Transport of oxygen and carbon dioxide in the blood 8.4

Question 1

what is the most specialised transport role of the blood

Answer 1

the transport of oxygen by the erythrocytes. The erythrocytes are also involved in the removal of carbon dioxide from the body

Question 2

How is the shape/structure of an erythrocyte an aid to its function

Answer 2

Erythrocytes have a biconcave shape. This shape has a larger surface area than other shapes and so allows for more efficient gaseous exchange, it also helps them to pass through narrow capillaries.

Once mature and ready to be released into circulation the erythrocytes lose there nucleus to allow for maximum space for haemoglobin

Question 3

How does the production of erythrocytes aid its function

Answer 3

Haemoglobin is constantly being produced in the red bone marrow and so if any is lost it does not take long at all to replenish the stock of blood in the body to its maximum amount for the most gaseous exchange process

Question 4

What pigment do erythrocytes contain

Answer 4

Haemoglobin

Question 5

what is haemoglobin

Answer 5

Haemoglobin is a very large globular conjugated protein made up of 4 polypeptide chains, each with an iron-containing haem prosthetic group

Question 6

How many molecules of haemoglobin are there in 1 erythrocyte

Answer 6

300 million haemoglobin molecules in each red blood cell

Question 7

How many oxygen atoms can bind to 1 red blood cell

Answer 7

300 million haemoglobin molecules in each red blood cell and haemoglobin molecule can bind to 4 oxygen molecules

this means 300,000,000 x 4 = 1,200,000,000 oxygen atoms
1.2 billion

Question 8

what forms when oxygen and haemoglobin bind

Answer 8

The oxygen binds quite loosely to the haemoglobin forming oxyhemoglobin. This reaction is reversible

Question 9

what is the reaction equation for the reaction between haemoglobin and oxygen

Answer 9

Question 10

explain why the oxygen would move from the alveoli to the erythrocytes in the capillaries

Answer 10

• diffusion as there is a high concentration of O2 in the alveoli and a relatively low concentration in the blood
• ^there is a steep concentration gradient

Question 11

Explain what is meant by positive cooperativity

Answer 11

• as soon as 1 oxygen molecule binds to a haem group,
• ^the haemoglobin molecules tertiary structure changes
• ^making it easier for the next oxygen molecule to bind

Question 12

How is the concentration gradient maintained when oxygen begins to bind to haemoglobin

Answer 12

Because oxygen is bound to haemoglobin, the free oxygen concentration in the erythrocyte stays low, so a steep diffusion gradient is maintained until all of the haemoglobin is saturated with oxygen

Question 13

explain why the oxygen on the erythrocytes would leave it when it travels to the body cells

Answer 13

The concentration of oxygen in the cytoplasm of the body cells is lower than in the erythrocytes. As a result, oxygen moves out of the erythrocytes down a concentration gradient.

Question 14

explain how positive cooperativity comes into play when oxygen is leaving the erythrocytes

Answer 14

Once the first oxygen molecule is released by the haemoglobin, the molecule again changes shape and it becomes easier to remove the remaining oxygen molecules

Question 15

what is partial pressure

Answer 15

Partial pressure is a useful way of talking about the concentration of a chemical when it is one of a mixture of gases

Question 16

what is the oxygen dissociation curve used for and what does it show us

Answer 16

An oxygen dissociation curve is an important tool for understanding how the blood carries and releases oxygen

Oxygen dissociation curves show the affinity of haemoglobin for oxygen

Question 17

what are on the axis of an oxygen dissaciation curve

Answer 17

The percentage saturation of haemoglobin in the blood Is plotted against the partial pressure of oxygen (pO2)

Question 18

What is meant by affinity

Answer 18

the strength by which two (or more) molecules interact or bind.

