Monobiontic life cycle: only one generation can grow



Monobiontic life cycle: only one generation can grow
Monobiontic life cycle: only one generation can grow and divide
Example in the green algae Ulothrix the only diploid phase is limited to
the single-celled zygote. It can undergo meiosis to produce gamete.
Dibiontic life cycle: both haploid and diploid generations can grow and
divide mitotically. The generations can be heteromorphic or
An example is the green algae Ulva which is dibiontic and
Algae - usefulness to humans, harmful blooms, lifecycles
Phytoplankton - phyto (plant) plankter (wanderer) microscopic
floating algae.
Important as first tier of the food chain because they are
Productivity is 3.26 quintillion (3.26 x 1018) kcal of
photosynthate /year or 4x crop land total
Important for many unique chemicals they produce that we
use for food, industrial uses, pharmaceuticals, etc.
Negative impact: harmful algal blooms and toxins produced
Algae – general features.
All are protists
They require moist environments because they lack a cuticle
They lack vascular tissues
Algae are photosynthetic and reproduce both sexually and asexually
Beneficial Aspects of Algae
Food for humans, food for fish in aquaculture, animal feed
Soil fertilizers and conditioners in agriculture
Treatment of waste water
Diatomaceous earth (= diatoms)
Chalk deposits
Phycocolloids (agar, carrageenan from red algae; alginates from
brown algae)
•  Drugs
•  Model system for research
•  Phycobiliproteins for fluorescence microscopy
Seaweeds are an important part of the human diet in several parts of the world.
It is a good source of iodine. One million metric tons of the brown algla
Laminaria is harvested per year in China for iodine. It is used to treat goiter in
Nori - The red alga Porphyra is used in Japanese cuisine.
Limu - the Polynesians in Hawaii used more than 75 species of seaweed in their
Dulce - The red alga Palmaria palmate has been eaten in the British Isles for
more than 1200 years.
Irish moss, a red alga, Chondrus crispus, when boiled with milk produces a
jelly dessert that the French call blancmange
Nevertheless, algae do not have much direct nutritional value for
humans - they are mostly indigestible.
Industrial uses:
Diatomaceous earth (diatomite) is a great filter material.
It is used in cement, grout, paper, paint, pesticides, etc. and it is also
an abrasive.
The original formulation of dynamite
is diatomaceous earth and
Agar - polysaccharide from red algae (agarose is purified from agar).
It is used in baking to make icing. It is not digestible and is also used as a
Carrageenan - polysaccharide from red algae (Irish moss). Named after the
town of Carragheen, Co. Cork. It is added to most foods including ice cream,
bread, toothpaste etc. Harvested off the coast of Maine.
Algin - polymer from brown algae is a major component
of the cell wall. One tablespoon added to 1 liter of water
gives the consistency of honey. Several species of
brown algae are harvested for algin including Laminaria,
Macrocyctis, Fucus, and Ascophyllum.
Harmful algal blooms
Red tide in Maine
Red tide in La Jolla, CA
Amnesic shellfish poisoning
Domoic acid - the neurotoxin associated
with amnesic shellfish poisoning. It
bioaccumulates in plankton feeders such
as shellfish and fish. It causes permanent
short-term memory loss, brain damage and
death. It can kill marine birds and
mammals. It activates AMPA kainate
receptors allowing Ca2+ influx.
Pseudonitzschia a diatom produces
domoic acid
First discovered in Nova Scotia, where it
killed 3 people in 1987. Has been
implicated in sea bird and mammal deaths
in California.
Sea lion affected by domoic acid
Ciguatera fish poisoning
Gambierdiscus toxicus a dinoflagellate
Ciguatoxin accumulates in reef
fishes (that eat herbivorous fish).
Occurs in tropical waters. Symptoms
include nausea, diarrhea, neurologial
symptoms such as paresthesia (“pins
and needles” sensation), muscle
aches, ataxia (loss of control of body
movements), and allodynia (pain
from non-painful stimulation).
