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B3 - Living Together - Food and Ecosystems Flashcards

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1
Q

What are enzymes?

A

Enzymes

Biological catalysts that the rate of a
chemical reaction go faster without being
permanently altered themselves.

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2
Q

What is the active site of an enzyme?

A

Active site

The region of an enzyme in which a
substrate molecule binds and the
reaction takes place.

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3
Q

Why are enzymes described as having a

‘high specificity’ for their substrate?

A

Enzymes ‘High specifity’ for their substrate

Only substrates with a specific,
complementary shape can fit into an
enzyme’s active site.

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4
Q

Describe the ‘lock and key’ model

A

Lock and key model

  1. The active site of the enzyme and the substrate
    come into contact
  2. Substrate binds, enzyme-substrate complex forms
  3. Substrate converted to products
  4. Products released from the active site. The active
    site is now free to bind to another substrate.
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5
Q

What factors affect the rate of an

enzyme-controlled reaction?

A

Factors that affect enzyme activity

● Temperature
● pH
● Substrate concentration

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6
Q

Explain how increasing temperature
initially affects the rate of an
enzyme-controlled reaction

A

How initial temp increase affects enzyme activity

● As temperature increases molecules have more KE
● Movement of molecules increases
● Probability of a successful collision increases
● More enzyme-substrate complexes form
● Rate of reaction increases

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7
Q

Explain how increasing temperature
above the optimum affects the rate of an
enzyme-controlled reaction

A

How temp above optimum affects enzyme activity

● Temperature increases above the optimum
● Increased vibrations break bonds in enzyme’s structure
● Active site changes shape, enzyme is denatured
● No more enzyme-substrate complexes can form
● Rate of reaction decreases

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8
Q

Draw a graph to show the effect of increasing
temperature on the rate of an enzyme-catalysed
reaction.

A

Check PM tutor

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9
Q

Explain how pH affects the rate of an

enzyme-controlled reaction

A

How pH affects enzyme activity

● Enzymes have an optimum pH
● pH shifts from the optimum
● Bonds in the enzyme’s structure are altered
● Active site changes shape, enzyme is denatured
● Rate of reaction decreases

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10
Q

Draw a graph to show the effect of
increasing pH on the rate of an
enzyme-catalysed reaction

A

Chem PM tutor or search

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11
Q

Explain how substrate concentration
affects the rate of an enzyme-controlled
reaction

A

How substrate conc affects enzyme activity

● Substrate concentration increases
● Number of substrate molecules in the same volume increases
● Probability of a successful collision increases
● More enzyme-substrate complexes form
● Rate of reaction increases
● Once all active sites become full, the rate of reaction plateaus

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12
Q

Draw a graph to show the effect of
increasing substrate concentration on
the rate of an enzyme-catalysed reaction

A

.

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13
Q

What is photosynthesis?

A

Photosynthesis

A chemical reaction that takes place inside
photosynthetic organisms (e.g. plants, algae)
converting light energy into chemical energy
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14
Q

Write the word equation for

photosynthesis

A

Word equation for photosynthesis

Write the word equation for photosynthesis
carbon dioxide + water → glucose + oxygen

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15
Q

Write the symbol equation for

photosynthesis

A

Symbol equation for photosynthesis

6CO2 + 6H2O → C6H12O6 + 6O2

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16
Q

Why is photosynthesis important?

A

Photosynthesis produces glucose which has a wide range of uses:
● Used in respiration to release energy
● Converted to starch and stored - starch can be broken down to
glucose when the plant requires energy
● Used to make a wide range of organic molecules such as lipids,
proteins and other sugars which are used for growth

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17
Q

Where does photosynthesis take place?

A

Where does photosynthesis take place?

Within chloroplasts

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18
Q

What type of reaction is photosynthesis?

A

What type of reaction is photosynthesis?

An endothermic reaction that takes in
energy (in the form of light)

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19
Q

What is chlorophyll?

