Ch7: Gas Exchange

Question 1

Define respiration:

Answer 1

The exchange of gases between an organism and its environment

Question 2

Compare aerobic and anaerobic respiration:

Answer 2

AEROBIC:
- occurs in the mitochondria
- More efficient + produces more ATP (for same amount of glucose) (32-38)
- MAY have allowed for multicellularity and larger organisms

ANAEROBIC:
- occurs in the cytoplasm (undergoes glycolysis)
- less efficient
- produces less ATP (2)
- rears energy quicker

Question 3

What is Fick’s Law?

Answer 3

Rate of Diffusion = (SA x Partial Pressure x Diffusion coefficient) / Diffusion distance

NOTE: diffusion coefficient is unique to each gas

Question 4

How do we maximise the rate of diffusion? (Hint: there are 3 points)

Answer 4

1) Allow for branching and specialised systems (increase SA)

2) Have a thin membrane = minimise diffusion distance

3) Make sure the membrane is permeable = allow desired gases to enter organism/cell

Question 5

What is the diffusion coefficient determined by? What does this mean for gases?

Answer 5

Molecular weight and solubility.

Meaning that each gas/molecule gas a unique diffusion coefficient

Question 6

Describe simple diffusion

Answer 6

Diffusion is the movement of gases across a (permeable) membrane from an area of HIGH concentration to low concentration.

It does NOT require energy.

Molecules will eventually reach a dynamic equilibrium (no net movement of particles/gases)

Question 7

Define stomal complex and describe stomata

Answer 7

Stomatal complexes possess two guard cells that separate in the middle to form the stomatal pore, where transpiration and gas exchange take place. Stomatal complexes can help plants to regulate leaf temperature via evaporative cooling.

Stomata: are openings that can be kidney or dumbbell shaped that allow for the exchange of gases (able to open and close)

Question 8

Describe the stomata of grasses

Answer 8

They mostly have their stomata at the BASE of their leaves to control water loss from evaporation, as water can be lost when the stomata open to allow gas exchange. The more sunlight hits an area, the more water it will lose.
- the stomata are adjacent to leaf veins (irrigation?)

Question 9

Stomatal density determined by? (Hint: there are 3 main ones, and 1 one in terms of the plant itself)

Answer 9

1) Humidity
2) Temperature
3) Partial pressure of gases

4) also determined by affects of GROWTH

Question 10

Do plants have specialised systems for gas exchange?

Answer 10

NO, they don’t have specialised systems for gas exchange

Question 11

Where do plants have the highest density of stomata and why?

Answer 11

Their leaves: because they are the most photosynthetically and metabolically active

To accomodate for this leaves are: thin (minimise diffusion distance), have HIGH SA and LOW volume

Question 12

How do roots increase their SA to access air pockets in soil?

Answer 12

Small root hairs

Question 13

Define mesophyll cells, and how they allow for gas to travel/exchange more rapidly/

Answer 13

The middle cell layer of a leaf containing chloroplasts and representing the main site of photosynthesis

They have gaps between them that allow for gas to travel/exchange more rapidly (because gases move easier through other gases than diffusing through membranes)

Question 14

Define aerenchyma cells, what do they rely on to work?

Describe specifically how they work in large plants/trees with bark

Answer 14

Tubes that run through plants that allow for gases to travel through them (from stem to root)

They rely on pressure gradients of gases to bring them to areas they are needed (high to low pressure)

Thicker plants/trunks the inner most part of the plant is dead (XYLEM) that provides mechanical support. the LIVING tissue are just below the bark to minimise diffusion distance

Question 15

What are the stomata replacement on trunks, shoots and stems called? What do they allow for?

Answer 15

Lenticel cells = pores

Allow for gases to directly interact with tissues

Question 16

What do rhizomes in wetland plants allow for? What is this ability dependent on?

Answer 16

See Doc, 7a:
Rhizomes and roots that connect plants.

They connect to dead or broken plants allowing for exchange of O2 (inputs) and CO2 (wastes) to healthy plants

Exchange is based on pressure differences in aerenchyma cells due to the difference in size of the broken plants

Question 17

Do fungi have specialised gas exchange systems?

Answer 17

No

Question 18

How do fungi perform gas exchange? What does this allow them to produce?

Answer 18

They have mycelium (root networks) that find air pockets and use HYPHAE (increase SA) to undergo gas exchange

This allows them to produce fruiting bodies that undergo gas exchange (diffusion) with their THIN walls (minimise diffusion distance)

Question 19

Do animals have specialised gas systems?

Answer 19

Yes

Question 20

What are the 2 main processes for gas distribution through the body?

Answer 20

1) Ventilation: movement of the body or gas exchange surface to move gas along gas exchange surface
- Allowing for optimisation of pressure gradient and increased rate of diffusion (ex~ gills)

2) Circulation: gas is moved to and from gas exchange surface, either through the dissolution into circulatory fluid (blood) or directly via branching tubes

Question 21

What issue do terrestrial organisms face?

Answer 21

Whilst they have ample access to oxygen, they must maintain moisture of gas exchange surface

Question 22

What gas exchange system do insects have? How do these systems maintain moisture?

Answer 22

See Doc, 7b:
They have spiracles (holes) in their abdomen and chest (THORAX) that allow for gases to exchange through them

These spiracles lead to trachea and then to thinner tubes (tracheoles) that branch (increase SA) and allow for individual cells to get their required gases

They maintain moisture, the spiracles can shit and prevent water loss. As well as the insect can contract their abdomen to inhale air (ventilation)

Question 23

What are the ventilation of larger terrestrial animals described as?

Answer 23

Specialised methods: air enters mouth/nose then goes to trachae and bronchi, in MORE specialised beings they enter the bronchioles and alveoli.

NOTE; walls of lungs are thin to minimise diffusion distance and are surrounded by capillaries.

Question 24

Describe the role of surfactants and where they come from.

Answer 24

Surfactants come from pneumocyte cells: they have a hydrophilic and phobic end

They line the lungs to maintain: moisture and reduce surface tension to aid diffusion

Question 25

Describe the specialised ventilation system of birds. Why do they need a specialised system?

Answer 25

They need specialised system because they have a high demand for energy.

See Doc, 7c:
They have unidirectional air flow: air travels from an air sac (ventilated) (posterior) to distribute O2 to lungs where it then travels to the anterior air sac

Meaning there is a constant supply of fresh air

Question 26

What are parabronchi in bird lungs?

Answer 26

Additional tissue that increases SA and interacts directly with capillaries to transport gases around the body

Question 27

Describe the way gills work, what are the 2 kinds?

Answer 27

1) internal
2) external

They are made of individual filaments that have lamellae to increase SA;
- water flows over gill surfaces, and O2 diffuses into blood from H2O, using gill capillaries
- CO2 diffuses out into the H2O

Question 28

Are internal or external gills more efficient?

Answer 28

Internal gills are more efficient, because they use COUNTERCURRENT movement (blood moves opposite to water direction) to maintain concentration gradient = maximise O2 uptake and CO2 removal