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A-level Biology (Edexcel Salters) > Topic 5 > Flashcards

Topic 5 Flashcards

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1
Q

Define ecosystem

A

All the organisms living in a particular area and all the abiotic factors

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2
Q

Define habitat

A

The place where an organism lives

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3
Q

Define population

A

All the organisms of one species in a habitat

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4
Q

Define population size

A

The number of individuals of one species in a particular area

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5
Q

Define community

A

All of the organisms of different species that live in the same habitat and interact with each other

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6
Q

Define abiotic factors

A

Non-living features of the ecosystem

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7
Q

Define biotic factors

A

Living feature of the ecosystem

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8
Q

Define abundance

A

The number of individuals of one species in a particular area (same as population size)

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9
Q

Define distribution

A

Where a species is within a particular area

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10
Q

Why does population size vary?

A

Because of the abiotic factors
E.g. the amount of light, water or space

Because of the biotic factors
E.g. Interspecific competition, intraspecific competition and predation

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11
Q

What happens if the abiotic conditions are ideal for a species? Include an example

A

Organisms grow fast and reproduce successfully
E.g. when temp of a mammal’s surrounding is ideal for metabolic reactions to take place, they don’t use up as much energy maintaining body temp. More energy for growth and reproduction so population will increase.

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12
Q

Define interspecific competition

A

Competition between different species

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13
Q

Define intraspecific competition

A

Competition within a species

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14
Q

What is carrying capacity?

A

The maximum stable population size of a species that an ecosystem can support

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15
Q

Explain intraspecific competition (5)

A

1) The population of a species increases when resources are plentiful
2) As population increases, they’ll be more organisms competing for the same amount of food and space
3) Eventually resources become limiting and population begins to decline
4) A smaller population means there is less competition for resources which is good for growth and reproduction so population grows
5) Carrying capacity is reached

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16
Q

Define predation

A

Where an organism kills and eats another organism. The population sizes of predators and prey are interlinked.

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17
Q

Why does distribution vary?

A

Because of abiotic factors
- Organisms can only exist where abiotic factors they can survive in exist
E.g. Some plants only grow on south-facing slopes in northern hemisphere ad solar input (light intensity) is greatest.

Because of biotic factors
- Interspecific competition, if 2 species are competing and one is better adapted the other is likely to be out-competed
E.g. the native red squirrel has disappeared from large areas as the grey squirrel has a better chance of survival because it’s larger and can store more fat for winter.

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18
Q

Define niche

A

The role of a species within it’s habitat

  • Its biotic interactions
    E.g. the organisms it eats and those its eaten by
  • Its abiotic interactions
    E.g. the oxygen it breathes in and the carbon dioxide it breathes out
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19
Q

How many species can occupy a niche?

A

1

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20
Q

Explain abundance in terms of the niche concept

A

Two species occupying similar niches will compete so fewer individuals of both species will be able to survive in the same area.

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21
Q

Explain distribution in terms of the niche concept

A

Organisms can only exist in habitats where all the conditions that make up their role exist.
E.g. the soprano pipistrelle bat feds on insects and lives in farmland, open woodland, hedge lands etc. It couldn’t exist in a desert because there would be different insects.

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22
Q

What do you look at to investigate populations of organisms?

A

Abundance
- Estimated by counting the number of individuals in samples taken or using percentage cover for plants

Distribution

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23
Q

How do you avoid bias in your results?

A

The sample should be random

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24
Q

When is it necessary to do a non-random sample?

A

When in habitats where there’s a lot of variety in the abiotic features and/or distribution of species in the habitat and you want to make sure all the different areas or species are sampled

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25
Q

What is systematic sampling?

A

A type of non-random sampling.
Samples are taken at fixed intervals, often along a line
E.g. quadrats placed along a transect in a habitat where the abiotic factors change gradually from one end of the sample to the other (environmental gradient)

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26
Q

What are the benefits of using a frame quadrat

A
  • Useful for quickly investigating areas with species that fit within a small quadrat
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27
Q

What is a frame quadrat?

A

A square frame, usually divided into 100 smaller squares by strings attached across the frame.
They’re place on the ground within the area you’re investigating.
In random sampling this can be done by selecting random coordinates.

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28
Q

What is a point quadrat?

