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.
Organelles 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.
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