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OCR Biology > 6.3.1 - Ecosystems > Flashcards

6.3.1 - Ecosystems Flashcards

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1
Q

What is an ecosystem?

A

The community of organisms (biotic) and non-living (abiotic) components of an area and their interactions

They are dynamic, and are influenced by both biotic and abiotic factors

Can be a range of sizes (eg oak tree, rock pool, playing field)

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2
Q

What are biotic factors?

A

Living factors of an ecosystem

Eg:
• predation
• competition for space, food, water, light etc
• cooperation between organisms (same/different species)
• parasites
• pathogenic diseases caused by microorganisms
• mankind (hunting, farming, habitat loss)

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3
Q

What are abiotic factors?

A

Non-living/physical factors affecting an ecosystem

Eg:
• light
• temperature
•water availability
• oxygen availability
• soil composition (
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4
Q

How does light affect ecosystems?

A
  • most plants are directly affected as light needed for photosynthesis
  • in general, greater light availability = greater success of a plant species
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5
Q

How does temperatures affect ecosystems?

A
  • increased temperature increases enzyme activity
  • plants and ectotherms develop more rapidly in warmer temperatures (endotherms less affected by external temperature)

• changes in temp of an ecosystem (eg due to changing seasons) can trigger migration/hibernation

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6
Q

How does oxygen availability affect ecosystems?

A
  • in aquatic ecosystems, cold, fast running water beneficial due to high concentration of oxygen. If water too warm/slow, organisms may suffocate
  • in waterlogged soil, air spaces between oil particles are filled with water, reducing oxygen available for plants
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7
Q

What is is a trophic level?

A

The position of an organism in a food chain

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8
Q

What is a producer?

A

Photosynthetic organisms that convert light energy into chemical energy + produce biomass

Start of the food chain (first trophic level)

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9
Q

What is a consumer?

A

Organism that feed on other organisms to obtain energy

Primary consumer - eats producer
Secondary consumer - eats primary consumer
Tertiary consumer - eats secondary consumer
Quaternary consumer - eats tertiary consumer

Food chains rarely have more trophic levels as there is insufficient biomass/stored energy left to support further organisms

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10
Q

What is biomass?

A

The mass of living material present in a particular place/particular organisms

It’s important in the study of food chains/webs as it can be equated to energy content

Measured in kgm-2yr-1 (land) / kgm-3yr-1 (water)
• per year allows for changes, as biomass isn’t constant (due to seasonal changes, consumer feeding patterns etc)

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11
Q

How is biomass calculated?

A

Multiply biomass in each organism by total number of organisms in that trophic level

Only represents biomass at a particular time - doesn’t take into account seasonal changes

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12
Q

How is biomass measured?

A

Dry mass of organisms calculated

Organisms killed, placed in an oven at relatively low temperature (to prevent burning and loss of biomass, and dried until all water has evaporated (at least 2 identical mass readings)

A small sample is taken to minimise destruction

Advantages:
No water, so all mass is biomass

Disadvantages:
Organisms must be killed
Sample is small to minimise damage, but this may not be representative of population

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13
Q

Why does biomass decrease as you move through the trophic levels (consumers)?

A
  • not all of the biomass is eaten by the consumer
  • not all of the biomass consumed is digested (lots passes through as faeces)
  • the consumer converts a lot of the biomass (chemical energy) into movement and heat

Therefore, only a small proportion of biomass consumed is converted into new tissue (biomass)

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14
Q

What is ecological efficiency?

A

The efficiency at which biomass/energy is transferred from one trophic level to the next

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15
Q

Why is ecological efficiency between the sun and producers low?

A
  • not all solar energy can be used for photosynthesis - most is reflected, some transmitted and some is an unusable wavelength
  • some of the energy is used for photosynthetic reactions, respiration, etc
  • other factors may limit the rate of photosynthesis (eg water availability)
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16
Q

How can ecological efficiency be calculated?

A

Efficiency = (biomass transferred/biomass intake) x 100

Where:
• Biomass transferred = biomass that has passed to the higher trophic level
• Biomass intake = biomass of the lower trophic level that has been consumed

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17
Q

How can net productivity of producers be calculated?

