Answer: a. the amount of water 
Independent variable can be defined as a variable which can be changed or manipulated in an experimental set up to record and observe it's effect on the dependent variable. A dependent variable is a variable which is dependent on the independent variable. The outcome of the dependent variable is the result of the experiment. A controlled variable is a variable which does not change in a reaction, and kept as a constant. 
1. Here, in the given situation, the amount of water is an independent variable, as it can be manipulated or change in an experiment and it's impact on the growth of plant, which is a dependent variable needs to be observed. 
2.Here, in the given, situation, the type of plant is a constant or control variable, as it is irrespective of the changes that occur in the dependent variable with respect to the independent variable. 
 
        
                    
             
        
        
        
Without staining them you wouldn't be able to see them
        
             
        
        
        
Answer:
Bacteria and protozoa are the examples of unicellular organisms.
Explanation: 
Unicellular are the organisms which madeup of single cell such as bacteria and protozoa. Bacteria are prokaryotic organisms i. e. no true nucleus. Some bacteria make their own food from photosynthesis and some bacteria are parasites and other are decomposers. 
Protozoa are eukaryotic organisms which are heterotrophic in nature i. e. feed on other organisms. Amoeba and paramecium are the examples of protozoa. 
 
        
             
        
        
        
Selective breeding
In selective breeding, the
desired genes from one organism are combined with genes of another
organism, resulting in a new combination of genes.
The selective breeding is quite voluntary and is not necessarily natural or congenital. It is the act of how people or individuals can choose traits in the gene pool of their choice  to produce their desired or goal organism in the process. This trait is influenced in the host of the specific sperm and egg cell which makes up the chromosomes.