Since the other answer got deleted, i'll just answer it for you.
a sinoatrial node is the main pacemaker that begins each heartbeat located in the junctions of superior vena cava and the right atrium. It signals from the node that spread through the atria and determines the heart rates.
        
             
        
        
        
Answer:
The correct answer is - to make food for the seedling’s continued growth.
Explanation:
The true leaves that emerge from the seedlings are the leaves that are capable of performing photosynthesis and start generating food and energy. These support the plant for the rest of its life in terms of food and energy.
Seedlings grow from the soil, two leaves in beginning called cotyledons that are not the true leaves and not able to perform photosynthesis and generate their food for the seedling’s continued growth.
 
        
             
        
        
        
Answer:
<em>Hey there!</em>
3) Well injection is usually done through the vein because they need the substance to go into the blood. 
4) Some people believe that the heart is on the left side because its the left ventricle and atrium responsible and when people hear left they think the heart is on the left.
5) People living in high altitudes don't get as much oxygen so their bodies evolved into carrying ,more RBC so more oxygen is carried into their bodies.
<em>Hope this helps :)</em>
 
        
             
        
        
        
They classify on how they reproduce.
        
             
        
        
        
All chemical reactions involved in maintaining the living state of the cells and the organism. Metabolism<span> can be conveniently divided into two categories.</span>