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2-4 Looking
Inside Cells
Parts of the Cell
• Cells (which you remember are the
smallest unit of structure and
function in the body) contain smaller
structures called organelles.
• Organelles carry out specific
functions in the cell much as organs
like the heart and lungs carry out
functions in your body.
From Outside In
• Plant cells (unlike animal cells) have a
rigid layer of non-living material
surrounding the cell called a cell wall.
The cell wall acts like the plants
skeleton giving it support.
• Inside this plant cells have a cell
membrane. Animal cells outermost
layer is the cell membrane.
Cell Membrane
• All cells have cell membranes. It acts like the
skin of the cell.
• The main function of the cell membrane is to
control what substances come into and out of
a cell.
• Things cells need like oxygen, water, and
food enter through the cell membrane while
waste products like carbon dioxide leave
through it.
Nucleus
• In the center of the cell is a large oval
structure called a nucleus.
• The nucleus acts like the cells “brain”- it is the
control center of the cell directing all of its
activities like growth and reproduction.
• It is filled with a substance called chromatin.
Chromatin contains genetic material, the
instructions that direct the functions of the
cell. For example, it tells the cell how to grow.
Cytoplasm
• The region between the cell membrane and
the nucleus is filled with a jelly-like substance
called cytoplasm.
• Most cell organelles are found floating in the
cytoplasm.
• These organelles function to produce energy,
build and transport needed materials, and
store and recycle wastes.
Mitochondria
• Mitochondria are bean-shaped
organelles in the cell’s cytoplasm that
are called the “powerhouse” of the cell
because they produce most of the
energy the cell needs to carry out its
functions.
Endoplasmic Reticulum
• The E.R. is a maze-like collection of
passageways surrounding the nucleus.
• They carry proteins and other materials
from one part of the cell to another.
Ribosomes
• Ribosomes are small, round structures
found throughout the cytoplasm.
• They function as protein factories
• They pass these proteins on to the
endoplasmic reticulum. From inside the
e.r., they are transported to the golgi
bodies.
Golgi Bodies
• Golgi Bodies are a flattened bunch of
sacs and tubes.
• Act like a mailroom. They receive
proteins from the e.r. and distribute
them to other parts of the cell and even
outside the cell.
Chloroplasts
 Chloroplasts are found only in plant
cells (and some bacteria).
 Their function is to capture the sun’s
energy and use it to produce food as
energy.
 Their pigments make the plant green.
Vacuoles
• Vacuoles are large sacs filled with
water.
• They act as the cell’s water storage
tanks.
• Most plants have them, some animal
cells do, some don’t
Lysosomes
• Lysosomes are small round structures
containing chemicals that break down
food and old cell parts.
• They act like the cell’s cleanup crew.
The other Cell Type:
Bacteria
• Bacteria cells are much smaller than most
animal or plant cells.
• Bacteria like plants, do have cell walls and
cell membranes.
• But bacteria do not have a nucleus and
except for ribosomes, none of the other
organelles found in animal and plant cell.
Prokaryotes and Eukaryotes
• Cells (like bacteria) that have no nucleus are
called Prokaryotes (which means “before
the nucleus” because its thought they evolved
earlier in time before more advanced cells).
• Cells that do have a nucleus (like plant and
animal cells) are called Eukaryotes which
means “has a nucleus.”