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biology > module 3; organisms exchange substances with their environments > Flashcards

module 3; organisms exchange substances with their environments Flashcards

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1
Q

explain how SA: V ratio helps small organisms & give an example

A

small organisms (e.g. amoeba) have very large SA compared to their V - means that there is a big surface for exchange of substances & there is also a smaller distance from outside of organism to its middle
allows small organisms to simply exchange substances across their surface

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2
Q

why do larger organisms require adaptations for the exchange of substances across their surfaces?

A

the larger the organism = the smaller its SA compared to the V & larger distance from the middle to the outside
larger organisms usually have a high metabolic rate which demands efficient transport of waste out of cells & reactants into cells
these 2 factors lead to adaptations that help make the exchange more efficient

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3
Q

give some examples of adaptations that increase SA: V ratio

A

villi & microvilli - absorption of digested food (animal cells)
alveoli & bronchioles - gas exchange (animal cells)
spiracles & tracheoles - gas exchange (in insects)
gill filaments & lamellae - gas exchange (in fish)
thin wide leaves - gas exchange (plant cells)
capillary network (animal cells)

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4
Q

define breathing

A

it’s the movement of air into & out of the lungs

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5
Q

define respiration

A

it’s a chemical reaction to release energy in the form of ATP

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6
Q

define gaseous exchange

A

it’s the diffusion of oxygen from the air in the alveoli into the blood & of carbon dioxide from the blood into the air in the alveoli

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7
Q

what does the human gas exchange system consist of?

A

alveoli
bronchioles
bronchi
trachea
lungs

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8
Q

how do humans breathe?

A

the role of the diaphragm which is the antagonistic interaction between external & intercostal muscles allows us to breathe

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9
Q

explain how the the intercostal muscles allow us to breathe

A

the external intercostal muscles contract leading to inspiration whereas the internal intercostal muscles contract leading to expiration

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10
Q

describe what happens to the respiratory system when inspiration occurs

A
  1. the external intercostals contract & pull the ribs up & out
  2. internal intercostal relax
  3. diaphragm contracts to move down & flattens
  4. air pressure in the lungs initially drops & as air moves in it rises above atmospheric pressure
  5. lung volume increases
  6. air moves into lungs, as atmospheric pressure is higher than that of the thorax
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11
Q

describe what happens to the respiratory system when expiration occurs?

A
  1. external intercostal relax
  2. internal intercostal contract to pull the rib down & in
  3. diaphragm relaxes to move up & causes it to dome upwards
  4. air pressure initially greater than atmospheric drops as air moves out
  5. lung volume decreases
  6. air moves out lungs, as pressure on the thorax is higher than that of the atmosphere
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12
Q

what is pulmonary ventilation?

A

it’s the total volume of air that is moved into the lungs during one minute (dm3 min-1)

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13
Q

how is pulmonary ventilation calculated?

A

pulmonary ventilation (dm3 min-1) = tidal volume (dm3) x ventilation (min-1)

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14
Q

explain how the adaptation of the alveolar epithelium allows efficient gas exchange

A

there is a large no.of alveoli (tiny air sacks) = creates very large SA for gas exchange

alveoli epithelium cells are very thin = minimises diffusion distance

each alveolus is surrounded by capillary network to remove the conc gradient - which maintains conc gradient

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15
Q

describe the adaptations that terrestrial insects have

A
  1. exoskeleton made of fibrous material for protection & lipid layer to prevent water loss
  2. have a tracheal system
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16
Q

describe the insect tracheal system

A
  1. spiracles are round, valve-like openings that run along the length of the abdomen - O2 & CO2 enter / leave through spiracles, trachea attach to the opening
  2. trachea is a network of tubes - tubes have rungs within them to strengthen them & keep them open
  3. trachea branches into smaller tubes deeper into abdomen - called tracheoles. these extend throughout all the insect’s tissues & deliver O2 to respiring cells
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17
Q

describe the different methods to move gases in the tracheal system

A
  1. diffusion - when cells respire they use up O2 & produce CO2 creating a conc gradient from tracheoles to atmosphere
  2. mass transport - insect contracts & relaxes abdominal muscles to move gases on mass
  3. when insect in flight muscle cells respire anaerobically to produce lactate - lowers water potential of cells so water moves from tracheoles into cells by osmosis. this decreases volume in tracheoles = more air from atmosphere draws in
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18
Q

list adaptations in the tracheal system that enable efficient diffusion

A
  1. large no.of fine tracheoles = large SA
  2. walls of tracheoles are thin & short distance between spiracles & tracheoles = short diffusion pathway
  3. use of O2 & production of CO2 = sets up steep diffusion gradients
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19
Q

how do terrestrial insects lose water?

