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a2 biology > Energy and Ecosystems > Flashcards

Energy and Ecosystems Flashcards

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AP® Biology flashcards
1
Q

Organisms in an ecosystem rely on what?

A
  • a source of energy (primarily sunlight) - which is conserved as chemical energy by plants
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2
Q

What are respiratory substrates ?

A
  • organic substances which are oxidised during respiration to release energy inside cells e.g. glucose
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3
Q

What are the two uses of organic compounds produced in photosynthesis ?

A
  • Respiratory Substrates (e.g. glucose used by plant again in respiration)
  • Building other biological molecules e.g. cellulose
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4
Q

In any ecosystem, plants synthesise organic compounds from what?

A

(atmospheric, or aquatic) carbon dioxide

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5
Q

Organisms can be divided into what three groups and according to what?

A
  • producers, consumers and saprobionts

- according to how they obtain their nutrients and energy

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6
Q

What are producers?

A
  • photosynthetic organisms that manufacture (i.e. produce) organic substances using:
  • light energy, water, carbon dioxide and mineral ions
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7
Q

What are consumers?

A
  • organism that obtain their energy by consuming other organisms instead of using energy from sunlight directly
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8
Q

State and describe the three types of consumers?

A

primary consumer - those that directly eat producers (plants) because they’re the first in the chain of consumers
secondary consumer - those animals eating primary consumers for energy
tertiary consumer - animals eating primary secondary consumers for energy

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9
Q

Secondary and tertiary consumers are usually what?

A
  • predators but can also be scavengers or parasites
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10
Q

What are saprobionts (decomposers)?

A
  • organisms that break down complex materials in dead organisms into smaller ones
  • causing them to release minerals and elements in a form that can be used be absorbed by plants (so recycling)
  • majority of work carried out by bacteria and fungi
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11
Q

describe a food chain

A
  • feeding relationship where producers are eaten by primary consumers, PC eaten by SC and SC eaten by TC (tertiary consumers may be eaten by quaternary consumers)
  • each stage in chain is a trophic level (energy lost at each trophic level)
  • arrows in food chain represent direction of energy flow
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12
Q

describe the following terms:
1 herbivore
2 carnivore
3 omnivore

A

1 herbivore = an animal that eats plants (producers) and so is a primary consumer
2 carnivore = animal eats animals and may be a secondary or tertiary consumer
3 omnivore = animal eats plants and animals and so may be a PC, SC or a TC

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13
Q

what’s a food web?

A

all of the food chains in an ecosystem

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14
Q

what is biomass?

A

The mass of living material or the chemical energy stored

i.e. the biological molecules produced by photosynthesis that aren’t respired

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15
Q

What are the two ways in which biomass can be measured? Suggest the units for biomass

A

two ways:
Mass of carbon in a given area, per unit time
Dry mass of tissue in a given area, per unit time

units:
● when an area is being sampled: gm-2
● when a volume (e.g. a pond) is being
sampled: gm-3

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16
Q

what do the arrows on a food web mean?

A

the direction of energy flow

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17
Q

How can the chemical energy store in dry biomass be measured?

A

Calorimetry :
Burn sample of dry mass (in pure O2)
(energy released heats water)
Change in temperature of water can be used to calculate chemical energy in sample

Energy released = specific heat capacity of water x volume of water (cm3) x temperature increase of water.

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18
Q

How can the dry mass (biomass) of a tissue be found ?

A

Dry a sample in an oven at a low temperature

keep heating and weighing at regular intervals until constant mass

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19
Q

Why is dry mass used instead of wet mass, as a measure of biomass ?

A

water content of living tissue varies too much

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20
Q

Why is biomass measured over a particular period of time ?

A

Biomass changes over time e.g. trees when leaves are shed

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21
Q

suggest four reasons why most of the sun’s energy isn’t converted to organic matter by photosynthesis

A
  • reflects light (back to clouds/absorbed by atmosphere)
  • light is wrong wavelength
  • light misses chlorophyll
  • a factor might limit rate of photosynthesis e.g. low CO2 levels
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22
Q

what is gross primary production (GPP)?

A

total chemical energy stored in plant biomass, in a given area or volume, per unit time

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23
Q

What is net primary production (NPP)? (3 things)

A
  • the chemical energy store in plant biomass after respiratory losses to the environment have been taken into
    account

i.e.
Total chemical energy available for:
(1) plant growth, (2) plant reproduction and (3) energy transfer to other trophic levels after respiratory losses

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24
Q

What is the formula for NPP (Net primary production)?