A

Chlorophyll

A pigment found in chloroplasts that
absorbs light

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20
Q

Describe the two main stages of

photosynthesis

A

2 main stages of photosynthesis
1. Chlorophyll absorbs light energy which is used to split
water into oxygen gas (waste product) and hydrogen ions

  1. Carbon dioxide combines with hydrogen ions to form
    glucose
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21
Q

What does the first stage of

photosynthesis require?

A

What does the first stage of photosynthesis require?

Light energy
Water, H2O

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22
Q

What are the products of the first stage

of photosynthesis?

A

What are the products of the first stage of
photosynthesis?

Oxygen gas, O2
(O2 is a waste product and is released into the atmosphere)
Hydrogen ions, H+

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23
Q

What does the second stage of

photosynthesis require?

A

What does the second stage of photosynthesis
require?

Carbon dioxide gas, CO2
Hydrogen ions, H+

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24
Q

What is produced in the second stage of

photosynthesis?

A

What is produced in the second stage of
photosynthesis?

Glucose, C6H12O6

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25
Q

What factors affect the rate of

photosynthesis?

A

What factors affect the rate of photosynthesis?

● Temperature
● Light intensity
● Carbon dioxide concentration

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26
Q

What is a limiting factor?

A

What is a limiting factor?

A variable that limits the rate of a
particular reaction

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27
Q

Explain how temperature affects the rate

of photosynthesis

A

How temp affects rate of photosynthesis
● Higher temperatures provide more KE for enzymes involved in (KE = Kinetic Energy)
photosynthesis so the rate increases as temperature rises
● The optimum temperature is usually 25°C
● If the temperature becomes too high (around 45°C) enzymes
become denatured and the rate of photosynthesis decreases

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28
Q

Explain how light intensity affects the

rate of photosynthesis

A

Explain how light intensity affects the rate of
photosynthesis

As light intensity increases, the rate of
photosynthesis increases until another
factor (e.g. temperature) becomes
limiting.

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29
Q

How can the effect of light intensity on
the rate of photosynthesis be measured
in the lab? (2)

A

How can the effect of light intensity on the rate of
photosynthesis be measured in the lab? (2) (higher)

● Using a light meter
● Using the inverse square law where:
Light intensity = 1/d2

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30
Q

Why does the rate of photosynthesis
decrease as the distance from a light
source increases?

A

Light intensity is inversely proportional to the
square of the distance from the light source.
Thus, as the distance increases, light intensity
decreases and the rate of photosynthesis
decreases.

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31
Q

Explain how carbon dioxide
concentration affects the rate of
photosynthesis

A

Explain how carbon dioxide concentration affects the
rate of photosynthesis

As carbon dioxide concentration
increases, the rate of photosynthesis
increases until another factor (e.g. light
intensity) becomes limiting.

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32
Q

What is diffusion?

A

What is diffusion?

The net movement of molecules from an
area of high concentration to an area of
low concentration down a concentration
gradient

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33
Q

Define osmosis

A

Define osmosis

The net movement of water molecules from
an area of high water concentration to an
area of low water concentration across a
partially permeable membrane

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34
Q

What is active transport?

A

What is active transport?

The movement of molecules across a cell
membrane from an area of low concentration
to an area of high concentration, against the
concentration gradient, using energy

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35
Q

By what process do substances enter

and leave single-celled organisms?

A

By what process do substances enter and leave
single-celled organisms?

Diffusion

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36
Q

Why can’t multicellular organisms rely on

simple diffusion alone?

A

Why is simple diffusion less efficient in multicellular
organisms?

● Small surface area to volume ratio
● Several layers of tissue too deep to
diffuse through

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37
Q

Why must carbon dioxide be
transported into plants and oxygen be
transported out?

A

Why must carbon dioxide be transported into plants
and oxygen be transported out?

Carbon dioxide is required for
photosynthesis.
Oxygen is a by-product of photosynthesis
so it is released.

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38
Q

How do gases such as oxygen and
carbon dioxide move into and out of
plants?

A

How do gases such as oxygen and carbon dioxide
move into and out of plants?

