Biology II Fall 2009
Transcript of Biology II Fall 2009
Biology II
Fall 2009
Chapter 23
Introduction to Plants
Section 1 Vocabulary
• Cuticle
• Spore
• Sporophyte
• Gametophyte
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What is a Plant? Let’s review..
• Most plants are autotrophs
– Which is….?
• Plants use photosynthesis
– Which is….?
– Where does photosynthesis occur?
– Requires energy from sun and carbon dioxide
to produce organic material (energy)
• Plants need sunlight, water, air, and
minerals to survive
Establishment of plants on land
• Dominant group of organisms on land based on
weight
• Plantae = Very diverse group
• Range from 2mm across to more than 100 m tall
• Most are photosynthetic
– Produce inorganic materials by photosynthesis
• Some are parasitic
• Probably evolved from multicellular aquatic green
algae that could not survive on land
Plants on Land
• THREE MAIN OBSTACLES….
– Absorbing nutrients
– Preventing water loss
– Dispersal on Land
Relationship between algae and
plants
Absorbing Nutrients
• Take nutrients from the water around them
• On land, most take nutrients from soil with their roots
• The first plants did not have roots
– Fossils show they lived underground and fungi lived on or within their parts
– Symbiotic relationship = what?
– Mycorhizae – symbiotic relationship between fungi and plant roots
• Today, 80% of all plants form mycorhizae
Preventing Water Loss
• Cuticle – waxy layer that covers the nonwoody
aboveground parts of most plants
– Before this, most plants lived near water where drying
out water not an issue
– PROHIBIT oxygen and carbon dioxide to pass
through
• Stomata – (singular =stoma) permit plants to
exchange oxygen and carbon dioxide
– Extend through the cuticle and the outer layer of cells
• Guard cells – border each stoma
Stomata and Guard Cells
Reproducing(Dispersal) on Land
• Aquatic algae reproduce sexually when
sperm swim through water
– The sperm of most plants, must be able to
move without water….
• Spores – unicellular reproductive cell that
is resistant to environmental conditions
– In seed plants, sperm is contained in POLLEN
• Pollen permits the sperm of plants to be carried by
wind or animals rather than water
Plant Life Cycles
• Plants have life cycles in which haploid gametophytes alternate with diploid sporophytes
• A life cycle in which a gametophyte alternates with a sporophyte is called alternation of generations.
• Unlike the green algae with alternation of generations, plants have gametophytes and sporophytes that look very different.
Quick Questions
• What structure produces gametophytes?
• Is a plant sporophyte diploid or haploid?
• End 23.1
23.2 Seedless Plants
• Archegonium
• Atheridium
• Sporangium
• Rhizome
• Frond
• sorus
2 types of seedless plants
•Nonvascular
•Vascular
Nonvascular
• Do not have a vascular system for
transporting water and nutrients
• Reproduce by spores
• Lack true roots, stems, and leaves,
although most have structures that
resemble them
Nonvascular, cont.
• Water transported by osmosis and
diffusion
– Moves materials short distances and very
slowly
• Limits the size of a nonvascular plant body
– Most are relatively small…
Kinds of Nonvascular Plants
• Mosses (phylum Bryophyta)
– The most familiar nonvascular plant
– “leafy” green plants you recognize as mosses
are gametophytes
• Sporophytes, which are not green, grow from the
tip of gametophyte
Example: Polytrichum
**Most have cuticle,
stomata, and simple
conducting cells
Nonvascular cont. • Liverworts (phylum Hepatophyta)
– Grow in mats of individuals, like mosses
– Gametophytes are green, flattened and have
lobes
– Sporophytes are very small and consist of a
short stalk topped by a spore capsule
Example: Marchantia
**Have no conducting
cells, cuticle, or
stomata
Nonvascular cont.
