topic 4.3 - gas exchange

Question 1

gas exchange in small organisms

Answer 1

for single-celled organisms (eg amoeba) nutrients/oxygen can diffuse directly into cell from external environment and waste products can diffuse directly out

Question 2

why does gas exchange work like that in small organisms

Answer 2

• diffusion distance from outside to inside is very small
• SA:V ration is very large; there is large SA so more substances can diffuse in/out
• metabolic demands are low so they don’t regulate own temp/ don’t use much o2 and produce much co2 hence don’t need gas exchange to happen rapidly
• don’t need specialised gas exchange/ transport systems as diffusion is enough to supply their needs

Question 3

gas exchange in larger organisms

Answer 3

larger organisms made up of billions of cells so substances need to travel a long distance from outside to reach cytoplasm of cells

Question 4

what is the metabolic rate like in larger organisms

Answer 4

• metabolic rate is higher as they control own body temp and are more active
• more demand for O2 + food and CO2 & waste produced is much higher than in smaller organisms

Question 5

where does gas exchange take place in:
- humans
- fish
- insects
- plants

Answer 5

• evolved specialised systems to exchange gases they need in and need to remove
• humans - in lungs
• fish - in gills
• insects - in tracheal system
• plants - in leaves

Question 6

what features make a good gas exchange system

Answer 6

• a large SA : V
• thin layers as minimise diffusion distance
• rich blood supply to maintain a steep concentration gradient
• moist surfaces to allow gases to dissolve in it
• permeable surfaces to allow free passage of respiratory gases

Question 7

nasal cavity in humans

Answer 7

• main entrance for gases into the body
• the lining secretes mucus and is covered in hairs; external air is ‘filtered’ from dust /small particles and pathogens such as bacteria breathed in
• rich blood supply raises temp of air if needed
• moist surfaces increase level of water vapour in air
• basically, air entering lungs has little effect on internal environment.

Question 8

functions of parts involved in gas exchange in mammals
- nasal cavity
- mouth
- epiglottis
- trachea

Answer 8

• Nasal cavity - main route by which air enters gas exchange system
• Mouth - air can enter but it misses out on the cleaning of the nasal system
• Epiglottis - Flap of tissue that closes over glottis when food is swallowed to stop food from entering gas exchange system
• Trachea - Airway to bronchi lined with mucus secreting cells and cilia to move mucus / dust / microorganisms away from lungs.

Question 9

• incomplete rings of cartilage
• left and right bronchus
• lung
• bronchioles
• alveoli

Answer 9

• incomplete rings of cartilage - prevent trachea + bronchi from collapsing + allow food to be swallowed and move to oesophagus
• Left & Right bronchus - Tubes leading to lungs (similar to trachea structure but narrower and divide to form bronchioles)
• Lung - organ where gas exchange takes place
• Bronchioles - small tubes that spread through lungs and end up in alveoli. (no cartilage and collapse easily)
• Alveoli - Main site of gas exchange in lungs (tiny air sacs)

Question 10

• Ribs
• Intercoastal muscles
• pleural membranes
• pleural cavity
• Diaphragm

Answer 10

• Ribs - protective bony cage around the gas exchange system
• Intercoastal muscles - found between ribs and important in breathing
• Pleural membranes - surround the lungs and + line the chest cavity
• Pleural cavity - space between the pleural membranes usually filled with lubricating fluid that allows membrane to slide easily with breathing movements
• Diaphragm - broad sheet of tissue that forms the floor of chest cavity + important in breathing movements

Question 11

alveoli structure

Answer 11

• made of single layer of flattened epithelial cells
• capillaries run close also one cell thick wall
• layer of elastic connective tissue between alveoli + capillaries
• hold everything together and help force air out lungs which are stretched when u breath in (elastic recoil of lungs)
• lung surfactant (phospholipids) coats alveoli - preventing alveoli from collapsing which makes breathing easier

Question 12

gas exchange in alveoli

Answer 12

• alveoili has high conc of O2 + blood has high conc of CO2
• o2 diffuses into deoxygenated blood’s red blood cells and makes it oxygenated where its then carried to rest of body to use
• CO2 diffuses into alveoli and is then breathed out

Question 13

adaptations of gas exchange system in mammals

Answer 13

1. Large SA:V - Many (480-500) alveoli in lungs
2. walls of alveoli + capillaries are one cell thick so short diffusion pathway
3. Continuous flow of blood in capillaries that maintains conc gradient
4. Moist walls for gases to dissolve in

Question 14

what is breathing/ventilation

Answer 14

The process in which physical movements of the chest change the pressure so that air is moved in or out

Question 15

process of inhalation

Answer 15

• inhalation - taking air into the chest
  [active, energy-using process]
• muscles around diaphragm contract; lowered & flattened
• intercostal muscles between ribs contracts; raising rib cage upwards & outwards
• volume pf chest cavity increases
• reduces pressure in cavity
• pressure within chest is less than atmospheric pressure in air outside
• air moves in through trachea - bronchi - bronchioles - lungs to equalise the pressure inside and out

Question 16

process of exhalation

Answer 16

• taking air out lungs - breathing air out
  [passive process]
• muscles surrounding diaphragm relax
• moves up into resting domed shape
• intercostal muscles relax; ribs move down & in
• volume of chest cavity decreases
• increase in pressure
• pressure inside . pressure outside
• air moves out of lungs through bronchioles - bronchi - trachea - out

Question 17

gas exchange in insects

Answer 17

• have high o2 requirement - their respiratory system evolved to deliver o2 directly to the cells and remove co2 same way

Question 17

How your lungs are protected from pathogens and other harmful particles we may breath in?

