Control and Coordination

The governing concept is the division of roles in coordination. A receptor detects a change such as heat, pressure, or light and converts it into a signal. An effector then carries out the response; muscles contract and glands secrete substances. Hence option A is correct. Option B reverses the definitions, while options C and D assign unrelated functions to both structures.

The governing concept is the pathway from receptor to coordinating centre. Photoreceptors can detect light, but the optic nerve must carry the resulting electrical signals toward the brain for visual interpretation. If that nerve is damaged, detection may occur locally but transmission and conscious processing are disrupted. Therefore option A is correct; the other options describe unrelated plant or endocrine claims.

The governing concept is classification by control mechanism. Writing is voluntary because it is consciously initiated. Heartbeat is involuntary because it continues automatically under autonomic control. Pulling the hand away from a hot object is a rapid reflex action, usually coordinated through a reflex arc before conscious awareness. Thus option A gives the requested order; the other options mix categories or unrelated processes.

The governing concept is that an effector may be a muscle or a gland. A salivary gland receives neural or chemical information and responds by secreting saliva, so option A clearly shows a gland acting as an effector. Options B and C involve skeletal muscles as effectors, while option D is a plant growth response involving hormones and unequal growth rather than a gland in the animal sense.

The governing concept is reflex action. When the hand touches a hot object, sensory receptors send an impulse through a reflex arc, and the spinal cord rapidly coordinates the withdrawal before conscious thinking by the brain. Therefore, option A disproves the statement. Memorising, deliberate thinking, and drawing generally involve conscious brain activity, so they are not suitable counterexamples.

The governing concept is comparison of nervous and chemical coordination. Nervous impulses travel rapidly along specific neurons and pathways, whereas plants lack a nervous system and use chemical hormones, whose effects are usually slower and may alter growth direction. Thus option A is correct. Plants do not possess a brain or spinal cord, hormones do not travel only in blood in plants, and both systems respond to stimuli.

The governing concept is tropism, a directional growth response of a plant part to an external stimulus. Phototropism is caused by light, hydrotropism by water, and chemotropism by chemicals, so option A correctly matches each term with its stimulus. Option B swaps the stimuli, option C confuses chemicals with gravity, and option D incorrectly limits all tropisms to touch.

The governing concept is directional growth, or tropism. A shoot commonly shows positive phototropism and grows toward light, while a root generally shows positive gravitropism and grows in the direction of gravity into the soil. Therefore, option A is correct. The opposite claims in B are wrong, C uses animal structures that plants do not have, and D gives unsupported universal statements about tendrils and roots.

The governing concept is coordination in plants without a nervous system. Plants detect stimuli such as light, water, gravity, and touch, then respond through chemical signals, changes in hormone distribution, and growth patterns. Thus option A correctly corrects the misconception. Plants have no spinal cord, they do not circulate messages through blood like animals, and they can respond to several environmental stimuli.

The governing concept is control and coordination as a life function. Organisms detect internal or external stimuli, process information, and coordinate the activities of different organs so that a suitable response occurs at the right time. Hence option A is the broadest and correct explanation. The other choices describe neither coordination nor the diversity of organisms: they restrict it to colouring food, making bones, or plants alone.

The governing concept is sensory receptors and stimulus detection. Receptors in the eye respond to light, those in the ear detect sound, receptors in the nose detect smell-related chemicals, and taste receptors on the tongue respond to dissolved substances. Therefore, option A correctly matches the organs and stimuli. The other options describe unrelated functions or incorrectly place these receptors only in plant roots.

Homeostasis is the maintenance of a relatively stable internal environment despite changes. When blood glucose rises, pancreatic beta cells release insulin; body cells take up more glucose and the liver can store it as glycogen, bringing the level down toward normal. Therefore option A directly describes internal regulation. Options B, C, and D are plant movements or tropic responses to external stimuli, not regulation of an animal’s internal conditions.

The governing concept is coordination across different kinds of organisms. Animals use the nervous system for rapid electrical control and hormones for slower, sustained regulation. Plants lack a brain and nerves like animals, but chemical messengers and growth responses such as phototropism help them respond to stimuli. Thus option A correctly combines both parts. The other options wrongly give plants a brain, spinal cord, blood-based control, or an exclusive dependence on light.