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IGCSE Biology - Extended > 19. Organisms & Their Environment > Flashcards

19. Organisms & Their Environment Flashcards

1
Q

Producers definition

A

organisms that produce their own organic nutrients usually using energy from sunlight, Plants are producers as they carry out photosynthesis to make glucose

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2
Q

herbivore definition

A

an animal that gets its energy by eating plants

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3
Q

carnivore definition

A

an animal that gets its energy by eating other animals

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4
Q

primary consumers definition

A

herbivores - they feed on producers (plants)

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5
Q

secondary consumers definition

A

predators that feed on primary consumers

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6
Q

tertiary consumers definition

A

predators that feed on secondary consumers

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7
Q

decomposers definition

A

bacteria and fungi that get their energy from feeding off dead and decaying organisms and undigested waste (such as faces) by secreting enzymes to break them down

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8
Q

What does a food chain show?

A

A food chain shows the transfer of energy from one organism to the next, starting with a producer

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9
Q

What is the source of all energy in a food chain?

A

The source of all energy in a food chain is light energy from the Sun

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10
Q

What do the arrows in a food chain show?

A

The arrows in a food chain show the transfer of energy from one trophic level to the next

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11
Q

How is energy transferred from one organism to another?

A

Energy is transferred from one organism to another by ingestion (eating)

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12
Q

What is a food web?

A

A food web is a network of interconnected food chains

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13
Q

Why are food webs more accurate than food chains?

A

Food webs are more realistic ways of showing connections between organisms within an ecosystem as animals rarely exist on just one type of food source

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14
Q

What do food webs give us more information on?

A

Food webs give us a lot more information about the transfer of energy in an ecosystem

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15
Q

What type of relationship does a food web show?

A

interdependence

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16
Q

interdependent definition

A

how the change in one population can affect others within the food web

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17
Q

What causes most of the changes in populations?

A

Most of the changes in populations of animals and plants happen as a result of human impact – either by overharvesting of food species or by the introduction of foreign species to a habitat

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18
Q

Why is human impact on environments so harmful?

A

Due to interdependence, these can have long-lasting knock-on effects to organisms throughout a food chain or web

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19
Q

What is a trophic level?

A

Trophic levels describe the position of an organism in a food chain, web or pyramid

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20
Q

Does an animal have to be at only one trophic level? Why?

A

NO
Animals (known as consumers) can be at different trophic levels within the same food web as they may eat both primary, secondary and / or tertiary consumers

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21
Q

How does energy from the sun flow to the first trophic level?

A

Energy flows from the sun to the first trophic level (producers) in the form of light

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22
Q

How do producers make use of light energy?

A

Producers convert light energy into chemical energy and it flows in this form from one consumer to the next

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23
Q

Where is all energy eventually transferred to?

A

Eventually all energy is transferred to the environment – energy is passed on from one level to the next with some being used and lost at each stage

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24
Q

Is energy flow a cyclical or non-cyclical process?

A

NON-CYCLICAL
Energy flow is a non-cyclical process – once the energy gets to the top of the food chain or web, it is not recycled but ‘lost’ to the environment

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25
Q

What is energy flow a direct contrast to?

A

This is in direct contrast to the chemical elements that organisms are made out of, which are repeatedly recycled
(as energy is not recycled)

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26
Q

What has to happen to energy for it to be transferred ?

A

In order for the energy to be passed on, it has to be consumed (eaten)

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27
Q

Why is not all of the energy from e.g plants passed onto the primary consumer?

A

However not all of the energy grass plants receive goes into making new cells that can be eaten
Only the energy that is made into new cells remains with the organism to be passed on

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28
Q

Why may an organism not receive all of the energy in a plant?

A

Even then, some of this energy does not get consumed – for example few organisms eat an entire organism, including roots of plants or bones of animals – but energy is still stored in these parts and so it does not get passed on

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29
Q

In what 4 ways can energy in a an organism be “lost”?

