Q: Tropomyosin is a type of what, that winds around the chains of the actin filament and covers the myosin-binding sites to prevent actin from binding to myosin? Read this paragraph and choose the correct option from the provided answers: Tropomyosin is a protein that winds around the chains of the actin filament and covers the myosin-binding sites to prevent actin from binding to myosin. Tropomyosin binds to troponin to form a troponin-tropomyosin complex. The troponintropomyosin complex prevents the myosin "heads" from binding to the active sites on the actin microfilaments. Troponin also has a binding site for Ca++ ions. To initiate muscle contraction, tropomyosin has to expose the myosin-binding site on an actin filament to allow cross-bridge formation between the actin and myosin microfilaments. The first step in the process of contraction is for Ca++ to bind to troponin so that tropomyosin can slide away from the binding sites on the actin strands. This allows the myosin heads to bind to these exposed binding sites and form cross-bridges. The thin filaments are then pulled by the myosin heads to slide past the thick filaments toward the center of the sarcomere. But each head can only pull a very short distance before it has reached its limit and must be "re-cocked" before it can pull again, a step that requires ATP. Choices: - enzyme - bacteria - amine - protein A:
protein

(Question)
Q: What are plants that grow where people don't want them to and can take up space and use resources which hinders growth of more desirable plants? Read this paragraph and choose the correct option from the provided answers: We obviously can't live without plants, but sometimes they cause us problems. Many plants are weeds. Weeds are plants that grow where people don't want them, such as gardens and lawns. They take up space and use resources, hindering the growth of more desirable plants. People often introduce plants to new habitats where they lack natural predators and parasites. The introduced plants may spread rapidly and drive out native plants. Many plants produce pollen, which can cause allergies. Plants may also produce toxins that harm human health (see Figure below ). Choices: - native plants - shrubs - grasses - weeds A:
(Answer)
weeds

Ques: Q: What carbohydrate from fruit juices is a gel-forming substance important in jelly making? Read this paragraph and choose the correct option from the provided answers: Pectin, a carbohydrate from fruit juices, is a gel-forming substance important in jelly making. Silica gel, a colloidal dispersion of hydrated silicon dioxide, is formed when dilute hydrochloric acid is added to a dilute solution of sodium silicate. Canned Heat is a gel made by mixing alcohol and a saturated aqueous solution of calcium acetate. Choices: - potassium - gelatin - cellulose - pectin A:
Ans: pectin

(Q).
Q: What is capable of altering the rate of time passing? Read this paragraph and choose the correct option from the provided answers: Strong gravitational fields can alter the rate of time passing. True. Choices: - strong planetary fields - weak gravitational fields - strong magnetic fields - strong gravitational fields A:
(A).
strong gravitational fields

Ques:Q: What is always conserved in chemical reactions? Read this paragraph and choose the correct option from the provided answers: A: All chemical equations must be balanced. This means that there must be the same number of each type of atom on both sides of the arrow. That's because mass is always conserved in chemical reactions. Count the number of hydrogen and oxygen atoms on each side of the arrow. There are two hydrogen atoms in both reactants and products. There are two oxygen atoms in the reactants but only one in the product. Therefore, equation 1 is not balanced. Choices: - energy - bonds - force - mass A:

Ans:mass

Ques: Q: What keeps various species from mating and reproducing outside their own species? Read this paragraph and choose the correct option from the provided answers: Figure 18.19 The shape of the male reproductive organ varies among male damselfly species, and is only compatible with the female of that species. Reproductive organ incompatibility keeps the species reproductively isolated. Choices: - digestive system incompatibility - brain organ incompatibility - cancer organ incompatibility - reproductive organ incompatibility A:
Ans:
reproductive organ incompatibility