Homeostasis Notes

Engage: How do you lift books? Stack one book/notebook/folder/ on top of another one. Lift the two stacked books in front of you so the lowest book is about level with your shoulders. Hold for 30 seconds. Think about: how do your arms feel at the beginning? Toward the end? Balance one book on your head and walk three steps. Next, make a list in your science notebook of all the parts of your body to perform the activities we just completed.

The Sandlot - Homeostasis can be a learning experience!

The Sandlot

Homeostasis Homeostasis is the body’s tendency to keep an internal balance. Homeostasis is the process by which an organism’s internal environment is kept stable in spite of changes in the external environment.

Homeostasis For example, if you are well, your body keeps the same internal temperature whether the air around you is chilly or hot.

What does Sheldon say about homeostasis?

Stimulus and Response A stimulus is something inside or outside an organism’s body that causes the organism to react in some way.

Stimulus and Response An organism’s response is its action or change in behavior that occurs as the result of a stimulus.

Stress and homeostasis Stress is your body’s reaction to threatening, challenging, or disturbing events. Stress upsets homeostasis. A chemical called adrenaline is released into your bloodstream. Adrenaline gives you energy and causes other changes in your body that prepare you to take quick action.

Human body and homeostasis: All systems, including the human body, need a way of maintaining equilibrium, or balance. When a system is in equilibrium, it is stable, and all its parts function smoothly. The process by which the body’s internal environment is kept stable in spite of changes in the external environment is called homeostasis.

Negative feedback: Negative feedback is one way in which living systems maintain internal equilibrium, or homeostasis. In negative feedback, a process is turned off by the condition it produces. Negative feedback helps control the body temperature of birds and mammals.

Negative feedback: The evaporation of perspiration from the skin cools the body by removing the heat used to evaporate water. Shivering helps warm the body because the muscle contractions involved in shivering require energy, the production of which generates heat.

Negative feedback: Negative feedback also helps control the level of the sugar glucose in the blood. This type of feedback involves chemical reactions that are controlled by hormones. A hormone is a chemical produced by an endocrine gland that affects the activity of a tissue or organ.

Negative feedback: One hormone that helps regulate glucose levels is insulin, which is produced by an organ called the pancreas. When the blood sugar level is high, the pancreas releases insulin. Insulin stimulates the body cells to take up sugar from the blood. Low levels of sugar in the blood "turn off " the production of insulin.

Negative feedback: Plants need to maintain water equilibrium in spite of changing conditions in the environment. Many plants obtain water through the roots. Substances (like sugars) move back and forth through the cell membranes of root cells by a process called diffusion.

Negative feedback: In diffusion, molecules move from an area in which they are highly concentrated into one in which their concentration is lower. The diffusion of water, called osmosis, contributes to a plant’s ability to maintain water balance.

Negative feedback: The pressure of water against the cell wall of a plant cell is called turgor pressure. Turgor pressure helps give shape and firmness to plant stems and leaves.

Negative feedback: When plant cells contain a lot of water and turgor pressure is high, the movement of water molecules into the cells slows down. Equilibrium is reached when the number of water molecules that enter the cell is equal to the number of water molecules that leave the cell.

Negative feedback Animals also need to maintain water balance. Thirst makes animals drink water. The kidneys adjust the amount of water in the blood by changing the concentration of water in the urine.

Positive feedback: Positive feedback is less common, which is understandable, as most changes to steady state pose a threat, and to enhance them would be most unhelpful.

Positive feedback: In positive feedback the response is to amplify (or increase) the response based on the stimulus. Therefore, the change in that variable increases more in the same direction.

Positive feedback: A baby begins to suckle her mother's nipple and a few drops of milk are released (the stimulus). This encourages the baby and releases a hormone in the mother which further stimulates the release of milk (the response). The hungry baby continues to suckle, stimulating more milk release until she stops. The more the baby suckled the milk, the more milk the mother produces.

Positive feedback: A ripening apple releases the plant hormone ethylene (the stimulus). Ethylene accelerates the ripening of unripe fruit in its vicinity so nearby fruit also ripens, releasing more ethylene (the response). All the fruit quickly becomes ripe together. You know the saying "One 'bad' apple has ruined the bunch.

Exit Ticket: Define homeostasis and give one example in your OWN words! You cannot leave the room without completing this!!!