MODULE 3 - EXCHANGE SURFACES

Question 1

why do larger organisms need specialised exchange surfaces?

Answer 1

As organisms increase in size their SA:V ratio decreases
- nThere is less surface area for the absorption of nutrients and gases and secretion of waste products
- The greater volume results in a longer diffusion distance to the cells and tissues of the organism
- therefore diffusion alone is not enough –> would be too slow

Question 2

why do larger organisms need specialised exchange surfaces in terms of metabolic activity?

Answer 2

while smaller organisms have a higher metabolic rate per unit of body mass, larger organisms need to support the metabolism of more cells, so will consume more oxygen within a given period of time than smaller organisms

Question 3

how do you calculate the surface area to volume ratio of an organism?

Answer 3

volume

Question 4

list the features of an efficient exchange surface

Answer 4

• large surface area
• short diffusion distance
• good blood supply
• ventilation to maintain diffusion gradients

Question 5

how does a short diffusion distance increase the efficiency of an exchange surface?

Answer 5

When the distance is short, molecules don’t have as far to travel from one side of the surface to the other, significantly speeding up the overall rate of diffusion which is needed to meet metabolic demands

Question 6

how does a good blood supply increase the efficiency of an exchange surface?

Answer 6

ensures constant delivery of fresh, substance-rich (or waste-rich) blood and removing used blood, which maintains a steep concentration gradient, ensuring substances like oxygen and nutrients keep diffusing rapidly into the body, and waste like CO2 diffuses out

Question 6

how does ventilation increase the efficiency of an exchange surface?

Answer 6

maintains a steep conc. gradient by constantly bringing in oxygen and expelling CO2

Question 6

how does a large surface area increase the efficiency of an exchange surface?

Answer 6

providing more space for substances (like gases, nutrients) to move across at once, boosting the rate of diffusion

Question 6

give an example of an organism with a specialised exchange surface which increases surface area

Answer 6

root hair cells in plants - long, thin, hair-like extensions that poke into soil

Question 6

give an example of an organism with a specialised exchange surface which reduces diffusion distance

Answer 6

alveoli - walls, and the surrounding capillaries, are only one epithelial cell thick, creating an extremely short path for oxygen and carbon dioxide to travel

Question 7

give an example of an organism with a well ventilated specialised exchange surface

Answer 7

The process of breathing (ventilation) constantly replenishes the air in the alveoli. Inhaled fresh air, which is rich in oxygen, replaces the stale air, which is high in carbon dioxide. This maintains the necessary concentration gradients for the gases to diffuse passively across the alveolar and capillary membranes

Question 8

give an example of an organism with a specialised exchange surface which has a good blood supply

Answer 8

the gills in fish - A dense network of blood capillaries within the lamellae ensures blood is always present to pick up oxygen and carry it away, preventing saturation.

Question 9

outline the stages in inhalation

Answer 9

• external intercostal muscles contract causing the ribs to move up and out
• the internal intercostal muscles relax
• the diaphragm contracts and flattens increasing the volume in the thorax
• this causes oxygen to move in down
• pressure in the thorax decreases so air moves in down the pressure gradient

Question 10

outline the stages in exhalation

Answer 10

• external intercostal muscles relax causing the ribs to move down and in
• the internal intercostal muscles contract
• the diaphragm relaxes and domes, decreasing the volume in the thorax
• this causes oxygen to be forced out
• pressure in the thorax increases so air moves out down the pressure gradient

Question 11

outline the structure and function of the trachea

Answer 11

conducts air from the mouth towards the lungs - lined with rings of cartilage to keep it open
- lined with ciliated epithelium and goblet cells

Question 12

what is the role of the ciliated epithelium in the trachea?

Answer 12

to waft mucus and trapped debris (dust, bacteria) upwards towards the throat to be swallowed

Question 13

what is the role of goblet cells in the trachea?