A

water evaporates off the surface of terrestrial insects

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20
Q

how do terrestrial insects limit water loss?

A
  1. small SA: V ratio where water can evaporate from
  2. have a waterproof exoskeleton
  3. spiracles (where water can evaporate from) can open & close to reduce water loss
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21
Q

why do fishes require a gas exchange surface?

A

as they have a small SA:V ratio so they require gills

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22
Q

why have fish adapted to exchange gases?

A

to maintain the conc gradient to enable diffusion to occur

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23
Q

what features are crucial for gas exchange surfaces?

A
  1. large SA: V ratio
  2. short diffusion distance
  3. maintained conc gradient
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24
Q

how is the rate of diffusion calculated?

A

can be calculated by using Fick’s law:
diffusion is proportional to = SA x difference in conc / length of diffusion path

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25
Q

describe the structure of the gills & how its important for gas exchange

A

4 layers of the gills on both sides of the head:
1. gills made of stacks of gill filaments

  1. each gill filament is covered in gill lamellae, positioned at right angles to the filament = creating large SA
  2. when a fish opens its mouth water rushes in & over the gills & then out through holes in the sides of their heads
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26
Q

describe how fish have adapted to efficiently exchange gases by diffusion

A

fishes have a short diffusion distance due to the capillary network in every lamellae & have very thin gill lamellae

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27
Q

how is the concentration gradient maintained in fish?

A

by the countercurrent flow mechanism

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28
Q

what is the countercurrent exchange mechanism?

A

the principle states that when water flows over the gills in the opposite direction to the flow of blood in the capillaries, the countercurrent flow ensures that equilibrium is not reached

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29
Q

why does the countercurrent flow ensure that equilibrium is not reached?

A

so that O2 can continue diffusing from the water into the capillaries in the gill lamellae across the entire gill lamellae

ensures that diffusion gradient is maintained across the entire length of gill lamellae

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30
Q

what is the difference between the concurrent flow & the countercurrent flow?

A

in concurrent flow the water & blood flow in the same direction - causes equilibrium to be reached halfway across lamellae = no diffusion of gases

whereas in the countercurrent flow the water & blood flow in opposite directions - so equilibrium will never be reached = always higher conc of O2 in water than the blood so conc gradient is always maintained across entire gill lamellae

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31
Q

how does gas exchange occur at the stomata?

A
  1. O2 diffuses out of the stomata
  2. CO2 diffuses in through the stomata
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32
Q

how is water lost in the stomata & what adaptations does it have to minimise the loss?

A

water is lost by evaporation
the stomata close at night when photosynthesis wouldn’t be occurring to reduce water loss

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33
Q

explain how xerophytic plants are adapted to survive in environments with limited water

A

they have structural features to enable efficient gas exchange to occur whilst limiting water loss

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34
Q

give an example of a xerophytic plant & its adaptations

A

marram grass:
curled leaves to trap moisture - increases humidity
hairs to trap moisture to increase humidity
sunken stomata to trap moisture - also increases humidity
thicker cuticles - reduces evaporation
longer root hair network to reach more water

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35
Q

what occurs during digestion?

A

large biological molecules are hydrolysed into smaller molecules that can e absorbed across cell membranes

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36
Q

name the biological molecules that are digested mammals

A

carbohydrates
lipids
proteins

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37
Q

where does digestion occur?

A
  1. begins in the mouth
  2. continues in duodenum
  3. completed in the ileum
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38
Q

what enzymes hydrolyse carbohydrates?

A

amylases & membrane-bound disaccharides (sucrase & lactase) hydrolyse carbs into monosaccharides

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39
Q

what produces amylase & where?

A

by the pancreas in the salivary glands

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40
Q

what does amylase hydrolyse?

A

hydrolyses polysaccharides into the disaccharide maltose by hydrolysing the glycosidic bonds

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41
Q

what do membrane-bound enzymes hydrolyse?

A

sucrose & lactose into monosaccarides

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42
Q

what enzymes hydrolyse proteins & how?

A
  1. endopeptidases - hydrolyses peptide bonds in the middle of a polymer chain
  2. exopeptidases - hydrolyses peptide bonds at the end of the polymer chain
  3. membrane-bound dipeptidases - hydrolyse peptide bonds between 2 amino acids
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43
Q

what hydrolyses/breaks down lipids?

