Why are individuals who are heterozygous for the cystic fibrosis allele unaffected by the disease?
a. They make enough of a particular protein to allow their cells to work properly
b. They have an extra copy of the allele on their X chromosome
c. Cystic fibrosis only occurs in males, so females are unaffected
d. Their cells can transport chloride ions through diffusion channels
Ans: a. They make enough of a particular protein to allow their cells to work properly
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Which of the following features is most important for true mosses and ferns to reproduce in the desert?
A) that the sporophytes occupy only permanently shady, north-facing habitats B) that the sporophytes hug the ground, growing no taller than a couple of inches C) either that their gametophytes grow close together, or that they be hermaphroditic D) that the sporophytes have highly lignified vascular tissues E) that the gametophytes contain secondary compounds to deter herbivores
What factors are attributed to the high productivity of continental slopes?
a. Sunlight and substrate availability b. Concentration of nutrients and sunlight c. Temperature and salinity d. Concentration of nutrients and salinity
Each DNA double helix has a backbone that consists of alternating ____
a. covalent and ionic bonds b. nitrogen-containing bases c. hydrogen bonds d. sugar and phosphate molecules e. covalent and hydrogen bonds
Which of the following is the most likely cause for the sudden sharp increase in atmospheric carbon dioxide levels?
A. natural events, including fires and volcanic activity B. normal fluctuations in the natural levels of carbon dioxide in the atmosphere C. human activities, including the use of fossil fuels, changes in agricultural practices, and deforestation D. respiration from the earth's many living organisms