Transcript Plants An Overview

Plants An Overview
the
Four Major Groups
of Plants
Evolutionary History of Plants
Reduction in the Size of the
Gametophyte
Other Terrestrial Adaptations
• Vascular tissue transports water and
nutrients to the body of the plant
• Cuticle provides an effective barrier to
water loss
• Stomata bordered by guard cells that
regulate opening, and thus water loss
Protection of Eggs and
Embryos
Leaves of Vascular Plants
Hornwort
Hornworts have small sporophytes that carry on photosynthesis
Liverwort, Marchantia
Liverworts have either flattened thallus or leafy appearance
Moss (Polytrichum) Life Cycle
Mosses usually have a leafy shoot,
although some are secondarily flattened
Vascular Plants
• Xylem conducts water and dissolved minerals up
from roots
• Phloem conducts sucrose and other organic
compounds throughout the plant
• Lignin strengthens walls of conducting cells in xylem
• Most seedless vascular plants do not have gametes
– Windblown spores are dispersal agents
• All seed plants have male and female gametophytes
– Seeds disperse offspring
Vascular Tissue
Diversity of ferns
Seed Plants
• Seed plants are the most plentiful plants in
the biosphere
– Seed coat and stored food allow an embryo to
survive harsh conditions during long period of
dormancy
– Heterosporous
– Drought-resistant pollen grains
• Ovule develops into seed
Seed Plants
• Gymnosperms have ovules and seeds
exposed on the surface of sporophylls
• Conifers, as well as other gymnosperm
phyla, bear cones
• Tough, needlelike leaves of pines conserve water
with a thick cuticle and recessed stomata
Angiosperms
• Angiosperms (phylum Anthophyta)
• An exceptionally large and successful
group of plants
• Ovules are always enclosed within diploid
tissues
• Became dominant group of plants in the
late Cretaceous and early Paleocene
periods
Monocots and Eudicots
• Two classes of flowering plants
– Monocotyledones (Monocots)
• One cotyledon in seed
– Eudicotyledones (Dicots)
• Two cotyledons in seed
Generalized Flower
Flowers and Diversification
• Wind-pollinated flowers are usually not showy
• Bird-pollinated flowers are often colorful
• Night-blooming flowers attract nocturnal mammals or
insects
– Usually white or cream-colored
• Fruits of flowers protect and aid in dispersal
– Utilize wind, gravity, water, and animals for dispersal
Plant Structure
Plant Organs
• Roots
– Generally, the root system is at least equivalent in size and
extent to the shoot system
• Anchors plant in soil
• Absorbs water and minerals
• Produces hormones
– Root hairs:
• Projections from epidermal root hair cells
• Greatly increase absorptive capacity of root
Organization of Plant Body
Stems
• Shoot system of a plant is composed of
the stem, branches, and leaves
– Stem is the main axis of a plant that elongates
and produces leaves
– Stem also has vascular tissue that transports
water and minerals
Leaves
• Leaves are the major part of the plant that
carries on photosynthesis
– Foliage leaves are usually broad and thin
– Tendrils - Leaves that attach to objects
– Bulbs - Leaves that store food
Plant Tissues
• Epidermal Tissues
– Contain closely packed epidermal cells
• Covered with waxy cuticle
– Roots contain root hairs
– Lower leaf surface contain stomata
– Woody plants covered by cork
Modifications of
Epidermal Tissue
Ground Tissue Forms Bulk Of
Plant
– Parenchyma cells:
• Least specialized, found in all organs of plant
• Like stem cells, Can give rise to more specialized
cells
– Collenchyma cells:
• Have thicker primary walls, Form bundles
• Flexible cellulose support to immature regions of
the plant
Ground Tissue Cells
• Sclerenchyma cells:
– Have thick secondary walls impregnated with
lignin
– Most are nonliving
– Primary function is to support mature regions
of the plant
• Fibers
• Sclereids
Vascular Tissue
• Xylem transports water and minerals from the
roots to the leaves
– Tracheids- Long, with tapered ends, Pits
– Vessel Elements
• Larger, with perforated plates in their end walls
• Phloem transports sucrose & organic
compounds from the leaves to the roots
– Sieve-tube members are conducting cells
• Plasmodesmata connects cells for transport of nutrients
Xylem Structure
Phloem Structure
Tissues of Eudicot Root
• Epidermis
• Cortex
• Endodermis
– Casparian Strip
• Vascular Tissue
– Pericycle
Eudicot Roots
Monocot Root
Root Diversity
• Primary root (taproot) -Stores food
• Fibrous root system - Anchors plant to soil
• Adventitous roots - Roots develop from
organs of the shoot system, Prop roots
Root Diversity
• Haustoria:
– Rootlike projections that grow into host plant
– Make contact with vascular tissue and extract
water and nutrients
• Mycorrhizas:
– Associations between roots and fungi
– Assist in water and mineral extraction
• Root nodules - Contain nitrogen-fixing
bacteria
Root Diversity
• Woody stems have no
vascular tissue, and
instead have three
distinct regions
– Bark
– Wood
– Pith
Leaf Diversity
• Blade of a leaf can be simple or compound
• Leaves are adapted to environmental
conditions.
