Materials move down a concentration gradient . Passive or active ?

the electromagnetic energy from the sun arrives in the form of visible and invisible light.

both male and female gametes are produced by meiosis of the germ cells. therefore, both male and female gametes are haploid. one male and one female gamete unite during the fertilization to form the diploid zygote. in seed bearing plants, pollen grain is the male gametophyte, which produces sperm cells.

the solute can move "downhill," from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. this process is called passive transport or facilitated diffusion, and does not require energy.

d. planting trees

the trees take in carbon to make oxygen.