● Diffuse through stomata on the lower surface of the
leaf and through air-filled spaces within the leaf
● Move between cells via simple diffusion across
partially permeable cell membranes

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39
Q

Why do plants require water?

A

Why do plants require water?
● Photosynthesis
● Maintenance of structure (turgidity)
● Cooling effect

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40
Q

Why do plants require mineral ions?

A

Why do plants require mineral ions?

For growth e.g. nitrates are required to
produce proteins

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41
Q

How are water and minerals transported

into plants?

A

How are water and minerals transported into plants?

● Lower concentration of water in root hair cells than in the
soil. Water diffuses down its concentration gradient into
root hair cells by osmosis.
● Lower concentration of mineral ions in the soil than in the
root. Root hair cells take up mineral ions by active
transport.

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42
Q

Outline how root hair cells are adapted

for the absorption of water and minerals

A

Outline how plant roots are adapted for the
absorption of water and minerals

Plant roots are composed of millions of root hair cells which have:
● Long hairs that extend from the cell body, increasing the
surface area for absorption
● Many mitochondria which produce ATP for active transport of
mineral ions

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43
Q

Name the two plant transport tissues

A

Name the two plant transport tissues

Xylem
Phloem

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44
Q

What is the function of the xylem?

A

What is the function of the xylem?

Transports water and minerals up the
plant, from the roots to the leaves via the
transpiration stream

45
Q

Describe how the xylem is adapted to

its function

A

Describe how the xylem is adapted to its function

● Composed of dead cells laid end-to-end to form a long,
hollow, continuous column
● No end walls which provides little resistance to the
passage of water
● Thick cell wall, composed of cellulose, is strengthened
with lignin to provide support

46
Q

What is the function of the phloem?

A

What is the function of the phloem?

Transports sugars up and down the stem
from photosynthetic tissues (e.g. mature
green leaves) to non-photosynthetic tissues
(e.g. developing seeds) via translocation

47
Q

What are the two cell types that make up

the phloem?

A

What are the two cell types that make up the
phloem?

Sieve tube elements
Companion cells

48
Q

Describe how the phloem is adapted to

its function

A

Describe how the phloem is adapted to its function
● Sieve tube elements are long, thin cells, laid end-to-end, with
perforated end plates to enable the flow of sugars
● Sieve tube elements contain no nucleus and little cytoplasm to allow
the unimpeded flow of sugars
● Companion cells contain a dense cytoplasm, nucleus and
mitochondria
● They provide energy for metabolic processes in both cell types

49
Q

What is transpiration?

A

What is transpiration?

The loss of water vapour from the parts
of a plant exposed to the air due to
evaporation and diffusion

50
Q

Describe the process of transpiration

A

Describe the process of transpiration
● Water evaporates from the mesophyll cell surfaces and diffuses
out of the stomata
● Water molecules (which have cohesive properties) are drawn
up the xylem vessels to replace the water that has been lost
● This causes more water molecules to be absorbed from the soil
into root hair cells

51
Q

What are stomata?

A

What are stomata?

Pores found in the lower epidermis of a
leaf that allow gas exchange

52
Q

What are guard cells?

A

What are guard cells?

Specialised cells surrounding the stoma
that change shape to control the size of
the pore

53
Q

In response to stimuli such as light, the

stomata open. Explain how this happens.

A

In response to stimuli such as light, the stomata
open. Explain how this happens.

● Stimuli e.g. light
● Potassium ions are actively pumped into guard cells
● Reduces the water concentration in the guard cells
● Water diffuses into the guard cells by osmosis
● Guard cells swell and become turgid
● Bend and draw away from each other, opening the stomata

54
Q

Describe what happens to the stomata
when potassium ions leave the guard
cells.

A

Describe what happens to the stomata when
potassium ions leave the guard cells.