Symptoms can last from days to
years. Sometimes misdiagnosed as
multiple sclerosis. There is no
effective treatment, the toxin(s)
affects ion channels in the nervous
system. "
Diarrhetic shellfish poisoning, gastrointestinal symptoms caused by eating shellfish
that have fed on Dinophysis sp., an alveolate. Problem in Spain, Ireland and
around Mediteranean.
The toxin is okadaic acid.
okadaic acid
Dinophysis acuminata
A Dinophysis bloom in Norway
Brevitoxin and Neurotoxic shellfish poisoning. Restricted to the Gulf of
Mexico and Caribbean. Exposure can occur through eating shellfish or
breathing sea spray. Has affected fisheries of Florida and Texas, has killed
off manatees and has affected human health. Toxins open voltage gated Na+
channels and cause depolarization. The toxins are heat and acid stable.
Causes respiratory irritation, cough, bronchoconstriction, and skin rashes or
acute gastroenteritis if exposure is through shellfish. Symptoms subside after
a few days.
Karenia brevis (formerly Gymnodinium breve) is a dinoflagellate and causes Florida red tides.
Saxitoxin and Paralytic Shellfish Poisoning. Occurs over a wide range, on both east
and west coasts of US. In Alaska, the butterclam bioaccumulates saxitoxin. STX
has been implicated in the deaths of humpback whales and Mediterranean monk
seals. Saxitoxins block Na+ channels.
Alexandrium tamarense
is a dinoflagellate
Fusion of
(plasmogamy and
resting stage
Diploid (2 n)
Life cycle of green
algae Ulothrix is
Monobiontic. The
filaments are haploid.
The zygote is only
capable of meiosis.
Haploid ( n)
– filament
with isogametes
vegetative cell
escape from
parent cell
new filament
arises through
meiospores escape
+ filament
holdfast cell
meiospore settles;
new filament
arises through
Life cycle of green algae Ulva
is diobiontic and isomorphic.
The gametophyte (haploid
generation produces
anisogametes (the two types
differ in size).
Life cycle of green algae (chlorophyte) Derbesia: it is dibiontic and
heteromorphic. The sporophyte (diploid) appears different then the
gametophyte. The gametophytes produce anisogametes.
Diatoms are different – they are monobiontic but the dominant generation is
the sporophyte. Repeated mitotic divisions of the sporophyte result in smaller
These go through meiosis to produce gametes (isogametes) that fuse and
produce a new sporophyte generation that makes a new wall.
asexual reproduction by mitosis; all cells are 2n
forms cell
fusion of isogametes to produce a diploid zygote
sexual reproduction by meiosis, leading to isogametes
Red Algae
Large group with 3900 species
They are red because they have phycobilisomes, their red color is due to
phycoerythrin. Red algae store fixed carbon as floridean starch (a branched glucose
polymer). They lack plasmodesmata but have cellular connections called pit
They have complex life cycles than completely lack swimming cells.
General life cycle of red alga, it is dibiontic and heteromorphic.
• Red algae
• Commercial uses: Carrageenan used for making ice cream, jellies, syrups, breads.
• Also for lotions, toothpaste, pharmaceutical jellies.
• Agar for growing bacteria and fungi for research purposes.
• As food.
Brown algae, closely related to diatoms.
They are all multicellular and almost all marine algae. They have holdfast, stipe,
blade and air bladder, are up to 50 meters long.
The brown alga Fucus.
The brown alga Ectocarpus
Is dibiontic and isomorphic.
The gametes are
The life cycle is not too
Haploid (n) Diploid (2n)
n Gamete
n fusion
mitospores in
Life cycle of the brown alga
This is dibiontic, heteromorphic
and the gametes are not
similar, it is oogamous.
Antheridia - male gametangia (structure of the gametophyte that makes gametes)
Oogonia - female gametangia
Next time - Bryophytes (the mosses) read Ch. 20

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