A

lipase & bile salts

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44
Q

where are the enzymes that digest lipids produced?

A

lipase is produced in the pancreas - hydrolyses ester bonds in triglycerides to form monoglyceride & fatty acids

bile salts produced in liver - emulsifies liquids to form tiny droplets (micelles) which increases SA for lipase to act on

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45
Q

what are the stages for digesting lipids?

A
  1. physical stage - emulsification & micelle formation
  2. chemical stage - lipase
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46
Q

explain the 1st stage in lipid digestion

A

lipids are coated in bile salts to create an emulsion. many small droplets of lipids provide large SA = faster hydrolysis by lipase

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47
Q

explain the 2nd stage in lipid digestion

A

lipase hydrolyses lipids into glycerol & fatty acids

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48
Q

what are micelles?

A

they are vesicles formed of the fatty acids, glycerol, monoglycerides & bile salts

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49
Q

how do micelles aid in lipid absorption?

A

when micelles encounter the ileum epithelial cells they simply diffuse across a membrane (as fatty acids & monoglycerides are non-polar) to enter cells of epithelial cells

once in the cell, these will be modified back into triglycerides inside endoplasmic reticulum & golgi body

then can form vesicles & be released from the cell into the lacteal & be transported around the body

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50
Q

where do the products of digestion get absorbed?

A

across the cells lining the ileum

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51
Q

what features does the ileum have that maximise absorption?

A

ileum wall is covered in villi which have thin walls surrounded by a capillary network & epithelial cells have smaller microvilli

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52
Q

how do the ileum’s features maximise absorption?

A

they increase SA, decrease the diffusion distance & maintain a conc gradient

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53
Q

why is active transport & co-transport required for monosaccaride & amino acid absorption?

A

to absorb glucose & amino acids from the lumen to the gut there must be a higher conc in the lumen compared to epithelial cell (for facilitated diffusion) but there is usually more in the epithelial cells

54
Q

state the structure & function of haemoglobin

A

groups of protein with a quaternary structure & it transports oxygen with red blood cells

55
Q

what does the oxyhaemoglobin dissociation curve show?

A

oxygen is loaded in regions with high partial pressure of oxygen (e.g. alveoli) & is unloaded in regions of low partial pressure (e.g. respiring tissues)

56
Q

why is it important that oxygen has cooperative binding?

A

the cooperative nature of oxygen binding to haemoglobin changing shape when the 1st oxygen binds - makes it easier for further oxygens to bind

57
Q

what is the bohr effect?

A

it’s when a high CO₂ conc causes the oxyhemoglobin curve to shift to the right causing the affinity of oxygen decreasing as the acidic CO₂ changes the shape of the haemoglobin slightly

58
Q

explain why the oxyhaemoglobin curve would shift to the left

A

caused by low partial pressure of carbon dioxide in the alveoli

59
Q

what happens to O₂’s affinity when the curve shifts to the left

A

increased affinity = uploads more O₂

60
Q

explain why the oxyhaemoglobin curve would shift to the right

A

caused by the high partial pressure of CO₂ at respiring tissues

61
Q

what happens to O₂’s affinity when the curve shifts to the right

A

decreased affinity = unloads more O₂

62
Q

state why animals have different types of haemoglobin

A

due to adaptation to their environment, different animals have different affinities for O₂ resulting in different haemoglobins

63
Q

state the adaptation that a human foetus has for O₂ affinity

A

human foetuses have myoglobin/foetal haemoglobin which has a higher affinity for O₂ even at the same partial pressure compared to an adult’s haemoglobin

64
Q

explain why the adaptation that a human foetus has for O₂ affinity is important

A

it’s an advantage as blood is circulating through the umbilical cord the foetus’s haemoglobin can load the O₂ off the mother’s adult haemoglobin

65
Q

state where the oxyhaemoglobin curve is for the human foetus compared to the haemoglobin curve

A

the curve shifts to the left

66
Q

state the adaptation that llamas have for O₂ affinity & why

A

as llamas are found at very high altitudes (& very low partial pressures of O₂) they have haemoglobin that has a higher affinity for O₂ even at low partial pressures

67
Q

state where the oxyhaemoglobin curve is for llamas compared to haemoglobin curve

A

the curve shifts to the left

68
Q

state the adaptation that doves have for O₂ affinity

A

as doves need more O₂ to match their faster metabolism (for respiration to provide energy for contracting muscles - flying) they have a lower affinity for O₂ so O₂ is more readily unloaded

69
Q

state where the oxyhaemoglobin curve is for doves compared to the haemoglobin curve

A

the curve shifts to the right

70
Q

state the adaptation that earthworms have for O₂ affinity

A

as earthworms are underground (& there is a low partial pressure of O₂) they have haemoglobin that have very high affinity even at low partial pressures can load O₂

71
Q

what type of circulatory system do mammals have?

