Energy Transfer And Nutrient Cycles

Question 1

How do Plants Photosynthesise and Produce Biomass, demonstrating the food chain?

Answer 1

Some organisms get energy from Sun, others get it from other organisms.
- An ecosystem includes all organisms living in a particular area
- and all non-living (abiotic) conditions
-
- In all ecosystems, there are producers - organisms that make own food, e.g. through photosynthesis
- In photosynthesis plants use sun energy and CO2
> (from atmosphere in land-based ecosystems,
> or dissolved in water in aquatic ecosystems)
to make glucose and other sugars

• Some of sugars produced are used in respiration; releases energy for growth.
• rest of glucose makes other biological molecules, eg cellulose
• The biological molecules make up plant’s biomass
  > mass of living material; the chemical energy stored in the plant.
• Energys transferred through living organisms of an ecosystem
• e.g. producers eaten by primary consumers.
  -. This is a food chain

Question 2

Hows Biomass Measured as Dry Mass or Using a Calorimeter

Answer 2

• Biomass can be measured in terms of the mass of carbon
• an organism contains or the dry mass of its tissue per unit area.
  > water content of living tissue varies, > so dry mass’ a measure of biomass

..
1) Dry mass is mass of organism w the water removed.

2) To measure dry mass, a sample of organism is dried, in oven at low temp
- sample’s weighed at regular intervals (e.g. every day).
- Once mass becomes constant, all the water has been removed.

3) If needed, result from sample can be scaled up to give
- dry mass (biomass) of total pop
- or the area being investigated.
- unit for dry mass = kg m-2.

• can estimate amt of chemical energy stored in biomass
• by burning biomass in calorimeter.
• ## The amt of heat given off tells you how much energys in it (J)1) A sample of dry biomass is burnt; energy released is used to heat a known volume of water.
  2) The change in water temp calculates chemical energy of dry biomass.

Question 3

How are GPP and NPP described as Chemical Energy Stores

Answer 3

• Gross primary production (GPP)
• the total of chem. energy converted from light by plants in a given area.
  -
• Approx 50% of gross primary production is lost to environment
• ## as heat when plants respire. This is called respiratory loss (R).
• remaining chemical energy is net primary production (NPP).
• NPP = GPP - R.
• The NPP is energy available to plant for growth and reproduction
• this energys stored in biomass.
• is also the energy available to organisms at next trophic level
• includes herbivores / decomposers.
• Often primary production is expressed as a rate
  — i.e. total of chemical energy/ biomass in a given area, in given time.
  — kj ha- year- (kj per hectare per year) .

When primary production is expressed as a rate,
it is called primary productivity.

Question 4

Why isnt all chemical energy stored in consumers food transferred to the next trophic level

Answer 4

Consumers also store chemical energy in their biomass.
- get energy ingesting plant material, or animals that ate plant material.
- However, not all chemical energy stored in consumers’ foods transferred to next trophic level
— around 90% of total available energy is lost in various ways.
—
- not all of the food is eaten (plant roots, bones) so energy contained is not taken in.
-
- Some are indigestible, so are egested as faeces.
- The chemical energy stored in these parts is so lost to the environment.
-
- Some energys lost to environment by respiration/excretion of urine.

..

The energy left after is stored in biomass
>is available to next trophic level.
>This energy is the consumers’ net production.

Question 5

How to calculate net production for consumers 🟡
and to calculate efficiency of energy transfer between trophic levels 🟡

Answer 5

N = I - (F+R)
- N net production
- I chemical energy in ingested foods
- F chemical energy lost in excretion
- R energy lost through respiration

The net production of consumers can also be called secondary production
- (or secondary productivity expressed as a rate).
-
- You might also be asked to calculate how efficient energy transfer from one trophic level to another is:

(current trophic level)/(prior trophic level energy) x 100