Gas exchange

Question 1

what happens to SA:V ratio as an organism gets larger?

Answer 1

decreases

Question 2

why do larger organisms have specialised gas exchange surfaces and systems?

Answer 2

• all organisms rely on diffusion for exchange of O2 and CO2 down conc. gradient (aerobic respiration)
• smaller organisms w large SA:V can meet gas exchange needs by diffusion across surface
• larger organisms can’t rely on diffusion alone

Question 3

what is ficke’s law?

Answer 3

diffusion rate= SA x conc. gradient
—————————–
diffusion distance

Question 4

what makes good exchange surface

Answer 4

• large SA
• large conc. gradient
• thin exchange surface

Question 5

how do insects limit water loss

Answer 5

1. waterproof covering over body - rigid outer skeleton covered in waterproof cuticle
2. small SA: V - minimise area water lost over

Question 6

How does oxygen move through the insect?

Answer 6

1. Oxygen diffuses in through the spiracles;
2. Spiracle closes;
3. Oxygen moves through the trachea into the tracheoles;
4. Oxygen delivered directly to the respiring tissues;

Question 7

Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange

Answer 7

1. Tracheoles have thin walls so short diffusion distance to cells;
2. Highly branched / large number of tracheoles so short diffusion distance to cells;
3. Highly branched / large number of tracheoles so large surface area (for gas exchange);
   4.Tracheae provide tubes full of air so fast diffusion (into insect tissues);
4. Fluid in the end of the tracheoles that moves out (into tissues) during exercise so faster diffusion through the air to the gas exchange surface;
   OR
   Fluid in the end of the tracheoles that moves out (into tissues) during exercise so larger surface area (for gas exchange);
5. Body can be moved (by muscles) to move air so maintains diffusion / concentration gradient for oxygen / carbon dioxide

Question 8

how does diffusion (gaseous exchange) happen in the gas exchange systems of insects?

Answer 8

O2 diffusion:
1. tissues respire using O2, so lower conc. O2 at tissue
2. O2 moves from area high con. to low so go from trachea to tissue
3. lowers O2 conc. in tracheae so O2 move into tracheae from outside insect via spiracles

CO2:
1) Respiration produces CO2, increasing conc. at tissue
2) CO2 moves from area high conc. at tissue to low conc. in tracheae.
3) CO2 then moves from high conc. in tracheae to low conc. outside the insect via the spiracles.

Question 9

how does ventilation happen in insects?

Answer 9

• Movement of the insects muscles creates a mass movement of air in and out of trachea
• speeding up the rate of gaseous exchange.
• small air sacs in trachea. Muscles around trachea contract and pumps the air in the sacs deeper into the tracheoles

Question 10

how do insects get additional O2 during flight?

Answer 10

• when at rest, H2O build up in tracheoles
• During flight, insect may partly respire anaerobically & produce lactate
• This lowers the water potential of muscle cells. As lactate builds up, water passes via osmosis from tracheoles into the muscle cells.
• This draws air into the tracheoles closer to the muscle cells so less diffusion distance for O2 when most needed.

Question 11

A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange

Answer 11

1 Large surface area provided by many lamellae over many gill filaments;
2 Increases diffusion/makes diffusion efficient;
3 Thin epithelium/distance between water and blood;
4 Water and blood flow in opposite directions/countercurrent;
5 (Point 4) maintains concentration gradient (along gill)/equilibrium not reached;
6 As water always next to blood with lower concentration of oxygen;
7 Circulation replaces blood saturated with oxygen;
8 Ventilation replaces water (as oxygen removed);

Question 12

Describe and explain the advantage of the counter-current principle in gas exchange across a fish gill.

Answer 12

1. Water and blood flow in opposite directions;
2. Maintains diffusion/concentration gradient of oxygen OR Oxygen concentration always higher (in water);
3. (Diffusion) along length of lamellae/filament/gill/capillary;

Question 13

Explain how the counter current mechanism in fish gills ensures the maximum amount of oxygen passes into the blood flowing through the gills (3)

Answer 13

1. Water and blood flow in opposite directions;
2. Blood always passing water with a higher oxygen concentration;
3. Diffusion / concentration gradient maintained throughout the length of the gill lamellae/filaments

Question 14

adaptations of a leaf for gaseous exchange

Answer 14

1. Flat – lager SA:V
2. Many Stomata – pores to allow air to move in and out of leaf.
3. Air spaces in leaf so short distance between mesophyll cells and air

Question 15

how does diffusion (gaseous exchange) happen in plants?

Answer 15

CO2:
1. Mesophyll cells photosynthesize so lower conc. of CO2 in cells
2. CO2 diffuses from air spaces into the cells.
3. which reduces CO2 conc. in air spaces causing CO2 to move into air spaces from the air outside the leaf, through the stomata

O2:
1. Mesophyll cells produce O2 by photosynthesis.
2. O2 diffuses into air spaces from cells
3. increases conc. O2 in air spaces, causing O2 to move from the air spaces to outside leaf via the stomata.

Question 16

adaptations of a plant to reduce water loss

Answer 16

1. Air spaces saturated with water vapour from xylem and water diffuses out of stomata as it evaporates.
2. At night, guard cells close stomata to prevent water loss.
   Less CO2 is required at this time of day due to the lack of available sunlight for photosynthesis.
3. Upper & lower surfaces have a waxy cuticle.
4. Most stomata are found / distributed on the lower surface.

Question 17

adaptations of xerophytic plants

Answer 17

• dry environments
  1. Reduced number of stomata - Less Surface Area for water loss
  2. Stomata in pits - Reduced concentration gradient
  3. Hairs to trap water vapour - Reduced concentration gradient
  4. Rolled leaves - Reduced concentration gradient
  5. Leaves reduced to spines - Less surface area for water loss
  6. Thick waxy cuticles - Increased diffusion distance

Question 18

Explain why plants grown in soil with very little water grow only slowly

Answer 18

1. Stomata close;
2. Less carbon dioxide (uptake) for less photosynthesis/glucose production;

Question 19

Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf. (4)

Answer 19

1. (Carbon dioxide enters) via stomata;
2. (Stomata opened by) guard cells;
3. Diffuses through air spaces;
4. Down diffusion gradient

Question 20

Describe the gross structure of the human gas exchange system and how we breathe in and out

Answer 20

1. Named structures – trachea, bronchi, bronchioles, alveoli;
2. Above structures named in correct order OR Above structures labelled in correct positions on a diagram;
3. Breathing in – diaphragm contracts and external intercostal muscles contract;
4. (Causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric, resulting in air moving in);
5. Breathing out - Diaphragm relaxes and internal intercostal muscles contract;
6. (Causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric, resulting in air moving out);