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BIOLOGY MODEL ANSWERS > Module 3 > Flashcards

Module 3 Flashcards

1
Q

Why larger organisms need transport systems and specialised surfaces for exchange

A
  • more active so higher oxygen demand
  • smaller SA:VOL
  • diffusion too slow
  • diffusion distance too great as many cells deep in body and not in contact with environment
  • outer cells use supplies
  • insufficient waste would be removed
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2
Q

Inspiration

A
  • Diaphragm contracts, flattens, moves down ( displaces digestive organs downwards )
  • external intercostal muscles contract, internal intercostal relax and move the ribs up and out
  • increases volume in thorax and lungs
  • reduces pressure in thorax below atmospheric pressure
  • air moves into lungs down a pressure gradient
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3
Q

Expiration

A
  • diaphragm relaxes and moves upwards
  • external intercostal muscles relax, internal intercostal muscles contract, ribs move down and in
  • this decreases the volume in the thorax and lungs
  • this increases the pressure in the thorax above atmospheric pressure
  • air moves out the lungs down a pressure gradient
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4
Q

Features of a good exchange surface

A
  • large SA- more space for molecules to pass through so more efficient
  • thin barrier- short diffusion distance
  • fresh supply of molecules on supply side, removal on demand to keep concentration gradient steep for quick diffusion
  • permeable to exchange molecule e.g has carrier proteins in cell surface membrane
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5
Q

How the lungs are efficient exchange surfaces

A

-large SA -millions of alveoli so more space for molecules to pas through
-thin barrier ( 2 cells thick )
Alveoli wall one cell thick
Capillary wall one cell thick
Squamous epithelial cells
Close contact
Narrow capillaries squish RBCs against wall so closed to alveoli and reduced rate of flow
-permeable - plasma membranes of cells fully permeable to oxygen and carbon dioxide

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6
Q

Tissue in trachea, bronchi, bronchioles

A
  • Cartilage ( not bronchioles )
  • keep airways open, prevent collapse during inspiration when low pressure
  • allows neck flexibility without constricting airways
  • Smooth muscle
  • contracts to constrict airway
  • reduces flow so harmful substances don’t enter
  • Elastic fibres
  • stretch when muscle contracts
  • recoil when muscle relaxes to dilate airway
  • Goblet cells ( not in small bronchioles )
  • secrete mucus which traps bacteria and particles to be removed to reduce infection
  • Ciliated epithelium
  • Waft to remove mucus from airways up to throat
  • Blood vessels
  • supply lung tissue with oxygen for aerobic respiration
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7
Q

Alveoli tissues

A
  • Elastic fibres
  • stretch on inhalation to increase lung volume and prevent alveoli from bursting
  • recoil on exhalation to expel more air
  • Squamous epithelium
  • one cell thick wall to provide short diffusion distance for gaseous exchange
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8
Q

Name the tissues in trachea and bronchi

A 
Cartilage 
Ciliated epithelium
Goblet cells
Smooth muscle
Elastic fibres
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9
Q

Name tissues in bronchioles

A

Ciliated epithelium
Smooth muscle
Elastic fibres
Goblet cells ( in larger )

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10
Q

Using a spirometer to measure mean tidal volume

A
  • don’t breathe through nose
  • breathe normally
  • measure height of waves for at least 3 waves
  • calculate mean ( add and divide)
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11
Q

Why the volume of oxygen in the spirometer decreases over time

A
  • when you exhale, carbon dioxide absorbed by soda lime
  • decreases volume in spirometer so trace line falls gradually
  • volume of carbon dioxide removes is equal to volume of oxygen used
  • use this to measure rate
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12
Q

Control of cardiac cycle

A
  • SAN initiates wave of electrical exitation
  • this spreads over atrial wall
  • causes atria to contract
  • simultaneously
  • fibres between atria and ventricles stops wave passing directly to ventricle walls
  • wave reaches AVN
  • delays wave for 0.1s to allow atrial systole to complete before ventricular begins
  • wave spreads down septum to bundle of his and purkyne fibres
  • ventricles contract simultaneously
  • from apex upwards to push blood up into arteries
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13
Q

Structure and function of arteries

A

Carry blood away from heart under high pressure
-small lumen to maintain pressure
Wall:
Thick and has collagen to give strength to withstand pressure
Elastic tissue allows stretch when heart pumps and recoil to maintain high pressure when heart relaxes
Smooth muscle contracts to constrict artery to narrow lumen ( e.g in vasoconstriction to redirect blood flow )

