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 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.

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.

The governing concept is endocrine transport through the circulatory system. An endocrine gland releases its hormone into the blood rather than sending it through a duct or a single nerve. Since blood circulates throughout the body, the hormone can be carried to distant tissues. Only cells with suitable receptors respond strongly to it. Thus A is correct; B and D describe restricted locations, while C confuses hormones with nerve impulses.

The pancreas is an endocrine organ whose islet cells secrete insulin, a hormone that helps regulate blood glucose, so option A is the correct match. The thyroid secretes thyroxine, not adrenaline; adrenaline is secreted by the adrenal glands. The pituitary secretes several hormones, whereas bile juice is produced by the liver, not by the pituitary. Hence the alternatives contain mismatched pairs.

The governing concept is the distinction between endocrine and exocrine glands. Endocrine glands are ductless; they secrete chemical messengers called hormones into the surrounding tissue fluid and then into the bloodstream. The blood transports these hormones to particular target organs or cells. Therefore option A is correct. Option B describes duct-based exocrine secretion, while options C and D refer neither to the definition nor the function of an endocrine gland.

The governing concept is endocrine coordination. Endocrine glands are ductless, so their hormones are released into the surrounding blood. The circulatory system transports these chemical messengers throughout the body, allowing them to reach distant target organs that possess suitable receptors. Thus option A is correct. Drying on skin, digesting food in the mouth, or remaining only in bones is not the normal function or route of endocrine hormones, so B, C, and D are distractors.

The governing concept is stomatal regulation in plants. Each stoma is surrounded by a pair of guard cells. Changes in their water content and turgor pressure alter their shape, opening the pore when appropriate and closing it to reduce water loss. Hence option A is correct. Nerve, blood, and bone cells are animal cell types and do not directly control stomatal movement.

Insulin is secreted by the beta cells of the islets of Langerhans in the pancreas. It helps regulate blood glucose, especially when its level rises. The thyroid gland secretes thyroxine, not insulin. Exam tip: Remember that both insulin and glucagon are associated with the pancreas.

Insulin is secreted by the beta cells in the islets of Langerhans of the pancreas. It helps regulate blood glucose, mainly by promoting the use and storage of glucose by body cells. The liver stores glucose but does not secrete insulin. Exam tip: remember the link—insulin, pancreas, and blood sugar control.