What contains instructions to cells about how to form a heart ?

DNA

Explanation: The Deoxyribonucleic acid contains information that instructs the cells to combine together to form a heart.

The basic structural and functional unit of life is cell. The cell division allows the cell to divide and form tissue and then from tissues to organ.

The instruction for cell division is generated by DNA. So, the instruction for cells to form heart will be given by DNA.

hormones in blood stream

image: dtc.ucsf.edu

endocrine glands secrete hormones into the blood stream near them; the hormones then travel in our bloodstream until it reaches its destination, called a target cell, in distance parts of the body. in the target tissue, hormones lock onto the target’s plasma membrane, called the receptor site.

the dark variety, as they are not visible on the dark tree barks

explanation: