Samacheer Class 10 Science - Transportation in Plants and Circulation in Animals

The human heart is enclosed within a protective double-layered sac known as the pericardium. The outer layer is the fibrous pericardium, a tough, inelastic sac that anchors the heart and prevents overfilling. Inside this lies the serous pericardium, which is further divided into two sub-layers. The parietal layer of the serous pericardium lines the inner surface of the fibrous pericardium, while the visceral layer, also called the epicardium, is directly adhered to the surface of the heart muscle. Between these two layers of the serous pericardium is the pericardial cavity, which contains a small amount of pericardial fluid. This fluid acts as a lubricant, reducing friction as the heart beats and allowing the layers to glide smoothly against each other.

The characteristic red color of blood is primarily due to the presence of a protein called hemoglobin, which is found within red blood cells (erythrocytes). Hemoglobin is a complex molecule containing iron, and it is this iron atom that binds with oxygen in the lungs. When oxygen binds to hemoglobin, it forms oxyhemoglobin, which has a bright red color. In the tissues, where oxygen is released for cellular respiration, hemoglobin becomes deoxygenated, forming deoxyhemoglobin, which has a darker, purplish-red hue. The abundance of red blood cells, each packed with hemoglobin, gives the blood its overall red appearance.

The lymph, a fluid that circulates in the lymphatic system, contains various types of cells, but its most significant cellular component consists of lymphocytes, which are a type of white blood corpuscle (leukocyte). Lymphocytes play a critical role in the immune system, identifying and neutralizing pathogens such as bacteria, viruses, and other foreign substances. While lymph also contains other types of white blood cells, such as monocytes and granulocytes, lymphocytes are particularly abundant and are the primary mediators of adaptive immunity. These cells are crucial for defending the body against infections and diseases.

The heart valves that are associated with the major arteries leaving the ventricles are known as the semilunar valves. There are two such valves: the aortic semilunar valve, located at the origin of the aorta, and the pulmonary semilunar valve, situated at the beginning of the pulmonary artery. These valves are shaped like half-moons and open outward to allow blood to be pumped from the ventricles into the arteries during ventricular contraction (systole). When the ventricles relax (diastole), the backflow of blood causes these valves to close, preventing blood from returning to the ventricles and ensuring unidirectional blood flow.

The artery that supplies oxygenated blood directly to the heart muscle itself is called the coronary artery. The heart, being a vital organ that works continuously, requires a constant and rich supply of oxygen and nutrients to function properly. The coronary arteries branch off from the aorta, the main artery carrying oxygenated blood from the left ventricle to the rest of the body, shortly after it leaves the heart. These arteries then spread across the surface of the heart, delivering blood to the cardiac muscle tissue. Blockage or narrowing of the coronary arteries can lead to serious conditions like angina or myocardial infarction (heart attack).

Cohesion refers to the attractive force that exists between molecules of the same substance. In the context of water transport in plants, cohesion is a crucial property of water molecules. Due to hydrogen bonding between water molecules, they tend to stick together. This cohesive force creates a continuous column of water within the xylem vessels, from the roots all the way up to the leaves. This property is essential for the upward movement of water against gravity, a process largely driven by transpiration pull.

True. The apoplastic movement of water in plants refers to the movement of water through the non-living components of the plant tissue, specifically the cell walls and intercellular spaces. This pathway allows water to move relatively freely and quickly until it encounters a barrier such as the Casparian strip in the endodermis, which forces it into the symplast pathway.

Symplast pathway: The movement of water through the interconnected cytoplasm of cells, facilitated by plasmodesmata, is known as the symplastic pathway. This movement is dependent on the water potential gradient, meaning water moves from areas of higher water potential to areas of lower water potential, driven by osmotic forces and the continuous cytoplasmic connection between cells.

Symplastic movement describes the transport of water through the living parts of plant cells, specifically moving from one cell's cytoplasm to another via plasmodesmata, which are small channels connecting adjacent cells. In contrast, apoplastic movement involves the transport of water through the non-living components of the plant, such as the cell walls and intercellular spaces, without passing through the plasma membrane or cytoplasm.

If the rate of transpiration from the leaves of a plant exceeds the rate at which water is absorbed by its roots, the plant will begin to lose more water than it can replenish. This water deficit causes the cells in the leaves to lose their turgor pressure, leading to wilting. To conserve water, the stomata, which are the pores on the leaf surface responsible for transpiration, may close. If this condition persists and the soil becomes dry, the leaves will eventually dry out, turn brown, and the plant may die due to severe dehydration and inability to perform essential physiological functions.

Circulation in humans is referred to as double circulation because the blood passes through the heart twice during one complete circuit of the body. This system involves two distinct circulatory pathways: the pulmonary circulation and the systemic circulation. In pulmonary circulation, deoxygenated blood is pumped from the right side of the heart to the lungs, where it gets oxygenated, and then returns to the left side of the heart. In systemic circulation, oxygenated blood is pumped from the left side of the heart to the rest of the body, delivering oxygen and nutrients, and deoxygenated blood returns to the right side of the heart. This double circulation ensures that oxygenated and deoxygenated blood do not mix, which is crucial for efficient oxygen delivery to the tissues and maintaining a high metabolic rate.

