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A Level Biology > ✅13 - Energy And Ecosystems > Flashcards

✅13 - Energy And Ecosystems Flashcards

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1
Q

What are producers?

A

Photosynthetic organisms that manufacture organic substances using light energy, water, CO2 and mineral ions

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2
Q

What are consumers?

A

Organisms that obtain their energy by feeding on other organisms rather than using the energy of the sunlight directly

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3
Q

What are saprobionts?

A

A group of organisms that break down the complex materials in dead organisms into simple ones, releasing valuable minerals and elements that can be absorbed by plants

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4
Q

What is a food chain?

A

A feeding relationship in which the producers are eaten by primary consumers

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5
Q

What is a trophic level?

A

Each stage in the food chain

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6
Q

What are food webs?

A

The way that different food chains link together

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7
Q

What is biomass?

A

The total mass of living material in a specific area at a given time

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8
Q

What is biomass measured in?

A

Grams per square metre of dry mass

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9
Q

Why is most of the sun’s energy not converted into organic matter?

A

Over 90% of it is reflected back to space by clouds and dust
Not all wavelengths of light can be absorbed by chlorophyll
Light may not fall on a chlorophyll molecule
Other factors such as low CO2 levels may limit the rate of photosynthesis

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10
Q

What is gross primary production?

A

The total quantity of chemical energy stored in plant biomass in a given area or volume in a given time

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11
Q

What is net primary productivity?

A

Gross primary production - respiratory losses

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12
Q

Why is the percentage of energy transferred at each trophic level low?

A

Some of the organism is not consumed
Some parts are consumed but cannot be digested
Some energy is lost in excretory materials eg urine
Some energy loss occurs from heat and respiration etc

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13
Q

What is the net production of consumers calculated as?

A

I-(F+R)
I = chemical energy ingested
F = energy lost in faeces and urine
R = energy lost in respiration

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14
Q

Why do most food chains only have four or five trophic levels?

A

Because insufficient energy is available to support a large enough breeding population at trophic levels higher than these

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15
Q

What intensive farming practices are used to conserve energy?

A

Movement restricted to reduce energy used for muscle contraction
Environment kept warm to reduce energy used for heat
Feeding controlled so that maximum growth and little wastage occurs
Predators excluded

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16
Q

What is the general pattern that all nutrient cycles follow?

A

Nutrient taken up by producers
Producer converts into complex organic molecule
Producer eaten, passes into consumer
Passes along food chain where animals eaten by other consumers
Complex molecules broken down by saprobiontic microorganisms

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17
Q

Why do living organisms require nitrogen?

A

To produce organic molecules such as proteins and nucleic acids

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18
Q

How do plants take up nitrogen?

A

As nitrate, NO3-, from the soil by active transport

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19
Q

How is nitrate concentration of soil increased in agriculture?

A

Through fertilisers

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20
Q

What are the four main stages on the nitrogen cycle?

A

Ammonification, nitrification, nitrogen fixation and denitrification

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21
Q

What do all the main stages of the nitrogen cycle involve?

A

Saprobionts

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22
Q

What is nitrogen fixation?

A

Conversion of nitrogen in the atmosphere into ammonium ions or ions

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23
Q

What is nitrification?

A

Turning ammonium ions into nitrite and then nitrate ions

24
Q

What is ammonification?

A

The production of ammonia from organic nitrogen containing compounds

25
Q

What type of reaction is nitrification?

A

Oxidation

26
Q

What are the two main types of nitrogen fixing bacteria?

A

Free-living nitrogen-fixing bacteria

Mutualistic nitrogen-fixing bacteri

27
Q

What are free-living nitrogen-fixing bacteria?

A

Bacteria that reduce gases nitrogen to ammonia which they use to manufacture amino acids. Nitrogen compounds released from them when they die and decay

28
Q

What are mutualistic nitrogen-fixing bacteria?

