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A-Level Biology > Unit 3 - Substance Exchange > Flashcards

Unit 3 - Substance Exchange Flashcards

1
Q

what is the physical breakdown of food?

A

food is ‘physically’ broken down into smaller pieces
increasing its surface area
by chewing, stomach churning & bile emulsification

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2
Q

what is the chemical digestion of food?

A

by enzymes
hydrolysing covalent bonds in large, insoluble molecules to form small, soluble molecules

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3
Q

describe the digestion of polysaccharides e.g. starch

A

polysaccharides digested by carbohydrases that hydrolyse the glycosidic bonds
1. salivary amylase produced in salivary glands digests starch into maltose
2. pancreatic amylase produced in pancreas digests starch into maltose

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4
Q

describe the digestion of disaccharides

A

disaccharides are digested by membrane-bound disaccharidases found in the csm of epithelial cells
1. maltase - maltose –> 2x alpha glucose
2. sucrase - sucrose –> alpha glucose + fructose
3. lactase - lactose –> alpha glucose + galactose

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5
Q

what category of enzymes are proteins digested by?

A

proteases that hydrolyse peptide bonds

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6
Q
  1. what is the function of endopeptidases?
A

they hydrolyse peptide bonds in the central region of a polypeptide
which forms shorter peptide chains
e.g. pepsin produced in the stomach

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7
Q
  1. where are exopeptidases produced & what is their function?
A

they are produced in pancreas & ileum
they hydrolyse peptide bonds at the ends of polypeptides on the terminal amino acids
which forms dipeptides & single amino acids

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8
Q
  1. where are dipeptidases found & what is their function?
A

they are bound in csm of epithelial cells lining the ileum
they hydrolyse peptide bonds b/w 2 amino acids of a dipeptide

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9
Q

what happens to lipids before digestion?

A

emulsification - lipids are split into tiny droplets by bile salts (produced in liver & stored in gall bladder)
increases surface area of lipids so lipase can work faster so hydrolysis is faster
then the tiny droplets are converted into micelles, which carry fatty acids & monoglycerides to epithelial cells

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10
Q

how are triglycerides digested?

A

by lipases which hydrolyse ester bonds
triglycerides –> monoglycerides + fatty acids

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11
Q

describe the absorption of the products of digestion of triglycerides

A
  1. micelles contain bile salts, fatty acids & monoglycerides
    they make fatty acids more soluble in water
  2. micelles carry fatty acids & monoglycerides to epithelial cells lining the ileum.
  3. micelles break down, releasing monoglycerides & fatty acids, which are non-polar so can simply diffuse across the csm into epithelial cells
  4. triglycerides reform in ser & in the golgi apparatus, they associate with cholesterol & lipoproteins to form chylomicrons
  5. vesicles containing chylomicrons move out of epithelial cells by exocytosis & enter lymphatic capillaries called lacteals
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12
Q

how is the ileum adapted for the absorption of the products of digestion?

A

absorption of digested food (glucose, aas, fatty acids & glycerol move into the blood by simple diffusion, facilitated diffusion & some active transport)
ileum surface is covered in millions of tiny villi, which increases the surface area for a higher rate of dif./fac. dif./at
ileum is very long, which increases surface area & time for absorption to happen

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13
Q

how is a villus adapted for the absorption of the products of digestion?

A

csm of epithelial cells is highly folded into many microvilli
- increased surface area for insertion of membrane proteins: many carrier & channel proteins for fac. dif. & co-transport, many carrier proteins for at
- increased sa for higher rate of absorption

epithelial cells are very thin
- short diffusion distance so faster diffusion/absorption

blood supply & capillaries close to surface
- moving blood maintains a steep concentration gradient for faster diffusion/absorption

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14
Q

how are glucose & aas absorbed?

A

when there is a greater concentration of glucose/aas in the ileum than in the blood, these molecules can move down the concentration gradient into the blood by fac. dif.

when there is a greater concentration of glucose/aas in the blood than in the ileum, all molecules are transported against their concentration gradient by co-transport, which is allowed by active transport

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15
Q

describe the process of co-transport

A
  1. (3) sodium ions are actively transported from the epithelial cell into the blood by the Na+/K+ pump (carrier protein that requires ATP hydrolysis)
  2. this lowers the concentration of Na+ in the epithelial cell & creates a concentration/diffusion gradient for Na+ from ileum into the epithelial cell
  3. Na+ ions move into the epithelial cell from the ileum by fac. dif. & brings a glucose/aa with it by co-transport
  4. glucose/aa moves into the blood by fac. dif. down a concentration gradient using a glucose or aa channel protein
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16
Q

as the size of the organism increases, what is the effect on sa:v ratio?

