8.4 Transport of Oxygen And Carbon Dioxide In The Blood

Question 1

What are the key adaptations of an erythrocyte?

Answer 1

-Biconcave shape
-No nuclei
-Contain haemoglobin

Question 2

Why does an erythrocyte have a biconcave shape?

Answer 2

To give it a large surface area, so more area available for diffusion of gases. Also helps them to pass through narrow capillaries

Question 3

Why does an erythrocyte have no nucleus?

Answer 3

To maximise the amount of haemoglobin that can fit into the cell (however this also reduces its lifespan)

Question 4

Why does an erythrocyte contain haemoglobin?

Answer 4

Allows RBC to carry oxygen because it binds to it.

Question 5

What is haemoglobin? (Simple answer, no protein)

Answer 5

A red pigment that carries oxygen, and gives erythrocytes their colour.

Question 6

How many oxygen molecules can each haemoglobin bind to?

Answer 6

4

Question 7

What is haemoglobin? (In terms of proteins)

Answer 7

Large globular protein, conjugated, made up of 4 peptide chains, each with an iron-containing prosthetic group

Question 8

What is formed when oxygen binds to haemoglobin?

Answer 8

Oxyhaemoglobin

Question 9

State the symbol equation for oxygen binding to haemoglobin.

Answer 9

Hb + 4O2 ⇌ Hb(O2)4

Question 10

What is loading/association?

Answer 10

Haemoglobin binding to oxygen at gas exchange surfaces

Question 11

What is unloading/dissociation?

Answer 11

Haemoglobin releases oxygen to respiring tissues

Question 12

What is affinity?

Answer 12

How readily/easily haemoglobin binds to or releases oxygen

Question 13

If haemoglobin has high affinity, what does it do?

Answer 13

Loads easily, unloads less easily

Question 14

What is partial pressure?

Answer 14

The individual pressure of a gas in a mixture of gases (kind of like concentration)

Question 15

What are the oxygen levels like in the lungs?

Answer 15

High than the red blood cells, to make a step concentration gradient

Question 16

How does the structure of haemoglobin make it easy for oxygen to bind to it?

Answer 16

As soon as one oxygen molecule binds to a haem group, the molecule changes shape, making it easier for the next oxygen to bind. Called CONFORMATIONAL CHANGE / POSITIVE COOPERATIVITY

Question 17

What is positive cooperativity?

Answer 17

Where the change in shape of the first subunit makes the binding of substrate to the second subunit easier. Found in haemoglobin

Question 18

How is a steep oxygen concentration gradient in an erythrocyte maintained despite having oxygen bound to haemoglobin?

Answer 18

The oxygen is bound to the haemoglobin (not the actual erythrocyte), so the free oxygen concentration in the RBC stays low.

Question 19

What is the difference in oxygen concentration between the cells of the body tissues and the red blood cells?

Answer 19

Conc. of oxygen in the cytoplasm of the body cells is lower than in the erythrocytes.

Question 20

What is the name of the binding involving oxygen binding to haemoglobin?

Answer 20

Co-operative binding

Question 21

What does the oxygen dissociation curve show?

Answer 21

The affinity of haemoglobin for oxygen

Question 22

What is the shape of the oxygen dissociation curve?

Answer 22

A sigmoidal curve.

Question 23

Why does a small change in partial pressure of oxygen make a significant difference to the saturation of the haemoglobin with oxygen?

Answer 23

-Because once a molecule becomes attached, the change in the shape of the haemoglobin molecule means other oxygen molecules are added rapidly.

Question 24

When does the oxygen dissociation curve level out? Why?

Answer 24

-At the highest partial pressures of oxygen, because all of the haem groups are bound to oxygen and cannot take up anymore.

Question 25

What does the levelling out of the oxygen dissocation curve represent?

Answer 25

The red blood cells in the capillaries surrounding the lungs being rapidly filled with oxygen from the lungs (with a high partial pressure of oxygen)

Question 26

What does a large decrease in saturation of haemoglobin as a result of a relatively small drop in the partial pressure of oxygen represent?

Answer 26

Oxygen releasing rapidly from the haemoglobin to diffuse into body tissues.

Question 27

When you are not very active, what % of the oxygen carried in your erythrocytes is released into the body cells?

Answer 27

Only about 25%

Question 28

What is the Bohr effect?

Answer 28

The process describing how the binding of oxygen to haemoglobin changes as carbon dioxide and pH levels change.

Question 29

What happens as the partial pressure of carbon dioxide rises?

Answer 29

-pH is slightly DECREASED, which causes the shape of haemoglobin to change, and the affinity for oxygen is lower -So haemoglobin unloads oxygen more readily -The oxygen dissociation curve is shifted to the RIGHT

Question 30

Why does haemoglobin change shape when pH changes?

