Endocrine system

Correct answer: A. Because insulin helps regulate blood sugar

The governing concept is hormonal regulation of blood glucose. Insulin is produced by the pancreas and helps body cells take up glucose from the blood and store excess glucose, thereby lowering or controlling the blood-glucose level. If insulin is deficient, glucose is not used or stored efficiently and its concentration rises. Thus option A is correct; the other choices assign insulin unrelated functions or an incorrect site of production.

Correct answer: A. It affects the working of many other endocrine glands

The governing concept is hormonal coordination by the endocrine system. The pituitary releases tropic hormones that regulate or stimulate several other endocrine glands, including the thyroid, adrenal glands and reproductive glands. Because it influences the activity of many glands, it is traditionally called the master gland. It does not digest food, fill the lungs, or colour blood, so options B, C and D are unrelated.

Correct answer: A. It produces insulin that controls blood sugar

The pancreas has an endocrine role because its islets release hormones into the blood. Beta cells produce insulin, which helps body cells take up glucose and thereby lowers or regulates blood glucose after a meal. In diabetes, insulin may be insufficient or ineffective, causing high blood sugar. Therefore option A is correct; the other choices describe functions of sensory organs, the brain, or the balance system, not the pancreas.

Correct answer: A. Because they secrete hormones directly into blood

Endocrine glands do not possess ducts or tubes leading to a body surface or a particular cavity. Their secretions, called hormones, are released into the surrounding tissue fluid and then carried by the bloodstream to target organs. This differs from exocrine glands, which use ducts to transport substances such as sweat or digestive juices. Hence option A correctly explains the term ductless glands.

Correct answer: A. Hormones reach target organs through blood

The governing concept is the mode and speed of communication. Endocrine glands release hormones into the bloodstream, and the blood carries them to distant target organs; this transport and the time needed for cellular action make the response relatively slow. Thus option A is correct. Hormones are not formed only in skin, they do reach target organs, and they occur in animals as well as plants, so B, C, and D are false.

Correct answer: A. Because they release secretions directly into blood

Endocrine glands are called ductless glands because they do not possess ducts or tubes through which their secretions can travel. Instead, they release hormones into the surrounding tissue fluid, from where the hormones enter the bloodstream and reach target organs. This differs from exocrine glands, which use ducts to carry secretions to a surface or cavity. Thus, direct release into blood makes option A correct; the other choices describe unrelated functions.

Correct answer: A. Body growth may remain reduced

The governing concept is hormonal control of growth. Growth hormone, secreted by the pituitary gland, supports normal growth of bones and other body tissues during development. If its secretion is much lower than normal, growth may be inadequate and a person may remain unusually short. Hence option A is correct. Blood-glucose regulation involves other hormones, while root growth and leaf folding are plant responses unrelated to pituitary growth hormone.

Correct answer: A. The effect can be slow but long lasting

The governing concept is hormonal or endocrine coordination. Endocrine glands release hormones into the bloodstream, so transport to a target organ is generally slower than a nerve impulse. However, hormones may remain active longer and influence processes such as growth, metabolism or reproduction. Their action is not limited to a moment, dendrites or the spinal cord; therefore option A is correct.

Correct answer: A. Body changes during adolescence

Hormones are chemical messengers released by endocrine glands. Their effects generally begin more slowly than nerve impulses and may continue for a long period. Changes during adolescence, such as growth and development of secondary sexual characteristics, are regulated largely by hormones. The other choices are rapid protective reflexes or automatic actions, so option A is the best answer.

Correct answer: A. Control of metabolism

Thyroxine is a hormone secreted by the thyroid gland. It helps regulate the body’s metabolic rate, influencing how cells use energy and process nutrients; iodine is needed for its normal production. Therefore, control of metabolism is the correct match. Instant hand withdrawal is a reflex, sound detection involves auditory receptors, and pollen-tube growth is a plant response.

Correct answer: A. Because insulin helps control the glucose level in blood

The governing concept is hormonal regulation of blood glucose. The pancreas, specifically its endocrine cells, secretes insulin when blood glucose rises. Insulin promotes uptake and use of glucose by body cells and supports its storage as glycogen, thereby lowering excess glucose in the blood. If too little insulin is produced, this regulation is impaired and blood glucose may remain abnormally high. Option A is correct; the other choices assign unrelated or false functions to insulin.

