MY SO: PLANTS!Division B+C Presentation

● Div B and C ○ Origins and basic photosynthesis○ Evolution & diversity of plants○ Phylogenetics○ Different plant groups○ Plant ecology○ Additional topics from the Botany trial event

● Div C only (slides with yellow background)○ More complex understanding of photosynthesis○ Alternation of generations for land plant reproduction○ Angiosperm life cycle

Topics covered

Plants are eukaryotes which means they have membrane-bound organelles

All plants have chloroplasts (organelles which are essential to photosynthesis) that contain chlorophyll a (only some plants produce chlorophyll b)

Chloroplasts originated from photosynthetic cyanobacteria (aka blue-green algae)

Ancestral plants gained chloroplasts by engulfing cyanobacteria through endosymbiosis

Origin of Plants

Plant CellsCan you identify which organelles are unique to plant cells and are not found in animal cells?

Answer: plastids/chloroplasts, plasmodesmata, cell wall, central vacuole

Author: Kevinsong Source: Wikimedia Commons

Endosymbiosis of ChloroplastsChloroplasts have an extra membrane resulting from infolding of the host cell membrane

Chloroplasts in basal plants (glaucophytes) have peptidoglycan in the membrane which is normally found in bacterial membranes

Green from pigments chlorophyll a & b

These pigments absorb light energy during photosynthesis

Thylakoids houses chlorophyll and important membrane proteins which facilitate photosynthesis

Structure of a Chloroplast

Author: Kelvinsong Source: Wikimedia Commons

Sunlight excites electrons in chlorophyll setting off a chain of chemical reactions called the light reactions followed which convert the sunlight into chemical energy in ATP (adenosine triphosphate).

In the Calvin Cycle (aka the light-independent or dark reactions), carbon dioxide and water are assimilated into organic sugars.

Photosynthesis

Author: CNX OpenStax Source: Wikimedia Commons

Author: CNX OpenStaxSource: Wikimedia Commons

Try to trace the path of electrons throughout the light reactions and see the importance of ATP and NADPH

More Detailed Photosynthesis

Author: CNX OpenStax Source: Wikimedia Commons

Ancestral characteristics (or basal): the same or very similar to the traits held by an ancestor

Derived state: a form of the characteristic which we think arose along the lineage from that ancestor to the present

All living taxa are equally evolved as all organisms have been evolving for the same amount of time since the beginning of life on earth

An organism that is considered basal is not less evolved, but rather more closely resembles its ancestors than other “derived” forms

Terms like “primitive” or “living fossil” give the false impression of being “less evolved” than other organisms

Intro to Phylogenetics

Phylogenetic trees (or cladograms) display evolutionary relationships

Branching points or “nodes” represent common ancestors of living taxa

More closely related organisms have more recent common ancestors

Synapomorphies are derived characteristics which are shared by a group of organisms to the exclusion of all others

All phylogenetic trees are hypotheses; it is impossible to know for sure how evolutionary history played out, but fossils, present morphology, and genetic data provide supporting evidence

Intro to Phylogenetics

A polytomy is an unresolved evolutionary relationship represented by more than two branches extending from the same node

Reading a Phylogenetic Tree

A

B

C

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polytony

rootE

D

C

B

A

living taxa

most recent common ancestor of all species

node at branch point

most recent common ancestor of C and D

branches

Reading a phylogenetic tree

A B C D E

E

D

C

B

A

=

A

B

C

D

E

C

B

E

D

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=

same tree, two different styles

same tree, just different order because the branches have been swiveled around the nodes

Monophyletic clade: The most recent common ancestor of a group of organisms AND all of its descendents

Polyphyletic clade: A group of organisms missing the most recent common ancestor and some of its descendents

Paraphyletic clade: A group containing the most recent common ancestor and some, but not all of its descendents

See primate example to the right:

Reading a Phylogenetic Tree

Author: Petter BøckmanSource: Wikimedia Commons

Green boxes around groups of plants

Blue marker labeled with synapomorphies

Note polytomy for hornworts, liverworts, and mosses

Plant Phylogenetic Tree

Most basal plants (retain most ancestral characteristics)

Unicellular

Found in freshwater

Only asexual reproduction

Retain peptidoglycan in chloroplast membrane

Rare

Glaucophytes

Author: James TranSource: Wikimedia Commons

Most basal multicellular plants, some unicellular

Found in marine environments

Found deeper than other algae - red pigment allows them to photosynthesize short-wave light

Produce more chlorophyll a when found near the surface, causing greener pigment

Seaweed in sushi (nori)

