Endocrine system

The governing concept is the endocrine system. Endocrine glands are ductless glands that synthesise hormones and release them directly into the bloodstream. The blood then transports these chemical messengers to target tissues, where they regulate activities such as growth, metabolism, and reproduction. Thus, option A is correct; bones, teeth, and hair are body structures, not hormone-secreting endocrine glands.

The governing concept is ductless endocrine secretion. Unlike exocrine glands, endocrine glands have no ducts, so their hormones pass directly into nearby capillaries and then circulate through the blood. The blood carries each hormone to its target organ or tissue. Therefore, option A is correct. The food canal, lungs, and external body surface are not the normal general routes for endocrine hormone release.

The endocrine system consists of ductless glands that secrete hormones directly into the bloodstream. These hormones act as chemical signals and coordinate functions such as growth, metabolism, and reproduction. Thus option A is correct. The nervous system uses electrical impulses and neurotransmitters for rapid coordination, while the skeletal and excretory systems have different primary functions and are not the system responsible for hormone secretion.

The governing concept is hormonal regulation of growth. Growth hormone, also called somatotropin, is released by the pituitary gland and promotes the growth of bones and other body tissues, especially during childhood and adolescence. Consequently, option A is correct. Insulin primarily controls blood glucose, adrenaline supports the emergency response, and thyroxine mainly regulates metabolic activity, although normal growth also requires adequate thyroxine.

Hormonal or endocrine control works through chemical messengers released into the bloodstream. They must be transported to particular target organs, so the response generally begins more slowly than a nerve impulse. However, hormones may remain effective for a longer period, giving a sustained response. Thus option A is correct; the other options incorrectly describe a very brief neural response or deny the chemical nature of hormones.

Endocrine glands are ductless glands. Their secretions, called hormones, pass from the gland cells into the surrounding tissue fluid and then enter nearby blood capillaries. The bloodstream transports them to specific target organs, often far from the gland. Thus option A is correct. The food pipe, skin surface, and lung air are not the normal routes for endocrine hormone release, so B, C, and D are incorrect.

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.

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.

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.

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.

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.

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.

The governing concept is the difference between endocrine and exocrine glands. Endocrine glands have no ducts or tubes for transporting their secretions. Instead, their hormones diffuse into nearby blood capillaries and are carried through the bloodstream to target tissues. Thus option A correctly explains the term ductless glands. Exocrine glands use ducts, while electrical message transmission is a function of nerve cells, not the defining feature of endocrine glands.

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.

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.

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.

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.

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.

Endocrine glands are called ductless because they do not use tubes to carry their secretions. Instead, they release hormones into the surrounding tissue fluid and then into the bloodstream. Blood transports these chemical messengers throughout the body, but only target cells with suitable receptors respond strongly. Thus option A explains how a distant organ is affected; the other options describe no endocrine mechanism.

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.