5. energy transfers

i am SCREAMING i hate knowt

give the eqn for the efficiency of biomass transfers between trophic levels by %:

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

describe and explain how leaves are adapted for photosynthesis:

• large SA - max light absorption

• thin - reduces diffusion distance for gases

• lots of chloroplasts in palisade cells - captures light efficiently

• stomata - allows gas exchange

• air spaces in spongy mesophyll - facilitates gas diffusion

• vascular bundles (xylem/phloem) - transports water and sugars

• transparent cuticle/epidermis - allows light through and reduces water loss

• leaf arrangement - minimises overlapping to capture more light

what is biomass?

measure of mass of carbon/dry mass of tissue per given area

what substance do plants used to synthesise organic compounds?

atmospheric/aquatic CO₂

what are sugars used for in plants?

• most used as respiratory substrates

• rest used to make other biological molecules which form the plant’s biomass

what can a calorimeter be used for?

to estimate the energy store in dry biomass

give 4 aspects of the setup of a calorimeter and explain their roles:

• water - high known SHC so chemical energy can be calculated from temp change

• stirrer - distributes heat energy evenly

• thermometer - measures temp changes

• insulated jacket - reduces heat loss/gain

what is gross primary production (GPP)?

total chemical energy store or biomass produced by plants/producers through photosynthesis in a given area/volume

what is net primary production (NPP)?

energy/biomass that remains after plants have used some for respiration

what is the eqn for net primary production?

NPP = GPP - R (where R = respiratory losses)

what is the net primary production available for?

• plant growth

• reproduction

• other trophic level consumers e.g. herbivores and decomposers

what are the units for biomass measurement?

kg / m²

which process increases gross primary production?

photosynthesis

what is the net production of consumers?

the energy/biomass available to consumers after accounting for energy losses due to respiration, excretion and egestion

give the eqn for the net production of consumers:

N = I - (F + R), where:

• I = chemical energy store in ingested food

• F = chemical energy lost to environment in faeces and urine

• R = respiratory losses to the environment

how can the yield of a plant be measured? how would this occur in practice:

calculate dry mass of plant:

• heat at 100^oC as this would evaporate water and not burn the material

• weigh at intervals and heat until weighings become constant

why is calculating the dry mass of a plant useful?

• dry mass measures/determines increase in biological/organic material

• water content varies

what is productivity?

the measure of biomass in a given area in a given time e.g. kJ ha^-1 year^-1

name and define the two types of productivity:

• primary productivity - rate of primary production by green plants

• secondary productivity - rate of secondary production by consumers

give 3 reasons why not all the light energy falling on producers is used in photosynthesis:

• reflected

• misses chlorophyll

• wrong wavelength

give 3 reasons for the low efficiency of energy transfer from secondary consumers to tertiary consumers in an ecosystem:

• heat loss from respiration

• faeces

• excretion i.e. urine

what is the difference between egestion and excretion?

• egestion involves the removal of undigested food from the body i.e. faeces

• excretion involves the removal of waste products e.g. CO₂, urea, sweat i.e. urine

freshwater marshes have one of the highest rates of GPP and NPP of all ecosystems.

carbon use efficiency (CUE) is the ratio of NPP:GPP. freshwater marshes have a high CUE.

use your knowledge of NPP to explain why freshwater marshes have a high CUE and the advantage of this - do not refer to abiotic factors in your answer (2)

• low respiration (due to anaerobic conditions)

• more growth/biomass/colonisation

a student investigated the growth rate of a freshwater marsh plant.

the growth rate (R) of a plant can be determined using this eqn (see image)

the student used to eqn, but substituted height for biomass - state the assumption the student has made and suggest why this assumption might not be valid (2)

• assumed height of the plant is proportional to its biomass

• plants may put biomass into other aspects of growth e.g. root growth

ethanol can be produced from cellulose by anaerobic R of cellulose-based biomass by microorganisms. the cellulose is pre-treated by adding cellulose-digesting enzymes before it is used in anaerobic R - suggest why pre-treatment is necessary (3)

any 3 from:

• microorganisms don’t have cellulose digesting enzymes

• cellulose is a polysaccharide

• cellulose is insoluble

• glycosidic bonds in cellulose must be hydrolysed into beta-glucose

• glucose used in P

give 4 farming practices which increase GPP/NPP:

