Countercurrent flow of water and blood increases the efficiency of gas exchange in _____
a. fishes c. birds
b. amphibians d. all of these
A
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Why don't all changes in DNA result in mutations? a. Mutations are never expressed
b. None of these choices. c. The cell never makes a mistake during transcription. d. The cell never makes a mistake during translation. e. The same amino acid can be produced by a variety of codons.
The brain knows how strong a stimulus is
because the brain interprets
a. action potentials of certain nerves in certain ways. b. variations in the rate of action potentials. c. the size variation in the action potential being propagated. d. all of these. e. all of these except size variation in the action potential being propagated
You are excited because your lab is studying the first microorganisms retrieved from Mars! Interestingly, their genetic material consists of a single-stranded nucleic acid with six different nitrogenous bases. Like organisms from Earth, segments of the nucleic acid contain the code for making proteins. If the genetic code in these organisms was read in groups of 2 bases instead of 3, what is the maximum number of amino acids that could be coded for assuming that only one codon functioned as a stop codon? (Enter your answer as a numeral not a word, e.g. enter 17 not seventeen.)
Fill in the blank(s) with the appropriate word(s).
Scientists estimate that at least 50-60% of all species now living will most likely become extinct in the next 20-50 years unless planned, coordinated action takes place.
Answer the following statement true (T) or false (F)