A

they have a closed, double circulatory system

72
Q

define the term closed in the context of circulatory systems

A

the blood remains within the blood vessels

73
Q

define the term double circulatory system

A

the blood passes tough the heart twice in each circuit, there is one circuit which delivers blood to the lungs & another circuit which delivers blood to the rest of the body

74
Q

why is it important that mammals have a double circulatory system?

A

to manage the pressure of the blood flow

75
Q

explain why blood flows through the lungs at a low pressure

A

to prevent damage to the capillaries in the alveoli & reduced speed at which the blood lows, allowing for time for gas exchange

76
Q

explain why oxygenated blood from the lungs to the heart flows at high pressure

A

to ensure that the blood reaches all respiring cells inn the body

77
Q

list the key blood vessels within the circulatory system

A
  1. heart - vena cava, aorta, pulmonary artery & pulmonary vein
  2. lungs - pulmonary artery & pulmonary vein
  3. kidneys - renal artery & renal vein
78
Q

state how the major blood vessels are connected to the circulatory system

A

through the arteries, arterioles, capillaries & veins

79
Q

describe the structure & properties of the cardiac muscle

A

the walls of the heart have a thick muscular layer
properties:
myogenic - means it can contract & relax without nervous or hormonal stimulation
never fatigues - as long as it has a supply of O₂

80
Q

describe the function & importance of coronary arteries

A

function: they supply the cardiac muscle with oxygenated blood (they branch off the aorta)

importance: if they become blocked the cardiac muscle won’t receive O₂, so it cannot respire = cells die - results in myocardial infarction (heart attack)

81
Q

state the 4 chambers of the heart

A

2 atria’s - left & right atrium
2 ventricles - left & right atrium

82
Q

describe the structure & function of the atria

A

thinner muscular walls
elastic walls to stretch when blood enters
do not need to contract as hard - as it only pumps blood to the ventricles

83
Q

describe the structure & function of the ventricles

A

thicker muscular walls to enable bigger contraction - creating a higher blood pressure to enable blood to flow longer distances (to lungs & rest of the body)

84
Q

describe the structure, function & importance of the right ventricle

A

structure: thinner muscular wall in comparison to left ventricle
function: pumps blood to the lungs
importance: needs to be at a lower pressure to prevent damage to the capillaries in the lungs

85
Q

describe the structure, function & importance of the left ventricle

A

structure: thicker muscular wall compared to right ventricle - to enable large contractions of muscle to create higher pressure
function: pumps blood to the body
importance: needs to be a higher pressure to ensure blood reaches all respiting cells in the body

86
Q

state the large blood vessels that transport blood to the heart & their functions

A

2 veins:
1. vena cava - carries deoxygenated blood from the body into the right atrium

  1. pulmonary vein - carries oxygenated blood from the lungs to the left atrium
87
Q

state the large blood vessels that transport blood away from the heart & their functions

A

2 arteries:
1. pulmonary artery - carries deoxygenated blood from the right ventricle to the lungs to become oxygenated

  1. aorta - carries oxygenated blood from the left ventricle to the rest of the body
88
Q

state the valves in the heart & where they are found

A

semi-lunar valves - in the aorta & pulmonary artery
atrioventricular valves - between atria & ventricles (there are 2 = bicuspid-left side & tricuspid-right side)

89
Q

state the function & importance of valves

A

function: they open when there is higher pressure behind the valve
they close when there is higher pressure in front of the valve
importance: as they prevent the backflow of blood

90
Q

state the function & importance of the septum

A

function: separates the deoxygenated & oxygenated blood
importance: maintains high conc of O₂ in oxygenated blood to maintain conc gradient to enable diffusion at respiring cells

91
Q

explain the process that transports blood away from the heart & state the blood vessels required