Also used to produce agar

Red Algae

Author: Johnmartindavies Source: Wikimedia Commons

Author: Lily_M Source: Wikimedia Commons

Author: Danaimage Source: Wikimedia Commons

Includes green algae plus all land plants

Synapomorphies:

Produce additional pigment: chlorophyll b

Chlorophyll b absorbs slightly different wavelengths from chlorophyll a; most strongly absorbs blue light

Store starch inside their chloroplasts

Green Plants

Author: Daniele PugliesiSource: Wikimedia Commons

Put in quotations because green algae is truly comprised of multiple groups, but you don’t need to know them

Sister group to all land plants (shares more recent common ancestor with land plants than any other group)

Might provide clues as to what the ancestor of land plants looked like

Can be unicellular or multicellular

“Green Algae”

Author: MicropicsSource: Wikimedia Commons

Author: W.carterSource: Wikimedia Commons

Living on land presented the following challenges for ancestral aquatic plants:

● Desiccation (drying out)● Need for physical support (no longer suspended in water)● Movement and transport of fluids and nutrients● Protection of gametes/embryos● Increased UV radiation

Plants had to evolve several adaptations to be able to survive on land

Land Plants

Synapomorphies of land plants

● Protected Embryo ○ Helped plants disperse on land rather than in

the water

● Waxy cuticle with stomata○ Reduced water loss and potential for drying

out○ Stomata are holes in the cuticle which can

open/close to allow air flow

Early land plants were small and short so that water and nutrients didn’t have to flow far against gravity

Characteristics of early land plants

Author: ReiSource: Wikimedia Commons

Chromosomes: organized package of genetic information in the form of DNA found in the cell nucleus

Gametes: sex cells with only one set of chromosomes (haploid), as opposed to cells with two sets of chromosomes (diploid)

Mitosis: division of cells resulting in two daughter cells genetically identical to the original cell

Meiosis: production of sex cells by dividing a single cell twice, creating 4 genetically different haploid cells

Alternation of Generations

All land plants undergo the alternation of generations

Plants alternate between the sporophyte and gametophyte generation

Sporophyte generation

● Diploid stage (2n = two sets of chromosomes)● Produces spores (2n)

Gametophyte generation

● Haploid stage (n = one set of chromosomes)● Produces gametes (n)

Alternation of Generations

Alternation of Generations

Author: CNX OpenStaxSource: Wikimedia Commons

Both the gametophyte and the sporophyte are multicellular and can be free-living organisms

Often, the two life stages look very different from one another

Different plants may have sporophyte or gametophyte dominated life-cycles such that they spend most of the time in one form or the other

Alternation of Generations

Author: RoRo Source: Wikimedia Commons

Non-vascular plants were the first to colonize land

Hornworts, liverworts, and mosses

Gametophyte-dominant life cycle

Low-growing, found in moist areas

Dependent on water for fertilization

Non-Vascular Plants

Author: Lairich RigSource: Wikimedia Commons

Author: Jason HollingerSource: Wikimedia Commons

Lack stomata (pores that can open and close for gas and water exchange)

Have stoma (pores that always remain open) instead

Liverworts

Author: Eric GuintherSource: Wikimedia Commons

Larger and more complex than liverworts

Have stomata (and all plants hereafter)

Possess fluid-transport system, but not truly vascular

Very diverse

MossesAuthor: Ali ZifanSource: Wikimedia Commons

Author: Yana SemenenkoSource: Wikimedia Commons

Less diverse than liverworts and mosses

Sporophytes have indeterminate growth and can become dominant generation

Hornworts

Author: Peter WoodardSource: Wikimedia Commons

Transition to more sporophyte dominance as plants become more complex

Includes lycophytes, ferns, and seed plants

Vasculature allows these land plants to grow larger and more complex as they are able to pump water throughout their tissues against the pull of gravity

Vascular Plants

Xylem and phloem are vascular plant tissues responsible for transport of nutrients and water throughout the plant

Xylem carries water up from the roots against the flow of gravity to the leaves where it is needed for photosynthesis

Phloem carries nutrients from the leaves around the plant and down to the roots where it is needed

Xylem & Phloem

Author: Nefronus Source: Wikimedia Commons

Microphylls (simple leaves with single vein)- all other vascular plants have megaphylls (complex leaves)

Spore-producing structures on upper surface of leaf

Wind-pollinated and dispersed

Male spores much smaller than female spores

Huge size, dominant vegetation in Carboniferous periods (about 300-350 million years ago)

