MCAT BIOLOGY STUDY EXAM GUIDE 2026 QUESTIONS
AND ANSWERS SURE A+
✔✔Lysozyme - ✔✔ENZYME IN THE NASAL CAVITY that
attacks the peptidoglycan cell walls of GRAM-POSITIVE BACTERIA
✔✔Mucociliary escalator - ✔✔Internal airways are lined with mucus which TRAPS
PARTICULATE MATTER and larger invaders
Underlying cilia propel the mucus up the respiratory tract to the oral cavity, where it is
EXPELLED OR SWALLOWED
✔✔Macrophages - ✔✔Seen in the lungs, especially alvoeli. ENGULF AND DIGEST
PATHOGENS and
SIGNAL to the rest of the immune system that there is an invader
PHAGOCYTIZE FOREIGN SUBSTANCES and help activate T cells
✔✔Mast cells - ✔✔Can also be SEEN IN LUNGS. Has preformed antibodies on its
surface. When the right antigen attaches to the antonody, the mast cell will release
INFLAMMATORY CHEMICALS to promote an IMMUNE RESPONSE upon contact with
the antigen
Can Cause allergic reactions (to pollen and molds)
✔✔Bicarbonate buffer system equation
SUPER IMPORTANT - ✔✔For pH balance in blood -
CO2 (g) + H2O (l) <-> H2CO3 (aq) <-> HCO3- (aq) + H+ (aq)
Fast breathing- low CO2 - shifts to the left- loss of H+ - raises ph
little/no breathing- high CO2- shifts to the right- more H+- lower pH
✔✔Physiological pH - ✔✔7.35-7.45
✔✔Acidemia - ✔✔pH of blood is too low - [H+] is too high
Acid-sensing chemoreceptors just outside the blood-brain barrier send signals to the
brain to increase the respiratory rate.
Shifts buffer system to the LEFT, so higher CO2 needs to be blown off. HIGHER
RESPIRATORY RATE IS RESULT.
,✔✔Effects of acidemia - ✔✔Because pH is too low:
CO2 concentration increases due to excess of H+
Ventilation center senses this and INCREASES RESPIRATORY RATE TO BLOW OFF
MORE CO2
Decreased CO2 pushes bicarbonate buffer equation to left until H+ concentration is
normal again
✔✔Alkalemia - ✔✔pH of blood is too high/basic
then the body will seek to increase acidity.
Pushes buffer system to the RIGHT. Respiratory rate slows so that CO2 can be turned
into H+ until it's levels stabilize.
✔✔Effects of alkalemia - ✔✔Because the pH is too high:
RESPIRATORY RATE IS SLOWED TO increase CO2 concentration and shift
bicarbonate buffer equation to right produce more H+ , causing a decrease in
pH/making it more acidic
✔✔If H+ is an acid and HCO⁻3 is a base, then why doesn't increasing both of them
maintain a constant pH? - ✔✔The reason is because H+ IS A STRONG ACID, while
HCO⁻3 IS A WEAK BASE. (buffer system!)
✔✔Difference between lung response and kidney response to pH imbalances -
✔✔LUNG RESPONSE IS FASTER
KIDNEY RESPONSE IS SLOWER, more LONG-TERM
(sees chapter 10 for more info)
✔✔The immune system - ✔✔Your bodies defense system. Can be broken into:
1) Innate immunity
2) Adaptive immunity
✔✔Innate immunity - ✔✔Composed of defenses that are always active, but cannot
target a specific invader and cannot maintain immunologic memory:
also called nonspecific immunity.
phagocytes - macrophages and dendritic cells
,✔✔Adaptive immunity - ✔✔Composed of defenses that take time to activate, but that
target a specific invader and can maintain immunologic memory
✔✔also called specific immunity.
B-cells and T-cells - ✔✔
✔✔Immune system organs/tissues - ✔✔1) Bone marrow = origin of immune cells,
leukocytes
2) Spleen and lymph nodes = sites where immune response can be mounted, and in
which B-cells are activated, and then turn into plasma cells that produce antibodies
3) Thymus = site of T-cell maturation
4) Gut-associatied lymphoid tissues (GALT) incude tonsils and adenoids, Peyer's patch
5) lymph nodes = where an immune response can be mounted, B-cell activation
✔✔Leukocytes - ✔✔White blood cells and are involved in the immune defense.
✔✔Antigen - ✔✔a toxin or other foreign substance that induces an immune response in
the body, especially the production of antibodies.