Answer 13

to produce mucus which traps pathogens and dirt to stop it entering the lungs where they could cause harm

Question 14

outline the structure and function of the bronchi (singular = bronchus)

Answer 14

conducts air from the trachea into the bronchioles of each lung
- made up of smooth muscle surrounded by cartilage
- lined with epithelial cells

Question 15

what is the role of the smooth muscle in the bronchi?

Answer 15

controls airway diameter (caliber) by contracting (bronchoconstriction) or relaxing (bronchodilation), thereby regulating the volume of air reaching the alveoli

Question 16

what is the role of cartilage in the bronchi?

Answer 16

provide structural support and keep the airways open
- less than in the trachea
- also c shaped

Question 17

outline the structure and function of the bronchioles

Answer 17

small air passages in the lungs that branch from the bronchi and lead to the alveoli
- no cartilage
- smooth muscle - The contraction and relaxation of this muscle layer (bronchoconstriction and bronchodilation) regulates the airflow into the alveoli
- lined with epithelium - makes some gas exchange possible

Question 18

outline the structure and function of the alveoli

Answer 18

sites of gas exchange
- extremely thin walls (one cell of squamous epithelium thick)
- a vast network of surrounding capillaries
- moist surface
- elastic fibres

Question 19

how do elastic fibres aid the alveoli in gas exchange?

Answer 19

allows elastic recoil
- allows them to stretch open during inhalation to take in air and then recoil passively during exhalation, which helps force air out

Question 20

how does being moist aid the alveoli in gas exchange?

Answer 20

gases can dissolve which makes diffusion faster

Question 21

list the 6 tissues in the respiratory system of mammals

Answer 21

- ciliated epithelium - smooth muscle - cartilage - squamous epithelium - capillary endothelium - connective tissue in the lungs - provides structural support to airways and the lungs themselves

Question 22

ho many types of tissue are there In the respiratory system of mammals?

Answer 22

6

Question 23

what is the buccal cavity in fish?

Answer 23

the mouth cavity

Question 24

what is the operculum in fish?

Answer 24

a bony flap the protects the gills - opens and closes to let water pass over the gills + out of the fish

Question 25

what are the Gill filaments in fish?

Answer 25

thin, comb-like structures extending from gill arches that form the primary respiratory surface - are packed with lamellae

Question 26

what are the gill lamellea in fish?

Answer 26

tiny, plate-like structures on gill filaments that dramatically increase the surface area for efficient gas exchange

Question 27

what is the function of the afferent blood vessel in fish?

Answer 27

carries deoxygenated blood from the heart (via the ventral aorta) towards the gills for oxygenation

Question 28

what is the function of the efferent blood vessel in fish?

Answer 28

carries oxygenated blood away from the gills to the rest of the body

Question 29

what are spiracles in fish?

Answer 29

openings behind the fishes eyes allowing it to draw oxygenated water into the mouth

Question 30

explain the counter current exchange system in fish

Answer 30

blood flows through gill capillaries in the opposite direction to water flowing over the gills, maximizing oxygen uptake by maintaining a steep oxygen concentration gradient

Question 31

why do fish have a high oxygen demand?

Answer 31

they are usually very active

Question 32

how are the gills in fish adapted fro efficient gas exchange?

Answer 32

- large SA:V - good blood supply - very thin - buccal pumping + ram ventilation

Question 33

outline the first stage of buccal pumping

Answer 33

mouth opens and buccal cavity floor lowers. the operculum shuts - volume increases and pressure decreases - water therefore moves in

Question 34

outline the second stage of buccal pumping

Answer 34

- the opercular cavity expands, lowering the pressure here - buccal cavity rises, decreasing the volume an increasing the pressure -water moves from the buccal cavity to over the gills

Question 35

outline the third and final stage of buccal pumping

Answer 35

- the mouth closes + the operculum opens and the sides of the opercular cavity move inwards --> all increase the pressure in the opercular cavity to force water out of the operculum, over the gills - the floor of the buccal cavity moves steadily upwards

Question 36

how does the countercurrent exchange system in fish help has exchange?