A

Net production = gross production - respiratory losses

Where:
•net production = energy available to the next trophic level
• gross production = total solar energy that plants convert to organic matter
• respiratory losses = energy used for respiration

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18
Q

Why do humans manipulate the transfer of biomass through ecosystems?

A
  • having complex food chains with many trophic levels reduces the biomass available for consumption at the top
  • in agriculture of plants, there are only 2 trophic levels - the producer (crops) and the primary consumer (humans)
  • in agriculture of animals/animal produce, there are 3 tropic levels - producer (animal feed), primary consumer (animal), secondary consumer (human)

The best way to maximise the efficiency is to maximise agricultural productivity

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19
Q

How can arable farmers maximise agricultural productivity?

A
  • Providing artificial light in greenhouses on overcast days
  • Irrigation to maximise growth in dry weather
  • Use of fertilisers
  • Selective breeding for fast growth
  • Use of fungicides/pesticides
  • Fencing to exclude grazers
  • Ploughing and herbicides to kill weeds
  • Plant crops that store energy in edible form e.g. seeds, fruit, tubers
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20
Q

How can livestock farmers maximise productivity

A
  • Use of good quality feeds / food supplements
  • Use antibiotics and vaccines to reduce disease
  • Control predation with fencing or with indoor animal husbandry
  • Reduce competition for grazing e.g. rabbits, deer
  • Indoor husbandry to reduce energy loss from movement or from getting cold outside
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21
Q

Why can biomass be equated to energy?

A

Biomass consists of the cell and tissues within an organism, including carbohydrates and other carbon compounds within them

Bcs carbon compounds are a store of energy, biomass can be equated to energy

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22
Q

What is decomposition?

A

A chemical process in which a compound is broken down into small we molecules/constituent elements

Important because nitrogen/carbon often cant be used directly in dead/waste matter

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23
Q

What is a decomposer?

A

An organism that feeds on and breaks down dead plant/animal matter into nutrients photosynthetic producers can use

Primarily microscopic fungi and bacteria

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24
Q

What is saprobiotic nutrition?

A

The method of obtaining nutrients from dead/waste organic material via extra cellular digestion

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25
Q

What are saprotrophs?

A

Organisms that obtain nutrients via saprobiotic nutrition (eg decomposers)

The enzymes secreted by the decomposers break down complex organic molecules into simple soluble molecules they can absorb

Not all of these molecules are absorbed by the decomposers and are absorbed by other organisms (eg plants)

26
Q

What are detritivores?

A

Speed up the decay process by feeding on dead/decaying matter

Perform internal digestion

By breaking it down into smaller materials, the increase the SA decomposers can work on

27
Q

Why does nitrogen need to be recycled?

A
  • it is important for making amino acids and nucleic acids
  • animals obtain N from what they eat, but plants must obtain it from the environment
  • N is abundant in atmosphere (78%) but N2 cant be taken up by plants - it must be combined with other elements eg H or O
  • bacteria converts into a form usable by plants
28
Q

What is the nitrogen cycle?

A

The cycle through which nitrogen moves between living organisms and the environment

Involves ammonification, nitrification, nitrogen fixation and denitrification

29
Q

What is nitrogen fixation?

A

The conversion of atmospheric nitrogen gas into ammonia by nitrogen fixing bacteria in the soil (azotobacter) or root nodules of legumes (rhizobium)

Can also happen by non-living processes eg lightning, Haber process

30
Q

What are nitrogen-fixing bacteria?

A

Microorganisms responsible for the conversion of atmospheric nitrogen gas into nitrogen-containing compounds

Can be free living (azotobacter) or mutualistic (rhizobium)

31
Q

How do azotobacter and rhizobium work?

A

They contain the enzyme nitrogen are which combines N2 with H2 to form ammonia (NH3)

Azotobacter is free living in the soil

Rhizobium live inside rooot nodules of legumes and have a symbiotic mutualistic relationship:
• the plant gains amino acids from rhizobium, which are produced by fixing N2 to ammonia
• the bacteria gains carbs produced but plant during photosynthesis

32
Q

What is nitrification?

