energy & ecosystems

How do plants use the sugars from photosynthesis?

Primarily as respiratory substrates

To synthesise other biological molecules, e.g. cellulose

What process do plants synthesise sugars and what kind of biological molecules are produced from these sugars?

By photosynthesis

Can make polysaccharides like cellulose and starch, lipids, and proteins

What does the GPP primarily depend on?

The total chemical energy stored in plant biomass in a given area/volume in a given time

And it depends on photosynthesis

List the reasons why not all the energy is transferred from a herbivore primary consumer

• A herbivore does not eat all the producer

• Some of the parts of the producer and are in digestible

• Some energy is lost through excretion

What is arable farming?

Growing crops such as wheat, barley oats, et cetera

What is livestock farming?

Rearing animals, e.g. cows, sheep, chickens, pigs, et cetera

How do farmers reduce energy losses to non-human food chains?

Use pesticides to kill pests so less of the crop is eaten by pest meaning the yield is higher for harvest

Define biomass

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

What are the units for biomass?

• when an area is sampled gm-2

• When the volume e.g. pond is being sampled gm-3

How can the chemical energy store in dry biomass be estimated?

Using calorimetry

• Energy released equals =shc of water x volume of water x temp increase of water

Why is it preferable to use bomb calorimetry instead of simple calorimetry?

Reduces heat loss to surroundings

How could a student ensure that all water had been removed from a sample before weighing it?

Keep the sample and re-wait until the mass reading is constant

Define gross primary production (GPP)

The total chemical energy in plant biomass within a given volume or area

Define net primary productivity (NPP)

The total chemical energy available for plant growth plant reproduction and energy transfer to other tropic levels after respiratory losses

Give the mathematical relationship (equation) between GPP and NPP

NPP = GPP - R

(R is respiratory losses)

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

• most solar energy is absorbed by the atmosphere or reflected by the clouds

• Photosynthetic pigments cannot absorb some wavelengths of light

• Not all light falls directly on a chlorophyll molecule

• Energy loss as heat during respiration/photosynthesis

How can the net production of consumers be calculated?

N = I - (F +R)

I: chemical energy from ingested food

F: energy lost as species and urine

R: respiratory losses

Why does biomass decrease along food chain?

Some energy is lost in nitrogen waste like urine and faeces

Some of the organism is not consumed

Energy is lost to the surroundings as heat

Define primary and secondary productivity

The rate of primary or secondary production

Biomass in a specific area over a given time period for example kilojoules per ha per year

Outline some common farming practices used to increase the efficiency of energy transfer

• Exclusion of predators, so no energy is lost to other organisms in food webs

• Artificial heating to reduce energy loss to maintain constant body temperature

• Restriction of movement

• Feeding is controlled at the optimum

If the general equation for percentage efficiency

Explain why the length of food chain is limited?

• Energy is lost at each tropic level so there is insufficient energy to support a higher tropic level

What is a pyramid of biomass?

The diagram that shows the biomass at each tropic level

How do farmers reduce respiratory losses within human food chains?

• restrict movement of livestock so less energy used for muscle contraction

• keep animals in warmed environments so less energy used to maintain body temperature

• give animals antibiotics so less energy from animals expended onto immune system ‘fighting’ pathogens

• give animals concentrated food so less food is in digestible so less energy lost in egestion

• Slaughter animals while young because as animals get older do not grow as much so food they eat does not need to increase biomass

why does use of fertilisers increase productivity of crops?

increases amount of nutrients available to crops (eg nitrates, which are used for forming amino acids and proteins, phosphates and potassium)

so nutrient availability is no longer a limiting factor

what are the advantages of natural fertilisers like manure or compost?

nutrients are released more slowly (less likely to chase leaching)

wider range of micronutrients

improve structure of soil

what are the disadvantages of natural fertilisers?

can carry/contain pathogens or pests

cannot control contents

bulky so difficult to store/ transport/ apply (requires more heavy machinery)

what are some strengths of artificial fertilisers?

can control contents exactly

easier to store/ transport/ apply (bcs less bulky)

what are some disadvantages of artificial fertilisers?

can less to leaching because nutrients released more quickly

fewer micronutrients

what is leaching? and in what situations/ conditions might leaching be high?

• when chemicals drain ways through soil (often end up in bodies of water)

• more leaching caused by

  • more rainfall

  • too much fertiliser applied (so cannot all be absorbed by the plants)

describe the process of eutrophication

• increase in concentration of nitrates/ phosphates in water

• causes algal bloom

• blocks the light from reaching the plants beneath the surface

• plants beneath surface cannot photosynthesise so die

• so population on aerobic saprobiotic bacteria (decomposes) increases

• these bacteria respire aerobically, so higher biological oxygen demand

• causes oxygen levels in water to drop

• so aerobic organisms (eg fish and also aerobic bacteria) die

• allows populations of anaerobic bacteria to increase

• anaerobic bacteria produce toxins which make water putrid

at a certain point, using more fertiliser no longer increases crop yield. why?

a factor (limiting factor) unrelated to concentration of mineral ions limits rate of photosynthesis so rate of growth cannot increase any further

what are 2 environmental issues caused by the use of fertilisers

1. Leaching- nitrates dissolve in rainwater and ‘runoff’ into water sources

2. 2. Eutrophication- water source becomes putrid as a result of algal bloom

how can the risk of eutrophication be reduced?

• sewage treatment marshes on farms

• pumping nutrient-enriched sediment out of water

• using phosphate-free detergent