U2T1ab - Principles of Exchange & Transport Flashcards

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1
Q

What 2 things do cells need to be able to do?

A

Obtain essential substances and remove waste.

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2
Q

Where does exchange take place in unicellular organisms?

A

Through the cell surface membrane.

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3
Q

How does exchange take place in multicellular organisms?

A

They have specialised exchange surfaces. More complex have a transport system which links the exchange surface to the cells throughout the organism. e.g. gills. This increases rate of substance exchange to meet greater metabolic need. Metabolites supplied by surrounding environment.

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4
Q

What does rate of exchange of substances depend on?

A

Surface area.

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5
Q

What does the requirement of metabolites depend on?

A

The volume of metabolically active tissue in an organism.

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6
Q

Describe how surface area and volume are related as an organism increases in size.

A

As an organism gets bigger, so does surface area and volume. However, volume increases much more than SA.

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7
Q

As an organism increases in size, how does their surface area to volume ratio change? What does this mean?

A

SA/V ratio decreases. Small organisms can get all requirements + remove waste through body surface. (CSM) Larger organisms don’t have a big enough SA to meet metabolic needs of larger num of cells in larger volume. Larger num cells aren’t in direct contact with surrounding environment. Rate of diffusion will be too slow. Smaller = higher ratio. Larger = lower ratio. Cube illustration.

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8
Q

What are 5 key features of exchange surfaces?

A

Large surface area relative to volume so gas exchange occurs rapidly, thin membrane to allow for short diffusion pathway for rapid diffusion, large concentration gradient + moist surface so gases can dissolve first + permeable to O2 + CO2.

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9
Q

How do some smaller organisms increase surface area and what are the benefits of this?

A

Flattened shape. (flatworm) Increase SA/V ratio. Allows more diffusion of respiratory gases more quickly so don’t need a specialised respiratory exchange surface. Also decreases diffusion distance.

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10
Q

What is required for the diffusion of gases?

A

A moist surface.

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11
Q

What are the 2 types of specialised exchange surfaces? (e.g.s) How do they increase SA?

A

External (folded external membrane of external gills in tadpoles or internal (alveoli in lungs + fish gills). Large SA as they are folded.

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12
Q

How does a thin exchange surface help?

A

Short diffusion pathway. e.g. Alveoli + blood capillary walls are 1 cell thick so oxygen only has to diffuse through 2 layers. Max diffusion rate.

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13
Q

How does a large concentration gradient help?

A

Diffusion only happens where a concentration gradient exists. Larger organisms have a ventilation system to maintain a high O2 conc in lungs so O2 blood constantly moving away from alveoli. Low O2 in cells + high in atmosphere gives conc gradient.

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14
Q

How are root hair cells adapted to increase SA?

A

Hair like extensions from epidermis. Required because O2 is necessary for respiration to provide ATP for active transport of mineral ions into root hair cells. Ions can also go in by facilitated diffusion.

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15
Q

How are erythrocytes adapted for exchange?

A

Biconcave to increase SA/V ratio for O2 uptake + also ensures short diffusion distance to haem. No nucleus, tightly packed haemoglobin. Conc gradient between alveolus + capillary maintained as transported in blood away from lungs. Increase SA.

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16
Q

How are fish gills adapted for exchange?

A

Extensively folded internal membranes + feathery filaments with secondary lamellae which are 1 cell thick. Rich blood supply + water pumped over to counter-current blood.

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17
Q

How is the leaf mesophyll adapted for exchange?

A

Loosely arranged cells with air spaces, thin, stoma open + close. Stomatal pores allow diffusion of CO2, as do air spaces.

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18
Q

How are blood capillaries adapted for exchange?

A

Very narrow, sit tight against alveolar walls + flow of blood through capillaries maintains conc gradient. RBCs squeeze through so on contact with wall, reducing diffusion pathway.

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19
Q

How does the transport of substances within large organisms happen?

A

Mass Flow

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20
Q

What 5 factors affect the rate of gas exchange?

A

Large surface area, moist surface, diffusion gradients for O2 + CO2, permeable to O2 + CO2 + short diffusion pathway (thin).

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21
Q

Finish these sentences:
As surface area increases, rate of diffusion —-.
As conc gradient increases, ROD ___.
As membrane thickness increases, ROD —-.

A

Increases, increases, decreases.

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22
Q

In plants, what is the dominant process during these times:

Midday, midnight.

