tailieunhanh - Read know english 3

Tham khảo tài liệu 'read know english 3', ngoại ngữ, anh ngữ phổ thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | ----------------------- ACT SCIENCE REASONING TEST PRACTICE ----------------------------------------- After a few weeks Mark observed a cotton-like substance in some of his L-alanine samples. He was sure that these weren t L-alanine crystals. After spending some time in the library he found that the amino acid L-alanine is prone to bacterial attack. He hypothesized that bacteria were eating his samples and that the cotton-like substance was a bacterial byproduct. He prepared 20 new L-alanine samples. All of the samples were 40 supersaturated in 2 g of water at room temperature. Mark took great care to keep his samples sterile. He used water that had been passed through a pm filter and treated by UV rays. Mark was able to obtain crystals from 15 out of 20 solutions. 6. The goal of Mark s research was f. to eliminate bacteria from his samples. g. to determine why L-alanine didn t crystallize. h. to heat his samples without damaging them. j. to grow and analyze the crystals of two amino acids. 7. According to the passage above what best supports the statement 40 supersaturation is sufficient for glycine crystal growth at room temperature. a. L-alanine is prone to bacterial attack. b. When Mark increased the supersaturation to 50 he obtained crystals. c. Crystals formed in 40 supersaturated samples prepared using filtered and treated water. d. Filtering water causes crystallization in all samples. 8. If filtering water through a pm filter without UV treatment were enough to eliminate the bacterial attack problem what could be said about the bacteria in Mark s samples f. They are too large to pass through a pm filter. g. They are too small to pass through a pm filter. h. After passing through a pm filter the L-alanine stops being a food source for the bacteria. j. After passing through a pm filter the bacteria stops being a food source for L-alanine. 9. It can be inferred from the passage that UV treatment is used to a. increase .