Scientists believe that the Earth's early atmosphere lacked __________ gas because photosynthetic organisms did not yet exist.

The theory of endosymbiosis suggests that chloroplasts and mitochondria were once free-living prokaryotes, that were engulfed by larger prokaryotic cells. Eventually, this relationship lead to the development of eukaryotic cells with cellular organelles. These organelles included mitochondria, and in some cases, chloroplasts.

Why would engulfing these smaller prokaryotic cells be an advantage to the larger prokaryotic cells?

According to the theory of _____________, mitochondria in cells today are the descendants of aerobic prokaryotes that used oxygen to generate energy.

Before organisms with nuclei evolved, life on earth consisted only of unicellular

The organelle pictured is found in cells of ______________ and is theorized to have once been an independent organism.

The theory of endosymbiosis suggests that the ancestors of mitochondria were

It is thought that organelles of eukaryotic organisms, such as mitochondria and chloroplasts (in plant cells) came from

Some species of present day protists contain living organisms within their cytoplasm. Paramecium bursaria are hosts for zoochlorellae, photosynthetic protists, that live within the cytoplasm of the paramecium. The relationship appears to be symbiotic; the zoochlorellae gain protection and possibly some essential nutrients from the host cytoplasm and the paramecium host has an available food source when its usual food source is depleted.

This symbiotic relationship provides support for the theory of endosymbiosis, which states that...

There are currently millions of species of single-celled organisms, and million of others that were once here and are now extinct. Which of these would BEST describe the first, most primitive organism to arise on Earth from which all other life evolved?

Based on the current model of evolutionary history, the first living cells to evolve on earth were...

Scientists study similarities between groups of organisms to determine how they may have changed over time.

All of the following are used as evidence for the similarities between the two organisms shown above EXCEPT

The pictures show two different ferns that lived millions of years apart. The early fern is extinct, but is drawn based on fossil evidence. Scientific data reveals that the early fern is an ancestor of the modern fern. Which statement BEST explains why the fern changed over time?

A scientist drew some diagrams of ancestors of elephants based on fossil evidence.

Which is the BEST conclusion that can be made from comparing the diagrams?

Fossil records indicate that species changes generally

Fossil records indicate that Earth was first inhabited by bacteria-like organisms. These organisms

A cow and a frog have similar bone structures in their forelimbs. Both have phalanges, radius, ulna, and humerus bones. However, the cow and frog are animals with very different life cycles from each other. Which MOST likely describes why the body structures of these animals are so similar?

In Africa there are two species of elephants. One species lives in the forest of central Africa and another species lives in the savanna of Africa. It was recently hypothesized that an isolated group of elephants living in western Africa may be a different species from the other two groups. Which development in technology would BEST be used to determine if the elephants are the same species?

Researchers have discovered that the ear bones of mammals are homologous to some bones in fish jaws. Which claim is BEST supported by this fact?

To determine how closely related organisms are, scientists consider all of the following EXCEPT

The exotic plant Melaleuca, or Australian Pine, has increased the intensity of fires across the Everglades. The amount of fuel available for fires has increased due to the presence of the Melaleuca. The Melaleuca releases massive numbers of seeds in response to fire, drought, and herbicide damage. Which BEST describes the reason the Melaleuca has been able to survive?

Natural selection is a mechanism that acts on individuals within a population. Which is a result of the process of natural selection?

A shift in climate changes a forested area with little annual snowfall to an area with snowfall most of the year. Natural selection would MOST likely favor a rabbit with which adaptation?

A particular organism is able to survive in an environment due to a thick layer of fat beneath its skin. In which situation would the layer of fat MOST likely be a survival advantage?

An ocotillo shrub is a desert plant that is characterized by small leaves and a wax-coated stem. How do these structures MOST likely provide a survival benefit for this plant?

The fur color of a bear varies with its environment. Polar bears found in the Arctic have white fur, while black bears found in Pennsylvania have dark fur. Which BEST describes the variation of fur color amongst the bear species?

The process by which organisms with favorable variations reproduce at higher rates than those without such variations is

The graph indicates the changes over time in a particular trait in a population of shrew.

Which statement BEST explains what occurred after 10 years?

Polar bears are well adapted to the Arctic environment due to their white fur coats. Which statement BEST explains why white coat color was possibly favored by natural selection over other coat colors?