– Shade leaves
– Spines
– Climbing leaves
Leaf
Structure
Leaf Diversity
Plant Responses
• Tropisms
– Plant growth toward or away from a
unidirectional stimulus is called a tropism
• Positive is towards stimulus
• Negative is away from stimulus
– Phototropism - Light
– Gravitropism - Gravity
– Thigmotropism - Touch
Phototropism
• Positive phototropism:
– Occurs because cells on the shady side of the
stem elongate
– A pigment related to riboflavin thought to act
as a photoreceptor when phototropism occurs
• Auxin migrates to shady side of stem
• Shady sides elongate faster than bright side
Gravitropism
• the stem grows upward, opposite of the
pull of gravity
• Stems with root caps grow downward
– Root cells contain statoliths
• Auxin is responsible for:
– Positive gravitropism of roots, and
– Negative gravitropism of shoots
Gravitropism
Thigmotropism
• Unusual growth due to contact with solid
objects is called thigmotropism
– Coiling of tendrils
• Thigmomorphogenesis occurs when the
entire plant responds to the presence of
environmental stimuli
– Wind
– Rain
Plant Hormones
• Almost all communication on a plant is
done by hormones
– Synthesized in one part of the plant
– Travels within phloem in response to the
appropriate stimulus
Auxins
• Auxin promotes shoot
and young leaves
growth
• Auxin applied to
woody cutting causes
rapid growth of
adventitious roots
• Promotes fruit growth
Gibberellins
• Gibberellins:
– Growth promoting
hormones
– Bring about elongation
of the resulting cells
– Gibberellic acid
• Stem elongation
• Breaking of dormancy
Cytokinins
• Cytokinins
– A class of plant
hormones that
promote cell division
– Derivatives of
adenine
• Prevent
senescence –
leaves falling off
• Initiate growth
Abscisic acid (ABA):
• Abscisic acid (ABA):
– Initiates and maintains seed and bud dormancy,
and
– Brings about closure of stomata
Ethylene is involved in abscission
• Once abscission has
begun:
• Ethylene stimulates
certain enzymes
• Cause leaf, fruit, or flower
to drop
– Also ripens fruit by
increasing activity of
enzymes that soften fruit
Phytochrome
• Phytochrome is a bluegreen leaf pigment that
alternately exists in two
forms
– Phytochrome red (Pr),
Phytochrome far-red
(Pfr)
• Conversion of forms
allows a plant to detect
photoperiod changes
• Also promotes seed
germination and inhibits
stem elongation
Plant Reproduction
Reproductive Strategies
• All plants have a two-stage, alternating life
cycle
– Sporophyte produces haploid spores by
meiosis
– Spores divide mitotically to become haploid
gametophytes
– Gametophytes produce gametes
– Gametes fuse to produce zygote
– Zygote divides mitotically to become diploid
sporophyte
Generations
in Flowering Plants
Reproductive Strategies
• Flower produces two types of spores
– Microspore - Male gametophyte
• Undergoes mitosis, Becomes pollen grain
– Megaspore - Female gametophyte
• Undergoes mitosis, Becomes embryo sac within
an ovary, within an ovule
• Ovule becomes seed
Anatomy of a Flower
Flowers
• Stamens are male portion of flower
– Anther - Saclike container
– Filament - Slender stalk
• Carpel is female portion of flower
– Stigma - Enlarged sticky knob
– Style - Slender stalk
– Ovary - Enlarged base enclosing ovules
Life Cycle of Flowering Plants
Pollination
• Pollination is the
transfer of pollen from
an anther to the
stigma of a carpel
– Self-pollination occurs
if the pollen is from the
same plant
– Cross-pollination
occurs if the pollen is
from a different plant
Asexual Reproduction in Plants
• Plants contain nondifferentiated meristem
tissue
• Allows them to reproduce asexually by
vegetative propagation
• Plant hormone auxin:
– Can be used to cause roots to develop
– Expands the list of plants that can be
propagated from cuttings
Asexual Reproduction in
Plants