Damaged tissue releases chemicals that activate platelets and stimulate the form

Question

Damaged tissue releases chemicals that activate platelets and stimulate the formation of blood clots. Which of the following predictions about the activity of platelets best describes a positive feedback mechanism? 7. 8. Bacteriophages are viruses that infect bact acteria an experiment, bacteriophages were labeled widh either radioactive phosphorus or radioactive sulfur. The labeled bacteriophages were incubated with bacteria for a brief amount of time and then removed. The infected bacteria cells were found to contain significant amounts of radioactive phosphorus but not radioactive sulfur Based on the results of the experiment, which of the following types of molecules did the bacteriophages most likely inject into the bacteria cells? (A) Activated platelets release chemicals that inhibit blood clot formation. (B) Activated platelets release signaling molecules that inhibit cell division in (C) Activated platelets constrict the blood (D) Activated platelets release chemicals that damaged tissue. vessels, stopping blood flow activate more platelets (A) Simple carbohydrate (B) Amino acid (C) DNA (D) Polypeptide

Explanation / Answer

Ans. #7. Correct option- D. Activated platelets release chemicals that activate more platelets. A positive feedback mechanism is the pathway in which the end product of the pathway stimulates the production of more end products.

For the given case, triggering the activation of more platelets by the pre-existing platelets is a positive feedback mechanism.

# In a negative feedback mechanism, the end product of the pathway triggers the inhibitions of formation of end products.

#8. Correct option- C. DNA.        [see, Hershey and Chase Experiment]

# Phosphorous is present in DNA and RNA only. So, P-radiolabelled bacteriophage actually have their DNA radiolabelled with P.

# Sulfur is present in amino acids (methionine, cysteine ; protein) only. So, S-radiolabelled bacteriophage actually have their protein/ polypeptides radiolabelled with S.

# Presence of radiolabelled-P in the host bacterial cells indicate that viral DNA has entered into the bacterial cytoplasm during infection. Therefore, bacteriophage injected its DNA into the host bacterial cells.

# Since radiolabelled-S is not detected in host bacteria, neither of viral amino acids and polypeptides (polymer of amino acids) enters into the cell.

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