A

Photosynthesis, respiration.

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23
Q

At what kind of light intensity might you find the compensation point?

A

Low light.

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24
Q

What is necessary for a plant to grow?

A

Carb being produced by plant in photosynthesis must be more than carb loss in respiration. Over 24 hours, net intake of CO2 must be greater than net produced of CO2.

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25
Q

How does the leaf minimise the diffusion pathway for gases?

A

Being thin, cells in spongy mesophyll are loosely arranged creating air spaces and large surface area. SM cells are large + moist. Stomata + guard cells open + close.

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26
Q

What forms the gaseous exchange surface in the leaf?

A

Cell-surface membrane of spongy mesophyll layer.

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27
Q

What is the purpose of closing stomata at night?

A

Reduces water loss by transpiration. Guard cells change shape depending on whether cells are turgid or not. Guard cells contain chloroplasts.

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28
Q

What does the mammalian respiratory system allow?

A

Mass flow of gases into an organism and maintaining diffusion gradient. Exchange surface is the alveolar wall.

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29
Q

What are some of the features of a gaseous exchange surface in animals?

A

Large surface area (700 million alveoli), thin respiratory membrane, alveoli lined with 1 layer of simple squamous epithelium + capillaries right next to them with 1 layer endothelial cells, creating short diffusion pathway. Inner alveoli surface is moist to aid gaseous diffusion, in moisture layer there’s a lung surfactant, phospholipid rich substance which helps reduce surface tension of alveoli so they can flex easily as lungs inflate + deflate. Vast capillary system surrounds alveoli, each is fed by branch of pulmonary artery + drained by branch of pulmonary vein. Constant flow of blood past alveoli helps maintain diffusion gradient coupled with good ventilation (breathing). Bronchi divide into bronchioles.

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30
Q

Describe the alveolus.

A

Lined with squamous epithelial cells + lung surfactant secreting cells, also contains macrophages. Surfactant stops them collapsing which would reduce SA.

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31
Q

How is air drawn into the lungs?

A

When air pressure in lungs is lower than atmospheric pressure. Forced out when it’s higher than atmospheric pressure. Since thorax is an air tight chamber, pressure changes when thorax volume changes.

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32
Q

How are alveoli adapted to ensure these properties:
Large Surface Area
Short Diffusion Distance
Concentration Gradient

A

600,000,000 alveoli.
Each alveolus is 1 cell thick.
Constant ventilation (Breathing)

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33
Q

How are fish gills adapted to ensure these properties:
Large Surface Area
Short Diffusion Distance
Concentration Gradient

A

Extensively folded internal membranes + feathery filaments with secondary lamellae.
Lamellae are 2 cells thick.
Rich blood supply + water constantly pumped over gills.

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34
Q

How is the leaf mesophyll adapted to ensure these properties:
Large Surface Area
Short Diffusion Distance
Concentration Gradient

A
Loosely arranged cells with air spaces in spongy layer.
Very thin (flattened structure).
Stoma open + close + cells constantly respire.
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35
Q

How are erythrocytes adapted to ensure these properties:
Large Surface Area
Short Diffusion Distance
Concentration Gradient

A

Biconcave shape.
RBC bigger than capillary + so close to capillary sides.
Haemoglobin has differential affinity for oxygen.

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36
Q

How are the blood capillaries adapted to ensure these properties:
Large Surface Area
Short Diffusion Distance
Concentration Gradient

A

Capillary beds.
Thin walls.
Flow of blood through capillaries.

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37
Q

Describe how inspiration occurs.

A

External intercostal muscles contract, ribcage moves up + out, diaphragm muscles contract, diaphragm flattens, thorax volume increases, thorax pressure decreases, air flows into lungs down pressure gradient.

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38
Q

Describe expiration.

A

External intercostal muscles relax, ribcage moves down + in, diaphragm muscles relax, diaphragm bulges upwards, thorax volume decreases, thorax pressure increases, air flows out of lungs down pressure gradient. Occurs passively by elastic recoil but can be assisted by contraction of internal intercostal muscles.

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39
Q

What toxic chemicals are in tobacco smoke? What can it do and what diseases might it cause?

A

Tar, many being carcinogens. Can damage DNA in epithelial cells lining lungs. Lung cancer, emphysema, bronchitis.

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40
Q

What correlates with number of years as a smoker and cigarettes per day?

A

Lung cancer

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41
Q

What is xylem tissue made up of?