A

A horizontal bar on two legs with a series of hole at set intervals along its length.
Pins are dropped through the holes in the frame and every plant that touches the pin is recorded.

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29
Q

How to calculate the percentage cover using a frame quadrat?

A

Count how much of the quadrat is covered by the plant (you count a square if its more than half covered)

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30
Q

How to calculate the percentage cover using a point quadrat?

A

Calculating the number of pins that touch a given species, as a percentage of the total number of pins dropped.

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31
Q

When are point quadrats useful?

A

In areas where there is lots of dense vegetation close to the ground

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32
Q

What are transects?

A

A line to help find out how plants are distributed across an area.

There are 3 types:

  • Line transects
  • Belt transects
  • Interrupted transects
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33
Q

What is a line transect?

A

A tape measure is placed along the transect and the species that touch the tape measure are recorded

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34
Q

What is a belt transect?

A

Data is collected along the transect using frame quadrats placed next to each other

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35
Q

What is a interrupted transect?

A

Instead of investigating the whole transect of either a line or belt, you take measurements at intervals

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36
Q

What type of diagram is used to show abundance and distribution?

A

Kite diagram

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37
Q

What feature of a kite diagrams represents abundance?

A

The thickness of the kite

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38
Q

What feature of a kite diagrams represents distribution?

A

The x-axis

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39
Q

What is topography?

A

The shape and features of the earth’s surface

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40
Q

What are edaphic factors?

A

Soil conditions

41
Q

How can you measure dissolved oxygen levels in aquatic habitat?

A

Using a oxygen sensor

42
Q

How can you measure humidity?

A

Using an electronic hydrometer

43
Q

How can you measure rainfall?

A

Using a rain gauge

44
Q

What is succession?

A

The process by which an ecosystem changes over time. The biotic conditions change as the abiotic conditions change

45
Q

What is primary succession?

A

This happens on land that’s been newly formed or exposed. There is no soil or organic material to start with, e.g. bare rock.

46
Q

What is secondary succession?

A

This happens on land that’s been cleared of all the plants but where the soil remains, e.g. after a forest fire or deforestation

47
Q

What are the stages of succession?

A

1) Primary succession starts when a species colonise a new land surface (pioneer species)
- seeds and spores are blown in by the wind and begin to grow
- the abiotic conditions are hostile (only pioneer species grow as they’re specially adapted to cope)

2) Pioneer species change the abiotic conditions as they die and microorganism decompose the dead organic material (humus). This forms basic soil
3) Makes conditions less hostile so new organisms with different adaptations move in and grow
4) These then die and are decomposed adding more organic material, making the soil deeper and richer in minerals
5) Larger plants such as shrubs can now grow in deeper soil
6) Some new species may change the environment so it becomes less suitable for previous species

7) Secondary succession happens in same way but soil layer is already there so succession starts at a later stage.
- pioneer species are larger plants (e.g. shrubs)

8) At each stage, different plants and animals that are better adapted for improved conditions move in and out-compete the organisms already there. They become the dominant species.

9) The ecosystem becomes more complex
- new species move in alongside existing species so biodiversity increases

10) The final stage is called the climax community
- the ecosystem is supporting the largest and most complex community of plants and animals it can.
- it won’t change much more so is in a stable state

48
Q

What determines what species make up the climax community?

A

The climate in the ecosystem

49
Q

What type of species are in a climax community in a temperate climate?

A

Large trees as they can grow in these conditions when soil deepens due to plenty availability of water, mild temps and not much change in seasons

50
Q

What type of species are in a climax community in a polar climate?

A

Large trees cant grow so only herbs or shrubs as not much water, low temp and massive changes in season

51
Q

Define plagioclimax

A

When succession is stopped artificially

52
Q

Define phosphorylation

A

Adding phosphate to a molecule

E.g. ADP is phosphorylated to ATP

53
Q

Define photophosphorylation

A

Adding phosphate to a molecule using light

54
Q

Define photolysis

A

The splitting of a molecule using light energy

55
Q

Define hydrolysis

A

The splitting of a molecule using water

E.g. ATP is hydrolysed to ADP

56
Q

Define redox reactions

A

Reactions that involve oxidation and reduction

57
Q

What do plants need energy for?