• pesticides - insecticides and herbicides

• biological agents - parasites and pathogenic bacteria/viruses

• integrated systems (pesticides and biological agents)

• keeping animals in pens

explain how using pesticides increases GPP/NPP:

• killing of pests simplifies food web

• insecticides - kill insect pests so less biomass lost from crops ∴ NPP greater

• herbicides - kill weeds, removing direct competition for solar energy and removes insect pests’ habitat/food source

explain how biological agents increase GPP/NPP:

• reduces no. of pests so simplifies food web

• crops lose less energy and biomass, increasing efficiency of energy transfer to humans

• parasites - live in/lay eggs on pest insect, killing it/reducing its ability to function

• pathogenic bacteria/viruses also kill pests e.g. by secreting toxins

explain how integrated systems increase GPP/NPP:

• combination of pesticides and biological agents

• has greater effect on reducing pest numbers, further increasing NPP

explain how keeping animals in pens increases GPP/NPP:

• restricts movement and increases warmth (indoors) - decreases rate of respiration ∴ less energy wasted via movement/thermoregulation

• increases biomass production and chemical energy storage, further increasing NPP and efficiency of energy transfer to humans

• BUT ethical concerns - may cause distress to animals as they cannot exhibit natural behaviour

describe and explain the process of eutrophication:

1. soluble nutrients e.g. nitrates/phosphates washed out of soil, into water

2. increased nitrates/phosphates increase plant growth, causing algal bloom

3. plants cover surface and lock out light, meaning that aquatic plants cannot photosynthesise, causing them to die

4. death of aquatic plants initiates increase in saprobionts which decompose plants and respire aerobically, using up oxygen

5. less oxygen is available to aquatic animals, so they are unable to respire and die

what is leaching?

the process in which water soluble compounds e.g. fertilisers are lost from soil and washed off into bodies of water

give 2 factors which make leaching more likely:

• fertiliser applied just before heavy rainfall

• inorganic ions in artificial fertilisers - soluble so more likely to leach if not immediately used

give 2 factors which make leaching less likely:

• N/P in organic fertilisers less likely to leach as contained in organic compounds, making their release into soil more controlled

• phosphates less soluble than nitrates so leaching less likely

compare natural and artificial fertilisers:

how does productivity differ between natural and artificial ecosystems?

• relatively low in natural ecosystems

• increases in agricultural ecosystems due to additional energy input and exclusion of other species via pesticides/herbicides, reducing competition for abiotic factors

compare and contrast natural and agricultural ecosystems:

methane is produced by anaerobic microorganisms in the soil. the scientists found that rice fiels that are not flooded do not produce large amounts of methane - suggest why (2)

• rice fields that are not flooded have more aerobic conditions

• not flooded so fewer active anaerobic microorganisms

explain why the mass of crop produced stays the same in both fields when more than 40kg of fertiliser is added (2)

• NO₃^- no longer limiting

• another element is limiting growth

in the previous year, field A had been used for grazing cattle. field B had been used to grow the same crop as this year. when no fertiliser was added, the mass of crop from field A was higher than from field B - explain this difference (2)

• cattle excreted/produced faeces

• field B - crops used minerals/nutrients last year

give 6 phosphorous containing compounds:

• DNA

• ATP

• RNA (mRNA, rRNA, tRNA)

• phospholipids

• NADP

• triose phosphate

what is weathering?

the breakdown of rocks by wind, water or biological activity, releasing phosphate into soil and water, making it available for producers

what is deposition?

the process where particles, including phosphates, settle out of water and accumulate in layers

what is erosion?

the breakdown of rock/soil particles, often containing phosphate, by wind/water/ice

what is sedimentation?

the buildup of layers of particles, like phosphate-rich sediments, at the bottom of bodies of water

what is run-off?

water flowing over land that carries dissolved phosphates into rivers/lakes/oceans

what is guano?

nutrient-rich bird droppings that add phosphate to soils when they decompose

what is the main store of phosphorous?

mainly found as a phosphate ion, in mineral form in sedimentary rock

describe the phosphorous cycle:

• phosphates in rocks are released into the soil and the sea through weathering, erosion and sedimentation

• saprobionts secrete extracellular digestive enzymes onto the dead and waste matter, hydrolysing cell tissues into smaller molecules

• PO₄^3- ions are released into the soil and assimilated by root network of plants

• PO₄^3- ions absorbed by aquatic producers including algae before being passed along the food chain to zooplankton and fish and into seabirds

label this diagram!

