All multicellular organisms arise from totipotent cells. These cells undergo specialization in order to perform all functions that are necessary to support life. This BiologyWise post explains what exactly specialization is, along with some examples for your better understanding.
You were once a female!
Gender differentiation arises due to the activation of the SRY gene present on the Y chromosome at around five weeks. This gene is responsible for the production of Testis Determining Factor (TDF), which later influences the formation of the male sex organ.
All living organisms may either be unicellular or multicellular. In unicellular organisms, a single cell is capable of performing all life functions on its own, for its survival. In multicellular organisms, this gets more complex. There is a division of labor in higher multicellular organisms.
Every organism is made of organ systems, every organ system has a few organs comprising it, every organ is made of tissues performing a particular function, and every tissue is made of a group of specialized cells. So, it is safe to say that a specialized cell is the basic functional unit of all living systems.
What are Specialized Cells?
A group of cells that are assigned one particular function are said to be specialized cells. Pluripotent cells (cells that are capable of differentiating into other cells) undergo a process of differentiation to form specialized cells that are said to be uni potent. These cells have different shapes, sizes, and cellular makeup depending on the type of function they perform. However, the genetic makeup of every cell in an organism’s body is the same. These structural and functional variations arise due to the expression of different genes in different specialized cells. Now, certain genes are constitutively expressed in all cells and are responsible for the maintenance of normal cellular functions. Some genes are only expressed in certain specialized cells, and it is these genes that are responsible cell specialization.
In plants, the undifferentiated meristematic tissues are found in the apical tips and allow the plant to grow throughout its lifetime. In animals, these undifferentiated tissues can only be found in early embryos or found only at particular sites.
Examples of Cell Specialization in Animals
The central nervous system consists of glial cells and neurons. Neurons specialize in the function of transmission of signals from different parts of the body to the brain, and transmit an appropriate response from the brain to different parts of the body.
Neurons can be up to one meter in length depending on where they are present. The neurons consist of the soma, dendrites, and axons. Soma is the cellular part of neurons containing all the major cell organelles. Dendrites are the cellular extensions that receive impulses, and axons are long cable-like projections that transmit the impulse to the next neurons. The axon terminates into a synaptic junction that transmits impulses from one neuron to the next with the help of chemicals called neurotransmitters.
Smooth Muscle Cells
All involuntary functions of our body are carried out by smooth muscle cells. They form the walls of blood vessels, gastrointestinal tract, urinary tract, respiratory tract, etc. These can be classified into single-unit smooth muscle cells and multi-unit smooth muscle cells.
Single-unit muscle fibers are compactly packed together, while multi-unit muscle fibers are more loosely packed and usually intertwined with connective tissues. Single-unit smooth muscles are spindle-shaped with a prominent nucleus in the center. They contract and relax just like striated muscle fibers, but have greater elasticity. They possess proteins like myosin and actin that aid in the contraction of cells.
Red Blood Cells
Red blood cells perform the function of carrying oxygen from the lungs to different parts of the body; they also carry carbon dioxide from different parts of the body to the lungs. These are button-shaped, i.e., biconcave, and lack a nucleus as well as many other cell organelles. They possess a protein called hemoglobin that is responsible for their oxygen-carrying capacity.
These are the male reproductive cells. Mature sperm cells are haploid and motile, which fertilize the matured female reproductive cells, i.e., the ova, to produce a zygote. The sperm cells are made of the head, mid piece, and tail. The head consists of a nucleus (the haploid chromosome) and acrosome.
The nucleus fuses with the haploid female nucleus to bring about fertilization and gives rise to a diploid individual. The acrosome contains enzymes like hyaluronidase and acrosin that dissolve the outer cell membrane of the ovum and help in the release of the nucleic material. The mid piece consists of centrioles and mitochondria wrapped around the axial filament of the flagellum. The centrioles after fertilization form the centrioles of the zygote, whereas the mitochondria provides energy for the movement of the flagellum (responsible for cell motility). The flagellum moves in a whip-like manner and propels the cell forward.
Examples of Cell Specialization in Plants
These are specialized epithelial cells that are present on the leaves and stems. A pair of guard cells controls the stomatal pore. They determine the rate of transpiration, carbon dioxide uptake, and the amount of oxygen released. Turgor pressure in these cells is responsible for the opening and closing of stomata. When guard cells take up water, their Turgor pressure increases and the stomatal pores open. When guard cells give out water, their Turgor pressure decreases, they become flaccid, and the stomatal pores close.
Root Hair Cells
Again, these are specialized epithelial cells that are present on the root. They help in the uptake of minerals and water. These cells have a hair-like outgrowth on the cell surface. This increases their surface area for the uptake of nutrients and water. They have a large vacuole that extends itself in a hair-like outgrowth. This vacuole is so large that it displaces the cell organelles to the periphery, and the cell seems to have only a thin layer of cytoplasm surrounding it.
Cells undergo specialization in the inter phase or in the G0 phase of the cell cycle. An adult human has more than two hundred specialized cells.