Plants Flashcards
Plants
Domain Eukarya,
Kingdom Plantae
- multicellular eukaryotes
- well-developed tissues
- mostly terrestrial and sessile
- exhibit embryo protection
- Photoautotrophic
Plants: Major groups
Non-Vascular Plants (all are seedless)
Vascular Seedless Plants
Gymnosperms
Angiosperms
Present number of species of land plants
roughly 290,000 species
The earliest plants
Fossil spores from about 475 million years ago.
Tough-skinned spores provide excellent fossil records.
(Fungi fossils show 470 myo),
Plants: Life on Land (475 mya)
To adapt to life on land, plants evolved features that allow them to
- resist drying out (absorb and retain water)
- absorb nutrients
- stand upright without outside support
- reproduction not dependent on water
These features appeared over time
Key traits of land plants
- apical meristems
- tough, resistant spores from sporangia
- special organs for production of gametes
Plant Adaptations:
Embryo Protection
all plants nourish a multicellular embryo in the body of the female plant
- this feature distinguishes plants from green algae
first appeared in the non-vascular plants (the bryophytes)
Non-Vascular Plants (Bryophytes)
Simplest, most primitive plants
Lack roots and vascular tissue
- water and nutrients move by diffusion
- small in size
- dependent on water for reproduction
Ex: mosses, liverworts, hornworts
Earliest plants
mosses
Bryophytes
mosses (15,000 species)
liverworts (100)
hornworts (9,000)
Qualities of earliest plants
- have cuticle
- don’t have roots or true leaves (require moisture)
- are small
- today compose 7% of plant species
vascularity
93%
Plant Adaptations:
Vascular Tissue
Distinguishes vascular plants from non-vascular plants
Xylem transports water and minerals from roots upward
Phloem transports organic nutrients from photosynthesis downward
Xylem
transports water and minerals from roots upward.
Made of dead cells with rigid cell walls.
Provides the plant with structural support.
Phloem
transports organic nutrients (sugar) from photosynthesis downward from the leaves.
Made up of living cells with thinner cell walls.
Seedless Vascular Plants
Includes club mosses, ferns, horsetails, and whisk ferns.
The first to evolve vascular tissue to transport:
- water and inorganic nutrients from roots upwards (xylem)
- dissolved sugar the leaves downward (phloem)
- Are larger than bryophytes as a result
- Use spores for reproduction
wind-dispersed
Eariliest vascular plants (extant species numbers)
Lycophytes: (1,200 species)
Pterophytes: ferns 12,000 species (ferns) and horsetails 15 species
Horsetails: all in the genus Equisetum
Plant Adaptations:
Seeds
- Distinguishes plants with seeds from the seedless vascular plants
- Seed: an embryo and stored nutrients within a protective coat
Vascular Seed Plants (Gymnosperms)
- The first plants to evolve seeds; use seeds for dispersal rather than spores.
- Most are cone-bearing (conifers)
- “naked seeds”
- Do not need water to reproduce
- Do not produce flowers or fruit
Examples: conifers: pine, spruce, cycads, ginkos
160 mya, gymnosperms dominated forests
Very successful
- deserts to tundra
- sea level to tree line
- taller and older than any other plants
In the beginning, the seeds were naked…
gymn = naked
Gymnosperm = “naked seeds”
Gymnosperms 4 Phyla
Cycadophyta (cycads)
Gnetophyta
Gingkophyta (ginko: only extant species is Gingko biloba)
Coniferophyta (conifers) (about 600 species)
Plant Adaptations:
Flowers and Fruits
Flowers: reproductive structures that attract pollinators and develop into fruit
Flowers distinguish the angiosperms from the gymnosperms
Angiosperms: 1 Phylum
Anthophyta (a.k.a., Magnoliophyta)
= about 90% of all plant species
the first and only plants to have flowers and produce fruit.
Highly diverse: ~six times as many species of angiosperms as there are of all other plant species combined
The flowers of angiosperms
The flower is a modified shoot (stem with leaves) with up to four whorls of modified leaves encircling the stem
2 whorls are “sterile” (i.e., not directly involved in reproduction): sepals & petals
2 whorls are “reproductive”:
stamens (produce pollen) and carpels (contain the ovule(s))
Flowers
In angiosperms, the ovule is buried in the tissue of a flower (i.e., not naked)
- Pollen lands on the stigma and grows through the style to reach the micropyle of the ovule
- Leads to more female control of reproduction and sexual selection (e.g., pollen tube can be rejected)
Sepals
outermost, green, leaf-like parts that protect the growing bud
Petals
parts just inside the sepals; often colorful to attract pollinators
Stamen
male flower parts:
- anther (produces pollen)
- filament (supporting stalk)
Carpel
female flower parts:
- stigma (sticky tip)
- style (stalk)
- ovary (contains the ovules)
Pollination begins when
a pollen grain sticks to the stigma
Pollination and Fertilization
One sperm fertilizes the egg cell
- becomes the diploid zygote
- grows via mitosis to become the embryo
Preventing self-fertilization
The stamens and carpels of the flowers of some angiosperms mature at different times
Many angiosperms display self-incompatibility
Biochemical blocks prevent pollen from same plant (or closely related individuals) from reaching an egg cell.
Explaining angiosperm success
Many gymnosperms have slow life cycles (take many years to reach maturity)
Many angiosperms have short reproductive cycles (think, herbaceous flowers), which can evolve more rapidly because of more generations in shorter time(think, natural selection)
AND Angiosperms advertise for sex and advertise for dispersal
Plant-Pollinator Coevolution
Plants have become more effective at attracting specific pollinators
Pollinators have become more effective at exploiting specific plant resources
The features of the flower can often tell us about the type of animal that likely pollinates it
Fruits develop from pollinated flowers
The embryo will grow to become a seed:
an embryo plus stored food inside a protective seed coat.
The wall of the ovary typically grows to form some kind of fruit.
The next challenge: Seed Dispersal
Fruit structure can tell you a lot about its dispersal
Animal-dispersed seeds/fruits
are colorful and conspicuous, taste good, and are usually good for animals
Essentially bribes plants pay animals to disperse their seeds
