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A drawing of the plasma membrane. The top of the diagram is labeled outside of cell, the bottom is labeled cytoplasm. Separating these two regions is the membrane which is made of mostly a phospholipid bilayer. Each phospholipid is drawn as a sphere with 2 tails. There are two layers of phospholipids making up the bilayer; each phospholipid layer has the sphere towards the outside of the bilayer and the two tails towards the inside of the bilayer. Embedded within the phospholipid bilayer are a variety of large proteins. Glycolipids have long carbohydrate chains (shown as a chain of hexagons) attached to a single phospholipid; the carbohydrates are always on the outside of the membrane. Glycoproteins have a long carbohydrate chain attached to a protein; the carbohydrates are on the outside of the membrane. The cytoskeleton is shown as a thin layer of line just under the inside of the phospholipid bilayer.
The eukaryotic plasma membrane is composed of a lipid bilayer with many embedded or associated proteins. It contains cholesterol for the maintenance of membrane, as well as glycoproteins and glycolipids that are important in the recognition other cells or pathogens.

Membrane transport mechanisms

The processes of simple diffusion , facilitated diffusion , and active transport are used in both eukaryotic and prokaryotic cells. However, eukaryotic cells also have the unique ability to perform various types of endocytosis , the uptake of matter through plasma membrane invagination and vacuole/vesicle formation ( [link] ). A type of endocytosis involving the engulfment of large particles through membrane invagination is called phagocytosis , which means “cell eating.” In phagocytosis, particles (or other cells) are enclosed in a pocket within the membrane, which then pinches off from the membrane to form a vacuole that completely surrounds the particle. Another type of endocytosis is called pinocytosis , which means “cell drinking.” In pinocytosis, small, dissolved materials and liquids are taken into the cell through small vesicles. Saprophytic fungi, for example, obtain their nutrients from dead and decaying matter largely through pinocytosis.

Receptor-mediated endocytosis is a type of endocytosis that is initiated by specific molecules called ligands when they bind to cell surface receptors on the membrane. Receptor-mediated endocytosis is the mechanism that peptide and amine-derived hormones use to enter cells and is also used by various viruses and bacteria for entry into host cells.

a) Phagocytosis. A large particle outside of the cell is engulfed by a folding of the plasma membrane. This folding continues until the large particle is fully wrapped in a vacuole and is taken into the cell. b) Pinocytosis. Small particles are taken in through infoldings of the membrane. The membrane folds to form a vesicle that brings the small particles into the cell. Receptor-mediated endocytosis. Particles such as sugars bind to receptors on the membrane. The membrane then folds inward to form a coated vesicle. Inside this vesicle are the receptors still bound to the sugar.
Three variations of endocytosis are shown. (a) In phagocytosis, the cell membrane surrounds the particle and pinches off to form an intracellular vacuole. (b) In pinocytosis, the cell membrane surrounds a small volume of fluid and pinches off, forming a vesicle. (c) In receptor-mediated endocytosis, the uptake of substances is targeted to a specific substance (a ligand) that binds at the receptor on the external cell membrane. (credit: modification of work by Mariana Ruiz Villarreal)

The process by which secretory vesicles release their contents to the cell’s exterior is called exocytosis . Vesicles move toward the plasma membrane and then meld with the membrane, ejecting their contents out of the cell. Exocytosis is used by cells to remove waste products and may also be used to release chemical signals that can be taken up by other cells.

Cell wall

In addition to a plasma membrane, some eukaryotic cells have a cell wall . Cells of fungi, algae, plants, and even some protists have cell walls. Depending upon the type of eukaryotic cell, cell walls can be made of a wide range of materials, including cellulose (fungi and plants); biogenic silica, calcium carbonate, agar, and carrageenan (protists and algae); or chitin (fungi). In general, all cell walls provide structural stability for the cell and protection from environmental stresses such as desiccation, changes in osmotic pressure, and traumatic injury. M. Dudzick. “Protists.” OpenStax CNX. November 27, 2013. http://cnx.org/contents/f7048bb6-e462-459b-805c-ef291cf7049c@1

Questions & Answers

what is mutation
Janga Reply
what is a cell
Sifune Reply
how is urine form
Sifune
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mahase Reply
classification of plants, gymnosperm features.
Linsy Reply
what is the features of gymnosperm
Linsy
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Samuel Reply
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Samuel
What is Atoms
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Merolyn
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Merolyn
what's bulbourethral gland
Eduek Reply
urine is formed in the nephron of the renal medulla in the kidney. It starts from filtration, then selective reabsorption and finally secretion
onuoha Reply
State the evolution relation and relevance between endoplasmic reticulum and cytoskeleton as it relates to cell.
Jeremiah
what is heart
Konadu Reply
how is urine formed in human
Konadu
how is urine formed in human
Rahma
what is the diference between a cavity and a canal
Pelagie Reply
what is the causative agent of malaria
Diamond
malaria is caused by an insect called mosquito.
Naomi
Malaria is cause by female anopheles mosquito
Isaac
Malaria is caused by plasmodium Female anopheles mosquitoe is d carrier
Olalekan
a canal is more needed in a root but a cavity is a bad effect
Commander
what are pathogens
Don Reply
In biology, a pathogen (Greek: πάθος pathos "suffering", "passion" and -γενής -genēs "producer of") in the oldest and broadest sense, is anything that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ. The term pathogen came into use in the 1880s.[1][2
Zainab
A virus
Commander
Definition of respiration
Muhsin Reply
respiration is the process in which we breath in oxygen and breath out carbon dioxide
Achor
how are lungs work
Commander
where does digestion begins
Achiri Reply
in the mouth
EZEKIEL
what are the functions of follicle stimulating harmones?
Rashima Reply
stimulates the follicle to release the mature ovum into the oviduct
Davonte
what are the functions of Endocrine and pituitary gland
Chinaza
endocrine secrete hormone and regulate body process
Achor
while pituitary gland is an example of endocrine system and it's found in the Brain
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what's biology?
Egbodo Reply
Biology is the study of living organisms, divided into many specialized field that cover their morphology, physiology,anatomy, behaviour,origin and distribution.
Lisah
biology is the study of life.
Alfreda
Biology is the study of how living organisms live and survive in a specific environment
Sifune
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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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