Answer: It is approximately the membrane potential at which the electrochemical gradient for Na+ is zero. 
Explanation:
The charge in plasma membrane occurs with diffusion and electric fields. 
For example, if there are two solutions, let's assume solution X and Solution Y are separated by a porous barrier (to diffuse in equal proportions).
The fundamental principle of diffusion states that solution from a high concentration diffuses to a lower concentration.
For instance, if the X solution contains 40 sodium ions and 40 chloride ions, the Y solution only has 30 sodium and 30 chloride ions. Due to the diffusion, these two solutions will mix and reach a steady-state.
The like charges repel, and opposite charges attract. 
 
        
             
        
        
        
Out of the following given choices;
a)	The amount of oxygen produced
b)	The rate of ATP synthesis by ATP synthase in the chloroplast
c)	The rate at which NADPH is produced
d)	The rate at which the protons are transported into the thylakoid
The answer is; A
The photosystem captures energy from sunlight and uses it to split a water molecule.   After splitting the water molecule (by taking an electron), the protein complex transports the electron to plastoquinone. The splitting of water molecules results in evolving of oxygen molecules. The hydrogen is what is used to reduce carbon dioxide to glucose. 
 
        
                    
             
        
        
        
Androgen hormone is the primary determinant of whether a baby will develop male or female external genitalia.
Androgen is usually a steroid hormone. The predominant and most active androgen in testosterone, which is produced by the male testes. Some androgens are naturally produced in the body and if the body doesn't make them properly they can be obtained through prescription medication.
        
             
        
        
        
It is not it something like sand because it would keep the fossil preserved.