allowing nutrients to be recycled

Question 14

Outline how farmers simplify food webs to reduce energy loss to non-humans

Answer 14

• Reduce pests using chemical pesticides:
• Insecticides kill insects
• Herbicides kill weeds removing direct competion
• Biological agents also reduce no. pests:
• Paracites kill insect or reduce ability to function
• Pathogenic bacteria + viruses

Question 15

Outline how farmers reduce respiratory losses w/i humanfood chain

Answer 15

• Controlling conditions so energy is used for growth + less lost in respiration:
• Movement is restricted
• Indoors + kept warm so less energy is lost by generating body heat

Question 16

Define a natural ecosystem

Answer 16

Ecosystem that hasn’t been changed by human activity

Question 17

Define saprobionts and outline what they do

Answer 17

• Feed on remains of dead plants and animals and on their waste products
• Secrete enzymes + digest food externally, then absorb nutrients they need - extracellular digestion

Question 18

Outline how fungi form symbiotic relationships (mycorrhizae) w/ roots of plants

Answer 18

• Fungi made up of long, thin strands called hypae, which connect to plant’s roots
• Hypae inc SA of plant’s root system, helping plant to absorb ions from soil, also inc uptake of water
• In turn fungi obtain organic compound from plant

Question 19

Why do plants and animals need nitrogen?

Answer 19

To make protein and nucleic acids

Question 20

What are the 4 different processes in the nitrogen cycle?

Answer 20

• Nitrogen fixation
• Ammonification
• Nitrification
• Denitrification

Question 21

Outline what happens during nitrogen fixation

Answer 21

• N gas from atm is turned into nitrogen-containing bacteria
• Carried out by bacteria (rhizobium) which turn N into ammonia, going on to form ammonium ions that can be used by plants
• Rhizobium: found inside root nodules of leguminous plants
• Form mutualistic releationship w/ plants: provide plants w/ N compounds + plants provide carbs

Question 22

Outline what happens during ammonification

Answer 22

• N compounds from dead organism are turned into ammonia by saprobionts, forming ammonium ions
• Animal waste (faeces + urine) also contains N compounds + so go through the same process

Question 23

Outline what happens during nitrification

Answer 23

• Ammonium ions in soil change into nitrogen compounds that can be used by plants
• Nitrifying bacteria change ammonium ions into nitrites
• Other nitrifying bacteria change nitrites to nitrates

Question 24

Outline what happens during denitrification

Answer 24

• Nitrates in soil are converted into N gas by denitrifying bacteria - use nitrates for respiration
• Happens under anaerobic respiration eg. waterlogged soil

Question 25

Why do plants and animals need phosphorus?

Answer 25

To make phospholipids, DNA and ATP

Question 26

Outline the phosphorus cycle

Answer 26

• Phosphate ions in rocks are released in soil by weathering
• Ions taken in by plants through roots. Mycorrhizae inc rate ions can be assimilated (absorbed + used to make complex ions)
• Ions transferred through food chain
• Lost from animals in waste
• When plants + animals die, saprobionts break down organic compound, releasing ions into soil for assimilation by plants. Also release in urine + faeces
• Weathering of rocks release ions in seas, lakes + rivers - taken in by aquatic producers (algae) + passed to birds
• Waste product of sea bird (guano) contains high proportion of ions + return to soil - natural fertilisers

Question 27

Describe how mineral ions are lost from the env

Answer 27

• Crops take in minerals to make new tissue, when harvested they’re removed from field - decomposers unable to return minerals to soil
• Animals that eat the grass and take in the nutrients are removed from land - unable to replace nutrients through remains or waste

Question 28

Why are fertilisers added to soils?

Answer 28

Replace lost nutrients, more energy from ecosystem used for growth, inc efficiency of energy transfer

Question 29

What are artificial fertilisers?

Answer 29

• Inorganic
• Contain pure chemicals as powders/pellets

Question 30

What are natural fertilisers?

Answer 30

• Organic matter
• Manure, composted veg, crop residue + sewage sludge

Question 31

Describe the process of leaching when using fertilisers

Answer 31

• When water soluble compounds in soil are washed away into ponds/rivers
• Can lead to eutrophication
• More likely to occur if fertiliser applied before heavy rainfall
• Inorganic fertilisers: relatively soluble, excess minerals not used up immediately more likely to leach
• Organic fertilisers: organic molecules need to be decomposed before being absorbed so more controlled + less leaching
• Phosphate less soluble than nitrates so less leaching

Question 32

Nitrate from fertiliser applied to crops may enter ponds and lakes. Explain how nitrate may cause the death of fish in fresh water (5)

Answer 32

• Stimulate rapid growth of algae
• Block light reaching plants below
• Plants die bc unable to phototsynthesise
• Saprobionts feed on dead plant matter, inc no. bacteria reduce O₂ conc in water by carrying out aerobic respiration
• Fish die bc not enough oxygen to respire

Question 33

Upwelling often results in high primary productivity in coastal waters.
Explain why some of the most productive fishing areas are found in coastal waters (2)

Answer 33

• Nutrients used by algae/plants for growth
• More food = fish produce more

Question 34

Describe the role of microorganisms in producing nitrates from the remains of dead organisms (3)

Answer 34

• Saprobionts break down remains into ammonia
• Ammonia/ammonium ions into nitrite then into nitrate
• By nitrifying bacteria

Question 35

Denitrification requires anaerobic conditions. Ploughing aerates the soil. Explain how ploughing would affect the fertility of the soil (2)

Answer 35

• Fertility inc bc more nitrates are formed
• Less/no denitrification