Correct answer: A. Increased heartbeat, faster breathing, and greater glucose availability

Adrenaline is a hormone involved in the fight-or-flight response. During fear, it prepares the body for rapid action by increasing the heart rate and breathing rate, while also making more glucose available for immediate energy. Therefore, option A is correct. Options B, C, and D describe effects that are either opposite, unrelated to adrenaline, or associated with plant responses.

Correct answer: A. Hormones must enter the blood to reach their target organs

Endocrine glands are ductless glands. They release hormones directly into the bloodstream, which transports these chemical messengers to specific target organs. If a duct carried the secretion outside the body, much of the hormone would fail to enter the blood and would not reach its target in the required amount. Therefore option A is correct; the other statements do not describe endocrine function.

Correct answer: A. Hormones travel through the blood, whereas nerve impulses travel along nerves

The governing concept is the difference between endocrine and nervous coordination. Endocrine glands release hormones into the bloodstream, allowing chemical signals to reach target tissues, often with slower but longer-lasting effects. Nerve impulses are electrochemical signals conducted along neurons and are generally rapid and localized. Therefore option A gives the valid transport-based distinction; the words “always” in B and the claims in C and D are scientifically false.

Correct answer: A. Because it makes hormones that regulate many other endocrine glands

The governing concept is hormonal coordination by the pituitary gland. It secretes several hormones, including tropic hormones that influence glands such as the thyroid, adrenal glands, and reproductive glands. Through these signals, it helps coordinate growth, metabolism, reproduction, and other functions. Therefore A best explains the term “master gland.” Digestion, synaptic blocking, and auxin production are not functions of the human pituitary gland.

Correct answer: A. Because it releases insulin into blood

An endocrine gland releases hormones into the bloodstream rather than sending them through a duct. The pancreas contains endocrine cells in the islets of Langerhans, which secrete insulin directly into blood. Insulin helps body cells take up glucose and thereby assists in maintaining blood sugar. Thus option A gives the defining reason; the other choices describe unrelated structures or an impossible plant function.

Correct answer: A. Insulin helps control glucose level in blood

The governing concept is endocrine control of blood glucose. The pancreas releases insulin, which helps body cells take up glucose and helps maintain an appropriate glucose concentration in the blood. If insulin production is insufficient, glucose regulation is disturbed and the blood level may rise. Thus option A is correct. The other options incorrectly assign insulin roles in vision, plant growth, or balance of the ear.

Correct answer: A. Because it secretes hormones that control many other endocrine glands

The governing concept is endocrine coordination through regulatory hormones. The pituitary secretes hormones that influence important target glands, including the thyroid, adrenal glands, and reproductive glands. Because it helps regulate the activity of several endocrine organs, it is commonly called the master gland at this level. Hence option A is correct. The remaining choices describe digestion, plant regulation, or synaptic action, not pituitary control.

Correct answer: A. Hormones are secreted directly into blood and reach target organs

The governing concept is endocrine coordination. Endocrine glands are ductless, so they do not deliver their secretions through tubes. Instead, they release hormones into the surrounding blood. The circulatory system transports these chemical messengers to specific target organs or tissues, where receptors enable a response. Sound waves, neurons, and leaf stomata are unrelated to endocrine secretion; therefore, option A is correct.

Correct answer: A. Because it controls growth, metabolism, and long-term body functions

Hormones are chemical messengers released by endocrine glands and transported through the blood, so their effects generally begin more slowly than nerve impulses. Their advantage is sustained, widespread regulation of processes such as growth, metabolism, development, reproduction, and water balance. Thus option A is correct. Hormonal control is not always faster than a reflex arc, it acts on target tissues, and it is not limited to taste detection.

Correct answer: A. Its hormones influence the functioning of many other endocrine glands

The governing concept is hormonal coordination through the pituitary gland. The pituitary releases several hormones, including tropic hormones that stimulate or regulate other endocrine glands such as the thyroid, adrenal glands, and gonads. This regulatory influence explains the description “master gland,” so option A is correct. The pituitary does not filter blood, detect light, or produce auxin; those claims confuse it with other organs or with plant hormones.

Correct answer: A. For both immediate response and long-term control

Animals need nervous coordination for rapid, localized responses, such as withdrawing from a painful stimulus or adjusting movement. They need endocrine coordination for slower, longer-lasting regulation of growth, metabolism, puberty, and reproduction. These systems complement rather than replace one another, so option A is correct. The systems are not used for plant growth or colouring food, and they do not operate at the same speed: nerve impulses are generally faster than hormonal effects.