What is Homeostasis & immunity on the Living Environment Regents?

Homeostasis & immunity is a Human Systems topic on the Living Environment Regents. RegentsLab has 22 practice questions on it, each with a full worked solution.

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Homeostasis & immunity: Living Environment Regents Practice

Practice Homeostasis & immunity for the Living Environment Regents with real-style questions and full worked solutions. Miss one? Read the solution — the exam reuses the same ideas every year.

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Question 65 · 2 pts

After a person eats a meal high in sugar, the pancreas releases insulin. Insulin signals body cells to take in glucose, which lowers the blood sugar level back toward normal. This process is an example of

(A) a mutation occurring in the cells of the pancreas
(B) natural selection acting on body cells
(C) an immune response to a disease-causing pathogen
(D) a feedback mechanism that maintains homeostasis ✓

Worked solution

$\text{high blood glucose} \to \text{pancreas releases insulin}$ A change away from the set point triggers a response.

$\text{cells absorb glucose} \to \text{blood glucose returns to normal}$ The response reverses the change, which is negative feedback.

Answer: \text{a feedback mechanism that maintains homeostasis}

Negative feedback detects a change from the normal set point and triggers a response that reverses it, keeping the internal environment stable (homeostasis).

Question 66 · 2 pts

Which type of blood cell is mainly responsible for defending the body against disease-causing organisms?

(A) red blood cells
(B) white blood cells ✓
(C) platelets
(D) muscle cells

Worked solution

$\text{pathogen enters body} \to \text{white blood cells respond}$ Some white blood cells engulf pathogens while others produce antibodies.

Answer: \text{white blood cells}

White blood cells are the immune system's main defenders, engulfing invaders and producing antibodies against them.

Question 76 · 2 pts

Which type of blood cell defends the body by engulfing and destroying invading bacteria?

(A) nerve cells
(B) white blood cells ✓
(C) red blood cells
(D) platelets

Worked solution

$\text{pathogen enters} \Rightarrow \text{white blood cells respond}$ Some engulf invaders while others make antibodies.

$\Rightarrow \text{pathogen destroyed}$ This helps maintain a stable internal environment.

Answer: white blood cells

White blood cells are the body's main immune defenders; some engulf and destroy pathogens while others produce antibodies.

Question 10 · 2 pts

After a meal, a person's blood glucose level rises. The pancreas responds by releasing insulin, which causes body cells to take up more glucose, lowering blood glucose back toward a normal level. This process is an example of

(A) negative feedback maintaining homeostasis ✓
(B) asexual reproduction of pancreatic cells
(C) positive feedback increasing blood glucose further
(D) an immune response to a pathogen

Worked solution

$Homeostasis is the maintenance of a stable internal environment despite external changes.$ definition

$A rise in blood glucose triggers insulin release, which lowers glucose back toward the normal range, reversing the original change.$

$A response that counteracts and reverses an initial change is negative feedback.$

Answer: negative feedback maintaining homeostasis

Negative feedback mechanisms detect a change from a normal set point and trigger a response, such as insulin release, that counteracts the change and restores the internal environment toward normal, maintaining homeostasis.

Question 33 · 1 pt

When a person becomes too warm, they begin to sweat, which cools the body. This is an example of

(A) asexual reproduction
(B) a genetic mutation
(C) natural selection
(D) maintaining homeostasis ✓

Worked solution

$\text{stimulus} \to \text{response} \to \text{balance}$ Negative feedback restores the set point.

Answer: \text{homeostasis}

Sweating is a feedback response that returns body temperature toward its set point, maintaining a stable internal environment (homeostasis).

Question 67 · 2 pts

A foreign molecule on the surface of a bacterium that the immune system recognizes and reacts against is called

(A) a hormone
(B) an antigen ✓
(C) an enzyme
(D) an antibody

Worked solution

$\text{foreign marker} = \text{antigen}$ Antigens are recognized as not belonging to the body.

$\text{antigen} \to \text{body produces matching antibody}$ The antigen is the trigger; the antibody is the made-to-fit response.

Answer: \text{an antigen}

Antigens are foreign markers that the immune system recognizes, prompting white blood cells to make antibodies shaped to bind that specific antigen.

Question 68 · 2 pts

A vaccine for measles contains weakened or inactivated measles viruses. The vaccine protects a person mainly by

(A) stimulating the immune system to produce antibodies and memory cells against the measles virus ✓
(B) supplying antibodies that were made by another person's immune system
(C) directly killing measles viruses found in the surrounding environment
(D) changing the DNA of body cells so the virus can no longer enter them

Worked solution

$\text{weakened virus antigens} \to \text{immune response}$ The body treats the vaccine antigens as a real threat.

