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Wjec A Level Biology > 3.5 Population Size And Ecosystems > Flashcards

3.5 Population Size And Ecosystems Flashcards

1
Q

Ecology

A

The study of living things and their interactions with each other and their environment

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2
Q

Ecosystem

A

A characteristic community of interdependent species interacting with the abiotic components of their habitat

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3
Q

Population

A

All the members of one species in an area

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4
Q

Habitat

A

The place in an ecosystem where an organism lives

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5
Q

Niche

A

The role of an organism in an ecosystem, generally a feeding role

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6
Q

Biotic

A

All the living and organic component of an ecosystem

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7
Q

Abiotic

A

All the non-living parts of an ecosystem

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8
Q

Is an ecosystem static

A

No
Ut is dynamic

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9
Q

What is the source of energy for an ecosystem

A

The sun

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10
Q

How does the sun being the source of energy for an ecosystem mean an ecosystem is subject to change

A

The duration and intensity of sunlight changes which effects the energy flow

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11
Q

What does population size depend on

A

Reproduction rate
Death rate
Immigration rate
Emigration rate

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12
Q

Population size will increase when

A

Reproduction and immigration rates are higher than death and emigration rates

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13
Q

Population size will decrease when

A

Reproduction and immigration rates are less than death and emigration rates

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14
Q

lag phase of animal growth curve

A

Animals first arrives in an area
Population increases slowly
Time is needed for enough individuals to reach sexual maturity

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15
Q

Log phase of animal growth curve

A

Plenty of food
Population increases exponentially
Competition for food, territory and habitats are low

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16
Q

Stationary phase of animal growth curve

A

Carrying capacity is reached
Numbers will fluctuate around this in response to environmental changes such as predator-prey negative feedback.
If an overshoot occurs when growth exceeds carrying capacity there may be a degraded carrying capacity due to resource destruction

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17
Q

What are density dependent factors

A

Biotic factors such as competition, predation and disease
The effect of the factor is bigger when the population is higher

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18
Q

What are density independent factors

A

Abiotic factors eg light intensity, temperature, wildfires
Effects the population whether it is large, small or just the same

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19
Q

Why does sampling need to be random

A

Each individual has an equal chance of being included
It ensures the sample is representative of the whole population of each species
It reduces subjectivity and removes bias

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20
Q

Examples of ecosystems

A

Tropical rainforest
Tundra
Desert

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21
Q

What is the first energy transfer in an ecosystem

A

From sunlight to plants

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22
Q

Why is not all of the light hitting the leaf used in photosynthesis

A

• some is reflected by the waxy cuticle
• some is of the wrong wavelength to be absorbed
• some is transmitted through the leaf as it doesn’t hit a chloroplast

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23
Q

What are producers

A

Autotrophic organisms at the start of a food chain that convert light energy into chemical energy

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24
Q

Why is less than 10% of energy incorporated into biomass and is available to the next trophic level

A

Most energy is released in respiration and incorporated into other molecules or into electrochemical gradients

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25
Q

What are trophic levels

A

The feeding level within a food chain and shows the number of times that energy has been transferred to successive organisms along a food chain

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26
Q

What is biomass

A

The mass of biological material in living or recently living organisms

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27
Q

What are primary consumers

A

Herbivores
They feed on producers

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28
Q

What are secondary and tertiary consumers

A

Include carnivores
Feed on trophic levels below
Some feed at more than 1 trophic levels

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29
Q

What kind of organisms does decomposition involve

A

Detritivores and decomposera

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30
Q

Detritivores

A

Earth worms and woodlice
They feed on detritus

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31
Q

What is detritus

A

Remnants of dead organisms and leaves

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32
Q

Decomposers

A

Bacteria and fungi
Feed via external digestion
Complete process started by detrivores

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33
Q

What trophic level do decomposers feed on

A

All

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34
Q

How to calculate photosynthetic efficiency?

A

Quantify of light energy fixed by plants/Quantity of light energy falling on plant X 100

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35
Q

What is Gross primary production

A

Rate of production of chemical energy in organic molecules by photosynthesis in a given area, in a given time
Unit = kJm-2y-1

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36
Q

What is net primary production

A

Energy in the plant’s biomass which is available to primary consumers
Units= kJm-2y-1

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37
Q

How to calculate NPP

A

NPP= GPP-R

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38
Q

Why is the true value of biomass even lower than predicted

A

Some of the biomass is used to form inedible materials such as bark or its biomass in roots which is out of reach of primary consumers

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39
Q

What kind of NPP does a tropical rainforests have?

