Unlike other gymnosperms, gnetophytes have which of the following?
a. vessel elements in their xylem
b. separate male and female gametes
c. seeds exposed on modified leaves
d. small spores that germinate
a. vessel elements in their xylem
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What has caused this strange result?
A scientist has been growing a bacteria strain for some time in culture media containing very few nutrients. The cells are growing slowly, so she enriches the media with amino acids and carbohydrates. To her dismay, instead of growing faster and to higher densities, the bacteria begin to die. A. A prophage switched from the lysogenic cycle to the lytic cyle. B. A prophage switched from the lytic cycle to the lysogenic cycle. C. The bacteria is infected with a temperate phage. D. The bacteria is infected with a virulent phage, and has switched from the lysogenic cycle to the lytic cycle. E. The bacteria is infected with a temperate phage, and has switched from the lysogenic cycle to the lytic cycle.
All cells in our body (e.g., a neuron or muscle cell) possess a type of protein that the immune system uses to identify them as our own cells. This protein is
A. CD4. B. lactoferrin. C. MHC I. D. MHC II. E. antigen.
The __________ are very common arthropod Paleozoic fossils, and are extinct today
A. moss animals B. trilobites C. lophophorate animals D. tardigrades E. phoronids
Who first described cells?
A. Darwin B. Leeuwenhoek C. Linnaeus D. Hooke E. Golgi