5b (energy transfer/ nutrient cycles)

Question 1

what is an ecosystem?

Answer 1

all the organisms living in a particular area and all the abiotic conditions

Question 2

what is a producer?

Answer 2

an organism that makes its own food

Question 3

what is biomass?

Answer 3

the mass of living material (an organisms biomass includes bio mols such as cellulose etc)
can be thought of as chemical energy stored in the plant

Question 4

what is a food chain

Answer 4

the way energy is transferred through living organisms- primary consumers eating producers who are eaten by secondary consumers etc

Question 5

how can you measure biomass?

Answer 5

in terms of dry mass (mass of organism w water removed) of tissue per unit area
dry mass used as water content of organisms varies
weigh sample at reg intervals until mass becomes constant
scale up dry mass of sample, can scale up to whole pop
typical units- kgm-2

Question 6

what is calorimetry?

Answer 6

way to estimate amount of chem energy stored in biomass
heat given off= how much energy is in it
sample is burnt and energy released is used to heat known vol of water
change in temp is used to calculate chem energy of biomass

Question 7

roles of diff parts of the calorimeter
(water, thermometer, stirer, ignition wires, oxygen atmosphere, air space)

Answer 7

water- to measure temp change (know SHC and vol)
thermometer- to measure temp change of water
stirer- to keep temp consistent throughout (distribute)
ignition wires- to create sparks/ start the reaction
oxygen atmosphere- for complete combustion
air space- insulation

Question 8

what is gross primary production?
what is respiratory loss?
what is net primary production?

Answer 8

total amount of chem energy converted from light energy by plants in a given area

the aprox 50% of gpp that is lost as heat in resp

the remaining energy after (available for growth, repair, and at next trophic level)

Question 9

what is primary prductivity?

Answer 9

when primary production is expressed as a rate
KJ ha-1 yr-1

Question 10

why isnt all of the chem energy stored in consumers passed onto next trophic level?

Answer 10

90% lost in various ways
- not all the food is eaten eg roots, bones
- some parts are indigestible so excreted
- some energy lost to environment through resp/ excretion of urine

Question 11

how can you calculate the net production of consumers (secondary production)?

Answer 11

N= I- (F+R)
N= net production
I= chemical energy ingested in food
F= chemical energy lost in faeces and urine
R= energy lost through resp

Question 12

how can you calculate efficiency of energy transfers?

Answer 12

% efficiency = (net production of trophic level / net production of previous trophic level) x 100

Question 13

what happens to efficiency as you move up a food chain?

Answer 13

more efficient energy transfers
plants contain more indigestible matter than consumers

Question 14

what is a food chain/ web?

Answer 14

shows how energy is transferred through an ecosystem

Question 15

how can farmers increase efficiency / NPP and NP of crops and livestock?

Answer 15

• energy lost to other organisms can be reduced by simplifying food webs
• energy lost through resp of livestock can be reduced

Question 16

how can we simplify food webs?
why do we do this?

Answer 16

by removing food chains that dont involve humans
pests reduce amount of energy available for crop growth so NPP decreases so less energy for humans. simplifying food chains reduced energy losses and NPP increases

Question 17

3 ways pests can be reduced

Answer 17

• using chemical pesticides (insecticides and herbicides)
• using biological agents (parasites, pathogenic bacteria and viruses) that reduce no of pests so crops lose less energy
• can use integrated systems that combine both

Question 18

how can farmers reduce respiratory losses?

Answer 18

by controlling conditions that livestock live in so more energy used for growth and less lost through resp
more biomass is produced and more chem energy stored so increased net production and efficiency of transfer to humans

more food, less time, less cost, but ethical issues for animals

Question 19

what is a natural ecosystem?

Answer 19

one that hasnt been changed by human activity
nutrients such as nitrogen and phosphorus are recycled through food webs

Question 20

what are saprobionts?
what do they do?

Answer 20

a type of decomposer, microorganisms eg bacteria and fungi

• feed on dead plant/ animals remains and waste products- break them down allowing important chemical elements to be recycled
• secrete enzymes and digest food externally then absorb nutrients needed (extracellular digestion). this breaks organic mols in inorganic ions

Question 21

what is saprobiotic nutrition?

Answer 21

obtaining nutrients from dead organic matter and animal waste using extracellular digestion

Question 22

what are mycorrhizae?

Answer 22

relationships between fungi and roots of plants
fungi are made of long thin strands (hypae) that connect to plant roots and increase SA helping absorb scarce ions from soil
also increase water uptake
in turn, fungi obtain organic compounds eg glucose from the plant

Question 23

what is nitrogen used for plants and animals?

Answer 23

making proteins and nucleic acids

Question 24

what is the nitrogen cycle?