A

Cells which have no end walls (disintegrate, forming continuous column), no cell contents (as cell matures, cytoplasm disappears), become dead cells when fully formed, become strengthened by lignin which waterproofs it, column of vessels which produce long, continuous tube up plant for water transport.

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42
Q

What are the advantages of lignification?

A

Provides strength to prevent vessels from collapsing when under pressure by transpiration stream sucking water up plant, gives structural support + provides waterproofing, preventing leakage of water from plant.

43
Q

Why is the transport of materials such as sugars + amino acids made in photosynthesis an active process?

A

Requires energy because phloem is living tissue.

44
Q

What are the 2 most important phloem tissues?

A

Sieve tubes + companion cells.

45
Q

As smaller branches (Stems) branch, they form leaves. What happens to the vascular bundle?

A

Continues into leaf as midrib which branches to form smaller veins, distributed throughout leaf in spongy mesophyll layer.

46
Q

What are the 3 phases of movement of water + ions in plants?

A

Transport of water + ions into + across root, transport up root + stem in xylem + transport through leaf + evaporation from leaf.

47
Q

Why do root hair cells have a large surface area?

A

Facilitate the uptake of water + minerals. Water enters by osmosis and mineral ions by active transport.

48
Q

Why does water enter by osmosis?

A

The soil has a higher water potential than root hair cells as mineral ion concentration of soil is low. Mineral ions are therefore moved into root hair cells by active transport as a result of sugars present in higher conc in cells.

49
Q

How are root hair cells adapted for osmosis and active transport?

A

CSM is thin (short diffusion pathway), thousands of cells means larger surface area (large SA:V ratio) Cell wall is permeable to water.

50
Q

Once water has entered the root hair cells, what happens?

A

It moves across the cells of the cortex (parenchyma) to the xylem.

51
Q

What are the 2 main pathways once water has reached the xylem?

A

Apoplast pathway.

Symplast pathway.

52
Q

Describe the cellulose cell wall around endodermic cells.

A

Has casparian strip which allows water to move into protoplast via symplastic pathway.

53
Q

What happens after the water reaches the casparian strip and moves into the protoplast and moves along the symplast pathway?

A

Endodermal cells pump mineral ions into xylem by active transport using ATP, creating high water potential in endodermal cells so water moves into base of xylem tissue. Process creates root pressure.

54
Q

What helps water move from the endodermis into the xylem?

A

Root pressure + the pull of water up transpiration stream as a result of cohesive forces between water molecules.

55
Q

Is there a large or small distance for water to travel in plants? (Roots to leaves)

A

Large

56
Q

What happens when water evaporates out of the stomata in the leaf?

A

It creates a negative pressure (a pull) which pulls the water column up through the xylem as a mass flow movement. For this to work, water column must be continuous which is facilitated by cohesion. AKA. Cohesion-tension theory of transpiration.

57
Q

Describe the cohesion-tension theory of transpiration.

A

Cohesive forces allow water molecules to be sucked up the xylem in a continuous column.

58
Q

What 2 types of properties does water have?

A

Cohesion + adhesion.

59
Q

Describe how water Is transported through the leaf + evaporates.

A

Water enter leaf into midrib (vascular bundle) which splits into smaller veins and water passes from vein to surrounding cells. Drawn through mesophyll cells. Some water used in photosynthesis + turgor, rest lost in transpiration due to water evaporating from CSM of spongy mesophyll cells into air spaces. Water vapour then diffusion down conc gradient out of stomata (transpiration) from higher water potential in leaf to lower WP outside. Water moves across leaf (xylem to SMC by apoplast + symplast pathways). Transpiration through cuticle does occur + varies with thickness.

60
Q

What is responsible for the transpiration pull?

A

Water potential gradient.

61
Q

What factors affect transpiration rate?
Increases
Decreases

A

Increases:
Leaf surface area, light intensity, air currents, stomatal density, temperature, soil water availability.
Decreases:
Cuticle Thickness, humidity.

62
Q

What does translocation in the phloem require? Describe.

A

Energy. It occurs in 2 directions. It can transport sucrose up + down the plant.

63
Q

What is different about companion cells in the phloem?

A

The are also involved in uptake of sucrose from photosynthesising cells + loading sucrose into STEs via plasmodesmata before transport around plant.

64
Q

What do metabolic inhibitors do?

A

Stop respiration in plant cells which inhibits translocation. e.g. cyanide.

