Grade 8 Science Practice Test: Natural Selection, Earth's History and Human Impact

Dark moths were better hidden on sooty bark, so they were eaten less often and left more offspring, and the dark color became more common over generations. Individual moths cannot change their inherited wing color, and soot on the wings would not be passed to offspring.

Natural selection works on inherited variation: if some individuals have traits that help them survive and reproduce, those traits become more common. If all individuals were genetically identical, there would be nothing to select.

The antibiotic removes bacteria that are not resistant, while resistant ones survive and reproduce, passing on the resistance gene. Over time resistant bacteria become a larger part of the population. The change happens to populations exposed to the drug, not to all bacteria at once.

When people choose which individuals reproduce based on traits they want, the process is artificial selection (selective breeding). In natural selection, the environment, not people, determines which individuals survive and reproduce.

Adaptation happens across generations as helpful inherited traits are passed on more often. Traits gained by use during an animal's life, such as stronger muscles, are not inherited, so using a body part does not change the offspring.

Moving a gene from one organism into another to give it a new trait is genetic engineering. Selective breeding only chooses among traits that already exist in a species; it cannot give bacteria a human gene.

In undisturbed sedimentary rock, each layer is deposited on top of the one before, so the bottom layer, Layer 4, is the oldest. Layer 1 at the top is the youngest layer.

Rock X cuts through Layers 2, 3 and 4, so it is younger than they are. It does not cut Layer 1, so Layer 1 was deposited after X formed. Putting X first ignores that a rock must exist before something can cut through it.

The fossil series shows step-by-step changes from mammals with legs toward a fully aquatic body, which is evidence that whales descended from land-dwelling mammals. Losing a body part from disuse during an individual's life is not inherited.

Shared patterns in early development are evidence of common ancestry. The throat pouches become gills in fish but parts of the ear, throat and jaw in humans, so humans never have working gills.

A worldwide iridium layer points to material from a large asteroid spread around the globe, and the disappearance of non-bird dinosaur fossils right above it links the impact to a mass extinction. Dinosaurs first appeared far earlier, over 200 million years ago.

300,000 ÷ 4,600,000,000 × 86,400 seconds is about 5.6 seconds, so humans appear in the last few seconds of the day. This shows how recent humans are compared with the whole history of Earth.

Orangutans depend on rainforest trees for food, nesting and travel. Clearing the forest destroys their habitat, so fewer can survive there. Habitat loss is one of the main ways human land use reduces biodiversity.

Plant buffer strips slow the runoff and take up nutrients before they reach the stream, so less fertilizer feeds the algae. A paved road would increase runoff, and adding more fertilizer would make the problem worse.

Burning fossil fuels, along with clearing forests, releases large amounts of carbon dioxide, and this is the main cause of the rise. Volcanoes release far less carbon dioxide each year than human activities, and photosynthesis takes in carbon dioxide rather than releasing it.