Exchange- Gas Exchange

Question 1

Why do Fish have Specialised Gas Exchange Systems?

Answer 1

 multicellular organism so has a small surface area to volume ratio, large diffusion distance, high demand
& body surface impermeable
 therefore, cannot perform gas exchange (O2 in/CO2 out) via their surface, they require a specialised gas
exchange system called Gills

Question 2

Structure of Gills in Fish?

Answer 2

 many gill filaments and gill lamellae = large surface area
 gill lamellae have a thin wall (short diffusion distance) and are permeable
 ventilation brings in pure water (high oxygen, low carbon dioxide) and circulation brings in deoxygenated
blood (low oxygen, high carbon dioxide), the water and blood pass over in opposite directions (countercurrent
flow), which maintains concentration gradient all the way along the gill lamellae

Question 3

Why do Insects have Specialised Gas Exchange Systems?

Answer 3

 multicellular organism so has a small surface area to volume ratio, large diffusion distance, high demand
& body surface made of exoskeleton (impermeable barrier to reduce water loss)
 therefore, cannot perform gas exchange (O2 in/CO2 out) via their surface, they require a specialised gas
exchange system called Tracheal System

Question 4

Structure of Tracheal System in Insects?

Answer 4

 starts with openings on body surface called Spiracles
 spiracles contain valves, open = gas exchange, closed = prevent water loss
 spiracles connect to Trachea
 trachea connect to Tracheoles
 tracheoles connect directly to Respiring Cells (delivering oxygen, removing carbon dioxide)

Question 5

How does Gas Exchange occur in Tracheal System of Insects?

Answer 5

 at rest = down a concentration gradient, oxygen moves in & carbon dioxide moves out by
simple diffusion
 when active = by ventilation, air inhaled for mass flow of O2 in & air exhaled for mass flow of CO2 out

Question 6

Function of Lungs?

Answer 6

 site of gas exchange in mammals (oxygen
into blood – used in cells for respiration,
 carbon dioxide out of the blood – toxic waste product of respiration)

Question 7

What is Lungs made up of?

Answer 7

Trachea, Bronchi, Bronchioles, Alveoli (+ capillaries)

Question 8

Function of trachea, bronchi, bronchioles?

Answer 8

transport of air and filter air, (bronchioles also

controls amount of air reaching alveoli)

Question 9

Adaptation of alveoli?

Answer 9

 millions of tiny alveoli that are folded (large surface area)
 thin wall/one cell thick/squamous epithelial cells (short diffusion distance)
 elastic tissue in wall (stretches when breathing in to increase surface area, recoils when breathing out to
push the air out)
 ventilation maintains concentration gradient (high oxygen, low carbon dioxide)

Question 10

Adaptation of capillaries?

Answer 10

 millions of tiny capillaries (large surface area)
 thin wall/one cell thick/squamous epithelial cells (short diffusion distance)
 narrow lumen (increases diffusion time, decreases diffusion distance)
 circulation maintains concentration gradient (low oxygen, high carbon dioxide)

Question 11

How O2 moves from the alveoli to the capillaries?

Answer 11

by simple diffusion

Question 12

How CO2 moves from capillaries to the alveoli?

Answer 12

by simple diffusion

Question 13

Describe the process of Inhalation?

Answer 13

Breathing In/Inhalation = external intercostal muscles contract (rib cage moves up and out) & diaphragm
contracts (flattens), therefore increase in volume in chest and decrease in pressure, so air moves in

Question 14

Describe the process of exhalation?

Answer 14

Breathing Out/Exhalation = external intercostal muscle relax (rib cage moves down and in) & diaphragm
relaxes (back to dome shape), therefore decrease in volume in chest and increase in pressure, so air pushed
out (aided by elastic recoil in the alveoli)

Question 15

Formula for Pulmonary Ventilation?

Answer 15

PV = tidal volume x ventilation rate

 tidal volume = volume of air breathed in/out in one breath
 ventilation rate = number of breaths per minute
 Pulmonary Ventilation = volume of air breathed in/out per minute

Question 16

Why do Humans/Mammals require a Specialised Transport System?

Answer 16

 multicellular organisms therefore have large diffusion distances and high demand
 need a transport system to deliver nutrients and remove waste from all cells
 transport system in humans/mammals called Circulatory System
 Circulatory System made of heart, blood vessels, blood
(heart pumps blood, blood vessels carry blood, blood carries nutrients/waste)

Question 17

Structure of Leaves?

Answer 17

 upper layer called Upper Epidermis
 waxy cuticle on upper epidermis (barrier to reduce water loss)
 beneath the upper epidermis are Palisade Cells
 palisade cells are were photosynthesis takes places
 beneath palisade cells are Spongy Mesophyll Cells
 are loosely packed leaving air spaces to allow ease of gas exchange
 lower layer called Lower Epidermis

Question 18

Adaptation of palisade cells for photosynthesis?

Answer 18

 located near top of leaf, closer to light
 large size, large surface area for light
 thin cell wall, short diffusion distance for carbon dioxide
 contains many chloroplasts, site of photosynthesis
 large vacuole, pushes chloroplast to the edge of the cell closer to light

Question 19

How does Exchange occur in Leaves?

Answer 19

 lower epidermis of leaf contains pairs of cells called Guard Cells
 when turgid, guard cells form an opening called Stomata
 gas exchange occurs via the stomata
 In Day, plant photosynthesises and respires, CO2 moves in for photosysnthesis and O2 moves out (some is used in respiration)
 At Night, plant only respires, O2 moves in for respiration and CO2 moves out

Question 20

What is Transpiration?

Answer 20

loss of water vapour from the leaf via the stomata

Question 21

How does Transpiration occur?

Answer 21

 moist lining of spongy mesophyll cells evaporate forming water vapour
 water vapour builds up in air spaces
 if water vapour concentration is high enough & stomata is open, water vapour diffuses out

Question 22

Factors that increase rate of transpiration?

Answer 22

 light = more light, more stomata open, increase surface area for transpiration
 temperature = more temperature, more evaporation (increase water vapour concentration) &
more kinetic energy
 wind = more wind, maintains concentration gradient
 humidity = less humidity, less water vapour in the surrounding air, increase in water vapour concentration gradient

Question 23

What is a Xerophyte?

Answer 23

a plant adapted to reduce water loss (reduce transpiration)

Question 24

Adaptations of Xerophyte?

Answer 24

 spiky, needle like leaves = reduced surface area
 thick waxy cuticle = waterproof, impermeable barrier
 densely packed spongy mesophyll = less air spaces, less water vapour build up
 sunken stomata/hairy leaves/rolled up leaves = traps moist layer of air, reduces concentration gradient

Question 25

Function of Phloem?

Answer 25

transport organic material (e.g. Sucrose) up and down a plant

Question 26

Structure of phloem?

Answer 26

made of 2 parts (Sieve Tube with Companion Cells alongside)

Question 27

How does phloem transport organic material like sucrose?

Answer 27

 by principle of Mass Flow (mass flow of water carries the sucrose)
 Sucrose loaded into Phloem at Source
 Hydrogen Ions (H+) actively transported from companion cells into source
 therefore, H+ diffuses back into companion cells from source
 as they do, they pull in sucrose with them by co-transport
 sucrose then diffuses into sieve tube
 this lowers the water potential of sieve tube so water follows by osmosis
 this water will carry the sucrose by hydrostatic pressure (mass flow)
 Sucrose unloaded from Phloem at Sink
 sucrose moves out of phloem/sieve tube into sink by diffusion
 water follows by osmosis