Valves in the heart are crucial structures that play a vital role in ensuring the unidirectional flow of blood. They act like one-way doors, opening to allow blood to move forward into the next chamber or vessel and closing tightly to prevent it from flowing backward. Specifically, the atrioventricular valves (tricuspid and bicuspid) prevent the backflow of blood from the ventricles into the atria during ventricular contraction. Similarly, the semilunar valves (pulmonary and aortic) prevent the backflow of blood from the arteries into the ventricles after the ventricles have contracted. This regulation of blood flow is essential for maintaining efficient pumping action of the heart and ensuring that the body receives a continuous supply of oxygenated blood.

The Rh factor was discovered by Karl Landsteiner and Alexander S. Wiener in 1940. They identified this factor while studying the blood of Rhesus monkeys. The factor was named 'Rh' because it was first identified in the blood of these Rhesus monkeys. This discovery was significant as it explained certain cases of transfusion reactions and hemolytic disease of the newborn, which were previously not understood.

Arteries and veins, the primary blood vessels, exhibit distinct structural differences related to their functions. Arteries are characterized by thick, elastic, and muscular walls, primarily due to a well-developed tunica media layer. This robust structure is necessary to withstand the high pressure of blood pumped directly from the heart. They typically have a narrower lumen (internal diameter) and, except for the pulmonary artery, carry oxygenated blood away from the heart. Veins, on the other hand, have thinner, less elastic walls with a less developed tunica media. They possess a wider lumen to accommodate blood returning to the heart under lower pressure. To prevent the backflow of blood, especially against gravity in the limbs, many veins are equipped with valves, which are generally absent in arteries.

A distributing vessel is a blood vessel that carries blood away from the heart to various parts of the body, which is characteristic of an artery. A collecting vessel is a blood vessel that gathers blood from different parts of the body and returns it to the heart, which is the function of a vein. Therefore, the distributing vessel is an artery, and the collecting vessel is a vein.

Blood in arteries is typically bright scarlet red because it is oxygenated, meaning it has picked up a fresh supply of oxygen in the lungs. This is true for all arteries except the pulmonary arteries, which carry deoxygenated blood from the heart to the lungs. Blood in veins, conversely, is usually a dark red or bluish-red color. This is because it is deoxygenated, having delivered its oxygen to the body tissues and picked up carbon dioxide. The exception is the pulmonary veins, which carry oxygenated blood from the lungs back to the heart.

Arteries are generally located deep within the body tissues. This deep positioning provides them with protection from external injuries, which is important given that they carry blood under high pressure. In contrast, veins are often found to be superficial, meaning they are located closer to the surface of the skin. This superficial location makes them more visible and accessible, which is advantageous for procedures like drawing blood or administering intravenous fluids.

Arteries are designed to transport blood away from the heart under significant force, so the blood flows through them under high pressure. This high pressure is necessary to ensure efficient distribution of oxygen and nutrients to all parts of the body. Veins, however, are responsible for returning blood to the heart, a process that occurs after the pressure has dropped considerably. Therefore, blood flows through veins under low pressure.

The wall of an artery is strong, thick, and elastic. This is because arteries carry blood away from the heart at high pressure, and the elasticity allows them to expand and contract with each heartbeat, helping to maintain blood flow. The wall of a vein, on the other hand, is relatively weak, thin, and less elastic. Veins carry blood under lower pressure, and their thinner walls are sufficient for this function. Additionally, many veins, particularly in the limbs, contain valves to prevent the backflow of blood.

Generally, all arteries carry oxygenated blood, which is bright red, away from the heart to the body tissues. The significant exception is the pulmonary artery, which carries deoxygenated blood from the right ventricle of the heart to the lungs for oxygenation. Similarly, most veins carry deoxygenated blood, which is dark red, back to the heart from the body tissues. The exception to this rule is the pulmonary veins, which transport oxygenated blood from the lungs back to the left atrium of the heart.

Arteries, which carry blood away from the heart, do not have internal valves. This is because the blood pressure in arteries is high, and the heart's pumping action ensures unidirectional flow. In contrast, veins, which carry blood towards the heart, often have internal valves. These valves are crucial in veins, especially in the limbs, to prevent the backflow of blood due to gravity, ensuring that blood returns to the heart effectively against the force of gravity.

The statement 'It starts from left ventricle and circulates oxygenated blood to various parts of the body' accurately describes systemic circulation. This is the main circulatory pathway where oxygenated blood is pumped from the left ventricle into the aorta and then distributed to all tissues and organs of the body, where oxygen is utilized and carbon dioxide is picked up. The statement 'It starts from the right ventricle to lungs with deoxygenated blood' describes pulmonary circulation. Here, deoxygenated blood is pumped from the right ventricle into the pulmonary artery, which carries it to the lungs for oxygenation.

