D) gravel on the bottom of the aquarium. "Abiotic" means "non-living," so you would essentially pick the answer that does not include any organisms (the organisms here are plants, fish, and algae).
        
                    
             
        
        
        
Answer: 
Living organisms that are made up of cells that have nucleus are called EUKARYOTES
Explanation:
Living organisms are grouped into two according to the composition of their cell components. These include:
--> The PROKARYOTES: these organisms possess a very simple cell structure with no definite nucleus. Example of such organisms include the eubacteria (that is, 'true' bacteria), archaebacteria ( which is also a type of bacteria) and blue green algae.
--> The EUKARYOTES: these organisms possess a complex cell structure with a well defined nucleus. The nucleus is found enclosed within a nuclear membrane. Hereditary materials are located within the nucleus and the cell has other components known as the cell organelles. These organelles include the mitochondria, Golgi apparatus, Endoplasmic reticulum, Ribosome, lysosomes. Example of eukaryotes are the animals, plants, fungi, and protists.
Therefore, Living organisms that are made up of cells that have nucleus are called EUKARYOTES 
 
        
             
        
        
        
Answer:
Primary succession occurs following an opening of a pristine habitat, for example, a lava flow, an area left from retreated glacier, or abandoned strip mine. In contrast, secondary succession is a response to a disturbance, for example, forest fire, tsunami, flood, or an abandoned field.
 
        
                    
             
        
        
        
Answer:
Benthos are organisms that live 
Examples:
Amphora
Cylindrotheca
Diploneis
Euglena
Fallacia
Gyrosigma
Navicula
Nitzschia
Plagiotropis
Staurophora
Please mark as brainliest please please
 
        
             
        
        
        
B. New substances are formed. In a chemical reaction, the starting molecule must be changed or turn into another. For example: rusts that form in a tin can is a chemical reaction. The iron in the can combines with the oxygen in the atmosphere, creating rust (iron oxide), which is a different substance.