Q.A mature mammalian red blood cell (erythrocyte) is structurally unusual among vertebrate blood cells because it

Erythropoietin, the peptide hormone that stimulates RBC (erythrocyte) production, is produced mainly by the kidneys.

Erythropoietin is a glycoprotein hormone that stimulates the process of erythropoiesis (formation of red blood cells) in the bone marrow. It is secreted mainly by specialised cells in the kidney (in response to low oxygen levels/hypoxia), with a small additional contribution from the liver. A fall in RBC count or oxygen supply to tissues triggers increased erythropoietin release, which in turn increases RBC production to restore normal oxygen-carrying capacity.

Moving from a high-altitude, low-oxygen environment to the oxygen-richer plains reverses the earlier high-altitude acclimatisation, so both haemoglobin content and RBC count fall back towards normal over months.

At high altitude, the atmospheric pressure - and hence the partial pressure of oxygen - is lower than at sea level/plains. The body detects this reduced oxygen availability (hypoxia) and responds by secreting more erythropoietin from the kidneys, which stimulates the bone marrow to produce extra red blood cells; haemoglobin content also rises. This is the well-known high-altitude acclimatisation response, and it is why people who live at high altitude typically have a higher RBC count and haemoglobin level than people living in the plains.

When such a person migrates down to the plains, where oxygen is far more available, the extra RBCs and haemoglobin are no longer required for adequate oxygen delivery. Over a period of months the erythropoietin-driven stimulus fades, and RBC production returns to a normal rate while older excess RBCs are gradually removed from circulation - so both haemoglobin quantity and RBC count fall together, moving toward the values typical of people who have always lived in the plains.

This statement is False: haemoglobin's oxygen-carrying metal is iron, not copper (copper is instead found in a different respiratory pigment, haemocyanin, used by some invertebrates).

Haemoglobin is the red, iron-containing respiratory pigment present inside red blood cells of humans and most vertebrates. Each haemoglobin molecule is made of four polypeptide (globin) chains, each associated with a haem group that holds a central ferrous (Fe2+) ion; it is this iron ion that reversibly binds and releases molecular oxygen, giving blood its red colour and its oxygen-carrying capacity. Copper, by contrast, is the metal found in haemocyanin, a blue, copper-containing respiratory pigment used by some molluscs and arthropods (e.g. snails, crabs) instead of haemoglobin - but this is not present in human blood.

RBCs are made in bone marrow.

In adult mammals, erythrocytes (RBCs) are formed in the red bone marrow (haematopoiesis). The liver and spleen make RBCs mainly during the foetal stage; the spleen later acts as a graveyard of old RBCs. So bone marrow is the site of RBC formation.

Red blood cells are also called erythrocytes.

Red blood cells are biconcave, enucleate (in mammals) blood cells packed with the red pigment haemoglobin, which binds and transports oxygen. Their scientific name, erythrocyte, comes from Greek 'erythros' meaning red and 'kytos' meaning cell/vessel. This is distinct from leucocytes (white blood cells, option b — the immune cells), platelets/thrombocytes (option c — cell fragments involved in clotting), and neutrophils (option d — one specific type of leucocyte, a granulocyte active in fighting infection).

Haemoglobin content of blood is measured with a haemoglobinometer, commonly Sahli's haemoglobinometer.

Haemoglobin is the iron-containing, oxygen-carrying pigment present in red blood cells. Its concentration in blood (expressed in g/dL) is an important clinical and physiological measurement, since low haemoglobin indicates anaemia.

The classical instrument used for this is Sahli's haemoglobinometer. A small, measured sample of blood is drawn into a graduated tube already containing a reagent (dilute hydrochloric acid), which converts haemoglobin into acid haematin, a brown-coloured compound. Distilled water is then added drop by drop until the colour of the solution matches a fixed brown-coloured standard on the instrument's comparator block. The level reached on the graduated scale directly gives the haemoglobin concentration in g/dL (or in a percentage scale relative to a normal value).

Modern laboratories also use automated photoelectric colorimeters/haemoglobinometers, but the underlying principle taught at this level is Sahli's method.

Haemoglobin, the iron-containing respiratory pigment in RBCs, transports oxygen in blood.

Haemoglobin is a conjugated protein made of four polypeptide (globin) chains, each bound to a heme group containing an iron (Fe2+) ion. Oxygen binds reversibly to the iron of the heme group in the lungs (forming oxyhaemoglobin) and is released to tissues where oxygen concentration is low, enabling efficient O2 transport throughout the body.

Mature mammalian RBCs (erythrocytes) are unique among vertebrate blood cells in losing their nucleus, an adaptation that maximises space for haemoglobin.

During erythropoiesis in mammals, the developing red blood cell extrudes its nucleus just before entering the bloodstream, so the mature, circulating RBC is a biconcave, non-nucleated cell filled with haemoglobin. This loss of the nucleus (and most organelles) frees up more room for haemoglobin, improving the cell's oxygen-carrying efficiency, and also gives it its flexible biconcave shape for squeezing through narrow capillaries.

White blood cells (WBCs), in contrast, retain a prominent nucleus throughout their life (needed for their immune functions), so "WBC", "Thrombocytes" and "All the above" are not correct as a general statement about nucleation for this level.