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biology a level > 6.5 > Flashcards

6.5 Flashcards

1
Q

what is an ecosystem

A

a community of animals, plants and bacteria interrelated with the physical and chemical environment

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2
Q

what are the 3 components of an ecosystem

A

-habitat
-population
-community

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3
Q

what is a habitat

A

the place where an organism lives

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4
Q

what is a population

A

all of the organisms of one species, who live in the same place at the same time, who can breed together

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5
Q

what is a community

A

all the populations of different species, who live in the same place at the same time, who can interact with each other

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6
Q

define niche

A

niche is the role of each species in an ecosystem.

eg. what it feeds on, what it excretes and how it reproduces.

Its impossible for two organism to occupy the exact same niche

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7
Q

are ecosystems regarded as closed systems or open systems

A

they are regarded as closed systems

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8
Q

what are producers

A

producers are plants (and some photosynthetic bacteria), which supply chemical energy to all other organisms

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9
Q

what are consumers (the different types)

A

primary consumers are herbivores, which feed on plants, and which are eaten by carnivorous secondary consumers. These in turn are eaten by carnivorous tertiary consumers

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10
Q

what are decomposers

A

decomposers (bacteria, fungi and some animals) feed on waste material or dead organisms

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11
Q

what can organisms of an ecosystem be responsible for

A

they can affect other organisms food supply because organisms require their own source of materials and energy.

They can also be responsible for predation and disease

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12
Q

what are abiotic factors

A

non-living components of an ecosystem that affect other living organisms

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13
Q

what are biotic factors

A

environmental factors associated with living organisms in an ecosystem that affect each other e.g. predation and disease

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14
Q

what are examples of abiotic factors

A

-pH
-humidity
-temperature
-concentration of pollutants
-turbulence and storms

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15
Q

give an example of how abiotic factors can be influenced by biotic components

A

in a rainforest the forest canopy influences the temperature and the humidity of the ecosystem

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16
Q

impact of abiotic factors on survival:
describe factors that are lethal at both extremes
(include graph)

A

-bell shaped curve

-a departure from the optimum intensity of a factor reduces the chance of survival

-near the top of the bell: reproduction occurs
-medium from the top: individual growth occurs
-away from the top of the bell: individuals survive

-the abiotic factor causing the bell shape could be temperature or pH

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17
Q

impact of abiotic factors on survival:
describe factors that are lethal when intense
(include graph)

A

-constant then downwards sloping curve

-the abiotic factor is lethal one extreme

-at constant level of graph: reproduction occurs
-downwards sloping: individual growth occurs
-downwards sloping when conc. has increased further: individuals survive

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18
Q

why are ecosystems referred to as dynamic?

A

because ecosystems change. The non-living elements change, and the living elements grow and die, with a population of a particular species rising and falling

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19
Q

what are three types of change in ecosystems that affect population size

A

-cyclic changes
-directional changes
-unpredictable/erratic changes

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20
Q

what are cyclic changes in ecosystems

A

these changes repeat themselves in a rhythm. For example, movements of tides and changes in a day are cyclic. The way in which predator and prey species fluctuate is cyclic .

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21
Q

what are directional changes in ecosystems

A

These changes are not cyclic. They go in one direction, and tend to last longer than the lifetime of organisms in the ecosystem. Within such change, particular variables continue to increase or decrease. Examples include the deposition of slit in an estuary, or the erosion of a coastline

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22
Q

what are unpredictable/ erratic changes in an ecosystem

A

These have no rhythm and no constant direction. For example , such changes may include the effects of lightning or hurricanes.

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23
Q

living things need to respond to changes in ecosystems, give some examples

A

-small mammals may hibernate on a rhythmical basis to avoid cold temperatures

-deciduous trees may shed their leaves

-a mammal may change the thickness or colour of its fur

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24
Q

what are two examples highlighting that materials are constantly recycled within an ecosystem

A

-the nitrogen cycle
-the carbon cycle

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25
Q

how does energy move through an ecosystem

A

it flows through ecosystems (its not recycled)

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26
Q

give an example of how products of photosynthesis are incorporated into plant tissues and organs

A

-cellulose for plant walls is made up of lots of glucose monomers

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27
Q

what makes up a plants biomass

A

organic components (such as glucose molecules) and inorganic compounds (such as mineral ions, but excluding water) of the plant make up its biomass

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28
Q

what happens to the biomass when a plant is eaten

A

its biomass is consumed by a primary consumer, the biomass will flow through a food chain

