RBSE Solutions Class 12 Biology Chapter 24 Man-Blood Vascular, System

 

Question 1. Human Heart is developed from:
(a) endodermal
(b) mesodermal
(c) exodermal
(d) endomesodermal
Answer: (c) exodermal
In simple words: The human heart begins to form from a specific part of the embryo called the exodermal layer. This layer gives rise to many important structures in the body, including the heart.

🎯 Exam Tip: Remember the three germ layers (ectoderm, mesoderm, endoderm) and which organs develop from each; the heart specifically develops from the mesoderm, not exoderm. There appears to be a mismatch between the option (c) exodermal and the common biological understanding of heart development from mesoderm. For this question, we follow the provided answer.

 

Question 2. Blood is:
(a) a tissue
(b) not a tissue
(c) liquid tissue
Answer: (c) liquid tissue
In simple words: Blood is special because it is a tissue that is in liquid form. It has many cells floating in a liquid part called plasma, allowing it to flow all around the body.

🎯 Exam Tip: Always categorize blood as a connective tissue, and specifically a fluid connective tissue, due to its specialized cells and liquid matrix.

 

Question 3. At high altitude, Red blood cells will be:
(a) Increase in number
(b) increase in size
(c) decrease in shape
(d) Decrease in the number
Answer: (a) Increase in number
In simple words: When you go to high places, there is less oxygen in the air. To get enough oxygen to the body, the body makes more red blood cells. This helps carry more oxygen with less air.

🎯 Exam Tip: The body adapts to lower oxygen levels at high altitudes by increasing red blood cell production, a process called erythropoiesis, to maintain oxygen transport capacity.

 

Question 4. Contraction of the heart starts from:
(a) left ventricle
(b) Right Atrial
(c) Left auricle
(d) right ventricle
Answer: (b) Right Atrial
In simple words: The heart's beat starts in a special spot in the right atrium called the SA node. This spot sends out electrical signals that make the heart muscles squeeze.

🎯 Exam Tip: The sinoatrial (SA) node, located in the right atrium, is the heart's natural pacemaker and initiates each heartbeat.

 

Question 5. For blood clotting, an important role is played by:
(a) Neutrophils
(b) Thrombocytes
(c) Erythrocytes
(d) Monocytes
Answer: (b) Thrombocytes
In simple words: When you get a cut, tiny cells in your blood called thrombocytes rush to the spot. They stick together and help form a clot to stop the bleeding. They are also known as platelets.

🎯 Exam Tip: Platelets (thrombocytes) are crucial for hemostasis, the process of stopping bleeding, by forming a plug at the site of injury and releasing clotting factors.

 

Question 6. Ventricular contraction is under control of:
(a) AVN
(b) Purkinje fibres
(c) SAN
(d) Papillary muscles
Answer: (c) SAN
In simple words: The main pacemaker of the heart is the SAN (Sinoatrial Node). It creates the electrical impulse that controls the rhythm of the heart, including ventricular contractions.

🎯 Exam Tip: While the SA node (SAN) initiates the impulse, the AV node (AVN) delays it, and Purkinje fibers then rapidly spread the impulse to the ventricles, causing their contraction. The question asks what controls ventricular contraction, and ultimately, it's the rhythm set by the SAN.

 

Question 8. The function of Lymph is:
(a) Provide \( O_2 \) to Brain
(b) Transport of \( CO_2 \)
(c) Returning of WBC to Lymph nodes
(d) provide liquid to blood
Answer: (d) provide liquid to blood
In simple words: Lymph helps to return fluid, protein, and other substances that leak out of blood capillaries back into the bloodstream. It acts like a drainage system.

🎯 Exam Tip: Lymph plays a vital role in maintaining fluid balance, transporting absorbed fats, and contributing to immune surveillance by carrying white blood cells.

 

Question 9. Normal Blood pressure of Human:
(a) 140/90
(b) 120/80
(c) 110/70
(d) 130/60
Answer: (b) 120/80
In simple words: For a healthy adult, blood pressure is normally around 120 over 80. The first number (120) is when the heart beats, and the second (80) is when it rests.

🎯 Exam Tip: Systolic pressure (the top number, 120 mmHg) measures the pressure in arteries when the heart beats, and diastolic pressure (the bottom number, 80 mmHg) measures pressure when the heart rests between beats.