Answer 36

a concentration gradient is maintained and an equilibrium is never reached, ensuring a constant net movement of oxygen from the water into the blood - oxygenated blood meets water with a max concentration of of oxygen - the water therefore has a higher oxygen concentration so it diffuses from the water into the blood - deoxygenated blood meets water which has had almost all oxygen removed, yet the water still has a higher concentration of oxygen, therefore oxygen diffuses from the water into the blood

Question 37

how do gill filaments help diffusion nd gas exchange?

Answer 37

they increase water resistance, allowing more time for diffusion to occour

Question 38

what are spiracles in insects and what are their purpose?

Answer 38

small openings along the thorax and abdomen of an insect through which air enters and leaves - water can also be lost through spiracles - can be opened/closed by sphincters

Question 39

when do spiracles open and when do they close?

Answer 39

- open when insect is active to increase O2 intake, or when CO2 levels are high - closes when at rest to reduce water loss

Question 40

what is the structure and function of the tracheae in insects?

Answer 40

- tubes leading away from the spiracles to conduct air into the body + CO2 out - supported by rings of chitin

Question 41

why does little gas exchange occur in the tracheae of insects?

Answer 41

chitin is impermeable to gases

Question 42

what is the structure and function of the tracheoles in insects?

Answer 42

- very small branched tubes at the end of the tracheae - each trachiole is a single, greatly elongated cell - no chitin so they are gas permeable - they spread throughout the tissues/muscles of insects + between individual cells where the most gas exchange occurs - have moist walls

Question 43

why do insect tracheoles have moist walls?

Answer 43

so oxygen can dissolve into them and diffuse into surrounding cells

Question 44

in insects what fluid do tracheal cells secrete ?

Answer 44

tracheal fluid

Question 45

what is the role of tracheal fluid in insects when they are at rest?

Answer 45

reduces water loss and slows gas exchange - Fluid fills the tracheole tips, limiting O2/CO2 exchange and conserving water - increases the tracheal water potential

Question 46

what is the role of tracheal fluid in insects when they are active?

Answer 46

Water moves from tracheoles into cells by osmosis - Muscles use O2 and produce lactic acid through anaerobic respiration - lactic acid lowers the tracheole water potential - water moves down the water potential gradient and into the surrounding cells by osmosis - the tracheae has more space for gas exchange

Question 47

why do some insects need alternative methods of gas exchange?

Answer 47

they are large and therefore have higher demands

Question 48

what are the two alternative methods of ventilation in insects?

Answer 48

- mechanical ventilation - collapsable air sacs/enlarged tracheae

Question 49

explain mechanical ventilation in insects

Answer 49

- the thorax and abdomen carry out muscular pumping movements - these movements change the volume of the body and therefore pressure in the tracheae/tracheoles - air is forced in and drawn out as the pressure changes

Question 50

explain collapsable air sacs and enlarged tracheae in insects

Answer 50

they act as air reservoirs - they increase the amount of air which moves through the gas exchange system so more diffusion can occur - usually inflated/deflated by the ventilating movements of the thorax and abdomen

Question 51

what is an example of discontinuous gas exchange in insect?

Answer 51

spiracle fluttering

Question 52

what happens in insects when their spiracles are closed?

Answer 52

- no gas exchange occurs - oxygen moves from the tracheae and into the cells by diffusion - C02 diffuses into bodily fluids where it is held in a process called buffering

Question 53

when do insect spiracles open?

Answer 53

when CO2 levels are very high in the bodily fluids

Question 54

what happens in insects when their spiracles are open?

Answer 54

CO2 diffuses out of the widely opened spiracles rapidly

Question 55

what happens in insects when their spiracles are fluttering?

Answer 55

- spiracles open and close rapidly - moves fresh air into the system and replenishes the oxygen supply - minimises water loss