$\to \text{antibodies} + \text{memory cells}$ Memory cells allow a fast, strong response if the real virus appears later.

Answer: \text{stimulates production of antibodies and memory cells}

A vaccine exposes the immune system to harmless antigens so it builds antibodies and memory cells, providing active immunity before any real infection occurs.

Question 69 · 2 pts

A doctor explains that antibiotics will not help treat a patient's flu, which is a viral infection. The best explanation is that antibiotics

(A) only work after the patient has already received a vaccine
(B) cause the immune system to stop making white blood cells
(C) are broken down by the high body temperature of a fever
(D) act on structures and processes found in bacteria, which viruses do not have ✓

Worked solution

$\text{antibiotic} \to \text{targets bacterial cell wall and ribosomes}$ These structures exist in bacteria.

$\text{virus} \ne \text{bacterium}$ Viruses lack these structures, so the antibiotic has nothing to act on.

Answer: \text{antibiotics target bacteria, not viruses}

Antibiotics disrupt bacterial structures and processes; viruses are not cells and lack those targets, so antibiotics cannot treat viral infections.

Question 70 · 2 pts

During an allergic reaction, a person's immune system responds strongly to a substance such as pollen that is normally harmless. This reaction is best described as

(A) the immune system overreacting to a normally harmless antigen ✓
(B) a sign that the immune system has stopped working entirely
(C) the body producing extra red blood cells in response to pollen
(D) a beneficial mutation occurring in the person's white blood cells

Worked solution

$\text{harmless substance (pollen)} \to \text{immune response triggered}$ The immune system treats the harmless antigen as a threat.

$\text{overreaction} \to \text{allergy symptoms}$ Symptoms such as sneezing and swelling result from the excessive response.

Answer: \text{an immune overreaction to a harmless antigen}

An allergy is an exaggerated immune response to a substance that is not actually dangerous, showing the immune system is active but overreacting.

Question 73 · 2 pts

After a person eats a meal high in sugar, the blood glucose level rises. In response, the pancreas releases insulin, which lowers the blood glucose level back toward normal. This process is best described as

(A) positive feedback that amplifies the change
(B) negative feedback that maintains homeostasis ✓
(C) a mutation occurring in the pancreas
(D) an immune response to a pathogen

Worked solution

$\uparrow \text{glucose} \Rightarrow \text{pancreas releases insulin}$ The hormone signals body cells to take up glucose.

$\Rightarrow \text{glucose returns to set point}$ The response opposes the original change.

Answer: negative feedback

Insulin from the pancreas counteracts a rise in blood glucose and returns it to the set point, a negative feedback loop that maintains homeostasis.

Question 75 · 2 pts

A vaccine usually contains a weakened or dead form of a pathogen. Receiving a vaccine helps protect a person because it

(A) supplies antibiotics that kill the pathogen directly
(B) provides extra red blood cells to carry oxygen
(C) stimulates the immune system to make antibodies and memory cells ✓
(D) changes the person's genes so they cannot get sick

Worked solution

$\text{weakened pathogen} \Rightarrow \text{immune response}$ The body reacts as if to a real invader.

$\Rightarrow \text{antibodies} + \text{memory cells}$ Memory cells allow a fast response if the real pathogen appears later.

Answer: produces antibodies and memory cells

A vaccine exposes the immune system to a harmless form of a pathogen so it makes antibodies and memory cells, giving a fast response if the actual pathogen is encountered later.

Question 77 · 2 pts

A person's immune system reacts strongly to pollen, a normally harmless substance, causing sneezing and watery eyes. This reaction is best described as

(A) an inherited blood-type disorder
(B) an allergic reaction ✓
(C) a successful vaccination
(D) normal homeostasis with no immune involvement

Worked solution

$\text{harmless pollen} \Rightarrow \text{immune system overreacts}$ The body treats a harmless allergen as a threat.

$\Rightarrow \text{allergy symptoms}$ Such as sneezing and watery eyes.

Answer: allergic reaction

An allergy is an immune response directed against a normally harmless substance called an allergen, producing symptoms such as sneezing and watery eyes.

