Dynamic EquilibriumDynamic Equilibrium

Constant small changes to help Constant small changes to help maintain homeostasis.maintain homeostasis.

What does it all mean?What does it all mean?

Let’s deconstruct the term “dynamic Let’s deconstruct the term “dynamic equilibrium”.equilibrium”.

Dynamic means that it is always in motion. Dynamic means that it is always in motion. The opposite to dynamic is “static”.The opposite to dynamic is “static”.

Equilibrium means that it exists within a Equilibrium means that it exists within a narrow range.narrow range.

In other words, homeostasis and dynamic In other words, homeostasis and dynamic equilibrium are homonyms.equilibrium are homonyms.

Graphing dynamic equilibriumGraphing dynamic equilibrium

A common example of A common example of dynamic equilibrium in the dynamic equilibrium in the human body is the human body is the maintaing of blood sugar maintaing of blood sugar levels.levels.

After eating a meal, blood After eating a meal, blood sugar levels increase.sugar levels increase.

In response to this, the In response to this, the body secretes insulin to body secretes insulin to remove sugar.remove sugar.

If the blood sugar level If the blood sugar level goes to low, glucagon is goes to low, glucagon is secreted which converts secreted which converts glycogen back into sugar.glycogen back into sugar.

Effect of time on blood sugar level

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Guard Cells in plantsGuard Cells in plants

Plants also need to Plants also need to maintain homeostasis.maintain homeostasis.

The the bottom side of The the bottom side of a plants leaf are small a plants leaf are small openings known as openings known as stomates.stomates.

The stomate is a pore The stomate is a pore through which excess through which excess water vapor is water vapor is released by the plant.released by the plant.

Guard cells cont.Guard cells cont.

On either side of the stomate On either side of the stomate are two specialized cells called are two specialized cells called guard cells.guard cells.

During dry times, the guard cells During dry times, the guard cells change shape and close over change shape and close over the stomate.the stomate.

With the stomate closed, the With the stomate closed, the plant retains more water.plant retains more water.

If there is enough water present, If there is enough water present, the guard cells revert to their the guard cells revert to their original shape and the stomate original shape and the stomate remains open.remains open.

Feedback mechanismsFeedback mechanisms

There are two types of feedback mechanism, There are two types of feedback mechanism, negative and positive.negative and positive.

Negative feedback mechanism: a mechanism of Negative feedback mechanism: a mechanism of the endocrine system that chemically corrects an the endocrine system that chemically corrects an imbalance; called “negative feedback” because imbalance; called “negative feedback” because when the level of the imbalance decreases, the when the level of the imbalance decreases, the feedback stops the correcting effects. feedback stops the correcting effects.

The pancreas regulating blood sugar level is an The pancreas regulating blood sugar level is an example of a negative feedback mechanism.example of a negative feedback mechanism.

Negative feedback mechanisms promote stability.Negative feedback mechanisms promote stability.

Feedback mechanism cont.Feedback mechanism cont.

Positive feedback mechanism: A Positive feedback mechanism: A mechanism that enhances the process that mechanism that enhances the process that causes the mechanism in the first place causes the mechanism in the first place

These do not promote stability.These do not promote stability. Much rarer in living organisms.Much rarer in living organisms. Childbirth is an example of a positive Childbirth is an example of a positive

feedback mechanism. The childs head feedback mechanism. The childs head pressing on the uterus causes a contraction, pressing on the uterus causes a contraction, which increases pressure which leads which increases pressure which leads

Regents questions on dynamic Regents questions on dynamic equilibriumequilibrium

What usually results when an organism fails to What usually results when an organism fails to maintain homeostasis?maintain homeostasis?

(1) Growth rates within organs become equal.(1) Growth rates within organs become equal.(2) The organism becomes ill or may die.(2) The organism becomes ill or may die.(3) A constant sugar supply for the cells is (3) A constant sugar supply for the cells is produced.produced.(4) The water balance in the tissues of the (4) The water balance in the tissues of the organism stabilizes.organism stabilizes.

Question 2Question 2

If a human system fails to function properly, If a human system fails to function properly, what is the most likely result?what is the most likely result?

(1) a stable rate of metabolism(1) a stable rate of metabolism(2) a disturbance in homeostasis(2) a disturbance in homeostasis(3) a change in the method of cellular (3) a change in the method of cellular respirationrespiration(4) a change in the function of DNA (4) a change in the function of DNA

Question 3Question 3

An increase in the level of insulin in the An increase in the level of insulin in the blood would most directly result in blood would most directly result in

(1) a decrease in the amount of glucose in (1) a decrease in the amount of glucose in the bloodthe blood(2) a decrease in the amount of protein in (2) a decrease in the amount of protein in the bloodthe blood(3) an increase in the amount of fat in cells(3) an increase in the amount of fat in cells(4) an increase in the amount of carbon (4) an increase in the amount of carbon dioxide in cells dioxide in cells

Question 4Question 4

Which statement describes a feedback Which statement describes a feedback mechanism involving the human pancreas?mechanism involving the human pancreas?

1 The production of estrogen stimulates the 1 The production of estrogen stimulates the formation of gametes for sexual reproduction.formation of gametes for sexual reproduction.2 The level of oxygen in the blood is related to 2 The level of oxygen in the blood is related to heart rate.heart rate.3 The level of sugar in the blood is affected by the 3 The level of sugar in the blood is affected by the amount of insulin in the blood.amount of insulin in the blood.4 The production of urine allows for excretion of 4 The production of urine allows for excretion of cell wastecell waste

Question 5Question 5

Negative feedback mechanisms are best Negative feedback mechanisms are best described as processes that helpdescribed as processes that help

(1) reduce hormone levels to below normal (1) reduce hormone levels to below normal in the bloodin the blood(2) destroy hormones in the blood(2) destroy hormones in the blood(3) directly control muscle contraction in the (3) directly control muscle contraction in the legleg(4) keep body conditions near a normal, (4) keep body conditions near a normal, steady statesteady state