Question 19

How can a very small change in the partial pressure change the saturation of haemoglobin within oxygen a lot

Answer 19

A very small change in the partial pressure of oxygen makes a significant difference to the saturation of haemoglobin with oxygen, because once the first molecules becomes attached or detached the change in shape makes it easier for oxygen to either bind or unbind to the haemoglobin rapidly

Question 20

what does the the oxygen dissaciation cuve look like at very high partial pressures of oxygen

Answer 20

The curve levels out at the highest partial pressure of oxygen because all the haem groups are bound to oxygen and so the haemoglobin is saturated and cannot take up any more

Question 21

what can decrease the saturation of oxygen in haemoglobin

Answer 21

• as one oxygen unbinds it becomes easier for oxygen to be lost from molecule
• enhanced by low pH in respiring tissues
• low concentration of oxygen in cytoplasms of respiring cells generates conc gradient

Question 22

when you are inactive how much of the oxygen in your erythrocytes is released

Answer 22

When you are inactive, about 25% of the oxygen carried in your erythrocytes is related into the body cells. The rest acts as a reservoir for when the demands of the body increase suddenly

Question 23

What is the Bohr effect

Answer 23

As the partial pressure of carbon dioxide rises, haemoglobin gives up the oxygen more easily

Question 24

what are some reasons why the bohr effect is important for the body

Answer 24

• In active tissue with a high partial pressure of carbon dioxide, haemoglobin gives up its oxygen more readily
• In the lungs where the proportion or carbon dioxide in the air is relatively low, oxygen binds to the haemoglobin molecules easily

Question 25

Explain how fatal haemoglobin differs from normal haemoglobin and why is this important

Answer 25

Fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin at each point along the dissociation curve. So It removes oxygen from the maternal blood as they move past each other

If the blood of the foetus has the same affinity for oxygen as the blood of the mother, then little or no oxygen would be transferred to the blood of the fetus

Question 26

what 3 different ways are carbon dioxide transported in the blood

Answer 26

• 5% dissolved in blood plasma
• 10-20% combined with amino groups in polypeptide chains to form carbaminohaemoglobin
• 75-85% is converted into HCO3- in the cytoplasm of erthyrocytes

Question 27

How does carbon dioxide react with water and why is this reaction important

Answer 27

Carbon dioxide reacts slowly with water to from carbonic acid (H2CO3 -). The carbonic acid then dissociates to from hydrogen ions and hydrogen carbonate ions

Question 28

where is most of the carbonic acid produce in the body and why is it produced there

Answer 28

In the cytoplasm of the red blood cells there are high level of the enzyme carbon anhydrase. This enzyme catalyses the reversible reaction between carbon dioxide and water to from carbonic anhydrase. The carbon acid then dissociates to from hydrogen carbonate ions and hydrogen ions

Question 29

explain the movement of hydrogen carbonate ions once produced in the cytoplasm

Answer 29

the negatively charged hydrogen carbonate ions move out of the erythrocytes into the plasma by diffusion down a concentration gradient

Question 30

What is the chloride shift and why does it come about

Answer 30

As negatively charged hydrogen carbonate ions diffuse out of he erythrocytes, negatively charged chloride ions move into the erythrocyte, this maintains the electrical balance of the cell and the blood

Question 31

why is it important that CO2 is converted into hydrogen carbonate ions and hydrogen ions

Answer 31

• By removing CO2 and converting it to hydrogen carbonate ions, steep concentration gradient maintained
  ^allows CO2 to diffuse from tissues into erythorocytes

Question 32

How does carbon dioxide form when the blood reaches the lung so it gas be diffused out

Answer 32

When the blood reaches the lung tissue where there is a relatively low concentration of carbon dioxide, carbon anhydrase catalyses the reverse reaction, breaking down carbonic acid into carbon dioxide and water.
Hydrogen carbonate ions diffuse back into the erythrocytes and react with hydrogen ions to from carbonic acid. When that is broken down by carbonic anhydrase it releases free carbon dioxide, which diffuses out of the blood into the lungs.

Question 33

what happens to the chloride that shifted into the erythrocytes once the hydrogen carbonate ions have formed back into neutral carbonic acid

Answer 33

Chloride ions diffuse out of the red blood cells back into the plasma down an electrochemical gradient

Question 34

How does haemoglobin act as a buffer

Answer 34

it acts as a buffer and prevents changes in the PH by accepting free hydrogen ions in a reversible reaction to from haemoglobinic acid