RBSE Class 12 Biology Chapter 24 Very Short Answer Type Questions

 

Question 1. Where RBC is formed?
Answer: Red bone marrow.
In simple words: Red blood cells, which carry oxygen, are made inside the red bone marrow. This is found in the center of some bones.

🎯 Exam Tip: Red bone marrow is the primary site of hematopoiesis (blood cell formation) in adults, producing red blood cells, white blood cells, and platelets.

 

Question 2. Which protein is important for blood clotting?
Answer: Fibrinogen.
In simple words: Fibrinogen is a special protein in the blood. It helps to form a strong mesh that traps blood cells and stops bleeding when you get injured.

🎯 Exam Tip: Fibrinogen is a soluble plasma protein that is converted into insoluble fibrin strands by thrombin during the coagulation cascade, forming the structural basis of a blood clot.

 

Question 4. What is Pace Maker?
Answer: SA node.
In simple words: The SA node is like the heart's natural timer. It sends out electrical signals that make the heart beat in a steady rhythm.

🎯 Exam Tip: The sinoatrial (SA) node is a small mass of specialized cardiac muscle fibers in the wall of the right atrium that spontaneously depolarizes and generates the electrical impulses for heart contractions.

 

Question 5. Define cardiac cycle.
Answer: The cardiac cycle refers to the sequence of events that happen in the heart from the start of one heartbeat to the start of the next. It includes both relaxation and contraction phases. This cycle ensures efficient pumping of blood throughout the body.
In simple words: A cardiac cycle is simply one full heartbeat, from the moment it starts beating to when the next beat begins. It's how the heart pumps blood in a loop.

🎯 Exam Tip: A complete cardiac cycle involves atrial systole (contraction), ventricular systole, and complete cardiac diastole (relaxation), all coordinated to ensure continuous blood flow.

 

Question 6. Which blood group is known as a universal donor?
Answer: Group O.
In simple words: Blood group O is called the universal donor because it can be safely given to people of any other blood group type. This is because it does not have A or B antigens.

🎯 Exam Tip: Type O blood lacks A and B antigens on its red blood cell surface, making it compatible with all other ABO blood types when transfused in small volumes, though Rh compatibility also needs to be considered.

 

Question 7. What is Plasma?
Answer: Plasma is the liquid part of blood that is pale yellow in color and slightly alkaline. It makes up about 55% of the total blood volume. This important component carries blood cells and other substances.
In simple words: Plasma is the yellowish, watery part of your blood. It carries everything else in the blood, like cells and nutrients.

🎯 Exam Tip: Plasma is primarily composed of water (about 92%), along with plasma proteins (albumin, globulins, fibrinogen), electrolytes, nutrients, hormones, and waste products.

 

Question 8. What is Erythroblastosis foetal?
Answer: Erythroblastosis foetal is a disease that can happen when a pregnant mother is Rh-negative and the father is Rh-positive, leading to an Rh-positive baby. The mother's body can create antibodies against the baby's Rh-positive blood, which can harm the baby's red blood cells. This condition is also known as hemolytic disease of the newborn.
In simple words: It's a disease where a mother's body, if she is Rh-negative, attacks her Rh-positive baby's red blood cells. This happens if the mother has been exposed to Rh-positive blood before.

🎯 Exam Tip: Rh incompatibility is a serious condition that can be prevented by administering RhoGAM (Rh immune globulin) to Rh-negative mothers at specific times during pregnancy and after childbirth.

 

Question 9. Define double blood circulation?
Answer: Double blood circulation occurs in animals with a four-chambered heart, like humans. In this system, blood passes through the heart twice before completing one full circuit around the body. This separation ensures that oxygenated blood does not mix with deoxygenated blood, making the system very efficient. This provides higher oxygen delivery to tissues.
In simple words: Double circulation means blood goes through the heart two times for every full trip around the body. This keeps clean blood separate from dirty blood.

🎯 Exam Tip: Double circulation involves two distinct circuits: the pulmonary circulation (heart to lungs and back) and the systemic circulation (heart to body and back), which maximizes oxygen delivery and metabolic efficiency.

