Plants
What are Plants?
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Multicellular eukaryotes
Have cell walls made of cellulose
Develop from multicellular embyros
Carry out photosynthesis
Evolution of Plants
• Started in water
– Evolved from an organism similar to multi-cellular
Cone-bearing
algae living today
plants
Ferns
Flowering
plants
Mosses
Seeds
Vascular
Tissue
Green algae
ancestor
Flowers; seeds
enclosed in fruit
Nonvascular Plants
• Called bryophytes
• Depend on water to
reproduce
• Lack vascular tissue
(draw up water by
osmosis)
• Mosses, liverworts, and
hornworts
Vascular Plants
• Have vascular tissue
(tissues that conduct
water and nutrients
throughout the plant)
– Xylem: transports
water
– Phloem: transports
sugar
Vascular Plants - Tracheophytes
• Ferns
• Seedless plants ~ Reproduce with spores;
Need water for reproduction.
• Have roots, stems, and leaves
Gymnosperms
• Vascular
• Seed bearing plant
• Conifers ~ Seeds are in cones.
Angiosperms
• The flowering plants.
• Vascular
• Bear seeds in fruits.
Vascular Plants
Reproductive shoot (flower)
Terminal bud
• 3 basic organs:
– Roots
– Stems
– Leaves
Node
Internode
Terminal
bud
Shoot
system
Vegetative
shoot
Leaf
Blade
Petiole
Axillary
bud
Stem
Taproot
Lateral roots
Figure 35.2
Root
system
Root
• Organ that anchors
the vascular plant
• Absorbs minerals and
water
• Often stores organic
nutrients
Root Anatomy
(cross-section)
Stem
• Organ that consists of an alternating system of
nodes, the points at which leaves are attached
Stem
Leaves
• Is the main photosynthetic organ of most
vascular plants
• Leaves generally consist of:
– A flattened blade and a stalk
– The petiole, which joins the leaf to a node of the
stem
Leaf Anatomy
• Cuticle – Waxy layer that protects leaf.
• Epidermis – Outermost layer of cells. Upper
and lower.
• Palisade mesophyll ~ Hot dog shaped cells lined up
like Popsicle sticks under the epidermis. Have lots of
chloroplasts, and carry out most of the photosynthesis.
• Spongy mesophyll ~ Rounded, loosely arranged cells
under the palisade mesophyll. Spaces between the
cells allow oxygen and CO2 to circulate.
Leaf Anatomy
• Vein ~ A bundle of phloem and xylem
surrounded by protective cells. This
vascular tissue carries water to and
from the leaf for photosynthesis
VEIN
Gas Exchange in Leaves
• Stomata – Holes in
lower epidermis that
allow CO2 to enter
and O2 to leave.
• Guard cells – Pickleshaped cells on each
side of stoma that
open and close the
hole.
Plant cross-section
Turgor Pressure – Plant vocabulary
• Turgor Pressure – The
pressure of water
against the inside of
plant cell walls.
• Turgor pressure
maintains a plants
shape and stiffness. As
water is lost, turgor
pressure decreases the
plant wilts.
Nonvascular Plant Reproduction
Mosses produce sperm that
must swim to meet the
egg. Once egg and sperm
meet, a spore is produced.
Spores do not have a coat
to protect them like seeds
do, so they need moisture!
Gymnosperms
• Gymnosperms –
“Naked seeds”
• Produce seeds in
cones
• Leaves are needlelike
• Evergreens – don’t
shed leaves
seasonally.
• Pines, cedar
Gymnosperm Reproduction
1. The diploid sporophyte generation (pine tree)
produces male and female cones
(gametophytes)
2. The male cone produces pollen
3. The female cone holds the eggs
4. Pollen travels by the wind to the female cone
5. The pollen and the egg meet and form a seed
6. The seed grows into the sporophyte generation
(pine cone)
Angiosperms
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Angiosperms - “covered seeds”
Flowering plants
Produce seeds in fruits.
Leaves are broad
Deciduous – Lose and replace leaves
seasonally.
Flowers
• Flowers are the main
reproductive organ of
the plant.
• Flowers produce egg
and sperm cells
• Some flowers are
hermaphroditic
• Parts of the flower
eventually become
seeds and fruits.
Flower Anatomy
Flower Anatomy
• Pistil - Female
1. Stigma: sticky portion
where pollen grains
land
2. Style: stalk; pollen
tube forms inside the
style
3. Ovary: contains ovules
4. Ovules: produces
female gametophytes
Flower Anatomy
• Stamen - Male
1. Anther: produces
pollen grains (male
gametophytes)
2. Filament: supports
anther
Flower Anatomy
Angiosperm Reproduction
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The plant produces flowers
Flowers contain both male and female structures
The male part of the flower releases pollen
The pollen is carried by a pollinator to the female part
of the flower
The pollen lands on the female part and grows a
pollen tube
The pollen meets the egg and fertilization takes place
The egg and sperm make a seed
The ovary of the flower becomes a fruit to protect the
seed until it is planted
Pollination
• Process by which pollen is transferred to
plants
– Wind pollination: pollen is transferred via wind
– Animal pollination: pollen is transferred via
animals
Seeds and Seed Dispersal
• Purpose is to protect and provide nutrition for
a developing plant embryo
• Seeds are dispersed by:
– Animals (contained in fleshy, nutritious fruits; pass
through animals digestive system)
– Wind and water (seeds are generally lightweight)
Fruit
• As angiosperm seeds mature, the ovary walls
thicken to form a fruit that encloses the
developing seed