2.4: Protista: The Unicellular Eukaryotes
pg. 72
Key Terms: Protist, parasite, pseudopod, cilium, flagellum, and
red tide.
Characteristics of Protists
- most are unicellular
- do not fit into any other kingdom, yet some scientist place them
the plant kingdom.
- multi-cellular protist are divided into three distinct groups; red,
green, and brown algae.
- sometimes red and green algae are place in the plant kingdom and
brown in the protist kingdom.
Protist: a eukaryotic organism, usually unicellular, that is not a
fungus, plant, or animal.
Here we will classify the protists by how they obtain nutrition.
Animal – Like Protists
- protozoans, are heterotrophs
- they consume other organism for food
- Some are parasites; they get their nutrients from other organisms,
which are hosts.
Parasites: an organism that benefits by living in or on organisms
at the expense of that organism.
Pseudopod: (pseudopodia) a temporary cytoplasmic extensions
that amoeba use for feeding and movement.
a) The Cercozoans: Phylum Cercozoa
- example: amoeba
- has a cell membrane and is irregular in shape
- Use extensions known as psuedopods to trap their food and
locomotion.
- Environment: saltwater, freshwater, and mud.
- Entamoebia hystolitica is a parasite form.
Figure 2.18 When amoebas detect food, they form pseudopods from the cell
membrane and engulf their target.
b) The Ciliates: Phylum Ciliophora
- example: paramecium
- has hair like projections known a cilia
- cilia is used for locomotion and sweeping of food to the oral
groove in cell membrane surface.
- can grow very large, 100 µm in length
- some are parasites, such as; Balantidium coli.
Figure 2.19 Paramecia use cilia to move through the water and to move
food into the gullet.
Cilium: (cilia) a short, hair-like projection that functions in cell
movement and particle manipulation when coordinated with other
cilia.
c) Flagellates: Phylum Zoomastigina
- have one or more flagella
- have a hard protective coating over a cell membrane
- some are parasites and others live in a mutualistic
relationship. Some are free living.
Flagellum: (flagella) a long hair-like projection extending
from the cell membrane that propels the cell using a whiplike motion.
Figure 2.20: members of the genus Trichonympha have a
mutualistic relationship with termites.
d) The Sporozoans: Phylum Sporozoa
- are parasitic organisms
- hosts are harmed and sometime killed
- Plasmodium is a parasite which causes malaria
Figure 2.21 The life cycle of the malaria-causing protest Plasmodium
involves two hosts, a mosquito and a human. Symptoms of malaria include
high fevers, chills, nausea, and vomiting.
Fungus – Like Protists
- most are heterotrophs
- absorb nutrients from living organisms, dead organisms, and
wastes.
- produce spores like fungi
- has a cell wall like a fungi yet different
- There are two groups, slime and water moulds.
a) Plasmodial Slime Moulds: Phylum Myxomycota
- visible to the naked eye
- live in damp, decaying plant material
- Plasmodium contain more then one nuclei
- engulf their food similar to amoebas
b) Cellular Slime Moulds: Phylum Acrasiomycota
- Cells only contain one nuclei
- feeds on tiny bacteria or yeast cells
c) Water Moulds: Phylum Oomycota
- resemble fungi
- live on dead organic matter
- may be parasitic on fish, insects and plants
- use hair like structures to embed into their host and absorb
nutrients
Plant – Like Protists
- examples: diatoms, dinoflagellates, and euglenoids
- has chloroplasts which contain chlorophyll
- perform photosynthesis
a) Diatoms: Phylum Chrysophyta
- unicellular, free-floating aquatic organisms
- Most diverse and abundant phytoplankton
- important source of food for marine life
- have rigid cell walls made of silica
- walls are composed of two unequal parts
- reproduce asexually by mitosis, mostly
- sexual reproduction is less common, usually in harsh
conditions
b) Dinoflagellates: Phylum Pyrrophyta
- most are phytoplankton
- have two flagella (swimming tails) for locomotion
- Under suitable conditions they reproduce quickly producing
algae blooms. (Red tides)
Red Tide: a costal phenomenon in which dinoflagellates that
contain red pigments are so concentrated that seawater has a
distinct red colour.
c) Euglenoids
- there are 1000’s of species of euglenoids
- live in shallow freshwaters
- perform photosynthesis, as they contain chloroplasts
- have flagella and take in nutrients also
- Therefore they have both plant and animal characteristics.
- in sunlight they are autotrophs, and in dark environments
they are heterotrophs
- They have developed an eyespot, used to detect light
Activity 2.3: Slime Moulds: Science, Technology, Society, and the
Environment, pg. 75
Learning Check, questions 19 – 24, pg. 76
Section 2.4 Review, questions 1 – 13, pg. 78
Chapter 2 Review: questions 1 – 38, pg.83- 85
Chapter 2 Self – Assessment, questions 1 – 25, pg. 86 – 87