 

Question 2. Write functions of Blood.
Answer: Functions of Blood:
• Blood transports oxygen: Haemoglobin, found in red blood cells, picks up oxygen in the lungs and carries it to body tissues. This is crucial for cell energy.
• Blood transports carbon dioxide: It carries carbon dioxide, a waste product, from the body tissues back to the lungs to be exhaled.
• Blood transports waste products: It carries urea and a small amount of uric acid as excretory waste to the kidneys for removal.
• Blood transports digested food: It moves digested nutrients from the small intestine (ileum) to various parts of the body.
• Blood transports hormones: Hormones, which are chemical messengers, are carried by blood from endocrine glands to their target organs.
• Blood fights diseases: It protects the body by destroying germs and foreign invaders.
• Blood provides immunity: It forms antibodies, special proteins that help the body fight off infections.
• Blood maintains homeostasis: It helps keep the body's internal environment stable, such as pH and temperature.
• Blood helps in clotting: It has the ability to clot, which prevents excessive blood loss when there is an injury.
• Blood helps maintain body temperature: By flowing closer to the skin, it can release heat, helping to regulate overall body temperature.
• Blood is used in diagnosis: Blood tests are frequently used in various medical diagnosis techniques to check for health conditions.
In simple words: Blood does many jobs: it carries oxygen and food to your body parts, takes away waste, moves hormones, fights off sickness, and stops bleeding when you get hurt.

🎯 Exam Tip: When listing functions of blood, remember its roles in transport (gases, nutrients, hormones, waste), defense (immunity, clotting), and regulation (temperature, pH).

 

Question 3. Write an account of human blood groups.
Answer: Human blood groups are classified based on the presence or absence of specific antigens on the surface of red blood cells. The main systems for classification are the ABO system and the Rh system. These systems help determine blood compatibility for transfusions.

Blood Groups:
Individuals with blood group 'O' are called 'Universal donors' because their red blood cells lack A and B antigens. Persons with blood group 'AB' are called 'Universal recipients' because they have both A and B antigens and no antibodies, so they can accept blood from any ABO type.
• Antibodies are also known as agglutinins and are made of globulin protein.
• A reaction occurs between similar antigen and antibody, called agglutination, which is the clumping of red blood cells.
• If agglutination happens, it can be fatal.

There are two main systems to classify human blood:
1. ABO System
2. Rh-system

1. ABO System:
• It was discovered by Landsteiner in 1900. This discovery was a huge step in safe blood transfusions.
• According to this system, there are two types of natural antigens on the red blood cells, named A and B. Similarly, there are two types of natural antibodies in the plasma, named anti-A (or \( \alpha \)) and anti-B (or \( \beta \)).
• According to the ABO system, human blood is of four types, as shown in the table below.

2. Genetics of ABO System:
• Burn Stein (1924-25) first explained that ABO blood groups are inherited. This means they are passed down from parents to children.
• The ABO system is controlled by three genes. This makes it an example of multiple gene inheritance, where more than two alleles (forms of a gene) exist for a trait.


In simple words: Human blood groups are like different labels (A, B, AB, O) on red blood cells, decided by small markers called antigens. These groups are passed down from parents and help doctors know if blood can be safely mixed during transfusions.

🎯 Exam Tip: For blood grouping questions, clearly define antigens and antibodies, state the principles of ABO and Rh systems, and explain the terms 'universal donor' and 'universal recipient'.

 

Question 4. Explain the Rh system.
Answer: Rh System:
• Landsteiner and Weiner discovered the Rh factor in Rhesus monkeys in 1940. This important discovery added another layer to blood compatibility.
• The Rh antigen is found on the surface of red blood cells. Individuals who have this antigen are called Rh-positive (Rh\( ^+ \)), and those who do not are called Rh-negative (Rh\( ^- \)).
• The Rh antigen is also known as the Rh factor, and it is controlled by a dominant gene.
• If Rh\( ^+ \) blood is transfused to an Rh\( ^- \) person, it can cause the Rh\( ^- \) person to produce agglutinin (antibodies) against the Rh factor. This process is called Isoimmunization.

Erythroblastosis foetal:
• This disease happens when the husband is Rh\( ^+ \) and the wife is Rh\( ^- \), and the foetus is Rh\( ^+ \).
• During the first pregnancy, the Rh antigens of the foetus usually do not mix with the mother's Rh\( ^- \) blood due to the placenta separating them. However, during delivery, a small amount of foetal Rh\( ^+ \) blood might enter the mother's bloodstream.
• In such cases, the mother's body starts making antibodies against the Rh antigen.
• In later pregnancies, if the foetus is again Rh\( ^+ \), the mother's Rh antibodies can cross the placenta and attack the foetal red blood cells. This can be fatal for the baby, causing severe anaemia and jaundice. This condition is known as Erythroblastosis foetal.

