Question

1). Explain why positive feedback is more likely than negative feedback to disturb homeostasis.

2). What is the main chemical similarity between carbohydrates and lipids? What are the main differences between them?

3). Define hypotonic, isotonic, and hypertonic, and explain why

these concepts are important in clinical medical practice.

4). Summarize the structural and functional differences between DNA and RNA.

Answer 1

1. The biological definition of homeostasis is “the tendency of an organism or cell to regulate its internal environment and maintain equilibrium, usually by a system of feedback controls, so as to stabilize health and functioning”. Generally, the body is in homeostasis when its needs are met and its functioning properly.

Every organ in the body contributes to homeostasis. A complex set of chemical, thermal, and neural factors interact in complex ways, both helping and hindering the body while it works to maintain homeostasis.

Homeostatic control

To maintain homeostasis, communication within the body is essential. The image below is an example of how a homeostatic control system works. Here is a brief explanation:

1. Stimulus– produces a change to a variable (the factor being regulated).
2. Receptor– detects the change. The receptor monitors the environment and responds to change (stimuli).
3. Input– information travels along the (afferent) pathway to the control center. The control center determines the appropriate response and course of action.
4. Output– information sent from the control center travels down the (efferent) pathway to the effector.
5. Response– a response from the effector balances out the original stimulus to.

Negative feedback:

Almost all homeostatic control mechanisms are negative feedback mechanisms. These mechanisms change the variable back to its original state or “ideal value”.

A good example of a negative feedback mechanism is a home thermostat (heating system). The thermostat contains the receptor (thermometer) and control center. If the heating system is set at 70 degrees Fahrenheit, the heat (effector) is turned on if the temperature drops below 70 degrees Fahrenheit. After the heater heats the house to 70 degrees Fahrenheit, it shuts off effectively maintaining the ideal temperature.

Positive feedback:

A positive feedback mechanism is the exact opposite of a negative feedback mechanism. With negative feedback, the output reduces the original effect of the stimulus. In a positive feedback system, the output enhances the original stimulus. A good example of a positive feedback system is child birth. During labor, a hormone called oxytocin is released that intensifies and speeds up contractions. The increase in contractions causes more oxytocin to be released and the cycle goes on until the baby is born. The birth ends the release of oxytocin and ends the positive feedback mechanism.

2. Similarities: Complex carbohydrates (e.g. polysaccharides) and lipids both contain a lot of chemical energy and can be used for energy storage. Complex carbohydrates and lipids are both insoluble in water - they are not easily transported.

Differences: Lipid molecules contain more energy per gram than carbohydrates (about twice as much) Carbohydrates are more readily digested than lipids and release their energy more rapidly. Monosaccharides and disaccharides are water soluble and easier to transport to and from storage sites than lipids.

3. To a substance, isotonic solution means it has the same equal water potential to the substance. Hypertonic solution means the solution has lower water potential than the substanc. Hypotonic solution means the solution has higher water potential than the substanc.

Clinical importance-

Tonicity determines whether osmosis pushes water out of the cell or into it. Cells hypertonic to their environment can swell and burst from the water that flows in. Cells hypotonic to their environment can shrivel because the water in their cytosol flows out.

4. DNA and RNA are different from their structure, functions, and stabilities. DNA has four nitrogen bases adenine, thymine, cytosine, and guanine and for RNA instead of thymine, it has uracil. Also, DNA is double-stranded and RNA is single-stranded which is why RNA can leave the nucleus and DNA can't.

DNA is stable under alkaline conditions, while RNA is not stable. DNA and RNA perform different functions in humans. DNA is responsible for storing and transferring genetic information, while RNA directly codes for amino acids and acts as a messenger between DNA and ribosomes to make proteins.