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CHAPTER 2
LESSON 2 – THE CELL
Pages 50 - 58
CELL SHAPE AND FUNCTION
• Different types of cells have different shapes, structures, and
functions.
• Example: Nerve cells (axons) are long so they can send impulses
through the nervous system.
THE EXTERIOR OF CELLS
• The cell membrane is a flexible covering that protects the inside of a
cell from the environment outside a cell.
• mostly made of phospholipids
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• A cell wall is a stiff covering of cellulose outside the cell membrane. It
provides protection.
• Plant cells, fungal cells, and some protists have cell walls.
• Animal cells do not have a cell wall.
• Cell Appendages
• They are found on the exterior.
• Some kinds of cells have them.
• The flagellum is a tail-like structure.
o The single-cell euglena, a protest, uses this for moving in water.
• Cilia are fibers on the outside.
o The single-celled paramecium uses them for moving.
o Lung cells use them for moving fluids and particles.
THE INTERIOR OF CELLS
Cytoplasm
• This is the fluid inside cells.
• It is mostly water.
• It contains ions (salts), other molecules, & the cytoskeleton.
Cytoskeleton
• This is a network of threadlike proteins joined together.
• It gives a cell its shape.
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Cell Types
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With more advanced microscopes, scientists discovered that all cells can be
grouped into two types:
o prokaryotic cells
o eukaryotic cells
Prokaryotic Cells
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Most prokaryotic cells are unicellular organisms called prokaryotes.
They have no nucleus.
They have fewer cell parts (organelles) than eukaryotes.
Organisms in the domains bacteria and archaea are prokaryotes.
a prokaryote
Eukaryotic Cells
• Plants, animals, fungi, and protists are all made of eukaryotic cells and
are called eukaryotes.
Eukaryotic cells are larger and more complex than prokaryotic cells.
• Eukaryotes have membrane-surrounded organelles.
• The genetic material in eukaryotic cells is surrounded by a membrane to
form a nucleus.
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plant cell
animal cell
Organelles in Eukaryotic Cells
• Each type of organelle has a specialized function.
• They enable the cell to carry our different functions at the same time.
The Nucleus
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It may be the largest organelle in the cell.
It directs cell activities.
It contains DNA, proteins, and a nucleolus, seen as a dark spot.
DNA stores genetic information.
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It is organized in structure called chromosomes.
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Different species have a different number of chromosomes.
• The nucleolus makes organelles called ribosomes.
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They are involved in the production of proteins.
• The nucleus is surrounded by 2 membranes called the nuclear envelope.
o Pores in this let some molecules move through.
Ribosomes
• They are organelles without a surrounding membrane.
• Proteins are made on them.
• Ribosomes are located in the cytoplasm.
• They may be attached to another organelle, the rough endoplasmic
reticulum.
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Endoplasmic Reticulum (ER)
• It is spread though most of the cytoplasm.
• Two kinds: Rough and smooth
• Rough ER has ribosomes on the surface.
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Proteins are made on rough ER.
• Smooth ER lacks ribosomes.
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It makes cholesterol and other lipids.
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It can help remove harmful substances from the cell.
Mitochondria
(see p. 59)
• These organelles process energy.
• Most eukaryotic cells may contain hundreds.
• A mitochondrion is surrounded by 2 membranes.
• Chemical reactions in mitochondria release energy that gets stored in high
energy molecules called ATP.
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ATP stands for adenosine triphosphate.
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It provides energy for growth, cell division, and transport of
materials.
Chloroplasts
• These organelles are found in plant cells and some protists such as algae.
o Not present in animal cells
• Chloroplasts are surrounded by a membrane.
• They contain chlorophyll.
• Chlorophyll is a complex molecule involved in photosynthesis.
• With photosynthesis, water and carbon dioxide are used to make glucose (a
sugar) and oxygen.
o Sugar stores chemical energy.
Processing, Storing, and Transporting Molecules
• The Golgi apparatus prepares proteins for their specific functions and
packages the proteins into vesicles.
• Vesicles are tiny organelles that transport substances from one area of a cell
to another area of a cell. Each vesicle has a membrane.
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• Vacuoles—organelles found in some cells—store food, water, and waste
material.
o Some animal cells may have many small vacuoles.
o A plant cell may have one large vacuole.
See pages 52 & 53 for plant and animal cells.
Animal Cell: