The number of sea otters living along Alaska’s Aleutian Islands has fallen to 10% of what it was a decade ago. The investigation into what is happening to this population is revealing a great deal of information about the complex nature of food webs. It is also showing how fragile the links in a food web can be. The immediate cause of the sea otter’s decline seems to predation by killer whales, which are turning to sea otters as a food source. James Estes, a University of California marine ecologist, first witnessed a killer whale eating a sea otter in 1991. Since then, a dozen such attacks have been reported. Estes suspected that these attacks were ultimately caused by disruption of the marine food web. Many fish populations have declined dramatically, and species that marine mammals feed upon have been hit especially hard. The cause of this decline is not entirely understood, but it thought to be due to a combination of over fishing, warming ocean temperatures, and other factors. Killer whales normally eat sea lions and harbor seals, but with local fish populations so low, these deal populations have rapidly declined. This has caused killer whales to resort to a new food source, the smaller and less nutritious sea otter. This decline in the sea otter population has disrupted much of the coastal ecosystem along the Aleutian Islands. Sea otters prey upon sea urchins, which, in turn, feed upon kelp a type of large seaweed that is abundant in many coastal ecosystems. Kelp beds provide protection for many species of fish and other small animals and are an important basis of the coastal food web. In Estes’ view, these changes are “an ecological chain reaction” with events that occur far out at sea causing massive changes to the coastal ecosystem. A plan has been suggested to help preserve the sea otter population in the Alaskan coastal food web, shown below. This plan will reduce the number of fish that commercial fishing boats can catch from the coastal food web. ~Describe how the plan will affect the population of sea otters
~Will this plan increase or decrease the kelp population?

during the process of dna replication, brdu can replace thymidine and incorporate into the newly synthesized dna, cell proliferation thus can be reflected in the extent of brdu incorporation.

he movement of air through earth's or any planet's atmosphere is called wind, and the main cause of earth's winds is uneven heating by the sun. this uneven heating causes changes of atmospheric pressure, and winds blow from regions with high pressure to those with low pressure.

i hope this : )

an individual’s sex (i.e., whether they are a male or female) is determined by the sex chromosomes. most people have two sex chromosomes, one that is inherited from their mother and one that is inherited from their father. typically, females have two x chromosomes (xx) and males have one x chromosome and one y chromosome (xy). conditions caused by changes (“mutations”) in genes located on the x chromosome are considered x-linked.

x-linked recessive inheritance

most x-linked conditions are recessive. this means that in a person with two x chromosomes (most females), both copies of a gene (i.e., one on each x chromosome) must have a change or mutation whereas in a person with one x chromosome (most males), only one copy of a gene must have a mutation. a female with a mutation in one copy of a gene on the x chromosome is said to be a “carrier” for an x-linked condition. a male with a mutation in a gene on the x chromosome is typically affected with the condition. because females have two copies of the x chromosome and males have only one x chromosome, x-linked recessive diseases are more common among males than females. however, x-linked recessive diseases can occur in both males and females.

for x-linked recessive disorders, an unaffected carrier mother who has a mutation in a gene on the x chromosome can transmit either the x chromosome with this mutation or a “normal” x chromosome to her children. if the father is unaffected, none of her daughters will be affected and all of her daughters will be unaffected—since they will inherit at least one normal x chromosome from their father. however, each daughter will have a 50% chance of being an unaffected carrier like her mother and a 50% chance of both x chromosomes being normal.