You have the ability to respond to stimuli on so many levels - molecular, cellular, physiological, and behavioral!
You have the ability to respond to stimuli on so many levels - molecular, cellular, physiological, and behavioral! (0:55) Maintaining internal conditions despite external and internal changes is the basis of homeostasis. There are two types of feedback mechanisms used by organisms - negative (2:30) and positive. (4:48) Homeostasis links to several units of study in the curriculum (5:37).
The Question of the Day asks (7:18) What paramecium organelle pumps out excess water when the cell is placed in a hypotonic environment?
Thank you for listening to The APsolute RecAP: Biology Edition!
(AP is a registered trademark of the College Board and is not affiliated with The APsolute RecAP. Copyright 2020 - The APsolute RecAP, LLC. All rights reserved.)
Website:
EMAIL:
Follow Us:
Hi and welcome to the APsolute Recap: Biology Edition. Today’s episode will recap homeostasis
Zoom out:
Unit 4 - Cell Communication and Cell Cycle
Topic - 4.5
Big idea - Energetics
Rawr! “Scared ya, didn’t?” Maybe not scared, but possibly startled. You looked up briefly, or tilted your head to one side. You weren’t expecting that noise on this podcast. Congrats! You responded to a stimuli - an essential part of maintaining homeostasis. You have the ability to respond on so many levels - molecular, cellular, physiological, and behavioral.
Let’s Zoom in:
One of the characteristics that all living things share is the ability to respond to stimuli. These stimuli (or signals) might be external in the organism’s environment and perceived through an organism's sense organs. Sounds, sights, touch and smell may all trigger a response by you! Walk in the door to the smell of chocolate chip cookies baking - and I’m pretty sure your first reaction will be to head to the kitchen. Stimuli can also be internal, from a cell’s own biochemistry. Bacterial invader? White blood cells initiate a coordinated antibody response. Either way, cells, the enzymes they contain and the multicellular organisms they form function best within a specific range of conditions. I like to refer to this as their Goldilocks zone. Everything isn’t the same from one cell to another, but it is just right for optimal functioning. Maintaining these internal conditions despite external and internal changes is the basis of homeostasis.
There are two types of feedback mechanisms used by organisms - negative and positive. No, not “bad” and “good”, but named after their associations to an organism’s “set point” or internal set of conditions. Negative brings conditions back to normal range whereas positive brings conditions further past the normal range. Negative/Normal - positive/past.
If the response reverses the stimulus, then the system is operating by negative feedback. This often results in the stopping or slowing down of a process in order to return to a set point, maintaining homeostasis. Two great examples of negative feedback are maintaining body temperature and keeping blood sugar levels constant. When you’re too cold, you shiver. But too hot - the response is likely heavy breathing and sweating. Each of which triggers other physiological responses to trap or release heat, depending on circumstance. The goal? Return to baseline - 98.6 degrees Fahrenheit or 37 degrees Celsius. We will need to recruit a few organs to control and maintain glucose concentration in the blood. The liver stores sugar as glycogen which can be converted into glucose when blood sugar is low and the pancreas releases the hormone glucagon. However, if blood sugar levels increase (like if you’ve had a big pasta dinner), then the pancreas secretes insulin, signaling the liver to store excess glucose as glycogen. And balance returns. It should be noted that variation of range is normal and moving beyond that range is also normal, as long as it's temporary for negative feedback.
In contrast, positive feedback is a mechanism that results in the amplification or growth of an output signal. This moves the organisms farther from the setpoint, disrupting homeostasis. Positive pushes past normal range. This is more rare than negative feedback. But sometimes greater change is necessary. We see this with lactation in mammals - where suckling stimulates more milk production. This is also seen with fruit ripening, with ethylene gas production triggering more fruit to also ripen. This is the foundation of the paper bag trick - when you place an unripe tomato in a bag, trapping ethylene gas and causing the fruit to ripen faster! Yes… tomato is a fruit. That's for another episode.
Time for unit connections. Homeostasis is a large part of unit 2 as cells maintain internal conditions through transport mechanisms across membranes. Molecules are constantly moving which causes concentrations to continually shift. Homeostasis also correlates to Unit 7 - Natural Selection. Mechanisms that are conserved or diverged across related organisms suggests common ancestry or evolutionary change due selective pressures. It also connects to Unit 8 - Ecology with many examples of organisms responding to their environment, such as phototropism, taxis and kinesis, as well as nocturnal activity.
Alright - what about the exam? There may be questions about a disruption to the homeostasis - whether it be toxin, salinity, or temperature - you will need to draw conclusions. Cause & effect. Predict the outcome. Or maybe you’ll need to analyze a negative feedback loop with hormones and structures you’ve never heard of - like Calcitonin and the Thyroid. We’ve said this before, but we’ll say it again. Focus on the big picture concept and apply it to new circumstances. Those unknown terms are just placeholders in the biological equation.
To recap……
Homeostasis is the maintenance of constant internal conditions despite internal and external changes. The timing and coordination of biological mechanisms involved in reproduction, growth and dynamic homeostasis depend on living things reacting to environmental signals. Maintaining homeostasis is achieved by negative feedback and disrupted by positive feedback mechanisms.
Coming up next on the Apsolute RecAP Biology Edition: Mitosis
Today’s question of the day is about organelles.
Question of the day: What paramecium organelle pumps out excess water when the cell is placed in a hypotonic environment?