Control and Coordination — Important Questions

Answers

• Receptor: Detects the stimulus (e.g., heat).
• Sensory Neuron: Transmits the impulse from the receptor to the spinal cord.
• Relay Neuron (Interneuron): Located in the spinal cord, it processes the information and relays it to a motor neuron.
• Motor Neuron: Transmits the impulse from the spinal cord to the effector.
• Effector: A muscle or gland that responds to the stimulus (e.g., pulls hand away).
  Flowchart:
  Stimulus (Hot object) -> Receptor (Skin) -> Sensory Neuron -> Spinal Cord (Relay Neuron) -> Motor Neuron -> Effector (Muscle in arm) -> Response (Hand withdraws)
  5. Nervous System: Uses electrical impulses and chemical neurotransmitters transmitted through specialized nerve cells (neurons). The response is rapid but often localized and short-lived. It controls fine, precise movements and quick reactions.
  Endocrine System: Uses chemical messengers called hormones secreted into the bloodstream by endocrine glands. Hormones travel throughout the body and act on target cells. The response is slower but more widespread and longer-lasting. It regulates growth, metabolism, and reproduction.
  6. Human Brain Parts and Functions:
• Fore-brain: The main thinking part. Includes the cerebrum, which is responsible for intelligence, memory, learning, and processing sensory information (sight, hearing, smell, taste). It also controls voluntary actions and emotions. The hypothalamus, part of the fore-brain, regulates hunger, thirst, and body temperature.
• Mid-brain: Connects the fore-brain and hind-brain. It controls reflex movements of the head, neck, and eyes in response to visual and auditory stimuli.
• Hind-brain: Consists of the cerebellum, pons, and medulla.
• Cerebellum: Responsible for precision of voluntary movements, maintaining posture, and balance.
• Pons: Relays signals between the cerebellum and cerebrum; involved in regulating breathing.
• Medulla: Controls involuntary actions like heartbeat, blood pressure, breathing, salivation, and vomiting.
  7. The brain is protected by:
• Bony Box: The skull, a hard bony structure, encloses and protects the brain.
• Cerebrospinal Fluid (CSF): The brain is suspended in cerebrospinal fluid within the cranial cavity. This fluid acts as a shock absorber, cushioning the brain against mechanical injuries and jolts.
• Meninges: Three membranes (dura mater, arachnoid mater, pia mater) surround the brain, providing an additional protective layer.
  8. Response to Stimuli in Plants: Plants respond to stimuli through two main types of movements:
• Tropic Movements: These are directional growth movements in response to a stimulus.
• Phototropism: Growth movement in response to light (shoots grow towards light, roots away).
• Geotropism: Growth movement in response to gravity (roots grow downwards, shoots upwards).
• Hydrotropism: Growth movement in response to water (roots grow towards water).
• Chemotropism: Growth movement in response to chemicals.
• Nastic Movements: These are non-directional movements in response to a stimulus. They are not dependent on the direction of the stimulus. Example: The folding of leaves of the 'chhui-mui' plant (Mimosa pudica) upon touching. This movement is due to a change in water content in specialized cells (pulvini) at the base of the leaf stalk.
  Difference: Tropic movements are growth-dependent and directional, while nastic movements are not dependent on growth and are non-directional.
  9. Role of Plant Hormones: Plant hormones (phytohormones) are chemical substances that regulate growth, development, and responses to stimuli in plants. They are produced in specific parts and transported to other parts where they exert their effects.
  Phototropism and Auxin: Auxins are plant hormones primarily responsible for phototropism. When light falls on a plant shoot from one side, auxin, synthesized at the shoot tip, diffuses towards the shaded side. The higher concentration of auxin on the shaded side stimulates the cells there to elongate more rapidly than the cells on the illuminated side. This differential growth causes the shoot to bend towards the light source.
  10. Geotropism: Geotropism is the directional growth of a plant in response to gravity.
• Positive Geotropism: The growth of a plant part in the direction of gravity. Roots exhibit positive geotropism, growing downwards into the soil.
• Negative Geotropism: The growth of a plant part against the direction of gravity. Shoots exhibit negative geotropism, growing upwards and away from the earth.
  11. Chemotropism: Chemotropism is the growth of a plant part in response to a chemical stimulus. For example, the growth of pollen tubes towards the ovule is guided by chemical signals released by the ovule.
  Hydrotropism: Hydrotropism is the growth of a plant part in response to water. Roots show hydrotropism by growing towards sources of water, even if it means growing against gravity (positive hydrotropism). This is essential for the plant's survival, as water is necessary for photosynthesis and other metabolic processes.
  12. Plant Hormones and Functions: Plant hormones are chemical regulators of plant growth and development.
• Gibberellins: Promote stem elongation and germination of seeds.
