Download Chapter 9: Fungi and Aquatic Plants

Chapter 9. Fungi and Aquatic Plants
Introduction: The Big Step: DIVISION OF LABOUR
¾ In single cell organisms (protists)
all life functions are
performed by specialized organelles within one cell (a.k.a.
DIVISION OF LABOUR). Some algae; cyanobacteria (a.k.a.
blue-green algae) were also considered part of this group.
¾ In multi-cellular organisms individual cells have varying
degrees of specialization, beginning with ‘higher’ algae and
fungi. DIVISION OF LABOUR is now carried out by similar
groups of cell and organs.
¾ The higher algae and fungi are (sort of) considered plants
because of this degree of specialization.
‘Evolutionary’ Significance
• Fungi and aquatic plants (red, green and brown algae) are thought
to have made terrestrial life possible.
• Most biologists believe that true land pants probably evolved from
green algae.
• It is also believed that the early invasion of land plants was
facilitated by symbiotic relationships between fungi and plants via
mycorrhizal. That is, the fungi helped supply nutrients to the roots
of the land plants in exchange for nutrients.
Benefits of a water environment:
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• prevents cells from drying out
• gives structural support
• provides nutrients
• provides medium for fertilization
• accommodates dispersal of spores
Aquatic Plants v. Terrestrial Plants
Differences;
• aquatic plants lack roots, stems and leaves.
Similarities
• all have at least one of four different kinds of chlorophyll (pigment
needed to trap sunlight for photosynthesis
Fungi v. Plants
Similarities
• eukaryotes with numerous organelles
• most have cell walls
• parts of body are often anchored in soil
• generally stationary
• lower plants reproduce by spores
Differences
• Fungi
• not anchored by roots
• do not photosynthesize***
• (most) lack cellulose in their cell wall
• Higher plants reproduce by seeds.
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Kingdom Fungi
Figure of Mycelium and Hypha
Characteristics of fungi
• cells of fungi are eukaryotic
• digestion is extra-cellular (outside of the cell), with nutrients being
absorbed
• composed of single strands (hypha, pl. hyphae) into complex
masses called mycelium (pl. mycelia)
• hyphae can be septate (have cross-walls) non-septate
• (most) hyphae have chitin cell walls
• heterotrophs
• reproduction is asexual/sexual/both
• inhabit dark, warm, moist, high organic locations
Life Cycle
Figure
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Fungal diversity
Fungi have essentially two parts
• the visible reproductive structures. These include the sexual
gametangia (producing gametes) and asexual sporangia
(producing spores) which normally grow on top of the surface.
• the ‘invisible’ vegetative structures. This is the larger mycelium
mass growing below the surface which busies itself with taking up
nutrients to drive the reproduction train.
Ecological role of fungi
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• Organic decomposition - waste reduction and nutrient recycling
of dead and decaying matter. Breaks down living things into
useable nutrients that goes back into the soil to sustain life. Apart
from producers, decomposers are probably the next most
important life form on the planet.
• Toxin breakdown - certain fungi can be used to break down
harmful pollutants
Classification
Table 9.1
Fungal Symbionts
Two important symbiotic relationships:
a. Lichens
a symbiotic relationship between algae (green or blue-green) and
fungi. The algae provided photosynthetic nutrients (food) to the
fungus and the fungus surrounds the algae with carbon dioxide and
water (both necessary for photosynthesis). The fungus also provides
a support for the organism.
The ‘sandwich’
e.g. reindeer moss, maiden hair/old man’s beard
Lichens as air-quality monitors.
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Since lichens absorb water right out of the air, they are more
susceptible to air pollution and die if pollution reaches a certain level.
b. Mycorrhizae
A relationship between plant roots and fungi similar to that of lichens
except the fungus does not offer support to the roots. The roots
already contain cellulose and therefore are ‘self-supporting’.
Read p245 Fungal Mimicry
Do p245 Review Questions #1,2,3,4
…terrestrial adaptations
aquatic environment ⎯⎯→land environment
Sporophyte (spore) dominant ⎯→ Gametophyte (gamete) dominant
life cycles
life cycles
WHY?
Ecological Role of Algae
Unicellular
• marine and freshwater phytoplankton
• primary producers in aquatic/marine food webs
• produce 67% of global oxygen
• some commercial applications
Multicellular
• marine and freshwater ‘seaweeds’
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• chloroplasts plus other pigments, depends on depth. Water filters
out different wavelengths of light so chlorophyll comes in different
‘flavours’
• additional pigments also used
Reproduction in Algae
Alternation of Generations
• where a species alternates between the diploid spore-producing
(sporophyte) method of reproduction and the haploid gameteproducing (gametophyte)
Figure 9.10 Life cycle of Chlamydomonas
Definitions
zygote - the product of fertilization. Occurs when two gametes fuse.
Conjugation - the fusion of two gametes.
Zygospore - a tough shelled spore that can ‘weather bad conditions’
before going through meiosis and releasing more spores.
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Isogamy - when two gametes fuse that are the same size.
Heterogamy - when two gametes fuse where one is larger (female)
than the other (male)
Fragmentation - a form of sexual reproduction where a piece of the
parent falls off and starts growing.
Introducing The Green Algae
unicellular - ‘Clammy’ the Chlaydomonas.
Filamentous - The Rock Band “Spirogyra” (you think I’m kidding, don’t you?!)
Colonial - Volvo…I meant Volvox
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Multicellular -
U
lva
Red and Brown Algae.
General morphology
Fucus
p251 Review Questions 8,9,12 - 15
Kingdom Plantae
Characteristics
a) Photosynthesis - carbohydrate production using sunlight as an
energy source.
b) Cellulose cell walls
c) Alternation of generations in life cycle
d) Sessile (anchored)
Plant Diversity
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Plants can be largely broken into three categories:
a) aquatic plants
b) non-vascular plants (no xylem or phloem)
c) vascular plants (has xylem and phloem)
Terrestrial Adaptations
Since in the evolutionary scheme of things, terrestrial (land dwelling)
plants evolved from aquatic plants certain adaptations would have
been necessary.
a) A water transport system
b) Roots, stem and leaves
c) A reproductive system not dependent on the presence of water fro
fertilization and spread of new individuals.
Evolutionary Trend or Further Evidence of Intelligent Design?
A further trend is purported to have happened as well: the trend away
from a life cycle dominated by a haploid gametophyte dominated
plant to a diploid sporophyte dominated plant***
***gametophyte - gamete producing structures. In aquatic plants,
water-borne gametes were required for fertilization so it makes sense
for the plant to be dedicated to that life-style.
***sporophyte - spore producing structures. In terrestrial plants,
where water is not the medium in which the plant lives, there is a
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great need to prevent gametes from drying out. Consequently, a
system in which water-requiring gametes are down-played is the best
way to go.
Refer to Figure 9.6
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