Question

check your recall

1. what requirements of organisms does the external environment provide?
2. why is homeostasis important to survival?
3. describe two homeostatic mechanisms.

Explanation:

1.

Organisms need the external environment to provide nutrients (for energy and building materials), oxygen (for cellular respiration in aerobic organisms), water (for metabolic processes, transport, and maintaining cell structure), and a suitable temperature range (to ensure enzymes and metabolic reactions function properly). Also, some organisms need light (for photosynthesis in autotrophs) and a proper atmospheric pressure (especially for gas exchange in respiratory systems).

Homeostasis is the maintenance of a stable internal environment. Cells and biochemical reactions within organisms function optimally within a narrow range of conditions (e.g., pH, temperature, glucose concentration). If homeostasis is disrupted, enzymes may denature, metabolic pathways may fail, and cells/tissues/organ systems can be damaged. Without maintaining homeostasis, the organism's survival is threatened as essential life - sustaining processes will not occur properly.

• Negative Feedback (e.g., Temperature Regulation in Humans): When body temperature rises above the set point (around 37°C), thermoreceptors in the skin and hypothalamus detect the change. The hypothalamus sends signals to effectors: sweat glands secrete sweat (which evaporates to cool the body) and blood vessels in the skin dilate (to release heat). As body temperature decreases back to the set point, the feedback loop is inhibited. If body temperature drops below the set point, blood vessels constrict (to conserve heat) and skeletal muscles contract (shivering to produce heat), until temperature returns to normal.
• Blood Glucose Regulation (Negative Feedback): After a meal, blood glucose levels rise. The pancreas detects this and secretes insulin. Insulin causes cells (especially liver and muscle cells) to take up glucose, and the liver to convert glucose to glycogen. This lowers blood glucose levels. When blood glucose levels drop (e.g., between meals), the pancreas secretes glucagon. Glucagon causes the liver to break down glycogen into glucose and release it into the blood, raising blood glucose levels back to the normal range.

Answer:

The external environment provides organisms with nutrients, oxygen, water, suitable temperature, light (for autotrophs), and appropriate atmospheric pressure.

2.