4.20.23 - Topic 4 - Homeostasis/Transport - Keystone Review

In the human body, the steroid aldosterone is released by the adrenal glands to help regulate sodium and potassium levels. This regulation helps control blood pressure and the balance of- fluids in blood. Which statement best describes this process of regulation within the body?

• It is a feedback system that maintains homeostasis.

• It is a response that is only a result of medical intervention.

• It is a response by the body that is used only in extreme situations.

• It is a feedback system that moves the body further from equilibrium.

Answer explanation

The hormone aldosterone helps regulate blood volume as part of the negative feedback loop for water balance (homeostasis) in

the human body.

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NGSS.HS-LS1-3

How does a mitochondrion facilitate the movement of some materials between cells?

• It supplies the energy needed for moving molecules through membranes.

• It manufactures the proteins needed to form channels in cell membranes.

• It supplies digestive substances that break large molecules into smaller units.

• It produces fibers that attach to molecules and move them through the cytoplasm.

Answer explanation

Mitochondria convert glucose to ATP, the primary molecule of energy transfer for cells.

Which of the following is most involved in providing structure for a plasma membrane?

• the number of protein channels embedded in the membrane

• the types of carbohydrates attached to proteins on the surface

• the types of proteins that are attached to the surface of the membrane

• the arrangement of the hydrophobic and hydrophilic ends of the phospholipids

Answer explanation

The arrangement of the phospholipids makes the membrane thin and flexible and limits the substances that can pass into and out of the cell.

A sodium-potassium pump within a cell membrane requires energy to move sodium and potassium ions into or out of a cell. The movement of glucose into or out of a cell does not require energy. Which statement best describes the movement of these materials across a cell membrane?

• Sodium and potassium ions move by active transport, and glucose moves by osmosis.

• Sodium and potassium ions move by active transport, and glucose moves by facilitated diffusion.

• Sodium and potassium ions move by facilitated diffusion, and glucose moves by osmosis.

• Sodium and potassium ions move by facilitated diffusion, and glucose moves by active transport.

Answer explanation

Due to the fact that they are highly charged molecules (and “hate” the nonpolar cell membrane and can’t pass through it) and are trying to move against a concentration gradient (from low to high), sodium and potassium ions require a protein and energy to move across the cell membrane. Glucose is a large enough molecule (and polar), so it needs the ‘help’ of a protein to move it along (facilitated diffusion)

Select three changes experienced by the students and explain how each change can represent a homeostatic mechanism.

Answer explanation

•• Sweating is a response to increased temperature. The evaporation of sweat cools the body (lowers the temperature).

•• Muscle cramps are a response to depleted electrolytes, dehydration, depletion of ATP, or

build-up of lactic acid. The cramps will cause the person to slow down or stop, thus reducing the depletion of electrolytes, water, and ATP.

•• Decreased energy is a response to insufficient oxygenation of tissues, or depletion of fuel (glucose) or water. Fatigue will cause the person to slow down or stop, allowing time for the

body to stabilize.

•• Increased heart rate is a response to the tissues (especially muscles) needing more oxygen. The heart pumps faster in order to supply the muscles with oxygen faster. (This also helps the body get rid of carbon dioxide more quickly.)

•• Increased breathing rate is a response to the need for more oxygen and the need to rid the body of carbon dioxide. The faster breathing rate will help supply oxygen to muscles more quickly and also eliminate carbon dioxide more quickly.

•• Increased thirst is a response to dehydration caused by sweating and increased breathing rate. Thirst will cause the person to seek water to drink to achieve homeostasis.

•• Increased temperature is caused when some of the energy that powers muscles is lost as heat. The rise in temperature stimulates sweating, which helps cool the body and bring the

temperature back to normal. Increased temperature also contributes to increased heart rate and breathing rate. “Feeling hot” may cause a person to seek shade or air conditioning, or to slow down or stop, allowing the body to achieve homeostasis.

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NGSS.HS-LS1-3

A jackrabbit has large ears containing blood vessels that help it maintain a constant body temperature by adjusting heat exchange with the surrounding environment. Which characteristic of life is best described by this example?

• growth

• energy use

• organization

• homeostasis

Answer explanation

The process of adjusting heat exchange is an example of maintaining a stable internal environment, which is homeostasis.

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NGSS.HS-LS1-3

All living organisms must maintain homeostasis in order to survive. Which statement best describes one way humans maintain homeostasis?

• Temperature is regulated by giving off carbon dioxide.

• Water content is regulated by giving off carbon dioxide.

• Temperature is regulated by sweating.

• Water content is regulated by sweating.

Answer explanation

Sweating involves the release of water through pores in the skin, and as the water evaporates, heat is removed from the skin, reducing body temperature.

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NGSS.HS-LS1-3

Which statement best describes how active transport differs from passive transport?

• Only active transport requires ATP.

• Only active transport moves small particles.

• Only active transport relies on a plasma membrane.

• Only active transport allows substances to leave a cell.

Answer explanation

Active transport requires ATP energy; passive transport occurs without an input of energy.

The indicated protein is part of a cell membrane. What is the most likely purpose of this protein?

• It allows passage of particles into and out of the cell.

• It manufactures phospholipids to repair membrane damage.

• It releases stored chemical energy in membrane carbohydrates.

• It attracts unbalanced electrical charges in the cell’s environment.

Answer explanation

A protein that extends across the cell membrane functions as a pathway that allows ions and molecules to move into and out of the cell.

Which action is prevented by the plasma membrane?

• the flow of light into or out of the cell

• the flow of oxygen into or out of the cell

• unlimited flow of heat into or out of the cell

• unlimited flow of water into or out of the cell

Answer explanation

Water flow into or out of a cell is limited; it depends on the solute concentration inside or outside the cell.

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NGSS.HS-LS1-3