Ch 23 Protists
23.1 Evolution of Protists Involved Endosymbiosis (Pg 498)
Evolved 1.5 to 2 billion years ago
Endosymbiosis played an important role.
o Contain mitochondria and some contain chloroplasts
o earliest eukaryotes acquired mitochondria by engulfing proteobacteria becoming
o Cyanobacteria ingested by eukaryote that already had mitochondria.
o Formed symbiotic relationship
o Over evolutionary time, lost genes no longer required for independent existence and
transferred most of its genes to the host’s nuclear genome.
Gave the host cell better control of overall cell function
o Prokaryote became an organelle of an eukaryote
o Some evolved this way, other: eukaryote engulfed a photosynthetic eukaryote that
eventually became a chloroplast. 23.2 What is a Protist? Characteristics of Protists (Pg 499)
multiple linear chromosomes
cytoplasmic organelles: mitochondria and chloroplast (in some species)
microtubules and microfilaments.
o Provide motility and cytoskeletal support
characteristics of transcription and translation like eukaryotes
Phylogenetic relationship btw protists and eukaryotes is more complex.
o Over evolutionary time, the eukaryotic family tree branched out in many directions
o Plants, animals and fungi diverged from protest ancestors.
o Some features similar, other distinctive.
Most protists are motile or have motile stages in their life cycle and their cell walls are made of
o Fungi cell ways are made of chitin
Differences from plants:
o Photoautotrophic protists can also live as heterotrophs
Some combine both modes of nutrition
o Do not retain developing embryos in parental tissue
o Do not have highly differentiated structures equivalent to roots, stems and leaves
o Photosynthetic generally referred to as algae
Generally aquatic, unicellular and microscopic.
Diff groups of algae are not closely related to each other.
Differences from animals:
o Unlike protists, all animals are multicellular and have features such as an internal digestive
tract and complex developmental stages
o Protists lack nerve cells, highly differentiated structures such as limbs and a heart and
collagen (extracellular support protein)
Animals in protest are not fungi, plants, animals or prokaryotes
o Many were grouped into phyla under kingdom according to body form, nutrition modes and
movement, forms of meiosis and mitosis. paraphyletic
o Molecular data show that most protists do not share a common ancestor and the ones
grouped together in a phyla are not closely related.
Some evolutionists believe that protista kingdom is collection of many kingdoms (as many as 30).
23.3 Protists’ Diversity is reflected in their metabolism, reproduction,
structure and habitat (Pg 500) Habitat
o Live in aqueous habitats
Aquatic or moist terrestrial locations
Oceans, freshwater lakes, ponds, streams and moist soils and within host
extreme habitats (high/low pH, high/low salt, high/low temperature,
Phytoplankton: in bodies of water, small photosynthetic protists collectively make
Capture light energy
Provide organic substance and oxygen for heterotrophic bacteria, other
protists and animal larvae
Combined with large multicellular protists forming seaweeds, they account
for half of the total organic matter produced by photosynthesis
Zooplankton: animal larvae that feed of phytoplankton
In moist soilds of terrestrial environments, protists play important roles among the
detritus feeders that recycle matter from organic back to inorganic form
Enormously important in world ecosystems
Protists that live in host organisms are parasites, obtaining nutrients from the host.
Many human parasites are protists causing diseases such as malaria,
sleeping sickness and amoebic dysentery.
o Most single cells
o Other live as colonies in which individual cells show little or no differentiation and are
Within colonies, individuals use cell signaling to cooperate on tasks such as feeding
o Some are large multicellular organisms: giant kelp of coastal waters can rival forest trees in
o Many single celled and colonial protists have complex intracellular structures
Reflect key aspects of habitats in which they live.
Fresh water protists.
Cytoplasm is hypertonic, water flows in.
Contractile vacuole gradually fills with fluid, when it reaches its maximum
size, it moves to the plasma membrane and forcible contracts, expelling the
fluid to the outside through a pore in the membrane.
o Some are supported by an external cell wall or by an internal or external shell built up from
organic or mineral matter o Instead of cell wall, other protists have a pellicle: a layer of supportive protein fibers located
inside the cell just under the plasma membrane, providing strength and flexibility
o Almost all protists move sometime during their lives.
Some move by amoeboid motion
Cell extends one or more lobes of cytoplasm called pseudopodia.
Rest of cytoplasm and nucleus then flow into the pseudopodium,
completing the movement.
Other move by beating of the flagella or cilia.
Some protists: cilia are arranged in complex patterns, with an equally
complex network of microtubules and other cytoskel