Healthy ecosystems depend on plant and animal species as their foundations. When a species becomes endangered, it is a sign that the ecosystem is slowly falling apart. Each species that is lost triggers the loss of other species within its ecosystem. Humans depend on healthy ecosystems to purify our environment.
Answer:
a supposition or proposed explanation made on the basis of limited evidence as a starting point for further investigation.
Explanation:
It can damage collagen fibers, destroy vitamin A in skin, accelerate aging of the skin, and increase the risk of skin cancers. Excessive sun exposure can also cause cataracts and diseases aggravated by UVR-induced immunosuppression such as reactivation of some latent viruses.
Answer:
C
Explanation:
The origin of replication refers to the site at which DNA replication begins. The process of DNA replication - which occurs prior to cell division - generates a new copy of the DNA.
DNA replication involves unwinding of the DNA double helix, creating a Y shape called the replication fork. The two strands are then replicated, and now there are two DNA molecules, each containing one "old" DNA strand and one "new" DNA strand.
The first stage at the origin of replication is that the enzyme helicase begins splitting apart the strands of a DNA molecule. (C)
The answer is not A, as the two DNA strands are already in the double helix. The answer is not B, as the enzyme responsible for copying the DNA sequence is DNA polymerase, not RNA polymerase. The answer also cannot be D, because although short RNA primers are involved in DNA replication, this does not occur at the origin of replication.
