BY2.2

Question 1

What happens to the Surface area:volume ratio as the organism gets larger

Answer 1

The surface area:volume ratio gets smaller

Question 2

Why can’t large organisms use their external surface for gas exchange

Answer 2

The SA:V is too small, this means the external surface cannot supply O2 in a large enough quantity/rate to meet the high demand of the respiring cells, they have evolved specialised gas exchange surfaces

Question 3

Why can small organisms use their external surface for gas exchange

Answer 3

• large SA:V = large enough volume of O2 for supply
• short diffusion pathway = high rate of diffusion
• low metabolic rate = low demand for O2

Question 4

Why do large organisms have specialised gas exchange surface

Answer 4

• ensure a large volume of O2 can be supplied

* rate of O2 diffusion is fast

Question 5

What properties do the 4 large organism have in their gas exchange surfaces

Answer 5

• large surface area = more diffusion of gases
• thin surface = short diffusion pathway
• moist = allows gases to dissolve - faster diffusion
• permeable to gases = allows gases to move across
• ventilation = maintain a concentration gradient
• good blood supply = maintain a concentration gradient

Question 6

In fish where are the gills located

Answer 6

In the operculum cavity, protected by a ‘tough plate’ called the operculum

Question 7

What are the specialised gas exchange surface in fish

Answer 7

Gill lamellae

Question 8

How are the gill lamellae in fish adapted to gas exchange

Answer 8

• thousands of gill lamellae = high surface area (water must flow inbetween the filaments to spread them out, on land the filaments are compacted)
• thin = short diffusion pathway
• Permeable to gas
• good blood supply via the capillaries = circulates blood to maintain a concentration gradient between water and blood

Question 9

Why do the fish gills have to be very well adapted

Answer 9

Because water is a denser medium compared to air, and has a 30x lower O2 concentration, therefore gills must be very well adapted for efficient absorption of O2 dissolved in H2O

Question 10

What’s the main difference between parallel flow and countercurrent flow in fish lamellae

Answer 10

• Parallel flow = water and blood flowing in the same direction
• Counter current = water and blood flowing in opposite directions

Question 11

Why is the counter current flow in fish gills more efficient compared to parallel flow

Answer 11

the concentration gradient between water and blood for O2 to diffuse is maintained along the whole length of the gill lamellae. Due to the fact that there is always a higher O2 concentration in the water, compared to the blood it meets, this means an equilibrium is never reached

Question 12

What does the graph for parallel flow look like

Answer 12

O2 conc  |
               |
               | 
               |\_\_\_\_\_\_\_\_\_\_
      Distance over lamellae

\
| \_____ Top line = water
| / Bottom line = blood
|/________

Question 13

What does the graph for counter current flow look like

Answer 13

O2 conc | \  \
              |   \  \ 
              |     \  \
              |       \  \
              |\_\_\_\_\_\_\\_\_\_\_
       Distance over lamellae 

Top line = water
Bottom line = blood

Question 14

What is ventilation

Answer 14

Ventilation is the movement of O2 containing medium (H2O/air) over the gas exchange surface in order to maintain a concentration gradient

Question 15

In what way do fluids move in organisms

Answer 15

From a high pressure/small volume to a low pressure/large volume

Question 16

How do organisms later the pressure in their bodies

Answer 16

Change the volume of chambers/cavities containing fluid

Question 17

What happens during inspiration in a fish

Answer 17

• fish mouth opens
• muscles in buccal cavity floor contract to lower the buccal cavity floor
• increase of volume of buccal cavity
• decrease in pressure, lower than outside body, therefore water flows from high pressure to power pressure in buccal cavity

Question 18

What happens during expiration in a fish

Answer 18

• fish closes mouth
• muscles in buccal cavity floor relax, causing the rise of the buccal cavity floor
• decrease in volume of the buccal cavity
• increase in pressure

Question 19

What 2 factors do we need to consider when estimating the efficiency of gas exchange

Answer 19

• Surface area - supplying O2 to respiring tissues by diffusing
• Volume - demand for O2 by respiring cells

Question 20

What is the specialised gas exchange of insects

Answer 20

Branched, chitin-lined system of tracheae with openings called spiracles.
Gas exchange surface are the tracheole tubes which come into contact with every tissue

