Transport in Animals: Blood and O2

Question 1

What is tissue fluid?

Answer 1

• Plasma that seeps out of capillaries due to high hydrostatic pressure
• Contains dissolved oxygen, glucose, and ions
• Allows exchange of substances between blood and cells

Question 2

How is tissue fluid formed at the arterial end of capillaries?

Answer 2

• High hydrostatic pressure forces plasma out of capillaries, forming tissue fluid
• Blood pressure is high due to heart pumping + artery contraction
• Plasma proteins remain in the blood, keeping solute potential low
• Hydrostatic pressure is stronger than osmotic force, so more water leaves than returns

Question 3

What prevents all water from leaving the capillaries at the arterial end?

Answer 3

Plasma proteins lower the solute potential inside capillaries, creating an osmotic pull
Some water moves back into the capillaries via osmosis
However, hydrostatic pressure is stronger, so there is a net movement of water out

Question 4

What happens at the venous end of the capillary?

Answer 4

• Water moves back into capillaries via osmosis
• Hydrostatic pressure is lower (fluid was lost + blood is further from the heart)
• Plasma proteins remain in capillaries, making solute potential more negative
• Osmotic force is now stronger than hydrostatic pressure, so water re-enters capillaries
• Tissue fluid carries CO₂ and waste from cells, which diffuse back into capillaries

Question 5

What happens to the remaining tissue fluid that doesn’t return to capillaries?

Answer 5

It enters the lymphatic system
Excess fluid drains into lymph vessels
Lymph nodes filter bacteria and foreign material
Fluid is eventually returned to the blood

Question 6

How much tissue fluid returns to the blood via capillaries?

Answer 6

90% of the tissue fluid returns at the venous end

Question 7

What is the role of lymph nodes and lymph vessels?

Answer 7

• Lymph nodes kill of pathogens in the fluid
• Lymph vessels carry the fluid back to the bloodstream

Question 8

Q1: What two key properties must haemoglobin have to ensure effective oxygen transport?

Answer 8

**Ability to:
**Readily associates with oxygen at the lungs (high pO₂)
Readily dissociates from oxygen at respiring tissues (low pO₂)

Question 9

Wha are the seemingly congradictory things do contradictory things at lungs vs tissues?

Answer 9

It must bind oxygen tightly in the lungs where it’s abundant, and release it easily in tissues where oxygen is low and needed for respiration.

Question 10

What causes haemoglobin to change shape and affect oxygen affinity?

Answer 10

Binding of the first oxygen molecule changes haemoglobin’s shape, increasing its affinity for more oxygen (cooperative binding). In tissues, high CO₂ and H⁺ lower affinity, causing it to release oxygen.

Question 11

What is meant by “cooperative binding” in haemoglobin?

Answer 11

When one O₂ molecule binds, it induces a shape change in Hb, making it easier for the second and third O₂ molecules to bind. This increases Hb’s affinity with each oxygen bound.

Question 12

Why does the oxygen dissociation curve have an S-shape (sigmoidal)?

Answer 12

Due to cooperative binding — binding of each O₂ molecule makes it easier for the next to bind, but the** first one binds slowly** and the fourth requires a large increase in pO₂.

Question 13

How much oxygen can bind to one haemoglobin molecule?

Answer 13

Four oxygen molecules (O₂) — one per haem group, each containing an Fe²⁺ ion.

Question 14

What happens to haemoglobin’s affinity for oxygen in high CO₂ and low pH conditions?

Answer 14

Affinity decreases. This is the Bohr effect, helping Hb to release more oxygen in respiring tissues

Question 15

What is partial pressure of oxygen (pO₂)?

Answer 15

The pressure O₂ would exert if it were the only gas present; a measure of oxygen concentration.

Question 16

What are typical pO₂ values in the lungs vs respiring tissues?

Answer 16

Lungs: ~13–14 kPa (high pO₂)
Tissues: ~2–4 kPa (low pO₂)

Question 17

What would a linear oxygen dissociation curve lead to?

Answer 17

Constant increase in partial pressure needed for each oxygen to bind (e.g. 4, 8, 12, 16 kPa), meaning Hb would have low affinity at lower pO₂ and oxygen loading would be inefficient.

Question 18

What is the structural difference between fetal and adult haemoglobin?

Answer 18

Fetal Hb has two alpha and two gamma chains (α₂γ₂); adult Hb has two alpha and two beta chains (α₂β₂).

Question 19

Why does fetal haemoglobin have a higher affinity for oxygen than adult haemoglobin?
A2:

Answer 19

The different polypeptide structure allows fetal Hb to bind oxygen more readily, ensuring efficient oxygen uptake from maternal blood.

Question 20

Q3: Why is a higher oxygen affinity important for fetal haemoglobin?

Answer 20

It allows fetal Hb to absorb oxygen from maternal Hb across the placenta, even though maternal blood is partially deoxygenated.

Question 21

Do the mother’s and fetus’s blood mix at the placenta?

Answer 21

No. They flow close together across the placental barrier, allowing diffusion of oxygen from maternal to fetal blood.

Question 22

How does the oxygen dissociation curve of fetal haemoglobin differ from adult haemoglobin?

Answer 22

The curve is shifted to the left, meaning fetal Hb is more saturated at the same partial pressure of oxygen.

