B3.1 Gas exchange

Question 1

function of waxy cuticle

Answer 1

wax lipid layer that covers surface of leaves and prevents uncontrolled and excessive leaf water loss by evaporation

Question 2

function of palisade mesophyll

Answer 2

densely packed region in upper part of the leaf, has many chloroplasts and located to get max sunlight for photosynthesis

Question 3

function of spongy mesophyll

Answer 3

loosely packed blew the palisade layer and just above stomata, some chloroplasts, many air spaces for large SA for gas exchange

Question 4

function of veins

Answer 4

water moves up from the root system to the leaves in the xylem
water and dissolved sugars distributed to other parts in the phloem
veins located centrally in a leaf to provide access to all the cell layers

Question 5

function of upper epidermis

Answer 5

small cells on upper surface of leaves that secrete a waxy cuticle

Question 6

function of lower epidermis

Answer 6

small cells on lower surface of leaves that secrete a waxy cuticle-guard cells forming stomata are embedded in this layer

Question 7

function of stomata

Answer 7

numerous microscopic openings on lower surface
each stoma has 2 guard cells
when open-stomata allow CO2 to enter and O2 and water vapour to exit

Question 8

when is haemoglobin saturated?

Answer 8

when haemoglobin has a total of 4 iron atoms with 4 haem groups, it has the capacity to transport 4 oxygen molecules=saturated

Question 9

what is cooperative binding?

Answer 9

when any oxygen molecule bonded to haemoglobin increases its affinity for more oxygen and it is because the oxygen molecules are acting in concert with each other to increase the haemoglobin’s affinity for oxygen

Question 10

haemoglobin molecules that are carrying how many oxygen molecules have the greatest affinity for oxygen and why?

Answer 10

3 because each oxygen molecule that binds to haemoglobin changes the shape in a way that increases its affinity for another oxygen molecule so when haemoglobin is carrying 4 oxygens it has no affinity for oxygen

Question 11

what is allostery?

Answer 11

the binding of CO2 to the polypeptide chains of haemoglobin and the resulting change in haemoglobin’s affinity for oxygen

Question 12

what does CO2 bind to?

Answer 12

the polypeptide regions of the molecule

Question 13

what is the allosteric site?

Answer 13

the area of each polypeptide where CO2 binds

Question 14

what is the Bohr shift?

Answer 14

the binding of CO2 to haemoglobin results in an increase in the release of O2 molecules

Question 15

how does water move in transpiration?

Answer 15

by the process of transpiration pull, when water evaporates from the cells in the spongy mesophyll it ‘drags’ at the cell wall creating tension(adhesion), the tension pulls other water molecules into place, these water molecules in turn pull the others next to them, this goes on down the xylem to the roots(cohesion), whole process is passive

Question 16

how do guard cells open?

Answer 16

potassium ions pumped in, reduces water potential which causes water to leave the cell

Question 17

what is cellular respiration?

Answer 17

process in all living cells that releases energy in the form of ATP, energy is released when substrate molecules like glucose is oxidised

Question 18

why can’t large multicellar organisms not rely on diffusion alone?

Answer 18

because the external surface of the organisms are designed to provide protection to tissues underneath and not suitable as a respiratory surface

Question 19

properties of gas exchange surfaces

Answer 19

permeability(gases to move across surface); thin layer(short diffusion distance); moisture(so gases can dissolve); large SA so many gas molecules can diffuse at the same time

Question 20

how is a steep conc gradient maintained?

Answer 20

dense network of blood vessels for large SA; continuous blood flow in blood vessels so O2 always diffuses into blood and CO2 out of blood; ventilation to bring O2 close to the gas exchange surface and to remove CO2

Question 21

which 2 fluids are taken into account for respiratory gas concs in fish?

Answer 21

environmental water passing over the gill tissue and the blood within the capillaries of the gills

Question 22

which is the only blood vessel that allows exchange of substances?

Answer 22

capillaries

Question 23

why are animals with gills exothermic(cold blooded)?

Answer 23

bc of the high metabolic rates needed to be endothermic, the low O2 levels available in water wouldn’t support the metabolic rate needed for a constant internal body temp

Question 24

describe the blood before it is circulated to the gills in fish?

Answer 24

before, it’s recently been within capillaries of muscles and body tissues, body cells continuously respiring using CO2 and O2, blood that leaves body tissues have a higher conc of CO2 and lower conc of O2 compared to levels before blood reached body tissues, blood then transported to gill tissue

Question 25

in fish/humans which 2 events need to happen to keep the conc gradients in place?

Answer 25

water needs to be continuously passed over gills/air needs to continuously be refreshed in the lungs and there needs to be a continuous blood flow to the dense network of blood vessels in both the body tissues and the tissues of the gills/lungs

Question 26

what is a surfactant?

Answer 26

a thin phospholipid and protein film which lines the inner surface of each alveolus

Question 27

what does a surfactant do?

Answer 27

acts to reduce the surface tension of the moist inner surface and helps prevent each alveolus from collapsing each time air is expired