Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Hormones are chemical substances produced by endocrine glands and carried by the blood, which alter the activity of one or more specific target organs.
The endocrine system provides a slower, longer-lasting response compared to the nervous system, communicating via chemical signals rather than electrical impulses.
Adrenaline is the 'fight or flight' hormone secreted by the adrenal glands; it increases heart rate, breathing rate, and stimulates the liver to convert glycogen into glucose () to increase energy availability.
Homeostasis is the maintenance of a constant internal environment. This is achieved via negative feedback loops, where a change in a parameter (e.g., temperature at ) triggers a response that reverses that change.
Blood glucose concentration is regulated by the pancreas. When glucose levels are high, insulin is secreted to convert glucose into insoluble glycogen (). When levels are low, glucagon is secreted to convert glycogen back into glucose.
Type 1 Diabetes is caused by the failure of the pancreas to produce sufficient insulin, leading to dangerously high blood glucose levels.
Auxin is a plant hormone (specifically - Indole-3-acetic acid) that controls growth by stimulating cell elongation. In phototropism, auxin moves to the shaded side of the shoot, causing it to bend toward the light.
📐Formulae
💡Examples
Problem 1:
Explain the role of the liver and pancreas when blood glucose concentration drops below the normal threshold of approximately .
Solution:
The pancreas detects the decrease in blood glucose. The -cells in the Islets of Langerhans secrete the hormone glucagon into the blood. Glucagon travels to the liver, where it triggers the breakdown of glycogen into glucose (). This glucose is then released into the bloodstream to raise the concentration back to the set point.
Explanation:
This is a negative feedback mechanism. Glucagon acts as the chemical messenger that coordinates the response between the sensor (pancreas) and the effector (liver).
Problem 2:
Describe how auxin causes a plant shoot to grow towards a unidirectional light source.
Solution:
Auxin () is produced in the shoot tip. When light shines from one side, auxin molecules move away from the light and accumulate on the shaded side of the shoot. This high concentration of auxin stimulates cells on the shaded side to elongate more than cells on the light side. This unequal growth causes the shoot to bend toward the light ().
Explanation:
This process is known as positive phototropism. The hormone auxin redistributes itself to ensure the plant maximizes light absorption for photosynthesis.