The graph shows the activity of a human digestive enzyme measured at six pH values. At which pH is this enzyme most active?

The table shows oxygen bubbles released per minute by an Elodea sprig at different light intensities. What best explains the results above 6000 lux?

A leafy shoot was placed in four conditions and its water loss measured. Use the graph. Which condition raised water loss above still air, and why?

The diagram shows one turn of the cell cycle. A drug blocks the stage in which the DNA is copied. What is the most likely result for a treated cell?

A student with influenza asks for an antibiotic. Why would an antibiotic not help?

Which statement describes a real difference between a bacteriophage and the bacterial cell it infects?

A virus infects a bacterium and the infection becomes lysogenic. What happens to the viral genetic material?

Which statement correctly matches a plant transport tissue with what it carries?

A pollen grain lands on the stigma of a flower and a pollen tube grows down through the style. What does the tube deliver, and where does it go?

Blood that has just passed through a hard-working leg muscle is compared with blood entering it. Which difference would be measured?

During a run a person's body temperature rises. Sweat glands become active and blood vessels in the skin widen, and temperature returns to normal. This response is an example of what?

Red blood cells are placed in distilled water and quickly swell and burst. What is moving, and in which direction?

Which equation summarizes cellular respiration?

Plant cells carry out cellular respiration during daylight as well as at night.

The Punnett square shows a cross between two pea plants. Tall (T) is dominant to short (t). What fraction of the offspring in the square are expected to be short?

Red-green color blindness is carried on the X chromosome and is recessive. The square shows a cross. Which offspring genotype in the square is color blind?

A DNA template strand reads GGC ATA CCA. What messenger RNA sequence is transcribed from it?

A human skin cell containing 46 chromosomes divides by mitosis. What are the products?

Two siblings from the same parents are genetically different from each other. Which events of meiosis best explain that difference?

In one population, most individuals show the recessive phenotype for a trait while few show the dominant one. What does this show about the dominant allele?

Two black guinea pigs are bred together and produce a litter that includes one white pup. Black coat is dominant to white. What are the genotypes of the two parents?

Which base-pairing rule holds along the two strands of a DNA double helix?

A single base is deleted near the beginning of a gene's coding sequence. Why is the protein usually damaged more than by a substitution of one base?

Where in a cell does translation take place, and what does it build?

The diagram shows a branching pattern of ancestry with the trait that appears at each branch point. Which two animals share the most recent common ancestor?

The table gives the number of amino acid differences between the human form of a protein and the same protein in other species. What does the table support?

A bacterial infection is treated with an antibiotic. Almost all the bacteria die, but a few survive and the population regrows within days. What best explains the survivors?

Natural selection changes the makeup of a population over generations rather than changing an individual during its own lifetime.

A whale's flipper and a human arm contain the same bones arranged in the same order, though they are used very differently. What does this similarity suggest?

A river changes course and divides one beetle population into two groups that never meet again. Over many generations, what would lead to two separate species?

A newly discovered single-celled organism is placed in domain Eukarya. Which observation justifies that placement?

An organism is named Canis lupus. What does the first word of that name give?

A cliff face shows undisturbed layers of sedimentary rock, each holding fossils. What can be concluded about the fossils in the lowest layer?

Use the pond food web. A pollutant kills almost all of the snails. What is the most likely effect on the crayfish population, and why?

The diagram shows one turn of the carbon cycle. A large area of forest is cut down and burned. What are the two most direct effects on this cycle?

About a tenth of the energy at one trophic level is passed on to the next. Why does a food chain rarely support more than four or five levels?

Energy is recycled through an ecosystem in the same way that carbon and nitrogen are.

An oxpecker bird feeds on ticks it picks off a rhinoceros's hide. The bird gets a meal and the rhinoceros loses parasites. Which relationship is this?

A deer population introduced to an island grows quickly for several years, then levels off at about 500 animals and stays there. What does the number 500 represent?

A plant from another continent spreads across a prairie. Nothing living on the prairie eats it. What is the most likely effect on the native prairie plants?