To infect a cell, HIV must
A. bind both CD4 and a cytokine co-receptor.
B. bind both CD8 and a cytokine co-receptor.
C. bind both CD8 and a class I MHC proteins.
D. kill cytotoxic T cells and bind CD4.
A. bind both CD4 and a cytokine co-receptor.
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PCR typically results in the generation of fragments of all sizes
Indicate whether this statement is true or false.
The chewy, stringy cells in celery are which cells?
a. xylem b. collenchyma c. phloem d. sclerenchyma e. parenchyma
The oldest definitive trace of flowering plants in the fossil record consists of:
a. pollen grains in an anther. b. pistils on vegetative stems. c. petals and sepals. d. ovules enclosed in podlike fruits. e. primitive embryo sacs.
Mangrove plants live in areas regularly flooded with salt water. Which of these is not a possible mechanism for controlling their salt balance?
A. The succulent leaves contain large quantities of water that dilute salt that is absorbed. B. Excess salt is stored in special tissues. C. The roots block salt uptake. D. Modified roots emerge above the water level and help oxygen diffuse into the roots. E. Absorbed salt is secreted from special salt glands.