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14
Q

Structure and function of veins

A

Carry blood back to heart at low pressure
-large lumen to make flow easier
-thinner walls ( collagen, elastic tissue, smooth muscle) don’t need to withstand pressure and not used to constrict flow
-valves stop blood flowing in wrong direction
(Skeletal muscles assist)

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15
Q

Structure and function of capillaries

A

Allow exchange of materials between the blood and cells

  • thin walls of flat endothelial ( squamous epithelial ) cells to reduce diffusion distance
  • lumen narrow to squeeze rbcs next to wall to reduce diffusion distance further
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16
Q

Formation of tissue fluid

A
  • due to heart contraction, blood at high hydrostatic pressure at arteriole end
  • small gaps between capillary wall cells
  • hydrostatic above osmotic
  • forces fluid out capillary carrying plasma and dissolved substances ( oxygen and glucose and neutrophils - smol WBC ) this is the tissue fluid
  • RBC, protein, WBC can’t leave as too large
  • hydrostatic lower at venue end
  • osmotic in direction of capillary is greater
  • due to blood plasma proteins which lower water potential
  • fluid moves into capillary taking dissolved waste e.g CO2
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17
Q

Lymph formation

A
  • not all tissue fluid returns to capillaries
  • pores allow fluid to leave tissue fluid and enter lymph vessels
  • removes proteins out of tissue fluid
  • removes neutrophils
  • low in O2 and glucose as used up
  • more co2 and waste as made by cells
  • lots of fat from intestines
  • contains lymphocytes produced in lymph nodes which engulf and digest bacteria in lymph - immune system
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18
Q

Features of blood

A 
Erythrocytes
Neutrophils
Platelets 
Large proteins
Some fats
Glucose
Amino acids
Oxygen
Little co2
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19
Q

Features of tissue fluid

A 
Neutrophils
Proteins ?
Less glucose as respired
Less amino acids as cells use
Less oxygen as respired
More co2
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20
Q

Features of lymph

A 
Neutrophils 
Lymphocytes 
Large proteins?
Fats
Little glucose
Few amino acids 
Little oxygen 
Carbon dioxide
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21
Q

Oxygen dissociation curve

A
  • low pO2 , low saturation, haem group at centre makes it difficult to associate
  • as pO2 increases, faster increase in saturation
  • higher pO2, steeper gradient for diffusion into haemoglobin, so easier to diffuse and associate
  • when 1 O2 associates, conformational change makes it easier for more O2 to diffuse and associate
  • high pO2 , high saturation but unlikely to reach 100%
  • when 3 O2 associated, hard for 4th to diffuse in and associate even at highest pO2
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22
Q

Releasing O2 from haemoglobin, why important between 2-5 kPa

A
  • at low pO2 oxygen dissociates from haemoglobin
  • happens in respiring tissues
  • steepest part between 2-5 kPa- drop in pO2 gives large drop in saturation to release lots of O2
  • corresponds to pO2 in respiring tissue as need lots of oxygen for aerobic respiration
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23
Q

Why important that foetal haemoglobin different to adult

A
  • foetus gains O2 for respiration from mother across placenta
  • pO2 is low in placenta (2-4 kPa)
  • maternal haemoglobin releases O2
  • foetal haemoglobin has higher affinity for O2
  • maintains diffusion gradient

-oxygen diffuses into foetal blood, lowers pO2 causes maternal haemoglobin to dissociate, diffuses across placenta to foetus, further lowers pO2 causes further dissociation

24
Q

Why important that after birth adult haemoglobin replaces fetal

A
  • affinity of fetal would be to high
  • wouldn’t release oxygen readily enough
  • pregnant mothers would need a difference between the affinity of their haemoglobin and that of their foetus for oxygen
25
Q

Carbon dioxide carriage in blood

A
  • small amounts dissolved in plasma or combined with haemoglobin forming carbaminohaemoglobin
  • rest as hydrogencarbonate ions
  • CO2 diffuses into red blood cells
  • it reacts with water
  • catalysed by carbonic anhydrase
  • forms carbonic acid (H2CO3)
  • carbonic acid dissociates into H+ and HCO3- ions
  • H+ make it acidic
  • H+ combine with haemoglobin forming haemoglobinic acid
  • haemoglobin acts as buffer
  • HCO3 leave cell into plasma
  • Cl- ions move in to maintain charge- chloride shift
26
Q

