Transcript Chapters 21 - Plant slides

Plants
Chapters 21-23
Evolution of Plants
Adapting to Land
• Nothing lived on land until an ozone layer
formed – the ozone layer offered
protection from the sun’s intense UV
radiation. With life on land came
adaptations for survival:
– Preventing water loss
– Reproducing by spores & seeds
– Abilities to transport materials
throughout the plant
Preventing Water Loss
• Cuticle – a waxy protective covering
that prevents water loss
• The cuticle kept water in, but kept
O2 and CO2 out.
• Plants developed a stomata (little
mouth) – a small opening in the leaf
that allows for gas exchange.
Reproduction
• Reproduction by spores and seeds
helps protect reproductive cells from
drying out.
• spore – haploid (n) reproductive cell
surrounded by a hard outer wall
• Seed – embryo, diploid (2n)
surrounded by a protective coat
– endosperm – tissue that provides
nourishment for the developing embryo
Transporting materials throughout
the plant
• Vascular tissue – transports water
and dissolved substances from one
part of the plant to another
• Xylem – carries water and inorganic
nutrients from the roots to the
stems and leaves
• Phloem – carries organic compounds
and some inorganic nutrients in
any direction
• Some plants developed woody tissue
and grew to great heights
– This gave them an advantage in
gathering light.
• Woody tissue
– Several layers of xylem
– Usually brown, woody stems
• Non-woody plants
– Herbaceous
– Soft, green stems
Classifying Plants
Classifying
Plants
Non-Vascular
Bryophytes
Vascular
Seeds
Gymnosperm
Angiosperms
Unprotected
seeds
Protected
seeds
Cone-Bearing
Flowering
Plants
Monocots
Dicots
Ferns
Seedless
Mosses
Club
Mosses
Horsetails
Liverworts
Hornworts
A Cladogram of Plant
Groups
Flowering
plants
Cone-bearing
plants
Ferns and
their relatives
Flowers; Seeds
Enclosed in Fruit
Mosses and
their relatives
Seeds
Water-Conducting
(Vascular) Tissue
Green algae
ancestor
Go to
Section:
Bryophytes, Seedless Plants,
Gymnosperms & Angiosperms
• When we classify plants, what
question do we first ask?
– Vascular or non-vascular?
• Let’s look at non-vascular first
• Bryophytes do not have vascular
tissue
Bryophytes – Non-Vascular
• Bryophytes include:
– Mosses (most common)
– Liverworts
– Hornworts
• Help! I Need Water!!!
– Bryophytes have life cycles that depend
on water for reproduction
– Since they don’t have vascular tissue,
the plants draw up water by osmosis.
• Dependence on water keeps
bryophytes small in size
• Bryophytes are low-growing plants
found in moist, shaded areas.
• Lack of vascular tissue means that
bryophytes do not have true roots.
• Bryophytes have rhizoids – long, thin
cells that anchor them to the
ground and absorb water and
minerals from the soil (by
osmosis).
The gametophyte
stage of moss
Hornworts
Liverworts
Reproduction
• For fertilization to occur, the sperm
must swim to an egg.
• Because of this limiting factor,
bryophytes must live near water.
• Remember, bryophytes need water to
reproduce !!!
Vascular Plants
• Vascular plants have vascular tissue
• Xylem – carries water upward from
the roots to every part of the plant
• Phloem – transports solutions of
nutrients and carbohydrates produce
by photosynthesis (all directions)
• Produce lignin – makes cell walls
rigid.
– Allows vascular plants to grow
upright and reach great heights
• Vascular plants have true roots,
leaves and stems
• Roots – underground organs that
anchor plants, and absorb water and
minerals
• Leaves – photosynthetic organs – one
or more bundles of vascular tissue
gathered into veins made of
xylem and phloem
• Stems – supporting structures that
connect roots and leaves, carrying
water and nutrients between them.
• Vascular plants have a life cycle in
which the sporophyte is the dominant
stage.
• Remember, first we ask vascular or
non-vascular?
• Next, we ask seeds or seedless?
Seedless vascular plants
• Include:
–
–
–
–
Whisk ferns
Club mosses
Horsetails
Ferns (most common)
• Seedless vascular plants have true
vascular tissue, strong roots,
rhizomes (underground stems),
fronds (large leaves)
The whisk fern are rare. They are
usually found in tropical and subtropical
regions.
The club moss is sometimes known as a
ground pine.
Horsetails
Tree ferns
Seed Plants
• We have asked vascular or not-vascular?
• We then asked seeds or seedless?
• Seed plants can be further classified:
– Gymnosperms (unprotected seeds on cones)
• Includes conifers, cycads, ginkoes,
gnetophytes
– Angiosperms (flowering plants with
protected seeds)
• Includes grasses, flowering trees and
shrubs, wildflowers and cultivated
flowers
Reproduction free from water
• Adaptations that allow reproduction
without water
– Flowers or cones
– Transfer of sperm by pollination
– Protection of embryos in seeds
• A seed coat surrounds the embryo.
It also contains a stored food
supply for the embryo.