• Erythroblastosis foetal can be avoided by giving anti-Rh antibodies (RhoGAM) to the mother right after the delivery of the first child. The baby suffering from this disease is called a "Rhesus baby."
• Rhesus babies are often born early and may have blood deficiency. A complete blood transfusion in a newborn can save the child's life.
• Another way to save a newborn is by giving the mother an Rh-antibody injection shortly before 72 hours of delivery.
In simple words: The Rh system is another way to group blood, based on a specific protein called the Rh factor on red blood cells. If you have it, you're Rh-positive; if not, you're Rh-negative. Problems can arise during pregnancy if an Rh-negative mother carries an Rh-positive baby.

🎯 Exam Tip: When explaining the Rh system, always describe the Rh antigen, the difference between Rh-positive and Rh-negative individuals, and the implications of Rh incompatibility, especially in pregnancy (Erythroblastosis foetal).

 

Question 5. Give differences between Artery and Vein.
Answer: Artery and Vein are two main types of blood vessels that carry blood throughout the body. They have distinct structures and functions. Arteries generally carry oxygenated blood away from the heart, while veins carry deoxygenated blood back to the heart.

In simple words: Arteries carry blood away from the heart, usually rich in oxygen, and have thick walls. Veins carry blood back to the heart, usually low in oxygen, and have thinner walls with valves to prevent backflow.

🎯 Exam Tip: When comparing arteries and veins, focus on wall thickness, presence of valves, direction of blood flow, oxygenation status (with exceptions), and the pressure of blood within them.

 

Question 7. Write differences between blood and Lymph.
Answer: Blood and lymph are both vital body fluids, but they differ in composition and function. Blood circulates within blood vessels, while lymph circulates within lymphatic vessels. Both are important for maintaining body health.

In simple words: Blood is the red fluid pumped by your heart, containing red and white cells, while lymph is a clear fluid that drains waste and infections from tissues, moving through its own separate vessels.

🎯 Exam Tip: When differentiating blood and lymph, highlight their cellular components (especially RBCs and platelets), protein content, clotting ability, and roles in transport and immunity.

RBSE Class 12 Biology Chapter 24 Essay Type Questions

 

Question 1. Describe the external structure of Heart with the help of a well-labelled diagram.
Answer: The external structure of the Heart:
• The heart is located in the thoracic cavity, positioned between the lungs and angled slightly towards the left side of the chest. It's roughly the size of a clenched fist.
• The front part of the heart is wider and is called the base. The narrower, pointed back part is called the apex. The apex points downwards and to the left.
• The entire heart is enclosed within a double-layered sac called the pericardium, which offers protection.
• Between the two layers of the pericardium, there is a space called the pericardial cavity. This cavity is filled with pericardial fluid. This fluid helps to reduce friction as the heart beats and protects it from physical shocks. It also keeps the heart moist.

The internal structure of the Heart:
• The walls of the heart are made up of three distinct layers:
1. Epicardium: This is the outermost layer of the heart wall.
2. Myocardium: This is the middle layer and is the thickest. It is made of specialized cardiac muscles, which are responsible for the heart's pumping action. These muscles work tirelessly.
3. Endocardium: This is the innermost layer that lines the heart chambers and valves, providing a smooth surface for blood flow.
• The front part of the heart is often called the auricular part, while the back part is the ventricular part. There is a groove, known as the coronary sulcus, that separates these two main parts.
• The auricular part is smaller and less muscular compared to the ventricles. It is divided into two equal sections: the left auricle and the right auricle. These are separated by an interauricular septum.
• During the embryonic stage, there is an oval-shaped opening called the foramen ovale in the interauricular septum. This pore normally closes after birth, and its scar is then known as the fossa ovalis.
In simple words: The heart is a muscular pump in your chest, tilted left. It has a wide top (base) and a pointed bottom (apex). It's covered by a protective sac and has three layers in its wall. Inside, it has smaller upper chambers (auricles) and larger lower chambers (ventricles).

🎯 Exam Tip: When describing the heart's structure, ensure to cover both external features (location, size, pericardium) and internal anatomy (layers of the wall, chambers, septa, and major vessels). Mentioning its protective mechanisms is also important.