Pulmonary circulation, which carries deoxygenated blood from the right ventricle to the lungs for oxygenation and then returns oxygenated blood to the heart, ends in the left atrium with oxygenated blood. Systemic circulation, which carries oxygenated blood from the left ventricle to the rest of the body and returns deoxygenated blood to the heart, ends in the right atrium with deoxygenated blood.

Minerals cannot always be passively absorbed by the roots because their concentration in the soil is often lower than inside the root cells. The absorption of mineral ions requires energy, typically in the form of ATP, and is facilitated by specific carrier proteins embedded in the root cell membranes. This active transport mechanism allows the plant to accumulate essential minerals against a concentration gradient. While some ions might enter passively through diffusion or mass flow if external concentrations are high or if water movement is significant, active uptake is the primary and most efficient method for mineral absorption.

Minerals are not entirely lost when a leaf falls because plants have mechanisms to remobilize essential mineral nutrients from older, senescing leaves to younger, actively growing parts of the plant. Elements like phosphorus and sulfur, which are mobile within the plant, are often translocated from dying leaves to younger leaves or developing fruits and seeds. This process conserves valuable nutrients. Furthermore, there is a small but continuous exchange of materials between the xylem and phloem tissues, which can also contribute to the redistribution of some minerals, minimizing overall loss from the plant.

The walls of the right ventricle are thicker than those of the right auricle (atrium) because the right ventricle is responsible for pumping deoxygenated blood to the lungs, a task that requires generating higher pressure to push blood through the pulmonary circulation. The right auricle, on the other hand, primarily receives deoxygenated blood from the body via the vena cavae and simply delivers it to the right ventricle. This receiving function requires less muscular effort, hence its thinner walls compared to the ventricle.

Mature red blood cells (RBCs) in mammals are anucleated, meaning they lack a nucleus, and also lack most other cell organelles such as mitochondria, endoplasmic reticulum, and Golgi apparatus. This unique adaptation maximizes the internal space available for hemoglobin, the protein responsible for oxygen transport, thereby increasing the oxygen-carrying capacity of the blood. Additionally, the absence of mitochondria prevents the RBCs from consuming the oxygen they are transporting through aerobic respiration; instead, they rely on anaerobic glycolysis for energy.

Plants primarily absorb water through their root hairs, which significantly increase the surface area for absorption. This process occurs mainly via osmosis, where water moves from an area of higher water potential (in the soil) to an area of lower water potential (inside the root cells). Once inside the root hairs, water can move into the inner tissues of the root through different pathways: the apoplast pathway (through cell walls and intercellular spaces), the symplast pathway (through the cytoplasm of connected cells), and the transmembrane pathway (across cell membranes). Water then reaches the xylem vessels, from where it is transported upwards to the rest of the plant. This upward movement is driven by a combination of root pressure, capillary action within the xylem, and most significantly, the transpiration pull, which is the tension created by the evaporation of water from the leaves.

The apoplast pathway refers to the route of water movement through the non-living components of a plant's root tissue. This includes the cell walls and the intercellular spaces between cells. Water moves freely along this pathway, driven by differences in water potential, and it is generally a faster route for water transport. However, the apoplast pathway is interrupted at the endodermis by the Casparian strip, a band of waterproof material within the cell walls. This strip forces water to cross the plasma membrane of an endodermal cell and enter the symplast pathway before it can reach the xylem, ensuring that the plant has some control over the uptake of water and dissolved minerals.

The symplast pathway refers to the continuous movement of water through the cytoplasm of adjacent plant cells. This movement is facilitated by plasmodesmata, which are small channels that connect the cytoplasm of one cell to the next. Water enters the root cells, crosses the plasma membrane, and then travels from cell to cell via these plasmodesmata. This pathway is crucial for moving water across the endodermis and into the xylem vessels, allowing for efficient transport throughout the plant.

The phenomenon involved when dry plant material swells up upon being kept in water is called imbibition. Imbibition is defined as the process by which certain solid substances, particularly colloids, absorb water and swell up. This occurs because the solid material has a strong affinity for water molecules, which adhere to its surface and penetrate its structure. Examples of imbibition include the swelling of dry seeds before germination, dry grapes swelling to become raisins when rehydrated, or dry wood expanding when exposed to moisture.

Doctors use a stethoscope to listen to the sounds produced by internal organs, including the heart and lungs. The heart produces distinct sounds, known as heart sounds, during each cardiac cycle, which are primarily caused by the closing of heart valves. These sounds provide crucial information about the heart's rhythm, rate, and the functioning of its valves. By amplifying these sounds, a stethoscope allows the doctor to detect abnormalities such as murmurs, irregular rhythms, or valve defects. This non-invasive diagnostic tool is invaluable for assessing cardiovascular health, identifying potential problems, and monitoring the progression of heart conditions, enabling timely diagnosis and treatment.