<span>Answer
1. electrical signal travels toward the heart
2. signal by the nodes in the atrium</span>
3. the atria contract<span>
</span>4. signal received by the atrioventricular node
5. signal transferred to the ventricles
6. the ventricles contract
Heart has a pacemaker that will continually send a signal. The primary site of the pacemaker is at the sinoatrial node, on the top right atrium. This node will send a signal to atria (which will cause it to contract) and to the atrioventricular node. 
Atrioventricular node located between atrium and ventricle. It will send the signal to the ventricle(by the bundle of his) and cause it to contract.
        
                    
             
        
        
        
I would say carbon dioxide 
        
             
        
        
        
Answer: 50% ErWw (wild-type traits)  and 50% rrww (red eyes, white-banded wings)
To solve this, we need to analyze step by step all the data they give us.
First, they told you about two homozygous traits that are recessive in this kind of animal, Red eyes and withe-banded wings.
We'll assign the names rr and ww (lower because they are recessive)
You know the dominant traits are wild type and all are in the same chromosome. 
EE will be normal eyes, and WW  will be normal wings.
If you cross this F0, rrww x EERR  all the offspring are ErWw.
Crossing F1 with red eyes, with-banded wing you have to draw a Punnte square with ErWw x rrww and the ofsspring posibilities you'll find are 50% ErWw (wild-type traits)  and 50% rrww (red eyes, white-banded wings)
 
        
             
        
        
        
Answer:
A. keeping the strands separated during replication
Explanation:
Prior to the process of DNA replication, the double-stranded DNA must first be separated into single strands by an enzyme called DNA helicase. This is done so that each DNA strand can serve as template for the synthesis of another. 
After the unwinding and separation, the single strands still need to be kept apart during the synthesis of new nucleotides by DNA polymerase. This role of keeping the strands separated during replication is carried out by SINGLE STRAND BINDING PROTEINS.