- Multiple fission (schizogony):Multiple fission is when the nucleus of the
cell divides multiple times before the rest of the cell divides. Forms around
each nucleus when the nucleus divides then each nuclei separates into a
daughter cell.
Some protists are sexual and exchange genetic material from one cell to
another through conjugation, which is the physical contact between cells.
A protist can survive in an adverse environment by encapsulating itself with
a protective coating called a cyst.The cyst defends the protist in extreme tem-
peratures against toxic chemicals and even when there is a lack of oxygen, mois-
ture, and food.
PROTOZOA NUTRITION
Protists receive nutrients by breaking down organic matter (heterotrophic) and
can grow in both aerobic and anaerobic environments, such as protists that live
in the intestine of animals. Some protists, such as Euglena, receive nutrients
from organic matter and through photosynthesis because they contain chloro-
phyll. These protists are considered both algae and protozoa.
Protists obtain food in one of three ways:
- Absorption: Food is absorbed across the protist’s plasma membrane.
- Ingestion: Cilia outside the protist create a wave-like motion to move food
into a mouth-like opening in the protist called a cytosome. An example is
the paramecium. - Engulf:Pseudopods(meaning “false feet”) on the protist engulf food, then
pull it into the cell using a process called phagocytosis. An example of this
type of protist is the amoeba.
Food is digested in the vacuole after the food enters the cell. The vacuoleis
a membrane-bound organelle. Waste products are excreted using a process
called exocytosis.
AMEBA
Here are common amebas (Fig. 11-2):- Entamoeba histolytica: Also known as E. histolytica, this microorganism
is transmitted between humans through the ingestion of cysts that are
CHAPTER 11 The Eukar yotes^175