How are casts formed by decaying organisms? Organisms turn into rock over time.
Organisms leave carbon residue on a rock.
Organisms leave impressions in sediment that hardens into rock.
Impressions left by organisms are filled in with sediment that hardens into rock.

D.Impressions left by organisms are filled in with sediment that hardens into rock.

an active site is a region that is present on an enzyme where the reactants or the substrate molecules we can say bind and experience a chemical reaction. the substrate is basically a reactant whose concentration is changing and that is converting into a product after binding at the active site of an enzyme

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.