1. absorption

2. sedimentation

3. erosion and fertiliser use

4. deposition

5. erosion

6. excretion

7. excretion and decomposition

8. consumption

what are mycorrhizae? what type of relationship do they form with a plant?

• beneficial fungi growing in association with plant roots

• form a mutualistic relationship with plant

how is mycorrhizae beneficial towards plant growth?

• fungi increase SA for water and mineral absorption

• mycorrhizae acts like a sponge so holds water and minerals around the roots

• ∴ makes plants more drought resistant and able to take up more inorganic ions

• → enables plants to take up more relatively scarce ions e.g. PO₄^3- ions, improving plant growth

what do the mycorrhizae fungi receive in return as part of their mutualistic relationship with a plant?

carbon and sugar

give 5 examples of nitrogen containing molecules:

• amino acids

• DNA

• RNA

• ATP

• ADP

what is the significance of the N₂ cycle?

shows how different microorganisms are needed to convert N₂ gas into nitrogen-containing compounds that can be absorbed by plants and animals

give 3 conditions required for decomposition:

• warm temperature

• moisture

• oxygen

what is a detritivore? give 4 examples:

• organism that ingests/digests dead/decaying organic matter internally

• e.g. worms, millipedes, woodlice, slugs

what is a saprobiont? give an example:

• microorganism which secretes enzymes to decompose N containing compounds externally and absorbs simpler molecules

• e.g. microbes, primarily bacteria and fungi

give the stages of the nitrogen cycle:

1. nitrogen fixation

2. ammonification

3. nitrification

4. denitrification

describe the process of nitrogen fixation:

• free living nitrogen-fixing bacteria fix N₂ → NH₃/NH₄⁺

• mutualistic nitrogen fixing bacteria (e.g. Rhizobium) in root nodules of leguminous plants fix N₂ into NH₃ which is converted into amino acids

• in turn, the plant provides the bacteria w/ carbohydrates

• abiotic processes - lightning, artificial fertilisers, Haber process - can also fix N₂

what is nitrogen-fixation?

the conversion of atmospheric nitrogen gas into nitrogen containing compounds like ammonia

describe the process of ammonification:

• death/excretion of living organisms releases nitrogen containing substances e.g. urea, proteins, nucleic acids, vitamins

• saprobionts decompose these into ammonium ions (NH₄⁺)

• NH₄⁺ can now be absorbed (AT through root hair cells) and assimilated by plants

what is ammonification?

conversion of organic N₂ containing compounds in dead organisms or waste into NH₃ or NH₄⁺ ions by saprobionts

describe the process of nitrification:

• nitrifying bacteria oxidise NH₄⁺ ions to nitrite ions - NO₂^-

• these are then oxidised again into nitrate ions - NO₃^-

• (most nitrogen taken up by plants is in the form of nitrate ions)

what is nitrification?

NH₃ and NH₄⁺ are oxidised to NO₂^- then NO₃^- which plants can absorb via AT and assimilate

what is denitrification?

the reduction of NO₃^- ions back into N₂ gas by anaerobic denitrifying bacteria

what conditions might allow denitrification to take place?

anaerobic conditions

how might excessive denitrification -vely impact plant growth? what farming techniques can prevent this?

• excessive denitrification may lead to stunted growth as prevents the plant from making proteins

• to prevent this: frequently aerate the soil, keeping conditions aerobic

freshwater marsh soils are normally waterlogged - this creates anaerobic conditions.

use your knowledge of the nitrogen cycle to suggest why these soils contain relatively high concentrations of ammonium compounds and low concentrations of nitrite ions and nitrate ions (2)

• less nitrification

• less oxidation of NH₄⁺ → NO₂^- → NO₃^-

• more denitrification

• so more NO₃^- reduced to N₂ gas

where does the light dependent reaction of photosynthesis occur and how is it adapted to do so?

thylakoid membrane - has photosynthetic pigments and carrier proteins

where does the light independent reaction take place and how is it adapted to do so?

stroma - contains enzymes for the LIR

name the 2 types of chlorophyll in photosynthesis - what light do they reflect/absorb?

reflect green light and absorb red light:

• chlorophyll a

• chlorophyll b

give the primary pigment in photosynthesis:

chlorophyll a

what are accessory pigments? give their function:

• pigments which absorb wavelengths of light that are not easily absorbed by chlorophyll i.e. more wavelengths absorbed

• not directly involved in LDR

• channel more captured light energy to chlorophyll so more e^- can be excited

give 3 examples of accessory pigments:

• chlorophyll b

(category of carotenoids - reflect orange/yellow light and absorb blue light):

• carotene

• xanthophyll

what is the reaction centre?

chlorophyll (primary pigment) surrounded by a range of other proteins

what is the light harvesting system?

