Lecture 15 Botany & Mycology: plant and fungal diversity

Question 1

Plant diversity

Answer 1

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Question 2

1. Land Plants and Terrestrial Life

Answer 2

• Green algae & land plants shared a common ancestor > 1 BYA
• Multicellular autotrophs adapted to land

Question 3

A. Origin of Land Plants – Green algae

Answer 3

• Green algae & land plants shared a common ancestor > 1 BYA
• The green algae split into two major clades
  – Chlorophytes – Never made it to land
  – Charophytes – Sister to a

Key traits appear in nearly all plants
but are absent in the charophytes
● Alternation of generations
● Walled spores produced in
sporangia
● Apical meristems

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Question 4

B. Transition from water to land

Answer 4

• Limiting water loss and control of as exchange
• Limit UV damage to DNA
• Water transport through plant
• Resistance to effects of wind and gravity
• Protection and dispersal of reproductive structures
• Life cycles promoting genetic diversity

Adaptations to terrestrial life
* Protection from desiccation - Waxy cuticle and stomata
* Moving water using tracheids - Xylem and phloem to conduct water and food
* UV radiation caused mutations - Shift to a dominant diploid generation
* Haplodiplontic life cycle
– Multicellular haploid and diploid life stages
– Humans are diplontic

Question 5

C. Alternation of Generations

Answer 5

Multicellular haploid stage – gametophyte
– Spores divide by mitosis to produces gametes
– Gametes fuse to form diploid zygote (1st cell of next sporophyte generation)

Multicellular diploid stage – sporophyte
– Produces haploid spores by meiosis
– Diploid spore mother cells (sporocytes) undergo meiosis in sporangia
* Produce 4 haploid spores
* First cells of gametophyte generation

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Question 6

Highlights of plant evolution

Answer 6

1. Origin of plants (non vascular) - Bryophytes
2. Origin of vascular plants (seedless): Lycophytes and Monilophytes
3. Origin of seed plants (angiosperm and gymnosperm)

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Question 7

Bryophytes

Answer 7

• Closest living descendants of the first land plants
• Called nonvascular plants - they lack tracheids
• Simple organisms divided in 3 clades
  – Hornworts
  – Liverworts
  – Mosses
• Adaptations to living on land
  – Short (<7cm) – lack vascular system
  – Lack roots - Mycorrhizal associations important in enhancing water uptake
  – Gametophyte – dominant generation (photosynthetic)
  – Require water for sexual reproduction

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Question 8

Vascular Plants

Answer 8

• Tracheophytes - Seedless Vascular Plants
• Evolved Roots, Stems, and Leaves
• Vascular tissues
  – Xylem - Conducts water and dissolved minerals upward from the roots
  – Phloem - Conducts sucrose and hormones throughout the plant
• Enable enhanced height and size in the tracheophytes
• Life cycle is dominant sporophyte
• Cuticle and stomata also found in land plants
• Divided into three clades
  – Seedless vascular
• Lycophytes (club mosses)
• Monilophyta (ferns, whisk ferns, and horsetails)
  – Seed plants

Question 9

Major plant innovations

Answer 9

Stems - Early fossils reveal stems but no roots or leaves
– Lack of roots limited early tracheophytes
* Leaf - Increase surface area for photosynthesis
Higher stomatal densities favored larger leaves with a photosynthetic advantage that did not overheat

Evolved twice
o Euphylls (true leaves) found in ferns and seed plants
o Lycophylls found in seed plants
* Roots - Provide transport and support
– Lycophytes diverged before true roots appeared

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Question 10

The Evolution of Seed Plants

Answer 10

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Question 11

The Evolution of Seed Plants

Answer 11

• Seed plants first appeared 305–465 MYA
  – Evolved from spore-bearing plants known as progymnosperms
• Success attributed to evolution of seed: embryo + nutrient
  – Protects and provides food for embryo
  – Allows the “clock to be stopped” to survive harsh periods before germinating
  – Later development of fruits enhanced dispersal
• Seed plant life cycles are sporophyte-dominated

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Question 12

Seed vs spores

Answer 12

Seeds provide evolutionary advantages over spores
* Seeds are multicellular; spores are single cells
* Seeds can remain dormant for years until conditions are
favorable for germination, whereas spores are shorter-lived
* Seeds have stored food to nourish growing seedlings; spores
do not provide nourishment to gametophytes
* Seeds can be transported longer distances by wind or
animals, but spores usually drop closer to the parent plant

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Question 13

Seed plants produce 2 kinds of gametophytes

Answer 13

• Male gametophytes - Pollen grains
  – Dispersed by wind or a pollinator
  – No need for water
• Female gametophytes - Develop within an ovule
  – Enclosed within diploid sporophyte tissue in angiosperms

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Question 14

Gametophyte-sporophyte relationships in different plant groups

Answer 14

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Question 15

Two types of seed plants

Answer 15

Gymnosperm: plants with “naked seed”
- seeds are not enclosed in chambers

Angionsperm:seeds develop inside chambers
-90% of living plants
-consists of all flowering plants