A

High
Plentiful rainfall, high light intensity and high temperatures

40
Q

What kind of NPP does a tundra have and why?

A

Low
Cold, low light intensity

41
Q

How to calculate % efficiency

A

Energy fixed as biomass/energy available to next trophic level X 100

42
Q

Pyramid of numbers

A

Easy to construct
Shows the energy flow through a food chain
Doesn’t consider the size of the organisms

43
Q

Pyramid of biomass

A

More accurate than pyramid of numbers
Is difficult to measure and calculate
May be inverted

44
Q

Pyramid of energy

A

• most accurate way of representing feeding relationships
• shows the energy flow through an ecosystem
• Shows clearly the energy lost at each level
• is difficult to calculate

45
Q

What can pyramids not show

A

Organisms operating at several trophic levels

46
Q

What is succession

A

Change in structure and species composition of a community over time

47
Q

What is a seral stage

A

Each stage in succession where different communities dominate

48
Q

What is primary succession

A

Organisms invade spaces that did not previously support life

49
Q

What is secondary succession

A

The reintroduction of organisms into a habitat previously occupied by plants/animals

50
Q

Surface of primary and secondary succession

A

Primary - bare surface
Secondary - soil

51
Q

What are the pioneer species of primary and secondary succession?

A

Primary - mosses and lichens
Secondary - small weedy plants

52
Q

What is pioneer species?

A

The first species to colonise a new area in an ecological succession

53
Q

What is a climax community

A

A stable community that undergoes no further change

54
Q

What is a sere

A

Entire sequence of communities that changes successively in a given area

55
Q

What changes as succession progresses

A

• soil depth increases
• nutrient content increases
• humus content increases
• water content increases
• diversity increases
• stability increases

56
Q

What is it called when a climax community is not reached and what would cause this

A

Deflected or disclimax
Human intervention eg Monoculture and grazing

57
Q

Interspecific competition

A

Different species

58
Q

Intraspecific competition

A

Same species

59
Q

Term for species that exist in a relationship that is beneficial to both

A

Mutualism

60
Q

Term for when a species is able to obtain benefit from one species whilst other is unaffected

A

Commensalism

61
Q

What does the carbon cycle involve

A

Photosynthesis
Respiration
Combustion of fossil fuels

62
Q

Effect of photosynthesis on carbon cycle

A

Photo autotrophs remove CO2 from the atmosphere and fix it into organic molecules

63
Q

Effect of respiration on carbon cycle

A

Done by all organisms
Returns CO2 to the atmosphere

64
Q

Effect of combustion of fossil fuels on carbon cycle

A

• fossil fuels formed millions of years ago and derived from partially decayed remains of plants
• combustion releases CO2 into the atmosphere

65
Q

Human activities that affect the carbon cycle

A

Deforestation and combustion

66
Q

What is deforestation

A

Removal of trees and subsequent use of land for another purpose

67
Q

Effect of deforestation on carbon cycle

A

Significantly reduces the volume of CO2 removed from the atmosphere through photosynthesis

68
Q

How does increased atmospheric CO2 leads to global warming

A

CO2 is a greenhouse gas so it re-radiates infra-red back towards the Earth’s surface rather than allowing it to escape to space
Increase in CO2 emissions over recent decades are leading to an enhanced greenhouse effect

69
Q

What is the effect of global warming on species?

A

• global temperatures rise so polar ice melts so sea levels rise and coastal flooding occurs
• increases incidence of forest fires leading to desertification
• changes to climate patterns, temperature, wind patterns, rainfall, extreme weather conditions
• acidification of oceans due to increasing dissolved CO2

Species may not be able to adapt or migrate and many will become extinct

70
Q

What is desertification

A

The process by which fertile land becomes desert as it loses water, vegetation and wildlife

71
Q

Effect of acidification of ocean on fish and crustaceans

A

Fish - gills produce mucus and so reduces gas exchange
Crustaceans - lose CaCO3 from exoskeletons as it is soluble in acid

72
Q

Effect of global warming on farming

A

• decreased crop yields and failed harvests

73
Q

How to fix farming practices to help global warming

A

Use drought-tolerant crops

74
Q

Why is farming having a negative effect on global warming?