A

Bacteria that live in nodules on the roots of plants such as legumes. They obtain carbohydrates from the plant and the plant acquires amino acids from the bacteria

29
Q

What do denitrifying bacteria do?

A

Convert soil nitrates into gaseous nitrogen

30
Q

Why must soils be kept well aerated?

A

To prevent build up of denitrifying bacteria which reduce the availability of nitrogen containing compound for plants

31
Q

Why do denitrifying bacteria build up in less aerated soil?

A

Because they carry out denitrification in anaerobic conditions, while nitrifying and nitrogen-fixing bacteria work in aerobic conditions

32
Q

What is phosphorus used for?

A

ATP, phospholipids and nucleic acids

33
Q

What does the phosphorus cycle lack?

A

A gaseous phase

34
Q

What does phosphorus mostly exist as?

A

Phosphate ions, PO4 3-, in sedimentary rock deposits

35
Q

What helps phosphate ions to become dissolved?

A

The weathering of rocks

36
Q

What are dissolved phosphate ions absorbed by?

A

Plants

37
Q

How does excretion of phosphate occur?

A

In the waste products of plants and animals as well as when they die

38
Q

How can phosphate ions reach the oceans, lake and soils?

A

Erosion of rocks
Use of fertilisers
Excretion

39
Q

What are mycorrhizae?

A

Associations between certain types of fungi and the roots of the vast majority of plants

40
Q

How do mycorrhizae benefit the plants?

A

They increase the total surface area for the absorption of water and minerals and act like sponges to hold water and minerals around the plants even in drought

41
Q

How do mycorrhizae play a part in nutrient cycles?

A

The improve the uptake of relatively scarce ions such as phosphate

42
Q

What the the mycorrhizal relationship between plants and fungi?

A

Mutualistic

43
Q

How do the fungi benefit from mycorrhizal relationships?

A

They gain sugars and amino acids form the plant

44
Q

What is intensive food production?

A

Concentrated on specific areas of land that are used repeatedly to achieve maximum yield form the crops and animals on them

45
Q

Why do concentrations of mineral ions on agricultural land fall?

A

The crop is harvested rather than dying back, and the urine, faeces and dead remains of the consumer are rarely returned to the same area of land

46
Q

Why are fertilisers necessary?

A

To replenish mineral ions on the land

47
Q

What are natural/organic fertilisers?

A

Consist of dead and decaying remains of plants and animals as well as animal waste

48
Q

What are artificial/inorganic fertilisers?

A

Mined from rocks and deposits then converted into different forms and blended together to give the appropriate balance of minerals for a crop

49
Q

What has the greatest long term increase in productivity?

A

A mixture of natural and artificial fertilisers

50
Q

How do fertilisers increase productivity?

A

When more ions available, plants are likely to develop earlier, grow taller and have greater leaf area for more photosynthesis, increasing crop productivity

51
Q

What are the effects of nitrogen containing fertilisers?

A

Reduced species diversity
Leaching
Eutrophication

52
Q

Why is species diversity reduced by nitrogen containing fertilisers?

A

Nitrogen rich soils favour the growth of grasses, nettles and other rapidly growing species, which out compete others and they die as a result

53
Q

What is leaching?

A

The process in which nutrients are removed from the soil and rainwater dissolves soluble nutrients, carrying them deep into the soil and potentially reaching water courses

54
Q

What is eutrophication?

A

The process by which nutrient concentrations increase in bodies of water

55
Q

What is the sequence of events that causes eutrophication?

A

Low concentration of mineral ions is limiting factor of algal growth in water bodies
As nitrate ion concentration increases as a result of leaching, plant and algal growth increases - algal bloom
Light prevented from reaching lower layers of water
Plants at bottom of water die
Saprobiontic bacteria use dead organisms as food, use oxygen for respiration
Oxygen concentration decreases, aerobic organisms die
Anaerobic organisms increase in number, water toxic

A Level Biology (22 decks)

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