Ch.23

Question 1

Land Plants (part of Kingdom Plantae) General Characteristics:

Answer 1

• Land-dwelling (terrestrial)
– some have returned to aquatic (freshwater) habitats
• Eukaryotes
• Multicellular
• Sessile
• Photosynthetic (photoautotrophs)
• Cell walls made of cellulose
• Alternation of generations

•exceptions are ghost and corpse plants.
— lack chloroplasts therefore are parasitic.

• Charophytes and land plants
share a common ancestor
—most likely lived in aquatic environments.

•embryophytes and charophytes are sister clades.

• N.B. today’s Charophytes have also changed from ancestor

Question 2

Main groups

Answer 2

1. Non-vascular plants (e.g., mosses)
   Vascular plants:
2. Seedless vascular plants (e.g., ferns) Seed plants:
3. Gymnosperms (e.g., conifers, pines)
4. Angiosperms (flowering plants)

Question 3

Evolution of Land Plants

Answer 3

Ancestral green alga —> 1. Origin of plants (about 470 Mya) (non vascular plants = bryophytes) —> 2. Origin of vascular plants (about 425 Mya) —> 3. Origin of seed plants (about 360 Mya)

Non vascular plants:
— liverworts
—mosses
—hornworts

Vascular plants:
Seedless:
— lycophytes (club mosses, spikemosses, quillworts)
— monikphytes (ferns, horsetails, whisk ferns)
Seed plants:
—gymnosperms
—Angiosperms

• After 1. Able to adapt to shallow waters, still need moist environments.

• colonizations first most likely from cyanobacteria or fungi

•plants are hard to preserve

• when we find fossils they have already colonized the land, so it means they were there before we were able to find them, just hadn’t colonized it yet.

Early land plants

•most likely poikilohydric = able to shut down metabolic rate and vital functions = dormant state.
-do this when there is no water available.
- can do this for a very long time
-considered a primitive state as this was most likely beneficial when plants 1st colonized land

Evolutionary trend in land plants

Baryophytes —> seedless vascular plants —> Gymnosperms —> angiosperms

B: sporophytes (2n), gametophytes (n)

Same for seedless ^

G: sporophyte (2n) —> Microscopic male gametophytes (n) inside pollen cone —> microscopic female gametophytes (n) inside ovulate cone.

A: sporophyte (2n), Microscopic male gametophytes (n) inside parts of flower, microscopic female gametophytes (n) inside different part of flower.

From B—> A
• gametophytes become smaller and less important.

Ancestral green algae (Charophycean algae) —> zygote becomes a multicellular sporophyte that is nutritionally dependent on gametophyte (bryophytes) —> sporophyte becomes free living (not dependent on gametophyte) and fully autotrophic —> transpiration initiated with stomata change (Rhyine chert fossils) —> gametophyte passes through subterranean phase (now dependent on sporophytes) (living vascular plants)

Question 4

Mycorrhizae = fungi + plant

Answer 4

• Confirmed fossil evidence of mycorrhizae from approximately 450 Mya

• Possibly much older than that!

Question 5

Benefits of Terrestriality?
Challenges of Terrestriality?

Answer 5

• More sunlight
• More nutrients
• More CO2
• Less competition
• Fewer predators
• Fewer parasites/diseases

• Less water
•Lack support
• UV
• Changing conditions
• Reproduction

Question 6

Growing upright and away from competition

Answer 6

• Problem: Tissues need to withstand the force of gravity
→ Solution: lignin
-also needed to support water transportation in tissue.

• Problem: Plant needs to transport water in its tissues
→ Solution: Tissues adapted for transporting water

Question 7

A Series of Evolutionary Innovations Allowed Plants to Adapt to Life on Land

Answer 7

• Sporopollenin
• Cuticle,pores
• Stomata
• Embryophytes
• VascularTissue
• Roots
• True Leaves
• Alternation of generations

Question 8

Characteristics of land plants:
Sporopollenin Spores

Answer 8

Sporopollenin Spores – unique among Land Plants

1. Sporopollenin - tough polymer
   • in Charophytes: protects zygote from drying
   • in Plants: walls of plant spores
   • resistant to drying and physical stresses
   • ancestral charophytes with this trait favoured by natural selection – how?
   — b/c they were able to have a greater success in reproduction and handle the selective pressure better.

Question 9

Characteristics of land plants
2. Adaptations for water conservation

Answer 9

• waxy cuticle on epidermis: waterproofing, protection from microbial attack

• stomata (sing., stoma): pores in the epidermis of leaves and other photosynthetic organs
– allow gas exchange between air and leaf interior
– sites for water to exit via evaporation
– closed stomata: minimize water loss
— if mainly closed = dry environment
— if mainly open = moist environment

• stoma open or closed based on presents of water and helps prevent water loss.