Answer 17

• we breath in lots of tiny particles /dust /pollen / smoke particles/ pathogens (cause disease)
• respiratory system produces loads of mucus that lines airways & traps these little particles / organisms
• moved up the airway by cilia that sweeps up the back of throat
• mucus swallowed
• acid in stomach & digestive enzymes digest the mucus and what its carrying.

Question 18

spiracles

Answer 18

• found along the abdomen of most insect
• they are site of entry/exit of respiratory gases
• opened/closed by sphincters (these also control water loss)

Question 19

trachea

Answer 19

• largest tubes
• carry air directly into body for gas exchange with cells
• supported by spirals of chitin - hold the trachea open if they are squished
• Chitin makes trachea impermeable to gases hence little gas exchange takes place in these vessels
• Trachea divides to form narrower tubes - tracheoles

Question 20

tracheoles

Answer 20

• narrow tube - a single elongated cell
• no chitin hence are freely permeable to gases
• spread through the tissues of insect
• so small and run between and even penetrate into cells
• most gas exchange occurs in tracheoles

Question 21

adaptation in respiratory process

Answer 21

1. air enters through spiracles
2. air moves along the tracheae and tracheoles via diffusion so it reaches all the tissues
3. tracheoles may contain water towards end of their length - limiting penetration of gases
4. when insect is very active and needs more O2, lactic acid builds up in muscle tissues - effects osmotic conc
5. water moves out of tracheoles to the cells via osmosis - more SA on tracheoles for gas exchange
6. all oxygen needed is supplied by gas exchange system - up to 25% of co2 produced is lost through cuticles

Question 22

Some insects have very active lifestyles + very high energy demands.

How do they get extra O2 supplied?

Answer 22

1. mechanical ventilation
2. collapsible tracheae

Question 23

mechanical ventilation

Answer 23

• air actively pumped into tracheal system.
• when spiracles open, insects make muscular pumping movements of thorax/abdomen
• changes volume + pressure inside body
• drawing air in and out of trachea & tracheoles

Question 24

collapsible tracheae

Answer 24

• increase volume of air moved through respiratory system
• the ventilating movements of abdomen/thorax inflate/deflate them or some by general body movement

Question 25

why can gas exchange not occur in lungs in fish

Answer 25

• water is a lot dense and thick than air
• air is 20% o2 whilst water has a lot less dissolved o2
• lungs - would use up enormous amount energy to move water in and out
• so gills used instead - water flows over them in 1 direction only
• more effective + efficient in terms of energy for fast moving active animals living in water

Question 26

why does gas exchange occur in the gills in fish?

Answer 26

• have high o2 demand due to high active but cannot gas exchange through their scaly external as its not vry permeable to gases = use gills instead

Question 27

gas exchange in fish

Answer 27

• gills contained in a gill cavity + covered by a protective bony flap called the operculum
• operculum is important in maintaining flow of water over the gills, even when fish is stationary

Question 28

structure of the gills

Answer 28

• gill filaments (lamellae) occur in large stacks
• gill filaments - main site of gas exchange
• need water to keep them apart = to keep large SA needed
• out of water, gill filaments stick together due to lack of water; exposed SA not enough for effective gas exchange & not enough water & o2 can enter
• have a rich blood supply
• blood leaving gills flows in opposite direction to incoming water
• (counter current exchange system)
• steep conc gradient maintained

Question 29

Process of Ventilating the gills in bony fish that have an o…….?

Answer 29

• sharks & rays do not have an operculum
• they have to swim all the time to keep water flowing in through their mouths + out over their gills.
• bony fish have operculum so can ventilate their gills even when not moving

Question 30

process of ventilating in the gills

Answer 30

• The floor of the mouth opens, and the operculum (gill flap) closes.
• The floor of the mouth is then raised to increase the pressure but a valve stops water from leaving.
• The increased pressure forces the operculum open which forces water over the gills

Question 31

adaptation to the gas exchange system in fish

Answer 31

• Large SA due to gills ligaments being kept apart by water
• Rich blood supply
• thin walls (short diffusion distance)
• Countercurrent exchange system - blood in gill filaments flow in different direction than the water moving over the gills
• steep conc gradient maintained
• Overlapping gill filaments - tips of adjacent gill filaments overlap - increased resistance to flow of water - slows down the flow of water over gills surface - gives more time for exchange of gases to occur.