USABO OPEN EXAM (2025-2026)
QUESTIONS WITH 100%
CORRECT ANSWERS
Which Of The Following Ions Have Higher Extracellular Concentrations
Than Intracellular Concentrations?
I. Potassium
II. Sodium
III. Calcium
A. I Only
B. Ii Only
C. I And Ii
D. I, Ii, And Iii
E. Ii And Iii - <<<Answers>>>E. Ii And Iii
Select The Statement That Best Describes Movement Of O2 , Na+ ,
And Glucose Into And Out Of The Capillaries.
A. O2 And Glucose Diffuse Across Endothelial Cell Membranes; Na+
Diffuses Through Pores Between Cells.
B. O2 And Na+ Diffuse Across Endothelial Cell Membranes;
Glucose Diffuses Through Pores Between Cells.
C. O2 Diffuses Across Endothelial Cell Membranes; Na+ And
Glucose Diffuse Through Pores Between Cells.
D. O2 , Na+, And Glucose All Diffuse Across Endothelial Cell
Membranes.
E. O2 , Na+ , And Glucose All Diffuse Through Pores Between
,Endothelial Cells. - <<<Answers>>>C. O2 Diffuses Across
Endothelial Cell Membranes; Na+ And Glucose Diffuse Through Pores
Between Cells.
A New Chemical Is Found That Inhibits Muscle Function And In High
Enough Doses Causes Paralysis. Which Of The Following Is Not A
Plausible Mechanism By Which This Chemical Could Function?
A. Inhibition Of Acetylcholinesterase In The Synaptic Cleft Of
Peripheral Motor Neurons.
B. Inhibition Of Acetylcholine Release In Peripheral Motor
Neurons.
C. Inhibition Of Calcium Release In Peripheral Motor Neurons.
D. Inhibition Of The Binding Of Myosin Heads To Actin Filaments In
Muscle Cells.
E. InhibitionOf Calcium-Release Channels In The Sarcoplasmic
Reticulum Of Muscle Cells. - <<<Answers>>>C. Inhibition Of Calcium
Release In Peripheral Motor Neurons.
A Dog Breeder Wants To Breed Dogs With Thick, Shaggy Coats.
Assume That The Thick-Coat Trait Is Recessive. Two Dogs, Both With
Thick Coats And Of The Same Breed, Are Mated, But All The Puppies
Are Short-Haired. From This You Can Conclude That...
A. Having Two Copies Of The Thick Coat Allele Is Lethal.
B. There Is Another Gene Controlling The Expression Of The
Thick-Coat Genes By Epistasis.
C. Dogs Of This Breed With Thick Coats Are Never True Breeding For
The Thick Coat Trait.
D. There Are Two Thick-Coat Genes At Separate Loci; Each Parent Is
Double Recessive For A Different One, And The Genes Complement
Each Other In The Puppies. - <<<Answers>>>A. False
B. False
C. False
, D. True
A Pea Plant X Dihybrid For Flower Color And Height Is Crossed With A
Pea Plant Y True Breeding For Flower Color And Height. Pea Plant X Is
Tall And Has Purple Flowers While Pea Plant Y Is Short And Has White
Flowers. Given That The Genes Are On Separate Chromosomes, Tall Is
Dominant To Short And Purple Is Dominant To White, Find The
Phenotypic Ratios Of The Offspring.
A. 1 Tall Purple: 1 Short Purple: 1 Tall White: 1 Short White.
B. 9 Tall Purple: 3 Short Purple: 3 Tall White: 1 Short White.
C. 9 Tall Purple: 3 Short Purple: 4 Short White.
D. 9 Tall Purple: 7 Short White.
E. 9 Tall Purple: 4 Short White. - <<<Answers>>>A. 1 Tall Purple:
1 Short Purple: 1 Tall White: 1 Short White.
Which Of The Following Statements Apply To Viral Capsids?
A. Viral Capsomeres Display Self-Assembly And Depending On The
Virus Can Form Helical Or Icosahedral Capsids.
B. Each Viral Capsid Is Formed From Identical Capsomeres,
Which Allows For Self-Assembly.
C. Viral Capsomeres Are Derived From Host Proteins And
Undergo Virus-Specific Posttranslational Modifications
D. Viral Mrna Transcripts Are Translated By Eukaryotic Ribosomes To
Form Capsid Proteins. - <<<Answers>>>A. True
B. False
C. False
D. True
If A Yellow-Coat Colored Mouse Is Crossed With A Gray-Coat Colored
QUESTIONS WITH 100%
CORRECT ANSWERS
Which Of The Following Ions Have Higher Extracellular Concentrations
Than Intracellular Concentrations?
