energy and ecosystems

why are plants producers in a food web

bc they are able to produce their own carbohydrates (organic compounds) using co2 in atmosphere or water

describe how biomass produced in plants

during photosynthesis, plants make organic compounds from atmospheric/ aquatic co2

most sugars synthesised are used by the plant as respiratory substrates

rest used to make other groups of biological molecules (eg carbs/lipids/ proteins) → form biomass

how can biomass be measured

mass of carbon of dry mass of tissue per given area

how can chemical energy stored in dry biomass be estimated

using calometry

what is gross primary production (GPP)

chemical energy store in plant biomass

in a given area or volume, in a given time

it is total energy (transferred from light energy to chemical energy) from photosynthesis

what is net primary production (NPP)

chemical energy store in plant biomass after respiratory losses to the environment have been taken into account,

formula for NPP

NPP = GPP - R

net primary production = gross primary production - respiratory losses to environment

what does GPP and NPP only apply to

GPP and NPP only applies to producers like plants, not animals

formula for net production of consumers ( N )

N = I – (F+R)

net production of consumers = the chemical energy store in ingested food - (the chemical energy lost to the environment in faeces and urine + respiratory losses to environment)

reason for units in primary/ secondary productivity (rates of productivity)

kj - unit for energy

per hecta - per unit area - standardise results - enable environments to be compared - takes into acc diff environments vary in size

per year - takes into account the impact that seasons will have on rain, light and heat - annual average allows fair comparison between environemtsn

formula for efficiency of energy transfer

% efficiency = energy or biomass available after transfer / energy or biomass available before transfer x 100

what is biomass

mass of living/ organic material measures in terms of mass of carbon or dry mass of tissue per given area

Farming cattle for humans to eat is less efficient than farming crops because of energy transfer.

Explain why.

1. Energy lost between/at trophic/feeding levels;

Accept description of trophic levels e.g., food chain.

2. Energy lost via respiration/excretion/faeces;

Accept energy lost via heat/metabolism/food not

eaten/digested/muscle

contraction/movement/maintaining temperature.

Reject energy used in respiration.

Reject energy produced/generated.

Suggest appropriate units for gross productivity.

Unit of energy /or mass, per area, per year.

Explain the decrease in gross productivity as the woodland matures.

Less light / more shading / more competition for light;

Neutral: references to animals

2. Reduced photosynthesis.

Use the information in the graph and your knowledge of net productivity to explain

why biomass shows little increase after 100 years.

After 100 years, biomass shows little increase because net productivity becomes very low. This is because photosynthesis decreases so gross productivity decreases and respiration increases, so more energy produced is used up rather than stored as new biomass.

1. Net productivity = gross productivity minus respiratory loss;

2. Decrease in gross productivity / photosynthesis / increase in respiration

Suggest one reason for conserving woodlands.

1. Conserving / protecting habitats / niches;

2. Conserving / protecting (endangered) species / maintains / increases

(bio) diversity;

3. Reduces global warming / greenhouse effect / climate change / remove /

take up carbon dioxide;

4. Source of medicines / chemicals / wood;

5. Reduces erosion / eutrophication.

Accept: tourism / aesthetics / named recreational activity

Explain why determination of dry mass was an appropriate method to use in this

investigation.

1. Dry mass measures / determines increase in biological / organic

material;

2. Water content varies.

Suggest what the scientist should do to ensure that he has removed all the

water from the sample.

1. Weigh and heat;

Accept ‘heat until sample remains the same mass’

for 2 marks.

Ignore temperature.

2. (Until) mass is constant;

Accept weight for mass.

Record mas and reheat until a constant mass recorded

Explain why an increase in shoot biomass can be taken as a measurement of net primary productivity.

1. Represents dry mass / mass of carbon;

2. Represents gross production minus respiratory losses;

Accept: NPP = GPP −R.

Accept: Chemical energy minus respiratory

losses.

1 and 2. Chemical energy store minus respiratory

losses - 2 marks