BIo unit 14

1. Homeostasis: Blood Glucose Control

• Negative Feedback Mechanism: Blood glucose levels are maintained at a set point through the production of two hormones: insulin and glucagon.

• High Blood Glucose: Detected by receptors in the pancreas, which then releases insulin to lower blood glucose concentration.

• Low Blood Glucose: The pancreas releases glucagon, which is transported to the liver and muscles.

• Glucagon Action: Causes the liver to convert glycogen back into glucose, which is then released into the blood to return levels to the set point.

2. Type 1 Diabetes

• Condition: A state where the pancreas fails to produce insulin because insulin-secreting cells are damaged or non-functional.

• Symptoms: High blood glucose levels, glucose excreted in urine, slow wound healing, and feeling tired or thirsty.

• Treatment: Managed through insulin injections, regular blood glucose monitoring, and a controlled diet.

3. Temperature Control (Homeostasis)

• Skin Structure: Composed of the epidermis (outer layer) and the dermis (inner layer containing blood vessels and receptors).

• Cold Response (Heat Retention):

• Vasoconstriction: Arterioles narrow and shunt vessels open, diverting blood away from the skin surface to prevent heat loss.

• Piloerection: Hair erector muscles contract, causing hairs to stand upright and trap a layer of air that acts as an insulator.

• Shivering: Muscles contract and relax rapidly to generate heat through respiration.

• Heat Response (Heat Loss):

• Vasodilation: Arterioles widen and shunt vessels close, allowing more blood to flow near the skin surface to lose heat.

• Sweating: Sweat glands release sweat; the evaporation of this moisture requires energy, which cools the skin and body.

4. Plant Tropic Responses

• Definitions:

• Phototropism: Growth response to light.

• Gravitropism (Geotropism): Growth response to gravity.

• Direction of Growth:

• Shoots: Positively phototropic (grow toward light for photosynthesis) and negatively gravitropic (grow upward).

• Roots: Positively gravitropic (grow downward to anchor the plant and absorb water) and negatively phototropic.

• Auxins (Plant Hormones):

• Made in the shoot tips and move down to other parts of the plant.

• Phototropism Mechanism: Auxin accumulates on the shaded (dark) side of the shoot, causing those cells to elongate faster, which bends the tip toward the light.

• Gravitropism Mechanism: In a horizontal shoot, auxin collects on the lower side due to gravity, stimulating faster growth on that side and causing the shoot to bend upward.