• Cytokinins: Promote cell division and differentiation, delay aging of plant parts. They are found in areas of rapid cell division, like fruits and seeds.
  13. Abscisic acid (ABA) is a plant hormone that primarily inhibits growth. It plays a crucial role in:
• Dormancy: Inducing dormancy in seeds and buds.
• Wilting: Promoting the closure of stomata during drought conditions. This reduces water loss through transpiration, thus preventing wilting. When water is scarce, ABA levels increase, causing stomata to close and leaves to wilt as a water-conserving mechanism.
  14. Adrenaline and Fight or Flight: Adrenaline, a hormone secreted by the adrenal glands, prepares the body to deal with stressful situations by initiating the 'fight or flight' response. The immediate physiological changes include:
• Increased Heart Rate: The heart beats faster to pump more blood to muscles.
• Increased Breathing Rate: Diaphragm and rib muscles contract more forcefully, increasing oxygen intake.
• Blood Diversion: Blood flow to the skin and digestive system is reduced, while blood supply to skeletal muscles is increased.
• Glucose Release: Liver releases stored glucose into the bloodstream, providing energy for immediate use.
• Pupil Dilation: Pupils enlarge, allowing more light to enter the eyes, improving vision.
  15. Thyroid Gland and Thyroxin: The thyroid gland secretes thyroxin, a hormone that regulates carbohydrate, protein, and fat metabolism in the body. This regulation is essential for providing the right balance for overall growth and development.
  Importance of Iodised Salt: Iodine is a necessary component for the synthesis of thyroxin. A deficiency of iodine in the diet can lead to a condition called goitre, characterized by swelling of the neck due to an enlarged thyroid gland. Consuming iodised salt ensures an adequate intake of iodine, thus preventing goitre and supporting proper thyroid function and metabolism.
  16. Growth Hormone: Growth hormone (GH) is secreted by the pituitary gland and regulates growth and development of all organs in the body.
• Deficiency in Childhood: If there is a deficiency of GH during childhood, it leads to dwarfism, where an individual's growth is significantly stunted.
• Over-secretion in Childhood: Over-secretion of GH during childhood results in gigantism, where an individual grows to an abnormally tall stature.
  17. Insulin and Diabetes: Insulin is a hormone produced by the pancreas. Its primary function is to regulate blood sugar (glucose) levels. It facilitates the uptake of glucose from the blood into cells (like liver and muscle cells) for energy or storage (as glycogen).
  Diabetes Mellitus: If the pancreas does not secrete enough insulin, or if the body's cells become resistant to insulin's effects, blood glucose levels rise abnormally. This condition is called diabetes mellitus. High blood sugar levels can lead to various long-term health complications affecting the eyes, kidneys, nerves, and heart. Patients with diabetes are often treated with insulin injections to help manage their blood glucose levels.
  18. Hormones and Secondary Sexual Characteristics:
• Males: Testosterone, secreted by the testes, is the primary male sex hormone. It is responsible for the development of male secondary sexual characteristics during puberty, such as the growth of facial and body hair, deepening of the voice, development of muscles, and maturation of the reproductive organs.
• Females: Oestrogen, secreted by the ovaries, is the primary female sex hormone. It drives the development of female secondary sexual characteristics during puberty, including the development of breasts, widening of the hips, and the onset of the menstrual cycle. Progesterone, also from the ovaries, plays a role in the menstrual cycle and pregnancy.
  19. Feedback Mechanism: A feedback mechanism is a regulatory process where the output of a system influences its own operation. In hormonal regulation, it ensures that hormone levels are maintained within a precise range.
  Example: Insulin Secretion:
• When blood sugar levels rise (e.g., after a meal), specialized cells in the pancreas detect this increase.
• In response, the pancreas secretes more insulin into the bloodstream.
• Insulin promotes the uptake of glucose by cells, thus lowering blood sugar levels.
• As blood sugar levels fall back to normal, the stimulus for insulin secretion diminishes, and the pancreas reduces the amount of insulin released. This is an example of negative feedback, where the response counteracts the initial stimulus.
  20. In a drought situation, a plant would experience water scarcity. The plant hormones would respond as follows:
• Abscisic Acid (ABA): ABA levels would significantly increase. ABA is the primary hormone responsible for drought tolerance. It would cause the stomata on the leaves to close, reducing water loss through transpiration. It also induces dormancy in seeds and buds, helping the plant to survive unfavorable conditions.
• Gibberellins and Auxins: Their levels might decrease or their synthesis could be inhibited, as they generally promote growth, which would be detrimental during drought.
• Cytokinins: Their role might be complex, but they are generally involved in cell division and differentiation, which would likely be suppressed under severe water stress.
  Overall, the hormonal response would be geared towards water conservation and survival, prioritizing reduced water loss and maintenance of essential functions over active growth.