This MCQ module is based on: Blood Plasma Formed Elements
TOPIC 66 OF 90
Blood Plasma Formed Elements
🎓 Class 11
Biology
CBSE
Theory
Ch 15 – Body Fluids and Circulation
⏱ ~14 min
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Blood — Plasma and the Formed Elements
All living cells have to be provided with nutrients, O₂ and other essential substances, and the waste or harmful substances produced have to be removed continuously for healthy functioning. Simple organisms manage this by moving the medium itself — sponges and coelenterates circulate water from their bodies to transport such materials. More complex animals need a dedicated fluid, and blood is the most commonly used body fluid for the purpose. Another fluid, lymph, also helps in the transport of certain substances.
15.1 Blood
Blood is a special connective tissue consisting of a fluid matrix, plasma, and formed elements.
Why blood counts as a connective tissue. The classification surprises students, but it follows the standard definition from Chapter 7: a connective tissue is mesodermal in origin and consists of cells suspended in an extracellular matrix. Blood satisfies both — its formed elements are the cells and plasma is the matrix. The only unusual feature is that the matrix happens to be a liquid rather than the jelly of areolar tissue or the solid ground substance of bone. Its job, too, is a connective one: it links every tissue of the body to every other.
| Component | Share of blood | What it is |
|---|---|---|
| Plasma | Nearly 55 per cent | The fluid matrix |
| Formed elements | Nearly 45 per cent | Erythrocytes, leucocytes and platelets |
15.1.1 Plasma
Plasma is a straw coloured, viscous fluid constituting nearly 55 per cent of the blood. 90–92 per cent of plasma is water and proteins contribute 6–8 per cent of it.
The three major plasma proteins and their jobs
| Protein | Function |
|---|---|
| Fibrinogen | Needed for clotting or coagulation of blood |
| Globulins | Primarily involved in defense mechanisms of the body |
| Albumins | Help in osmotic balance |
What else plasma carries
- Small amounts of minerals like Na⁺, Ca⁺⁺, Mg⁺⁺, HCO₃⁻, Cl⁻, etc.
- Glucose, amino acids, lipids, etc. — present in the plasma as they are always in transit in the body.
- Factors for coagulation or clotting of blood, also present in the plasma in an inactive form.
Serum. Plasma without the clotting factors is called serum.
Why the clotting factors must be inactive. Notice the phrase “in an inactive form”. If the factors circulated in an active state, blood would clot inside intact vessels and kill the organism at once. The whole coagulation system is therefore built as a set of loaded but unfired switches, waiting for an injury signal — which is exactly the cascade we take up in Part 2.
15.1.2 Formed Elements
Erythrocytes, leucocytes and platelets are collectively called formed elements, and they constitute nearly 45 per cent of the blood.
Erythrocytes — red blood cells
- Erythrocytes or red blood cells (RBC) are the most abundant of all the cells in blood.
- A healthy adult man has, on an average, 5 millions to 5.5 millions of RBCs mm⁻³ of blood.
- RBCs are formed in the red bone marrow in the adults.
- RBCs are devoid of nucleus in most of the mammals and are biconcave in shape.
- They have a red coloured, iron containing complex protein called haemoglobin, hence the colour and name of these cells.
- A healthy individual has 12–16 gms of haemoglobin in every 100 ml of blood. These molecules play a significant role in transport of respiratory gases.
- RBCs have an average life span of 120 days, after which they are destroyed in the spleen (graveyard of RBCs).
Two features worth connecting to function. The biconcave shape gives a far larger surface area for its volume than a sphere would, and keeps no part of the interior far from the membrane — ideal for a cell whose entire job is loading and unloading a gas by diffusion. The absence of a nucleus frees up space for still more haemoglobin and removes the cell's own oxygen-consuming machinery. The cost is that a cell with no nucleus cannot repair itself, which is exactly why its life span is limited to about 120 days.
Leucocytes — white blood cells
Leucocytes are also known as white blood cells (WBC), as they are colourless due to the lack of haemoglobin. They are nucleated and are relatively lesser in number, which averages 6000–8000 mm⁻³ of blood. Leucocytes are generally short lived.