The saber-tooth trait appeared independently in the animals Thylacosmilus and Smilodon.

Which statement BEST explains why this trait evolved in both types of organisms?

The cheetah population around the world has decreased because of poaching and loss of habitat. The surviving population is found to have similar alleles. Which factor is endangering the species’ survival the MOST?

A comparison of a brittle star in the fossil record and of a modern-day brittle star shows strong similarities in their structure.

The similarities in their structure would BEST be explained by which statement?

Which of these BEST describes the benefit of genetic variation within a species?

According to Darwin's theory of evolution, the variations among finches that he observed in the Galapagos Islands resulted from...

Natural selection CANNOT occur without

The drawing shows a dark-colored peppered moth and a light-colored peppered moth.

The increased use of coal in 19th-century England lead to the coating of the landscape with black coal dust. The event coincided with a change in peppered moth populations. Over time, the frequency of dark-colored moths became greater than that of light-colored moths. What was the advantage of the dark-colored moths over the light-colored moths?

Two different species evolving from a common ancestor MOST likely occurs

Which is an example of geographic isolation? A)A species of chipmunk becomes extinct because of a lack of food. B)Two groups of albatross live on separate islands but commonly cross from one island to the other. C)A group of snakes is unable to cross a river and is separated from a group of snakes on the opposite side. D)One group of frogs mates in spring and another mates in fall, effectively isolating the two groups from breeding with each other.

20,000 years ago, two populations of the black-tailed rats became separated from each other by the formation of a large canyon, thus preventing their interbreeding. The condition described is...

A mountain separates a population of mice into two distinct eastern and western populations. The eastern area is inhabited by owls, which hunt at night. No owls live in the western area. Over time, the eastern population of mice will MOST LIKELY....

If two populations of the same species of insects have been geographically isolated from each other for an extended period of time, they will MOST LIKELY exhibit...

Several factors can lead to speciation. Eastern and western meadowlarks are similar birds whose habitats overlap in the United States. They do not breed because they have different mating songs. Which term is used by evolutionary biologists to describe this phenomenon?

In order for a genetic mutation in a species to result in the formation of a new species, what must occur?

The Grand Canyon was carved out by the Colorado River. This caused the separation of members of a squirrel species. Abert’s Squirrel lives on the southern side of the canyon and in other parts of the United States. A subspecies, the Kaibab Squirrel, is found around the northern rim of the canyon and nowhere else in the country. As shown here, the two squirrels differ in body and tail coloration. Their ears are also different. These variations are the result of....

Speciation has definitely occurred when two groups of related organisms....

A species is a group of organisms capable of mating and producing offspring, and ___________ is the process of forming a new species.

One way a new species may form is by geographic isolation. This occurs when members of a population are physically separated, for example, by a river, or a desert.

After the separation the two populations, responding to different conditions, will adapt differently, and so their evolutionary paths will be different.

The Galapagos Islands contain thirteen species of finches. Four are seen here. It is believed that all of these species had one common ancestor and, over time, the species evolved. What statement BEST describes the thirteen different finch species?

The cladogram seen here is a pictorial representation of descent through modification or...

A tree of life depicting the hypothetical phylogeny of the three domains is shown above. At which letter is located the common ancestor that would contain membrane-bound organelles?

Crocodiles, lizards, and snakes are all reptiles. However, lizards are more closely related to snakes than to crocodiles. Which statement MOST accurately describes how this relationship is explained in Darwin's Theory of Evolution?

What conclusion would be MOST appropriate about the genetic variation between humans and the three apes as illustrated by the phylogenetic tree?

The phylogenetic tree illustrates the relationship between humans and our closest living relatives. The tree was based on biochemical comparisons, including DNA and amino acid sequences.According to the biomolecular data, we COULD infer that...

Which organisms DNA will differ from the chimpanzee the MOST?

Study the cladogram. Which two organisms would be the least related?

Study the cladogram above. Which statement is true regarding the organisms on the cladogram?

Based on the cladogram, if moths undergo complete metamorphosis, we would MOST LIKELY infer that....

Which organism has fur and mammary glands, but does NOT have opposable thumbs?

Study the cladogram. What does the lizard share with the chimpanzee?