✔✔Antibodies
(important component) - ✔✔Specialized proteins that aid in destroying infectious agents
1) Variable component binds to specific antigens
✔✔The Innate Immune System - ✔✔Composed of physical and chemical nonspecific
defenses.
1) Skin
2) Tears/salvia
3) Stomach
4) Complement system
5) Interferons
✔✔Skin - ✔✔Acts as a physical barrier and secretes antimicrobial compounds, like
defense's.
Sweat also has antimicrobial properties.
✔✔Mucus - ✔✔Mucus membranes trap pathogens
, ✔✔in the respiratory system, the Mucus is propelled upward by cilia and can be
swallowed or expelled. - ✔✔
✔✔Tears & saliva - ✔✔Contain lysozyme, an antimicrobial compound
✔✔Stomach - ✔✔Produces acid, killing most pathogens. Colonization of the gut helps
prevent overgrowth by pathogenic bacteria through competition.
✔✔Complement system - ✔✔Pokes holes in the cell walls of bacteria, making them
osmotically unstable.
✔✔Interferons - ✔✔Proteins given off by virally infected cells. Interferons cause nearby
cells to decrease production of both viral and cellular proteins.
1) Also decrease permeability of these cells, making it harder for viruses to infect them.
2) Cause up regulation of MHC to allow better identification of healthy cells.
3) Responsible for flu-like symptoms.
✔✔Innate immune system
(Cellular defenses) - ✔✔1) Macrophages
2) MHC Class I (MHC-I)
3) MHC Class II (MHC-II)
4) Dendritic cells
5) Natural killer cells
6) Granulocytes
7) Neutrophils
8) Eosinophils
9) Basophils
✔✔Macrophages - ✔✔Ingest pathogens and present themselves on major hits-
compatibility complex (MHC) molecules.
1) Secrete cytokines.
2) Presents small pieces of broken down peptides to cell surface with MHC where it can
be recognized by the adaptive immune system.
✔✔Cytokines - ✔✔Chemical substances that stimulate inflammation and recruit
additional immune cells to the area.
✔✔MHC class I (MHC-I) - ✔✔Present in all nucleated cells and displays endogenous
antigen (proteins within the cell) to cytotoxic T-cells (CD8+ cells).
AND ANSWERS SURE A+
✔✔Lysozyme - ✔✔ENZYME IN THE NASAL CAVITY that
attacks the peptidoglycan cell walls of GRAM-POSITIVE BACTERIA
✔✔Mucociliary escalator - ✔✔Internal airways are lined with mucus which TRAPS
PARTICULATE MATTER and larger invaders
Underlying cilia propel the mucus up the respiratory tract to the oral cavity, where it is
EXPELLED OR SWALLOWED
✔✔Macrophages - ✔✔Seen in the lungs, especially alvoeli. ENGULF AND DIGEST
PATHOGENS and
SIGNAL to the rest of the immune system that there is an invader
PHAGOCYTIZE FOREIGN SUBSTANCES and help activate T cells
✔✔Mast cells - ✔✔Can also be SEEN IN LUNGS. Has preformed antibodies on its
surface. When the right antigen attaches to the antonody, the mast cell will release
INFLAMMATORY CHEMICALS to promote an IMMUNE RESPONSE upon contact with
the antigen
Can Cause allergic reactions (to pollen and molds)
✔✔Bicarbonate buffer system equation
SUPER IMPORTANT - ✔✔For pH balance in blood -
CO2 (g) + H2O (l) <-> H2CO3 (aq) <-> HCO3- (aq) + H+ (aq)
Fast breathing- low CO2 - shifts to the left- loss of H+ - raises ph
little/no breathing- high CO2- shifts to the right- more H+- lower pH
✔✔Physiological pH - ✔✔7.35-7.45
✔✔Acidemia - ✔✔pH of blood is too low - [H+] is too high
Acid-sensing chemoreceptors just outside the blood-brain barrier send signals to the
brain to increase the respiratory rate.
Shifts buffer system to the LEFT, so higher CO2 needs to be blown off. HIGHER
RESPIRATORY RATE IS RESULT.
,✔✔Effects of acidemia - ✔✔Because pH is too low:
CO2 concentration increases due to excess of H+
Ventilation center senses this and INCREASES RESPIRATORY RATE TO BLOW OFF
MORE CO2
Decreased CO2 pushes bicarbonate buffer equation to left until H+ concentration is
normal again
✔✔Alkalemia - ✔✔pH of blood is too high/basic
then the body will seek to increase acidity.