A
  1. arteries carry blood away from the heart & into the arterioles
  2. arterioles are smaller than the arteries & connect to the capillaries
  3. the capillaries connect the arterioles to the veins
  4. the veins carry blood back into the heart
92
Q

explain the structure of arteries

A

muscle layer: thicker than veins so that construction & dilation can occur to control the vol of blood

elastic layer: thicker than veins to help maintain blood pressure & walls can stretch & recoil in response to the heartbeat

wall thickness: thicker walls than veins to prevent vessels from bursting due to high pressure

doesn’t have valves

93
Q

explain the structure of veins

A

muscle layer: thin - so it cannot control blood flow

elastic layer: thin - as pressure is low

wall thickness: thin - as there is low pressure, there is a low risk of bursting. the thinness means that the vessels are easily flattened which helps the flow of blood reach the heart

has valves

94
Q

explain the structure of arterioles

A

muscle layer: thicker than arteries to help restrict blood flow into the capillaries

elastic layer: thinner than in arteries as the pressure is lower

wall thickness: thinner as pressure is lower

doesn’t have valves

95
Q

explain the structure of capillaries

A

muscle layer: no muscle layer

elastic layer: no elastic layer

wall thickness: one cell thick - only consists of a lining layer. provides a short diffusion distance for exchanging materials between blood & the cells

doesn’t have valves

96
Q

state the 3 stages of the cardiac cycle

A
  1. diastole
  2. atrial systole
  3. ventricular systole
97
Q

explain the 1st stage of the cardiac cycle

A
  1. the atria & ventricular muscles are relaxed
  2. this is where blood enters the atria via the vena cava & pulmonary vein
  3. the blood flowing into the atria increases the pressure within the atria
98
Q

explain the 2nd stage of the cardiac cycle

A
  1. the atria muscular walls contract, increasing the pressure further - causing atrioventricular valves to open & flow into the ventricles
  2. the ventricular muscular walls are relaxed (ventricular diastole)
99
Q

explain the 3rd stage of the cardiac cycle

A
  1. after a short delay, the ventricle muscular walls contract, increasing the pressure beyond that of the atria - causing atrioventricular valves to close & semi-lunar valves to open
  2. the blood is pushed out of the ventricles into the arteries (pulmonary & aorta)
100
Q

define the term cardiac output

A

the volume of blood which can leave one ventricle in one minute

101
Q

how is the cardiac output calculated?

A

cardiac output = heart rate x stroke volume

heart rate: heartbeats per min (min-1)
stroke volume: vol of blood that leaves the heart per dm3

102
Q

what is tissue fluid?

A

fluid containing water, glucose, amino acids, fatty acids, ions & oxygen which bathes the tissues

103
Q

how are tissue fluids formed?

A

caused by capillaries having small gaps in the walls so that liquids & small molecules can be forced out

as blood enters the capillaries from arterioles, the small diameter results in a high hydrostatic pressure so water, glucose, amino acids, fatty acids, ions & oxygen are forced out - AKA ultrafiltration

104
Q

state what is forced out of the capillary

A

water molecules
dissolved minerals & salts
glucose
small proteins & amino acids
fatty acids
oxygen

105
Q

state what remains in the capillary

A

red blood cells
platelets
large proteins

106
Q

explain how the liquid from the tissue fluid is reabsorbed into the capillaries

A

the large molecules in the capillaries create a lowered water potential
towards the venule end of capillaries, the hydrostatic pressure is lowered due to loss of liquid - water potential is also low
water re-enters the capillaries by osmosis

107
Q

why isn’t all the liquid from the tissue fluid reabsorbed into the capillaries?

A

as equilibrium is reached

108
Q

what happens to the rest of the tissue fluid?

A

it’s absorbed into the lymphatic system & eventually drains back into the bloodstream near the heart

109
Q

what is transpiration?

A

the loss of water vapour from the stomata by evaporation

110
Q

state what conditions affect transpiration

A

light intensity: +ve correlation
more light causes more stomata to open = larger SA for evaporation

temperature: +ve correlation
more heat = more KE - faster moving molecules & so more evaporation

humidity: -ve correlation
more water vapour in the air will make the water potential more +ve outside of the leaf, reducing the water potential gradient

wind: +ve correlation
more wind will blow away humid air containing water vapour, maintaining the water potential gradient

111
Q

what factors allow the movement of water in the xylem?

A

cohesion
capillarity - adhesion
root pressure

112
Q

what creates cohesion between water molecules?

A

as water is a dipolar molecule, it enables hydrogen bonds to form (between the H & O of different water molecules) creating cohesion between the molecules, making them stick together

113
Q

why is cohesion between water molecules important for the movement of water in the xylem?

A

the cohesion allows water to travel up the xylem as a continuous water column against gravity allowing water to be transported faster

114
Q

what is the adhesion of water?

A

it’s where water sticks to other molecules

115
Q

why is adhesion between water molecules important for he movement of water in the xylem?