Releasing more oxygen e.g during exercise ( Bohr effect )

A
  • low pO2 ( respiring cells) oxyhaemoglobin dissociates to release oxygen
  • when CO2 present, more carbonic acid to dissociate and form more H+ ions
  • H+ ions displace oxygen molecules on haemoglobin to form more haemoglobinic acid
  • in CO2 more oxygen released
  • oxygen more readily released when CO2 produced , releasing more CO2 means they need more O2 for aerobic respiration
27
Q

Structure and function of xylem

A
  • continuous hollow tubes with no end walls or contents. Less resistance to flow and more space due to lack of contents.
  • walls impregnated with lignin. Strengthens wall and prevents collapse under tension. Waterproofs wall reducing lateral flow. Improves adhesion of water to wall, increases capillarity.
  • lignin in spiral pattern. Allows flexibility and bending or stretching of stem.
  • bordered pits in walls- allows lateral movement to get around blockages e.g air bubbles ( prevent continuous column )
  • narrow lumen- more capillary rise so more effective capillary action.
28
Q

Structure and function of phloem- sieve tube elements

A
  • little cytoplasm, most organelles absent ( no nucleus). Less resistance for transport and more space
  • sieve plates. Connect sieve tube elements to allow sao through.
  • joined end to end to form tube, allows continuous transport
  • bi-directional flow. Allows sucrose up and down
  • living, allows active processes
29
Q

Structure and function of phloem ( companion cells )

A
  • many mitochondria. Lot of respiration needed to provide large amounts of ATP for active processes. E.g actively loading sucrose into sieve tubes
  • nucleus, control functions of both companion cell and sieve tube element
  • plasmodesmata, allows continuation of cytoplasm between companion cell and sieve tube element
30
Q

How water moves from soil to xylem

A
  • minerals actively transported into root hair through carriers
  • water moves via osmosis from soil into root hair across cell surface membrane through aquaporins down the water potential gradient.
  • can move via cell walls in apoplast pathway
  • moves via cytoplasm in symplast pathway, through plasmodesmata, linking cytoplasm in neighbouring cells
  • at casparian strip, Suberin, blocks apoplast
  • so water enters symplast
  • water potential most negative in xylem due to active transport of minerals into it
  • causes water to move into xylem from endodermis and cortex cells.
31
Q

How does transpiration result in the movement of water up a stem?

A
  • water evaporates from surface of mesophyl cells in leaf and forms water vapour
  • water vapour diffuses from high water vapour potential to low water vapour potential out of the leaf, through the stomata
  • more water drawn from mesophyyl cells via symplast amd apoplast pathways in leaf replacing water just evaporated
  • this occurs via osmosis down the water potential gradient
  • this water is replaced by water from the xylem vessels ( moving out via osmosis )
  • loss of water from xylem causes low hydrostatic pressure at top
  • water moves from higher pressure (roots, where water is moved into the xylem) to a lower pressure ( down a pressure gradient ) under tension
  • water pulled up by mass flow
  • cohesion of water molecules due to hydrogen bonds causes them to stay as a long unbroken column - the transpiration stream
32
Q

Setting up a potometer

A
  • cut a healthy shoot underwater ( stops air entering xylem )
  • cut at slant ( to increase SA)
  • check potometer is bubble free
  • insert shoot into potometer under water
  • remove potometer from water and ensure airtight around shoot
  • dry leaves
  • keep conditions constant
  • allow time for shoot to acclimatise
  • shut screw clip
  • keep ruler fixed, record position at regular intervals
  • start timing and measure distance moved per minute
33
Q

Why potometer not exact measure of rate of transpiration

A
  • transpiration is loss of water by evaporation from leaves
  • potometer measures water uptake to replace loss
  • some water used in photosynthesis
  • rather than all evaporating from leaves
  • uptake by detached shoot may not be the same as the whole plant
34
Q

How number of leaves affects transpiration

A
  • more leaves=more water loss
  • larger SA for water to evaporate out
  • ( more stomata)
35
Q

How number and size of stomata affects rate of transpiration

A
  • more/bigger = more loss

- larger SA for water to evaporate out via stomata

36
Q

How waxy cuticle affects transpiration

A
  • present=less loss

- reduces water evaporating from leaf surface as hydrophobic

37
Q

How light affects transpiration

A
  • lighter= more water loss

- stomata open wider in light ( allows gas exchange for photosynthesis ) if open= larger SA for water to evaporate out

