Question

in a molecule of double - stranded dna, the amount of adenine present is always equal to the amount of ______.
o a uracil
o b cytosine
o c guanine
o d thymine
question 23
english ivy is a plant that has the ability to grab onto objects and grow upward to get sunlight. this same ivy can also be found growing flat along the ground. what causes the variation in the ivy growth?
o a the ivy, that grows flat but has nearby objects to climb, and is exhibiting gravitropism.
o b the ivy grows where it will receive the least amount of sunlight for photosynthesis.
o c the ivy, that grows upward, has nearby objects to climb, and is exhibiting thigmotropism.
o d the ivy grows where it will be able to blend into its environment to avoid predation.
question 24
bacteria were some of the first organisms to be genetically modified because they have a relatively small genome and reproduce quickly. all of the following are reasons to study and modify a bacterial cells genome for beneficial uses except
o a to determine the genes that code for proteins such as those used to produce insulin in large amounts.
o b to determine genes that code for toxins against other bacterial cells to make antibiotics from these toxins.
o c to use bacteria cells as a vector to add genes that code for useful products.
o d to modify bacteria into an infectious form that has the ability to mutate quickly.

Explanation:

• Question 1: In double - stranded DNA, according to Chargaff's rules, Adenine pairs with Thymine. So the amount of Adenine is equal to Thymine.
• Question 2: Thigmotropism is the growth response of plants to touch. English ivy growing upward when there are objects to climb is an example of thigmotropism. Gravitropism is the response to gravity. Plants grow where they can get sunlight (not the least). Blending to avoid predation is not related to the described growth variation.
• Question 3: Modifying bacteria into an infectious form that mutates quickly is not a beneficial use. Determining genes for useful proteins (like insulin), toxins for antibiotics, and using bacteria as vectors for useful product - coding genes are beneficial.

Answer:

• Question 1: d. Thymine
• Question 2: c. The ivy, that grows upward, has nearby objects to climb, and is exhibiting thigmotropism.
• Question 3: d. to modify bacteria into an infectious form that has the ability to mutate quickly.