How can substances be transported across a membrane against their concentration gradient?

To move substances against a concentration or electrochemical gradient, a cell must use energy.

Explanation:

This occurs because During active transport, substances move against the concentration gradient from an area of low concentration to an area of high concentration which is a  “active” progress which requires the use of energy (usually in the form of ATP). It is the opposite of passive transport.

c

explanation:

water is a polar molecule. a chemical bond is a force of attraction between atoms or ions. bonds form when atoms share or transfer valence electrons. atoms form chemical bonds to achieve a full outer energy level, which is the most stable arrangement of electrons. so, false

explanation:

in h2o molecule, two water molecules are bonded by a hydrogen bond but the bond between two h - o bonds within a water molecule are covalent. the greater the electronegativity difference, the more ionic the bond is. bonds that are partly ionic are called polar covalent bonds. nonpolar covalent bonds, with equal sharing of the bond electrons, arise when the electronegativities of the two atoms are equal.