A

NPP = GPP - R

Net primary production = gross primary production - respiratory losses

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25
Q

What is the difference between net primary production and net production?

A

Net primary production is plants

Net production is consumers

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26
Q

Give ways why not all chemical energy (i.e. biomass) is transferred to the next trophic level?

A
  1. Not all the food is eaten (i.e. roots and bones)
  2. Some is indigestible and egested as faeces
  3. Some is lost by excretion or urine
  4. Some is respired (organisms like mammals with higher body temps lose more energy to respiration as much energy is needed to maintain body temp when heat is constantly being lost to environment)
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27
Q

what is net production?

A

The energy in the consumer’s biomass available to the next trophic level

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28
Q

What is the formula for net production?

A 
N = I -(F + R)
N = net production 
I = chemical energy store of ingested food 
F = enery lost in faceces and urine 
R = energy lost in respiration
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29
Q

the relative inefficiency of energy transfer between trophic levels explains what three things?

A
  • most food chains have few (e.g. 4/5) trophic levels because insufficient energy available to support large enough breeding population at higher trophic levels
  • biomass is less at higher trophic levels
  • amount of energy available is less at each level as you move up a food chain
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30
Q

explain why most food chains rarely have more than four trophic levels

A
  • proportion of energy transferred at each trophic level is small (less than 20%)
  • after 4 trophic levels there’s insufficient energy to support large enough breeding population
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31
Q

how do you calculate the percentage efficiency of energy transfers?

A

energy available after the transfer/energy available before the transfer x100

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32
Q

Why is bomb calorimetry preferable to simple calorimetry?

A

Reduces heat loss to surroundings.

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33
Q

How could a student ensure that all water had been removed from a sample before weighing?

A

Heat the sample and reweigh it until the

mass reading is constant

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34
Q

Define primary and secondary productivity

A

● rate of primary or secondary
production
● biomass in a specific area over a given
time period e.g. kJ ha–1 year–1

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35
Q

rates of productivity are recorded using what units?

A

kJ ha-1 year-1

36
Q

describe the importance of kJ in kJ ha-1 year-1

as the unit for productivity

A

unit for energy, but these units also include per unit area and per year

37
Q

describe the importance of per hm (hectare) in ha-1 year-1 as the unit for productivity

A

recorded per unit area to standardise the results to enable environments to be compared, it takes into account that different environments will vary in size (1 hm2 = 10,000 m2)

38
Q

describe the importance of per year in ha-1 year-1 as the unit for productivity

A
  • to take into account the impact seasons will have on rain, light, and heat
  • provides an annual average to allow fair comparisons between environments
39
Q

what is primary productivity? what is secondary productivity?

A

primary productivity = rate energy
converted to organic substances by photosynthetic producers i.e. productivity of autotrophs
secondary productivity = rate consumers convert chemical energy of their food into their own biomass i.e. productivity of heterotrophs

40
Q

Why does the efficiency of energy transfer increase up a food chain?

A

Consumers contain less indigestible matter than plants

41
Q

How do farmers try to increase efficiency of energy transfer?

A
  1. Simplifying food webs

2. Reducing energy lost through respiration of livestock

42
Q

How do farmers simplify food webs?

A

Get rid of pests

  1. Insecticides
  2. Herbicides
  3. Parasites/pathogenic bacteria or viruses
43
Q

How do farmers reduce respiratory losses?

A
  1. Reduce movement (keep in pens)

2. Keep warm (keep indoors) - so less heat lost to atmosphere trying to maintain body temp

44
Q

What are the positives and negatives of increasing efficiency of food chains for farmers?

A

Greater rate of primary/secondary productivity
Lower cost

Ethical issues (distress or cause animals pain)

45
Q

contrast flow of energy through an ecosystem and flow of nutrients

A
  • flow of energy is linear i.e. in one direction, flow of nutrients is mostly cyclic
46
Q

What do saprobionts do?

A
  1. Secrete enzymes externally onto dead organisms/waste products
  2. Breaks down the biological molecules
  3. Absorb SOME of the nutrients
47
Q

Why are saprobionts important ?

A
  • they’re a type of decomposer and recycle important nutrients in ecosystems
48
Q

What is extracellular digestion?

A
  • enzymes secreted onto the food and it is digested externally

further explanation:

  • enzymes catalyze the digestion of the food into molecules small enough to be taken up by passive diffusion
  • e.g. fungi feed on their food by secreting digestive enzymes to digest their food externally, which they later absorb
49
Q

What do mycorrhizae do ?

