What is the structure within cells? What do clusters of cells create? How does cell nutrition work and what is the role of specialized cells?

Cells contain organelles inside of them. Each organelle has a job for the cell to function. All of the organelles work together for the cell to function as a whole. For example: the mitochondria provide energy for cells by producing ATP. Clusters or groups of cells make tissues. This is part of the levels of organization. Cell ­­-->Tissue --> Organs --> Organ System --> Organism. Cells need nutrients to survive and then to make more cells. They get their nutrients from the body and those nutrients can enter the cell through the cell membrane. The membrane is composed of a phospholipid bilayer. Some materials can pass through the membrane through simple diffusion, meaning they just slip through. Some materials enter through facilitated diffusion, meaning they need a protein to get through. An example of this is glucose entering a red blood cell. Others that are large may need to get into the cell through active transport. An example is a Sodium/Potassium pump. Our bodies are made of lots of different specialized cells. Neurons are a specialized cell to transport electrical signals. Muscle cells are specialized for contraction to help our bodies move (skeletal muscle), help food get through our digestive system (smooth muscle), or make our heart pump (cardiac muscle). Muscle cells tend to have more mitochondria than a skin cell because they need more energy (mitochondria produce energy). Our bodies need to have specialized cells to be able to perform the variety of functions we have.