• reaction centre is surrounded by accessory pigments and proteins

• these accessory pigments and proteins = light harvesting system

what is a photosystem?

the reaction centre and light harvesting system (i.e. chlorophyll a and proteins surrounded by accessory pigments and proteins)

give the 2 photosystems present in photosynthesis and the wavelengths of light they absorb:

• photosystem II - 700 nm (chlorophyll p700)

• photosystem I - 680 nm (chlorophyll p680)

why is photosynthesis important?

• the energy we rely on has been captured by photosynthesis from sunlight

• photosynthesis also produces the oxygen we breathe by releasing it from water molecules

• life depends on the continuous transfer of energy - in plants

give 8 adaptations of leaves:

• palisade cells have a large SA

• leaves arranged on plant to minimise overlapping

• palisade cells long and thing in a continuous later

• transparent cuticle and epidermis

• long

why do palisade cells have a large SA?

to absorb as much sunlight as possible

why are leaves arranged on the plant to minimise overlapping?

to avoiding shadowing of one leaf

why are palisade cells long and thin in a continuous layer?

so that sunlight is absorbed in the first few micrometres of the lead and for a short diffusion distance for gases

why is the cuticle and epidermis transparent?

to let light through the photosynthetic mesophyll cells beneath

why is the mesophyll long and narrow and has many chloroplasts?

for maximum light absorption

why are there many stomata?

so that all mesophyll cells are only a short diffusion pathway from a stomata increasing the rate of diffusion

why does the leaf have a network of xylem and phloem?

to bring water to leaf cells and carry sugars away

why are there many air spaces in lower mesophyll?

to ensure rapid diffusion in the gas phase of CO₂ and O₂

why are stomata open during the day and closed at night?

allows plants to optimise CO₂ uptake for P during the day and minimise water loss at night

define photosynthesis and give the simplified eqn:

• process of energy transferral in which some of the energy in light is conserved in the form of chemical bonds

• 6H₂O + 6CO₂ → C₆H₁₂O₆ + 6O₂

describe the structure and function of chloroplasts:

structure:

• double membrane

• contains thylakoids - folded membranes embedded w/ pigments

• fluid filled stroma contains enzymes for photosynthesis

• 70S ribosomes and own DNA

function: site of photosynthesis

describe the stages of the light independent reaction (Calvin cycle):

• CO₂ reacts w/ RuBP to form unstable 6C compound - catalysed by rubisco

• 6C compound splits into 2x GP molecules

• ATP and NADPH from LDR are used to reduce GP to triose phosphate

• some triose phosphate used to regenerate RuBP in the Calvin cycle, using ATP

• some triose phosphate converted to useful organic substances

which enzyme catalyses ADP + Pi → ATP?

ATP synthase

which enzyme catalyses ATP → ADP + Pi?

ATP hydrolase

discus the efficiency of the Calvin cycle:

low:

• one hexose sugar (e.g. glucose) is made by joining 2 molecules of TP

• 5/6 Cs used to regenerate RuBP

• so Calvin cycle needs to happen 6x to make 1 hexose sugar

how does lack of light cause the amount of radioactively labelled GP to increase? what caused the amount of radioactively labelled glucose to decrease after the light was switched off?

• ATP and NADPH not formed so GP is not being used to form RuBP

• glucose used in respiration / formation of starch/cellulose

between 0 and 300 secs, the conc of radioactive GP is constant - why?

RuBP combines w/ CO₂ to produce 2x GP

between 300 and 380 secs, the conc of radioactive RuBP increases - why?

• less used to combine w/ CO₂ 

• less used to form GP

why may the % of C in a leaf not reach 0?

any 2 from:

• some used to make cellulose/cell walls

• some converted into starch

• not all fixed/used in photosynthesis OR not enough RuBP

• some used to reform RuBP/some still in GP