Question 10

Characteristics of land plants
3. Multicellular, dependent embryos

Answer 10

• In contrast to most green algae, zygotes of land plants are retained within tissues of the female parent
• Parent provides nutrients, embryo has specialized placental cells (transfer nutrients)

Why is this important for terrestrial survival?
• The group’s formal name is Embryophyta, literally, the
“embryo-plants”
• The retention of the fertilized egg in embryophytes is analogous to pregnancy in mammals

Question 11

Characteristics of land plants
4. Lignified vascular tissue for internal transport

Answer 11

• Contain lignin (a complex polymer), which strengthens

• Xylem cells carry water and minerals up from roots
– Dead wall act as microscopic water pipes
— key in transportation of water. The minerals are in the water.

• Phloem cells distribute organic products
– Living cells
— supports the sugars and amino acids.
— photosynthesis —> support sugar —> important b/c plants use sugar for vital functions. But also make enough for other organisms, hence why so many are dependent on plants.

Question 12

Characteristics of land plants
5. Resources more compartmentalized

Answer 12

• most plants show structural specialization for searching for water & minerals underground (roots) and light and gases aboveground (shoots)
– Note: early land plants did not have roots (that’s why they), relied on symbiotic relationships with mycorrhizal fungi (which helped plants colonize land)
— without fungi, wouldn’t have been able to colonize land.
• elongation and branching maximizes root and shoot exposure to environmental resources —> apical meristems

Question 13

Apical Meristems

Answer 13

• Undifferentiated tissue (localized) from which new, differentiated cells arise.
– Simple in non-vascular plants
– More complex structures
at tips of shoots and roots in vascular plants

• Cellsproducedby meristems differentiate into various tissues, including epidermis and internal tissues. And later on roots of plants

Question 14

Characteristics of land plants:
6. Alternation of generations

Answer 14

• Alternation of Haploid (n) multicellular and diploid (2n) multicellular body forms alternate
—spores do not make gametes
— sporophytes are in gametophytes

Gametophytes make gametes through mitosis (n) —Gametes—> fertilization —zygote (2n)—> mitosis (2n) —> diploid multicellular organism (sporophyte) (2n) —sporophytes make spores through meiosis (2n) —meiosis—> spores (n) —mitosis (n)—> haploid multicellular organism (gametophyte) (n) —mitosis—> gametophytes make gametes through mitosis (n) —> and so on.

• All land plants undergo alternation of generations

• Why is alternation of generations an important adaptation?

• Mitosis before meiosis!!

• Delayed Meiosis = many copies through mitosis before making spores

• Amplification, which is good for harsh conditions of land (more spores, more survive)

Differences in alternation of generations
(Deals with increased adaptation to land)

• Bryophytes (mosses) are gametophyte dominant

• Ferns, gymnosperms, angiosperms are sporophyte dominant.

Question 15

Dispersal

Answer 15

• b/c they can’t move (sessile) must find another way to reproduce it become fertilized.

Ex:
• Malpe tree seeds
• palm seedling
• seeds in poop
• seeds on animals
• mymecochory (like an ant grasping elaiosine(a seed))

Question 16

Evolutionary History of Land Plants

Question 17

Adaptive Radiation: Angiosperms

Answer 17

• An adaptive radiation occurs when a single lineage produces a large number of descendant species that are adapted to a wide variety of habitats

• Angiosperms represent one of the great adaptive radiations in the history of life

Question 18

Decreasing dependence on water

Answer 18

Moist habitats
|
V
Non-vascular plants lack complex conducting tissues found in vascular plants
|
V
Dry habitats

Question 19

Bryophytes (= Nonvascular plants)

Answer 19

• Not a monophyletic group
• Dotted lines indicate uncertainty of relationships of the phyla

Characteristics of Bryophytes
• Lack true vascular tissue (no lignin)
– limits their size

• Most tissues only one or a few cells thick

• Haploid (1n) gametophytes are the most conspicuous, dominant phase of the life cycle – diploid (2n) sporophytes smaller & dependent
– diploid present only part of the time

• Often entire plants are either male or female
- sperm swim through water film to fertilize eggs
- Must live in moist places
- Not yet fully terrestrial
➢ Parallels with animals?
— amphibians

Question 20

Bryophyte Life Cycle

Answer 20

Key steps:
1. Spore dispersal
2. Gametophyte germination
3. Gamete production (fertilization)
4. Sporophyte generation
5. Sporangium development
6. Spore production and dispersal
→ New gametophyte is produced, and cycle starts again!