Answer 24

78% of atmosphere is nitrogen gas but plants plants and animals cant use in that form- bacteria convert it into nitrogen- containing compounds first

nitrogen cycle shows how N is converted into useable form and passed between organisms in living and non-living environment

Question 25

what are the 4 processes in the nitrogen cycle?

Answer 25

nitrogen- fixation
ammonification
nitrification
denitrification

Question 26

what is nitrogen fixation?

Answer 26

N gas in the atmosphere is turned into nitrogen-containing compounds by nitrogen-fixing bacteria which turn N -> ammonia -> ammonium ions in solution to be used by plant

rhizobium (type of N fixing bacteria) are found in root nodules and leguminous plants. form a mutualistic relationship w the plants- provide the plant w N compounds and plant provides them w carbohydrates

other nitrogen-fixing bacteria are found in soil

Question 27

what is ammonification?

Answer 27

N compounds from dead organisms and animal waste are turned into ammonia by saprobionts which goes onto form ammonium ions

Question 28

what is nitrification?

Answer 28

when ammonium ions in soil are changed into N compounds that can be used by plants
first nitrifying bacteria change ammonium ions into nitrites
then into nitrates

Question 29

what is denitrification?

Answer 29

nitrates in soil are converted into N gas by denitrifying bacteria- use nitrates in soil to carry out resp and produce N gas
happens in anaerobic conditions eg waterlogged
nitrogen also gets into ecosystem by lightning or artificial fertilisers

Question 30

what do plants and animals need phosphorus for?

Answer 30

to make biological mols eg phospholipids, DNA, ATP

Question 31

what is the phosphorus cycle?

Answer 31

shows how phosphorus is passed through an ecosystem

Question 32

where is phosphorus found?
what happens to this phosphorus?

Answer 32

in rocks and dissolved in oceans in form of phosphate ions
phosphate ions dissolved in water in soil can be assimilated (absorbed and used to make more complex mols) by plants and other producers

Question 33

describe the phosphorus cycle

Answer 33

• phosphate ions in rocks released to soil by weathering
• phosphate ions taken to plant through roots, mycorrhizae increase rate of phosphorus assimilation
• phosphate ions transferred through food chain as animals eat plants and are themselves eaten
• phosphate ions lost from animals in waste products
• organisms die, sapprobionts break down organic compounds, releasing phosphate ions into soil for assimilation by plants. microorganisms release phosphate ions from urine and faeces
• rock weathering releases phosphate ions into sea, lake, river and is taken up by aquatic producers eg algae and passed along food chain to birds
• watse produced by sea birds is called guano and contains high proportion of phosphate ions. guano returns signif amount of phosphate ions into soils and is often used as natural fertiliser

Question 34

how does loss of nutrients occur?

Answer 34

crops take in minerals from soil as they grow to build tissue. when theyre harvested and removed from field, mineral ions they contain arent returned to soil by decomposers

phosphates and nitrates lost when animals or animal products are moved from land (take in nutrients from field when eat, arent replaced through their remains if taken away)

Question 35

what are artificial fertilisers?

Answer 35

inorganic
contain pure chemicals as powders or pellets

Question 36

what are natural fertilisers?

Answer 36

organic matter
include manure, composted veg, crop residue and sewage sludge

Question 37

what are environmental issues of fertilisers?

Answer 37

more fertiliser added than needed/ able to be used
leads to leaching into waterways (water-soluble compounds in soil are washed away often into ponds/rivers)
leads to eutrophication

Question 38

when is leaching more likely to occur?

Answer 38

• if fertiliser is added just before heavy rainfall
• chemical fertilisers- inorganic ions in them are relatively soluble so excess minerals not used immediately are more likely to leach into waterways

Question 39

when is leaching less likely?

Answer 39

with natural fertilisers
nitrogen and phosphorus are still contained in organic molecules that need to be decomposed by microorganisms before they can be absorbed
means their release into soil is more controlled
leaching of phosphates less likely than leaching of nitrates because phosphates are less soluble in water

Question 40

other than leaching, why are fertilisers bad?

Answer 40

change balance of nutrients in soil- too much of one can cause death of crops

Question 41

what is eutrophication?

Answer 41

• mineral ions such as nitrates leached from fertilised fields stimulate rapid growth of algae in ponds and rivers
• large amounts of algae block light from reaching plants below
• plants die as they can’t photosynthesise enough
• saprobionts feed on dead plant matter so increased no of bacteria so reduced oxygen conc in water as bacteria carry out aerobic resp
• fish and other aquatic organisms die as not enough dissolved oxygen
• anaerobic bacteria decompose fish and relase hydrogen sulphide