Question 11 · 2 pts

When a virus first infects the human body, white blood cells produce specific proteins that recognize and bind to the surface of the virus, marking it for destruction. These specific proteins are called

(A) antibodies ✓
(B) enzymes that digest food
(C) hormones
(D) receptor molecules on muscle cells

Worked solution

$The immune system responds to foreign antigens, such as those on a virus's surface, by activating specific white blood cells.$ immune response

$These white blood cells produce antibodies, proteins shaped to bind specifically to a particular antigen.$

$Binding of antibodies marks the pathogen for destruction by other immune cells.$

Answer: antibodies

Antibodies are specific proteins produced by white blood cells in response to a particular antigen; they bind to that antigen, marking pathogens such as viruses for destruction by the immune system.

Question 18 · 2 pts

After a person exercises, their body temperature rises above normal. Which response would help return body temperature to normal through negative feedback?

(A) The hypothalamus stops monitoring body temperature until it rises further
(B) The body increases its temperature further to match the exercise level
(C) Blood vessels near the skin constrict and shivering begins
(D) Blood vessels near the skin dilate and sweat glands become more active ✓

Worked solution

$The hypothalamus detects that body temperature is above the normal set point.$ Detection

$In negative feedback, the body responds in a way that opposes the change and brings the variable back toward normal.$ Negative feedback principle

$Dilating skin blood vessels increases heat loss to the environment, and increased sweating allows evaporative cooling.$ Cooling mechanisms

$These responses lower body temperature back toward the normal set point.$ Restoration of homeostasis

Answer: Blood vessels near the skin dilate and sweat glands become more active

Negative feedback works to reverse a deviation from the normal internal set point; when body temperature rises, vasodilation and sweating increase heat loss and cool the body back toward normal, whereas vasoconstriction and shivering are responses to being too cold.

Question 55 · 4 pts · constructed response

After a person eats a meal high in carbohydrates, their blood glucose level rises. Describe the role of insulin in returning blood glucose to a normal level, and explain what would likely happen to a person's blood glucose level if their pancreas stopped producing insulin.

Model answer: Insulin, released by the pancreas, signals body cells (such as liver and muscle cells) to take up glucose from the blood and store it as glycogen, which lowers blood glucose back to normal levels. If the pancreas stopped producing insulin, cells would not take up glucose efficiently, so blood glucose levels would remain abnormally high, a condition known as diabetes.

Worked solution

$\text{Blood glucose rises after eating carbohydrates}$ Stimulus

$\text{Pancreas detects high glucose and releases insulin}$ Response begins

$\text{Insulin signals cells to absorb glucose and store it as glycogen}$ Mechanism of action

$\text{Blood glucose returns to normal (homeostasis)}$ Feedback restores balance

$\text{Without insulin, glucose stays high in the blood (hyperglycemia/diabetes)}$ Consequence of insulin absence

Answer: Insulin, released by the pancreas, signals body cells (such as liver and muscle cells) to take up glucose from the blood and store it as glycogen, which lowers blood glucose back to normal levels. If the pancreas stopped producing insulin, cells would not take up glucose efficiently, so blood glucose levels would remain abnormally high, a condition known as diabetes.

Insulin is a key hormone in glucose homeostasis; it enables cells to remove excess glucose from the blood, and without it glucose accumulates in the blood, producing chronically high blood sugar.

Question 71 · 2 pts

A very high fever can be dangerous because body temperatures far above $37^\circ\text{C}$ can change the shape of enzymes. How does this threaten homeostasis?

(A) Enzymes that lose their normal shape can no longer catalyze the reactions cells depend on, disrupting normal functions ✓
(B) The fever increases the number of enzymes so that reactions happen too fast to control
(C) Enzymes are burned as fuel during a fever, leaving cells without energy
(D) The high temperature bonds enzymes permanently to DNA, causing new mutations

Worked solution

$T \gg 37^\circ\text{C} \;\Rightarrow\; \text{enzyme denatures}$ Above roughly $37^\circ\text{C}$ many human enzymes lose their specific shape.

$\text{altered active site} \to \text{reaction cannot proceed}$ Without functioning enzymes, needed cell reactions stop and homeostasis is disrupted.

Answer: \text{denatured enzymes can no longer catalyze cell reactions}

Enzymes work only at their proper shape; excessive heat denatures them, halting the chemical reactions cells need and disrupting the stable internal environment.

Question 72 · 2 pts

Hormones released into the bloodstream travel throughout the body, yet each hormone affects only certain target cells. A target cell responds to a particular hormone because it has

(A) DNA that is different from the DNA in all other body cells
(B) specific receptor molecules with a shape that matches that hormone ✓
(C) a thicker cell membrane that physically traps the hormone
(D) a larger number of mitochondria than other body cells

Worked solution

$\text{hormone shape} \leftrightarrow \text{receptor shape}$ Only cells carrying the matching receptor can bind the hormone.

