Control and Coordination

An organism performs many activities at the same time, such as movement, nutrition, breathing, and responding to changes around it. Control and coordination connect these activities and ensure that organs work in an orderly and suitable manner. Therefore, option A is correct. Changing body colour, removing food, or increasing height may be specific processes, but none expresses the overall purpose of control and coordination.

In the usual direction of impulse transmission, dendrites receive signals and pass them to the cell body. The axon is the long extension that conducts the nerve impulse away from the cell body toward another neuron, muscle, or gland. Hence option B is correct. The nucleus controls cell activities and cytoplasm supports cellular reactions; neither is the specialised conducting extension. Dendrites generally carry incoming rather than outgoing signals.

Most neighbouring neurons do not touch one another directly. The tiny junctional gap between the axon ending of one neuron and the receiving part of the next is called a synapse. A nerve impulse reaches the end of the first neuron, where chemical neurotransmitters help transmit the signal across this gap. Therefore, option B is correct; a receptor detects stimuli, an endocrine gland releases hormones, and an effector performs the response.

A reflex arc is the specific neural pathway followed during a reflex action. A receptor detects a stimulus, the sensory neuron carries the impulse to the spinal cord, and a motor neuron carries the instruction to an effector such as a muscle. Thus, option A is correct because it describes the message pathway; the other options refer to routes of food, blood, or air, not nerve impulses.

A stimulus is a detectable change in the internal or external environment, such as light, sound, heat, or pressure. A receptor is a specialised cell, tissue, or sense-organ structure that detects this change and starts a nerve impulse. Therefore, option B is correct. An effector produces the response, while a gland or muscle may be an effector rather than the detecting structure.

In a response pathway, the receptor first detects the stimulus and the nervous system carries the information to a responding organ. A muscle contracts or a gland releases a secretion, so either can carry out the response. Such a muscle or gland is called an effector; therefore option B is correct. A synapse is a junction between neurons, and a dendrite receives signals.

The nervous system has a central part and a peripheral part. The brain is the main processing centre, while the spinal cord conducts signals and coordinates many responses. Together, these two structures form the central nervous system, so option A is correct. The digestive, respiratory, and circulatory systems perform other body functions and do not consist of the brain and spinal cord.

The cerebrum is the largest part of the human brain and is associated with higher mental functions, including thinking, learning, reasoning, conscious sensations, and memory. Hence, option A is correct. The cerebellum mainly coordinates posture and balance, the medulla regulates several involuntary activities, and the spinal cord conducts impulses and mediates reflexes.

Maintaining balance requires the coordination of skeletal muscles, posture, and the timing of movements. The cerebellum receives information related to body position and helps refine muscular activity, so option A is correct. The cerebrum supports conscious thought, the medulla controls important involuntary functions, and the pituitary is an endocrine gland that releases hormones.

Involuntary actions occur automatically without conscious choice and are essential for survival. The medulla, a part of the brainstem, regulates important automatic activities such as breathing, heartbeat, and blood pressure. Therefore, option A is correct. The cerebrum mainly handles conscious thought, the cerebellum coordinates balance, and a dendrite is a neuron part that receives signals rather than controlling these actions.

A voluntary action is performed consciously and according to a person's choice. When someone decides to raise a hand, the brain plans and sends motor commands to the relevant muscles, so option B is correct. A reflex action is rapid and automatic, while digestion and secretion are physiological processes that are not the appropriate classification for a deliberate hand movement.

Bright light is a stimulus detected by the eye. The pupil then constricts automatically, reducing the amount of light entering the eye and helping protect the retina. Because this response is rapid, automatic, and not dependent on conscious decision, option A is correct. Digestion, growth, and excretion are different physiological processes and do not describe the pupil's immediate response to light.

Endocrine glands are ductless glands that release their secretions directly into the bloodstream. Their secretions are hormones, chemical messengers that travel to target cells or organs and regulate processes such as growth, metabolism, and reproduction. Thus, option B is correct. Digestive juices, saliva, and bile are secretions of particular digestive organs or glands and are not the general product of endocrine glands.

