I believe it is the nucleus.
        
             
        
        
        
Explanation:
<h2>Yeast is used for the leavening of bread. Yeast uses the sugars and oxygen in dough to produce more yeast cells and carbon dioxide gas. This is called multiplication. The carbon dioxide makes the dough rise which gives the bread a light and spongy texture.</h2>
 
        
             
        
        
        
I had to look for the options and here is my answer.
The GINGKOS, GNETOPHYTES and CYCADS are the closest relatives of the familiar pine and spruce trees. These plants are coniferous and belong to the plant <span>family Pinaceae. They are coniferous in a way that they produce hanging cones and have needle shaped leaves.</span>
        
             
        
        
        
I’m sorry, I’m not sure what you’re asking, if I can be of assistance let me know.
        
             
        
        
        
Answer: Shale changes into Slate. 
Explanation:
Shale is a sedimentary rock, formed by the deposition and compression of clay and silt. 
Shale layers is buried deep into the earth through the process of deposition (i.e the laying down of rock forming material by natural entities like glaciers, wind, and water).
Temperatures and pressures rise greatly because the shale’s layers are buried. When the temperatures and pressures become higher. The shale is changed into a metamorphic rock (with dark brown streak), called Slate.