A
  • making waste products eg (urine) that get removed from the organism
  • as movement
  • as heat (in mammals and birds that maintain a constant body temperature)
  • as undigested waste (faeces) that is removed from the body and provides food for decomposers
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30
Q

Why are food chains rarely longer than 5 organisms long?

A

This inefficient loss of energy at each trophic level explains why food chains are rarely more than 5 organisms long

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31
Q

If, for example, an organism would prey on the top consumer, why would this not be efficient?

A

In order to survive, it would have to:

  • eat a huge number of them every day to get the amount of energy it needed to survive (are there that many barn owls close together?)
  • not expend much energy itself hunting them (is this likely?)
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32
Q

How much energy is:

  • available to the organism at the next level
  • lost as heat and in undigested materials?
A
  • 10% of energy available to organisms at the next level to make new biomass
  • 90% of energy lost as heat an in undigested materials
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33
Q

What type of consumer are humans? What does this mean?

A

Humans are omnivores, obtaining energy from both plants and animals, and this gives us a choice of what we eat

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34
Q

What does humans being omnivores impact?

A

These choices, however, have an impact on what we grow and how we use ecosystems

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35
Q

Looking at this food chain, why would it be better for humans to eat the wheat, rather than the cow?

wheat → cow → human

wheat → human

A

Given what we know about energy transfer in food chains, it is clear that if humans eat the wheat there is much more energy available to them than if they eat the cows that eat the wheat
This is because energy is lost from the cows, so there is less available to pass on to humans
Therefore, it is more energy efficient within a crop food chain for humans to be the herbivores rather than the carnivores

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36
Q

What do humans feed animals and why?

A

In reality, we often feed animals on plants that we cannot eat (eg grass) or that are too widely distributed for us to collect (eg algae in the ocean which form the food of fish we eat)

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37
Q

What does a pyramid of number show?

A

A pyramid of numbers shows how many organisms we are talking about at each level of a food chain.

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38
Q

What does the width of a box in a pyramid of number suggest?

A

The width of the box indicates the number of organisms at that trophic level

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39
Q

Does a pyramid of numbers always have to be pyramid shaped? Why?

A

NO
This is because the size of the organism is also important – one large organism, like the oak tree in the pyramid above, contains enough energy to support many smaller organisms (the insects)

40
Q

What are two important things to remember when drawing a pyramid of numbers?

A

You cannot change the trophic level of the organisms – they must stay in the same order as in the food chain with producers on the bottom, followed by primary consumers, then secondary consumers, then tertiary consumers

Generally, the larger an individual organism is, the less of them there are

41
Q

What does a pyramid of biomass show?

A

A pyramid of biomass shows how much mass the creatures at each level would have without including all the water that is in the organisms (their ‘dry mass’)

42
Q

Do pyramids of biomass have to be pyramid-shaped? Why?

A

YES
This is because the mass of organisms has to decrease as you go up a food chain – if we take our first food chain as an example, it’s impossible to have 10kg of grass feeding 50kg of voles feeding 100kg of barn owls

43
Q

Why are pyramids of biomass better than pyramids of number?

A

Pyramids of biomass provide a much better idea of the quantity of the plant or animal material at each level of a food chain and therefore are a better way of representing interdependence within the food chain

44
Q

Why are there nutrient cycles?

A

Nutrients such as carbon and nitrogen are not endless resources

There is a finite amount of each element on the planet and as such, they need to be RECYCLED in order to allow new organisms to be made and grow

45
Q
  1. In what form is carbon take out of the atmosphere in and what is it used for?
A

Carbon is taken out of the atmosphere in the form of carbon dioxide by plants to be used for photosynthesis

46
Q
  1. Where does the carbon dioxide the plants have absorbed go?
A

It is passed on to animals (and microorganisms) by feeding

47
Q
  1. How is this carbon returned to the atmosphere?
A

It is returned to the atmosphere in the form of carbon dioxide by plants, animals and microorganisms as a result of respiration

48
Q
  1. What is a natural source of carbon in the Earth and how is this formed?
A

If animals and plants die in conditions where decomposing microorganisms are not present the carbon in their bodies can be converted, over millions of years and significant pressure, into fossil fuels

49
Q
  1. How is the carbon in fossil fuels released?
A

When fossil fuels are burned (the process is known as combustion), the carbon combines with oxygen and carbon dioxide is released into the atmosphere

50
Q

What is an increased use of fossil fuels causing?

