Cells have membranes that allow them to establish and maintain internal environments that are different from their external environments. The structure of the phospholipid bilayer influences its permeability.

Which statements accurately reflect the permeability of the cell membrane? Choose all that apply.

The hydrophilic part of the cell membrane is A, the phosphate head.
The lipid tails are hydrophobic and will only allow molecules which are small and polar to pass through.
Molecules that are large or charged must use a channel protein, such as D, to cross the cell membrane.
Molecules using membrane proteins, such as E, for transport require energy.
Charged molecules, such as K+ or Ca++ are unable to pass through the lipid bilayer because of their charge and must use a membrane protein to cross the cell membrane.
C, the lipid tails, are hydrophobic and repel water.

Dna has unique properties that allow it to accurately retain genetic information, even after multiple rounds of replication. one aspect of dna that allows it to accurately store genetic information is the base pairing from chargaff\'s first rule of the four nucleotide bases. if the c content of a dna molecule is 22%, what are the percentages of the remaining bases?

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.

Indicate the coat color and the proportion of offspring with that color for each of the following crosses of rabbits. assume all are homozygous. chinchilla x albino a) all chinchilla b) 1/2 chinchilla, 1/2 albino c) 3/4 chinchilla, 1/4 albino