Question

Define metabolism, metabolic rate, and homeostasis. (p. 10) a. Give an example of an external change and explain how the body responds to maintain homeostasis. b. Give an example of an internal change and explain how the body responds to maintain homeostasis. c. Briefly explain how a negative feedback mechanism works and how a positive feedback mechanism differs.

Short answer

Question: Define metabolism, metabolic rate, and homeostasis. Provide examples of an external change and an internal change and explain how the body responds to maintain homeostasis for each. Explain the differences between negative and positive feedback mechanisms. Answer: Metabolism is the sum of all chemical reactions within an organism, necessary for life maintenance, growth, and reproduction. Metabolic rate refers to the rate at which these reactions occur, usually measured in energy expenditure per unit of time. Homeostasis is an organism's ability to maintain a stable internal environment despite external and internal changes. An external change example is cold temperature exposure. The body maintains homeostasis by constricting blood vessels (vasoconstriction) and conserving body heat, as well as increasing heat production through shivering. An internal change example is increased blood sugar levels after a sugary meal. The body maintains homeostasis by releasing insulin, which promotes glucose uptake by cells and regulates blood sugar levels. Negative feedback mechanisms counteract changes in the body's environment to maintain homeostasis, like insulin release to lower high blood sugar levels. Positive feedback mechanisms amplify changes, often leading to escalated events like blood clotting, where platelets attract more platelets to seal a damaged blood vessel.

Step-by-step solution

Part a: Definition of metabolism, metabolic rate, and homeostasis

Metabolism is the sum of all chemical reactions occurring within an organism, which are necessary for the maintenance of life, growth, and reproduction. Metabolic rate is the rate at which metabolic reactions occur in an organism, generally measured in terms of energy expenditure per unit of time. Homeostasis is the ability of an organism to maintain a stable internal environment in response to changes in external and internal conditions.

Part a: External change example and response

An example of an external change is exposure to cold temperatures. When the body is exposed to cold, it responds to maintain homeostasis by constricting blood vessels, reducing blood flow to the skin, and conserving body heat. This process is called vasoconstriction. The body also increases heat production through shivering, which is involuntary muscle contractions that generate heat.

Part b: Internal change example and response

An example of an internal change is an increase in blood sugar levels after consuming a sugary meal. The body responds to maintain homeostasis by releasing insulin, a hormone produced by the pancreas. Insulin promotes the uptake of glucose (sugar) by cells and helps regulate blood sugar levels to prevent hyperglycemia (high blood sugar).

Part c: Explanation of negative and positive feedback mechanisms

A negative feedback mechanism is a physiological process that counteracts a change in the body's environment to maintain homeostasis. When a change is detected, negative feedback mechanisms initiate actions that restore the system to its normal state. For example, when blood sugar levels rise, the negative feedback response is the release of insulin, which lowers blood sugar levels back to their normal range. A positive feedback mechanism, on the other hand, amplifies a change in the body's environment, often leading to an escalation of events. Positive feedback mechanisms are usually involved in processes that need to be quickly completed, such as blood clotting. When a blood vessel is damaged, platelets begin to stick together and form a clot. This action releases chemicals that attract more platelets to the site, amplifying the clotting process until the blood vessel is sealed.

Key concepts

Metabolism

Metabolism is at the heart of virtually all biological processes. It refers to the complete set of chemical reactions taking place within a living organism. These reactions are crucial as they enable growth, reproduction, and the maintenance of cellular structures. Through metabolism, nutrients are broken down to produce energy, a process known as catabolism, and used to build up new cellular materials, called anabolism.

These dual processes ensure that organisms can adapt, evolve, and survive. Metabolic pathways can vary dramatically between different organisms, depending on their needs, environment, and evolutionary background. Metabolism is not static but responds dynamically to changes, both internal and external, such as temperature shifts or energy demands.

Metabolic Rate

Metabolic rate is essentially a measure of how quickly metabolism occurs. It represents the rate at which organisms convert nutrients into energy and new tissue. This rate is typically expressed as energy expenditure per time unit (like calories per hour).

• Basal Metabolic Rate (BMR): The energy expended while at rest in a neutrally temperate environment, in the post-absorptive state (meaning not actively digesting food).
• Influencing Factors: Age, sex, muscle mass, hormonal levels, and physical activity.

A person's metabolic rate is central to understanding how they process food, respond to exercise, and exploit stored energy. Individuals with a higher metabolic rate might require more food or energy to maintain their body functions compared to those with a lower metabolic rate.

Negative Feedback

Negative feedback is a balancing act performed by our body systems to maintain homeostasis. It works like a thermostat, detecting deviations from a set point and triggering processes to counteract those deviations. This ensures stability within the body's environment.

Consider how blood sugar is controlled: After eating, blood sugar levels rise. The pancreas, detecting this, releases insulin. Insulin facilitates the uptake of glucose by cells, thereby lowering blood sugar back to normal. This feedback loop prevents excessive swings in blood sugar levels, maintaining balance.

Negative feedback loops are critical for functions such as:

• Temperature regulation.
• Blood pressure stabilization.
• Hormonal level maintenance.

By constantly adjusting, negative feedback ensures that internal conditions remain within optimal limits.

Positive Feedback

Positive feedback, on the other hand, accelerates the change it feeds off. Unlike negative feedback, which aims to stabilize, positive feedback pushes processes to completion. It's like rolling a snowball down a hill, growing bigger and more forceful.

A classic example is childbirth: During labor, the release of oxytocin stimulates uterine contractions. These contractions cause further release of oxytocin, intensifying the contractions until delivery is achieved.

While less common than negative feedback, positive feedback is pivotal for processes requiring rapid or decisive action, such as:

• Blood clotting - where each step enhances the next until the process is complete.
• Neuronal action potentials - once fired, they lead to the propagation of nerve impulses.

Positive feedback is essential when swift progression is vital and when a runaway process needs to be rapidly concluded.