A

decreases

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17
Q

what is fick’s law?

A

rate of diffusion is proportional to sa x conc. gradient/diffusion distance

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18
Q

how does sa increase the rate of gas exchange?

A

folds & branches
more membrane area over which exchange can happen

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19
Q

how does short diffusion distance increase the rate of gas exchange?

A

surface is often 1 cell thick so rapid gas exchange e.g. squamous epithelium & capillary endothelium

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20
Q

how is a steep diffusion gradient maintained?

A

ventilation & mass flow of air or water
rich blood supply by dense capillary network

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21
Q

what does the tracheal system consist of?

A

1- pores = spiracles
opened & closed by valves & regulate exchange of air & water

2- trachea(e) tubes supported by chitin to prevent collapse

3- smaller tracheoles increase sa
dead-end tubes

4- tracheoles extend throughout body tissues of the insect so oxygen is brought directly to respiring tissues/muscle fibres

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22
Q

how are gases exchanged in the tracheal system?

A

along a diffusion gradient (passive)
mass transport/ventilation
ends of tracheoles filled with water

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23
Q

describe the movement of gas along the diffusion gradient in tracheal system

A

when cells are respiring oxygen is used up so conc, towards the ends of the tracheoles decreases = creates a diffusion gradient
O2 diffuses from atmosphere to tracheoles to muscles
when cells respire CO2 is produced - creates a diffusion gradient so CO2 diffuses from tracheoles to atmosphere

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24
Q

describe the movement of gases by mass transport/ventilation in tracheal system

A

contraction of abdominal muscles in insects squeeze trachea
so mass movement of air in & out
maintains concentration gradient of O2 & CO2