A

Photosynthesis, active transport, DNA replication, cell division and protein synthesis

58
Q

What do animals need energy for?

A

Muscle contraction, maintenance of body temp, active transport, DNA replication, cell division and protein synthesis

59
Q

What is photosynthesis?

A

The process where energy from light is used to break apart the strong bonds in H2O molecules.

60
Q

Where is hydrogen stored in the breakdown of H2O?

A

Glucose.

Formed when hydrogen is combined with CO2.

61
Q

Where does O2 go in the breakdown of H2O?

A

Into the atmosphere

62
Q

How do plants release the energy stored in glucose?

A

Respiration

63
Q

What is the immediate source of energy in a cell?

A

ATP

64
Q

Describe how ATP is synthesized. (3)

A

1) During respiration, glucose is broken down
2) Phosphorylation of ADP uses energy from an energy-releasing reaction (e.g. breakdown of glucose in respiration)
3) The energy is stored as chemical energy in the phosphate bond
4) The enzyme ATP synthase catalyses this reaction

65
Q

How does ATP get to the part of the cell that needs energy?

A

Diffuses

66
Q

How is energy released from ATP?

A

1) It’s broken down via hydrolysis into ADP and inorganic phosphate
2) Chemical energy is released from the phosphate bond and used by the cell
3) ATPase catalyses this reaction

67
Q

What are coenzymes?

A

A molecule that aids the function of a enzyme. They work by transferring a chemical group from one molecule to another.

68
Q

What coenzyme is used in photosynthesis?

A

NADP

69
Q

What does NADP do?

A

Transfers hydrogen form one molecule to another so it can reduce or oxidise a molecule.

70
Q

What are chloroplasts?

A

Flattened organelles found in plant cells where photosynthesis takes place.
They have a double membrane called the chloroplast envelope.

71
Q

Whats the advantage of having a double membrane in chloroplasts?

A

Keeps the reactants for photosynthesis close to their reaction sites

72
Q

What are thylakoids?

A

Fluid-filled sacs that are stacked up in the chloroplast into structures called grana. They have a large surface area to allow high absorption of light.

73
Q

What is a granum?

A

A structure within the chloroplasts of plants that is made up of stacked thylakoids and contains the chlorophyll and is the site of the light reactions of photosynthesis

74
Q

How are the grana linked together?

A

By bits of thylakoid membrane called lamella.

75
Q

What is present in the thylakoid membranes?

A

Lots of ATP synthase to produce ATP in light-dependent reactions.
Photosynthetic pigments.

76
Q

What are photosynthetic pigments?

A

Coloured substances that absorb light energy needed for photosynthesis.

77
Q

What wavelength does photosystem I absorb?

A

700 nm

78
Q

What wavelength does photosystem II absorb?

A

680 nm

79
Q

What is the stroma?

A

A gel-like substance in the inner membrane of the chloroplast and surrounds the thylakoids.
Contains all the enzymes, sugars and organic acids required for light-dependent reactions.
Also contains oil droplets (store non-carbohydrate organic material)

80
Q

Describe the Calvin Cycle (10)

A

1) CO2 enters leaf through stromata and diffuses into stroma of chloroplast
2) It combines with ribulose bisphosphate (RuBP).
3) Catalysed by RUBISCO
4) Gives unstable 6-carbon compound, quickly breaks down into 2 molecules of 3-carbon compound called glycerate 3-phosphate (GP)
5) Hydrolysis of ATP from LDR provides energy to turn 3-carbon compound, GP, into different 3-carbon compound called glyceraldehyde 3-phosphate (GALP)
6) This requires H+ ions which comes from reduced NADP. Reduced NADP is recycled to NADP
7) Some GALP is then converted to useful organic compounds (e.g. glucose) and some continues in the Calvin Cycle to regenerate RuBP
8) Two molecules of GALP can be used to make hexose sugar (6 carbon atoms), e.g. glucose
9) 5 out of 6 molecules of GALP produced aren’t used to make hexose but to regenerate RuBP
10) Regenerating RuBP uses rest of ATP produced by light-dependant reaction

81
Q

Where does the LDRs take place?

A

Thylakoid membranes of the chloroplast

82
Q

Where does the LIRs take place?

