Atherosclerosis is a disease that obstructs blood flow and, therefore, oxygen supply to target organs. A major component of atherosclerosis is the excessive reproduction of smooth muscle cells of the blood vessels. Certain drugs may have the potential to reverse or prevent the unregulated reproduction of the diseased blood-vessel cells. Which of these processes is the most likely target of these drugs?

Carbohydrates are more easily metabolized than lipids. However, on a gram-for-gram basis lipids provide cells with more —

Using a light microscope, a student identified the following characteristics of four organisms found in a sample of pond water.
Based on the observations of the student, which organisms most likely belong to the taxonomic group for bacteria?

Sexual reproduction in animals depends on the production of gametes. Which of these processes produces gametes in animals?

A marine ecosystem is represented below. 
What is lost to the environment at each of the trophic levels of this ecosystem?

The sequence of nitrogenous bases in DNA varies widely. The sequence of the bases in DNA is most important for which of the following?

Four different types of cells are shown below.
Which characteristic is shared by all four cells?

Scientists estimate that there are more than 20,000 species of ants. The species range in size from 1 mm long to 38 mm long and live in most environments. The diets of ants range from flowers and seeds to fluids from their own larvae. Ants have been able to successfully inhabit so many different environments because their populations have been able to —

Checkpoints occur between the stages of the cell cycle. If a cell does not meet certain criteria at the end of a stage, it will not move to the next stage.
Which of these occurs just before the cell enters the G2 stage of the cell cycle?

In any environment or ecosystem, organisms can have several different types of relationships. Three types of relationships are described below.
Which of these correctly describes the relationships between the organisms?

In the 1860s Gregor Mendel performed numerous dihybrid crosses between pea plants. Dihybrid crosses involve the study of the inheritance patterns related to two different traits. In guinea pigs the allele for black fur (B) is dominant over the allele for brown fur (b), and the allele for short fur (F) is dominant over the allele for long fur (f). What percentage of the offspring from a BbFf x bbff cross would be expected to be heterozygous for both traits?

Which group of organelles is directly responsible for the production of new molecules within a cell?

Which group of organelles is directly responsible for the production of new molecules within a cell?

The picture below shows a person’s karyotype.
Which of the following can best be determined by examining this karyotype?

The cellular process known as the sodium-potassium pump was discovered in the 1950s by Jens Christian Skou, a Danish scientist. This process is a form of active transport that moves three sodium ions to the outside of a cell for every two potassium ions that it moves into the cell. Which of these best explains why energy is needed for active transport?

Brazil nuts (Bertholletia excelsa) are tall canopy trees that make up a large portion of the Amazon rain forest. They produce large grapefruit-sized seedpods. The agouti, a grounddwelling rodent, has teeth strong enough to open the tough seedpods. While the agouti eats some of the tree’s seeds, it also buries caches in various spots on the rain forest floor.
Why is the agouti important to the rain forest ecosystem?

Researchers Robert Briggs and Thomas King used ultraviolet radiation to destroy the nuclear DNA of frog eggs. Nuclei from adult skin cells and from tadpole-gut epithelial cells were cultured and then injected into eggs that had their nuclei destroyed. The results were tadpoles.
Which conclusion is supported by the data from this investigation?

Sickle-shaped red blood cells result from a mutation in the gene that codes for hemoglobin. This mutation results in sickle-cell anemia. A partial sequence of bases from a normal hemoglobin gene and a sequence that results in sickle-cell anemia are shown below.
What type of mutation is depicted in this sequence?

In Madagascar scientists have discovered a moth, Xanthopan morganii praedicta, that has a 30.5 cm proboscis and feeds from and pollinates Darwin’s orchid, Angraecum sesquipedale. The orchid has a nectar-producing tube that is 27.9 cm long.
How is the moth’s proboscis size an adaptation for its environment?

The diagram below represents the nitrogen cycle in a student’s aquarium. Ammonia, nitrites, and, to a lesser degree, nitrates can be harmful to fish. The student wants to keep the nitrogen in this aquarium cycling normally without having to continually change the water.
Which of the following should the student add more of to help remove nitrates and improve the natural cycling of nitrogen in this aquarium?

Genome maps provide the DNA sequences of chromosomes. Some scientists have compared the genome maps of a hedgehog and a sloth. What do these genome maps allow the scientists to determine?

Tomato plants usually have hairy stems. Hairless stems are present in tomato plants that are homozygous recessive for this trait. If the stem characteristics are determined by a single gene, what is the expected outcome of crossing two tomato plants that are heterozygous for hairy stems?

Which of the following biomolecules typically contains both nitrogen and phosphate?

Telophase is a stage of a cellular process that begins after the chromosomes have moved to opposite poles of the cell. During which cellular process does telophase occur?

Which condition is essential for natural selection to result in a new species?