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25
how are tracheoles adapted for efficient gas exchange?
highly branched - increases sa thin walls - short diffusion distance permeable to oxygen muscle cells around tracheoles respire anaerobically & produce lactic acid which lowers the water potential of muscle cells so water carrying dissolved oxygen moves from tracheoles into muscle cells via osmosis final diffusion pathway is in air rather than liquid, so it is faster
26
how do insects lose water & how do they limit this water loss?
water evaporates from the surface of insects' bodies via spiracles (exoskeleton is waterproof) thin, permeable surface with large sa for efficient gas exchange - but = water loss adaptations: 1- spiracles can be closed by valves to reduce water loss 2- hairs around spiracles reduce water potential gradient 3- waxy waterproof layer covers exoskeleton of chitin 4- lower sa:v - minimise area over which water is lost
27
describe the structure & demands of fish
covered in scales & mucous so gas impermeable quite large so small sa:v high O2 demands to supply muscles for swimming
28
describe the structure of the gills
located behind the head gill filaments stacked in a pile - supported by gill arches at right angles - gill lamellae
29
how is water forced over the gills?
operculum - bony flap that acts as a valve to allow one way flow of water over the gills & is a tough protective layer pathway: water taken in through mouth, forced over gills & out through operculum
30
what are the features of the lungs?
ribcage - protects & supports lungs trachea bronchi bronchioles alveoli
31
what is the counter current exchange principle?
blood flows through the gill lamellae in the opposite direction to water flowing over the gills so blood with high O2 conc. meets water, which has a max conc. of O2 so O2 diffuses into the blood blood with low conc. of O2 meets water that has most O2 removed so O2 still diffuses into the blood therefore a diffusion gradient is maintained across the whole length of the lamellae
32
describe the bronchioles
branching sub-divisions of the bronchi smooth muscle walls lined with epithelial cells so can constrict to control air flow to alveoli
33
describe the trachea
flexible airway supported by C-shaped cartilage which prevents trachea from collapsing when air pressure decreases when breathing in tracheal walls are made of muscle, lined with ciliated epithelium & goblet cells that secrete mucous
34
why is the volume of of O2 absorbed & CO2 removed large in mammals?
they have a large volume of living cells they maintain a high body temperature which is related to their high metabolic & respiratory rates so evolved lungs
35
describe the bronchi
2 divisions of the trachea, each leading to a lung cartilage rings, ciliated epithelium, goblet cells
36
describe the alveoli
tiny air sacs lined with epithelium collagen & elastic fibres b/w alveoli so they can stretch & fill when breathing in & spring back when breathing out to expel CO2-rich air alveolar membrane is the gas exchange surface
37
describe the mechanism of breathing
inspiration: when the air pressure of the atmosphere is greater than that inside the lungs, air moves in down the pressure gradient active by muscle contraction expiration: when the air pressure of the lungs is greater than that of the atmosphere, air moves out, the pressure gradient is reversed pressure changes are due to change in volume of the thoracic cavity due to internal & external intercostal muscles & diaphragm
38
what happens to the body on inspiration?
external intercostal muscles contract internal relax ribcage moves up & out diaphragm muscles contract so diaphragm moves down & flattens volume in thorax increases so pressure in thorax decreases air moves in down the pressure gradient
39
what happens to the body on expiration?
external intercostal muscles relax internal contract ribcage moves down & in diaphragm muscles relax so diaphragm moves up volume in thorax decreases so pressure in thorax increases air moves out down the pressure gradient
40
what is the formula for pulmonary ventilation (volume of air exchanged per unit time dm^3min^-1)?
tidal volume (dm^3) x ventilation rate (min^-1)
41
define tidal volume
volume of air exchanged during normal breathing
42
define vital capacity
max. volume of air exchanged from full inspiration to full expiration
43
define residual volume
volume of air that cannot be expelled by forced expiration cartilage supports tubes & deflated alveoli
44
why is gas exchange important in plants?
to facilitate respiration & photosynthesis at times gas produced in one process can be used for the other, but not sufficient to meet the demands of the plant
45
when can gases from one process be used for the other?
see notes
46
describe the upper epidermis
few or no chloroplasts - transparent so light can pass through to palisade cells upper surface has thick, waxy, waterproof cuticle - protection & reduces water loss
47
describe palisade mesophyll cells
absorb light for ps many chloroplasts (that can move up & down)
48
describe spongy mesophyll cells
make movement of gases needed for ps more efficient air spaces b/w cells
49
describe lower epidermis
guard cells (contain chloroplasts) & stomata stomata control rate of gas exchange
50
how do stomata work?
located on underside of leaves bc it is cooler so less transpiration each stoma surrounded by guard cells that open & close the pore - regulate diameter, have chloroplasts for atp production --> active transport control rate of gas exchange important bc terrestrial plants lose water by evaporation/evapotranspiration down water potential gradient conflict b/w gas exchange & water loss
51
how does a stoma open?
active K+ ion movement into guard cell using atp from ps lowers water potential of cytoplasm water moves into guard cell by osmosis down water potential gradient cell becomes turgid stoma opens
52
how does a stoma close?
active K+ ion movement stops K+ gates open so K+ moves out of guard cell water follows, moving out of guard cell by osmosis down water potential gradient cells become flaccid stoma closes
