Gas exchange

Question 1

Describe and explain how the countercurrent system leads to efficient gas exchange
across the gills of a fish.

Answer 1

1. Water and blood flow in opposite directions;
2. Maintains diffusion gradient of water and blood
3. Along the length of the gill

Question 2

describe 2 effects of the lamellea in gills becoming thicker and fusing together

Answer 2

1. Thicker lamellae so greater
   diffusion pathway;
2. Lamellae fuse so reduced surface area;

Question 3

suggest why the volume of water passing over the gills increases if the temperature of the water
increases.

Answer 3

1. Increased metabolism

2. Less oxygen dissolved in water

Question 4

How do some SMALL fish get O2 into their cells without gills

Answer 4

1. diffusion across body surface
2. due to short diffusion pathway
3. as it has a large SA:V ratio;

Question 5

Explain how a fish’s gas exchange system with high metabolism is adapted for efficient gas exchange

Answer 5

1.large numbers of lamellae so large SA;
2.lamellae thin so short diffusion pathway to blood;
3 to allow high rate of oxygen uptake for respiration

Question 6

What slows down the rate of blood flow in blood vessels?

Answer 6

1. small diameter
2. therefore more surface is in contact with blood;
3. therefore greater friction;
4. which causes LOSS of pressure;

Question 7

• Which type of blood vessel has most elastic tissue in its wall?
• And how does this elastic tissue help to smooth out the flow of blood in the blood vessel?

Answer 7

artery

1.stretches to accommodate increase in blood pressure; 2.recoils when blood pressure decreases;

Question 8

Why is the rate of tranSPIRATION (water moving into cell through leaf) faster when the air is moving than when it is still even with the same temperature?

Answer 8

1.Removes water vapour
2.Increases water potential gradient
(therefore more diffusion by osmosis)

Question 9

Why does the rate of TRANSPIRATION faster in higher temperature even when the air is still?

Answer 9

1. Increases kinetic energy;
2. Water molecules move faster;
3. Increases diffusion

Question 10

When they ask you for the relationship between two graphs, what do you talk about?

Answer 10

1. the correlation - whether positive or negative

2. if it follows the same pattern - directly proportional(up to a point) or no pattern

Question 11

Explain why the rate of water movement in the xylem increases with increased light intensty?

Answer 11

1. Stomata open;
2. Photosynthesis increases;
3. More water pulled up;
4. Cohesion between water molecules

Question 12

Explain why the diameter of a trunk was less at higher rate of movement through the xylem than at a lower rate

Answer 12

1. Water moves up at fast rate;
2. Water column under tension;
3. Sticking/adhesion between water and xylem;
4. Pulls xylem in;

Question 13

Arteries and arterioles take blood away from the heart.

Explain how the structures of the walls of arteries and arterioles are related to their functions.

Answer 13

Elastic tissue 
1 Elastic tissue stretches under pressure; 
2 Recoils when pressure is reduced; 
3 Evens out pressure; 
Muscle 
4 Muscle contracts; 
5 Reduces diameter of lumen; 
6 Changes pressure; 
Epithelium 
7 Epithelium smooth; 
8 Reduces friction between blood and wall

Question 14

Explain how water enters xylem from the endodermis in the root and is then
transported to the leaves.

Answer 14

(In the root)
1. Casparian strip blocks apoplast pathway / only allows symplast pathway;
2. Active transport by endodermis;
3. (Of) ions/salts into xylem;
4. Lower water potential in xylem / water enters xylem by osmosis /down a water potential gradient;
(Xylem to leaf)
5. Evaporation / transpiration (from leaves);
6. (Creates) cohesion / tension / H-bonding between water molecules / negative pressure;
7. Adhesion / water molecules bind to xylem;
8. (Creates continuous) water colomn

Question 15

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

Answer 15

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

Question 16

Explain why abdominal pumping increases the efficiency of gas exchange between the tracheoles
and muscle tissue of the insect.

Answer 16

1. air oxygen enters quicker;

2. So maintains diffusion gradient;

Question 17

Explain how the structure of arterioles enables the regulation of blood flow to different parts of the body.

