natural selection, bc it is the process whereby organisms better adapted to their environment tend to survive and produce more offspring
The sun is a source of energy
Because the organism is distributed across the world, and isn't seen anymore, scientists can conclude tat they must have evolved. They can compare one species to the fossils they may have found, and determine that they were related. Then by looking at the species on another part of the world compare the same fossils to other animals and determine that they are similar, sharing a common ancestor.
Answer:
Physiological reactions to stress in the alarm stage include: <em>increased heart rate and blood pressure, dilated pupils, rapid and shallow breath, and increased cortisol levels.</em>
Explanation:
Hans Seyle, a medical doctor proposed a model called the General Adaptation Syndrome (GAS) to explain the effects and stages of coping with the stress. The GAS model has three stages, known as:
1. Alarm stage
2. Resistance stage
3. Exhaustion stage
The <em>alarm</em> stage is the first stage of responding to stress. During this stage, the fight-or-flight response is activated when an individual is experiencing stress. This stage involves the following physiological reactions:
1. Increased heart rate
2. Increased blood pressure
3. Dilated pupils
4. Rapid and shallow breath
5. Increased cortisol levels
Answer: A
Explanation:The Trp operon is responsible for synthesis of the amino acid trytophan when it is not available in the cellular environment.
When the tryptophan is plentiful, a repressor protein binds to two molecules of tryptophan.
Thiss repressor-tryptophan complex binds to the trp operator. This binding prevents the binding of RNA polymerase, so the operon is not transcribed, and no new trptophan is produce.
On the other hand, when tryptophan levels are reduced, the inactive repressor will not bind the tryptophan operator so the operon is transcribed.
Regulation of the trp operon is determined by the concentration of tryptophan; when adequate tryptophan is present in the growth medium, there is no need for tryptophan biosynthesis.
Transcription is turned off when a high concentration of tryptophan is present, and is turned on when tryptophan is absent. The regulatory signal is the concentration of tryptophan itself.
Therefore in the absence of tryptophan, the inactive repressor cannot bind trpO, so operon gene transcription occurs.
