Tahsili Biology 2 — Questions and Answers
Question 1: What is natural selection as described by Darwin?
- All organisms choose their traits
- Organisms with traits better suited to their environment survive and reproduce more, passing advantageous traits to offspring (Correct answer)
- Evolution happens randomly without direction
- Only the strongest organisms survive
Correct answer: Organisms with traits better suited to their environment survive and reproduce more, passing advantageous traits to offspring
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?
- A single-stranded helix
- A double helix of two antiparallel polynucleotide chains connected by hydrogen bonds between complementary base pairs (Correct answer)
- A linear chain of amino acids
- A branched polysaccharide
Correct answer: A double helix of two antiparallel polynucleotide chains connected by hydrogen bonds between complementary base pairs
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?
- Only transporting oxygen
- Returning fluid to blood, filtering pathogens through lymph nodes, and housing immune cells (Correct answer)
- Only digesting food
- Only producing hormones
Correct answer: Returning fluid to blood, filtering pathogens through lymph nodes, and housing immune cells
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?
- DNA is replicated
- A segment of DNA is used as a template to synthesize a complementary mRNA molecule (Correct answer)
- Proteins are assembled from amino acids
- Cells divide into two daughter cells
Correct answer: A segment of DNA is used as a template to synthesize a complementary mRNA molecule
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?
- They provide energy for reactions
- They are biological catalysts that lower activation energy, increasing reaction rates without being consumed (Correct answer)
- They are the reactants in metabolic pathways
- They store genetic information
Correct answer: They are biological catalysts that lower activation energy, increasing reaction rates without being consumed
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.
Question 6: What is homeostasis?
- The study of human homes
- The maintenance of a stable internal environment despite changes in external conditions (Correct answer)
- The process of cell division
- The movement of organisms to new habitats
Correct answer: The maintenance of a stable internal environment despite changes in external conditions
Homeostasis is the regulation of internal conditions (temperature, pH, glucose, water balance) within narrow ranges essential for survival. It uses feedback mechanisms: negative feedback (most common — corrects deviations) and positive feedback (amplifies changes, e.g., blood clotting).
Tahsili Biology 2
What is natural selection as described by Darwin?