Answer:
D. There is no enough oxygen in the culture fluid
Explanation:
The cells in the test tube need to carryout one of the important metabolic processes of living organisms - respiration. The process involves the breakdown of glucose to generate energy for other metabolic processes in the cell.
Respiration can be carried out in the presence of oxygen (aerobic) or in the absence of oxygen (anaerobic). Human cells are primarily aerobic but can carryout respiration anaerobically in the presence of inadequate oxygen.
For aerobic respiration, glucose is broken down in the presence of oxygen to produce carbon-dioxide, water and energy in the form of ATP:

<em>In the absence of oxygen, the glucose becomes converted to lactic acid and a smaller amount of ATP is produced as compared to aerobic respiration.</em>
<em>Hence, lactic acid gradually builds up in the absence of oxygen due to anaerobic respiration.</em>
The correct option is D.
 
        
                    
             
        
        
        
Passive diffusion is a form of passive transport and a type of diffusion by which particles from a high concentration gradient passes through a biological membrane to a low concentration gradient. Diffusion, or simple diffusion on the other hand, is the passage of molecules without the need of a membrane. 
        
             
        
        
        
Explanation:
Whereas primary tissues allow for vertical growth, secondary tissues allow for lateral growth: they allow stems and roots to become wider. In roots, the formation of both secondary meristems involves the pericycle.
 
        
             
        
        
        
Answer: d. mothering style affecting the developing brain
Explanation:
Epigenetics is the study of features or "phenotypes" which do not involve changes in the DNA sequence. Epigenetics is about how genes are expressed and used instead of the DNA sequence of the genes themselves. 
The behaviour of a person's genes depends not only on the DNA sequence of the genes, but also on so-called epigenetic factors. Effects on genes from the external environment can affect disease, and some of these effects can be inherited in humans. 
So, Mothering style which affects the brain development is an exampe of epigenetics which do not show any genetic feature.
Hence, the correct option is d.
 
        
             
        
        
        
A change in the substance by temp, color,