Answer:
Structure of the Human Heart:
The human heart is a muscular pump located in the thoracic cavity (chest), slightly to the left of the midline, between the two lungs. It is about the size of a clenched fist and weighs approximately 300 grams in adults.
Protective Coverings:
- Pericardium: A double-walled fibrous sac surrounding the heart. The outer fibrous pericardium protects the heart. The inner serous pericardium has two layers:
- Parietal layer (outer) — lines the fibrous pericardium
- Visceral layer / Epicardium (inner) — covers the heart surface
- Pericardial fluid fills the space between, reducing friction during heartbeats.
Chambers of the Heart: The heart has four chambers: 1. Right Atrium — receives deoxygenated blood from the body via the superior and inferior vena cava. Has the sinoatrial (SA) node (pacemaker). 2. Right Ventricle — pumps deoxygenated blood to the lungs via the pulmonary artery. 3. Left Atrium — receives oxygenated blood from the lungs via the four pulmonary veins. 4. Left Ventricle — pumps oxygenated blood to the entire body via the aorta. Has the thickest wall because it must generate the highest pressure.
Valves of the Heart:
- Tricuspid Valve (Right Atrioventricular Valve): Between the right atrium and right ventricle. Has three cusps.
- Bicuspid (Mitral) Valve (Left Atrioventricular Valve): Between the left atrium and left ventricle. Has two cusps.
- Pulmonary Semilunar Valve: At the base of the pulmonary artery. Prevents backflow from pulmonary artery to the right ventricle.
- Aortic Semilunar Valve: At the base of the aorta. Prevents backflow from aorta to the left ventricle.
Valves function: They prevent the backflow of blood and ensure one-way flow.
Septa:
- Interatrial septum: Separates the two atria
- Interventricular septum: Separates the two ventricles
Double Circulation:
Double circulation means blood passes through the heart twice during one complete circuit of the body. It consists of two components:
Answer:
Blood is a fluid connective tissue that flows through the blood vessels. It constitutes about 7–8% of body weight. In an adult, blood volume is approximately 5 litres.
Composition of Blood:
Blood consists of two main components:
A. Plasma (55% of blood volume): Plasma is the straw-coloured, slightly alkaline (pH 7.4) liquid portion of blood.
Composition of plasma:
- Water: 90–92%
- Plasma proteins (7%):
- Albumin — maintains osmotic pressure, transports fatty acids and hormones
- Globulins — includes immunoglobulins (antibodies) for immunity
- Fibrinogen — essential for blood clotting
- Prothrombin — for blood clotting
- Inorganic salts: Na+, K+, Ca2+, Cl–, HCO3– — maintain osmotic balance and pH
- Nutrients: glucose, amino acids, fatty acids, vitamins
- Hormones: transported dissolved in plasma
- Gases: dissolved O2, CO2, N2
- Waste products: urea, uric acid, creatinine
- Serum: Plasma minus clotting factors = serum
B. Formed Elements (45% of blood volume):
Functions of Blood:
Transport Functions: 1. Carries O2 from lungs to all body cells (via haemoglobin in RBCs) 2. Carries CO2 from body cells to lungs (70% as bicarbonate ions in plasma; 20% bound to haemoglobin) 3. Transports digested nutrients (glucose, amino acids, fatty acids) from intestine to liver and body cells 4. Transports hormones from endocrine glands to target organs 5. Carries waste products (urea, creatinine) from tissues to kidneys for excretion
Regulatory Functions: 6. Regulates body temperature by distributing heat evenly throughout the body 7. Maintains the pH of body fluids (buffer system: HCO3–/H2CO3) 8. Maintains osmotic pressure of body fluids
Protective Functions: 9. WBCs defend against infections (immunity) 10. Platelets and clotting factors prevent blood loss (haemostasis) 11. Antibodies in plasma provide humoral immunity
Answer:
ABO Blood Group System:
The ABO blood group system was discovered by Karl Landsteiner in 1900 (Nobel Prize 1930). Blood is classified based on the presence or absence of specific antigens (agglutinogens) on the surface of red blood cells and antibodies (agglutinins) in the plasma.
Antigens and Antibodies:
- Antigen A (type A sugar chain) on RBC surface
- Antigen B (type B sugar chain) on RBC surface
- Antibody anti-A (agglutinin α) in plasma — causes agglutination (clumping) of RBCs with antigen A
- Antibody anti-B (agglutinin β) in plasma — causes agglutination of RBCs with antigen B
| Blood Group | Antigen on RBC | Antibody in Plasma | Can Donate to | Can Receive from |
|---|---|---|---|---|
| A | A | Anti-B | A, AB | A, O |
| B | B | Anti-A | B, AB | B, O |
| AB | A and B | None (no antibodies) | AB only | A, B, AB, O |
| O | None | Anti-A and Anti-B | A, B, AB, O | O only |
Universal Donor: Blood group O — no antigens on RBCs, so anti-A and anti-B antibodies in the recipient's blood will not cause agglutination.
Universal Recipient: Blood group AB — no antibodies in plasma, so no agglutination occurs regardless of the donor's blood group.
