13. during diffusion, when the concentration of molecules on both sides of a
membrane is the same, the molecules will
a. move across the membrane to the outside of the cell.
b. stop moving across the membrane.
c. continue to move across the membrane in both directions.
d. move across the membrane to the inside of the cell.

What is called the "building block" of life?

This is the main structural axis of the plant that supports leaves, flowers and fruits; transports fluids; stores nutrients and produces new tissue.

Once an egg cell is fertilized by sperm, the cell then, as the embryo develops, it receives nourishment and eliminates wastes by transferring substances from its blood to its mother's blood. a. becomes a fetus immediately and exits the womb b. begins to divide and implants itself in the wall of the uterus c. remains in the uterus without dividing for several months d. travels back to the ovaries until the fetus is developed