53
describe the closed double circulatory system in mammals
closed - blood is contained in vessels double - blood flows through heart twice per complete circuit separation of oxygenated & deoxygenated blood can regulate blood flow & pressure - high P to body
54
what are the names of the blood vessels going to & from the kidneys?
to: renal artery from: renal vein
55
label a diagram of the heart
see notes booklet
56
what is the function of the coronary arteries?
supply cardiac muscle with oxygen-rich blood
57
what is coronary heart disease caused by & what might it cause?
atheroma - build up of fatty deposits within coronary artery endothelium decreased rate of blood flow decreased oxygen supply decreased rate of aerobic respiration so lactic acid buildup, causing pain (angina) cells may die lack of atp heart attack
58
explain the difference in thickness of the muscle of the atria, LV & RV walls
atria have thinner walls than ventricles bc low force of contraction, forcing blood a short distance LV wall is thicker than RV wall bc LV pumps blood a greater distance (around the body) so more force & higher pressure needed with each contraction RV only needs to pump blood a shorter distance than LV - to lungs
59
what is the function of valves?
to prevent backflow of blood to ensure blood flow is only one-way
60
where are the atrioventricular valves & describe their activity?
b/w atria & ventricles open when pressure in atria > pressure in ventricles closed when pressure in ventricles > pressure in atria
61
where are the semilunar valves & describe their activity?
b/w ventricles & arteries open when pressure in ventricles > pressure in arteries closed when pressure in arteries > pressure in ventricles
62
what maintains unidirectional flow of blood during the cardiac cycle?
pressure & volume changes valve movements
63
what are the 3 steps in the cardiac cycle?
1. atrial systole 2. ventricular systole 3. ventricular diastole
64
what happens in atrial systole?
atria contract pressure in atria increases above pressure in ventricles AV valves open & blood is forced from atria into ventricles SLVs shut to prevent backflow of blood into ventricles
65
what happens in ventricular systole?
ventricles contract pressure in ventricles increases quickly AV valves shut bc pressure in ventricles > pressure in atria pressure in ventricles increases above pressure in arteries so SLVs open blood is forced into arteries so ventricular blood vol. decreases
66
what happens in ventricular diastole?
ventricles relax so pressure in ventricles decreases quickly pressure in ventricles decreases below pressure in arteries so SLV shut pressure in ventricles decreases below pressure in atria so AV valves open ventricles fill passively with blood atria fill from veins heart completely relaxed
67
define cardiac output & what is its formula?
the volume of blood ejected by the heart per minute cardiac output = stroke volume (vol. ejected per heartbeat) x heart rate (bpm) cm^3min^-1
68
how does the structure of arteries relate to their function?
function: transport high pressure blood away from the heart blood is oxygenated except pulmonary (& umbilical) artery thick smooth muscular wall to withstand high pressure smooth to reduce friction lots of elastic tissue to allow stretch & recoil for smooth blood flow narrow lumen relative to diameter capable of vasoconstriction impermeable no valves except SLV has pulse
69
how does the structure of arterioles relate to their function?
function: to transport blood from arteries to capillaries muscular for vasoconstriction to redistribute blood, but less so than arteries
70
how does the structure of capillaries relate to their function?
function: site of substance exchange connects arterioles to venules blood is under decreasing pressure no muscular wall or elastic tissue large lumen relative to diameter to allow red blood cells to fit cannot vasoconstrict very permeable to allow substance exchange no valves
71
what is the function of venules?
function: connect capillaries to veins
72
how does the structure of veins relate to their function?
function: to transport lower pressure blood back to the heart blood is deoxygenated except in pulmonary (& umbilical) vein thinner muscular wall & less elastic tissue wider lumen relative to diameter incapable of vasoconstriction impermeable valves that prevent backflow of blood
73
what is tissue fluid?
watery liquid derived from blood plasma that bathes all cells of the body it forms the immediate environment of all cells & supplies them with substances
74
what does tissue fluid contain?
supplies cells with: glucose, AAs, O2, CO2, FAs, lipids, ions (Na+, Cl-, K+) receives from cells & tissues: waste materials inc. CO2 from respiration & urea from deamination
75
what is tissue fluid formed from?
blood plasma, which is continually forced from capillaries via pores b/w capillary endothelial cells
76
describe the formation & reabsorption of tissue fluid
1. hydrostatic pressure of the blood is higher at the arterial end 2. so water & small soluble molecules are forced out of the capillary to form TF 3. RBCs & plasma proteins are too big so remain in capillary 4. this decreases the water potential of the capillary as blood flows to the venous end 5. 90% water is reabsorbed by osmosis down the water potential gradient into the venous end of the capillary 6. excess TF is drained into the lymph, into the lymphatic system & later returns to circulatory system
77
why does high blood pressure lead to an accumulation of TF?
high blood pressure = high hydrostatic pressure which increases outwards pressure from arterial end of capillary so more tissue fluid is formed
78
table of comparison b/w blood, TF & lymph
see notes booklet
79
what are haemoglobins?
group of chemically similar protein molecules found in a wide variety of organisms Hb has a quaternary structure that has evolved to make it efficient at loading & unloading O2
80
what is the role of haemoglobin?
to transport O2
81