Two main categories. Granulocytes — neutrophils, eosinophils and basophils. Agranulocytes — lymphocytes and monocytes.
| WBC | Category | Percentage of total WBCs | Function |
|---|---|---|---|
| Neutrophils | Granulocyte | 60–65% — the most abundant | Phagocytic cells which destroy foreign organisms entering the body |
| Eosinophils | Granulocyte | 2–3% | Resist infections and are also associated with allergic reactions |
| Basophils | Granulocyte | 0.5–1% — the least | Secrete histamine, serotonin, heparin, etc., and are involved in inflammatory reactions |
| Lymphocytes | Agranulocyte | 20–25% | Of two major types, ‘B’ and ‘T’ forms; both are responsible for immune responses of the body |
| Monocytes | Agranulocyte | 6–8% | Phagocytic cells which destroy foreign organisms entering the body |
Platelets — thrombocytes
- Platelets, also called thrombocytes, are cell fragments produced from megakaryocytes (special cells in the bone marrow).
- Blood normally contains 1,50,000–3,50,000 platelets mm⁻³.
- Platelets can release a variety of substances, most of which are involved in the coagulation or clotting of blood.
- A reduction in their number can lead to clotting disorders, which will lead to excessive loss of blood from the body.
📐 Activity 15.1 — Examine a blood smear and count the leucocytes
What to do. Study a prepared, stained human blood smear under the high power of a microscope. Systematically scan across the slide and, for the first hundred white cells you meet, tally which type each one is. Use the shape of the nucleus and the presence or absence of granules to decide. Then convert your tallies into percentages and compare them with the table above.
Predict: which WBC will you meet most often, and which will you struggle to find at all? Also predict roughly how many RBCs you will see for every one WBC.
What you should find. Roughly 60 to 65 neutrophils out of your hundred — they are the most abundant cells of the total WBCs. Then about 20 to 25 lymphocytes, small cells with a large round nucleus filling most of the cell. About 6 to 8 monocytes, noticeably larger with a kidney-shaped nucleus. About 2 to 3 eosinophils, with coarse granules that take up the stain strongly. And you may well find no basophils at all in a hundred cells, since they are only 0.5 to 1 per cent — you would need to scan several hundred cells to be confident of meeting one.
The RBC : WBC ratio. RBCs number 5 to 5.5 million mm⁻³ and WBCs only 6000 to 8000 mm⁻³. That is a ratio of roughly 700 : 1 — so you must sweep past hundreds of red cells to find a single white one. This is exactly why a smear looks overwhelmingly red under the microscope.
How to tell the cells apart. First ask whether granules are visible in the cytoplasm: if yes it is a granulocyte (neutrophil, eosinophil or basophil); if not, an agranulocyte (lymphocyte or monocyte). Among granulocytes, the neutrophil's nucleus is lobed, the eosinophil's granules are large and uniform, the basophil's stain darkest. Among agranulocytes, the lymphocyte is small with little cytoplasm, the monocyte large with a bean-shaped nucleus.
Clinical relevance. This count is a real diagnostic test, the differential leucocyte count. A rise in neutrophils suggests bacterial infection; a rise in eosinophils suggests an allergic reaction or a parasitic infestation, consistent with eosinophils being associated with allergic reactions; a rise in lymphocytes suggests a viral infection.
🎯 Interactive: Pick a blood component
Amount / count: Nearly 55 per cent of blood
A straw coloured, viscous fluid. 90 to 92 per cent of plasma is water and proteins contribute 6 to 8 per cent. It also carries minerals, glucose, amino acids and lipids in transit, and the clotting factors in an inactive form.
🎯 Competency-Based Questions
Scenario: Four blood reports come back from a laboratory. Patient P has haemoglobin of 8 g per 100 mL. Patient Q has a platelet count of 40,000 mm⁻³. Patient R has a neutrophil count of 85 per cent of total WBCs. Patient S has an eosinophil count of 12 per cent.