A
  • fungi act like extensions and connect to plant roots and increase the surface area
  • this helps the plant absorb more ions (e.g. phosphate ions which are scarce) from the soil/ take up more water
50
Q

describe the relationship between plants and fungi

A
  • mutualistic
  • plant benefits from improved water and inorganic ion uptake while fungus receives organic compounds e.g. sugars and amino acids (from plant)
51
Q

What are mycorrhizae?

A
  • fungal associations between plant roots and beneficial fungi
52
Q

Why is nitrogen important in living organisms ?

A

DNA, RNA
ATP
Proteins (i.e. antibodies, enzymes, hormones, muscles)

53
Q

What are the stages of the nitrogen cycle ?

A
  1. Nitrogen fixation
  2. Ammonification
  3. Nitrification
  4. Denitrification
54
Q

why is nitrogen fixation necessary?

A
  • nitrogen in air can’t be used directly by plants (needs to be transformed in nitrogen fixation)
55
Q

Describe the process of nitrogen fixation

A

Nitrogen-fixing bacteria convert nitrogen into ammonia - forms ammonium ions which plants can use

56
Q

Describe the process of ammonification

A

Nitrogen compounds from dead organisms/waste products are converted to ammonia by saprobionts

57
Q

What is nitrification?

A

Ammonium ions in the soil are oxidised to nitrites (NO3-) and then to nitrates (NO2-) by nitrifying bacteria
(occurs mostly aerobically)

58
Q

What is denitrification?

A

Nitrates in the soil are converted to nitrogen gas by denitrifying bacteria (in anaerobic conditions e.g. waterlogged soil)

59
Q

Other than the nitrogen cycle, how can nitrogen get into ecosystems?

A 
Lightning (breaks strong bonds of nitrogen molceule)
Artificial fertilisers (Haber process)
60
Q

Outline some common farming practices used to increase the efficiency of energy transfer.

A

● Exclusion of predators: no energy lost to other organisms in food web.
● Artificial heating: reduce energy lost to maintain constant body temperature.
● Restriction of movement.
● Feeding is controlled at the optimum.

61
Q

Why is a pyramid of biomass preferable to a pyramid of numbers?

A

Shape of pyramid of numbers may be
skewed since a small number of
producers can support many consumers

62
Q

why and how do farmers avoid dentrification?

A
  • denitrifying bacteria are anaerobic
  • they convert nitrates in soil into nitrogen gas in atmosphere so losing nitrogen-containing compounds from soil
  • therefore farmers aerate soil to make sure there is oxygen to avoid denitrification.
63
Q

what do saprobionts convert urea/proteins in decomposed animals to?

A

ammonia therefore it is a form of ammonification

64
Q

describe the two kinds of bacteria in nitrogen fixation

A
  • one type of bacteria reduce gaseous nitrogen to ammonia, which can be used to manafacture AA
  • the other type of bacteria live in nodules on roots of plants; they obtain carboydrates from plants and the plant acquires amino acids from the bacteria (mutalistic)
65
Q

Why is phosphorus important to plants and animals?

A 
found in:
Phospholipids (cell membranes)
DNA/RNA
ATP
Therefore essential element for life
66
Q

How do phosphate ions initially enter ecosystems?

A

Phosphorous in rocks dissolves in oceans

67
Q

why are mycorrhizae beneficial for plant growth?

A
  1. the fungi increase the SA for water and mineral absorption
  2. the myocorrhizae acts like a sponge so holds water and minerals around the roots
    3 this makes plants more drought resistant and able to take up more inorganic ions
  • so improving uptake of scare ions like phosphate ions -

this is a MUTALISTIC relationship

68
Q

What are the stages of the phosphorus cycle ?

A
  1. Phosphate ions released into soil from rocks
  2. Plants taken up ions through roots
  3. Ions transferred through food chains and lost as waste/death
  4. Decomposition
69
Q

what is guano?

A
  • waste produced by sea birds which is very high in phosphate ions
70
Q

How are nutrients lost from ecosystems?

A

Harvested crops/animals are removed from fields

Mineral Ions not returned to the soil by decomposition of plants/waste by saprobionts

71
Q

how is the phosphorus cycle different to the nitrogen cycle?

