Which of the following is an example of active transport in a cell? Choose 1
A
Calcium passing through channel proteins, from a high to low concentration

B
Enzymes spreading evenly through cytoplasm

C
Oxygen entering the cell without the use of energy

D
Sodium moving out of the cell against its concentration gradient

The earth consists of a variety of different organisms. despite their diversity, however, some similarities on the structural and metabolic levels may be seen. these similarities can be attributed to a. similarities among organisms in their proteins and nucleic acids. b. the ability of organisms to readily adapt to sudden environmental changes. c. similarities in organisms' habitats and niches. d. the ability of all organisms to interbreed and produce new species.

Blood stem cells may develop into any kind of human blood cells. what kind of stem cells are blood stem cells? a. multipotent stem cells o b. totipotent stem cells o c. pluripotent stem cells o d. unipotent stem cells

Which of the following cell structures is significantly different between gram- positive and gram-negative bacteria?