The Cell

A cell is a primary structural and functional unit of an organism. It is the smallest living unit in the human body. It can perform 6 important life processes distinguishing living things from non-living things.

  1. Metabolism 
  2. Responsiveness
  3. Movement
  4. Growth
  5. Differentiation
  6. Reproduction

Metabolism includes catabolism i.e. the breakdown of complex chemical substances into simple components and anabolism i.e., the formation of complex substances from smaller and simple components. For example, digestion catabolizes the proteinous food into amino acids. These amino acids are used by the body to make new proteins that are needed by the body.

Responsiveness is the ability of the body to recognize and respond to changes. For example, Nerve cells respond by producing electrical signals called nerve impulses (action potentials). Muscle cells contract in response, generating force for the movement.

Movement includes the motion of the body, organ, cell, or organelle inside the cell. In case of infection, macrophages reach the site of infection to kill the micro-organism responsible for the infection. 

Growth is an increase in size (hypertrophy), an increase in number (Hyperplasia), or both. For example, exercise helps in increasing the size of the muscles.

Differentiation is the transformation of an unspecialized cell into a specialized cell. For example, Red blood cells and several types of white blood cells develop from the same unspecialized precursor cells (stem cells) in the red bone marrow.

Reproduction is the generation of new cells for tissue development, repair, or replacement.

Parts of a Cell

The cell is divided into three main parts: 

  1. Plasma Membrane
  2. Cytoplasm
  3. Nucleus
    Fig. 1: The Cell

Plasma Membrane

The plasma membrane is the cell's flexible outer surface. 

It separates the internal (inside the cell) environment from the external environment (outside the cell).

It is a selective barrier that controls how materials enter and leave cells. 

Additionally, the plasma membrane is essential for communication within cells as well as between cells and their surrounding environment.

Cytoplasm

The cytoplasm contains all of the cellular contents between the plasma membrane and the nucleus.

This compartment is made up of two parts: 

  • Cytosol
  • Organelles

Cytosol (the fluid portion of cytoplasm) contains water, dissolved solutes, and suspended particles.

Several types of organelles (little organs) are suspended in cytosol . Each type of organelle has its own distinct shape and function. The cytoskeleton, ribosomes, endoplasmic reticulum, Golgi complex, lysosomes, peroxisomes, and mitochondria are some examples.

Nucleus

The nucleus is a large organelle that contains the majority of the DNA in a cell. 

A single molecule of DNA (chromosome) contains thousands of hereditary units known as genes. DNA controls the majority of cellular structure and function through expressed proteins.

Watch the video for more information

 

 

 

Acknowledgment

The images were created on biorender.com

References

Tortora, Gerard J., and Bryan H. Derrickson. Principles of anatomy and physiology. John Wiley & Sons, 2018.

 

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