A

The conversion of ammonium ions in nitrate ions by nitrifying bacteria

Done in 2 stages:

1) nitrifying bacteria (eg nitrosomonas) oxidise ammonium compounds into nitrites (NO2-)
2) another nitrifying bacteria (eg nitrobacter) oxidise nitrites into nitrates (NO3-)

Nitrates are highly soluble and are teh form in which most nitrogen is absorbed into he plant

33
Q

What is denitrification?

A

The conversion of nitrate ions into nitrogen gas by denitrifying bacteria

Done in anaerobic conditions as a source of energy for respiration

34
Q

What is ammonification?

A

Teh production of ammonium compounds when decomposers feed on organic nitrogen-containing molecules

35
Q

Why does carbon need to be recycled?

A

C is a component of all major organic molecules eg fats, carbs, proteins

It is stored in various forms:
• atmosphere
• sedimentary rocks
• fossil fuels eg coal, oil, gas
• soil and other organic matter
• vegetation (eg cellulose)
•dissolved in oceans
36
Q

How is photosynthesis involved in the carbon cycle?

A
  • autotrophs use the energy of sunlight to ‘fix’ CO2, turning the carbon into sugars and other organic molecules
  • this removes CO2 from the atmosphere/oceans where it is dissolved
37
Q

How is feeding involved in the carbon cycle?

A
  • carbon containing molecules are passed to primary consumers when they feed on producers
  • carbon is passed up the food chain when the consumer is consumes
38
Q

How is respiration involved in the carbon cycle?

A

All organisms respire

Aerobic respiration releases CO2 into the atmosphere (ink reaction and kerbs cycle)

Anaerobic respiration releases CO2 into atmosphere via fermentation of yeast, mould, bacteria

39
Q

How are decomposers involved in the carbon cycle?

A

Dead plants/animals are fed upon by detritivores and decayed by saprotrophs, which:
• releases CO2 into surroundings
• supplies C to detritivores and saprotrophs

Waste matter can also be decayed and releases CO2 back into the air

40
Q

How is sedimentation involved in the carbon cycle?

A
  • if organisms aren’t fully decomposed, their bodies can form layers of sediment that build up over millions of years, locking the carbon they store into the ground
  • this sediment can form fossil fuels like peat, coal, oil and gas containing carbon
41
Q

How do fossil fuels affect the carbon cycle?

A
  • when fossil fuels are burnt, CO2 is released back into the atmosphere at a faster rate than its absorbed by plants and aquatic producers
  • CO2 level in atmosphere has risen dramatically
  • warmer temperatures mean less CO2 an be dissolved in oceans, so its released into atmosphere
  • this has caused dramatic climate change
42
Q

Why do CO2 levels fluctuate?

A

• photosynthesis requires light, so during the day, CO2 s removed from atmosphere
•respiration occurs constantly (day and night) , releasing CO2 into the atmosphere
Therefore, atmospheric CO2 levels are higher at night than during the day

CO2 tends to be lower in summer than winter as rate of photosynthesis is higher

43
Q

What is succession?

A

The progressive replacement of one dominant type of species/community by another in an ecosystem until a stable climax community is established

44
Q

What is primary succession?

A

The prioress that occurs when newly formed/exposed land with no species present is gradually colonised by an increasing number of species

New land includes:
• New rock formed after a volcanic eruption
• sand dunes in costal areas
• sea level dropping/lake drying up

45
Q

What is a seral stage (sere)?

A

A step in the process of succession

At each seral stage, key species can be identified that change he abiotic factors (esp soil) to make it more suitable for subsequent species

At each seral stage, different species are better adapted to the current conditions in the ecosystem, which outcompete other species and become the dominant species

46
Q

What is a pioneer community?

A
  • primary succession begins with the arrival of a pioneer species, which colonises the inhospitable environment
  • the species arrive as spores/seeds carried by wind from nearby environments, or by animal droppings (eg birds)
  • examples of pioneer species = algae, lichen
47
Q

How are pioneer species adapted to colonise bare environments?

A
  • produce large quantities of sees/spores which are blown by wind and deposited on new land
  • seeds germinate rapidly
  • can photosynthesise - light, rain and air (therefore CO2) often only abiotic factors present
  • tolerance to extreme environments
  • ability to fix nitrogen form atmosphere, adding to the mineral content
48
Q

How to pioneer species affect the conditions of an environment?