● Potassium ions leave the guard cells
● Increases the water concentration in the guard cells
● Water diffuses out of the guard cells by osmosis
● Guard cells become flaccid, closing the stomata

55
Q

What factors affect the rate of

transpiration? (3)

A

What factors affect the rate of transpiration? (3)

● Light intensity
● Temperature
● Air movement

56
Q

Describe how high light intensity affects

the rate of transpiration

A

Describe how high light intensity affects the rate of
transpiration

● High light intensity, greater number of stomata are open to
allow gas exchange for photosynthesis
● As photosynthesis increases, more water is taken up from
the soil, pushing water up the xylem
● More water vapour diffuses out of the stomata
● Rate of transpiration increases

57
Q

Describe how low light intensity affects

the rate of transpiration

A

Describe how low light intensity affects the rate of
transpiration

At a low light intensity, fewer stomata are
open so the rate of transpiration
decreases.

58
Q

Describe how temperature affects the

rate of transpiration

A

Describe how temperature affects the rate of
transpiration

● Temperature increases
● Water molecules have more KE so diffuse out of the stomata
more rapidly
● Photosynthesis also increases so more water is taken up from
the soil, pushing water up the xylem
● More water vapour diffuses out of the stomata
● Rate of transpiration increases

59
Q

Describe how air movement affects the

rate of transpiration

A

Describe how air movement affects the rate of
transpiration

● Air movement increases
● High water concentration gradient maintained between the
air spaces in the leaf and atmosphere
● Increased rate of diffusion of water molecules out of the
stomata
● Rate of transpiration increases

60
Q

What is translocation?

A

What is translocation?

The movement of sugars (sucrose,
amino acids etc.) up and down a plant,
from the source to the sink, via the
phloem

61
Q

Briefly describe the process of

translocation

A

Briefly describe the process of translocation

● Sucrose actively transported into the phloem using ATP
● Water enters the phloem by osmosis
● Sucrose diffuses into surrounding cells followed by water down its concentration gradient

62
Q

Explain the importance of small
molecules such as sugars, amino acids,
fatty acids and glycerol in the body

A

They are used to synthesise large organic molecules:
● Amino acids join to form proteins
● Simple sugars join to form larger, more complex sugars
● Fatty acids and glycerol combine to form lipids

63
Q

Describe how producers gain biomass

A

Describe how producers gain biomass
● Take in carbon and nitrogen-containing compounds from the environment
● During photosynthesis, carbon is combined with oxygen and hydrogen to
form glucose
● Glucose is converted into small molecules: others sugars, fatty acids,
glycerol and amino acids
● Larger organic molecules are synthesised from small molecules and are
used by the plant to build new structures e.g. cell membranes, organelles

64
Q

Give some examples of long-chain
carbohydrates and their functions in
organisms

A

Give some examples of long chain carbohydrates
and their functions in organisms

● Cellulose - component of cell walls in plants
● Starch - energy storage in plants
● Glycogen - energy storage in animals

65
Q

Describe the functions of lipids in

organisms

A

Describe the functions of lipids in organisms

● Energy storage
● Component of cell membranes

66
Q

How are amino acids formed from

glucose?

A

How are amino acids formed from glucose?

Glucose reacts with nitrate ions from the
soil to form amino acids

67
Q

Describe how consumers gain biomass

A

Describe how consumers gain biomass

● Ingest large organic molecules from producers or other consumers
● Large organic molecules broken down into smaller, simpler
molecules during digestion
● Small molecules absorbed across the surface of the gut wall
● They are transported to the required cells where large molecules
are resynthesised and used to build biomass in the consumer

68
Q

Outline the levels of organisation in an

ecosystem

A

Outline the levels of organisation in an ecosystem

● Individual
● Population
● Community
● Ecosystem

69
Q

Define population

A

Define population

All organisms of the same species living

with one another in a habitat

70
Q

Define community

A

Define community

All of the populations of different species

living together in a habitat

71
Q

Define ecosystem

A

Define ecosystem

The community of organisms and
non-living components of an area and
their interactions

72
Q

Organisms within a community are
described as being ‘interdependent’.
What does this mean?

A

Meaning of interdependent

Organisms are dependent upon each other.
e.g. if the population of producers in a food chain
decreases, there will be an accompanying decline in the population of primary consumers, secondary consumers and so on down the food chain.