Hormones are chemical messengers released by endocrine glands. They travel through the bloodstream to specific target organs or tissues and regulate activities such as growth, metabolism, and reproduction. Thus, the coordination produced by hormones is chemical coordination, making option A correct. Electrical coordination is mainly associated with nerve impulses, while the other choices do not describe a biological coordination system.

Adrenaline, also called epinephrine, is secreted by the adrenal glands, which are situated above the kidneys. During fear, stress, or danger, it prepares the body for the fight-or-flight response by increasing heart rate and directing more blood toward active muscles. Therefore option A is correct. The salivary gland, pancreas, and testis produce other substances or hormones, not adrenaline.

Adrenaline is released during danger, fear, or intense stress. It activates the sympathetic part of the autonomic nervous system and increases the rate and force of heart contraction. This helps deliver more oxygen and nutrients to muscles for rapid action, so option A is correct. Adrenaline does not stop the heart, remove it, or make the heart produce blood; blood cells are formed mainly in bone marrow.

Insulin is a hormone secreted by the beta cells of the pancreas. When blood glucose rises after a meal, insulin helps body cells take up glucose and promotes its storage as glycogen, thereby lowering and regulating blood sugar. Thus option A is correct. Adrenaline can raise blood glucose during emergencies, thyroxine mainly regulates metabolism, and auxin is a plant hormone involved in plant growth.

Insulin is produced by the beta cells located in the islets of Langerhans within the pancreas. It helps maintain blood glucose by promoting glucose uptake and storage, so the pancreas is both a digestive and endocrine organ. Therefore option A is correct. The pituitary controls several other glands, the thyroid secretes thyroxine, and the adrenal gland secretes hormones such as adrenaline, not insulin.

Thyroxine is the principal hormone secreted by the thyroid gland in the neck. It helps regulate metabolism, growth, and development, and its production requires iodine. Therefore option A is correct. The pancreas secretes insulin and glucagon, the adrenal gland secretes adrenaline and other hormones, and the salivary gland produces saliva rather than thyroxine. These differences identify the thyroid as the correct gland.

The thyroid gland requires iodine to synthesize thyroxine, a hormone involved in regulating metabolism, growth, and development. The body obtains iodine from dietary sources, and inadequate iodine can reduce thyroxine production and cause enlargement of the thyroid gland, called goitre. Therefore option B is correct. Iron, calcium, and sodium are essential nutrients for other functions but are not the specific raw material for thyroxine.

Iodine is required by the thyroid gland to produce thyroxine. If iodine intake is insufficient, thyroxine production may fall, and the thyroid gland can enlarge as it attempts to capture more iodine. This enlargement is called goitre, so option A is correct. Diabetes is associated with problems in insulin regulation, night blindness commonly relates to vitamin A deficiency, and malaria is caused by a parasite transmitted by mosquitoes.

The pituitary gland is called the master gland because it secretes hormones that regulate the activity of several other endocrine glands, including the thyroid, adrenal glands, and gonads. Its hormones also influence growth and reproduction. Therefore option A is correct. Digestion is mainly performed by the digestive system, blood filtration is associated with the kidneys, and bone formation is not the defining role of the pituitary.

Growth hormone is secreted by the pituitary gland and supports the growth of bones and other body tissues, especially during childhood and adolescence. A suitable amount is important for normal height and physical development, so option A is correct. Growth hormone does not determine the colour of blood, the taste of food, or dental cleanliness; those features are governed by different substances and processes.

The governing concept is tropic movement, a directional growth response to an external stimulus. When a plant organ, especially a shoot, grows towards a light source, the response is called positive phototropism. Geotropism responds to gravity, hydrotropism to water, and chemotropism to chemicals. Therefore, option A is correct.

Plants require light for photosynthesis, the process by which they manufacture food from carbon dioxide and water. A stem and its leaves therefore tend to grow towards available light, showing positive phototropism. Growing to lose water, escape soil, or become a root is not the biological purpose of this response. Thus, option A is correct.