$\text{match} \to \text{cell responds}$ This lock-and-key fit makes the signal specific to target cells.

Answer: \text{specific receptor molecules that match the hormone}

Cellular communication depends on receptor molecules; a hormone affects only cells whose receptors fit its shape, much like a key fits a specific lock.

Question 74 · 2 pts

Each type of antibody binds to only one specific antigen. This high specificity is most directly due to

(A) both molecules carrying the same genetic code
(B) the antigen being alive while the antibody is dead
(C) the complementary shapes of the antibody and its antigen ✓
(D) the antibody always being larger than the antigen

Worked solution

$\text{antibody shape} \leftrightarrow \text{antigen shape}$ They fit together like a lock and key.

$\text{shape match} \Rightarrow \text{specific binding}$ A mismatched antigen will not fit.

Answer: complementary molecular shapes

Antibodies recognize antigens by complementary molecular shape (a lock-and-key fit), which is why a given antibody acts on only one specific antigen.

Question 78 · 2 pts

HIV is a virus that infects and destroys certain white blood cells. As a result, a person infected with HIV is most likely to

(A) become less able to fight off other infections ✓
(B) lose the ability to clot blood
(C) develop stronger immunity over time
(D) produce more antibodies than a healthy person

Worked solution

$\text{HIV} \Rightarrow \downarrow \text{white blood cells}$ Key immune cells are destroyed.

$\Rightarrow \downarrow \text{defense} \Rightarrow \text{more infections}$ The body can no longer fight invaders it would normally control.

Answer: weaker defense against infection

By destroying white blood cells, HIV weakens the immune system and leaves the body vulnerable to other infections it would normally fight off.

Question 79 · 2 pts

Maintaining homeostasis, or dynamic equilibrium, in the human body requires the continuous

(A) use of energy ✓
(B) increase in body size
(C) loss of all body heat
(D) stopping of cellular respiration

Worked solution

$\text{feedback responses} \Rightarrow \text{require ATP}$ Pumping ions, making hormones, and muscle activity all cost energy.

$\Rightarrow \text{energy must be continuously supplied}$ Supplied by cellular respiration.

Answer: use of energy

Keeping internal conditions stable depends on active feedback processes that constantly use energy (ATP) supplied by cellular respiration.

Question 80 · 2 pts

A person is exposed to the same antigen twice. After the first exposure, antibody levels rise slowly to a low peak. After the second exposure, antibody levels rise much faster and reach a higher peak. The faster, larger response after the second exposure is best explained by

(A) memory cells formed during the first exposure ✓
(B) a mutation caused by the second exposure
(C) red blood cells multiplying rapidly
(D) the antigen becoming weaker the second time

Worked solution

$\text{1st exposure} \Rightarrow \text{slow, small response} + \text{memory cells}$ The immune system is responding for the first time.

$\text{2nd exposure} \Rightarrow \text{memory cells} \Rightarrow \text{fast, large response}$ This is the basis of long-lasting immunity.

Answer: memory cells from the first exposure

The first exposure produces memory cells, and on a second exposure these cells drive a faster and stronger antibody response, which is how lasting immunity works.

Question 24 · 2 pts

When a virus infects the body for the first time, white blood cells called lymphocytes produce specific antibodies to help destroy it, and some lymphocytes remain in the body as memory cells. If the same virus infects the body again years later, the immune response is usually

(A) slower because the immune system must relearn the virus's structure from scratch each time
(B) faster and stronger because memory cells recognize the antigen and quickly produce antibodies ✓
(C) nonexistent because antibodies provide no lasting protection against future infections
(D) identical to the first exposure because memory cells do not affect response speed

Worked solution

$During the first infection, specific lymphocytes are activated and some become long-lived memory cells.$ Primary response

$Memory cells 'remember' the specific antigen (surface markers) of that virus.$ Antigen recognition

$Upon reinfection, memory cells recognize the antigen immediately and rapidly multiply and produce large amounts of antibody.$ Secondary response

$This faster, stronger secondary response often destroys the pathogen before symptoms of illness develop, providing immunity.$ Result: immunity

Answer: faster and stronger because memory cells recognize the antigen and quickly produce antibodies

Memory cells produced during a first exposure to a pathogen allow the immune system to recognize the same antigen much more quickly on a later exposure, resulting in a faster and more powerful secondary immune response, which is the basis of long-term immunity.

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