Lycophytes

Source: Sam Noble Museum

Author: homeredwardpriceSource: Wikimedia Commons

One of the most diverse lineages of vascular plants

Occupy very diverse array of habitats including deserts and tundra

Fern spores located on bottom of leaves (complex, megaphyll leaves)

Spores dispersed by air; gametes dispersed by water

Ferns

Author: Sanjay ach

Source: Wikimedia Commons

Author: kaibara87

Source: Wikimedia Commons

Gymnosperms (naked seed) and angiosperms (flowering plants)

Represent most of plant diversity

Seeds are a key innovation

Sporophyte dominant generation

Gametophyte is not free-living or photosynthetic

Separate male and female gametophytes

Seed Plants (Spermatophytes)

Female spores produce the female gametophyte which produces the female gamete (egg)

The egg never leaves the spore wall; this structure is called the ovule

Male spores produce the male gametophyte; pollen is the male spore wall with the gametophyte growing inside

The pollen will land on the ovule and the male gametophyte (pollen tube) will burst through the spore wall, grow toward the egg, and eventually produce sperm to fertilize the egg

The fertilized egg is called an embryo; the fertilized ovule containing an embryo is called the seed

Seed Plant Life Cycle

Called “naked seeds” because the seed is exposed

Huge diversity of form and habitats

Includes conifers (like pines, spruces, junipers, etc), ginkgos, cycads, and gnetales

Gymnosperms

Author: Wendy Cutler Source: Wikimedia Commons

Author: James St. John Source: Wikimedia Commons Author: Rhododendrites Source: Wikimedia Commons

Synapomorphies: Flowers, seed enclosed by fruit, double fertilization

In double fertilization, one sperm fertilizes the egg, and another sperm fuses with two polar nuclei to form the endosperm

The endosperm is tissue inside the seed which provides nutrients to the developing embryo

Dominant group of plants on earth

Angiosperms

Source: pixabay

Flowers first evolved around 150 million years ago

Stamen: male reproductive parts

Male spores produced in the anther

Pistil (or carpel): female reproductive organs

Female spores produced in the ovary

Parts of a Flower

Author: Anjubaba Source: Wikimedia Commons

Angiosperm Life Cycle

Author: Sarah Greenwood Source: Wikimedia Commons

Unlike gymnosperms, seeds are “enclosed” and mature within the ovule deep inside the ovary

The ovary matures and ripens into what we call fruit

Because plants are autotrophic (they make their own food) producers, they form the base of ecosystem food webs

Impacts on plant species (like disease, pollution, invasive species etc) can cause trophic cascades in which consumers throughout the food chain are impacted (bottom-up cascade)

Plants As Producers

Author: Suwachanee Maneeratanachot Source: Wikimedia Commons

Top-down cascades can also occur in which impacts on organisms higher up in the food web (normally apex predators) cascade down to the other organisms

The example on the right shows a top-down cascade in which the population size of the apex predator (a wolf in this case) has cascading impacts

When there are few wolves, there are many deer due to predator release which reduces the population of primary producers

A bottom-up cascade using this web might happen if primary producers at the bottom level greatly reduce in number

This will result in consumers at level 2 reducing, and organisms at the top level will also decrease

Trophic Cascade Example

Author: ZirgueziSource: Wikimedia Commons

Plants occur on earth’s surface depending largely on the climate

Distribution of plant Communities

Author: Sten PorseSource: Wikimedia Commons

The two main drivers determining plant community composition are precipitation and temperature

Plants then determine what consumers can inhabit an ecosystem

Know the distribution of biomes on the right!

Plant Biomes

Author: NavarrasSource: Wikimedia Commons

In primary succession, bare rock is slowly colonized beginning with lichens and small plants (pioneer species) which break down the rock into soil, followed by grasses and small herbaceous plants, then intermediate species like small trees and shrubs followed finally by the climax community.

Secondary succession occurs when soil is already present, but other plant species have been removed, like after a fire.

Climax communities are different in each biome. For example, in a temperate deciduous forest, large hardwood trees would comprise the climax community whereas in northern boreal forests, large conifers would be the climax community.

Succession

Examples of different taxonomic plant groups (especially angiosperms)

Plant cell structure & function of different organelles

Plant genetics and reproduction

The process of photosynthesis (in detail for div C)

The names of land plant structures & their function (e.g. meristem, roots, leaf layers, etc)

Plant interactions with other organisms (pollination, competition, consumption)

Topics from the Botany trial event: history of botany, GMOs, plant diseases

Things to Know

Special thanks to Science Olympiad at Cornell for the development of this resource.