Unifying Themes in Plants Flashcards
What is a plant?
Ambiguous definition!
Can be defined in 2 ways:
Traditional way: define by characters
Evolutionary history: requires evolution of life
Domains of life
Eukarya
Archaea
Bacteria
Eukarya
Uni/multicellular
Linear DNA
Replicate by mitosis
With organelles
Bacteria & Archaea
Unicellular
Circular DNA
Replicate by fission
Lack organelles
How did chloroplast evolve?
Endosymbiosis:
Engulfment & retention of cyanobacteria
Became transformed
Retain own DNA
Ability to replicate
No ability to live independently
Endosymbiosis:
Evidence:
Plastid circular DNA
70S ribosome
Replicate by fission
All prokaryotic by nature!
Primary & Secondary Endosymbiosis
Primary - Engulfment of photosynthetic bacterium (prokaryote) by an eukaryotic cell
Secondary - Engulfment of photosynthetic eukaryote by another eukaryotic cell
Chlorobionta
Green algae + Embryophytes (land plants)
Land plants
Monophyletic; common to lay people
Evolutionary novelties:
Outer cuticle
Specialized gametangia w/ protective layer of sterile cells
Sporophyte = embryo
Bryophytes
Polyphyletic group
Shared characters:
Small organisms
Without lignin
Gametophyte = dominant phase
Sporophyte = embryo, very reduced (in size and time)
Ferns
Polyphyletic group
Shared characters:
Tracheid = vessel element with lignin
Spores
Lateral branching + roots
Secondary components
Gymnosperms
Monophyletic
Evolutionary novelties:
“naked seed”
Wood (sporophyte)
Gametophyte totally dependent from the sporophyte
Heterospory
Pollen grain
Angiosperms
Monophyletic
Evolutionary novelties:
“hidden seed” = Flower
Specialized leaf tissues
Specialized pollen
Cambium
APG IV (2016)
Comprehensive phylogeny of every family of flowering plants
Common Concepts in Plants
They have multiple pigments with multiple functions
Plants use water & its properties
Plants use anabolic metabolism
Plants have cell wall that performs variety of functions
Plant life cycle alternates between gametophyte (n) and sporophyte (2n)
Meristematic activity continues throughout plant’s lifetime
Plant organs are initially up of 3 tissues
Plant body consists of 4 organs (angiosperms)
Fruits disperse seeds through space; Dormancy disperses seeds through time.
Many plants and animals have coevolved
Understanding plant structure requires a sense of scale
“Primary” and “secondary” are important concepts in plant anatomy
“Plant” can be broadly defined
They have multiple pigments with multiple functions
Chlorophyll - Photosynthesis
Anthocyanins - Guide pollinators
Carotenoids - Attract fruits dispersers
Phytochrome - Protection against UV
Cryptochrome - Track the time of the day; season of the year
Pigments are visual signals for attraction;
They are responsible for the bright colors of various plants, fruits, flowers, and vegetables.
Plants use water & its properties
Since plants are devoid of muscles, they have evolved to take advantages of the physical properties of water & laws of physics to generate force that drives movement
The structures and design of the water-conducting cells of xylem control water movement
Plants use hydraulics: Roots split rocks & crack concrete sidewalks
Insectivorous plants close their traps by rapid water movements
Plants use anabolic metabolism
Plants are photoautotrophic
They manufacture every molecule needed for growth & produce virtually no waste!
For protection, plant evolved to have biosynthetic pathways that synthesize lots of toxic compounds
While plants grow & develop, they produce minimal toxic wastes!
Plants have cell wall that performs variety of functions
Plants possess a non-living but biologically active cell wall ~ made up of cellulose
Functions:
Enclose the protoplasm of the cell
Site of active cell secretion
Plant life cycle alternates between gametophyte (n) and sporophyte (2n)
Plant life cycle: sporic (meiosis produces spores; mitosis produces gametes)
Protist : zygotic
Animals: gametic
Meristematic activity continues throughout plant’s lifetime
There is continuous growth in the life of plant (vs. animals which have a set size and form that once reached is not exceeded)
Even the oldest tree have newly formed tissues every year.
Types of growth in plants:
Primary growth - increase in length
Secondary growth - increase in diameter
Plant organs are initially made up of 3 tissues
Dermal
Vascular
Ground tissue
Plant body consists of 4 organs (angiosperms)
During the approximately 475 millions years of land evolution, there have been significant diversification of plant species and modifications of plant body.
The 4 angiosperm organs: roots, stems, leaves, flowers.
Fruits disperse seeds throughs pace; Dormancy disperses seeds through time.
Animals - mobile; plants - sessile;
Plants must disperse too!
In angiosperms, this is the role of fruits
Fruit it the unit of seed dispersal.
Unlike animals, plant embryo can stay dormant for extended period of time, allowing dispersal of the next generation through time.
Many plants and animals have coevolved
Many plant families have intricate reproductive strategies that have coevolved with animals
Plant rewards: food, shelter, ovipositories;
Animals in return aid in pollination & seed dispersal.
Understanding plant structure requires a sense of scale
Structures of interest to plant anatomists range in size over 10-11 orders of magnitude
“Primary” and “secondary” are important concepts in plant anatomy
Primary & Secondary Growth
Primary & Secondary Xylem & Phloem
Primary & Secondary Cell Wall
“Plant” can be broadly defined
Eukaryotic, photosynthetic organisms
Opinions vary among scientists, but using the broad definition, the major groups of green plants are:
Green algae
Bryophytes
Fern and fern allies
Gymnosperms
Angiosperms
Why Study Plants?
Photosynthesis change the Earth in 2 ways:
Altered the Earth’s atmosphere;
Compounds produced in the process are utilized directly or indirectly by heterotrophic organisms
Importance to humans
