Homeostasis & Transport

Homeostasis is the process through which an organism regulates its internal environment in order to maintain a stable and constant condition.
An example of homeostasis is the regulation of the glucose sugar level in blood through the interaction of the hormones insulin and glucagon.  
What happens if the body is unable to maintain its blood glucose level?

• This regulation is unnecessary to the viability of organisms.
• The body adapts to a different blood glucose level.
• New hormones are created to solve the problem.
• Diseases, such as diabetes and hypoglycemia, result.

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How is homeostasis important to the survival of organisms?

• Homeostasis makes organisms grow bigger and taller.
• Homeostasis helps organisms locate food.
• Homeostasis allows organisms to regulate their temperature.
• Homeostasis makes all organisms hibernate.

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Cells can function

• at any temperature and pH.
• only in a narrow range of temperature and pH.
• in rapidly changing temperatures and pHs.
• in a wide range of pHs and temperatures.

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Homeostasis is the regulation of metabolic processes within an organism in order to maintain the stable internal conditions required for life.
The human respiratory system includes the nose, the larynx, and the lungs.  This body system helps maintain homeostasis by

• enabling gas exchange in the body.
• transporting oxygen to other organ systems.
• removing solid waste from the body.
• regulating hormone levels in the body.

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Homeostasis is classified under which of the following?

• transcription
• cell regulation
• photosynthesis
• cell respiration

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The cell membrane is a highly selective barrier that controls the movement of substances in and out of the cell.  In fact, polar molecules are unable to go across unless

• they are broken down into smaller pieces.
• they are enclosed in water-filled vesicles.
• they pass through channels in the cell membrane.
• they react with other substances to become nonpolar.

Permeability is the condition of being capable of having materials flow into and out of a membrane.  The permeability of a cell membrane is determined by how easily a molecule can diffuse across the membrane.  Usually, only molecules that are fat-soluble can permeate across a cell membrane.  Why is this the case?

• Water-soluble molecules are nonpolar.
• Water-soluble molecules are too large.
• Cell membranes are composed of a lipid bilayer.
• Cell membranes are composed of cytosol.

Organisms must be able to adapt to a changing external and internal environment.  An organism's ability to maintain a stable internal environment is known as homeostasis.  How does a cell's membrane help an organism maintain homeostasis?

• Cell membranes directly control the temperature of the cell.
• Cell membranes control the substances that enter or leave cells.
• Cell membranes use a large portion of the cell's energy supply.
• Cell membranes protect the cell organelles from large doses of radiation.

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The cell membrane, or plasma membrane, is made up of a lipid bilayer in which hydrophilic heads face outward and hydrophobic tails face inward.
This arrangement within the cell membrane allows it to 

• fuse with ribosomes during DNA replication.
• absorb water from the cytoplasm whenever necessary.
• keep out all viral and bacterial infections.
• control the movement of substances in and out of the cell.

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The fluid mosaic model shown above describes the structure and function of

• chloroplasts.
• chromosomes.
• nuclei.
• cell membranes.