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Question 16

Defining Fungi

Answer 16

• Mycologists - 1.5 million fungal species
• Most are multicellular - mycelium
• Unicellular or single-celled (yeast)
• Sexual or asexual
• Heterotrophs and absorb nutrients from surroundings
• Hydrolytic enzymes to break down complex molecules into smaller
  organic compounds

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Question 17

Unicellular Yeast

Answer 17

• Unicellular ascomycetes
• Most reproduce asexually by budding
• Yeasts can ferment carbohydrates
  – Break down glucose into ethanol and CO2
  – Used to make bread, beer, and wine
  – Saccharomyces cerevisiae
• long-standing model system for genetic research
  – First of the eukaryotes to be genetically engineered extensively
  – Saccharomyces cerevisiae first eukaryote to have genome sequenced
  – Other fungi are being sequenced and studied which may affect our
  understanding of their evolution

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Question 18

A- Structure - Fungal mycelium

Answer 18

• Mycelium – mass of connected hyphae
  – Grows through and digests its substrate
• Fungal cell walls include chitin
  – Also found in the hard shells (exoskeletons) of arthropods
  – Both fungi and animals store glucose as glycogen
• Multicellular fungi consist of long, slender filaments called hyphae
  – Some hyphae are continuous called coenocytic hyphae
  – Others are divided by septa – septate hyphae
• Cytoplasm flows throughout hyphae
  – Allows rapid growth under good conditions

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Question 19

C - Cell division

Answer 19

• Fungi have an unusual mitosis
  – Cell is not relevant unit of reproduction
  – Nuclear envelope does not break down and re-form
  – Instead, the spindle apparatus is formed within it
• Fungi lack centrioles (except in chytrids)
  – Spindle pole bodies form mitotic spindles

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Question 20

D -Reproduction

Answer 20

• Capable of both sexual and asexual reproduction
• Sexual reproduction
  – Fusion of two haploid hyphae of compatible mating types
• In some fungi, fusion immediately results in a diploid (2n) cell
• Others, have a dikaryon stage (1n + 1n) before parental nuclei form diploid nucleus
  – May form motile zoospores, zygosporangia, basidia, or asci
• Spores - most common means of reproduction among fungi
  – May form from sexual or asexual processes
  – Most are dispersed by wind or insects

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Question 21

Generalized life cycle of fungi

Answer 21

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Question 22

E. Nutrition

Answer 22

• Heterotrophs - obtain carbon and energy from the digestion of polymers
• External digestion- secrete digestive enzymes into surroundings
• Absorb the organic molecules produced by this external digestion
  – Decomposers – food = dead plants and animals
  – Parasites - invade the living cells of their hosts and absorb nutrients directly
• Fungi can break down cellulose and lignin
  – Decompose wood
  – Some fungi are carnivorous

majority of dead plants and
plant-based materials are
decomposed by fungi

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Question 23

Ecology of Fungi

Answer 23

• Principal decomposers in the biosphere (also bacteria)
• Break down cellulose and lignin from wood
  – Releases carbon, nitrogen, and phosphorus
  – Makes the elements available to other organisms

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Question 24

Fungal relationships

Answer 24

• Fungi symbioses
  – Obligate symbiosis – essential for fungus survival
  – Facultative symbiosis – nonessential (fungus can survive without the partner)
• Three kinds of Interactions:
  – Pathogen (harm host : disease) or parasites –harm host : no disease
  – Commensal relationships benefit one partner but does not harm the other
  – Mutualistic relationships benefit both partners

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Question 25

Mycorrhizae

Answer 25

• Mutualistic relationships between fungi and plants
• Found on the roots of about 90% of all known vascular plant species
• Function as extensions of root system - Increase soil contact and absorption
  – allow plants to grow in the infertile soils
• Two principal types
  – Arbuscular mycorrhizae - Hyphae penetrate the root cell wall but not plant membranes
  – Ectomycorrhizae - Hyphae surround but do not penetrate the root cells (pine, oaks)

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Question 26

Animal mutual symbioses

Answer 26

• Ruminant animals host neocallimastigamycete fungi in their gut
  – Fungus degrades plant materials with high cellulose and lignin content
  – Host provides nutrient-rich environment
• Leaf-cutter ants have domesticated fungi which they keep in
  underground gardens
  Obligate symbiosis
  – Ants provide fungi with leaves
  – Fungi are food for the ants

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Question 27

Fungal Parasites

Answer 27

• Fungal species cause many diseases in plants
  – Among most harmful pests of living plants
  – Can also spoil harvested or stored food products
  – Secrete toxic substances in food
• Cause billions of dollars in agricultural losses
• In Plants - Fungi may secrete substances making food unpalatable,
  carcinogenic, or poisonous
• Aspergillus flavus – aflatoxin
• Ustilago maydis – edible corn smut (not harmful to animals)
• In animals - difficult to treat (close phylogenetic relationship with animals)
  – Candida – thrush; vaginal infections
  – Pneumocystis jiroveci – pneumonia in AIDS
  – Ringworm, thrush, athlete’s foot, and nail fungus

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