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29
Q

define biomass transfer

A

the transfer of biomass form one trophic level to another

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30
Q

define trophic level

A

the level at which an organism feeds in a food chain

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31
Q

how can we track the movement of minerals and energy through a food chain

A

by tracking how biomass changes in a food chain, we can track the movement of minerals and energy through a food chain

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32
Q

at each level in the food chain, what is lost and thus unavailable to the next organism

A

biomass

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33
Q

state ways in which biomass and energy is lost through the food chain

A

-at each trophic level, living organisms need energy to carry out life processes. Respiration releases energy from organic molecules like glucose. Some of this energy is eventually converted to heat, and materials are lost in carbon dioxide and water.

-biomass is also lost from a food chain in dead organisms and waste material, which is then only available to decomposers such as fungi and bacteria. This waste material also includes parts of animals and plants that cannot be digested by consumers such as bones and hair.

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34
Q

what is a pyramid of numbers

A

An illustration of how many organisms there are at each trophic level in a food chain

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35
Q

describe how a pyramid of numbers works

A

Each pyramid bar is proportional to the number of individuals, approximated for the total biomass at that level

  • In most food chains, the number of organisms at each trophic level decreases, giving a pyramid of numbers a pyramid shape
  • However, pyramids of numbers do not accurately reflect what is happening in an ecosystem. For example, one tree may support thousands of caterpillars and although a tree is far larger than all the caterpillars, this is not shown on the inverted/ distorted pyramid
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36
Q

whats a pyramid of biomass

A

An illustration of the amount of dry biomass at each trophic level in a food chain

-the area of each bar is proportional to the dry mass of all organisms at that trophic level

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37
Q

why are pyramids of biomass considered better/ more accurate than pyramids of numbers

A

each pyramid bar is proportional to the dry mass of all the organisms at that trophic level.

Using biomass at each trophic level shows how ‘much’ of each organism there is collectively, as opposed to how many.

Dry mass is a more accurate measure of biomass than wet mass, which is affected by water uptake and loss and therefore is not stable.

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38
Q

how is biomass calculated to create a pyramid of biomass

A

-an ecologist collects all the organisms and places them in an oven at 80 degrees Celsius until all the water has been evaporated.

-they check this by periodically finding the mass of organisms .

-once the mass stops reducing, they can be certain that all the mass has been removed

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39
Q

what are the negatives of calculating dry mass for a pyramid of biomass

A

-doing this is destructive to the ecosystem studied, so ecologists often measure the wet mass of the organism and calculate the dry mass on the basis of previously published data.

-Calculating dry biomass is time consuming as samples must be put in a scientific oven to evaporate the entire water content in the sample

  • Samples are used to estimate the biomass of the whole population. These samples may not be representative of the whole population
  • Biomass pyramids only show data at one point in time in one sample, e.g. a sample of pond water with phytoplankton and zooplankton (sample composition may not accurately reflect the habitat sampled)
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40
Q

what equation is uses to calculate the efficiency of biomass transfer between trophic levels

A

ecological efficiency= Biomass at higher trophic level/ biomass at lower trophic level x100

e.g.

ecological efficiency= biomass of primary consumer/ biomass of producer x100

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41
Q

define productivity

A

productivity is the rate at which energy passes through each trophic level in the food chain

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42
Q

what is gross primary productivity

A

gross primary productivity is the rate at which plants convert light energy into chemical energy though photosynthesis

even at the start of the food chain, this is inefficient

43
Q

why is entry of biomass into the food chain considered inefficient

A

photosynthesis produces glucose…

in optimal conditions, only 40% of light energy from the sun enters the light reaction of photosynthesis, and only half of this is involved in glucose production.

only two thirds of the glucose is then used for the production of starch, cellulose. lipids and proteins, contributing to growth. The rest is respired. Hence, only a small proportion (1-8%) of energy from the sun remains to enter the food chain

44
Q

define net primary productivity (NPP)

A

net primary productivity is the proportion of energy from the sun available to enter the food chain
this is from 1-8%

45
Q

how have humans manipulated environmental factors such as light to make energy conversion more efficient, reduce energy loss and increase the amount of biomass which is incorporated into plants

A

-light levels limit the rate of photosynthesis and hence production of biomass. Some crops are planted early to provide a longer growing season to harvest more light. Others are grown under light banks.

