Gametes are
reproductive organs
reproductive cells
reproductive tissues

Answer : The correct answer for the blank is-

reproductive cells.

Gametes are the haploid, sex cell (also called reproductive cells) that are produced in sexually reproducing organisms through the process of cell division, called meiosis.

During this process, a diploid mother cell produces four haploid gametes (such as egg and sperm) through two rounds of cell division (meiosis I and meiosis II).

The gametes produced by each parent fuse together to form diploid zygote (fertilization), which develops into fetus (through proliferation and differentiation).

Thus, reproductive cell is the right answer for the blank.

4.) metal

"-the movement of carbon from the nonliving environment into living things and back to the environment

-carbon is the essential component of proteins, fats, and carbohydrates (which make up all organisms)

-carbon exists in air, water, and living organisms

-producers convert carbon dioxide in the atmosphere into carbohydrates during photosynthesis

-bacteria in the atmosphere cycles through the system in filtration units

-in cellular respiration, carbon is released back into the atmosphere as carbon dioxide

-some carbon is stored in limestone (forming one of the largest "carbon sinks" on earth)

-largest carbon reservoir on earth= limestone

-carbon stored in the bodies of organisms as fat, oils, or other molecules may be released into the soil or air when the organism dies

-this may form deposits of coal, oil, or natural gas (fossil fuels, which increased the atmospheric carbon dioxide)

-fossil fuels store carbon left over from bodies of organisms that died millions of years ago

-they are located in the surface of earth, deep within the earth and beneath the ocean floor."