Pushes buffer system to the RIGHT. Respiratory rate slows so that CO2 can be turned
into H+ until it's levels stabilize.
✔✔Effects of alkalemia - ✔✔Because the pH is too high:
RESPIRATORY RATE IS SLOWED TO increase CO2 concentration and shift
bicarbonate buffer equation to right produce more H+ , causing a decrease in
pH/making it more acidic
✔✔If H+ is an acid and HCO⁻3 is a base, then why doesn't increasing both of them
maintain a constant pH? - ✔✔The reason is because H+ IS A STRONG ACID, while
HCO⁻3 IS A WEAK BASE. (buffer system!)
✔✔Difference between lung response and kidney response to pH imbalances -
✔✔LUNG RESPONSE IS FASTER
KIDNEY RESPONSE IS SLOWER, more LONG-TERM
(sees chapter 10 for more info)
✔✔The immune system - ✔✔Your bodies defense system. Can be broken into:
1) Innate immunity
2) Adaptive immunity
✔✔Innate immunity - ✔✔Composed of defenses that are always active, but cannot
target a specific invader and cannot maintain immunologic memory:
also called nonspecific immunity.
phagocytes - macrophages and dendritic cells
,✔✔Adaptive immunity - ✔✔Composed of defenses that take time to activate, but that
target a specific invader and can maintain immunologic memory
✔✔also called specific immunity.
B-cells and T-cells - ✔✔
✔✔Immune system organs/tissues - ✔✔1) Bone marrow = origin of immune cells,
leukocytes
2) Spleen and lymph nodes = sites where immune response can be mounted, and in
which B-cells are activated, and then turn into plasma cells that produce antibodies
3) Thymus = site of T-cell maturation
4) Gut-associatied lymphoid tissues (GALT) incude tonsils and adenoids, Peyer's patch
5) lymph nodes = where an immune response can be mounted, B-cell activation
✔✔Leukocytes - ✔✔White blood cells and are involved in the immune defense.
✔✔Antigen - ✔✔a toxin or other foreign substance that induces an immune response in
the body, especially the production of antibodies.
✔✔Antibodies
(important component) - ✔✔Specialized proteins that aid in destroying infectious agents
1) Variable component binds to specific antigens
✔✔The Innate Immune System - ✔✔Composed of physical and chemical nonspecific
defenses.
1) Skin
2) Tears/salvia
3) Stomach
4) Complement system
5) Interferons
✔✔Skin - ✔✔Acts as a physical barrier and secretes antimicrobial compounds, like
defense's.
Sweat also has antimicrobial properties.
✔✔Mucus - ✔✔Mucus membranes trap pathogens
, ✔✔in the respiratory system, the Mucus is propelled upward by cilia and can be
swallowed or expelled. - ✔✔
✔✔Tears & saliva - ✔✔Contain lysozyme, an antimicrobial compound
✔✔Stomach - ✔✔Produces acid, killing most pathogens. Colonization of the gut helps
prevent overgrowth by pathogenic bacteria through competition.
✔✔Complement system - ✔✔Pokes holes in the cell walls of bacteria, making them
osmotically unstable.
✔✔Interferons - ✔✔Proteins given off by virally infected cells. Interferons cause nearby
cells to decrease production of both viral and cellular proteins.
1) Also decrease permeability of these cells, making it harder for viruses to infect them.
2) Cause up regulation of MHC to allow better identification of healthy cells.
3) Responsible for flu-like symptoms.
✔✔Innate immune system
(Cellular defenses) - ✔✔1) Macrophages
2) MHC Class I (MHC-I)
3) MHC Class II (MHC-II)
4) Dendritic cells
5) Natural killer cells
6) Granulocytes
7) Neutrophils
8) Eosinophils
9) Basophils
✔✔Macrophages - ✔✔Ingest pathogens and present themselves on major hits-
compatibility complex (MHC) molecules.
1) Secrete cytokines.
2) Presents small pieces of broken down peptides to cell surface with MHC where it can
be recognized by the adaptive immune system.
✔✔Cytokines - ✔✔Chemical substances that stimulate inflammation and recruit
additional immune cells to the area.
✔✔MHC class I (MHC-I) - ✔✔Present in all nucleated cells and displays endogenous
antigen (proteins within the cell) to cytotoxic T-cells (CD8+ cells).