A
  • when organisms of a pioneer species die and decompose, small organic products are released - this organic component is called humus
  • over time, bare rock weathers and combines with the humus to form a soil
  • the soil becomes able to support secondary colonisers (eg moss) which arrive as spores or seeds. This is because the soil contains nitrates and can retain some water
  • pioneer species may also provide a food source for consumers, so some animal species will start to colonise the area
49
Q

What is an intermediate community?

A
  • pioneer species alter the environment, making to possible for secondary colonisers to settle
  • as environmental conditions continue to improve, tertiary colonisers (eg ferns) arrive
  • at each stage, rock continues to be eroded and mass of organic matter increases
  • when organisms decompose, they contribute to a deeper, nutrient rich soil which makes abiotic conditions more favourable for small flowers, later shrubs and eventually trees
  • in many cases, multiple seral stages evolve during the intermediate period
50
Q

What is deflected succession?

A

Changes to the natural flow of succession due to human activity that result in a stable community called a plagioclimax

51
Q

Why does deflected succession occur?

A

AGRICULTURE
• grazing and trampling of vegetation by domesticated animals resulting in large areas remaining as grassland
•removing existing vegetation to plat crops - crop becomes final community
• burning as a means of forest clearance - often leads to an increase in biodiversity as it provides space and nutrient-rich ash for other species to grow

CONSERVATION
• intermediate stages of succession often hold a distinctive diversity that wouldn’t exist if climax community was reached
• these environments also provide food and habitat for a high diversity of animals which may also be of conservation importance
• deflected succession can maintain an environment at an intermediate level eg heathland

52
Q

Hoe cam distribution of organisms within an ecosystem be measured?

A

LINE TRANSECT
• lay a line/surveyors tape along the ground and take samples at regular intervals

BELT TRANSECT
• 2 parallel lines are marked
• samples taken of the area between these specified points

Both are systematic sampling techniques

53
Q

Why may systematic sampling be better than random sampling when measuring the distribution of organisms?

A
  • in SS, different areas within a habitat are identified and sampled separately
  • this allows scientists to study how the differing abiotic factors in different areas may affect the distribution of species
54
Q

What is the distribution of organisms within an ecosystem?

A

Refers to where individual organisms are found within an ecosystem

55
Q

What is abundance?

A

The number of individuals of a species in a specific area at any given time

This may fluctuate daily due to immigration, emigration, birth and death

56
Q

Why can populations rarely be counted accurately?

A
  • Some animals elude capture
  • May be too time-consuming to count all members of the population
  • Counting process could damage environment

They are therefore estimated using sampling techniques

57
Q

What is a population?

A

All organism of the same species living with one another in a habitat at the same time

58
Q

How can you increase the accuracy of a sample?

A
  • use a large sample size - greater number of individuals studied = lower probability chance will influence results
  • use random sampling to reduce the effect of sampling bias
59
Q

How is plant abundance measured?

A
  • quadrats are placed randomly in an area
  • abundance in that area is measured by counting the no. Of individual plants contained within quadrat

P = N÷A

Where:
• P = estimated number in population (m^-2)
• N = number of individuals in sample
•A = area of sample (m^2)

60
Q

How can animal abundance be measured?

A

Using the capture-mark-release-recapture technique

P = (F x S)/R

Where:
• P = estimated population size
•F = number of individuals in first sample
• S = number of individuals in the second sample
• R = number of recaptured marked individuals

61
Q

What is the capture-mark-release-recapture technique?

A

1) capture as many individuals as possible in a sample area
2) mark/tag each individual
3) release the marked animals back into the sample area and allow them to redistribute themselves through the habitat
4) recapture as many individuals as possible in the original sample area
5) record the number of marked and unmarked individuals present, then release back into their habitat
5) use the Lincoln index to estimate population size

62
Q

What is Simpson’s index?

A

Used to calculate biodiversity in a habitat

Value of 0-1, with higher values = higher biodiversity

D = 1- Σ(n/N)²

Where:
• D = Simpson’s index
• n =number of individuals in each species
•N = total number of organisms in the ecosystem

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