Genetic Basis:
- Controlled by three alleles: I^A, I^B, and i
- I^A and I^B are codominant; i is recessive
- Blood group A: I^A I^A or I^A i
- Blood group B: I^B I^B or I^B i
- Blood group AB: I^A I^B
- Blood group O: ii
Rh Factor:
- Discovered by Karl Landsteiner and Alexander Wiener in 1940
- Named after the Rhesus monkey (Macaca rhesus) in which it was first identified
- Based on the presence or absence of a specific protein (Rh antigen / D antigen) on RBC surface:
- Rh positive (Rh+): Rh antigen present on RBCs (about 85% of population)
- Rh negative (Rh–): Rh antigen absent on RBCs (about 15% of population)
- Unlike ABO system, Rh-negative individuals do NOT naturally have anti-Rh antibodies. They develop them only after exposure to Rh-positive blood.
Erythroblastosis Foetalis (Rh Incompatibility):
- Occurs when an Rh-negative mother carries an Rh-positive foetus (second pregnancy onwards)
- During first delivery, foetal Rh+ blood enters mother's circulation → mother produces anti-Rh antibodies
- In the second pregnancy with an Rh+ foetus, maternal anti-Rh antibodies cross the placenta → attack foetal RBCs → haemolytic disease of the newborn
- Prevention: Inject anti-Rh antibodies (RhoGAM) to Rh-negative mother within 72 hours of delivery
Significance in Blood Transfusion:
1. Mismatched blood transfusion causes agglutination → clumping of RBCs → blocks blood vessels → kidney failure → death 2. Before transfusion, blood grouping (ABO and Rh) and cross-matching are mandatory 3. In emergencies, O-negative blood can be given (universal donor) 4. AB-positive individuals can receive any blood (universal recipient)
Answer:
Plants absorb water and dissolved minerals from the soil through roots and transport them to all parts of the plant. This upward movement occurs through the xylem tissue.
Absorption of Water:
Water is absorbed from the soil by root hair cells through osmosis (passive diffusion across a semi-permeable membrane from a region of lower solute concentration to higher solute concentration). Root hair cells have large vacuoles with high solute concentration, creating a water potential gradient.
Transport of Water Through the Plant:
Once absorbed, water moves from root hair cells through the cortex into the xylem in two pathways:
1. Apoplastic Pathway: Water moves through the non-living parts (cell walls and intercellular spaces) without crossing cell membranes. Faster route. Blocked at the endodermis by the Casparian strip (a band of suberin that prevents further apoplastic movement).
2. Symplastic Pathway: Water moves through the living parts (cytoplasm and plasmodesmata — cytoplasmic connections between cells). Slower route but allows selective control.
Forces Responsible for Upward Movement of Water (Ascent of Sap):
Transport of Minerals:
- Minerals are absorbed from soil solution by active transport (requires energy/ATP)
- They enter the xylem and are carried upward along with water
- Unlike water transport (physical process), mineral absorption requires metabolic energy
Translocation (Transport of Organic Solutes):
- Photosynthesis products (mainly sucrose) are transported from leaves (source) to other parts (sink — roots, fruits, seeds) through the phloem tissue
- Mechanism: Pressure Flow Theory (Mass Flow Hypothesis) — proposed by Ernst Munch
- Sugar is actively loaded into phloem sieve tubes at the source (leaf) → water enters sieve tubes by osmosis → turgor pressure increases at source end
- At the sink (root, fruit), sugar is unloaded → water moves out → turgor pressure decreases
- This pressure difference drives mass flow of sugary solution from source to sink
- Phloem transport is bidirectional (upward and downward), unlike xylem (unidirectional upward)
Answer:
The lymphatic system is a network of tissues, organs, and vessels that works alongside the cardiovascular system. It is a one-way drainage system that collects excess interstitial fluid (fluid that leaks out of blood capillaries into tissues) and returns it to the bloodstream.
Components of the Lymphatic System:
Functions of the Lymphatic System:
1. Fluid Balance: Returns excess interstitial fluid (about 3 litres per day) to the blood. Without this, tissue swelling (oedema) would occur.
2. Fat Absorption: Lacteals in intestinal villi absorb dietary fats (as chylomicrons) and transport them to the bloodstream, bypassing the portal circulation.
3. Immune Defence:
- Lymph nodes filter pathogens and foreign particles from lymph
- Lymphocytes in lymph nodes mount specific immune responses
- T cells and B cells are activated in lymph nodes when they encounter antigens
4. Transport of Immune Cells: Lymph carries lymphocytes and antibodies throughout the body.
5. Removal of Waste: Carries away metabolic waste products from tissues to the bloodstream for eventual excretion.
Clinical Significance:
- Lymphoedema: Blockage of lymph vessels (e.g., by filaria worms — elephantiasis) causes severe swelling of limbs
- Lymphoma: Cancer of lymphocytes (Hodgkin's and non-Hodgkin's lymphoma)
- Metastasis: Cancer cells spread through lymphatic vessels to distant parts of the body (hence lymph nodes are checked during cancer staging)
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