4.2 Gas exchange

Question 1

why can single celled organisms have oxygen and nutrients diffuse directly into their cells?

Answer 1

• the diffusion distances are very small
• they have a large surface area to volume ratio
• their metabolic demands are low, so they don’t need much oxygen supplied to them

Question 2

why don’t single celled organisms not need complex gas exchange systems

Answer 2

• diffusion supplies them with enough oxygen to supply their needs

Question 3

why do larger organisms need complex gas exchange systems

Answer 3

because if it all worked by simple diffusion then oxygen and nutrients wouldn’t be supplied to their cells fast enough because:
1. the diffusion distance is too long
2. they maintain their own body temperature so have greater metabolic needs and require more oxygen

Question 4

name and explain the factors that affect diffusion rate

Answer 4

• surface area, the bigger the surface area, the faster the diffusion rate
• conc. gradient, the bigger the concentration gradient, the faster the diffusion rate
• diffusion distance, the shorter the distance, the faster the diffusion rate

Question 5

what are the features of an effective gas exchange system

Answer 5

• a large surface area
• thin layers to minimise diffusion distances
• rich blood supply to respiratory surfaces to maintain the concentration gradient
• most surfaces
• permeable surfaces

Question 6

hoe is the nasal cavity adapted for its function

Answer 6

• The lining of the nasal cavity secretes mucus and is covered in hairs, to prepare external air for internal system
• the hairs and mucus filter out a lot of the particles and pathogens

Question 7

what are alveoli made of

Answer 7

a single layer of epithelial cells
lung surfactant to stop them collapsing

Question 8

what’s the elastic recoil of the lungs

Answer 8

the elastic tissue in the lungs helps force air out of the lungs, which stretch when you breathe in

Question 9

how is the site of gas exchange adapted for gas exchange

Answer 9

• alveoli are folded single layers of epithelial cells and capillaries are one cell thick, provide a large SA and short diff. distance
• capillaries have a very good blood supply, so maintains a steep concentration gradient

Question 10

define ventilation

Answer 10

the process of moving air between the lungs and the external environment

Question 11

what is the chest cavity

Answer 11

a sealed unit of air, air can only enter or leave through the trachea

Question 12

what happens during inhalation

Answer 12

1. active process
2. muscles around diaphragm contract, lowered and flattened
3. intercostal muscles contract, raises rib cage, expands chest cavity volume
4. cavity pressure < outside air, so air moves into lungs to equalise pressure

Question 13

what happens during normal exhalation

Answer 13

1. passive process
2. muscles around diaphragm relax, so it moves up
3. intercostal muscles relax
4. ribs move down and in
5. elastic fibres around lungs and alveoli return to normal length so volume of chest cavity decreases
6. chest cavity pressure > outside air, so air leaves lungs to equalise pressure

Question 14

what happens when you actively force air out of your lungs

Answer 14

1. intercostal muscles contract, pulling ribs down and in
2. abdominal muscles contract which force diaphragm upwards
3. increases pressure in chest cavity and forces exhalation

Question 15

how does the respiratory system protect the lungs

Answer 15

it produces a lot of mucus that lines the airways and traps tiny particles and organisms, it is moved upwards by the cilia towards the back of the throat where its swallowed and digested by stomach acid

Question 16

what are spiracles

Answer 16

the site of entry and exit of respiratory gases, found along the abdomen and opened or closed by sphincters (which also control water loss)

Question 17

what are tracheae

Answer 17

largest tubes that carry air directly into the body for gas exchange
supported of spirals of chitin that hold them open, but also makes it impermeable to gases

Question 18

what are tracheoles

Answer 18

minute tubes made from single elongated cells, permeable to gases, spread throughout tissue and penetrate individual cells

Question 19

how does insect respiratory system work

Answer 19

1. air enters through spiracles, sphincters keep them closes as much as possible to minimise water loss
   2.air moves along trachea then tracheoles by diffusion
2. air moves into cells

Question 20

how do spiracles know when to open and close

Answer 20

• it is a response from the insects nervous system
• nervous system stimulated by increasing CO2 levels or built up lactic acid

Question 21

what are the features of the gas exchange system in very active insects

Answer 21

1. mechanical ventilation
   - air is pumped actively into tracheal system, spiracles open, insect makes pumping movements of the thorax/ abdomen
   - these movements change the volume and pressure inside the body and draw air in and out of trachea and tracheoles
2. collapsible trachea and air sacs that act as reservoirs
   - increase volume of air moving through respiratory system
   - ventilating movements of the thorax inflate and deflate air sacs

Question 22

how is the gas exchange system in fish adapted for their environment

Answer 22

• they have a large surface area for diffusion
• they have a good blood supply to maintain concentration gradients
• they have thin walls for short diffusion distances

Question 23

describe the structure of gills

Answer 23

• the fragile gill filaments occur in large stacks
• they need water to keep them apart to expose the large surface area
• gill lamellae is the main site of gas exchange and they have a very rich blood supply
• blood leaving the gills leaves in the opposite direction of incoming water, ensuring the most effective exchange of gases

Question 24

describe the ventilation of the gills in fish

Answer 24

• most fish have evolved a system of ensuring the constant flow of water in the mouth and gills even when they’re not moving / their mouths are closed
• when the mouth is open, buccal chamber expands and operculum cavity is closed
• when the mouth is closed the buccal chamber contracts and the operculum cavity is open, water flows out

Question 25

how is gas exchange maximised in gills

Answer 25

1. countercurrent exchange system
   - blood in the gill filaments and water moving over the gills flow in different directions
   - this maintains a steeper conc. gradient for the diffusion of gases than if they were flowing in the same direction, more gas exchange can occur
2. overlapping gill filaments
   - diffusion in water tends to be slow, so if water passes over gills too quickly, it limits gas exchange.
   - the tips of the adjacent gill filaments overlap, increasing the resistance of water flow, slowing it down and giving more time for gas exchange to occur

Question 26

what is the main site of gas exchange in plants

Answer 26

• the leaves

Question 27

what are the adaptations of the leaf for gas exchange

Answer 27

• leaves provide a large surface area
• spongy mesophyll cells have irregular shapes, increasing their surface area and leaving gaps between the cells, this also allows for the flow of gases between cells and air spaces
• surfaces of spongy mesophyll cells are moist
• waxy cuticle acts as a barrier to water evaporation through the leaf’s surface

Question 28

how is gas exchange controlled in plants

Answer 28

• pores on the underside of the leaf called stomata, surrounded by two guard cells
• when conditions are favourable for photosynthesis, water moves into guard cells from surrounding epidermal cells and by osmosis and stomata open
• when conditions are less favourable, active pumping of potassium ions into the cells stops and water leaves the cells by osmosis and turgor is reduced and the stomata closes