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

Biology & Microbiology

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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

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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

Biology & Microbiology

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.

Biology & Microbiology

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

Biology & Microbiology