A

Increased use of fossil fuels is contributing to an increase in the carbon dioxide content of the atmosphere

51
Q

What is mass deforestation causing, in relation to the carbon cycle?

A

In addition, mass deforestation is reducing the amount of producers available to take carbon dioxide out of the atmosphere by photosynthesis

52
Q

What is mass deforestation specifically for land causing, in relation to the carbon cycle?

A

This problem is exacerbated by the fact that in many areas of the world, deforestation is taking place for land rather than for the trees themselves, and as such they are burnt down, releasing yet more carbon dioxide into the atmosphere

53
Q

What are the 4 basic steps of the carbon cycle?

A
  • Carbon is taken out of the atmosphere by photosynthesis
  • It is passed on to animals and decomposers by feeding
  • It is returned by respiration; in plants, in animals and in decomposing
    microorganisms
  • In addition, it is returned (in increasing amounts) by combustion of fossil fuels
54
Q
  1. Where do water molecules move between?
A

Water molecules move between various locations – such as rivers, oceans and the atmosphere – by specific processes

55
Q
  1. How is water able to move between certain locations?
A

This is possible because water changes state at a relatively low temperature

56
Q
  1. In what form does water enter the atmosphere?
A

Water enters the atmosphere as water vapour

57
Q
  1. In what two processes can water vapour enter the atmosphere?
A
  • evaporation

- transpiration

58
Q
  1. How does evaporation work?
A

Energy from the Sun heats the Earth’s surface and water evaporates from oceans, rivers and lakes

59
Q
  1. How does transpiration work?
A

Transpiration from plants releases water vapour into the air

60
Q
  1. What does the warmer air of the lower atmosphere do?
A

The warmer air of the lower atmosphere rises, taking the water vapour with it

61
Q
  1. What happens to the warm air as it rises and what does this form?
A

The moist air cools down as it rises

Water vapour condenses back into liquid water, forming clouds

62
Q
  1. How does water return to the earth?
A

Water returns to Earth in the form of precipitation

63
Q
  1. How does precipitation occur?
A

As the water droplets in the cloud get bigger and heavier, they begin to fall as rain, snow and sleet
This is called precipitation

64
Q
  1. What is nitrogen used for?
A

Nitrogen as an element is required to make proteins

65
Q
  1. Why is N2 gas not very useful?
A

Neither plants nor animals can absorb it from the air

66
Q
  1. Why can N2 gas not be absorbed from the air?
A

N2 gas is very stable and the bonds holding the nitrogen atoms together would need massive amounts of energy to break (the two nitrogen atoms in a nitrogen molecule are held together by a triple covalent bond)

67
Q
  1. In what two ways can N2 be taken out of the air and converted into something which can be used?
A
  • nitrogen fixing bacteria

- lightning can ‘fix’ it

68
Q
  1. How can nitrogen fixing bacteria convert N2 to a useable form?
A

take N2 gas and change it into nitrates in the soil

69
Q
  1. How can lightning convert N2 to a useable form?
A

splitting the bond between the two atoms and turning them into nitrous oxides like N2O and NO2 that dissolve in rainwater and ‘leach’ into the soil

70
Q

7 Where can nitrogen fixing bacteria be found?

A

found ‘free living’ in soil and also in the root nodules of certain plants (peas, beans, clover – we call them leguminous plants)

71
Q

8 In what form do plants absorb N?

A

Plants absorb the nitrates they find in the soil and use the nitrogen in them to make proteins

