Which of the following is the source of embryonic stem cells?
A) Inner cell mass
B) Spermatozoa
C) Trophoblast
D) Blastocoel
E) Enucleated egg cells
A
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Many terrestrial arthropods exchange gases with their environments by using tracheae, tubes that lead from openings (called spiracles) in the animal's exoskeleton or cuticle directly to the animal's tissues. Some arthropods can control whether their spiracles are opened or closed; opening the spiracles allows the carbon dioxide produced in the tissues to travel down the tracheae and be released outside the animal. Klok et al. measured the carbon dioxide emitted over time (represented by ) by several species of centipedes. The figure below presents graphs of their results for two species, Cormocephalus morsitans and Scutigerina weberi. (C. J. Klok, R. D. Mercer, and S. L. Chown. 2002. Discontinuous gas-exchange in centipedes and its convergent evolution in tracheated arthropods. Journal of Experimental Biology 205:1019-29.) Copyright 2002 The Company of Biologists and the Journal of Experimental Biology. Look at the graph for Cormocephalus morsitans in the figure above. What is the best interpretation of these results? A) The centipede had its spiracles open the entire time. B) The centipede had its spiracles closed the entire time. C) The centipede had its spiracles open when carbon dioxide (CO2) emission peaked and closed when CO2 emission was low. D) The centipede had its spiracles closed when carbon dioxide (CO2) emission peaked and open when CO2 emission was low.
The cross GE/ge × ge/ge produces the following progeny: GE/ge 404, ge/ge 396, gE/ge 97, Ge/ge 103. From these data, one can conclude that the G and E loci assort independently
Indicate whether the statement is true or false
Which stimuli most directly causes the Venus flytrap to catch an insect?
a. gravity b. light c. touch d. scent e. sound
Cholesterol is a structural component of cell membranes. Amount of cholesterol present can affect membrane stability and permeability. What is the role of cholesterol in a membrane?
A. Membranes with high amounts of cholesterol are very stable and have decreased permeability. B. A membrane that needs to be rigid, such as a protective barrier, would have low cholesterol ratios. C. A membrane that needs to be more rigid and more permeable, would have high cholesterol ratios. D. Membranes with low amounts of cholesterol are very stable and have increased permeability.