The heart is the structure that pumps blood to the rest of the body. it’s composed of and surrounded by four kinds of tissues—connective, muscle, epithelial and nervous tissues. how do you think the four tissue types support the function of the heart? how do the different tissue types support the idea that systems of specialized cells are critical for body functions?

Humans—and other large multicellular animals—are made up of four basic tissue types: epithelial tissue, connective tissue, muscle tissue, and nervous tissue. 
Epithelial tissue consists of tightly packed sheets of cells that cover surfaces—including the outside of the body—and line body cavities. For instance, the outer layer of your skin is an epithelial tissue, and so is the lining of your small intestine.
Epithelial cells are polarized, meaning that they have a top and a bottom side. The apical, top, side of an epithelial cell faces the inside of a cavity or the outside of a structure and is usually exposed to fluid or air. The basal, bottom, side faces the underlying cells. For instance, the apical sides of intestinal cells have finger-like structures that increase surface area for absorbing nutrients.

Connective tissue consists of cells suspended in an extracellular matrix. In most cases, the matrix is made up of protein fibers like collagen and fibrin in a solid, liquid, or jellylike ground substance. Connective tissue supports and, as the name suggests, connects other tissues.

Muscle tissue is essential for keeping the body upright, allowing it to move, and even pumping blood and pushing food through the digestive tract.

Nervous tissue is involved in sensing stimuli—external or internal cues—and processing and transmitting information. It consists of two main types of cells: neurons, or nerve cells, and glia.

All of these tissues are essential in keeping the body running, including the cardiovascular system in which the heart is involved. All of these tissues play a key role in maintaining the function of the heart, whether it be indirectly, or directly, each of these will keep your heart sustained, but without them you wont live long lol. 
Hope this helped. 

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Cell division is important to single celled organisms because it allows the cells to reproduce. through cell division, cells make exact copies of themselves. when single celled organisms go through cell division, they make exact copies of themselves which is how they reproduce.