Unit 3 Surface Area:Volume & Gas Exchange

Question 1

How does the size of an organism relate to its surface area: volume ratio.

Answer 1

The larger the organism size the ratio of surface area: volume ratio decreases

Question 2

Describe why a smaller organism might have a higher metabolic rate.
PPQ

Answer 2

• The smaller the organism the larger the SA: V ratio
• So more heat is lost in relation to body size than in larger organisms which have a smaller SA:V ratio
• Therefore there is a faster rate of respiration which releases heat

Question 3

Describe why smaller organisms don’t need any special adaptations.

Answer 3

• They have a larger SA: V ratio so there is a big surface for the exchange of substances
• So can simply exchange substances like OXYGEN & CARBON DIOXIDE across their surface by diffusion

Question 4

Describe why the shape of an organism can affect heat exchange.

Answer 4

• Animals which are more compact have a smaller SA: V ratio minimising heat loss compared to those which are less compact have higher SA:V ratio e.g big ears

Question 5

Describe why larger organisms need special exchange surfaces.

Answer 5

• Larger organisms have a smaller SA: V ratio = means they overcome a long diffusion pathway
• Larger organisms usually have a higher metabolic rate= Demands efficient transport of waste out of cells

Question 6

Name 3 features of an efficient gas exchange surface.

Answer 6

• Larger surface area
• Thin/Short diffusion distance
• Steep concentration gradient

Question 7

Define breathing and ventilation & respiration

Answer 7

Breathing = movement of air in (inspiration) and out (expiration) of the lungs
Ventilation = special word for breathing
Respiration = chemical reaction to release energy in form of ATP

Question 8

Describe the adaptations of the alveolar epithelium.

Answer 8

• Alveoli epithelium are one cell thick = which creates a short diffusion pathway
• A large number of alveoli = large surface area for faster rate of gas exchange
• Surrounded by a network of capillaries = Maintains concentration gradient for oxygen and carbondioxide

Question 9

Describe how gases move into the blood of the human body.

Answer 9

Nasal cavity ➜ Trachea➜ Bronchi(2) ➜ Bronchioles➜Alveoli➜Alveolus➜Across alveolar epithelium➜Capillary endothelium➜Blood

Question 10

Describe the mechanism of breathing

INSPIRATION

Answer 10

External intercostal muscles!
= Contract to pull ribs up & out
Internal intercostal muscles
= Relax
Diaphram!
= Contracts to move down & flattens
Air pressure in the lungs
= Pressure decrease in thoracic cavity below atmospheric pressure
Lung volume!
= Increases
Movement of air
= Air moves into lungs down a pressure gradient
REQUIRES ATP = ACTIVE PROCESS

Question 11

Describe the mechanism of breathing

EXPIRATION

Answer 11

External intercostal muscles!
= Relax
Internal intercostal muscles
= Contract to pull ribs down & in
Diaphram!
= Contracts to move up & dome
Air pressure in the lungs
= Pressure increase in thoracic cavity above atmospheric pressure
Lung volume!
= Decreases
Movement of air
= Air moves out of lungs up a pressure gradient
DOES NOT REQUIRE ATP = PASSIVE PROCESS

Question 12

Give the equation for pulmonary ventilation

Answer 12

Pulmonary Ventilation = Tidal volume × Ventilation rate

dm3min-1 dm3 min-1

Question 13

Describe the adaptations of the insect’s tracheal system.

Answer 13

Tracheoles have thin walls
= Creates a short diffusion pathway to cells
Highly branched/ Lots of tracheoles
= Creates a large surface area for gas exchange
Body can be moved by muscles to move air
= maintains concentration gradient for oxygen & co2
Fluid at end of tracheoles that move out into tissues during exercise
= Faster diffusion through air to gas exchange surface

Question 14

Describe the main features in an insect’s gas exchange system.

Answer 14

Spiracles, valve-like openings (O2 & CO2 leave)➜
➜Attached to the Tracheae, a network of internal tubes - supported by rings to prevent collapse➜
➜Tracheoles (smaller tubes) - extend throughout tissues to deliver oxygen to respiring cells

Question 15

Describe the process of gas exchange in insects

Answer 15

• Gases move in and out of tracheae through spiracles
• Diffusion gradient generated as cells respiring allows for oxygen to diffuse into body cells while CO2 diffuses out
• Contraction of abdominal muscles of tracheae allows for mass movement of air in and out

Question 16

Describe how insects are adapted to reduce water loss

Answer 16

• Insects have a waterproof exoskeleton
• Insects have a small surface area to volume ratio where water can evaporate from
• Spiracles can open or close to reduce water loss

Question 17

Give the equation for Fick’s Law.

Answer 17

Diffusion ∝surface area × difference in concentration/

length of diffusion path

Question 18

Describe the adaptations of a Fish’s gas exchange system.

Answer 18

Countercurrent flow- Water & blood continuously flow in opposite directions= maintains concentration gradient of oxygen across entire length of lamellae (Equilibrium never reached)
GIll has many gill filaments - covered in lamellae = Creates a large surface area for gas exchange
Capillary network in lamellae & very thin gill lamellae =
Creates a short diffusion distance for gases

Question 19

Describe why fish cant use their bodies as an exchange surface

Answer 19

• Have a waterproof outer membrane

- & Small surface area to volume ratio

Question 20

Explain the process of gas exchange in a Fish

Answer 20

• Fish opens its mouth to enable water to rush over gills
• Passes over lamellae (O2 diffuses into bloodstream/waste CO2 diffuses out into water)
• Flows out through the back of gills

Question 21

Describe the adaptations of a Leaf for gas exchange.

Answer 21

Thin & Flat = Short diffusion pathway for gas exchange
Mesophyll cells = have a large surface area for rapid diffusion
Many minute pores on underside of leaf allow = Allow gases to easily enter

Question 22

Describe gas exchange in Dixotyledonous plants

Answer 22

• Oxygen diffuses out of the stomata

- and carbon dioxide diffuses into stomata for photosynthesis so more growth

Question 23

Describe how plants are adapted to reduce water loss and xerophyatic adaptations
MORE STOMATA MAY MEAN MORE WATER LOSS SO LESS PHOTOSYNTHESIS AND LESS GROWTH

Answer 23

• Stomata close at night when photosynthesis is not occurring
  XEROPHYTIC ADAPTATIONS
• Curled leaf & layers of hair trap moisture increase local humidity
• Thicker, waxy cuticle to reduce evaporation