plant tissues. plant tissues & organs cells of a vascular plant are organized into different...
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Plant Tissues & Organs
• Cells of a vascular plant are organized into different tissues and organs
• Three major organs are: roots, stems, and leaves
Dermal tissue
Vascular tissue
Ground tissue
Stem
Root
Leaf
Plant Organs
• Roots – absorb water and nutrients from soil, anchor plant, hold plant upright
• Stems – supports plant, transports water and nutrients
• Leaves – carry out photosynthesis, have adjustable pores to help conserve water, allow O2 to leave and CO2 to enter
Roots
• Two main types – taproots (found in dicots) and fibrous roots (found in monocots– Taproots – long primary root like that of
carrots or trees– Fibrous roots – branching root system with no
single root growing larger than the rest (many plants, such as grasses)
Root Function
• Anchors plant
• Absorbs water and nutrients– Active transport proteins in the root pump
minerals and nutrients into the plant (moves from low to high concentration and requires ATP/energy to do so)
Stems
• Vary greatly in size and shape
• Three important functions:– Produce leaves, branches, and flowers– Hold leaves up in sunlight– Transport substances between roots and
leaves
Growth in Stems
• Primary growth of stems– For the life of the plant, new cells are produced at the tips of the
roots– Plant gets taller
• Secondary growth of stems– Stem increases in thickness/width– Most evident in woody plants– The vascular cambium is a cylinder of actively dividing cells
between the primary xylem and primary phloem.– Secondary growth adds cells on either side of the vascular
cambium.
Growth in Stems
KeyDermal tissue system
Vascular tissue system
Ground tissue system
Year 1Early Spring
Growth
Primaryxylem
Vascularcambium
Cortex
Epidermis
Primaryphloem
GrowthGrowth
Late Summer
Shedepidermis
Secondaryxylem(wood)
Secondaryphloem
Corkcambium
Cork
Bark
Year 2Late Summer
Secondary xylem(2 years’ growth)
Formation of Wood in Trees
• Actually layers of xylem that build up year after year
• Tree growth is seasonal– In spring, light-colored xylem cells with thin
cell walls form– In fall/winter, xylem cells becomes dark and
have thicker cell walls– This light and dark pattern is called tree rings.
Each ring is composed of a band of light wood and dark wood
Formation of Wood in Trees (continued)
– One ring = one year of growth– Counting rings = approximate age of tree– Thick rings = favorable conditions/good growing
season– Thin rings = less favorable conditions/bad growing
season
Layers of a Tree Trunk
Annual rings
Heartwood
Sapwood
Vascular cambium
Secondary phloemCork cambiumCork
Bark
Leaves
• Main organ of photosynthesis
• Leaves vary in shape, but all collect sunlight on flattened sections called blades
• Epidermis of leaves covered by a waxy cuticle to prevent water loss
Leaf Functions
• Photosynthesis – bulk of leaf tissue is called mesophyll, where many chloroplasts are
• Gas exchange – leaves take in CO2 and give off O2 during photosynthesis
Leaf Functions (continued)
– Leaves have stomata – pore-like openings on the underside of the leaf that allow gas exchange to occur
– Stomata are open just enough to allow photosynthesis to occur, but not so much that they lose excess amounts of water
– Guard cells surrounding the stomata control the opening/closing of the stomata and thus regulate the movement of gases into and out of the leaf (also regulates water loss)
– In general, stomata open during the day and close at night
Function of Guard Cells
Stoma Open Stoma Closed
Guard cells
Inner cell wall
Stoma
Guard cellsInner cell wall
Function of Guard Cells
Stoma Open Stoma Closed
Guard cells
Inner cell wall
Stoma
Guard cellsInner cell wall
The Internal Structure of a Leaf
Veins
Xylem
PhloemVein
Cuticle
Epidermis
Palisademesophyll
Epidermis
Stoma
Guardcells
Spongymesophyll
Tissue Types
• Three tissue types:– Dermal– Vascular– Ground
Dermal tissue
Vascular tissue
Ground tissue
Stem
Root
Leaf
Dermal Tissue
• Dermal Tissue – outermost layer of cells covered with a waxy cuticle to protect against water loss
Vascular tissue
• Vascular tissue – transports water and nutrients through plant by xylem and phloem– Xylem – conducts WATER throughout the
plant– Phloem – conducts NUTRIENTS throughout
the plant
Ground Tissue
• Ground Tissue – cells that lie between dermal and vascular tissues; site of photosynthesis
The Working Plant: The Transport of Water
– To thrive, a plant must be able to transport• water and • dissolved ions from its roots to the rest of the plant.• Xylem is used for this purpose.
– Transpiration, the loss of water vapor from the leaves of a plant by evaporation,
• mostly occurs through the stomata of leaves and• pulls liquid through the xylem up the plant against
gravity.
The Working Plant: The Transport of Water
– Transpiration relies on two special properties of water.1. Adhesion is the sticking together of molecules of
different kinds.
2. Cohesion is the sticking together of molecules of the same kind
– Together, adhesion and cohesion create a continuous string of water molecules that stick• to each other and
• to the inside walls of the xylem tubes.
Xylem sap
Soil particle
Root hair
Water
Water uptake from soil
Root
Flo
w o
f w
ate
r
Cohesion,by hydrogenbonding
XylemcellsCohesion and
adhesion in the xylem
Cell wallWatermolecule
AdhesionStem
Transpiration
Leaf
Outside air
Water molecule
Stoma
Air space within leaf
Mesophyll cells
Xylem sap
1
2
3
4
The Working Plant: The Transport of Water
– Transpiration• helps to distribute water within a plant but• can cause plants to lose large amounts of water.
– Plants adjust their transpiration rates to changing environmental conditions.
The Working Plant: The Transport of Sugars
– Phloem moves sugar in various directions,• from a sugar source, where sugar is produced,• to a sugar sink, where sugar is stored or
consumed.
– Phloem moves sugar from a sugar source to a sugar sink by active transport as well as help from osmosis
The Working Plant: Response to Stimuli
– Plants can respond to physical stimuli from the environment, including
• light,• touch, and • gravity.
The Working Plant: Response to Stimuli
– Tropisms are directed growth responses that cause parts of a plant to grow
• toward or• away from a stimulus.
The Working Plant: Response to Stimuli
• Phototropism is the directional growth of a plant shoot in response to light.
• Thigmotropism• is a response to touch and• occurs when a pea plant tendril coils around a string or wire it
touches for support.• Gravitropism
• is the directional growth of a plant organ in response to gravity and occurs when
– shoots grow upward and– roots grow downward.
The Working Plant: Response to Stimuli
TROPISMS
Phototropism Thigmotropism Gravitropism
Seedlings bending towardthe light
Growth in response to touch Seedlings reacting togravity
The Working Plant: Response to Stimuli
– Light• provides energy for photosynthesis,
• directs growth, and
• regulates a plant’s life cycle, including– flowering,– seed germination, and– the onset and ending of dormancy.
– A photoperiod • is the relative lengths of day and night and
• the environmental stimulus that plants most often use to detect the time of year.