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Title: Plants
Description: These notes go over the diversity of plants and how they have evolved throughout time. These notes were taken for an introductory college biology course.
Description: These notes go over the diversity of plants and how they have evolved throughout time. These notes were taken for an introductory college biology course.
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Plants
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•
Plant characteristics
o Eukaryotic and multicellular
o Sessile (like fungi)
o Autotrophic and makes food via photosynthesis
o Sexual and asexual reproduction
o Most plants live on land
▪ Differentiates them from the protists
o First plants appeared around 475 mya and preceded land animals
▪ Able to change atmosphere from mostly CO2 to O2
Plants are divided into four lineages from four main adaptations
o Adaptation # 1: Embryonic protection
▪ Since plants no longer lived in water, had to prevent embryos from drying
out
▪ In all plants the embryo is retained and nourished in the female sexual
organ
• Provides protection from desiccation
• Differentiates plants from algae and seaweed
▪ The nonvascular plants (bryophytes) are the first plants to break from the
phylogeny
o Mosses, liverworts, hornworts, etc
o Probably most resembles the earliest land plants
o Relatively simple compared to other lineages, but still has embryo
protection
o Lack a vascular system and roots
• Must grow close to the ground in order to directly absorb water
and other nutrients
• Only a few centimeters tall because they cannot transport water
in the tissue very far
• Tend to go dormant during drought and not viable in
environments with limited water
o Adaptation #2: Vascular tissue
▪ Needed an effective way to transport water and nutrients in the plant
▪ Vascular tissue evolved
o More efficient transportation system of water and nutrients
o Allows taller plant growth and the ability to live in more diverse and
dry environments
o The vascular tissue structure
• Xylem: transports nutrients and water up
• Phloem: transports products of photosynthesis down
▪ Seedless vascular plants are next on the phylogeny
o Ferns, horsetails, whisk ferns
o Have vascular tissue and can grow taller than bryophytes
o Reproduce via spores
• Travel by wind, land, and produce a new organism
Plants
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•
Advantageous to be bigger, because spores blow farther
o Adaptation #3: Seeds
▪ Spores were pretty simple and limited reproduction
▪ Seeds evolved
o Embryo encased in a protective coat
o Provides food and helps growth for the new embryo
▪ Gymnosperms evolved thirdly
o Conifers, cycads, gnetophytes, etc all have seeds
o Naked seeds: produces seeds without fruit
o Dependent on wind for fertilization
o The biggest group are conifers --> cone bearing gymnosperms
• Cones produce sperm and eggs for reproduction
• Tallest and longest living trees
o Very diverse and found in many different environments
o Adaptation #4: Flowers
▪ Reproductive structures used to attract pollinators increased the chances of
reproduction
▪ Angiosperms were the plants that evolved with flowers
o Dominant plant species in the present day
o 250,000 species and the largest group of plants
o Most angiosperms depend on pollinators to carry pollen from one
individual to another
• Insects, birds, bats, some mammals, etc
▪ Flowers have female and male plant parts
o The stamen is the male, and the carpel is the female
o Pollination is achieved when pollen fertilizes the ovary
o Some flowers have both male and female parts and can self fertilize,
and others have just one part
Polyploidy in plants
o Polyploidy is also known as whole genome duplication
o Very rare in animals, and usually leads to developmental problems
o However, there is a different outcome in plants
▪ 1/2 to 2/3 of all angiosperms are polyploid
▪ There has been evidence for multiple polyploid events in some plant
lineages
▪ Plants have more flexible body plans than animals
o Makes it easier to tolerate biological consequences of polyploidy
▪ Some think that in plants, polyploidy might confer new adaptations on
plants
o Tolerance for different ecological conditions, etc
o However, there is no concrete evidence that proves this hypothesis
▪ Polyploidy actually seems to be a speciation mechanism
o Scientists agree that polyploidy confers some new traits to a plant,
effectively acting as a driver of speciation
Plants
•
•
•
Plant-pollinator coevolution
o Plants have become more effective at attracting specific pollinators
o Pollinators have become more effective at exploiting specific plant resources and
becoming better pollinators
o The features of the flower can often tell us about the type of animal that
pollinates it
o Fruits develop from the pollinated flowers
▪ The embryo will grow to become a fruit
o An embryo plus stored food inside a protective seed coat
▪ The wall of the ovary typically grows to form some kind of fruit
o Fruit structure can tell you a lot about its seed dispersal
▪ Spiny ones hitch rides on animals, feathery ones are carried by the wind,
fleshy fruits are eaten and the seeds come out in waste material from other
animals
▪ Animal dispersed seeds/fruits
o Are colorful and noticeable
o Taste good
o Are usually nutritious for the animal
o Fruits and flowers have benefitted angiosperms greatly
▪ Ability to use other organisms as pollinators makes reproduction much
more efficient
Angiosperms have a huge economic importance
o Domesticated for fruit and nonflowering, vegetative parts
Plant domestication
o Before agriculture, humans were nomadic hunters and gatherers
o Shift to agriculture took place gradually around 8-12k years ago
o Why the shift to agriculture?
▪ Changing climate
▪ Increase in population size
▪ Could have come around by accident from manure piles
o Domestication is a relationship between two species where one species exercises
substantial control over the other in terms of…
▪ Breeding (when they breed and with whom)
▪ Morphology (physical appearance)
▪ Genetic makeup
o The timeline of domestication of plants and animals matches the shift from the
hunter/gatherer lifestyle to agriculture
o What did early farmers want in plant crops?
▪ Increase in seed/fruit size
▪ Decrease in seed/fruit coat thickness
▪ Loss of seed dispersal mechanisms
▪ Annual plants: only live for one year, grow quickly, and produce seeds
quickly
Plants
▪
•
Self-compatible: can produce with itself, no need to use a pollinator, does
not produce with wild relatives
Ohio Plant Domestication
o Soybeans ($2
...
9 billion/yr)
▪ Wild relative is native to Mexico and Central America
o Teosinte has hard seeds and smaller ears than corn
▪ Used for starch, flour, and a source of carbs
▪ By 1500s spread throughout all of North and South America
▪ We are the 8th largest corn producer in the USA
o Wheat (147
...
4 million/yr)
▪ Wild species native to Mexico and Central and South America
▪ Probably domesticated after corn, in Mexico or the Andes
▪ Has relatives that are poisonous, so not accepted by the Europeans until
the 1800s
▪ Good source of vitamin C
▪ We are the 3rd largest tomato producer in the USA
o Apples ($20
...
9 million/yr)
o Grapes ($1
Title: Plants
Description: These notes go over the diversity of plants and how they have evolved throughout time. These notes were taken for an introductory college biology course.
Description: These notes go over the diversity of plants and how they have evolved throughout time. These notes were taken for an introductory college biology course.