Question 21

To clarify:
Gametophyte-dominant vs. Sporophyte-dominant

Answer 21

✓Gametophyte-dominant: (ex. fern)
— also considered gametophyte-independent

• gametophyte stage is the dominant and independent stage of the life cycle;
sporophyte stage is reduced and nutritionally dependent on the gametophyte

• gametophyte stage can carry out all of the necessary functions to sustain the organism, including photosynthesis, nutrient uptake, and reproduction

✓Sporophyte-dominant: (ex. flowering plants/angiosperms)
— also considered sporophyte-dependent

• sporophyte stage is the dominant and independent stage of the life cycle

• gametophyte stage is relatively small and dependent on the sporophyte for nutrients and protection

Question 22

Origin of Vascular Plants

Answer 22

• Bryophytes probably Earth’s only plants for first 100 million years

• Aglaophyton (~425 MYA) first plant to have sporophytes not continuously nutritionally dependent on gametophytes (a feature of vascular
plants)
– did not have leaves or roots – no vascular tissue… yet

• Fossils of other simple plants from early Devonian show evidence of vascular tissue in the stem

• Later came leaves, and then roots

Characteristics of vascular plants
• Complex multicellular roots
– absorb nutrients, provide anchor
• Complex multicellular leaves
– photosynthetic organs
• Microphylls: single strand of vascular tissue, usually small
- no leaf gap, single vein on leaf
• Megaphylls: branching vascular system, usually large
- leaf gap, branching veins on leaf

Vascular plants
• Sporophylls
– Modified leaves that bear sporangia (spore-producing organ)
– sporangia + sporopollenin walls→terrestrial adaptation!

• Sporophyte dominant in life cycle
– increased size, complexity and persistence
– not continuously nutritionally dependent on gametophyte

Characteristics of Seedless Vascular Plants
• Sporophyte–dominant form

• Gametophytes: tiny independent plantson or just below soil surface

• Flagellated sperm: must swim in a film of water to reach eggs
– Similar to bryophytes, seedless vascular plants most common in relatively damp habitats
– Still need water to reproduce

Question 23

Fern life cycle

Answer 23

Key steps:
1. Spore Production
2. Spore Dispersal
3. Gametophyte
Formation
4. Gamete
Production
5. Fertilization
6. Sporophyte
Development
7. Sporangia Formation → Then Spore
Production again

Question 24

Seed plants

Answer 24

Seed Plants Shared features:

• seeds!

• heterospory (microspores/male and megaspores/female = no flagellated spores)

• Pollen(non- swimming sperm)

• sporophyte independent

• gametophyte dependent

Main Clades of Seed Plants
• Gymnosperms
✓Gymnos = naked, sperm = seed

• Angiosperms
✓Angio = container, vesse

• Seeds changed the course of plant evolution

• Seed-bearing plants are the dominant producers in most terrestrial ecosystems
— which makes it really successful on land

• A seed consists of an embryo and nutrients surrounded by a protective coat

• Domestication of seed plants had begun by 8,000 years ago and allowed for permanent settlements

Question 25

Evolution of Seed (Vascular) Plants

Answer 25

• Non-vascular Bryophytes: gametophyte dominant, sporophyte dependent

• Seedless vascular plants: sporophyte dominant, but gametophyte
independent

• Seed plants have sporophyte dominant and gametophyte dependent

The Evolutionary Advantage of Seeds
• Seeds provide some evolutionary advantages over spores:
– They may remain dormant for days to years, until conditions are favourable for germination
– Seeds have a supply of stored food
– They may be transported long distances by wind or animals (dispersal)

Question 26

Gymnosperms

Answer 26

• Characterized by seed that is relatively ‘naked’

• 1st to appear in fossil record

• ovule and seed develops on surface of sporophylls

• sporophylls normally in cones (strobila)

• 4 extant phyla:
– Ginkgophyta: 1 living species
– Gnetophyta: ~ 70 spp.
– Cycadophyta: ~130 spp.
– Coniferophyta: ~ 600 spp.

Angio = ‘vessel’
Gymno = ‘naked’

Gymnosperm Evolution

Question 27

Gymnosperm Life Cycle (ex. white pine)

Answer 27

Key steps:
1. Germination
2. Pollination
3. Fertilization
4. Seed (embryo) development
5. Seed dispersal
→ Germination again
Note: these numbers don’t match exactly the number in the textbook!

Question 28

Angiosperms - “Flowering Plants”

Answer 28

• Produce flowers, fruit and seeds

• Seeds contained within fruit

Evolution of Angiosperms
• Gymnosperms dominant seed plants until middle Mesozoic (~140 MYA), when angiosperms appear in the fossil record.

