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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

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/x 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 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. & carries 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

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

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

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

25
Q

how are tracheoles adapted for efficient gas exchange?

A

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
Q

how do insects lose water & how do they limit this water loss?

A

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
Q

describe the structure & demands of fish

A

covered in scales & mucous so gas impermeable
quite large so small sa:v
high O2 demands to supply muscles for swimming

28
Q

describe the structure of the gills

A

located behind the head
gill filaments stacked in a pile - supported by gill arches
at right angles - gill lamellae

29
Q

how is water forced over the gills?

A

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

29
Q

what are the features of the lungs?

A

ribcage - protects & supports lungs
trachea
bronchi
bronchioles
alveoli

29
Q

what is the counter current exchange principle?

A

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

30
Q

describe the bronchioles

A

branching sub-divisions of the bronchi
smooth muscle walls lined with epithelial cells so can constrict to control air flow to alveoli

30
Q

describe the trachea

A

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

30
Q

why is the volume of of O2 absorbed & CO2 removed large in mammals?

A

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

31
Q

describe the bronchi

A

2 divisions of the trachea, each leading to a lung
cartilage rings, ciliated epithelium, goblet cells

32
Q

describe the alveoli

A

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

33
Q

describe the mechanism of breathing

A

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

34
Q

what happens to the body on inspiration?

A

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

35
Q

what happens to the body on expiration?

A

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

36
Q

what is the formula for pulmonary ventilation (volume of air exchanged per unit time dm^3min^-1)?

A

tidal volume (dm^3) x ventilation rate (min^-1)

37
Q

define tidal volume

A

volume of air exchanged during normal breathing

38
Q

define vital capacity

A

max. volume of air exchanged from full inspiration to full expiration

39
Q

define residual volume

A

volume of air that cannot be expelled by forced expiration
cartilage supports tubes & deflated alveoli

40
Q

why is gas exchange important in plants?

A

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

41
Q

when can gases from one process be used for the other?

A

see notes

42
Q

describe the upper epidermis

A

few or no chloroplasts - transparent so light can pass through to palisade cells
upper surface has thick, waxy, waterproof cuticle - protection & reduces water loss

43
Q

describe palisade mesophyll cells

A

absorb light for ps
many chloroplasts (that can move up & down)

44
Q

describe spongy mesophyll cells

A

make movement of gases needed for ps more efficient
air spaces b/w cells

45
Q

describe lower epidermis

A

guard cells (contain chloroplasts) & stomata
stomata control rate of gas exchange

46
Q

how do stomata work?

A

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

47
Q

how does a stoma open?

A

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

48
Q

how does a stoma close?

A

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

A-Level Biology (5 decks)

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