Answer:
The correct answer is option B.
Explanation:
The immune system found within a human being comprises millions of cells that circulate all through the body with the help of blood. These cells help the body to fight against foreign invasions like viruses, bacteria, and other pathogens. The immune cells that primarily fight against the invasions are the white blood cells, which are further differentiated into phagocytes and lymphocytes.
However, at the time of stress, the immune system loses the tendency to fight against the foreign invasions or the antigens, and thus, the person becomes more vulnerable to infections. At the time of stress, a hormone gets discharged known as a corticosteroid that diminishes the efficacy of the immune system, that is, by reducing the concentration of lymphocytes. Hence, option B is correct.
Answer: mutations that natural selection can work on. 4.) How do scientists calibrate a molecular clock? ... they compare the number of positive mutations that have occurred in a particular species with the number of negative mutations that have occurred
Explanation:
The definition of a biological species is that they will only breed with members of their own species. If the two populations of chimps will no longer interbreed, then they are considered separate species = speciation.
B. Speciation
Answer:
E. All of these mechanisms are used; there is no single universal mechanism.
Explanation:
Gene expression is regulated at many levels. Some of them are:
- Chromatin remodeling regulation includes altered histone modifications such as methylation which can regulate gene expression (up or down).
- Transcription is regulated via transcriptional factors and specificity factors such as repressors and activators.
- RNA processing can be regulated through the alternative splicing (different introns can be excised and combinations of different exons connected)
- Post-translational modification refers to modification of proteins after being synthesized.
Protections the ozone layer
Maintaining animal and human food chain
Preserving potable water and making efficient use of non renewable resources