Enzymes speed up reactions by
a. lowering activation energy.
b. adding some energy to the system.
c. increasing activation energy.
d. lowering activation energy and adding
some energy to the system.
e. doing all of these
A
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Scientists measured the pressure in the xylem of redwood trees at different heights and found that the higher they made their measurements, the lower the pressure. They extrapolated this to a pressure of zero, and concluded that the tallest a tree could grow is 122–130 meters. The tallest known tree on Earth is 112.7 meters. Which of the following most likely limits the height of trees?
A. amount of transpiration in leaves B. ability to take up CO2 C. strength of water cohesion D. amount of energy needed to pump water to the tops of the trees E. amount of photosynthesis in leaves
The perforin-granzyme pathway involves
A) the production of fever, which kills the pathogen. B) the production of antibodies toward the invading pathogen. C) the production of special cell-killing proteins that act on infected or abnormal cells. D) presenting the foreign antigen to B cells. E) binding CD95L to infected cells, which eventually leads to cell apoptosis.
Which of the following contributes to protecting the eyes from microbial invasion?
A) Tears contain lysozyme and salt. B) A mucus layer traps and removes microbes. C) Tears mechanically flush particles from the eyes. D) Tears contain lysozyme and salt and mechanically flush particles from the eyes. E) Tears and mucus combine to trap microbes and remove them.
Biotechnology expects to provide the following benefits:
A. Improved agricultural crops. B. Control of human breeding. C. Cheaper medicines. D. Improved agricultural crops and cheaper medicines.