Please enable JavaScript.
Coggle requires JavaScript to display documents.
Chapter 19: Algae and the Origin of Eukaryotic Cells (Green Algae (Body…
Chapter 19: Algae and the Origin of Eukaryotic Cells
Concept
protozoans & algae
some species died out quickly
others more successful and persisted
diversifying into many forms
numerous groups of organisms
embryophytes
#
gave rise algae
include green algae which in turn produced true plants
endosymbiosis
two organisms lived together
one inside the other
over 100 millions of yrs
evolved into sophisticated form of eukaryotic cell
with real mitochondria
Origin of Eukaryotic Cells
DNA Structure
"naked"
not complexed with proteins
numerous negative charges being neutralized by calcium ions instead
in eukaryotes
DNA is more elaborately packaged
being complexed with nucleosome histones
forming chromosomes
Nuclear Structure and Division
DNA of prokaryotes lies directly in cytoplasm
no nucleus is present
nuclei of plants are
virtually identical to those of animals
fungi in structure
metabolism
mitosis
meiosis
eukaryotes=ture nucleus
Organelles
prokaryotes lack membrance-bounded organelles
cytoplasm is rather homogeneous
containing only ribosomes&storage granules
Origin Of Mitochondria and Plastids: The Endosymbiont Theory
autogenous theory
until the early 1970s
assumed some had given rise to eukaryotes
by gradually becoming more complex
developing an endomembrane system
part of which eventually specialized came mitochondria&plastids
endosymbiont theory
revived
in the 1960s
primary endosymbiosis
gave rise to clade containing red algae
green algae
small group called glaucophytes
secondary endosymbiosis
produced other lines of algae
euglenoids arose after early eukaryote engulfed an entire green alga
heterokonts
another group of early eukaryotes
stramenopiles
involved in one or several endosymbioses with entire cells of red algae
name for fact that all have two flagella of different types
smooth
hairs
phycoplast
in some green algae
cytokinesis occurs
microtublues oriented parallel to the plane where the new wall will form
perpendicular to orienta tion of the spindle
Green Algae
Body Construction in Green Algae
motile colonies
if cells adhere loosely
resulting structure is a colony
not an individual organism
nonmotile colonies
occur if the cells lose their flagella or never develop them
filamentous body
results if cells are held tightly by middle lamella& if all cells divide transversely
membranous body
results if the orientation of cell divisions is controlled precisely
such all new walls occur in only two planes
parenchymatous body
if cell division occurs regularly in all three planes
bulky
three-dimensional
coenocytic
or siphonous body
results if karyokinesis occurs without cytoinesis
giant multinucleate cel result
Life cycles of Green Algae
dibiontic
alternation of generations between haploid&diploid
monobiontic species
occurs in only one free-living generation exists
nation of isomorphic genetrations
two may be very different in appearance&construction
alternation of heteromorphic generations
exploit dfferent ecological niches almost if they were two species
gametophytes do not compete directly with sporophytes
Representative Genera of Green Algae
conjugation
swimming gametes not formed
instead
filaments undergo
zoospores
zygote germinates by meiosis
producing four haploid
charophytes
undergo cell division by means of phragmoplast
just as plant cells do
Green Algae and Embryophytes
streptophytes
they form a monophyletic clade
some people have suggested clade be named
even definition of embryophytes should extended
charophytes should be considered true plants,no algae
green algae
constitute an extremely important group
not only could some early green algae organize complex differentiated multicellular bodies
some moved onto land
Red Algae
red algae
constitute a large group of especially distinct
fascinating algae
floridean starch
excess photosynthate is stored
branched polymer of glucose somewhat similar to glycogen
occurs as granules in the cytoplasm
never in the chloroplast
pit connections
walls of red algae lack plasmodesmata
of type of occurs in plants
have distinctive
Brown Algae and Their Relatives: The Heterokonts
Brown Algae
almost exclusively marine
few fresh water species are known
littoral zone
can found most easily on rocky coasts growing
the region between low tide and high tide
also called intertidal zone
laminarin
storage product of brown algae
a polymer of glucose
mannitol
fats
not starch
Diatoms
easy to recognize
distinctive morphology
diatomaceous earth
deposits
become 100m thick&cover many square km
Yellow-Green Algae
occur mostly in fresh water
formerly
many thought to be green algae until chlorophyll c was discovered in them
Vaucheria
Golden-Brown Algae
consist of about 70 genera
325 species
coccolithophorids
usually called coccoliths
relatively inert
do not decompose
Dinoflagellates
Oomycetes
diverse in structure
nutrition
lack chloroplasts
must be parasitic or saprophytic
such as
Saprolegnia
Achlya
have many unusual characters
"red tide"
bodies color the water reddish brown
Gonyaulax
Gymnodinium
Euglenoids
have been discovered
named
placed into 36 genera