• Angiosperms can be further
classified:
– Named for the number of seed
leaves (cotyledons) in the plant
embryo
– Monocots have one seed leaf
– Dicots have two seed leaves
Comparison of
Monocots and Dicots
Monocots
Go to
Section:
Dicots
Seeds
Single
cotyledon
Two
cotyledons
Leaves
Parallel
veins
Branched
veins
Flowers
Floral parts
often in
multiples of 3
Floral parts often
in multiples
of 4 or 5
Stems
Vascular
bundles
scattered
throughout stem
Vascular
bundles
arranged in
a ring
Roots
Fibrous roots
Taproot
Roots, Stems and Leaves
• The three principle organs of
seed plants are:
– Roots
– Stems
– Leaves
Roots
• Two main types of roots
– Taproots – found mainly in dicots
– Fibrous roots – found mainly in
monocots
• Two functions of roots
– Anchor a plant in the ground
– Absorb water and dissolved
nutrients from the soil
Stems
• Three functions of stems:
– Produce leaves, branches and flowers
– Hold leaves up in the sunlight
– Transport substances between roots and
leaves
• The vascular tissue of stems lifts water
from the roots to the leaves (xylem) and
sends the products of photosynthesis
from the leaves to other parts of the
plant (phloem)
Leaves
• Main function is photosynthesis
– The broad, flat surface of leaves
helps increase the amount of
sunlight absorbed by plants
• Other functions of leaves:
– Transpiration
– Gas exchange
• Connects with exterior through
stomata – allows CO2 and O2 to
diffuse in and out of the leaf
• Each stoma consists of two guard
cells that control the opening and
closing of the stomata by
responding to changes in water
pressure.
Transpiration
• Transpiration is the loss of
water from a plant through
its leaves.
• The water is replaced by
water drawn into the leaf
through the xylem vessels in
the vascular tissue.
A
Evaporation of water
molecules out of leaves.
B
Pull of water molecules
upward from the roots.
Gas Exchange
• Plants keep their stomata open just
enough to allow photosynthesis to
take place, but not so much that they
lose an excessive amount of water.
• Guard cells control the stomata
through changes in water pressure.
– when water pressure in guard cells is
high, stoma is open
– When water pressure in guard
cells is low, stoma is closed.
• In general, stomata open in
the daytime, when
photosynthesis is active, and
close at night to prevent
water loss.
• A plant will close its stomata
any time water
conservation is an issue.
Reproduction of Seed Plants
• Reproduction in gymnosperms takes
place in cones.
• Pollen cones – male cone – produce
pollen grains (male gametophytes)
• Seed cones – female cone – produce
female gametophytes
• Gymnosperm pollen is carried
by the wind to female cones
(pollination)
Angiosperms
• Flowers are reproductive organs
composed of four kinds of specialized
leaves:
•
•
•
•
Sepals
Petals
Stamen
Carpels
• Sepals – resemble leaves. Enclose the
bud before it opens; protect the
flower while it is developing.
• Petals – often brightly colored (the
pretty part). It attracts insects and
other pollinators.
• Stamen (boy parts)
• anther – produce male gametophytes
(pollen)
• filament – supports anther
• Carpel (girl parts) sometimes called
pistils
• ovary – produces female
gametophytes
• style – stalk
• stigma – sticky portion where pollen
lands
The Structure of
a Flower
Stamen
Anther
Filament
Ovule
Stigma
Style
Carpel
Ovary
Petal
Sepal
Pollination
• Most gymnosperms and some angiosperms
are wind pollinated
• Most angiosperms are pollinated by animals
(beneficial to both plant and animal)
• For fertilization to occur, pollen grains land
(or are carried) on the stigma of an
appropriate flower.
• Pollen (male gametes) reach the ovary
(where female gametes are made)
and fertilization occurs
Seed Development & Germination
• Once fertilization occurs, nutrients flow
into the flower tissue to support the
growing embryo within the seed.
• As seeds mature, ovary walls thicken to
form a fruit that encloses developing seeds
• A fruit is a ripened ovary that contains
angiosperm seeds.
• The term “fruit” applies to any seed (even
vegetables) enclosed within its
embryo wall
• Why do angiosperms produce fruit?
• To disperse seeds
• Two ways seeds can be dispersed
• animals
• Typically contained in fleshy, nutritious
fruits
• wind and water
• Typically lightweight
• Allows them to be carried in the
air or float on the surface of
the water
• Some plants develop right away,
others “wait”
• Environmental factors like
temperature and moisture
determine when a seed develops
• dormancy – embryo is alive but not
growing
• germination – early growth
stage of the plant embryo
Seed Germination
• Seed absorbs water
• Absorbed water causes the
endosperm to swell, cracking open the
seed coat
• Through the cracked seed coat, the
young root emerges and begins to
grow
Three categories of plant life
spans
• annuals – flowering plants that
complete a life cycle within one
growing season
• biennials – complete their life cycle in
two years
• perennials – flowering plants that live
for more than two years
Concept Map
Plants
are categorized as
Go to
Section:
Annuals
Biennials
Perennials
that complete
their life cycle in
that complete
their life cycle in
that complete
their life cycle in
1 growing
season
2 years
More than
2 years
Plant Responses
•The response of plants to
environmental stimuli are called
tropisms.
•Tropisms demonstrate the ability of
plants to respond effectively to
conditions in which they live
Light & Gravity
•The response of a plant to light is
known as phototropism
• Phototropism causes a plant to
grow toward a light source
•The response of a plant to gravity
is known as gravitropism
Gravitropism
• Gravitropism causes the shoots of a
germinating seed to grow out of the
soil - against the force of gravity
• It also causes the roots of a plant
to grow with the force of gravity and
into the soil
Response to Touch
•The response of plants to touch is
called thigmotropism.
•An example of thigmotropism is the
growth of vines and climbing plants.
Any Questions ???