A

Although it removes CO2 through photosynthesis energy is needed for
• insecticides and fertilisers
• powering farming machinery
• transport of produce to market

75
Q

What is carbon footprint

A

The total amount of CO2 attributable to the actions of an individual or a product or service over a period of one year

76
Q

Effect of the 3Rs to reduce carbon footprint

A

Reduces energy consumption and so reduces carbon footprint

77
Q

What is the nitrogen cycle

A

Flow of organic and inorganic nitrogen withon the abiotic and biotic components of an ecosystem where there is an interchange between certain nitrogenous compounds and atmospheric nitrogen

78
Q

In what form do plants uptake nitrogen by plant roots

A

Ammonium and nitrate ions

79
Q

What are the 4 main processes of nitrogen cycle

A

Nitrification
Deniftrification
Putrefaction
Nitrogen fixation

80
Q

Others words for ammonification

A

Putrefaction
Decomposition
Mineralisation

81
Q

What happens during ammonification

A

• Decomposers feed on dead and organic matter and feaces saprophytically by secreting enzymes onto their food and absorbing small soluble products
• proteases hydrolyse proteins to amino acids and deaminase reduce the amino group to ammonium ions

82
Q

What happens during nitrification

A

• addition of nitrogen to the soil most commonly as nitrite and nitrate ions
• ammonium is oxidised into nitrite by nitrosomonas bacteria
• nitrite oxidised to nitrate by nitrobacter conditions
• aerobic conditions required

83
Q

Simply what happens in nitrification

A

NH4+ —> NO2- —> NO3-

84
Q

What bacteria is used when ammonium is oxidised to nitrite

A

Nitrosomonas

85
Q

What bacteria is used when nitrite is oxidised to nitrate

A

Nitrobacter

86
Q

What is nitrogen fixation

A

The reduction of nitrogen atoms in nitrogen molecules to ammonium ions by prokaryotic organisms
It is carried out by nitrogen fixing bacteria such as azotobacter and rhizobium

87
Q

Azotobacter

A

Nitrogen fixing bacteria
Free living in soul
Accounts for most nitrogen fixation

88
Q

Rhizobium

A

• mutualistic bacterium found in root nodules of leguminous plants
• invades the roots of the legumes and the plant responds by forming a nodule where the bacteria will live
• nitrogen gas diffuses into the nodule where nitrogenase enzyme produced by the bacteria redcluces N2 to ammonium ions in anaerobic conditions
• the ammonium ions are converted to organic acids and amino acids for the bacteria
• excess ammonium and amino acids are exported to the plant through the phloem for protein synthesis
• this requires ATP

89
Q

How are anaerobic conditions maintained for Rhizobium

A

The plant provides this by producing the pigment leghemoglobin which takes up oxygen in the root nodule, removing it from the bacterial environment

90
Q

How does Rhizobium get ATP

A

Gains sugars from the plants photosynthetic product

91
Q

What is denitrification

A

Loss of nitrate from the soul by anaerobic bacteria, Pseudomonas, to atmospheric nitrogen
The denitrifying bacteria use the nitrate to provide oxygen for respiration and the remaining nitrogen atoms are converted into nitrogen gas

92
Q

Simply, what happens during denitrification

A

Nitrate —> nitrogen gas

93
Q

How does ploughing and draining soil increase soil aeration

A

• allows air to reach the roots of plants as nitrates and other minerals are uptaken by active transport which requires ATP from aerobic respiration
• favours the aerobic process of nitrogen fixation and nitrification
• inhibits denitrification which is anaerobic

94
Q

Effect of using excess fertilisers

A

• eutrophication occurs where the excess fertilisers runs off into aquatic habitats which increases the ion content of the water and forms an algal bloom
• algal blooms block light to aquatic plants so plants and algae die and form detritus which is aerobically decompose which causes other aerobic organisms to die and further add to the detritus
• eventually all the oxygen is used up and only anaerobic bacteria can survive - these release ammonia, methane, hydrogen sulphide into the water which causes a toxic environment for most organisms

95
Q

How can farmers reduce fertiliser run-off

A

• apply fertilisers when plants are actively grow
• not apply fertilisers within 10m of water courses
• dig drainage ditches to collect run off

96
Q

Pros and cons of draining land

A

• the soil doesn’t get water logged so denitrification slows down and more oxygen means nitrification is sped up so more nitrate is added to the soil and more decomposition occurs
• it means the loss of habitat and biodiversity for some wet-land ecosystems
• plant rich habitats are more subject to wild-fires which release locked in carbon

Wjec A Level Biology (13 decks)

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