A

Stoma of the chloroplasts

83
Q

What happes in LDRs in summary?

A
  • Light energy is used to add a phosphate group to ADP to form ATP and to reduced NADP to form reduced NADP
  • ATP tranfers energy and reduced NADP transfers hydrogen to LIRs
  • H2O is oxidised to O2
84
Q

What happes in LIRs in summary?

A
  • ATP and reduced NADP from LDRs supply energy and hydrogen to make glucose form CO2
85
Q

How do you make ATP?

A

From ADP and inorgani phosphate by a reaction called photophosphorylation

86
Q

What is photolysis?

A

Splitting water into protons, electrons and oxygen

87
Q

What does non-cyclic photophosphorylation produce?

A

ATP, reduced NADP and O2

88
Q

What does cyclic photophosphorylation produce?

A

ATP

89
Q

Explain the process of non-cyclic photophosphorylation (12)

A

1) Light is absorbed by photosystem 2 (PSII)
2) The light energy excites electrons in chlorophyll
3) Electrons move to a higher energy level
4) The high-energy electrons move along the electron transport chain to PSI
5) As the excited electrons from chlorophyll leave PSII to move along electron transport chain, they must be replaced
6) Light energy splits water into protons, electrons and oxygen - photolysis
7) This reaction is H2O –> 2H+ + 1/2O2
8) Excited electrons lose energy as they move along electron transport chain
9) Energy is used to transport protons into thylakoids so they have higher conc of protons than stroma. Form proton gradient across membrane.
10) Protons move down conc grad into stroma, via enzyme ATP synthase. Energy from this combines ADP and inorganic phosphate to form ATP.
11) Light energy absorbed by PSI excites electrons to even higher energy level.
12) Electrons transferred to NADP along with a proton from stroma to form reduced NADP.

90
Q

Explain cyclic photophosphorylation (4)

A

1) Only uses PSI
2) Called cyclic as electrons from chlorophyll molecules aren’t passed onto NADP but are passed back to PSI via electron carriers
3) Electrons are recycled
4) Only produces small amounts of ATP

91
Q

Why is the Calvin cycle also known as carbon dioxide fixation?

A

CO2 is fixed in a organic molecule

92
Q

What is genomics?

A

Branch of science that uses DNA technology to determine base sequence of an organisms genome and the functions of its gene.

93
Q

What is proteomics?

A

Study of proteins

E.g/ the size, shape and amino acid sequence

94
Q

What is evolution?

A

A change in allele frequency in a population over time. It occurs by natural selection.

95
Q

Explain evolution (6)

A

1) Individuals in a population vary because they have different alleles. The different alleles are due to gene mutations.
2) This means some individuals are better adapted to their environment.
3) Individuals that have an allele that increases their chance of survival are more likely to survive, reproduce and pass on their genes than individuals with different alleles.
4) This means a greater proportion of the next generation will inherit the beneficial allele.
5) So they are more likely to survive, reproduce and pass on their genes
6) The frequency of the beneficial allele increases from generation to generation.

96
Q

Explain how isolation leads to speciation (3)

A

1) Speciation happens when populations of the same species become reproductively isolated which reduces gene flow between two populations.
2) This means that natural selection acts on each population separately so new species can develop.
3) Reproductive isolation may occur because of geographical isolation (allopatric speciation) or because of random mutations in phenotype that prevent populations from mating (sympatric speciation)

97
Q

Explain allopatric speciation

A

1) Populations that are geographically separated will experience slightly different conditions
2) Populations will experience different selection pressures and so different changes in allele frequency could occur
3) Different alleles will be more advantageous in different populations
4) Natural selection will then act on these alleles, increasing the frequency of it
5) Allele frequencies will also change as mutations occur independently in each population
6) The changes in allele frequency will lead to differences accumulating in the gene pools of the separated populations, causing changes in phenotype frequencies
7) Eventually the populations become genetically distinct so individuals form different populations will have changed so much they wont be able to breed with eachother to produce fertile offspring - they have become reproductively isolated.
8) They are now separate species

98
Q

What ways can reproductive isolation occur?

A
  • Seasonal changes
  • Mechanical changes
  • Behavioural changes

A-level Biology (Edexcel Salters) (7 decks)

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