BIOL 203
BIOL 203 Exam 3 Practice Questions
and Answers GRADED A+ 2026
What is an obligate intracellular parasite?
A virus that must live and reproduce inside a host cell.
Why are viruses not considered living organisms?
They lack metabolism, cannot reproduce independently, and have no protein
synthesis machinery.
What two main components make up all viruses?
Capsid and nucleic acid.
What is a nucleocapsid?
Capsid + nucleic acid.
What is the difference between enveloped and naked viruses?
Enveloped viruses have a lipid membrane; naked viruses do not.
What is the function of viral spikes?
Attachment to host cells.
What are the three capsid shapes?
Helical, icosahedral, complex.
Which capsid type has 20 sides?
Icosahedral
BIOL 203
,BIOL 203
What makes complex viruses unique?
They have multiple structures (e.g., bacteriophage head and tail).
Do viruses contain both DNA and RNA?
No, only one or the other.
What is positive-sense RNA?
RNA that can be directly translated into protein.
What is negative-sense RNA?
RNA that must be converted before translation.
What enzyme converts RNA into DNA?
Reverse transcriptase.
Why do some viruses carry enzymes?
Host cells lack the necessary enzymes.
How are viruses classified?
By structure, nucleic acid type, envelope, and replication method.
What are bioelements?
Essential elements required for life (C, H, O, N, P, S).
What is the difference between macronutrients and micronutrients?
BIOL 203
, BIOL 203
Macronutrients are needed in large amounts; micronutrients in small amounts.
What defines an organic nutrient?
Contains carbon and hydrogen.
What percent of the cell is water?
About 70%
What 6 elements make up most of the cell?
Carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur.
Why is carbon essential?
Backbone of all organic molecules.
What is nitrogen used for?
Making amino acids and nucleic acids.
What is nitrogen fixation?
Conversion of N₂ into ammonia (NH₃).
What is oxygen used for in aerobes?
Final electron acceptor in metabolism.
What is sulfur's role?
Stabilizes proteins via disulfide bonds.
BIOL 203
BIOL 203 Exam 3 Practice Questions
and Answers GRADED A+ 2026
What is an obligate intracellular parasite?
A virus that must live and reproduce inside a host cell.
Why are viruses not considered living organisms?
They lack metabolism, cannot reproduce independently, and have no protein
synthesis machinery.
What two main components make up all viruses?
Capsid and nucleic acid.
What is a nucleocapsid?
Capsid + nucleic acid.
What is the difference between enveloped and naked viruses?
Enveloped viruses have a lipid membrane; naked viruses do not.
What is the function of viral spikes?
Attachment to host cells.
What are the three capsid shapes?
Helical, icosahedral, complex.
Which capsid type has 20 sides?
Icosahedral
BIOL 203
,BIOL 203
What makes complex viruses unique?
They have multiple structures (e.g., bacteriophage head and tail).
Do viruses contain both DNA and RNA?
No, only one or the other.
What is positive-sense RNA?
RNA that can be directly translated into protein.
What is negative-sense RNA?
RNA that must be converted before translation.
What enzyme converts RNA into DNA?
Reverse transcriptase.
Why do some viruses carry enzymes?
Host cells lack the necessary enzymes.
How are viruses classified?
By structure, nucleic acid type, envelope, and replication method.
What are bioelements?
Essential elements required for life (C, H, O, N, P, S).
What is the difference between macronutrients and micronutrients?
BIOL 203
, BIOL 203
Macronutrients are needed in large amounts; micronutrients in small amounts.
What defines an organic nutrient?
Contains carbon and hydrogen.
What percent of the cell is water?
About 70%
What 6 elements make up most of the cell?
Carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur.
Why is carbon essential?
Backbone of all organic molecules.
What is nitrogen used for?
Making amino acids and nucleic acids.
What is nitrogen fixation?
Conversion of N₂ into ammonia (NH₃).
What is oxygen used for in aerobes?
Final electron acceptor in metabolism.
What is sulfur's role?
Stabilizes proteins via disulfide bonds.
BIOL 203
