The Cellular Level of Organization

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The Cellular Level of Organization
Living things are constructed of cells. Living
things may be unicellular or multicellular. Cell
structure is diverse but all cells share common
characteristics.
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The cell theory states All organisms are
composed of one or more cells. Cells are the
basic unit of structure and function in
organisms. All cells come only from other cells.
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Eukaryotic Cells
All cells are surrounded by a plasma membrane
made of phospholipids and proteins. Eukaryotic
cells have membrane bound intracellular
organelles. The most prominent is the nucleus
that controls the workings of the cell.
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The plasma membrane regulates what enters and
exits the cell. Inside the plasma membrane, the
nucleus is surrounded by cytoplasm. Plant cells
have a cell wall in addition to the plasma
membrane.
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Animal and plant cells have organelles. Organelle
s compartmentalize functions within the
cell. The organelles of animal and plant cells
are similar to each other except that centrioles
are present only in animal cells, and
chloroplasts are present only in plant cells.
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Animal cell anatomy
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Plant cell anatomy
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Ribosomes
Protein synthesis occurs at tiny organelles
called ribosomes. Ribosomes are composed of a
large subunit and a small subunit. Ribosomes can
be found alone in the cytoplasm, in groups called
polyribosomes, or attached to the endoplasmic
reticulum.
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The endoplasmic reticulum
The endoplasmic reticulum (ER) is a system of
membranous channels and saccules. Rough ER is
studded with ribosomes and is the site of protein
synthesis and processing. Smooth ER lacks
ribosomes and is the site of synthesis of
phospholipids and the packaging of proteins into
vesicles, among other functions.
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The Golgi apparatus
The Golgi apparatus consists of a stack of curved
saccules. The Golgi apparatus receives protein
and also lipid-filled vesicles from the ER,
packages, processes, and distributes them within
the cell. This organelle may also be involved in
secretion.
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Lysosomes and vacuoles
Lysosomes are vesicles produced by the Golgi
apparatus. Lysosomes contain hydrolytic enzymes
and are involved in intracellular
digestion. Vacuoles (large) and vesicles (small)
are membranous sacs in the cell that store
substances.
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Energy-Related Organelles
The two energy-related organelles of eukaryotes
are chloroplasts and mitochondria. Both
organelles house energy in the form of ATP.
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Centrioles
Centrioles are short cylinders with a 9 0
pattern of microtubule triplets. Centrioles may
be involved in microtubule formation and
disassembly during cell division and in the
organization of cilia and flagella.