73
Q

Give some examples of interdependence

in a community

A

Give some examples of interdependence in a
community

● Plants depend on pollinators e.g. bees
● Herbivores are dependent on plants
● Animals are dependent on mates

74
Q

Why is competition important in a

community?

A

Why is competition important in a community?

Competition limits population sizes as
organisms must compete for resources.
This can stimulate evolutionary change.

75
Q

What does a food chain show?

A

What does a food chain show?

A food chain describes the feeding
relationships between organisms and the
resultant stages of biomass transfer.

76
Q

Define biomass

A

Define biomass

The total mass of living material

77
Q

What are trophic levels?

A

What are trophic levels?

The stages in a food chain

78
Q

What do arrows in a food chain

represent?

A

What do arrows in a food chain represent?

The direction of biomass transfer

79
Q

Describe a simple food chain

A

Describe a simple food chain

producer → primary consumer →
secondary consumer → tertiary consumer

80
Q

Why are producers the first trophic level?

A

Why are producers the first trophic level?

● Producers provide all biomass for the food
chain (via photosynthesis)
● The rest of the food chain involves the transfer
of this biomass

81
Q

What does a food web show?

A

What does a food web show?

It shows how different food chains are
interlinked and how members of an
ecosystem are interdependent.

82
Q

What does a pyramid of biomass

represent?

A

What does a pyramid of biomass represent?

It represents the dry mass of living
material at each trophic level of a food
chain.

83
Q

Why is a pyramid of biomass almost

always pyramid-shaped?

A

Why is a pyramid of biomass almost always
pyramid-shaped?

● Producers (at the bottom of the pyramid) have the
greatest biomass so have the longest bar
● As you move along the food chain (and up the
pyramid) biomass is lost so the bars decrease in
length

84
Q

Why is biomass lost between each

trophic level in a food chain?

A

Why is biomass lost between each trophic level in a
food chain?

● Glucose is immediately used for respiration in plants
● Respiration to generate heat energy, energy for movement
etc.
● Some parts of organisms are indigestible
● Egestion, excretion

85
Q

Why are there rarely more than four or

five trophic levels in a food chain?

A

Why are there rarely more than four or five trophic
levels in a food chain?

Above this, there is insufficient energy to
support another breeding population

86
Q

What is the equation for calculating the
efficiency of biomass transfer between
trophic levels?

A

What is the equation for calculating the efficiency of
biomass transfer between trophic levels?

Efficiency = (Biomass after transfer/Biomass before transfer) x 100

87
Q

What does a pyramid of numbers

represent?

A

What does a pyramid of numbers represent?

It represents the number of organisms at
each trophic level of a food chain.

88
Q

Why are the carbon and water cycles

important?

A

Why are the carbon and the water cycles important?

● Carbon and water are essential to life
● There is a fixed amount of both carbon
and water on Earth which must be
constantly recycled

89
Q

Describe the stages of the water cycle

A

Describe the stages of the water cycle
1. Energy from the sun evaporates water from bodies of water such as
lakes and oceans.
2. Transpiration also releases water vapour
3. Water vapour rises, cools and condenses forming clouds
4. Precipitation occurs
5. Water is absorbed by the soil and taken up by roots. Some is used in
photosynthesis or becomes part of the plant, entering the food chain.
6. Excretion returns water to the soil
7. Surface runoff returns to streams, rivers and eventually the sea

90
Q

Describe the stages of the carbon cycle

A

Describe the stages of the carbon cycle
1. Photosynthesising plants remove CO2
from the atmosphere
2. Eating passes carbon compounds along a food chain
3. Respiration in plants and animals returns CO2
to the atmosphere
4. Organisms die and decompose. Decomposers (bacteria and fungi)
break down dead material and release CO2
via respiration
5. Combustion of materials (e.g. wood, fossil fuels) releases CO2

91
Q

What is meant by decomposition?

A

What is meant by decomposition?

The breakdown of dead materials into
simpler organic matter

92
Q

How do decomposers break down dead

matter?

A

How do decomposers break down dead matter?

