Three weeks after conception, which of the following has happened in an embryo?

A) organ formation B) primitive eye formation
C) limb bud formation D) neural tube formation


Answer: D

Biology & Microbiology

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Glacier Bay in Alaska is a fjord whose lowlands were covered by glacial ice until around 230 years ago

As the glacier retreated, glacial till was exposed to plant colonization; remarkably (and fortunately for generations of ecologists), the location of the tip of the retreating glacier has been frequently documented since the late 1700's. This means that scientists have been able to develop a detailed timeline of the changes in the plant community, or _____ in Glacier Bay over time. A. ecological succession B. niche diversification C. niche divergence D. competitive exclusion E. none of these

Biology & Microbiology

How has gene duplication played a critical role in evolution?

a) It produces redundant copies of existing genes, which are then free to mutate and adopt new functions. b) It almost always introduces immediate benefits for the organism. c) It increases the amount of DNA in the genome. d) It increases the number of pseudogenes in the genome. e) It increases the likelihood of viral infection in cells.

Biology & Microbiology

Mutations that cause sickness and death after reproduction:

a. are unlikely to occur. b. can be passed on to future generations. c. are passed on to future generations only in species that have long life spans.

Biology & Microbiology

In 1947, prolonged flooding of the Kissimmee River, located in Florida's Heartland, inundated the Kissimmee basin as well as the surrounding cities, prompting citizens to cry out for flood control

The river was transformed into a canal, and associated wetlands with their populations of wetland-dependent flora and fauna declined drastically. The loss of wetlands could have resulted in A) an increase in native plant populations with an accompanying decline in herbivore species. B) a decrease in erosion of the river basin. C) enhanced natural water purification. D) a pollution problem. E) a decline in populations of invasive species.

Biology & Microbiology