Download 21.1 Plant Cells and Tissues

21.1 Plant Cells and Tissues
KEY CONCEPT
Plants have specialized cells and tissue systems.
21.1 Plant Cells and Tissues
Plant tissues are made of three basic cell types.
• Parenchyma cells are the most common plant cell
type.
– store starch, oils and
water
– help heal wounds to
the plant
– have thin flexible walls
21.1 Plant Cells and Tissues
• Collenchyma cells provide support to a growing plant.
– they are strong and flexible.
– celery strings are strands of collenchyma.
– they have unevenly thick cell walls.
21.1 Plant Cells and Tissues
• Sclerenchyma cells are the strongest plant cell type.
– second cell wall hardened by lignin
– die when they reach maturity
– used by humans to make linen and rope
21.1 Plant Cells and Tissues
Plant organs are made of three tissue systems.
• Dermal tissue covers the outside of a plant.
– protects the plant
– secretes cuticle of leaves
– forms outer bark of trees
21.1 Plant Cells and Tissues
• Ground tissue is found inside a plant.
– provides support
– stores materials in roots and stems
– most commonly made of parenchyma
21.1 Plant Cells and Tissues
• Vascular tissue transports water, minerals and organic
compounds.
– two networks of hollow
tubes
– xylem transports water
and minerals
– phloem transports
photosynthetic products
stem
leaf
root
21.1 Plant Cells and Tissues
• The cohesion-tension theory explains water movement.
– Plants passively transport water through the xylem.
– Cohesion is the tendency of water molecules to bond
with each other.
– Adhesion is the
tendency of water
molecules to bond
with other
substances.
21.1 Plant Cells and Tissues
• Water travels from roots to the top of trees.
– absorption occurs at roots
– cohesion and adhesion in xylem
– transpiration at leaves
21.1 Plant Cells and Tissues
• Transpiration is the loss of
water vapor through leaves.
– water vapor exits leaf stomata
– helps pull water to the top
branches
21.1 Plant Cells and Tissues
Roots anchor plants and absorb mineral nutrients from
soil.
• Roots provide many
functions.
– support the plant
– absorb, transport,
and store nutrients
– root hairs help
absorption
21.1 Plant Cells and Tissues
• There are several parts of a root.
– root cap covers the tip
– apical meristem is an area of
growth
– vascular cylinder contains
xylem and phloem
vascular cylinder
apical meristem
root
cap
21.1 Plant Cells and Tissues
Stems support plants, transport materials, and provide
storage.
• Stems have many functions.
– support leaves and flowers
– house most of the vascular system
– store water
– grow underground for storage
– form new plants
Strawberry
stolons
21.1 Plant Cells and Tissues
• Primary growth increases a plant’s length.
• Secondary growth increases a plant’s width.
21.1 Plant Cells and Tissues
Most leaves share some similar structures.
• The blade is usually broad and
flat.
– collects sunlight for
photosynthesis
– connects to the stem by a
petiole
blade
petiole
21.1 Plant Cells and Tissues
• Mesophyll is between the leaf’s dermal tissue layers.
cuticle
upper
epidermis
palisade
mesophyll
spongy
mesophyll
lower
epidermis
21.1 Plant Cells and Tissues
• Guard cells surround each stoma.
– Stomata open and close when guard cells change
shape.
– When stomata are open, water evaporates and gas
exchanges.
– Stomata close at night and when plant loses too much
water.
guard cells
stoma
21.1 Plant Cells and Tissues
• Leaves may be simple, compound, or double compound.
Simple leaf
Compound leaf
Double compound leaf
21.1 Plant Cells and Tissues
• Leaf veins may be parallel or pinnate.
Parallel veins
Pinnate veins
21.1 Plant Cells and Tissues
• Leaf margins may be toothed, entire, or lobed.
Toothed margin
Entire margin
Lobed margin
21.1 Plant Cells and Tissues
• Leaves have many adaptations.
– for extreme temperatures,
ex: pine needles
21.1 Plant Cells and Tissues
• Leaves have many adaptations.
– for extreme temperatures,
ex: pine needles
– for water loss,
ex: cactus spines
21.1 Plant Cells and Tissues
• Leaves have many adaptations.
– for extreme temperatures,
ex: pine needles
– for water loss,
ex: cactus spines
– for aquatic environments,
ex: water lily
– for getting food,
ex: Venus’ flytrap