Energy + Ecosystems

Question 1

What does an ecosystem in a particular area include?

Answer 1

• biotic (living) factors: e.g. organisms + their interactions
• abiotic (non-living) factors: e.g. T°C + rainfall

Question 2

What do all ecosystems depend on?

Answer 2

• primary producers

Question 3

What are (primary) producers?

Answer 3

• organisms able to make their own usable carbon compounds (e.g. glucose) using CO2 in atmo

Question 4

How does energy enter an ecosystem?

Answer 4

• through producers: e.g. plants convert sunlight to CPE stored in organic molecules from CO2 in atmo (terrestrial ecosystems) or CO2 dissolved in water (aquatic ecosystems) by photosynthesis

Question 5

What are e.g.s of products formed from photosynthesis?

Answer 5

• respiratory substrates (e.g. glucose)
• starch: ST energy storage molecule
• cellulose: structural component of plant cell walls
• lipids: LT energy storage molecule
• proteins: sugars combine w nitrates to make AAs = used to produce proteins

Question 6

What is biomass?

Answer 6

• total mass of living material in a specific area over a set period of time

Question 7

How can biomass be measured?

Answer 7

• dry mass/mass of C of organism/tissue in a given area

Question 8

What is dry mass?

Answer 8

• mass or organism/tissue once water has been removed

Question 9

What can be used to estimate the chemical energy stored in dry biomass?

Answer 9

• calorimetry

Question 10

Describe the method of how calorimetry can be used to estimate the chemical energy stored in dry biomass.

Answer 10

Find dry mass of plant sample:
- weight crucible w/o sample then place sample in crucible + place in oven
- remove + weigh crucible at regular intervals during drying
- once mass of crucible stops dec. + becomes constant, sample is fully dehydrated
- subtract original mass of crucible to find dry mass of sample

Find energy released by sample of plant biomass:
- use a calorimeter to burn dried sample which uses energy released to heat a known volume of water
- measure T°C change of water (used to estimate chemical energy stored in sample)
- energy measured in J or kJ

Question 11

What are the limitations of using calorimetry to estimate the chemical energy stored in dry biomass?

Answer 11

• can take a long time to fully dehydrate plant sample to find dry mass
• precise equipment (e.g. precise digital balance + thermometer) required
• more simple + basic calorimeter = less accurate estimate will be bc heat energy lost to surroundings

Question 12

What is Gross Primary Productivity (GPP)?

Answer 12

• chemical energy store in plant biomass, in a given area/volume, in a given time resulting from photosynthesis

Question 13

What is Net Primary Productivity (NPP)?

Answer 13

• chemical energy store, available to next trophic lvl in a food web (can be used to create new biomass), in plant biomass after energy lost from respiration (R)

Question 14

What is the equation for Net Primary Productivity (NPP)?

Answer 14

NPP = GPP - R

Question 15

What are the units for Gross Primary Productivity (GPP) + Net Primary Productivity (NPP)?

Answer 15

• kJ m^-2 yr^-1
• per unit area to standardise results: allows comparison of envi.s
• recorded per yr to account impact seasons have on rain, light + heat: provides annual avg to allow fair comparisons between envi.s

Question 16

What is a tropic level?

Answer 16

• position of an organism in a food chain, web or pyramid

Question 17

What is a food chain?

Answer 17

• linear sequence of organisms that show how energy + nutrients pass through an ecosystem

Question 18

What is a food web?

Answer 18

• network of food chains in an ecosystem that shows how energy + nutrients move between organisms

Question 19

What are consumers?

Answer 19

• organisms that obtain energy by eating other organisms bc it can’t make its own food

Question 20

What are decomposers?

Answer 20

• organisms that break down dead organic matter into small soluble food molecules that they absorb by secreting digestive enzymes
• also release nutrients back into ecosystem: essential for growth of plants + other producers

Question 21

How is energy transferred between organisms in an ecosystem?

Answer 21

• primary producers convert light energy into chemical energy, stored as biomass in biological molecules, by photosynthesis
• consumers (organisms in higher trophic lvls) ingest producers, transferring chemical energy in biomass of producers to biomass of consumers

Question 22

How is energy lost along a food chain (why isn’t all energy transferred to consumer)?

Answer 22

• not all biomass of food is eaten (e.g. roots of plants/bones of animals) so chemical energy in this biomass is lost to envi.
• consumers can’t digest 100% of food they ingest so chemical energy in biomass of faeces egested is lost to envi.
• chemical (heat) energy lost to envi. when consumers respire + during excretion of waste products

Question 23

How do you calculate the net production of consumers (N)?

Answer 23

N = I - (F+R)
- I: energy from ingested food
- F: energy lost to envi through faeces + urine
- R: energy lost from respiration

Question 24

How do you calculate the % (efficiency) of energy transfer from 1 trophic lvl to the next?

Answer 24

• % efficiency = (chemical energy in consumer / chemical energy in ingested food) x 100

Question 25

What strategies do farmers use to inc the yield of their crops or livestock?

Answer 25

• dec energy lost from crops to other organisms by removing pests
• dec energy lost from livestock through respiration by restricting their movement (pens) + keeping them warm (indoor + heated pens)

Question 26

How do you calculate % yield?

Answer 26

% yield = (actual yield / theoretical yield) x 100

Question 27

How can farmers remove pest species?

Answer 27

• using chemical pesticides: insecticides (chemicals that kill insect pests that eat + damage crops) + herbicides (chemicals that kill weeds that compete w crops for sunlight + water)
• using biological control: e.g. introducing a consumer of pest