DNA replication is said to be semi-conservative because:
A. Replication occurs in both directions from the origin
B. Both strands of the new DNA molecule are newly synthesized
C. Each new DNA molecule consists of one old (parental) strand and one newly synthesized strand
D. DNA is replicated only during the S phase
Answer: Option C
Solution (By JKSSB Mock Tests)
Semi-conservative replication means that when a new DNA double helix is formed, it consists of one original (parental) strand and one newly synthesized strand. This was proven by the Meselson-Stahl experiment in 1958 using isotopes of nitrogen (15N and 14N) in E. coli. This mechanism ensures genetic continuity.
Explanation:
Fungal cell walls contain chitin, a strong, flexible polysaccharide also found in arthropod exoskeletons. Cellulose is in plant walls, peptidoglycan in bacterial walls, lignin in secondary plant walls. Chitin provides structural support and protection against environmental stress.
Explanation:
Pteridophytes (ferns and their relatives) are the first terrestrial plants to possess vascular tissues (xylem and phloem) for water and nutrient transport. However, they do not produce seeds or flowers and reproduce via spores. Hence, they are called 'vascular cryptogams'. Bryophytes are called 'amphibians of the plant kingdom'.
Explanation:
Rhodopsin (visual purple) is a photopigment in rod cells consisting of opsin and retinal (from vitamin A). It bleaches upon absorbing light, initiating signal transduction for vision in low light. Cone cells contain iodopsin for color vision. Melanin is skin pigment, hemoglobin carries oxygen.
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