Question 21

How is a concentration gradient maintained in the gas exchange surface of Insects

Answer 21

Muscles in thorax and abdomen contract/relax causing rhythmical movements with ventilated the tracheole tubes, maintaining a concentration gradient

Question 22

What are the advantages of the tracheal system

Answer 22

• every tissue is directly supplied with oxygen
• no haemoglobin is needed
• reduced water loss

Question 23

What features or structures reduce the diffusion pathway and generate a high surface area in insects

Answer 23

Very highly branched = lots of tracheoles which touch the tissues

Question 24

What is the tissue or structure which acts as gas exchange surface in mammals

Answer 24

Alveoli - made from epithelial cells

Question 25

What features or structures reduce the diffusion pathway and generate a high surface area in mammals

Answer 25

• capillary and alveoli cell membrane are 1 cell thick

* millions of alveoli and are very highly folded

Question 26

How is the concentration gradient between atmosphere/water and blood maintained in mammals

Answer 26

Air constantly passed over alveoli

Question 27

Tissues of structure which acts as gas exchange surface of plants

Answer 27

Spongy mesophyll layer

Question 28

What features or structures reduce the diffusion pathway and generate a high surface area in plants

Answer 28

• thinner than normal cell wall - spongy mesophyll layer is surrounded by gas
• leaves are broad and thin

Question 29

How is the concentration gradient between atmosphere/water and blood maintained in plants

Answer 29

Stomata located on lower epidermis = open and close to allow for diffusion

Question 30

In mammalian lungs what are the functions of the epiglottis, trachea, bronchi and bronchioles

Answer 30

• epiglottis = covers pointing to airways when food is swallowed
• trachea = strengthen by rings of cartilage to keep airway open
• bronchi = to carry air to and from each lung
• bronchioles = small passageways to alveoli

Question 31

What is the function of these structures - alveoli, pleural membranes, ribs and intercostal muscles, and diaphragm in the mammalian lungs

Answer 31

• Alveoli = respiratory gas exchange surface
• Pleural membranes = reduces friction
• Ribs and intercostal muscles = alters size of pleural cavity to change volume/pressure
• Diaphragm = alters size of pleural cavity to change volume/pressure

Question 32

Describe adaptations of alveoli

Answer 32

• large surface area = millions of alveoli
• short diffusion pathway = thin gas exchange surface:
- flattened epithelial cells
- flattened capillary wall cells
- O2 & CO2 only has to move though 2 layers of epithelial cells form alveolus to blood
• moist
• permeable to gases
• large concentration gradient
- blood flow through large capillary network around each of the alveolus maintains a steep concentration gradient, by bringing low O2 concentration blood to alveoli, and moving the high O2 concentration blood after exchange
- ventilation

Question 33

Describe inspiration in mammalian ventilation

Answer 33

• nerve impulses from the brain cause the diaphragm muscle and external intercostal muscles to contract
• the diaphragm moves down/ rib cages moves up and out
• volume in the pleural cavity increases
• pressure in the lungs decreases
• so air moves down a pressure gradient from outside into the lungs

Question 34

Describe expiration in mammalian ventilation

Answer 34

• diaphragm muscle and external intercostal muscles relax
• diaphragm muscle moves up/ the rib cage down and in
• volume of pleural cavity decreases
• pressure inside the lungs increases
• so air moves down a pressure gradient form in the lungs to the outside

Question 35

Advantages of internal lungs

Answer 35

• infolding reduces heat loss
• infolding reduces water loss
• protected by rib cage

Question 36

Describe the function of the cuticle, epidermis, palisade mesophyll and spongy mesophyll in plants

Answer 36

• cuticle = impermeable to water, reduces water loss
• epidermis = prevents mechanical damage
• palisade mesophyll = main site of Ps
• spongy mesophyll = gas exchange surface

Question 37

Describe the functions of vascular bundle, air space, stomata, guard cells in plants

Answer 37

• vascular bundles = transport of water/ mineral ions in xylem and transport of sucrose in phloem
• air space = gas exchange
• stomata = entry and exit of gases
• guard cells = open and close stomata