Answer 17

Muscle (in wall);
Contraction / narrowing of arteriole reduces (blood flow) / relaxation /
dilation
increases (blood flow). 2

Question 18

Give 5 pieces of evidence supporting mass flow

Answer 18

1. there is pressure within sieve tubes, as shown by sap being released when they are cut
2. the concentration of sucrose is higher in leaves (source) than in roots (sink)
3. downward flow in the phloem occurs in daylight, but ceases when leaves are shaded, or at night
4. increases in sucrose levels in the leaf are followed by similar increases in sucrose levels in the phloem a little later
5. metabolic poisons and or lack of oxygen inhibit translocation of sucrose in the phloem
6. companion cells possess many mitochondria and readily produce ATP

Question 19

Give 3 pieces of evidence against mass flow

Answer 19

1. the function of sieve plates is unclear, as they would seem to hinder mass flow
2. not all solutes move at the same speed - they should do if movement is by mass flow
3. sucrose is delivered at the same rate to all regions, rather than going more quickly to ones at lowest sucrose concentration

Question 20

Describe 2 experiments to show that sucrose is translocated in the phloem

Answer 20

1. ringing experiments - a piece of the circumference of the woody stem is removed and swelling occurs above the part where it has been removed where sucrose has accumulated
2. tracer experiments - an isotope of carbon (C14) is incorporated into the sugars of plants as 14CO2 and is radioactive. Using a autoradiography you can see the blackened regions that the isotope has left travelling through the phloem

Question 21

What are 3 pieces of evidence that organic molecules (sucrose) are translocated in the phloem?

Answer 21

1. When phloem is cut, a solution of organic molecules flow out
2. plants provided with radioactive CO2 can be shown to have radioactively labelled carbon in phloem
3. sucrose accumulates where a ring of phloem from the circumference has been removed

Question 22

Give 3 reasons why the potometer does not truly measure the rate of transpiration

Answer 22

1. Water used for turgidity;
2. Water used in photosynthesis;
3. Water produced in respiration;

Question 23

How does hydrostatic pressure fall from the arteriole end of the capillary to the venule end

Answer 23

loss of water

Question 24

High blood pressure leads to an accumulation of tissue fluid. Explain how.

Answer 24

1. high blood pressure = high hydrostatic pressure
2. Increases outward pressure from arterial end of capillary
3. So more tissue fluid formed

Question 25

Explain how water enters xylem from the endodermis in the root and is then transported to the leaves.

Answer 25

1. Casparian strip blocks apoplast pathway / only allows symplast pathway;
2. Active transport by endodermis;
3. Of ions into xylem;
4. Which lowers water potential in xylem so water enters xylem by osmosis

(Xylem to leaf)

5. Evaporation from leaves creates cohesion between water molecules / negative pressure
6. Adhesion to xylem; creates continuous water column;

Question 26

What is translocation?

Answer 26

the process by which organic molecules and mineral ions are transported from one part of the plant to another

Question 27

Describe the mass flow hypothesis for the mechanism of translocation in plants

Answer 27

1. In source sugars actively transported into
   phloem;
2. By companion cells;
3. Lowers water potential of sieve tube so
   water enters by osmosis;
4. Increase in pressure causes mass movement
   towards sink;
5. Sugars used in sink for respiration or for
   storage

Question 28

Describe the transmission and course of infection of pulmonary tuberculosis.

Answer 28

1. Bacteria transmitted in droplets;
2. engulfed by phagocytes;
3. encased in tubercle;
4. are activated and destroy alveoli;
5. which leads to fibrosis (scar tissue);
6. as a result less diffusion as diffusion pathway increases ;
7. Activation allows bacteria to enter
   blood so spreads to other organs

Question 29

People with emphysema may feel

weak and tired. Explain why

Answer 29

1. Alveoli walls thicken;
2. so diffusion pathway increases so less diffusion.
3. Loss of elastin;
4. means alveoli cannot recoil and expand to expel air;
5. so reduced diffusion gradient;
6. Therefore less oxygen enters blood;
7. so less respiration so less ATP produced;