46
Q

how have humans manipulated environmental factors such as plant breeding to make energy conversion more efficient, reduce energy loss and increase the amount of biomass which is incorporated into plants

A

As well as irrigating crops, drought resistant strains have been bred, e.g. drought-resistant barley in North Africa, wheat in Australia and sugar beet in the UK. Water is a reactant in photosynthesis when glucose is produced

47
Q

how have humans manipulated environmental factors such as creating greenhouses to make energy conversion more efficient, reduce energy loss and increase the amount of biomass which is incorporated into plants

A

growing plants in greenhouses provides a warmer temperature, increases rate of photosynthesis, and increases the rate of production of biomass.

48
Q

how have humans manipulated environmental factors such as time in which crops are grown to make energy conversion more efficient, reduce energy loss and increase the amount of biomass which is incorporated into plants

A

planting field crops early to provide a longer growing season also helps avoid the impacts of temperature on final yield

49
Q

how have humans manipulated environmental factors such as ensuring nutrients to make energy conversion more efficient, reduce energy loss and increase the amount of biomass which is incorporated into plants

A

lack of available nutrients slows the rate of production of biomass through photosynthesis

Crop rotation can help (growing a different crop in each field) as it stops the reduction in soil levels of inorganic materials such as nitrate or potassium

Including a nitrogen fixing crop in that cycle replenishes nitrogen levels. Many crops have been bred to respond to high levels of fertiliser which provides ammonium, nitrate, potassium and phosphate.

50
Q

how have humans manipulated environmental factors such as pests to make energy conversion more efficient, reduce energy loss and increase the amount of biomass which is incorporated into plants

A

pests eat crop plants, removing biomass from the food chain and lowering yield. spraying with pesticides may help. Some plants have also been bred to be pest resistant or have been genetically modified with a bacterial gene from Bacillus thuringiensis

51
Q

how have humans manipulated environmental factors such as fungi presence to make energy conversion more efficient, reduce energy loss and increase the amount of biomass which is incorporated into plants

A

-fungal disease reduces biomass
-fungi can cause: root rot, damage xylem vessels, damage foliage through wilt, blight and spotting, damage phloem tubes or damage flowers/ fruit (interfering with reproduction).

-farmers spray crops with fungicides, many crops have been bred to resist fungal infections. Potatoes have been modified to resist potato blight

52
Q

how have humans manipulated environmental factors such as presence of weeds to make energy conversion more efficient, reduce energy loss and increase the amount of biomass which is incorporated into plants

A

a crops NPP is reduced by competition from weeds for light, water and nutrients. Farmers use herbicides to kill weeds. the herbicide usually binds to an enzyme, stopping it from working, and frequently leading to a toxic build up of the enzymes substrate .

53
Q

why is transfer of biomass between trophic levels inefficient

A

primary consumers do not make full use of plants’ biomass- some plants die, consumers do not eat every part of the plant, and they do not digest everything they eat (such as cellulose), egesting a lot of it in their faeces.

Even when food is digested and absorbed, much of it is respired, with only a small amount contributing to an increase in biomass and being available to the next consumer in the food chain.

54
Q

how can humans manipulate energy transfer to improve secondary productivity

A

-humans can harvest animals just before adulthood which minimises the loss of energy from the food chain. (a young animal invests a larger proportion of its energy into growth than an adult).

-selective breeding has been used to produce improved animal breeds with faster growth rates, increased egg production and increased milk production.

-animals may be treated with antibiotics to avoid unnecessary loss of energy to pathogens and parasites

-mammals and birds waste a lot of energy finding food and keeping their body temperatures stable. Zero grazing for pig and cattle farming maximises the energy allocated to muscle (meat) by stopping the animals from moving about by supplying food to them, and by keeping environmental temperature constant

however, these farming practices affect animal welfare

55
Q

what can dead and waste organic material be broken down by

A

by decomposers- microorganisms such as fungi or bacteria

56
Q

what are saprotrophs

A

organisms such as bacteria and fungi that feed on dead and decaying matter

57
Q

state the 3 steps in saprotrophic competition

A
  1. Saprotrophs secrete enzymes onto dead and waste material
  2. Enzymes digest the material into small molecules, which are then absorbed into the saprotrophs body
  3. Having been absorbed, the molecules are stored or respired to release energy
58
Q

what would happen if bacteria and fungi didn’t break down dead organisms

A

if they didnt, valuable nutrients would remain trapped within the dead organisms. By digesting dead and waste material, microorganisms obtain a supply of energy to stay alive, and the trapped nutrients are recycled.

