13 - Energy and Ecosystems

Question 1

producers

Answer 1

photosynthesising organisms

Question 2

consumers

Answer 2

organisms that obtain energy through the consumption of other organisms

Question 3

saprobionts

Answer 3

decomposing organisms

Question 4

biomass

Answer 4

total mass of living material in a particular area at a given time (measured in grams/squared metre OR grams/cubed metre)

Question 5

stages in a food chain/web are called

Answer 5

trophic levels

Question 6

calorimetry can be used to

Answer 6

estimate the chemical energy store in dry mass

Question 7

bomb calorimetry process

Answer 7

1. sample of dry material weighed
2. sample burnt in pure oxygen in sealed chamber (bomb)
3. bomb is surrounded by water bath
4. heat of combustion causes temperature rise in water
   calculated energy released from mass of burnt biomass

Question 8

most of the sun’s energy is not converted into organic matter because:

Answer 8

over 90% of sun’s energy is reflected into space by clouds and dust, or absorbed by the atmosphere
some wavelengths of light cannot be absorbed or used for photosynthesis
light may not fall on a chlorophyll molecule
rate of photosynthesis may be limited by several factors

Question 9

net primary production calculation (for producers)

Answer 9

NPP = GPP - R

GPP gross primary production
R respiratory losses

Question 10

biomass/energy decreases at each trophic level because:

Answer 10

some of the organism is not consumed, some of the organism is consumed but not digested so is excreted as faeces, dissipation of heat from respiration, energy is used to maintain body temp

Question 11

most food chains only have 4/5 trophic levels because

Answer 11

biomass decreases as trophic level increases, this means insufficient energy is available to support a large enough breeding population at higher trophic levels

Question 12

reasons plants need nitrogen and the nitrogen cycle

Answer 12

it is present in DNA, RNA, amino acids, ATP, chlorophyll and most vitamins
nitrogen gas is insoluble so cannot be absorbed by plant roots
nitrogen cycle is required to enable plants to absorb nitrogen

Question 13

ammonification

Answer 13

decomposition of urea, amino acids, proteins nucleic acids and vitamins by saprobionts produces ammonia
these become ammonium ions in the soil

Question 14

nitrification by nitrifying bacteria

Answer 14

ammonia is oxidised by nitrifying bacteria to nitrite (nitrate III) and then nitrate V
plant roots can absorb the nitrates

Question 15

nitrogen fixing by nitrogen fixing bacteria in root nodules

Answer 15

bacteria have a symbiotic relationship with root nodules, convert N2 in the soil to ammonia

Question 16

free living nitrogen fixing bacteria

Answer 16

convert nitrogen in soil to ammonia, get enegy from oxidising organic molecules

Question 17

denitrification (effect and where it commonly occurs)

Answer 17

denitrifying bacteria use nitrates as an energy source, convert them to N2
reduces the amount of nitrates in soil
occurs commonly in waterlogged soil (little O2)

Question 18

phosphorus cycle

Answer 18

1. phosphate ions exist in sedimentary rocks
2. sedimentary rocks under the ocean get brought up to the surface by geographical uplifting
3. weathering and erosion results in dissolved phosphate ions
4. dissolved ions absorbed from the soil by plant roots and are incorporated into biomass
5. animals feed on the plants so absorb phosphate
6. exces ions are excreted and accumulate as waste materials
7. death of plants and animals allow sapriobionts o decompose biomass
8. phosphate ions released into soil and water
9. phosphate ions are transported in rivers/streams to lakes and oceans where they form sedimentary rocks

Question 19

mycorrhizae

Answer 19

symbiotic associations between certain fungi and plant roots
act as an extension of plants root system and greatly increase SA of roots
increases absorption of water and minerals
fungi benefit by recieving organic substances

Question 20

natural (organic) fertilisers

Answer 20

dead and decaying remains of dead plants and animals, as well as animal wastes (eg. manure)

Question 21

artificial (inorganic) fertilisers

Answer 21

compounds that have been mined from rocks before being converted into different forms and combined

Question 22

leaching

Answer 22

rainwater dissolves soluble nutrients in soil (eg. nitrates)
these are carried deep into soil, eventually beyond reach of plant roots
leached nutrients enter watercourses such as stream which may drain into freshwater lakes

Question 23

process of eutrophication

Answer 23

1. leached nitrate ions enter lakes
2. causes nitrate concentration to increase, and the plants an dparticularly algae to grow rapidly
3. this is because nitrate concentration is no longer a limiting factor
4. algae grow on surface and prevent sunlight penetrating to plants beneath
5. these plants cannot photosynthesis and so die
   dead plants are decomposed by saprobionts which use the oxygen in the water to respire
6. oxygen concentration in the water falls and so aerobic organisms in the water die from lack of oxygen