65
Q

Describe how the use of radioactively labelled CO2 demonstrates the transport of sugars in phloem.

  • Mature Leaf of a Green Plant in Light
  • Aphid eats from it
A
RAL CO2 (14CO2) is fed to it. Sugar produced is labelled with radioactive carbon. Movement of sugar is followed by autoradiography in thin stem sections, it shows radioactivity in phloem. 
Aphids that eat feed on phloem sugars tested for sugar presence in mouthparts which are always placed precisely into phloem. Aphid killed is situ, proboscis cut with mouthparts in place, these contain phloem sap which is found with radioactive sugar.
66
Q

What does the localised build up of sucrose create?

A

A hydrostatic gradient between some plant parts (leaves) + sink where sucrose levels are lower (roots/growing region where build up starch for storage/glucose for resp)

67
Q

Describe what bark ringing has found.

- Summer

A

Sugars from leaves accumulate above ring as starch + roots are deprived of carb. Water transport from roots to leaves continues as xylem vessels are unharmed bu it kills tree as phloem can’t function + roots deprived of sugar from leaves. During the day, diameter decreases as water column under more tension so thinner.

68
Q

Describe how rice is grown.

A

Paddy fields. Young plants planted in rich mud, once flooded, O2 conc falls rapidly. Plants have adaptations to overcome this.

69
Q

Xylem Tissue:

How is pressure difference generated.

A

Water evaporating from leaf creates tension (negative pressure) which pulls up water through xylem as part of transpiration system.

70
Q

Xylem Tissue:
(Flowering Plant)
What is its function.

A

Transports water + mineral ions from roots to shoots.

71
Q

Phloem Tissue:
(Flowering Plant)
How is pressure difference generated.

A

Energy expenditure is involved in moving sucrose into phloem. ATP used to move sucrose from companion cell to phloem sieve tube.

72
Q

Phloem Tissue:
(Flowering Plant)
What is its function.

A

Transport of sucrose (translocation) to roots (carb storage) + to growing regions (energy for growth)

73
Q

Circulation in Mammals:

How is pressure difference generated.

A

High pressure generated by pumping heart.

74
Q

Circulation in Mammals:

What is its function.

A

Transport of substances (oxygen, CO2, glucose, amino acids, lipids, urea) in blood system around body.

75
Q

Ventilation (breathing) in mammals:

How is pressure difference generated.

A

Pressure reduction in thorax causes air to enter lungs (inhalation) + increased pressure in thorax causes air to be expelled from lungs (exhalation)

76
Q

Ventilation (breathing) in mammals:

What is its function.

A

Ventilation of lungs by bringing in fresh air (rich O2, low CO2) into lungs + removing air (low O2, rich CO2). Ensures respiratory gas diffusion can occur between alveoli + capillaries.

77
Q

What is the word equation for photosynthesis?

A

Carbon Dioxide + Water — (light + chlorophyll) —> Glucose + Oxygen

78
Q

What is the symbol equation for photosynthesis?

A

6CO2 + 6H2O — (light + chlorophyll) —> C6H12O6 + 6O2

79
Q

What is the word equation for respiration?

A

Glucose + Oxygen -> Carbon Dioxide + Water + ATP

80
Q

What is the symbol equation for respiration?

A

C6H12O6 + 6O2 -> 6CO2 + 6H2O (+ 32ATP)

81
Q

Why don’t stomata close during the day when most transpiration occurs?

A

They need to be open to allow for gaseous diffusion for photosynthesis to occur.

82
Q

The higher the SA:V ratio, the ___ the cell metabolic activity.

A

Higher.

83
Q

How might a plant species be adapted for growth in shady conditions?

A

Low compensation point so photosynthesis exceeds respiration at low light.

84
Q

How does the body shape of a stick insect assist oxygen diffusion which has entered its fine tubes?

A

Large SA:V ratio, short diffusion distance.

85
Q

Why might the density of surface pores on the smaller male stick insect be greater than a female?
Why might it not?

A

Must respire more, needs more O2, higher density.

Smaller v, less tissue needing O2.

86
Q

Give evidence for the cohesion-tension theory.

A

If water column in xylem is broken + air gap appears, water below gap can’t be pulled up . e.g. cut flowers, when air enters cut stem, they will die.

