Arecent study of the marine hawksbill turtle's stomach contents revealed that sponges constitute a major portion of their diet. sponge beds are generally protected from predators by the sponge's calcium and silica crystals, but these were found in quantity in the turtles' digestive systems. these structures that protect the sponges from most predators, but not turtles, are .

Mouse liver cells were homogenized and the homogenate subjected to equilibrium density-gradient centrifugation with sucrose gradients. fractions obtained from these gradients were assayed for marker molecules (i.e., molecules that are limited to specific organelles). the results of these assays are shown in the figure. the marker molecules have the following functions: cytochrome oxidase is an enzyme involved in the process by which atp is formed in the complete aerobic degradation of glucose or fatty acids; ribosomal rna forms part of the protein-synthesizing ribosomes; catalase catalyzes decomposition of hydrogen peroxide; acid phosphatase hydrolysis monophosphoric esters at acid ph; cytidylyltransferase is involved in phospholipid biosynthesis; and amino acid permease aids in transport of amino acids across membranes. a) name the marker molecule and give the number of the fraction that is most enriched for each of the following cell components: lysosomes; peroxisomes; mitochondria; plasma membrane; rough endoplasmic reticulum; smooth endoplasmic reticulum.

Study the diagram of a cell. which structure is found only in plant cells and functions in the process of photosynthesis? w x y z

Dna replication or repair occurs in a cell in all of thw following situations except when