Tahsili Biology 2

Question 1

What is natural selection as described by Darwin?

Accepted Answer

Organisms with traits better suited to their environment survive and reproduce more, passing advantageous traits to offspring

Answer

Natural selection: variation exists within populations → some variations provide survival/reproductive advantages → organisms with advantageous traits reproduce more → these traits become more common over generations. This is the mechanism driving evolutionary adaptation.

Question 2

What is the structure of DNA?

Accepted Answer

A double helix of two antiparallel polynucleotide chains connected by hydrogen bonds between complementary base pairs

Answer

DNA is a double helix: two antiparallel sugar-phosphate backbone strands connected by hydrogen bonds between complementary bases (A-T with 2 H-bonds, C-G with 3 H-bonds). Discovered by Watson, Crick, Franklin, and Wilkins.

Question 3

What is the function of the lymphatic system?

Accepted Answer

Returning fluid to blood, filtering pathogens through lymph nodes, and housing immune cells

Answer

The lymphatic system: returns interstitial fluid to the bloodstream (maintaining fluid balance), filters pathogens and foreign material through lymph nodes, transports dietary lipids from the intestine, and houses lymphocytes (T cells, B cells) for immune defense.

Question 4

What happens during the process of transcription?

Accepted Answer

A segment of DNA is used as a template to synthesize a complementary mRNA molecule

Answer

Transcription: RNA polymerase binds to the promoter region, unwinds DNA, reads the template strand (3'→5'), and synthesizes a complementary mRNA strand (5'→3') using RNA nucleotides (A, U, G, C). This mRNA carries the genetic message to ribosomes.

Question 5

What is the role of enzymes in biological reactions?

Accepted Answer

They are biological catalysts that lower activation energy, increasing reaction rates without being consumed

Answer

Enzymes are biological catalysts (usually proteins) that lower the activation energy of reactions, dramatically increasing reaction rates (up to 10⁶ fold). They are highly specific (lock-and-key or induced-fit model), are not consumed, and are reusable.

Tahsili Practice Test

Tahsili Practice Test

Tahsili Biology 2