72
Q

9 How do animals absorb N?

A

Animals eat the plants (or other animals) and get the nitrogen they need from the proteins in the plant or animal

73
Q

10 How is N returned back to the soil from animals?

A

Waste (urine and faeces) from animals sends nitrogen back into the soil as ammonium compounds (the urea in urine contains nitrogen)

74
Q

11 What happens to the N present in animals and plants when they die?

A

When the animals and plants die, they decay and all the proteins inside them are broken down into ammonium compounds and put back into the soil by decomposers

75
Q
  1. Why are ammonium compounds not useful and how is this problem fixed?
A

The plants can’t absorb ammonium compounds though, so a second type of soil bacteria, nitrifying bacteria, are used to convert the ammonium compounds

76
Q
  1. What do nitrifying bacteria do? how is the useful?
A

nitrifying bacteria, convert the ammonium compounds to nitrites and then to nitrates, which can then be absorbed by plants – and so the cycle goes on

77
Q
  1. What third type of bacteria also uses N?
A

type of (anaerobic) bacteria called denitrifying bacteria

78
Q
  1. Where are denitrifying bacteria found?
A

found in poorly aerated soil (ie not much oxygen)

79
Q

16 What do denitrifying do?

A

These bacteria take the nitrates out of the soil and convert them back into N2 gas

80
Q

17 How can farmers help decrease the number of denitrifying bacteria?

A

Farmers can help reduce the amount of these unhelpful bacteria by ploughing and turning over soil

81
Q

Population definition

A

A population is defined as a group of organisms of one species, living in the same area at the same time

82
Q

Community definition

A

A community is defined as all of the populations of different species in an ecosystem

83
Q

Ecosystem definition?

A

An ecosystem is defined as a unit containing the community of organisms and their environment, interacting together (eg a decomposing log, a lake)

84
Q

What do living organisms compete with each other for?

A

All living organisms compete with each other for food, water and living space

85
Q

What type of organisms increase their populations the fastest?

A

Those which are the best adapted to their environments generally increase their populations at the expense of those less well adapted

86
Q

What 3 factors affect population growth?

A

Food supply
Predation
Disease

87
Q

In what way has human population been growing for the last 150 years?

A

Human population growth globally has been increasing exponentially for the last 150 years

88
Q

What are reasons for the exponential growth of the human population?

A

Improved technology leading to an abundance of food = rapid increase in birth rate

Improved medicine, hygiene and health care = decrease in death rate

89
Q

What is the name of a population growth graph which looks like an s?

A

The shape of this curve ( a little like an ‘S’), gives it its name – a sigmoid growth curve

90
Q

What 4 phases does a sigmoid graph have?

A 
lag phase
log
phase
stationary phase
death phase
91
Q

What is the lag phase on a s graph?

A

organisms are adapting to the environment before they are able to reproduce; in addition, at this stage there are very few organisms and so reproduction is not producing larger numbers of offspring

92
Q

What is the log phase on a s graph?

A

(aka exponential phase) – food supply is abundant, birth rate is rapid and death rate is low; growth is exponential and only limited by the number of new individuals that can be produced

93
Q

What is the stationary phase on a s graph?

A

population levels out due to a factor in the environment, such as a nutrient, becoming limited as it is not being replenished; birth rate and death rate are equal and will remain so until either the nutrient is replenished or becomes severely limited

94
Q

What is the death phase on a s graph?

A

population decreases as death rate is now greater than birth rate; this is usually because food supply is short or metabolic wastes produced by the population have built up to toxic levels

95
Q

Are organisms in natural environment likely to show a population growth like a sigmoid growth curve? Why?

A

NO

- because they’re affected by many other factors

96
Q

What factors affect can organisms in a natural environment? 5

A
  • changing temperature or light
  • predators
  • disease
  • immigration (individuals moving into the area)
  • emigration (individuals moving out of the area)

IGCSE Biology - Extended (22 decks)

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