A
  • phosphate ions mainly found in mineral form in sedimentary rocks rather than as a gas in the atmosphere like N2
72
Q

describe the phosphorus cycle in detail

A
  1. chemical weathering of rocks releases phosphate ions on land and these are washed into the soil by rain, ions are absorberd by plant roots by active transport and used to make ATP, phospholipids and nucleic acids
  2. primary consumers feed in laments and the biological molecules in their food are digested to smaller phosphate containing molecules like nucleotides. Phosphate ions may be present used to make ATP
  3. excess phosphate ions are excreted .
  4. when organism produces faeces, urine or dies the phosphorus containing substances are digested by saprobiotic bacteria. This releases the ions into the soil which are taken up by the plants
  5. Some phosphate ions produced by saprobiotic digestion are washed away into lakes and rivers and taken up by algae - algae are eaten by fish and so on
  6. when aquatic organisms die they sink to the bottom of the river/sea/lake where they decompose and the ions are trapped in their sediments.
  7. aquatic sediments form sedimentary rocks over long periods of time and eventually become exposed in land again.
  8. The cycle repeats itself
73
Q

what are fertilisers?

A
  • chemicals that contain nutrients e.g. nitrogen and phosphorus compounds
    can be:
  • natural (manure) consists of dead/decaying remains of plants and animals & their waste
  • artificial (inorganic chemicals) contain nitrogen, phosphorus and potassium
74
Q

why are fertlisers used?

A

to replace nitrate and phosphate ions lost when plants are harvested and removed from nutrient cycles as crops

75
Q

What are the advantages of natural fertilisers?

A

Cheap
Less likely to cause leaching
Increases humus levels in soil (humus has many nutrients that improves health of soil)

76
Q

What are the disadvantages of natural fertilisers?

A

May contain pathogens
Slow release of nutrients
Heavy machinery so may cause soil compaction (which reduces the size of pore space available for air and water)
Do not know exact composition/proportion of nutrients

77
Q

what are the advantages of artificial fertiliser?

A

Easy to store and handle
Exact composition/proportion of nutrients known
Light machinery so avoids soil compaction

78
Q

What are the disadvantages of artificial fertilisers?

A

Expensive
(can cause) Leaching
High concentrations can cause osmotic damage to plants

79
Q

explain the process of eutrophication

A
  • occurs when excessive amounts of fertiliser are used which end up in rivers and lakes
  • algae absorb the phosphate ions (and other nutrients) and this leads to an algal bloom
  • algae forms blanket on surface of eater blocking sunlight from plants below so they are unable to photosynthesise and die
  • SAPROBIOTIC bacteria feed and respire on the dead plant matter, which increases the amount of them, they use up all/ alot of the oxygen as they respire
  • so fish and other aquatic organisms don’t have enough (dissolved) oxygen to carry out respiration and die

(- now less competition of anaerobic organisms so their population rises, anaerobic organisms further decompose dead material releasing more nitrates)

80
Q

name three environmental effects of using nitrogen-containing fertilisers

A
  • reduced species diversity (nitrogen-rich soils favour growth of grass, nettles etc., these out-compete many other species which die as a result)
  • leaching
  • europhication
81
Q

what is leaching?

A

process by which nutrients are removed from soil

- leached (nitrate ions) are harmful to environment because they cause eutrophication

82
Q

what is eutrophication?

A

process by which nutrient concentrations increase in bodies of water

83
Q

state some causes of eutrophication

A
  • organic manures
  • animal slurry (manure + water)
  • human sewage
  • ploughing old grassland
  • natural leaching of artificial fertilisers (MAIN CAUSE)
84
Q

explain how legumes are able to convert nitrogen gas in air into nitrogen containing compounds

A
  • they have root nodules with nitrogen-fixing bacteria
  • these bacteria convert nitrogen gas into either ammonium or nitrates into plant
    (not all plants can do this as they don’t all have root nodules)
85
Q

microorganisms make the carbon in polymers in dead worm available to cells in a leaf. Describe how

A
  1. microorganisms are saprobionts
  2. secrete enzymes (onto dead tissues)/extracellular digestion
  3. absorb products of digestion/smaller molecules
  4. respiration by microorganisms produces CO2
  5. CO2 taken into leaves
  6. through stomata
86
Q

suggest appropriate units for gross productivity

A

Unit of energy / mass, per area, per year.

i.e. kJ ha-1 year-1

87
Q

suggest one reason for conserving woodlands

A
  1. Conserving / protecting habitats / niches;
  2. Conserving / protecting (endangered) species / maintains / increases (bio) diversity;
  3. Reduces global warming / greenhouse effect / climate change / remove /
    take up carbon dioxide;
  4. Source of medicines / chemicals / wood;
  5. Reduces erosion / eutrophication

a2 biology (13 decks)

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