Exchange - Surface Area To Volume Ratio And Gas Exchange

Question 1

Explain why large, multicellular organisms need specialised exchange surfaces and transport systems

Answer 1

Have smaller surface area to volume ratios
They cannot rely on simple diffusion across their surface alone to provide

Question 2

Explain how exchange surfaces are specially adapted to facilitate gas exchange

Answer 2

Large surface area
Large concentration gradients
Short diffusion distance

Question 3

Describe gas exchange in a single celled organism and relate features of exchange surfaces to the rate of diffusion

Answer 3

Simple organisms rely on simple diffusion for exchange of oxygen and carbon dioxide down their concentration gradients
Large surface area:volume ratio

Question 4

Describe gas exchange in an insect

Answer 4

1. Oxygen enters the insect through the spiracles and into the tracheae. Spiracle closes
2. Oxygen diffuses through the tracheae into the tracheoles
3. Oxygen is delivered directly to the tissues to be used for aerobic respiration

Question 5

Relate the feature of gas exchange in an insect to the rate of diffusion (surface area)

Answer 5

Many narrow and branching tracheoles

Question 6

Relate the feature of gas exchange in an insect to the rate of diffusion (concentration gradient)

Answer 6

• some insects have rhythmic abdominal pumping,
• some insects have air sacs,
• aerobic respiration in cells means oxygen move from tracheoles into the cells + carbon dioxide moves from the cells to the tracheoles creating a concentration gradient

Question 7

Relate the feature of gas exchange in an insect to the rate of diffusion (diffusion distance)

Answer 7

tracheoles branch into tissue next to cells respiring + the walls of the tracheoles are one squamous epithelial cell thick

Question 8

Describe gas exchange in a fish

Answer 8

Mouth open:
- volume increases
- pressure decreases
- water flows through the mouth
Mouth closed:
- volume decreases
- pressure increases
- water flows over gills
- H20 flows through gill flap

Question 9

Relate the features of gas exchange in a fish to the rate of diffusion (concentration gradient)

Answer 9

countercurrent flow

Question 10

Relate the features of gas exchange in a fish to the rate of diffusion (surface area)

Answer 10

many gill lamallae

Question 11

Relate the features of gas exchange in a fish to the rate of diffusion (diffusion distance)

Answer 11

capillaries in close proximity to lamellar walls, capillary walls and lamellar walls are one squamous epithelial cell thick

Question 12

Describe gas exchange in a dicotyledonous plant

Answer 12

Diffusion of carbon dioxide:
- Carbon dioxide diffuses from the air spaces into the cells down a concentration gradient
- reduces the carbon dioxide concentration in the air spaces

Question 13

Relate the features of exchange surfaces in a dicotyledonous plant to the rate of diffusion (surface area)

Answer 13

• many small stomata
• air spaces

Question 14

Relate the features of exchange surfaces in a dicotyledonous plant to the rate of diffusion (diffusion distance)

Answer 14

Flat

Question 15

Relate the features of exchange surfaces in a dicotyledonous plant to the rate of diffusion (concentration gradient)

Answer 15

-photosynthesis uses carbon dioxide and produces oxygen

Question 16

Describe gas exchange in a human

Answer 16

Oxygen differs from the alveoli into the blood by:
- diffusing across the alveolar epithelium
- then through the capillary endothelium
- and then combines with haemoglobin in red blood cells

Question 17

Describe the countercurrent flow system

Answer 17

• Water and blood flow in opposite directions
• This maintains the concentration gradient of oxygen so oxygen concentration is always higher in water than in the blood along the whole length of the gill lamellar
• So diffusion of oxygen occurs along the whole length of the gill lamellar

Question 18

Describe the process of ventilation (inhaling)

Answer 18

-external intercostal and diaphragm muscles contract
- ribcage mora upwards and outwards and diaphragm flattens
- thoracic cavity volume increases and pressure decreases
-air flows from the atmosphere to the lungs down a pressure

Question 19

Describe the process of ventilation (exhaling)

Answer 19

• diaphragm muscles relax + internal intercostal muscles contract
• ribcage moves downwards and inwards and diaphragm domes
  -thoracic cavity volume decreases and pressure increases
• air flows from lungs to atmosphere down a pressure gradient

Question 20

Explain how insects limit water loss

Answer 20

• waterproof exoskeleton
• small surface area to volume ratio

Question 21

Relate features of exchange surfaces in a human to the rate of diffusion (diffusion distance)

Answer 21

• alveolar walls = one squamous epithelial cell thick
• capillary walls =one squamous endothelial cell thick
• capillaries are in close proximity to the alveoli

Question 22

Relate features of exchange surfaces in a human to the rate of diffusion (concentration gradient)

Answer 22

• circulation and blood supply removes oxygenated blood
• ventilation replaces air in alveoli
• elastic tissue removes deoxygenated air

Question 23

Relate features of exchange surfaces in a human to the rate of diffusion (surface area)

Answer 23

• many narrow capillaries + many small alveoli

Question 24

Describe the adaptations of xerophytic plants to limit water

Answer 24

1. Thick cuticle - stops water from leaving
2. Hairy leaves - water vapour gets trapped in hairs and reduces water potential gradient
3. Stomata in pits - water gets trapped and reduces water potential gradient
4. Rolled leaves
5. Leaves reduced to spines - reamed surface area for evaporation
6. Reduced number of stomata