U2T1ab - Principles of Exchange & Transport

Question 1

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

Answer 1

Obtain essential substances and remove waste.

Question 2

Where does exchange take place in unicellular organisms?

Answer 2

Through the cell surface membrane.

Question 3

How does exchange take place in multicellular organisms?

Answer 3

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.

Question 4

What does rate of exchange of substances depend on?

Answer 4

Surface area.

Question 5

What does the requirement of metabolites depend on?

Answer 5

The volume of metabolically active tissue in an organism.

Question 6

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

Answer 6

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

Question 7

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

Answer 7

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.

Question 8

What are 5 key features of exchange surfaces?

Answer 8

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.

Question 9

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

Answer 9

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.

Question 10

What is required for the diffusion of gases?

Answer 10

A moist surface.

Question 11

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

Answer 11

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

Question 12

How does a thin exchange surface help?

Answer 12

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.

Question 13

How does a large concentration gradient help?

Answer 13

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.

Question 14

How are root hair cells adapted to increase SA?

Answer 14

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.

Question 15

How are erythrocytes adapted for exchange?

Answer 15

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.

Question 16

How are fish gills adapted for exchange?

Answer 16

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

Question 17

How is the leaf mesophyll adapted for exchange?

Answer 17

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

Question 18

How are blood capillaries adapted for exchange?

Answer 18

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.

Question 19

How does the transport of substances within large organisms happen?

Answer 19

Mass Flow

Question 20

What 5 factors affect the rate of gas exchange?

Answer 20

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

Question 21

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

Answer 21

Increases, increases, decreases.

Question 22

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

Midday, midnight.

Answer 22

Photosynthesis, respiration.

Question 23

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

Answer 23

Low light.

Question 24

What is necessary for a plant to grow?

Answer 24

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.

Question 25

How does the leaf minimise the diffusion pathway for gases?

Answer 25

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.

Question 26

What forms the gaseous exchange surface in the leaf?

Answer 26

Cell-surface membrane of spongy mesophyll layer.

Question 27

What is the purpose of closing stomata at night?

Answer 27

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

Question 28

What does the mammalian respiratory system allow?

Answer 28

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

Question 29

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

Answer 29

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.

Question 30

Describe the alveolus.

Answer 30

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

Question 31

How is air drawn into the lungs?

Answer 31

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.

Question 32

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

Answer 32

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

Question 33

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

Answer 33

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

Question 34

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

Answer 34

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

Question 35

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

Answer 35

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

Question 36

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

Answer 36

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

Question 37

Describe how inspiration occurs.

Answer 37

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.

Question 38

Describe expiration.

Answer 38

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.

Question 39

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

Answer 39

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

Question 40

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

Answer 40

Lung cancer

Question 41

What is xylem tissue made up of?

Answer 41

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.

Question 42

What are the advantages of lignification?

Answer 42

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.

Question 43

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

Answer 43

Requires energy because phloem is living tissue.

Question 44

What are the 2 most important phloem tissues?

Answer 44

Sieve tubes + companion cells.

Question 45

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

Answer 45

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

Question 46

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

Answer 46

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

Question 47

Why do root hair cells have a large surface area?

Answer 47

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

Question 48

Why does water enter by osmosis?

Answer 48

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.

Question 49

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

Answer 49

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

Question 50

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

Answer 50

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

Question 51

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

Answer 51

Apoplast pathway. | Symplast pathway.

Question 52

Describe the cellulose cell wall around endodermic cells.

Answer 52

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

Question 53

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

Answer 53

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.

Question 54

What helps water move from the endodermis into the xylem?

Answer 54

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

Question 55

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

Answer 55

Large

Question 56

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

Answer 56

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.

Question 57

Describe the cohesion-tension theory of transpiration.

Answer 57

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

Question 58

What 2 types of properties does water have?

Answer 58

Cohesion + adhesion.

Question 59

Describe how water Is transported through the leaf + evaporates.

Answer 59

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.

Question 60

What is responsible for the transpiration pull?

Answer 60

Water potential gradient.

Question 61

What factors affect transpiration rate? Increases Decreases

Answer 61

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

Question 62

What does translocation in the phloem require? Describe.

Answer 62

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

Question 63

What is different about companion cells in the phloem?

Answer 63

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

Question 64

What do metabolic inhibitors do?

Answer 64

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

Question 65

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

Answer 65

``` 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. ```

Question 66

What does the localised build up of sucrose create?

Answer 66

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)

Question 67

Describe what bark ringing has found. | - Summer

Answer 67

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.

Question 68

Describe how rice is grown.

Answer 68

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

Question 69

Xylem Tissue: | How is pressure difference generated.

Answer 69

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

Question 70

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

Answer 70

Transports water + mineral ions from roots to shoots.

Question 71

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

Answer 71

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

Question 72

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

Answer 72

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

Question 73

Circulation in Mammals: | How is pressure difference generated.

Answer 73

High pressure generated by pumping heart.

Question 74

Circulation in Mammals: | What is its function.

Answer 74

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

Question 75

Ventilation (breathing) in mammals: | How is pressure difference generated.

Answer 75

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

Question 76

Ventilation (breathing) in mammals: | What is its function.

Answer 76

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.

Question 77

What is the word equation for photosynthesis?

Answer 77

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

Question 78

What is the symbol equation for photosynthesis?

Answer 78

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

Question 79

What is the word equation for respiration?

Answer 79

Glucose + Oxygen -> Carbon Dioxide + Water + ATP

Question 80

What is the symbol equation for respiration?

Answer 80

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

Question 81

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

Answer 81

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

Question 82

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

Answer 82

Higher.

Question 83

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

Answer 83

Low compensation point so photosynthesis exceeds respiration at low light.

Question 84

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

Answer 84

Large SA:V ratio, short diffusion distance.

Question 85

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

Answer 85

Must respire more, needs more O2, higher density. | Smaller v, less tissue needing O2.

Question 86

Give evidence for the cohesion-tension theory.

Answer 86

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.

Question 87

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

Answer 87

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.

Question 88

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

Answer 88

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.

Question 89

Where are the 2 areas that water will diffuse out?

Answer 89

Stomata + waxy cuticle.

Question 90

How do we know that translocation uses energy?

Answer 90

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

Question 91

Xerophytes: | How does leaf curvature reduce water loss by transpiration?

Answer 91

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.

Question 92

Xerophytes: | How does reduced SA reduce water loss by transpiration?

Answer 92

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.

Question 93

Xerophytes: | How does cuticular thickening reduce water loss by transpiration?

Answer 93

Makes It more efficient at waterproofing so reduces evap.

Question 94

Xerophytes: | How do leaf hairs reduce water loss by transpiration?

Answer 94

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.

Question 95

Xerophytes: | How do sunken stomata reduce water loss by transpiration?

Answer 95

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.

Question 96

Xerophytes: | How does succulent tissue reduce water loss by transpiration?

Answer 96

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

Question 97

Xerophytes: | How do deep roots reduce water loss by transpiration?

Answer 97

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

Question 98

How is oxygen delivery maximised to tissues in mammals?

Answer 98

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.

Question 99

What is the main carbohydrate transported in sieve tubes?

Answer 99

Sucrose

Question 100

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

Answer 100

Nitrates all used up or transported in xylem.

Question 101

Describe how source to sink transport occurs in the phloem.

Answer 101

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.

Question 102

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

Answer 102

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.

Question 103

How do you calculate surface area of a cube?

Answer 103

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

Question 104

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

Answer 104

Reduces air flow/blocks light so stomata close.