Answer 30

Because haemoglobin is a globular protein, and proteins' structures are affected by changes in pH.

Question 31

Is carbon dioxide acidic or alkali?

Answer 31

Acidic

Question 32

What happens as the partial pressure of carbon dioxide decreases?

Answer 32

-pH is slightly increased, so the affinity of Hb for oxygen is LOWER (Hb unloads oxygen more readily) -The oxygen dissociation curve is shifted to the LEFT

Question 33

Is the partial pressure of CO2 in the lungs high or low?

Answer 33

Low

Question 34

Is the partial pressure of CO2 in respiring tissue high or low?

Answer 34

High

Question 35

How does the body ensure there is always sufficient oxygen for respiring tissues? (Model Answer)

Answer 35

-If the rate of respiration in tissues is high, more CO2 will be produced -The pH of the tissues is reduced -This causes the shape of the haemoglobin to change -As a result, the affiinity of haemoglobin for oxygen is reduced -So, more oxygen is unloaded at the tissues -So more oxygen is available for aerobic respiration

Question 36

How does a fetus recieve oxygen while it is developing?

Answer 36

-Oxygenated blood from teh mother runs close to the deoxygenated fetal blood in the plasma -Fetal haemoglobin has a higher affinity for oxygen than adults, so the mother can remove oxygen from the maternal blood and pass it on as the blood moves past eachother

Question 37

Is maternal circulation and fetal circulation counter-current or parallel?

Answer 37

Parallel

Question 38

Does fetal haemoglobin have a higher or lower affinity for oxygen than adult haemoglobin?

Answer 38

Higher

Question 39

What percent of carbon dioxide is carried in the plasma?

Answer 39

5%

Question 40

What happens to CO2 in erythrocytes that do not react with water?

Answer 40

They are combined with amino groups in the polypeptide chains of haemoglobin to form a compound called CARBAMINOHAEMOGLOBIN

Question 41

What is the name of the product formed when CO2 combines with amino acids in Hb?

Answer 41

CARBAMINOHAEMOGLOBIN

Question 42

What are the 3 different pathways for CO2 transported to the lungs from the tissues?

Answer 42

-Carried in the plasma -Combined with amino groups in Hb to form carbaminohaemoglobin -Converted to hydrogen carbonate ions in the cytoplasm of erythrocytes

Question 43

When carbon dioxide reacts slowly with water, what is formed?

Answer 43

Carbonic acid (H2CO3)

Question 44

How is carbonic acid (H2CO3) formed?

Answer 44

When carbon dioxide reacts slowly with water in the cytoplasm of RBCs

Question 45

What is the next step for carbonic acid once it is formed?

Answer 45

Then dissociated to form hydrogen ions (H+) and hydrogencarbonate ions (HCO3-)

Question 46

What enzyme catalyses the reaction between Carbon Dioxide and Water?

Answer 46

Carbonic Anhydrase

Question 47

What chemical dissociates to form Hydrogen Ions and Bicarbonate?

Answer 47

Carbonic Acid

Question 48

What is the chloride shift?

Answer 48

When the HCO3- ions move out of the erythrocytes into the plasma by diffusion, so negatively charge chloride ions move into the RBCs, which maintains the electrical balance of the cell

Question 49

Why is important that the chloride shift takes place?

Answer 49

To maintain the electrical balance of the cell

Question 50

What happens to the H+ ions in erythrocytes?

Answer 50

They are accepted by the haemoglobin, which acts as a buffer and prevents changes in pH. The haemoglobin and hydrogen ion form haemoglobinic acid

Question 51

What is produced when haemoglobin accepts a hydrogen ion?

Answer 51

Haemoglobinic acid

Question 52

Why is it important that CO2 is removed and converted to HCO3- in erythrocytes?

Answer 52

So that a steep concentration gradient can be maintained for carbon dioxide to diffuse from respiring tissues

Question 53

What happens to HCO3- in the blood once it has reached the lung tissue?

Answer 53

-It diffuses back into the erythrocytes, and reacts with a hydrogen ion to form more H2CO3. -This is broken down by carbonic anhydrase to release free carbon dioxide -This diffuses out of the blood into the lungs

Question 54

What happens to Chlorine ions once HCO3- has been converted back to CO2 and removed via the lungs?

Answer 54

They diffuse out of the erythrocytes and back into the plasma down an electrochemical gradient

Question 55

What name is given to a change in the oxygen dissociation curve due to increasing carbon dioxide concentration?

Answer 55

The Bohr Effect