Which has the strongest effect on whether stomata are open or closed?
a. sunlight
b. ion concentrations in the xylem
c. CO2 concentration
d. O2 concentration
e. abscisic acid
E
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A biologist ground up some plant leaf cells and then centrifuged the mixture to fractionate the organelles. Organelles in one of the heavier fractions could produce ATP in the light
, whereas organelles in the lighter fraction could produce ATP in the dark. The heavier and lighter fractions are most likely to contain, respectively, _____. A) mitochondria and chloroplasts B) chloroplasts and peroxisomes C) peroxisomes and chloroplasts D) chloroplasts and mitochondria E) mitochondria and peroxisomes
The presence of cyanobacteria ____ in rock dating to 2.5 billion years ago is direct evidence of the first water-splitting
photosynthesizers.
a. microfossils b. biosignatures c. stromatolites d. cytoskeletons e. endosymbiont
Thymine dimers are caused by
A) X-rays. B) active oxygen species. C) a mutagen such as ethylmethane sulfonate (EMS). D) depurination. E) UV light.
Which gland produces/releases hormones that have the widest range of effects on the body?
a. pineal b. pituitary c. thyroid d. adrenal e. pancreas