The Cell

The simplest, most fundamental structure and functional unit of all life is the cell. In contrast to the billions of cells that make up the human body, a bacteria or ameba only has one cell. They are combined to form tissues, each of which has a specific purpose, such as that of muscle, bone, and blood. Systems are made up of various tissues that each execute a specific task to keep the body in a state of equilibrium. For instance, the urinary system is in charge of fluid and electrolyte absorption, waste removal, pH regulation, and fluid balance in the body.

cell

Three layers of cells in the embryo known as the primary germ layers, which form two weeks after conception, are the source of all mature tissue in the body. Ectoderm, mesoderm, and endoderm are the three. The epidermis and nervous system are derived from the ectoderm, an outer layer of germ cells. The respiratory tract's lining and the lining of the digestive tract are both produced by the endoderm, an inner layer. The middle laver cell that develops into muscle, bone, blood, and a variety of other tissues is known as the mesoderm. Tissue derived from two or more primary germ layers makes up the majority of organs.

Structure and Function 

The ovum (the female sex cell) and the spermatozoa fuse to form the "zygote," which is the single cell from which the human body is formed. (Sex cell for men) Since they are too small to be seen with the naked eye, individual cells. Phospholipids, cholesterol, glycolipids, and carbohydrates make up its composition (oligosaccharides). The cell is divided into three sections, which can be seen under a microscope:

• Plasma membrane or Cell membrane
• Cytoplasm
• Nucleus

Plasma Membrane

The plasma membrane or cell membrane is a semi-permiable membrane that surrounds cell, forms the outer boundary of the cell. It separates the cytoplasm from the external environment. It contains cytoplasm, and made up of lipids bilayer (phospholipids, cholesterol and other lipids), proteins (integral and peripheral proteins) and carbohydrates (proteoglycans). The phospholipids of lipid this bilayer are arranged in two layers: the outer part of each phospholipids is hydrophilic and inner part is low hydrophobic in nature. Semi-permeability of plasma membrane is provided by lipid bilayer whereas as a protein layer provides structural integrity of cell membrane. The thickness of cell membrane is 7.5 to 10 nano meters. The plasma membrane is of important for muscle cells and nerve cells because it carries electrical impulses.

plasma membrane

Functions of the plasma membrane

• It provides shape for the cell and separates the cell from one another.
•  It protects the cytoplasm and other cytoplasmic organelles.
• It regulates the movement of materials to and out of cells.
•  It provides immunological identity to and out of cells.
•  It provides an abundant surface on which chemical reaction can occur.

Movement across-Plasma Membrane

In order for the cell cytoplasm to communicate with the external environment, materials must be able to move through the plasma membrane. Transport of materials across the plasma membrane is essential to the life of a cell. Movement across plasma membrane takes place in two ways, depending on whether they require cellular energy.

•  Passive movement/mechanism
•  Active movement /mechanism

    Passive movement

This happens when chemicals can pass across the partially permeable organelle and plasma membranes as well as the concentration gradient without expending any energy. The word "concentration gradient" refers to the differential in concentration between two locations. Movement that is passive uses energy while movement that is active uses energy in the form of ATP. Passive motion consists of:

• Simple diffusion: Mostly occurring in gases, liquids, and solutions, it is the movement of particles from a high concentration to a low concentration.
• Facilitated diffusion: In essence, facilitated diffusion is the same as simple diffusion in that carrier proteins aid or facilitate the solute's descent of concentration gradients. A membrane protein helps a particular substance cross the membrane during this process. An amino acid, for instance, can pass through the plasma membrane.
• Osmosis: Osmosis is a particular kind of diffusion that describes the movement of water through a membrane with selective water permeation from a region of higher water concentration to a region of lower water concentration.
• Filtration: In filtration, small molecules pass through selectively permeable membrane by hydrSmall molecules are filtered through selectively permeable membranes by hydrostatic pressure, or the pressure that water puts on the membrane.ostatic pressure, the force exerted by water on a membrane.

Active movement

It is the flow of molecules from lower concentration areas on one side of a membrane to greater concentration areas on the opposite side of a selectively permeable membrane. Contrary to the concentration gradient, this movement happens. On it is active transportation.

•   Active transport: In a carrier-mediated process known as active transport, solutes are moved up or against concentration gradients. It involves the use of ATP, the highly energetic molecules found inside cells, as a source of energy. Until the equilibrium of the substances is maintained by passive movement, this is the transfer of substances up their concentration (uphill), or from a lower to a higher concentration. However, if equilibrium is attained and additional molecules are still required, they must be pushed through the membrane against a gradient of concentration. The sodium, potassium, and calcium pump is one example of such a process. These molecules interact with the carrier protein in this process, pass through the protein, change back to their original shapes, and then repeat the process.

• The Sodium-potassium pump: This active transport mechanism maintains the unequal concentration of sodium (Na+) and potassium (K) ions on either side of the plasma membrane It may use up to 30% of cellular ATP (energy) requirements. This pump indirectly support other transport mechanism such as glucose uptake, and is essential in maintaining the electrica gradient needed to generate action potentials in the nerve and muscle cells. All cells have thousands of sodium-potassium pumps in their plasma membranes. These sodium -potassium pumps maintain a low concentration of Nat in the cytosol by pumping them into the extracellular fluid against the Nat concentration gradient. At the same time, the pumps move into cells against the K+ concentration gradient. This pumps must work nonstop to maintain a low concentration of Na+ and a high concentration of K+ in the cytosol.

• Endocytosis: During endocytosis, various materials move in to a cell in a vesicle formed by plasma membrane.

• Pinocytosis: Cell drinking

• Phagocytosis: Cell eating

• Exocytosis: contrary to endocytosis. Exocytosis causes the release of hormones and mucus.