I. Potassium
II. Sodium
III. Calcium
A. I Only
B. Ii Only
C. I And Ii
D. I, Ii, And Iii
E. Ii And Iii - <<<Answers>>>E. Ii And Iii
Select The Statement That Best Describes Movement Of O2 , Na+ ,
And Glucose Into And Out Of The Capillaries.
A. O2 And Glucose Diffuse Across Endothelial Cell Membranes; Na+
Diffuses Through Pores Between Cells.
B. O2 And Na+ Diffuse Across Endothelial Cell Membranes;
Glucose Diffuses Through Pores Between Cells.
C. O2 Diffuses Across Endothelial Cell Membranes; Na+ And
Glucose Diffuse Through Pores Between Cells.
D. O2 , Na+, And Glucose All Diffuse Across Endothelial Cell
Membranes.
E. O2 , Na+ , And Glucose All Diffuse Through Pores Between
,Endothelial Cells. - <<<Answers>>>C. O2 Diffuses Across
Endothelial Cell Membranes; Na+ And Glucose Diffuse Through Pores
Between Cells.
A New Chemical Is Found That Inhibits Muscle Function And In High
Enough Doses Causes Paralysis. Which Of The Following Is Not A
Plausible Mechanism By Which This Chemical Could Function?
A. Inhibition Of Acetylcholinesterase In The Synaptic Cleft Of
Peripheral Motor Neurons.
B. Inhibition Of Acetylcholine Release In Peripheral Motor
Neurons.
C. Inhibition Of Calcium Release In Peripheral Motor Neurons.
D. Inhibition Of The Binding Of Myosin Heads To Actin Filaments In
Muscle Cells.
E. InhibitionOf Calcium-Release Channels In The Sarcoplasmic
Reticulum Of Muscle Cells. - <<<Answers>>>C. Inhibition Of Calcium
Release In Peripheral Motor Neurons.
A Dog Breeder Wants To Breed Dogs With Thick, Shaggy Coats.
Assume That The Thick-Coat Trait Is Recessive. Two Dogs, Both With
Thick Coats And Of The Same Breed, Are Mated, But All The Puppies
Are Short-Haired. From This You Can Conclude That...
A. Having Two Copies Of The Thick Coat Allele Is Lethal.
B. There Is Another Gene Controlling The Expression Of The
Thick-Coat Genes By Epistasis.
C. Dogs Of This Breed With Thick Coats Are Never True Breeding For
The Thick Coat Trait.
D. There Are Two Thick-Coat Genes At Separate Loci; Each Parent Is
Double Recessive For A Different One, And The Genes Complement
Each Other In The Puppies. - <<<Answers>>>A. False
B. False
C. False
, D. True
A Pea Plant X Dihybrid For Flower Color And Height Is Crossed With A
Pea Plant Y True Breeding For Flower Color And Height. Pea Plant X Is
Tall And Has Purple Flowers While Pea Plant Y Is Short And Has White
Flowers. Given That The Genes Are On Separate Chromosomes, Tall Is
Dominant To Short And Purple Is Dominant To White, Find The
Phenotypic Ratios Of The Offspring.
A. 1 Tall Purple: 1 Short Purple: 1 Tall White: 1 Short White.
B. 9 Tall Purple: 3 Short Purple: 3 Tall White: 1 Short White.
C. 9 Tall Purple: 3 Short Purple: 4 Short White.
D. 9 Tall Purple: 7 Short White.
E. 9 Tall Purple: 4 Short White. - <<<Answers>>>A. 1 Tall Purple:
1 Short Purple: 1 Tall White: 1 Short White.
Which Of The Following Statements Apply To Viral Capsids?
A. Viral Capsomeres Display Self-Assembly And Depending On The
Virus Can Form Helical Or Icosahedral Capsids.
B. Each Viral Capsid Is Formed From Identical Capsomeres,
Which Allows For Self-Assembly.
C. Viral Capsomeres Are Derived From Host Proteins And
Undergo Virus-Specific Posttranslational Modifications
D. Viral Mrna Transcripts Are Translated By Eukaryotic Ribosomes To
Form Capsid Proteins. - <<<Answers>>>A. True
B. False
C. False
D. True
If A Yellow-Coat Colored Mouse Is Crossed With A Gray-Coat Colored