87
Q

How do these factors affect transpiration rate:
Stomatal Density
Leaf Surface Area
Cuticle Thickness

A

More stomata per unit area of leaf, more transpiration, more diffusion routes.
Larger SA, more transpiration as pos correlation leaf area - stomatal number.
Thicker cuticles lose less water than thinner as larger diffusion pathway.

88
Q
How do these factors affect transpiration rate:
Light Intensity
Wind Speed
Temperature
Humidity
Soil Water Availability
A

Rate of transp during day is greater as stomata are open.
Wind removes diffusion shells by blowing humid air away from leaf, steep water pot gradient, more transp, evaps rapidly into sub-stomatal air spaces in ambient temp + stomata close for water conservation.
Higher temp, faster transp as water vap in air evaps with higher temp so increasing water pot gradient. H2O molecules have more kinetic energy so easier + faster to evap. High temp causes leaf wilting.
Higher humid, less transp, lower water pot gradient, no diff if no grad, water won’t evap from mesophyll cell surfaces + builds up in sub-stomatal air space.
Less water, less transp. More water, higher water pot gradient so water moves in quicker.

89
Q

Where are the 2 areas that water will diffuse out?

A

Stomata + waxy cuticle.

90
Q

How do we know that translocation uses energy?

A
Companion cells have high metabolic rate, load sucrose into STEs.
Metabolic inhibitors (cyanide) stop resp, inhibit translocation.
91
Q

Xerophytes:

How does leaf curvature reduce water loss by transpiration?

A

Some fold their leaves so lower epidermis is enclosed within leaf (marram grass). Creates layer of humid air within leaf, reducing water potential gradient, limiting evap, reducing transpiration.

92
Q

Xerophytes:

How does reduced SA reduce water loss by transpiration?

A

Many cacti have leaves as spines/needles which reduces SA over which transpiration can take place. Also stops herbivores eating them as they have juicy stems. Leaves don’t photosynthesise, stem does.

93
Q

Xerophytes:

How does cuticular thickening reduce water loss by transpiration?

A

Makes It more efficient at waterproofing so reduces evap.

94
Q

Xerophytes:

How do leaf hairs reduce water loss by transpiration?

A

Many leaves have layer of hairs, often confined to lower epidermis. Restricts air flow over surface + traps humid air around stomata. Reduces water potential gradient + therefore transp.

95
Q

Xerophytes:

How do sunken stomata reduce water loss by transpiration?

A

Stomata sunken in pits/grooves reduces transpiration losses by creating layer of humid air around stomata called diffusion shells. Reduces water potential gradient. Usually also has fewer stomata.

96
Q

Xerophytes:

How does succulent tissue reduce water loss by transpiration?

A

Stores lots of water and can be used in drought periods.

97
Q

Xerophytes:

How do deep roots reduce water loss by transpiration?

A

Reach water far down into ground. Can also have shallow roots which cover wide area around plant. Infrequent water can be quickly absorbed.

98
Q

How is oxygen delivery maximised to tissues in mammals?

A

Arteries deliver oxygenated blood to metabolically active cells, divide into dense network of blood capillaries which permeate all tissues ensuring no body cell is far from a capillary. Thin capillary walls for easy diffusion, large SA for metabolites to diffuse rapidly into all cells. RBCs biconcave, increasing SA. Haemoglobin high affinity for O2. Heart pumps blood to all tissues, double circulation, vascoconstriction controls blood flow to diff organs.

99
Q

What is the main carbohydrate transported in sieve tubes?

A

Sucrose

100
Q

Why might there be no nitrates in sieve tubes which have amino acids synthesised from nitrates in them?

A

Nitrates all used up or transported in xylem.

101
Q

Describe how source to sink transport occurs in the phloem.

A

Sucrose actively loaded into STE + reduces water pot, water follows by osmosis + increases hydrostatic pressure in STE, water moves down ST from higher at source to lower hydrostatic pressure at sink, sucrose removed from ST by surrounding cells + increases water pot in ST, water moves out of ST + reduces hydrostatic pressure. Translocation ensures this process is faster than by diffusion alone.

102
Q

Why does the trunk of a tree swell above a cut where It has been bark ringed?

A

Sugars can’t pass cut, water potential decreases, water moves into cells. Damage triggers increased cell division to produce sugar storing cells. Cut causes infection.

103
Q

How do you calculate surface area of a cube?

A

(length x length) x num of sides i.e. 6

104
Q

Covering part of the leaf with cobalt chloride paper will reduce transpiration, why might this be?

A

Reduces air flow/blocks light so stomata close.