what is the process by which Hb binds with O2 called & where does it happen?
loading/association happens at gas exchange surface = alveolar epithelium
82
what is the process by which Hb releases its O2 called & where does it happen?
unloading/dissociation happens at respiring tissue e.g. muscle
83
how does Hb change under different conditions & why?
its affinity (chemical attraction) for O2 bc its shape changes in the presence of specific substances e.g. CO2, lactic acid or temp. (increasing these factors decreases affinity)
84
Hb: what happens at the gas exchange surface?
high O2 conc. low CO2 conc. Hb has high affinity for O2 so O2 associates w Hb
85
Hb: what happens at respiring tissues?
low O2 conc. high CO2 conc. Hb has low affinity for O2 so O2 readily dissociates from Hb
86
what is the oxyhaemoglobin dissociation curve?
graph of the relationship b/w the partial pressure of O2 vs saturation of Hb with O2
87
describe & explain the shape of the oxyhaemoglobin dissociation curve
sigmoid shape 1. shallow at start loading the first O2 molecule onto Hb is difficult 2. steeper once 1st O2 is bonded, Hb changes shape, exposing the 2nd haem binding site so it is easier for the 2nd & 3rd O2 molecule to bind = positive cooperativity of O2 binding 3. binding the 4th O2 molecule is more difficult bc there is a decreased chance of O2 colliding with the 'empty' haem group
88
what happens at the steepest part of the O2 dissociation curve?
as RBCs & oxyHb enter tissues, partial pressure of O2 decreases rapidly bc O2 is used up in respiration over the steepest part of the curve a small decrease in ppO2 causes a big drop in % saturation of Hb ie. oxyHb rapidly loses affinity so O2 rapidly dissociates & offloads lots of O2 into tissues that need it
89
describe & explain the O2 dissociation curve at high ppO2
high % saturation bc in alveoli in lungs, Hb is 98% saturated w O2 bc Hb has a high affinity for O2 so readily associates
90
what is the Bohr effect?
Hb has a reduced affinity for O2 in the presence of CO2 bc of conformational change in shape the greater the conc. of CO2, the more readily the Hb releases its O2 the graph shifts right this explains why Hb changes behaviour in different regions of the body (lungs vs tissues)
91
explain how the Bohr effect impacts the O2 dissociation curve
as conc CO2 increases, affinity for bound O2 decreases & Hb is less saturated so oxyHb offloads more readily
92
define high affinity haemoglobin
Hb that loads/associates O2 more readily but dissociates less readily in tissues
93
define low affinity haemoglobin
Hb that loads/associates O2 less readily (bc needs higher ppO2 in environment to saturate) but dissociates more readily in tissues
94
why do species have different haemoglobins?
1. environmental conditions: higher or lower O2 availability (high altitude has lower ppO2) can have low affinity Hb in O2-rich environments bc Hb can get v saturated 2. SA:V body size & heat loss high SA:V = tissues need more O2 per gram 3. metabolic demand - energy requirements e.gs in notes booklet
95
how does Hb of more active species allow the greater level of activity?
oxyHb dissociation curve shifts right so Hb dissociates more readily so more oxygen is delivered to tissues so rate of respiration increases
96
what is the role of phloem in plants?
to transport sucrose & AAs (organic assimilate) from source to sink flow is bidirectional
97
what is the structure of the phloem?
living cells 1. sieve tube elements (STE) - elongated cells connected end-to-end, peripheral cytoplasm 2. sieve plates connect cells - perforated w pores to let phloem sap flow 3. companion cells connected to STE via plasmodesmata - have lots of mitochondria to provide lots of ATP for translocation
98
what is translocation?
the active, mass flow of sucrose & AAs from source to sink (bc of positive hydrostatic pressure)
99
what are sources & sinks?
sources: cells where sucrose is made/released from storage into phloem e.g. leaves sinks: cells where sucrose is removed from phloem, where it is needed for respiration, storage as starch or to make cellulose e.g. roots & fruits
100
describe the mass flow hypothesis for the mechanism of translocation
1. companion cells actively load sucrose into STE at source 2. this lowers water potential of STE so water enters STE by osmosis down water potential gradient 3. so hydrostatic pressure of STE increases 4. sucrose moves by mass flow towards sink/respiring tissue 5. sucrose is actively unloaded at sink and used e.g. for respiration 6. water leaves STE & mass flow of phloem sap occurs down pressure gradient
101
what 3 experiments give evidence for translocation?
ringing experiments tracer experiments aphids
102
describe ringing experiments & how do they give evidence for translocation?
bark & phloem removed from plant, not xylem after time, the region above the ring swells samples from the swollen region have high conc. of sucrose & AAs non-photosynthetic tissue in region below ring withers & dies whilst these regions above the ring continue to grow conclusion: phloem, not xylem, is responsible for translocation of sugars
103
describe tracer experiments & how do they give evidence for translocation?
radioactive isotopes used to trace movement of substances the 14C isotope makes radioactively labelled 14CO2 if plant is grown in atmosphere of 14CO2, 14CO2 is taken up by photosynthesis & turned into heavy sucrose (w 14C) heavy sucrose can be traced using autoradiography 14C only in phloem & with time, it is shown to be in all areas of plant conclusion: only phloem is responsible for translocation of sugars
104
describe the role of aphids on proving translocation
aphids = insects that feed on plants needle-like mouth penetrates STE & extracts contents of STE the contents are analysed & identified as organic assimilate, which proves organic assimilate is transported in phloem by translocation
105
what is the evidence for (6) & against (3) the mass flow hypothesis?
see table in notes booklet

A-Level Biology (14 decks)

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