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An aminoacyl-tRNA synthetase joins a particular amino acid to its matching tRNA using ATP. Why does the same enzyme not normally attach a different amino acid? A. ATP can supply energy to only one chemical reaction in a cell B. The active site has substrate…
Nutrients move from the intestinal lumen into the circulation and then reach the liver. Explain adaptations of villus epithelial cells for absorption and what can happen to absorbed nutrients in the liver.
A pathway converts substrate A through several steps into product Z. These constructed data show the first enzyme’s activity when Z is added. Which conclusion follows? A. Z is required for the enzyme to have any activity B. Z reduces activity at lower…
Which molecule carries electrons and associated chemical energy from matrix oxidation reactions to the mitochondrial electron transport chain? A. Cellulose B. Reduced NAD C. Oxygen bound permanently to DNA D. A newly formed chromosome
How can the proximity of xylem to phloem help translocation at a sugar-loading region? A. Xylem transfers all its lignin into sieve tubes B. Water can enter the sugar-rich phloem osmotically and help generate pressure C. The two tissues use the same continuous…
Which event occurs at step 1 in the simplified Calvin-cycle diagram? A. Rubisco catalyses the addition of carbon dioxide to ribulose bisphosphate B. ATP synthase directly splits ribulose bisphosphate C. Water is split to form molecular oxygen D. NADP is…
A plant grows in saline soil. Which adaptation could help maintain water uptake while limiting salt damage to cytoplasmic enzymes? A. Transporting absorbed ions into vacuoles, lowering cellular solute potential while keeping cytoplasmic ion levels controlled…
How does crossing over contribute to variation in gametes? A. It removes all recessive alleles B. It creates recombinant combinations of alleles on homologous chromosomes C. It makes every gamete diploid D. It ensures that all offspring are genetically…
For a typical seed relying on aerobic respiration during germination, which environmental supply is required to support that respiration? A. Bright light at all times B. Oxygen C. Nitrate fertilizer added each hour D. Carbon dioxide as the terminal electron…
In a model insect, dark wings and long antennae are dominant traits. Which cross is most useful for testing whether the two loci are linked? A. A double heterozygote crossed with a double homozygous recessive B. Two double homozygous dominant parents C. A…