NEET Practice Questions (MCQs) with Answers & Solutions

While not explicitly stated in the provided text as the reason for the sigmoidal shape, the cooperative binding of oxygen to haemoglobin (where binding of one $O_2$ molecule increases the affinity for subsequent $O_2$ molecules) is the well-known biological explanation for the sigmoidal pattern of the oxygen dissociation curve. The text only asks to 'suggest any reason for its sigmoidal pattern' as an exercise, implying it's a concept to be understood.

A shift to the right indicates decreased affinity of haemoglobin for oxygen, favouring dissociation. The NCERT states that high $pCO_2$ and high $H^+$ concentration (which corresponds to low pH) favor dissociation in tissues. Therefore, an increase in $H^+$ concentration would cause a right shift.

The NCERT states, 'About 97 per cent of $O_2$ is transported by RBCs in the blood.'

The NCERT mentions, 'About 97 per cent of $O_2$ is transported by RBCs in the blood.' Erythrocytes are Red Blood Cells (RBCs).

The NCERT states, 'Partial pressure of $CO_2$, hydrogen ion concentration and temperature are the other factors which can interfere with this binding.'

This statement directly reflects the dynamic nature of oxygen-haemoglobin binding, where affinity changes based on local conditions ($pO_2$, $pCO_2$, H+ concentration, temperature). This is the core concept explained by the oxygen dissociation curve and its shifts.

A leftward shift of the oxygen dissociation curve signifies that for a given $pO_2$, haemoglobin is more saturated with oxygen, meaning it has a higher affinity for oxygen and holds onto it more tightly.

According to the NCERT text, 'Gill slits are separate and without operculum (gill cover)' in Class Chondrichthyes. Therefore, the presence of an operculum is not a characteristic of this class.

The NCERT states, 'The skin is tough, containing minute placoid scales' for Class Chondrichthyes. Teeth are also modified placoid scales.

The NCERT text explicitly states, 'Due to the absence of air bladder, they have to swim constantly to avoid sinking.' This highlights a key adaptation of cartilaginous fish.