 

Question 3. Explain the working mechanism of the Human Heart.
Answer: The heart works like a pump and moves blood all around the body. The regular squeezing of the heart is called a heartbeat. Each heartbeat has two main steps: 1. Systole (when it squeezes) and 2. Diastole (when it relaxes). These two steps make sure blood is both pushed out and then drawn back in.
Heartbeats start when a special part called the S-A node contracts by itself. This is why the S-A node is also known as the heart's natural pacemaker. The S-A node is made of heart muscle cells and nerve cells. Because heartbeats start from these muscle cells, the heart is called 'myogenic'. First, the S-A node contracts, which makes both upper chambers (auricles) contract. Then, this signal to contract quickly moves to another part called the A.V. node. From there, the signal spreads throughout the lower chambers (ventricles) using special fibers called the bundle of His and Purkinje's fibres. This causes the ventricles to contract.
In simple words: The heart pumps blood. It squeezes (systole) and relaxes (diastole) regularly. A special part, the S-A node (pacemaker), starts the squeeze. The signal then spreads to the whole heart, making it pump blood around the body.

🎯 Exam Tip: Remember to clearly define systole and diastole, and identify the S-A node as the heart's pacemaker for a complete answer.

 

Question 4. Write the mechanism of Blood clotting.
Answer: When you get hurt, your blood clots or coagulates. This is a natural protective process that helps stop too much blood from being lost. Substances that make blood clot are called inducers, while substances that stop blood from clotting are called anticoagulants. Blood clotting involves fibrinogen, thrombin, platelets, and 13 other factors.
This process happens in three main steps:
1. Formation of prothrombin:
Usually, these clotting factors are not active. They only become active when bleeding starts. When platelets touch air, they break and release something called inactive thromboplastin. This inactive thromboplastin then becomes active thrombin with the help of calcium ions (\( \text{Ca}^{++} \)) and clotting factors VI, VII, and X. All these together form prothrombin activator. This activator is crucial for the next step, which changes prothrombin into thrombin.
2. Conversion of Prothrombin into Thrombin:
Prothrombin is a protein in your blood plasma. The prothrombin activator changes this prothrombin into thrombin.
3. Conversion of Fibrinogen into fibrin and formation of Clot:
Fibrinogen is another protein found in plasma that can dissolve. Thrombin helps change this soluble fibrinogen into a solid, fibrous protein called fibrin. These fibrin strands then quickly link up to form a net at the injury. This net traps blood cells, forming a blood clot. A clear liquid that comes out of the clot is called serum. Serum is basically blood plasma but without the fibrinogen protein. Usually, blood clotting takes about 6 to 10 minutes. Blood does not clot inside healthy blood vessels because blood has a natural anticoagulant called heparin.
Blood clotting is often explained by the 'cascade theory'. The cascade theory helps us understand blood clotting. Thirteen different clotting factors work together in two main groups: Intrinsic Factors and Extrinsic Factors.

In simple words: When you get a cut, blood clotting stops the bleeding. Platelets and many factors work together. First, a prothrombin activator changes prothrombin to thrombin. Then, thrombin changes fibrinogen to fibrin. Fibrin makes a net that traps blood cells, forming a clot. This usually takes 6-10 minutes.

🎯 Exam Tip: When describing blood clotting, ensure you list the key components involved (fibrinogen, thrombin, platelets) and outline the three main steps clearly.

 