Question 23

Give an example of the difference in saturation between fetal and adult Hb at the same pO₂.

Answer 23

At ~5 kPa:
* Fetal Hb ≈ 80–90% saturated
* Adult Hb ≈ 60% saturated

Question 24

What happens to fetal haemoglobin after birth?

Answer 24

It is gradually replaced by adult haemoglobin, which has lower affinity for oxygen and is better at unloading O₂ to tissues.

Question 25

How does the higher affinity of fetal haemoglobin impact oxygen transfer from mother to fetus?

Answer 25

It ensures that oxygen moves from maternal Hb (lower affinity) to fetal Hb (higher affinity) by diffusion, following the gradient of partial pressure and binding strength.

Question 26

Where do lugworms live, and what is the oxygen availability like there?

Answer 26

Lugworms live in burrows in sandy shores, where oxygen levels are low due to stagnant water.

Question 27

Why do lugworms have a low metabolic rate?

Answer 27

Because they live in low-oxygen environments, conserving energy with a low metabolic rate helps reduce oxygen demand.

Question 28

How is lugworm haemoglobin adapted to its environment?

Answer 28

It has a very high affinity for oxygen, allowing it to bind oxygen even at very low partial pressures.

Question 29

What does the oxygen dissociation curve of lugworm haemoglobin look like?

Answer 29

It is shifted far to the left of the human haemoglobin curve, showing higher affinity at all pO₂ levels.

Question 30

When does lugworm haemoglobin release oxygen?

Answer 30

Only when the partial pressure of oxygen is very low, such as during intense activity.

Question 31

Why do llamas need haemoglobin with higher oxygen affinity

Answer 31

Llamas live at high altitudes where atmospheric pO₂ is lower, so higher affinity allows them to bind oxygen efficiently in their lungs.

Question 32

How is the haemoglobin dissociation curve of llamas adapted?

Answer 32

t is shifted to the left, indicating a higher affinity for oxygen across all partial pressures.

Question 33

What is a common feature between lugworms and llamas in terms of oxygen transport?

Answer 33

Both have haemoglobin with a left-shifted dissociation curve, allowing oxygen loading in low pO₂ environments.

Question 34

What happens to haemoglobin when CO₂ concentration increases?

Answer 34

CO₂ dissolves in blood → forms carbonic acid → releases H⁺ ions → lowers pH → haemoglobin changes shape → affinity for oxygen decreases.

Question 35

How does increased CO₂ affect oxygen unloading?

Answer 35

It causes haemoglobin to release oxygen more readily, making unloading more efficient in respiring tissues.

Question 36

At high CO₂ levels, is haemoglobin more or less saturated at a given pO₂?

Answer 36

Less saturated — because reduced affinity causes oxygen to be unloaded more easily.

Question 37

What is the Bohr effect?

Answer 37

The rightward shift of the oxygen dissociation curve at higher CO₂ concentrations or lower pH, due to reduced haemoglobin affinity for oxygen.

Question 38

Why is the Bohr effect useful in active tissues

Answer 38

Active tissues produce more CO₂ → increases H⁺ ions → lowers pH → haemoglobin releases more O₂ where it’s needed most.

Question 39

What happens at low CO₂ concentrations (e.g. in lungs)?

Answer 39

Lower CO₂ → less H⁺ → higher pH → haemoglobin has higher affinity and binds oxygen more readily (forms oxyhaemoglobin).

Question 40

How does pH influence haemoglobin’s affinity for oxygen?

Answer 40

Lower pH (more acidic) = lower affinity → more O₂ released Higher pH (less acidic) = higher affinity → more O₂ loaded

Question 41

What are the three ways carbon dioxide is transported in the blood?

Answer 41

1. Dissolved in plasma (5%) 2. Bound to haemoglobin as carbaminohaemoglobin (10%) 3. As hydrogen carbonate ions (HCO₃⁻) in plasma (85%)

Question 42

What enzyme catalyses the reaction between CO₂ and H₂O in red blood cells?

Answer 42

Carbonic anhydrase

Question 43

Write the full reaction showing how CO₂ is converted in red blood cells.

Answer 43

CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃⁻ (catalysed by carbonic anhydrase)

Question 44

What is the chloride shift and why is it important?

Answer 44

Chloride ions (Cl⁻) move into RBCs to balance the loss of negatively charged HCO₃⁻ ions and maintain electrochemical neutrality.

Question 45

What happens to the H⁺ ions produced in the RBC?

Answer 45

They bind to haemoglobin, forming haemoglobonic acid (HHb) — this buffers the pH and prevents the RBC from becoming too acidic.

Question 46

How do H⁺ ions affect oxyhaemoglobin

Answer 46

H⁺ ions cause oxyhaemoglobin to release oxygen, forming Hb and free O₂ — this is part of the Bohr effect.

Question 47

What is the Bohr effect?

Answer 47

The Bohr effect is the decrease in haemoglobin’s affinity for oxygen in the presence of high CO₂, due to more H⁺ ions being produced — causing more oxygen to be released to respiring tissues.

Question 48

Why is most CO₂ transported as HCO₃⁻ ions in the plasma?

Answer 48

Highly soluble in plasma Low CO2 concentration insice RBCs maintained, allows for **diffusion gradient**