what structural differences makes adenine and guanine different from cytosine, thymine, and uracil? (figure 2-24)

Nitrogenous bases have two distinct families known as purines and pyrimidine, nitrogenous are the building blocks or monomer units of the nucleic acids.

The major and significant difference between purines and pyrimidines is the difference in their structures-

The purines are divided into two different bases called adenine and guanine and each of them have a two-ringed structure formed with a 9-membered molecule and 4 nitrogen atoms which makes it a large in size than purines.

The pyrimidines are divided into 3 bases that are cytosine, uracil, and thymine and all these have only one single ring of six members and 2 nitrogen atoms.  These are smaller in size.

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.

blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.