Q1. Which values are abnormal, and what are the normal ranges? L3 Apply
All four are abnormal. P: normal is 12–16 g of haemoglobin in every 100 mL of blood, so 8 g is well below normal. Q: normal is 1,50,000–3,50,000 platelets mm⁻³, so 40,000 is very low. R: neutrophils are normally 60–65 per cent of total WBCs, so 85 per cent is raised. S: eosinophils are normally 2–3 per cent, so 12 per cent is markedly raised.
Q2. What clinical problem would you expect in patient Q, and why? L3 Apply
A bleeding tendency. Platelets can release a variety of substances, most of which are involved in the coagulation or clotting of blood, and a reduction in their number can lead to clotting disorders, which will lead to excessive loss of blood from the body. With a count less than a third of the lower normal limit, even minor injuries would bleed for far longer than usual, and spontaneous bruising may appear.
Q3. Fill in the blanks: Plasma constitutes ______ per cent of blood, of which ______ per cent is water and ______ per cent proteins. The formed elements constitute ______ per cent. Plasma without clotting factors is called ______. L1 Remember
nearly 55; 90–92; 6–8; nearly 45; serum.
Q4. Patients R and S both have raised WBC fractions, yet their likely causes are quite different. Analyse. L4 Analyse
Because the two cells do different jobs. Neutrophils are phagocytic cells which destroy foreign organisms entering the body, so a rise in them points to an acute infection by invading organisms, typically bacterial — the body is manufacturing more of the cells that engulf microbes. Eosinophils resist infections and are also associated with allergic reactions, so a rise in them points to an allergic condition or a parasitic infestation rather than an ordinary bacterial infection. This is why a laboratory reports not just a total WBC count but the proportions — the pattern of which cell has risen is more informative than the total.
Q5. “Blood cannot be a connective tissue, because connective tissue holds things together and blood is a liquid that flows.” Evaluate. L5 Evaluate
The objection rests on two misunderstandings, one about the definition and one about the word “connective”.
(i) The definition is structural, not mechanical. A connective tissue is defined by cells suspended in an extracellular matrix, together with a mesodermal origin — not by whether it binds structures physically. Blood is a special connective tissue consisting of a fluid matrix, plasma, and formed elements: the formed elements are the cells, plasma is the matrix. The criterion is met exactly.
(ii) A matrix need not be solid. Compare the range within connective tissue itself: bone has a hard mineralised matrix, cartilage a firm one, areolar tissue a soft jelly, and blood a liquid. Fluidity places blood at one end of a continuum, not outside the category. NCERT signals this by calling it a special connective tissue.
(iii) Blood does connect. It is the tissue that links every organ to every other — carrying nutrients, O₂ and other essential substances to the cells and taking wastes away, delivering hormones, and distributing heat and immune cells. Functionally it is the most thoroughly connective tissue in the body.
A fair verdict: the objection would be sound if “connective” meant “binding”, but the histological definition rests on cells in a matrix of mesodermal origin, which blood satisfies. The lesson is a general one — biological categories are defined by stated criteria, not by what their names suggest.
(i) The definition is structural, not mechanical. A connective tissue is defined by cells suspended in an extracellular matrix, together with a mesodermal origin — not by whether it binds structures physically. Blood is a special connective tissue consisting of a fluid matrix, plasma, and formed elements: the formed elements are the cells, plasma is the matrix. The criterion is met exactly.
(ii) A matrix need not be solid. Compare the range within connective tissue itself: bone has a hard mineralised matrix, cartilage a firm one, areolar tissue a soft jelly, and blood a liquid. Fluidity places blood at one end of a continuum, not outside the category. NCERT signals this by calling it a special connective tissue.
(iii) Blood does connect. It is the tissue that links every organ to every other — carrying nutrients, O₂ and other essential substances to the cells and taking wastes away, delivering hormones, and distributing heat and immune cells. Functionally it is the most thoroughly connective tissue in the body.
A fair verdict: the objection would be sound if “connective” meant “binding”, but the histological definition rests on cells in a matrix of mesodermal origin, which blood satisfies. The lesson is a general one — biological categories are defined by stated criteria, not by what their names suggest.