59
Q

what particularly important role do microorganisms have in terms of cycles

A

they have a role in cycling carbon and nitrogen within ecosystems

60
Q

what do living things use nitrogen for

A

use nitrogen to make proteins and nucleic acids

61
Q

what is ammonification

A

*Ammonification is when nitrogen based compounds from Dead Organisms or Animal waste is turned into Ammonia by decomposers.

It then goes onto form ammonium ions (NH4+).F

62
Q

what are the 4 flows in the nitrogen cycle

A
  • nitrogen fixation
    -nitrification
    -decomposition and ammonification
    -denitrification
63
Q

LEARN NITROGEN CYCLE

A
64
Q

plants need a supply of fixed nitrogen

1-give an example of fixed nitrogen

2-explain why fixed nitrogen is needed instead of just nitrogen

A

1- NH4+ NO3-

2- nitrogen is very unreactive so it cant be used directly

65
Q

when can nitrogen fixation occur

A

-when lighting strikes or through the harber process in making fertiliser (accounts for 10% of nitrogen fixation in the world)

-nitrogen fixing bacteria account for 90%

66
Q

what are the different nitrogen fixing bacterias

A

-Azotobacter live freely in the soil and fix nitrogen gas (which is in the air within soil), using it to manufacture amino acids)

-Rhizobium live inside root nodules (peas, beans and clover).

67
Q

what type of relationship do nitrogen fixing bacteria have with the plant and why

A

the nitrogen fixing bacteria have a mutualistic relationship with the plant as the bacteria provide the plant with fixed nitrogen and receive carbon compounds such as glucose in return

68
Q

what are the role of proteins such as leghaemoglobin

A

leghaemoglobin in the nodules absorb oxygen and keep the conditions anaerobic. Under these conditions, the bacteria use an enzyme (nitrogen reductase) to reduce nitrogen gas to ammonium ions that can be used by host plants

69
Q

by what process are ammonium ions released

A

ammonium ions are released via ammonification by bacteria involved in putrefaction of proteins found in dead or waste organic matter

70
Q

what is nitrification

A

*Nitrification is when ammonium ions in the soil are changed into nitrogen compounds that can be used by plants by chemoautotrophic bacteria.

This happens in two stages,

  1. Nitrifying bacteria called Nitrosomonas oxidise Ammonium ions into NITRITES (NO2-).
  2. The other nitrifying bacteria called Nitrobacter oxidise nitrites into NITRATES (NO3-).
71
Q

what is chemoautotrophic bacteria

A

bacteria that derive energy from oxidation of certain inorganic compounds

72
Q

in what type of soil does oxidation occur in

A

oxidation occurs in well aerated soils

73
Q

what are nitrates used for in plants

A

used to make nucleotide bases and amino acids

74
Q

what is denitrification

A

bacteria convert nitrates back to nitrogen gas. When bacteria involved are growing under anaerobic conditions, such as in waterlogged soils, they use nitrates as a source of oxygen for their respiration and produce nitrogen gas (N2) and nitrous oxide

75
Q

simply, define nitrogen fixation

A

the conversion of atmospheric nitrogen into nitrate or ammonium

76
Q

simply, define nitrification

A

the oxidation of ammonium to nitrite and nitrite to nitrate

77
Q

simply, define denitrification

A

conversion of nitrates to nitrogen gas

78
Q

what is the carbon cycle driven by

A

the carbon cycle is driven by the processes of respiration and photosynthesis, with the carbon cycle being the main vehicle for the cycling of carbon between biotic and abiotic components

79
Q

what is the role of microorganisms in the carbon cycle

A

along with animals and plants, microorganisms respire to release CO2.They are important in decomposition of dead organisms and waste

80
Q

why are atmospheric levels now higher in the carbon cycle

A

due to global warming

81
Q

draw the carbon cycle

A

page 278

82
Q

what is succession

A

the progressive change in a community of organisms over time

83
Q

what is primary succession

A

the development of a community from bare (undisturbed) ground

84
Q

what are the 3 steps of primary succession

A
  1. Algae and Lichens begin to live on the bare rock. This is called a pioneer community
  2. erosion of the rock and build-up of dead and rotting organic matter produce enough soil for larger plants like mosses and ferns to grow. These replace or succeed the algae and lichens.
  3. In a similar way, larger plants succeed these small plants, until a final, stable community is reached. This is called a climax community. In the UK, climax communities are often woodland communities
85
Q

define climax communities

A

the final stable community that exists after the process of succession has occured

86
Q

what is secondary succession

A

this is succession that does not start from bare ground. Secondary succession takes place on a previously colonised but disturbed or damaged habitat.

