Unicellular organism
Protista - Amoeba
Facts:
• Kingdom - Protista
• The amoeba is a tiny, one-celled organism. You
need a microscope to see most amoebas - the
largest are only about 1 mm across.
• Amoebas live in fresh water, salt water, in wet
soil, and in animals (including people).
Anatomy
• An amoeba consists of a single cell surrounded by a
porous cell membrane.
• Gaseous exchange takes place through this
membrane - oxygen gas from the water passes into
the amoeba through the cell membrane and carbon
dioxide gas leaves through it - diffusion.
• Jelly-like cytoplasm fills most of the cell. A large
nucleus within the amoeba controls its growth and
reproduction.
Pseudopodium; a protuberance from the surface
of the amoeba into which the cytoplasm flows; in
this way the amoeba moves about over the
mud at the bottom of the pond. (pseudopodium
means ‘false foot’)
Contractile vacuole; the concentration of solutes
in the cytoplasm is greater than that in the
surrounding fresh water, so water tends to enter
the cytoplasm by osmosis via the partially
permeable cell membrane. This excess water
collects in the contractile vacuole which swells
and discharges its contents to the outside from
time to time.
Diet and feeding
• Amoebas eat algae, bacteria, plant cells, and
microscopic protozoa. Some amoebas are
parasites.
• They eat by surrounding tiny particles of food
with pseudopods, forming a bubble-like food
vacuole. The food vacuole fuses with a lysosome.
• Food is then digested and absorbed.
These 2 pictures show
an amoeba feeding.
Notice the pseudopods
that are used to enclose
a small ciliate.
Locomotion
• Amoebas move by changing the shape of
their body, and oozing in random
directions. The ooze forms a pseudopod.
The word pseudopod means "false foot."
I examined
the sample
under the
microscope it
looked like
nothing more
than dirt but
between it
were some
big
gelatinous
spheres.
Then I
noticed that
they were
slowly
moving!
Amoeba Proteus, the largest amoeba of them all.
They can become truly huge for a single celled organism.
Some of them can be 5 millimeters.
1. Nucleus
2.Contractile
vacuole
3.Food
vacuole
4. Pseudopod
An Amoeba
is seen here
splitting by
cell division.
When
complete
division is
complete,
there will be
two new
amoebas.
This is what a typical amoeba could look like under your
microscope. They appear as dirt until you notice they MOVE!
Things to identify on your amoeba:
•
•
•
•
•
•
Nucleus
Food vacuole
Contractile vacuole
Describe pseudopod
Cytoplasm
Cell Membrane