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Cells
Composite Cells
Movements Through Membranes
Cell Cycle
Composite Cell
• Describing a “typical” cell is difficult due to
the variation in cells.
• A composite cell shows many of the typical
structures of a cell. Cells have most, but not
all of these structures.
• Nucleus, cytoplasm, and cell membrane are
easily seen under a microscope.
Organelles
• Specialized structures within the cytoplasm.
• Suspended in cytosol
• Perform specific functions, divide the
“work” of the cell.
• Nucleus – directs all of the cells activities
and houses the genetic material.
Cell Membrane
• Regulates movement of substances and is
the site of much biological activity.
• Extremely thin, but flexible and elastic
• Folded for increased surface area
• Selectively permeable – controls what
comes in and out of the cell.
Cytoplasm
• Contains networks of membranes and
organelles suspended in a clear liquid called
cytosol.
• Cell activities occur here: nutrients are
received, processed and used.
• The following slides deal with organelles
contained in the cytoplasm.
Endoplasmic Reticulum
• Called “ER” for short
• Flattened, elongated canals and bubbles
called vesicles.
• Interconnected and communicate with the
cell membrane, nuclear envelope, and other
organelles
• Tubular network that transports molecules
to other organelles.
Smooth and Rough
• ER that contains ribosomes is called
“rough” ER
• ER that doesn’t contain ribosomes is called
“smooth” ER
• Ribosomes – site of protein synthesis in the
cell. Composed of protein and RNA
molecules
Golgi Apparatus
• Composed of a stack of about 6 flattened,
membranous sacs
• Refines, packages, and delivers proteins
synthesized on ribosomes.
Mitochondria
• Can move slowly through cytoplasm and
reproduce by dividing.
• Inner layer contains folds called “cristae”
• Major site of chemical reactions that
transform energy into ATP = gives the
cell energy.
Lysosomes
• “garbage” disposals of the cell
• Contain powerful enzymes that break down
nutrient molecules or foreign particles
• Help body fight disease w/white blood cells
• Also destroy worn cellular parts
Homeostasis
And
Transport
Passive Transport
• Substances can cross through the plasma
membrane without using energy from the
cell.
Types of Passive Transport
• Diffusion- movement of molecules from an
area of higher concentration to an area of
lower concentration.
– Difference in concentrations of molecules
across a space is called a concentration
gradient.
Osmosis
• The process by which water molecules
diffuse across the plasma membrane from
an area of higher concentration to an area of
lower concentration.
Facilitated Diffusion
Homeostasis
• Maintaining stable internal conditions in a
changing environment.
– Example:
• The cell membrane allows some substances in while
keeping other substances out.