As the basic units of life, cells carry out important functions in prokaryotes and eukaryotes. Cell physiology focuses on the internal structures and processes inside living organisms.

From division to communication, this field studies how cells live, work and die.

One part of cell physiology is the study of how cells behave. There is an important link between cell structure, function and behavior. For instance, organelles in eukaryotes have specific roles that help the cell function and behave properly.

When you understand physiology and cell biology, the way a cell behaves makes sense. Coordinated behavior is important for multicellular organisms because there are many cells that have to work together. Proper cell behavior creates functional tissues and a healthy organism.

However, when cell behavior goes wrong, it can lead to diseases, such as cancer. For example, if cell division is out of control, cells can multiply and form tumors.

Although cells can differ, there are basic behaviors that many of them share. They include:

• Cell division and growth. Cells need to grow and divide over time. Mitosis and meiosis are the two most common types of cell division. Mitosis produces two identical daughter cells, while meiosis makes four different daughter cells with half the DNA.
• Cellular metabolism. All living things need energy or fuel to live, and metabolism helps them accomplish this. Most cells use either cellular respiration or photosynthesis, which are a series of chemical processes.  
• Cellular communication. Living cells often need to communicate and spread information throughout an organism. They can use receptors or ligands, gap junctions or plasmodesmata to communicate.
• Cellular transport. Cell transport moves materials across a cell membrane. This can be active or passive transport.
• Cellular motility. Motility allows cells to move from one location to another. They may swim, crawl, glide or use other methods.
  

It is important to understand cell physiology and membrane transport. Organisms need to carry substances in and out of their cells and across the lipid bilayer of the plasma membrane.

Passive and active transport are two common types of cellular transport. There are some essential differences between active and passive transport.

Passive transport does not use energy to move substances. One method that cells use is diffusion, and you can divide it into simple or facilitated diffusion. Substances can move from areas of high concentration to areas of low concentration. Osmosis is an example of simple diffusion that involves water.

Simple diffusion involves molecules moving down the concentration gradient through the plasma membrane. These molecules are small and nonpolar. Facilitated diffusion is similar but involves membrane transport channels. Large and polar molecules depend on facilitated diffusion.

Active transport needs energy to move substances. Molecules can move against the concentration gradient from areas of low concentration to areas of high concentration thanks to energy sources like ATP. Carrier proteins help the cells during this process, and the cells can use a proton pump or ion channel.

Endocytosis and exocytosis are examples of active transport in cells. They help move large molecules inside vesicles. During endocytosis, the cell captures a molecule and moves it inside. During exocytosis, the cell moves a molecule to the outside of its membrane.

Cells can receive, interpret and respond to signals. This type of communication helps them respond to their environment and spread information within a multicellular organism. Signaling guides cell behavior by allowing cells to respond to specific signals from their environment or other cells.

Signal transduction is another term for cell signaling and refers to the transmission of information. A signal transduction cascade is a pathway or series of chemical reactions that happens inside the cell after a stimulus starts it. Signaling can control cell growth, movement, metabolism and more. However, when cell communication goes wrong, it can cause disease like cancer.

It is important to understand the basics of cell communication. The general process starts when the cell detects a chemical signal. This sets off a chemical reaction that ultimately helps the cell respond to it. There is an end response that leads to the desired outcome.

For example, a cell receives a signal from the body saying that it needs more cell division. It goes through a signaling cascade that ends with the expression of genes that will drive cell division, and the cell starts to divide.

Most of the signals in a cell are chemical. Cells have proteins called receptors and molecules called ligands that help them during signaling.

For example, a cell can release a protein into the extracellular space to alert other cells. The protein can float to a second cell, which picks it up because the cell has the right receptor for it. Then, the second cell receives the signal and can respond to it.

You can find gap junctions in animal cells and plasmodesmata in plant cells, which are channels that help cells communicate. These channels connect nearby cells. They allow small molecules to pass through them, so signals can travel.

After cells receive signals, they can interpret them. This happens through a conformational change or biochemical reactions. Signal transduction cascades can move the information through the cell. Phosphorylation can activate or deactivate proteins by adding a phosphate group.

Some signal transduction cascades include intracellular messengers or second messengers, such as Ca²⁺, cAMP, NO and cGMP. These tend to be non-protein molecules, like calcium ions, that may be abundant in the cell.

For example, some cells have proteins that can bind calcium ions, which can change the shape and activity of the proteins.

Cells can respond to signals in a variety of ways. For example, they may make changes in gene expression that can change how the cell behaves.

They may also send feedback signals to confirm that they received the original signal and responded. Ultimately, signaling can affect cell function.

Cell motility is important because it helps organisms move from one location to another. This may be necessary to acquire food or escape danger. Often, the cell needs to move as a response to environmental changes. Cells may crawl, swim, glide or use other methods.

The flagella and cilia can help a cell move. The role of the flagella or whiplike structures is to propel a cell. The role of the cilia or hairlike structures is to move back and forth in a rhythmic pattern. Sperm cells have flagella, while the cells that line the respiratory tract have cilia.

Cell signaling can lead to cell movement in organisms. This movement may be toward or away from signals, and it can play a role in disease. Chemotaxis is cell movement toward or away from a higher chemical concentration, and it is an important part of the cellular response.

For instance, chemotaxis allows cancer cells to move toward an area of the body that promotes more growth.

Cells can contract, and this type of movement happens in muscle cells. The process starts with a signal from the nervous system.

Then, the cells respond by starting chemical reactions. The reactions affect the muscle fibers and cause contractions.