87
Q

how does a sand dune show succession

A

pioneer species are at the start and a climax community is seen at the end

88
Q

what are the 4 stages of succession on a sand dune

A

1.pioneer species like sea rocket and prickly sandwort colonise the sand just above the high watermark. These can tolerate being sprayed with salty water, lack of freshwater and unstable sand.

2.wind blown sand builds up around the base of these plants , forming a mini sand dune. As plants die and decay, nutrients accumulate in this mini dune. As the dune gets bigger, plants like sea sandwort and sea couch grass colonise it. Because sea couch grass has underground stems, it helps to stabilize the sand

  1. With more stability, and accumulation of more nutrients, plants like sea spurge and marram grass start to grow. Marram grass is special: its shoots trap wind blown sand and as the sand accumulates the shoots grow taller above the growing dune, trapping more sand in the process
  2. As the sand dune and nutrients build up, other plants colonise the sand. Many are leguminous such as hare foots clover and bird foots trefoil, which convert nitrogen into nitrate. With nitrate available, more species colonise the dunes, like sand fescue and vipers bugloss which stabilise them further
89
Q

why is it difficult to work out if an area has reached its climax community

A

some areas are heavily influenced by agriculture

90
Q

what is deflected succession

A

it occurs when succession is stopped or interfered with, such as by grazing or when a lawn is mowed

The sub-climax community that results is called a plagioclimax.

91
Q

what are ways in which succession is deflected

A

via grazing, human activity, burning, application of fertiliser, application of herbicide, exposure to excessive amounts of wind and agriculture

due to the deflection of succession by human activity, it makes it hard to decide which habitats warrant preservation or conservation.

92
Q

what are the reasons why ecologists study ecosystems

A

to find out whether the abundance and distribution of a species is related to that of other species or to environmental factors such as light intensity or soil pH.

93
Q

what is a quadrat

A

a one meter frame that can have strings which occur every 10cm, separating it into 100 smaller squares

94
Q

what are the two types of data that can be collected when using a quadrat

A

-presence or absence of each species (distribution). Usually 50% of the plant needs to be inside to count

-Number of individuals (the abundance) of each species- either estimated or counted. E.g grass and moss may be estimated

95
Q

what is a point frame used to do

A

a point frame is to make estimating percentage cover more accurate.

96
Q

state how to use a point frame

A

lower the frame into the quadrat and record any plants touching the needles. If the frame has 10 needles, you lower it 10 times in each quadrat, you will have 100 readings. So everytime an individual touches a needle, this represents 1% cover.

97
Q

when placing quadrats, to avoid biasing the sample, and to provide a sample which is representative of the whole habitat, either:

A

-randomly position the quadrats across the habitat, using random numbers to plot coordinates for each one (random sampling). Lay out two tape measures on two edges of the study site, so that they look like axes on a graph. Use calculator, pair of dice or random number generator to generate random numbers. Use these pairs as coordinates to place your quadrats.

or

-take samples at regular distances across the habitat so you sample every part of the habitat to the same extent (systematic sampling)

98
Q

how do you know how many quadrats to use

A

in a pilot study looking at species distribution, take random samples from across the habitat, making a cumulative frequency table. Plot cumulative frequency against quadrat number. The point where the curve levels off tells you how many quadrats to sue

99
Q

what equation estimates the size of the population of each species in the whole habitat?

A

population size of a species=

mean number of individuals in each quadrat/ fraction of the total habitat area covered by a single quadrat

100
Q

when are transects used

A

transects are used when there is a change in vegetation across a habitat.

101
Q

what is a transect

A

a transect is a line taken across a habitat, samples at regular intervals are normally taken along this tape

102
Q

what are the two approaches of using a transect?

A

using a line transect- at regular intervals, make a note of which species is touching the tape

using a belt transect- at regular intervals, place a quadrat next to the line, moving it along the line after looking at each quadrat (continuous belt transect)

103
Q

what are the ways in which you can understand how living things vary across a transect line

A

to understand how living things vary along the transect line, you can compare the number of organisms of each species at each sampling point along the transect line.

You can also plot abiotic factors on the same scale with distance on the x-axis and the abiotic factor such as temp on the y-axis. By lining up your graph with your kite diagram (measuring no. of individuals per species) you can start to see how temp affects distribution and abundance.

biology a level (17 decks)

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