🧠 Assertion–Reason Questions
For each pair choose: (A) Both A and R are true and R is the correct explanation of A. (B) Both A and R are true but R is not the correct explanation of A. (C) A is true but R is false. (D) A is false but R is true.
Assertion (A): RBCs have a limited life span of about 120 days.
Reason (R): RBCs are devoid of a nucleus in most mammals, so they cannot repair themselves or make new proteins.
Answer: A. Both are true and the reason explains the assertion. The loss of the nucleus makes room for more haemoglobin but leaves the cell unable to renew itself, and the worn-out cells are destroyed in the spleen.
Assertion (A): Blood does not clot inside intact blood vessels.
Reason (R): The factors for coagulation of blood are present in the plasma in an inactive form.
Answer: A. Both are true and the reason is the correct explanation. The clotting machinery is present everywhere in the plasma but switched off until an injury activates it.
Assertion (A): Basophils are the most abundant of the white blood cells.
Reason (R): Basophils secrete histamine, serotonin and heparin, and are involved in inflammatory reactions.
Answer: D. The assertion is false — basophils are the least abundant at 0.5–1 per cent; neutrophils are the most abundant at 60–65 per cent. The reason correctly states what basophils do.
Coming next. Part 2 takes up Sections 15.1.3 to 15.2 — ABO and Rh blood grouping with donor compatibility and erythroblastosis foetalis, the cascade of blood coagulation, and lymph as the tissue fluid.
Frequently Asked Questions - Blood — Plasma and Formed Elements
Why is blood considered a connective tissue?
Because it consists of cells suspended in an extracellular matrix and is mesodermal in origin, which is the definition of a connective tissue. Blood is a special connective tissue in which the matrix, plasma, happens to be a fluid rather than a jelly or a solid.
What is plasma made of?
Plasma is a straw coloured viscous fluid making up nearly 55 per cent of blood. 90 to 92 per cent of it is water and 6 to 8 per cent proteins, chiefly fibrinogen, globulins and albumins. It also contains minerals such as sodium, calcium, magnesium, bicarbonate and chloride, plus glucose, amino acids and lipids in transit, and the clotting factors in inactive form.
What are the functions of the three major plasma proteins?
Fibrinogens are needed for clotting or coagulation of blood. Globulins are primarily involved in the defense mechanisms of the body. Albumins help in osmotic balance.
What is serum?
Plasma without the clotting factors. Since the coagulation factors are present in plasma in an inactive form, removing them leaves a fluid that cannot clot.
What are the formed elements of blood?
Erythrocytes or red blood cells, leucocytes or white blood cells, and platelets or thrombocytes. Together they constitute nearly 45 per cent of the blood.
Describe the red blood cells.
RBCs are the most abundant cells in blood, 5 to 5.5 million per cubic millimetre in a healthy adult man. They are formed in the red bone marrow, are devoid of a nucleus in most mammals and are biconcave. They carry haemoglobin, an iron containing complex protein, at 12 to 16 g per 100 mL of blood, and live about 120 days before being destroyed in the spleen.
What are the types of leucocytes and their percentages?
Granulocytes are neutrophils at 60 to 65 per cent, eosinophils at 2 to 3 per cent and basophils at 0.5 to 1 per cent. Agranulocytes are lymphocytes at 20 to 25 per cent and monocytes at 6 to 8 per cent. Total WBC count averages 6000 to 8000 per cubic millimetre.
What do the different white blood cells do?
Neutrophils and monocytes are phagocytic cells that destroy foreign organisms entering the body. Basophils secrete histamine, serotonin and heparin and are involved in inflammatory reactions. Eosinophils resist infections and are associated with allergic reactions. B and T lymphocytes are responsible for the immune responses of the body.
What are platelets and what happens if their number falls?
Platelets, or thrombocytes, are cell fragments produced from megakaryocytes in the bone marrow, numbering 1,50,000 to 3,50,000 per cubic millimetre. They release substances involved in coagulation, so a reduction in their number leads to clotting disorders and excessive loss of blood from the body.
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