• Huge radiation of angiosperms, and decline of many gymnosperm groups in the Cretaceous.

Angiosperm Phylogeny
• Angiosperms/Gymnosperms likely diverged~300MYA

• Angiosperms related to Bennettitales
– extinct woody seed plants with flowerlike structures

The Angiosperm Radiation
• The diversification of angiosperms is associated with three key adaptations:
1. Water-conducting vessels
2. Flowers
3. Fruits
• These adaptations allow angiosperms to transport water, pollen, and seeds efficiently.

Question 29

Angiosperm Life Cycle
(any flowering plant)

Answer 29

Key steps:
1. Germination
2. Vegetative growth
3. Reproductive growth
4. Pollination
5. Fertilization
6. Seed (embryo) development
7. Seed dispersal
→ Germination again
Note: these numbers don’t match exactly the number in the textbook!

Question 30

Fruit

Answer 30

• Mature ovary containing seeds
✓the ‘container’ part of angiosperm
✓mature ovary may look different

• Fruit protects dormant seed & aids dispersal
✓by catching wind
✓by catching/attracting animals

Question 31

Flower

Answer 31

Sporophylls:

Non-reproductive: sepals, petals

Reproductive:
• Stamens (microsporophylls):
anther + filament
— anthers→ microspores→ gametophyte→ sperm (within pollen grain)

• Carpels (megasporophylls):
stigma + style + ovary
— ovule→ megaspore → gametophyte → egg

• Usually many stamens per flower

• 1 or more carpel (may be fused)

• Ovary contains 1 or more ovules

Question 32

Nuts

Answer 32

• Nuts are fruits, but not all nuts are really nuts

• Nut = is a fruit that is filled with typically only one seed, that also has a hard outer shell that typically doesn’t split, or fall off, when the nut ripens.

• Fruit = the distinctive mature ovary of any flower, plant, or tree, that contains seeds.

Question 33

Seed and Fruit
Dispersal

Answer 33

• Most gymnosperms rely on wind for pollination, as do some
angiosperms…but
— 80% angiosperm species rely on animals for pollination

•Flowers with Different Scents, Shapes, and Colours Attract Different Pollinators

Question 34

Pollination

Answer 34

• Biotic:pollination by animals – Insects
– Birds
– Bats, other mammals
• Abiotic
– Wind pollination – Water pollination
• Self-pollination

Question 35

“Co-evolution” between plants and pollinators

Answer 35

• Mutual evolutionary influence between two species. Each of the species involved exerts selective pressure on the other, so they evolve together (co-evolve).

Mutualistic relationship:
• The plant spends less energy on pollen production and instead produces showy flowers, nectar, and/or odors.

• The pollinator gets pollen/nectar as a reward for “helping” to pollinate the plant.

Question 36

KEY CONCEPTS
Plant Diversity: How Plants Colonized Land

Answer 36

• Land plants evolved from green algae (specifically Charophytes)

• Innovations allowed plants to colonize land
─ sporopollenin, multicellular, nourished embryo, vascular tissues, etc.

• Mosses and other nonvascular plants have life cycles dominated by gametophytes

• Ferns and other seedless vascular plants were the first plants to grow tall ̶ had well developed roots and leaves

Question 37

KEY CONCEPTS
Seedless Vascular plants

Answer 37

• Had well-developed roots and leaves

• In contrast to bryophytes, seedless vascular plants have life cycles
dominated by free-living sporophytes

• A change in environment at end of Carboniferous reduced moisture leading to seed plants evolving.

Question 38

KEY CONCEPTS
The Evolution of Seed Plants

Answer 38

• Seeds and pollen grains are key adaptations for life on land

• Gymnosperms bear “naked” seeds typically on cones

• Angiosperms have seeds encased in “fruit”

Question 39

KEY CONCEPTS
The Evolution of Seed Plants

Answer 39

• Angiosperms have seeds encased in “fruit”

• Fertilization occurs twice = double fertilization (once for embryo and
once for endosperm)
– hence no resources are wasted if egg is unfertilized

• Pollination is mainly by animals vs. gymnosperms which are wind pollinated

• Co-evolution occurs between plant and pollinators

Question 40

Plasmogamy and karyogamy

Answer 40

Plasmogamy is the fusion of two cells such that they share a common cytoplasm but keep the two original nuclei separate. It results in a cell that has two distinct nuclei, also called a dikaryon, with ploidy of n + n.

Karyogamy is the fusion of the two nuclei; when this occurs, the cell ceases being an n + n dikaryon and instead becomes a true 2n diploid cell.