A

as water adheres to xylem walls it allows it to travel against the gravity - the narrower the xylem the bigger the impact of capillarity

116
Q

what is root pressure?

A

as water moves into the roots by osmosis it increases the volume of liquid inside the root so the pressure in the root also increases - AKA root pressure

117
Q

why is root pressure important for the movement of water in the xylem?

A

the increase in the roots forces water above it upwards (+ve pressure)

118
Q

explain the movement of water against several meters of gravity up a tree, referring to the cohesion tension theory

A
  1. water vapour evaporates out if the stomata on leaves - loss of water creates a lower pressure
  2. when this water is lost by transpiration more water is pulled up the xylem to replace it (moves due to -ve pressure)
  3. due to H bonds between water molecules, they are cohesive - creates a column of water within the xylem
  4. water molecules also adhere to the walls of the xylem - helps pull the water column upwards
  5. as this column of water is pulled up the xylem it creates tension, pulling the xylem in to become narrower - which increases the action of capillarity
119
Q

how are organic substances transported in a plant?

A

through the phloem

120
Q

name & explain the structure & functions of the key cells in the phloem tissue

A
  1. sieve tube elements:
    living cells
    contains no nucleus
    contains few organelles
  2. companion cells:
    provide ATP required for active transport of organic substances
121
Q

explain the transport of organic substances using the source to sink explanation

A

the ‘source cell’ in the model refers to a photosynthesising leaf cell & the ‘sink cell’ where the sugars are delivered as a respiring cell

122
Q

explain the function of the cells using the source to sink explanation

A

at the source cells, there are photosynthesising cells (sucrose/glucose that is made during photosynthesis) that lower the water potential of those cells & so any surrounding water in the plant/xylem will enter those cells by osmosis

on the other end of the source to sink model there are respiring zinc cells that use up sugars for respiration which means there will be more +ve water potential inside the cell compared to the outside - so water leaves the sink cell by osmosis to other cells in the plant/xylem

123
Q

explain the effects of the source to sink model

A

there is an increase in the hydrostatic pressure in the source cell but there is a decrease in hydrostatic pressure in the sink cell

the source cell has a higher hydrostatic pressure than the sink cell so the solution is forced towards the sink cell via the phloem

124
Q

how does sucrose transports from the source to the sieve tube element?

A

by translocation:
there is a high conc of sucrose at the site of production (due to photosynthesis), therefore sucrose diffuses down its conc gradient into the companion cell by facilitated diffusion

active transport of H⁺ occurs from the companion cell into the spaces within the cell walls using energy - creates a conc gradient via carrier proteins into sieve tube elements

co-transport of sucrose with the H⁺ ions occur via the protein co-transporters to transport the sucrose into the sieve-tube elements

125
Q

explain the movement of sucrose within the phloem sieve tube element

A

also by translocation:
increase of sucrose in the sieve tube element lowers the water potential

water enters the sieve tube elements from the surrounding xylem vessels by osmosis

the increase in water vol in the sieve tube element increases the hydrostatic pressure causing the liquid to be forced towards the sink

126
Q

explain how sucrose is transported to the sink (respiring cells)

A

also by translocation:
sucrose is used in respiration at the sink, or stored as insoluble starch

more sucrose is actively transported into the sink cell, which causes the water potential to decrease - result in osmosis of water from sieve tube element into sink cell (some water also return to xylem)

the removal of water decreases the volume in the sieve tube element & so the hydrostatic pressure decreases

movement of soluble organic substances is due to the difference in hydrostatic pressure between the source & sink end of the sieve tube element

127
Q

state the ways in which translocation is investigated

A
  1. by using tracers
  2. the ringing experiment
128
Q

what is tracing?

A

this is where plants are provided with only radioactively labelled carbon and over time this is absorbed into the plant & used in photosynthesis to create sugars which all contain this carbon

129
Q

explain the process of tracing

A
  1. plants provided with only radioactively labelled carbon
  2. thin slices from the stems are then cut & placed on x-ray film that turns black when exposed to radioactive material
  3. when the stems are placed on the section from the stem containing the sugars turns black, showing where the phloem are & shows sugars are transported in the phloem
130
Q

explain the process of the ringing experiment

A
  1. a ring of bark & phloem are peeled & removed off a tree trunk - the result of removing the phloem is that the trunk swells above the removed section
  2. analysis of the liquid in this swelling shows it contains sugars - also shows that when the phloem is removed sugars cannot be transported & so proves that the phloem transports sugars

biology (6 decks)

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