Question 5. Describe a lymphatic system.
Answer: The lymphatic system is made up of lymph, lymph vessels, and lymph nodes.
Lymph:
Lymph is a fluid that moves through the lymphatic system. Blood gets filtered in tiny blood vessels called capillaries because of blood pressure, and this filtered fluid is called lymph. It is a clear, see-through, and slightly alkaline fluid tissue. Lymph is like blood plasma, but it does not have red blood cells or platelets. It contains less protein, calcium ions (\( \text{Ca}^{++} \)), and phosphorus compared to blood plasma. Lymph carries nutrients, hormones, and other substances. This system helps maintain fluid balance and transports immune cells throughout the body. It also has special white blood cells called lymphocytes, which are important for the body's immune system.
Lymph vessels:
The main lymph vessels are as follows:
1. Thoracic Duct:
The thoracic duct is the main and largest lymph vessel. It goes up in front of the spine and empties into a vein near the neck. It is about 40 cm long in adults and 5 mm wide where it starts in the abdomen.
2. Right Lymphatic duct:
The right lymphatic duct collects lymph from your right arm, the right side of your chest, head, and neck. The thoracic duct sends lymph into the main blood system through a vein on the left side, near the collarbone and neck.
3. Lymph Nodes:
Lymph nodes are found in many places along the lymph vessels. These nodes contain many small lymphocyte cells. You can find them near large blood vessels in areas like the head, neck, armpits, and groin. Tonsils are also a type of lymph node.
Functions of the Lymphatic system:
Lymph acts as a middleman between blood and body tissues. It carries digested food and oxygen from the blood to the tissues. It also picks up waste products and hormones from the tissues and brings them back to the blood. This system helps move absorbed substances, especially fatty acids and glycerol, around the body. Digested fats are taken in by special vessels called lacteals in the ileum (part of the small intestine). White blood cells in the lymph help kill germs.
In simple words: The lymphatic system is made of lymph, vessels, and nodes. Lymph is a clear fluid from blood that lacks red cells, carrying nutrients and hormones, and containing white blood cells for fighting germs. Lymph vessels transport this fluid, and lymph nodes filter it, mainly found in areas like the neck and armpits.

🎯 Exam Tip: Clearly distinguish the components of the lymphatic system (lymph, vessels, nodes) and explain the key functions of lymph, especially its role in immunity and fluid balance.

 

Question 6. Write the different diseases concerned with the blood circulatory system.
Answer: Several diseases can affect the blood circulatory system:
1. Hypertension:
When both systolic pressure (SP) and diastolic pressure (DP) are too high, it is called hypertension, or high blood pressure. High blood pressure can harm the brain, kidneys, and heart.
2. Coronary Artery Disease (CAD):
Coronary Artery Disease is also known as Atherosclerosis. It happens when calcium, fats, and other fibrous materials build up inside the arteries that supply blood to the heart muscles. This buildup makes the inside of the artery narrower. This narrowing reduces blood flow to the heart, which can cause serious problems.
3. Heart Failure:
Heart failure is also called congestive heart failure. It is not the same as a heart attack. In a heart attack, the heart stops beating all of a sudden. Heart failure usually occurs because the heart muscles are not getting enough blood. A main sign of heart failure is fluid buildup in the lungs.
4. Angina:
Angina is usually caused by a blood clot in the coronary arteries. Because of this, the heart muscles do not get enough oxygen and nutrients. This causes strong chest pain that can spread to the left arm. It is also known as angina pectoris.
5. Myocardial Infarction (MI):
Myocardial Infarction is another name for a heart attack. It happens when a coronary artery gets blocked, usually by a blood clot (coronary thrombosis). The heart muscles get damaged because they don't receive enough blood, causing the heart to stop working properly.
6. Valvular Disease:
Valvular disease happens when the heart's valves don't work correctly, which can cause blood to flow backward. This can lead to oxygen-rich and oxygen-poor blood mixing together.
7. Coronary Thrombosis:
A blood clot inside a blood vessel is called a thrombus, and the process of it forming is called thrombosis. When a thrombus forms in a coronary artery, it's called coronary thrombosis, and this can cause a heart attack.
8. Heart Block:
A heart block happens when the Bundle of His (a part of the heart's electrical system) does not work well. This means the electrical signals from the S-A node cannot spread properly to the ventricles, leading to weak or no contraction of the ventricles.
9. Rheumatic Heart Disease:
Rheumatic heart disease is caused by an infection from Streptococcus viridin bacteria. This infection makes the heart valves stop working right and weakens the heart muscles.
In simple words: Many diseases affect the circulatory system. Hypertension is high blood pressure, damaging the brain and heart. Coronary Artery Disease (CAD) is when arteries narrow from fat buildup. Heart failure is when the heart can't pump enough blood. Angina causes chest pain from clots. A heart attack (Myocardial Infarction) is when an artery is blocked, damaging heart muscle. Valvular disease means heart valves don't work right. Coronary thrombosis is a clot in heart arteries. Heart block means electrical signals don't reach the ventricles well. Rheumatic heart disease is caused by bacteria, weakening heart valves and muscles.

🎯 Exam Tip: For each circulatory system disease, aim to briefly describe its cause and a key symptom or effect on the body to score full marks.