Choose the right sequential phenomena among following during the delivery of `O_(2)` from blood to tissue
P. Absorption of `CO_(2)` by the blood
Q. Reaction of absorbed `CO_(2) " with " H_(2)O` to from `H_(2)CO_(3)` within RBC and its conversion into `H^(+)` and `HCO_(3)^(-)` ions
R. Reaction of absorbed `CO_(2) " with " H_(2)O` in plasma to form `H_(2)CO_(3)` and its conversion into `H^(+) " and " HCO_(3)^(-)`
S. Combination of `H^(+)` with haem portion of `HbO_(2)` to release `O_(2)`
T. Comnbination of `HCO_(3)^(-)` with haem portion `HbO_(2)` to form reduced haemoglobin and release of `O_(2)`

Options

A. p,q,t
B. p,r,s
C. p,q,s
D. p,r,t

Answer

To solve the question regarding the sequential phenomena during the delivery of oxygen (O₂) from blood to tissues, we need to analyze the provided statements (P, Q, R, S, T) in the context of physiological processes.

### Step-by-Step Solution:

1. **Understanding the Process**: The delivery of oxygen from blood to tissues involves the dissociation of oxygen from hemoglobin (HbO₂) in the red blood cells (RBCs). This process is influenced by several factors, including the concentration of carbon dioxide (CO₂), temperature, and pH.

2. **Identifying the Steps**:
- **P**: Absorption of CO₂ by the blood.
- This is the first step as tissues release CO₂, which is then absorbed by the blood.
- **Q**: Reaction of absorbed CO₂ with H₂O to form H₂CO₃ within RBCs and its conversion into H⁺ and HCO₃⁻ ions.
- This is the second step. CO₂ reacts with water to form carbonic acid (H₂CO₃), which dissociates into bicarbonate (HCO₃⁻) and hydrogen ions (H⁺).
- **R**: Reaction of absorbed CO₂ with H₂O in plasma to form H₂CO₃ and its conversion into H⁺ and HCO₃⁻.
- This statement is incorrect in the context of the sequence as the majority of CO₂ is converted in the RBCs, not in plasma.
- **S**: Combination of H⁺ with the heme portion of HbO₂ to release O₂.
- This is the third step. The increase in H⁺ concentration (lower pH) favors the release of O₂ from hemoglobin.
- **T**: Combination of HCO₃⁻ with the heme portion of HbO₂ to form reduced hemoglobin and release of O₂.
- This statement is incorrect as it is the H⁺ ions that facilitate the release of O₂, not HCO₃⁻.

3. **Correct Sequence**: Based on the analysis above, the correct sequence of events during the delivery of O₂ from blood to tissues is:
- **P** (Absorption of CO₂ by the blood)
- **Q** (Reaction of absorbed CO₂ with H₂O to form H₂CO₃ and its conversion into H⁺ and HCO₃⁻ ions)
- **S** (Combination of H⁺ with the heme portion of HbO₂ to release O₂)

Thus, the correct answer is **P, Q, S**.