• Hornworts (phylum Anthocerophyta)
– Completely lack conducting cells
– Gametophyte is green and flattened
– Green hornlike sporophytes grow upward
from the gametophyte
• Have stomata and cuticle
Example: Anthoceros
Reproduction in Nonvascular
• Gametophyte is dominant generation
– Must be covered by film of water for
fertilization
– Produce gametes (eggs and sperm) in two
separate structures
• Archegonium – produces eggs
• Atheridium – produces sperm
• The sporophyte produce spores in
sporangium
– Grow on gametophytes
• Depend on them for nutrition
Life Cycle of a Moss • Spores form by meiosis inside spore capsule
– Spores are haploid
• Spore capsule opens when spores are
mature
– Spores are carried by wind or water
• When spore settles, it germinates and grows
into leafy green gametophyte
• Archegonia and antheridia form at tips of
haploid gametophytes
– Eggs and sperm form by mitosis inside
A&A
Seedless Vascular Plants
• Do not produce seeds
• Have horizontal underground stems, or
rhizomes
Key Features of seedless vascular
plants
• Vascular system – Can grow much larger due to vascular system
– Develop true roots, stems, and leaves
• Larger sporophyte – Small gametophtes develop on or below surface of
soil
– Size makes it easier for wind to carry spores
– Water is needed for fertilization • When enough water is present, sperm swim to eggs
Seedless vascular cont. • Club Mosses (phylum Lycophyta)
– Have roots, stems, and leaves unlike true
mosses
– Spores develop in sporangia that form on
specialized leaves
– In some species, spore-bearing leaves form a
structure called a cone
Example: Lycopodium
*Sometimes called
ground pines
Ferns and Fern Allies
• Phylum Monilophyta
• Most common seedless vascular
plants
• Most abundance in the tropics
• Plants recognized as ferns are
sporophytes
• Most are anchored by rhizomes and
have leaves called fronds
– Coiled fronds are called fiddleheads
Example: Sword Fern
Reproduction in Seedless
Vascular Plants • Like nonvascular plants, seedless vascular
plants can reproduce sexually only when a
film of water covers the gametophyte.
• Unlike nonvascular plants, seedless
vascular plants have sporophytes that are
much larger then their gamtophytes.
• Archegonia and antheridia develop on the
lower surfaces of the gametophytes
– Sperm and egg mostly produced by same
individual
Spores
• Haploid reproductive cell
• Produced by meiosis
– Capable of developing into adult without
fusing with another cell
• Have thickened walls that allow spores to
withstand tough environmental conditions
• Easily dispersed by wind
• Produced in sporangia of sporophytes
• Sorus – cluster of sporangia on a fern
frond
– Look like brown dots under leaves of ferns
23.3 Seed Plants
• Seed – a structure that contains the
embryo of a plant
– Embryo – an early stage in the development
of plants and animals
• Most plants today are seed plants –
vascular plants which produce seeds
• First seed was roughly 380 mya
Structure and Function of Seeds
Gymnosperms – Seed Plants
• Seed plants whose seeds do not develop
within a sealed contain (fruit)
• Word comes from Greek words “gymnos,”
meaning “naked,” and sperma, meaning
“seed.”
• Most seeds develop within a cone
Angiosperms – Seed Plants
• Flowering plants
• Produce seeds that develop enclosed
within a specialized structure called a fruit
• Word angiosperm comes from the Greek
words angeion, meaning “case,” and
sperma, meaning “seed.”
**Gymnosperms v.
Angiosperms • Key difference… unlike seeds of
angiosperms, seeds of gymnosperms do
not develop within a fruit…
Reproduction in Seed Plants
• Do not require water to reproduce sexually
• Have greatly reduced gametophyte and a
dominant sporophyte
• Produce 2 kinds of spores which develop
into gametophytes
– Female – eggs
– Male - sperm
Reproduction, cont.