38
Q

How temperature affects transpiration

A

Higher temp= more water loss

-more KE , water evaporates faster and water vapour diffuses out faster

39
Q

How humidity affects transpiration

A
  • higher humidity= less water loss

- air more saturated with water ( still higher in leaf spaces ) so shallower water potential gradient

40
Q

How wind affects transpiration

A

More windy= more loss
-carries water vapour that has just diffused out leaf away, makes air surrounding lead less saturated, maintains steeper water potential gradient

41
Q

How water availability affects transpiration

A

More in soil= more loss

-if not available can’t replace lost water

42
Q

Xerophyte - epidermis covered in hairs

A

Hair traps water vapour, stops wind removing it so humid air around leaf reduces water potential gradient so less evaporation and less transpiration

43
Q

Xerophyte- thicker waxy cuticle

A

Hydrophobic so prevents water passing through epidermis so less evapiration and transpiration

44
Q

Xerophyte- small leaves/ needles

A

-small surface area so fewer stomata so less evaporation so less transpiration

45
Q

Xerophyte - sunken stomata in pits

A

Hair traps water vapour which stops wind removing it so air more humid around leaf and lower water potential gradient and less evaporation and transpiration

46
Q

Xerophyte - curled leaves

A

Lower epidermis not exposed to atmosphere, traps water vapour, stops wind removing water vapour so more humid air around leaf, reduces water vapour potential gradient so less evaporation and transpiration.

47
Q

Xerophyte- small air spaces in mesophyll

A

Less water can evaporate into air spaces, they quickly become full reducing area for loss

48
Q

Xerophyte- stomata shut in day, open in night

A

Transpiration occurs via stomata. Warmer in day so more evaporation and more transpiration. Shutting in day reduces loss

49
Q

Translocation, active loading

A
  • H+ ions actively transported ( requires ATP ) out of companion cells
  • this produces a diffusion gradient for the H+ ions
  • they move back into the companion cell via facilitated diffusion through co-transporter carrier proteins along with sucrose
  • sucrose actively loaded into companion cell
  • there is a high concentration of sucrose in the companion cell compared to the sieve tube element so it diffuses in it down the concentration gradient through the plasmodesmata
50
Q

How does sucrose move along the phloem

A

At the source
-sucrose actively loaded into sieve tube element at source
-this reduces the water potential in the sieve tube element
-water enters the sieve tube elements by osmosis
-this increases hydrostatic pressure in the sieve tube element near the source
At the sink
-sucrose unloaded by diffusion (or active transport ) and used in respiration/ stored
-this increases water potential in the sieve tube element
-water moves into sink via osmosis down water potential gradient
-this reduces hydrostatic pressure in the sieve tube element near the sink
-water in sieve tube element moves down the hydrostatic pressure gradient from source to sink
-this creates a flow which carries the sucrose and assimilates along the phloem by mass flow up or down the plant

51
Q

How sieve tube elements adapted for mass flow

A
  • elongated, joined end to end to form a column
  • sieve plates with pores in end walls allow sucrose through
  • little cytoplasm and no nucleus - less resistance to transport
52
Q

Why if ring cut around bark, swelling occurs above

A
  • phloem is in bark so sucrose can’t pass cut
  • area above cut acts as sink so water moves into cells
  • damage triggers increased cell division
  • to produce cells to store sugars
  • cut causes infection
53
Q

How we know phloem used in translocation

A
  • radioactively labelled CO2 supplied for photosynthesis appears in phloem as assimilates
  • aphids feed on stems insert mouth into phloem, sugar drips down back
  • sugars collect above ring when tree ringed to remove phloem
54
Q

How we know ATP used in translocation

A
  • companion cells have many mitochondria
  • translocation stopped if poison which stops ATP production is given
  • flow of sugars high so ATP must be used, much faster than possible with diffusion
55
Q

How we know translocation

A

pH of companion cells higher than surrounding cells due to H+ ions reducing pH
-conc of sucrose higher in source than sink

56
Q

Evidence against translocation

A
  • not all solutes move at same rate
  • sucrose moves to all parts at same rate not lowest concentration fastest
  • role of sieve plates unclear

BIOLOGY MODEL ANSWERS (6 decks)

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