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Unit B: Cells and Systems
Topic 3: The Cell and its
Structures
Cells = Life
• Remember that one
of the principles of
cell theory says that
all living things are
either cells or made
up of cells.
• Unicellular organisms:
Organisms made up
of only one cell (eg.
paramecium).
Cells are the Basis for Life
• Multicellular
Organisms – An
organism that is made
up of multiple,
specialized cells. (eg.
fungi, plants, animals,
us).
Limitations of Unicellular Life
• Unicellular organisms must always be in
contact with water to help transport food
and wastes. Therefore unicellular
organisms must be near oceans.
• Multicellular organisms get around this by
taking in water from the environment and
keeping water internally. (eg. blood is very
similar to ocean water).
• Another limitation is that to keep wastes
moving out quickly enough and food
coming in, unicellular organisms must be
small in size.
How Cells Work
• Organisms have organs and systems to
carry out basic functions: reproduction,
eliminate wastes, take in energy, adapt to
environment, and growth.
• Cells have organelles (little organs) to
carry out the same functions. Cells have
the same basic needs that all living things
do.
Cytoplasm and Cell Membrane
• Cytoplasm is the part of the cell that acts
as the circulatory system. Nutrients,
wastes and vacuoles all move throughout
the cytoplasm. It is a jellylike goop
surrounding all the other organelles.
• Cell Membrane – is the covering of the
cell, acting as its skin. It keeps out wastes
and lets food and nutrients in. The one
substance that can pass through the
membrane is water.
Nucleus and Mitochondria
• The ‘brain’ of the cell. It controls the cell’s
activities. It also contains all of the genetic
material of the cell. The nucleus is responsible
for growth and reproduction of cells. (Cell
splitting). It is a large circular object in a cell that
is easily seen in a compound microscope.
• Vacuoles are bubble-like organelles that store
and transport food, wastes, and other materials.
They have their own membrane.
Plant Organelles: Cell Wall and
Chloroplasts
• The cell wall occurs only in plants and
fungi. It acts as the skeleton of a plant,
giving it structural support. They are made
of a tough, rigid material called cellulose.
• Chloroplasts only occur in plants. Inside
chloroplasts is a chemical, chlorophyll,
which is green in color giving the cell and
the plant its green color. This is where
photosynthesis takes place.