• Female gametophyte develops inside
ovule
• Following fertilization, ovule and contents
develop into seed
• Male gametophyte develops inside a
pollen grain
Pollination and Fertilization
• Pollination is the transfer of pollen grains
from the male reproductive structure to the
female reproductive structure
• When pollen grained reaches compatable
female reproductive, a tube emerges
(pollen tube)
– Grows to female gametophyte
• Allows sperm to pass directly to egg
• Fusion of egg and sperm = fertilization
Seed Formation
• After fertilization, ovule is termed seed
– Contains embryo
• Outer layers harden to form seed coat
– Protects embryo from harsh environment and
mechanical damage
• Contains tissue that provides nutrients
• Some angiosperms have a nutritious
tissue called endosperm
Seed Dispersal
• Can prevent competition for water,
nutrients, light, and living space between
plants
• Many have structures that help wind,
water, or animals carry them away
Kinds of Gymnosperms
• Conifers (phylum coniferophyta)
– Most familiar and most successful
gymnosperms
– have needle-like or tiny scales for leaves
which help them limit water loss
– Some of the tallest and oldest trees in the
world
Example: Juniper
Gymnosperms, cont.
• Cycads (Phylum Cycadophyta)
– Have short stems and palmlike leaves
– Cones produce pollen and those that produce
seeds develop on different plants
Example: Encephalartos
Gymnosperms, cont.
• Gingko (Phylum Gingkophyta)
– Only 1 living species
– Fan-shaped leaves
– Male and female gametophytes of gingko
develop on separate trees
– Seeds do not develop within a cone
Example: maidenhair tree
Gymnosperms, cont.
• Gnetophytes (Phylum Gnetophyta)
– Diverse group of trees, shrubs, and vines that
produce pollen and seeds in cones that
resemble flowers
– Only one type is common in the Western US
(ephedra)
Example: Ephedra
Life Cycle of Conifer
• Characterized by dominant sporophyte,
wind pollination, and the development of
seeds in cone
• The gametophytes of most gymnosperms develop in cones, which consist of circles of modified leaves called scales.
• Many gymnosperms produce both female and male cones on the same plant.
Cones
• Gametophytes of most conifers develop in
cones
– Consist of whorls (circles) of modified leaves
called scales
• Male (pollen cones)
• Female cones (seed cones)
• Can produce male and female on same
plant
23.4 Flowering Plants • Aka angiosperms
• Most successful group of plants today
• Tiny herbs to giant trees
• Subgroups
– Monocots (CORN)
• One leaf, or cotyledon
• Long, narrow leaves with parallel veins
• Parts in multiples of 3
– Dicots (BEAN)
• Seeds have two seed leaves, two cotyledons
• Branching leaves with veins
• Parts in 4 or 5
Reproduction In Angiosperms
• Flower = specialized structure of
angiosperms
• Male and female gametophytes develop
within flower
– Promote pollination and fertilization more
efficiently than cones
• Does not require water
Structure of Flowers • Arranged in 4 concentric whorls, or circular
swirls
• Sepals – protect flower from damage while
a bud
• Petals – attract pollinators
• Stamens – produce pollen
• Pistils – produce ovules
– Ovules develop in ovary deep within pistil
• Ovules develop into seeds
– Style rises from ovary, pollen lands on stigma (top of
style)
Kinds of Flowers
• May or may not have all four basic flower
parts
• Complete – has all 4 parts
• Incomplete – lacking any one of the 4
parts
Pollination
• Some can fertilize the plant’s own ovules
– Self-fertilization
• Cross-fertilization – unable to fertilize own
ovules
• Flowers are intended to attract pollinators
– Insects and birds, etc.
• If pollinated by wind, flowers are usually
small and lack bright colors, strong odors,
or nectar.
Will transfer pollen
to the next flower it
visits = cross
pollination
**Attractive Orchids… Did you
know?!?!
• Orchids have highly elaborate ways of attracting pollinators
– One resembles a female wasp to attract male wasps…
• The wasps picked up pollen trying to mate with the modified petals
– One holds a small pool of water • When a bee tries to collect nectar it falls into the
pool of water and can only escape via small passageway through forces the bee to brush against pollen
Fruits
• Ovary of a pistil is called fruit after ovules
are fertilized
– Fruits develop from an ovary of a flower and
contains seeds
• Botanical fruit different than everyday
meaning of fruit
• Fruits do provide some protection for
seeds, but primarily function in seed
dispersal
Vegetative Reproduction
• Most plants are able to reproduce
asexually
– Genetically identical to parent plant
• Use stems, roots, and leaves to reproduce
asexually
• Typically faster than sexual reproduction
– Can spread quicker