Decomposers release enzymes which
catalyse the breakdown of dead material
into smaller molecules

93
Q

What factors affect the rate of

decomposition?

A

What factors affect the rate of decomposition?

● Oxygen availability
● Temperature
● Water content

94
Q

Why is oxygen required for

decomposition?

A

Why is oxygen required for decomposition?

Most decomposers require oxygen for
aerobic respiration

95
Q

How does the availability of oxygen

affect the rate of decomposition?

A 
How does the availability of oxygen affect the rate of
decomposition? 
● As oxygen levels increase, the rate of
decomposition increases
● As oxygen levels decrease, the rate of
decomposition decreases
96
Q

Why can decomposition still occur in the

absence of oxygen?

A

Why can decomposition still occur in the absence of
oxygen?
Some decomposers respire anaerobically
*However, the rate of decomposition is slower as
anaerobic respiration produces less energy

97
Q

How does temperature affect the rate of

decomposition?

A

How does temperature affect the rate of
decomposition?
Decomposers release enzymes:
● Rate highest at 50°C (optimum temperature for enzymes)
● Lower temperatures, enzymes work too slowly, rate decreases
● High temperatures, enzymes denature, decomposition stops

98
Q

How does soil water content affect the

rate of decomposition?

A

How does soil water content affect the rate of
decomposition?
Decomposers require water to survive:
● In moist conditions the rate of decomposition is high
● In waterlogged soils there is little oxygen for
respiration so the rate of decomposition decreases

99
Q

Why does decomposition require water?

A

Why does decomposition require water?

Water is required for the secretion of
enzymes and absorption of dissolved
molecules.

100
Q

How do decomposers in landfill sites

contribute to global warming?

A

How do decomposers in landfill sites contribute to
global warming?
● Landfill sites tend to be oxygen deficient
● Decomposers respire anaerobically, producing methane
● Methane is a greenhouse gas which traps energy in the
atmosphere, raising global temperatures

101
Q

What are abiotic factors?

Give some examples.

A

What are abiotic factors? Give some examples.

The non-living aspects of an ecosystem
e.g. climate, soil, light intensity, water
quality

102
Q

Describe how environmental conditions

affect communities

A

Describe how environmental conditions affect
communities
● Environmental conditions e.g. temperature, soil pH, light intensity affect the abundance and distribution of organisms within communities
● e.g rising global temperatures have been linked to the extinction of frog species (their thin skin makes them more vulnerable to temperature changes)

103
Q

Describe how toxic chemicals affect

communities

A

Describe how toxic chemicals affect communities
● Toxic chemicals (e.g. pesticides) bioaccumulate in food chains to deadly concentrations at higher trophic levels, killing tertiary and quaternary consumers
● Fertilisers that contaminate water sources can cause
eutrophication, killing multiple populations within a community

104
Q

What are biotic factors?

Give some examples.

A

What are biotic factors? Give some examples.

The living components of an ecosystem
e.g. plants, animals, bacteria, fungi

105
Q

Describe how a change in the size of
one population may affect other
populations within a community

A

Describe how a change in the size of one population
will affect other populations within a community

● A change in the size of one population in a community affects the size of other populations
● e.g. if the number of predators decreases, the number of prey will increase as fewer are killed
● e.g. if the number of prey decreases, the number of predators will decrease as there will be less food available

106
Q

Describe how competition affects

communities

A

Describe how competition affects communities

● The presence of competitors affects population distribution
and size
● e.g. when grey squirrels were first introduced to the UK
they outcompeted the native red squirrels (for food,
shelter etc.), population size of red squirrels declined

107
Q

Describe how food availability affects

communities

A

Describe how food availability affect communities

● Availability of food increases, organisms are more likely to
survive and reproduce so population sizes will increase
● Food becomes less readily available, competition between
organisms will increase and fewer are likely to survive

108
Q

Describe how new pathogens may affect

communities

A

Describe how new pathogens may affect
communities

If a new pathogen is introduced,
population sizes will decrease as many
organisms will become ill and die

Biology Flashcards - OCR 21st Century (11 decks)

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