Plant Structure and Function
Roots, Stems, and Leaves
What is a Plant?
• Plants are living things that have roots,
stems, and leaves ~ some have flowers
• Plants are made of cells that have cell
walls, a large central vacuole, and
chloroplasts
• Chloroplasts contain a green pigment
called chlorophyll that play a role in
photosynthesis
Photosynthesis
6H2O + 6CO2 ----------> C6H12O6+ 6O2
Origin and Evolution
• There are between 260,000 and
300,000 plant species identified to date
• Oldest fossil plants are about 420
million years old – descendants of algae
(aquatic)
– Cone-bearing plants, such as pines, probably
evolved from a group of plants that grew 350
million years ago
– Flowering plants did not exist until about 120
million years ago
Life on Land – Adaptations!
Problem
• Drying Out
• Making Food
• Reproduction
• Gravity & Support
• Getting water &
nutrients
Solution
• Waxy cuticle, stomata
• Formed leaves
• Develops spores &
seeds
• Bark (cork) & vessels;
cell walls (cellulose)
• Roots & vessels
Protections and Support - Leaf
Classification
• VASCULAR: have tube-like structures that carry
water, nutrients, and other substances through
the plant
• NONVASCULAR: do not have these tube-like
structures and use other ways to move water
and substances
• Binomial Nomenclature: two word system of
naming things, e.g., Quercus alba = white oak
Seedless Nonvascular Plants
• Don’t grow from seeds; just a few cells
thick and only 2 to 5 cm in height; no
flowers or cones ~ reproduce by spores
– Mosses
-Liverworts
-Hornworts
Nonvascular Plants and the
Environment
• Pioneer species: first organisms to
grow in new or disturbed areas
– As pioneer plant species grow and die,
decaying material builds up; this, along
with the slow breakdown of rocks, builds
soil ~ as a result, other organisms can
move into the area!
Seedless Vascular Plants
• Reproduce by spores
• Have long, tube-like cells that carry water,
minerals, and food to cells throughout the
plant
– Can grow bigger and thicker because of this
– 1,000 species of fern, ground pine, and spike
mosses; 12,000 species of ferns!
FERN
GROUND PINE SPIKE MOSS
HORSETAIL
Ferns
• Largest group of seedless vascular plants
• Fern leaves are called fronds
• Ferns produce spores in structures on
underside of fronds
• Ferns that lived 360 million years ago grew
as tall as 25 m, but today, tallest tree ferns
are about 3 m to 5 m in height
Club Mosses
• Ground pines and spike
mosses
• Have needle-like leaves
• Spores produced at end of
stem in structures that look
like tiny pine cones
• Endangered in some areas, as
they have been collected to
make wreaths
Horsetails
• Stem is jointed and has a hollow center
surrounded by a ring of vascular tissue;
at each joint leaves grow out from
around the stem
• Spores are produced in a cone-like
structure at the tips of some stems
• Stems contain silica, a gritty substance
found in sand – “scouring rush”
Importance of Seedless Plants
• When ancient seedless plants died, they
became submerged in water and mud before
they decomposed – over time, plant material
became coal!
• Today, decaying plants are compressed into a
substance called peat, which forms from the
remains of sphagnum moss – used as lowcost fuel in places such as Ireland and Russia
Uses of Seedless Vascular
Plants
• Peat and sphagnum mosses used for
gardening
• Peat used as soil conditioner
• Ferns used for weaving material and basketry
• Rhizomes and young fronds of ferns are
edible
• Dried stems of one type of horsetail can be
ground into flour
• Folk medicines to treat bee stings, burns,
fevers, and even dandruff!
Seed Plants
• Have leaves, roots, stems, and vascular
tissue; produce seeds
• Gymnosperms and Angiosperms
• Leaf made up of different layers of cells
–
–
–
–
Waxy cuticle
Epidermis (Stomata surrounded by guard cells)
Palisade layer – most food produced here
Spongy layer – veins containing vascular tissue
found here
– Lower Epidermis
Leaf Structure
Stems and Roots
• Herbaceous stems: soft and green
• Woody stems: hard, rigid
• Roots have vascular tissue in which water
and dissolved substances move from the soil
through the stems to the leaves; roots also
act as anchors
• Roots can store food, e.g., carrots, beets
• Absorb oxygen for use in respiration ~
making energy for the plant’s cells
Vascular Tissue
• Xylem: hollow, tubular cells stacked one on
top of the other to form a structure called a
vessel; transport water and dissolved
substances
• Phloem: tubular cells that are stacked to
form structures called tubes; move food from
where it is made to other parts of the plant
where it is used or stored
• Cambium: between xylem and phloem;
produces new xylem and phloem
Gymnosperms
• Oldest trees alive
• Produce seeds not protected by fruit; “naked
seeds”; do not have flowers
• Leaves needle-like or scale-like
• Four divisions:
– Coniferophyta: conifers-pines, firs,
spruces, redwoods, junipers
– Cycads
– Gingkoes
– Gnetophytes
Angiosperms
• Vascular plant that flowers and has a
fruit that contains one or more seeds
• Division: Anthophyta
– Monocots – one cotyledon used for food
storage, e.g., corn, rice, wheat, barley,
lilies, orchids, grass
– Dicots – two cotyledons; shade trees, fruit
trees; petunias; geraniums; snapdragons
Monocots
• Flower parts in multiples of three
• Leaves are more narrow than long
• Vascular bundles show up as parallel
veins in leaves
• Vascular tissues are arranged as
bundles scattered throughout the stem
• Seeds have just one cotyledon
Dicots
• Flower parts in multiples of four or five
• Vascular bundles are the network of
veins in the leaves
• Vascular bundles occur in rings (annual
rings in woody stems)
• Seeds have two cotyledons
Life Cycles of Angiosperms
• Biennials: complete their life cycles
within two years
• Annuals: complete their life cycles in
one year
• Perennials: take more than two years
to grow to maturity
Some Products from
Gymnosperms
• Lumber, paper, soap, varnish, paints,
waxes, perfumes, edible pine nuts,
medicines
Some Products from
Angiosperms
• Foods, sugar, chocolate, cotton cloth,
linen, rubber, vegetable oils, perfumes,
medicines, cinnamon, flavorings
(toothpaste, chewing gum, candy, etc.),
dyes, lumber
• FLOWER PARTS
• SMARTBOARD REVIEW