Transportation in Animals and Plants-III

Stomata are microscopic pores found mainly on leaf surfaces that regulate gas exchange and water vapor loss. They open for photosynthesis and close to conserve water, making them the primary site of transpiration in plants.

Transpiration is the loss of water vapor through stomata in leaves. This process creates transpiration pull that draws water upward through the xylem from roots to leaves, aiding mineral transport and cooling the plant.

The passage of water across a selectively permeable membrane is called osmosis.

Leaves have the lowest water potential due to transpiration creating negative pressure (tension). This strong water potential gradient pulls water upward from roots through the xylem vessels, facilitating upward water movement.

The drooping of leaves due to loss of turgor pressure at noon and recovery in the evening is called temporary wilting.

Leaf hairs (trichomes) create a boundary layer of humid, still air near the leaf surface that reduces water loss through transpiration. They do not significantly affect gaseous exchange or guttation processes.

Root pressure is caused by osmotic flow of water into the xylem. Active transport of minerals into the root xylem lowers water potential there, causing water to move osmotically from the soil into the xylem, creating positive hydrostatic pressure.

Transpiration has multiple functions: translocation of minerals (moving nutrients upward), ascent of sap (creating upward pull), and cooling (evaporative cooling). Excretion of sap is NOT a function of transpiration - that is gutation.

In mammals, the urea is transported by haemoglobin.

Heart of a fish is special because it only has venous blood.

Root pressure is related to active water absorption because it requires active transport of minerals into the xylem to create osmotic gradient. This is distinct from passive transpiration pull which relies on physical evaporation.

Mammalian erythrocytes have short lifespan due to absence of nucleus.

All arteries except the pulmonary artery carry oxygenated blood. The pulmonary artery carries deoxygenated blood from heart to lungs. Conversely, most veins carry deoxygenated blood except pulmonary veins which carry oxygenated blood from lungs.

Blood capillaries are made of endothelium only.

Arteries have thick, muscular walls to withstand high pressure from heart pumping. Blood flows under high pressure. Veins are thin-walled with valves, carrying blood under diminished pressure back to heart.

The vagus nerve (parasympathetic) releases acetylcholine that slows heart rate by decreasing SA node activity. This is opposite to sympathetic stimulation which increases heart rate. Vagal stimulation can reduce heart rate to 40-60 beats/minute.

Brain requires continuous oxygen supply. Blood supply interruption for more than 5 seconds causes unconsciousness due to rapid depletion of oxygen and glucose in neurons. Permanent damage begins within minutes.

An antigen is a substance (usually protein or polysaccharide) that stimulates antibody formation when introduced into the body. It is the triggering molecule for immune response, not the antibody itself.

Blood group O has no A or B antigens on red blood cells but possesses both anti-A and anti-B antibodies in plasma. This makes O the universal donor (no antigens to react) but universal recipient for plasma only.

Frog hearts have myogenic properties, meaning they can generate their own electrical impulses without external nerve stimulation. When kept moist, the cardiac muscles continue to contract rhythmically for extended periods even after removal from the body. Option A correctly states this phenomenon. Option B is incorrect because dry conditions cause tissue damage. Option C is false as the heart will beat autonomously. This is a classic demonstration of cardiac muscle automaticity.