Energy and ecosystems

Question 1

What are producers?

Answer 1

Plants
produce their own carbohydrates from carbon dioxide
the start of the food web

Question 2

Energy transfer between trophic levels

Answer 2

between each trophic level, most of the energy is lost due to respiration and excretion. The remaining energy is used to form the biomass.

Question 3

What are consumers?

Answer 3

heterotrophs that cannot synthesise their own energy
obtain chemical energy through eating

Question 4

Biomass

Answer 4

measured in terms of mass of carbon and dry mass of tissue per given area

Question 5

How is the dry mass of tissue estimated?

Answer 5

Sample of organism dried in oven below 100C (avoiding
combustion + loss of biomass)
sample reweighed at regular intervals
all water removed when mass constant

Question 6

Why is dry mass a representative measure of biomass?

Answer 6

Water content in tissues varies
heating until constant mass allows standardisation of measurements
for comparison

Question 7

Calorimetry

Answer 7

Laboratory method used to estimate chemical energy stored in dry biomass

Question 8

Calorimetry method

Answer 8

Sample of dry biomass is burnt
energy released used to heat known volume of water
change in temperature of water used to calculate chemical energy

Question 9

Gross primary production

Answer 9

the chemical energy stored in plant biomass, in a given area or volume
It is the total energy resulting from photosynthesis.

Question 10

Net primary production

Answer 10

The chemical energy stored in plant biomass taking into account the energy that will be lost due to respiration

Question 11

How to calculate net primary production?

Answer 11

NPP = GPP - R
R = respiratory losses to the environment

Question 12

How to calculate NPP in consumers?

Answer 12

N = I - (F + R)
I = chemical energy store in ingested food
F = chemical energy store in faeces / urine
R = respiratory losses

Question 13

units of productivity rates

Answer 13

kJ Ha-1 year-1
kJ is the unit for energy
Ha is the unit area

Question 14

Why is productivity measured per area?

Answer 14

Because environments vary in size
it standardizes the results so environments can be compared

Question 15

why is productivity measured per year?

Answer 15

More representative of productivity
takes into account effects of seasonal variation (temperature) on biomass
environments can be compared with a standardised amount of time

Question 16

Why is energy inefficient after the producer?

Answer 16

Respiratory loss - energy used for metabolism (active transport)
lost as heat
not all plant / animal eaten (bones)
some food undigested (faeces)

Question 17

Why is energy transfer inefficient from sun to producer?

Answer 17

Wrong wavelength of light - not absorbed by chlorophyll
light strikes nonphotosynthetic region (bark)
light reflected by clouds / dust
lost as heat

Question 18

Farming Practices to increases energy transfer for crops

Answer 18

Simplifying food webs to reduce energy / biomass:
herbicides kill weeks = less competition
fungicides reduce fungal infections = more energy used to create biomass
fertilisers such as nitrates to promote growth

Question 18

Farming practices to increase energy transfer for animals

Answer 18

Reducing respiratory losses (more energy to make biomass)
restrict movement
keep warm
slaughter animal when young (most energy used for growth)
selective breeding to produce breeds with higher growth rates

Question 19

saprobionts

Answer 19

Feed on remains of dead organisms and their waste products (faeces / urea) and break down organic molecules
secrete enzymes for extracellular digestion

Question 20

Mycorrhizae

Answer 20

Symbiotic relationship between fungi and roots of plants
fungi act as extensions of roots
increase surface area of system
- increasing rate of absorption
mutualistic relationship as plants supply fungi with carbohydrates

Question 21

Nitrogen cycle stages

Answer 21

Nitrogen fixation
nitrification
denitrification
ammonification

Question 22

Importance of nitrogen in organisms

Answer 22

Used to create:
amino acids / proteins
DNA
RNA
ATP

Question 23

nitrogen fixation

Answer 23

Nitrogen fixing bacteria break triple bond between two nitrogen atoms in nitrogen gas
fix this nitrogen into ammonium ions

Question 24

Nitrogen fixing bacteria

Answer 24

Fix nitrogen gas into ammonium ions
free living in soil
or form mutualistic relationship on root nodules of leguminous plants
give plants N in exchange for carbohydrates

Question 25

Nitrification

Answer 25

Ammonium ions in soil are oxidised to nitrite ions
nitrite ions are oxidised to nitrate ions by nitrifying bacteria

Question 26

denitrification

Answer 26

Returns nitrogen in compounds back into nitrogen gas in atmosphere by anaerobic denitrifying bacteria

Question 27

Phosphorus cycle

Answer 27

Phosphate ions in oceans and soil.
absorption = phosphate ions in plants
consumption = phosphate ions in animals
excretion = returned to ocean or soil
decomposition = phosphate ions from waste/remains
erosion = returned to oceans and soil
deposition = phosphate ions in rocks

Question 28

importance of phosphorus

Answer 28

Used to create:
DNA
RNA
ATP
phospholipid bilayers
RuBP / GP/ TP

Question 29

ammonification

Answer 29

Proteins / urea / DNA can be decomposed in dead matter and
waste by saprobionts
return ammonium ions to soil - saprobiotic nutrition

Question 30

Fertilisers

Answer 30

Replace nutrients (nitrates and phosphates) lost from an ecosystem’s nutrient cycle when crops are harvested or livestock removed
can be natural (manure) or artificial (inorganic chemicals)

Question 31

Natural fertilisers advantages

Answer 31

Cheaper than artificial fertilisers
often free if farmer has own animals - recycle manure
organic molecules have to be broken down first by saprobionts so leaching is less likely

Question 32

Artificial fertilisers advantages

Answer 32

Contain pure chemicals in exact proportions
more water-soluble, so more ions dissolve in water surrounding soil.
higher absorption

Question 33

Natural fertilisers disadvantages

Answer 33

Exact minerals and proportions cannot be controlled

Question 34

Artificial fertilisers disadvantages

Answer 34

High solubility means larger quantities can leach away with rain
= risking eutrophication
reduce species diversity as favour plants with higher growth rates e.g., nettles

Question 35

Leaching

Answer 35

When water-soluble compounds are washed away into rivers / ponds
for nitrogen fertilisers, this can lead to eutrophication

Question 36

eutrophication

Answer 36

When nitrates leached from fields stimulate growth of algae
algal bloom
can lead to death of aquatic organisms

Question 37

How does eutrophication lead to the death of aquatic organisms?

Answer 37

Algal bloom creates blanket surface of water blocking light so plants cannot photosynthesize and die
aerobic bacteria feed and respire on dead plant matter
eventually, aquatic organisms die due to lack of dissolved oxygen in water

Question 38

mutualistic relationships

Answer 38

A type of symbiotic relationship where all species involved benefit from their interactions

Question 39

role of saprobionts in the nitrogen cycle

Answer 39

They use enzymes to decompose proteins/DNA/RNA/urea
releasing ammonium ions