Chapter 23-1. Chapter 23-2 CHAPTER 23 BUDGETARY PLANNING Accounting Principles, Eighth Edition.
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Transcript of Chapter 23
Chapter 23
Plant Structure and Function
Section 23-1Specialized Tissues in Plants
Structure of a Seed Plant 3 organs -> roots,
stems, leaves Linked by tissues
that provide support, protection, nutrient production and transport
Structure of a Seed Plant Roots
Anchor plants, prevent erosion, absorb nutrients/water and transport them, store food, hold plants upright
Stems Produce leaves/reproductive structures,
contain transport systems Leaves
Photosynthesis, have adjustable pores to reduce water loss and help gas exchange
Plant Tissue Systems 3 main tissue systems -> dermal, vascular,
and ground Dermal Tissue - protective, outer covering
Single cell layer in young plants called epidermis, the outer surface often covered with a waxy cuticle
In older plants usually many layers, sometimes covered with bark
Some epidermal cells have trichomes, which protect leaves and give them a fuzzy appearance
In roots, incudes root hairs to absorb water
Plant Tissue Systems Vascular Tissues –
support plant bodies, transport water and nutrients Xylem – transports
water Phloem –
transports products of photosynthesis
Xylem Cells called tracheids As they mature, they die and leave their
cell walls which contain lignin (gives wood strength)
Cells have connecting openings for water to pass
Pits allow water to diffuse into ground tissue
Xylem Angiosperms have
second xylem tissue called vessel elements – wider than tracheids, arranged end to end
Mature and die, cell walls develop slits at each end for water to move freely
Phloem Alive at maturity Main cells called sieve tube elements,
arranged end to end forming sieve tubes
Small holes at ends so nutrients can move from cell to cell
Lose nuclei and most organelles as they mature
Phloem Companion cells
surround sieve tube elements - keep nuclei/organelles
Plant Tissue Systems Ground tissue – produces/stores
sugars, contributes to physical support Parenchyma cells – thin walls, large
central vacuole surrounded by thin layer of cytoplasm – chloroplasts in leaves
Collenchyma cells – thicker walls, flexible, provide support
Sclerenchyma cells - thickest walls, rigid, makes up seed coat
Parenchyma Collenchyma Sclerenchyma
Plant Growth and Meristems Meristems –
regions of unspecialized cells in which mitosis produces new cells ready for differentiation
Apical meristems found in places of rapid division – tips of stems and roots
Plant Growth and Meristems At first, cells produced in apical
meristems are all thin, unspecialized Gradually mature and differentiate to
form each tissue system Meristems also create highly specialized
cells of cones and flowers Patterns of gene expression changes
the stem’s apical meristem
Section 23-2Roots
Root Structure and Growth As soon as a seed sprouts, its first root
brings in water/nutrients from soil Cells divide rapidly, pushing root tips
into soil, providing raw materials for developing stems and leaves
Root Structure and Growth Taproot Systems
Primary root grows long and thick (taproot) giving rise to smaller branches
Can store sugars and starches Fibrous Root Systems
Begin with one primary root, which is replaced by many equally sized branches that grow separately from the base of the stem
Help prevent soil erosion
Dandelion (taproot) Grass (fibrous root)
Anatomy of a Root Epidermis made of dermal tissue –
protection and absorption Surface covered in root hairs – penetrate
between soil particles and increase surface area
Cortex composed of ground tissue Water/minerals move from epidermis Stores products of photosynthesis and
starches
Anatomy of a Root Endodermis – layer of ground tissue
enclosing vascular cylinder – moves water and minerals to center of root
Vascular cylinder in the center composed of xylem and phloem Dicot roots have central column of xylem
Anatomy of a Root Apical meristems near root tip allow
roots to increase in length Root cap protects meristem, secretes
slippery substance to ease progress through soil Cells at tip scraped away and replaced
continually
Root Functions Uptake of plant nutrients
Soil contains sand, silt, clay, air, bits of decaying animal/plant tissue in varying amounts
Plants need inorganic nutrients like nitrogen, phosphorus, potassium, magnesium, calcium
Trace elements also important, but excessive amounts can be toxic
Root Functions Active transport of dissolved nutrients
Active transport proteins in root hairs, other epidermal cells
Bring in mineral ions from soil Water movement by osmosis
Mineral ions accumulate in root, water “follows”
Root Functions Movement into vascular cylinder
Move through cortex Cylinder enclosed by endodermis – cells
meet and cell walls from waterproof zone called Casparian strip
Casparian strip forces water/minerals to move through cell membrane rather than between cells – filter and control water
Ensures one-way flow
Root Functions Root pressure
Minerals pumped into vascular cylinder, water follows by osmosis creating pressure
Water has to go up - root pressure forces water through vascular cylinder into the xylem
Up and up!
Section 23-3Stems
Stem Function Produce leaves, branches and flowers Hold leaves up to sun Transport substances
Xylem and phloem form continuous tubes from roots to stems to leaves
In many plants they function in storage and aid in photosynthesis
Anatomy of a Stem Surrounded by layer of epidermal cells
with thick cell walls and a waxy protective coating
Anatomy of a Stem Growing stems have
nodes where leaves are attached
Buds contain apical meristems to produce new stems and leaves
Larger plants have woody stems to support leaves and flowers
Monocot Stems Vascular
bundles (clusters of xylem and phloem) scattered throughout ground tissue composed mainly of parenchyma cells
Dicot Stems Vascular bundles
arranged in a ring pattern
Parenchyma cells inside ring called pith, outside form cortex
Complexity increases as stem increases in diameter
Primary Growth Occurs in all seed plants – apical
meristems increase plant length
Secondary Growth Larger plants require older parts of stem
to increase in thickness Common in dicots and gymnosperms
Secondary Growth Takes place in meristems called
vascular cambium (produced vascular tissues, increase thickness of stem) and cork cambium (outer covering)
Growth from Vascular Cambium Thin layer of cells between xylem and
phloem Xylem pushed in, phloem pushed out Increases diameter of stem each year
Wood Formation Layers of secondary xylem produces by
vascular cambium Older xylem near center no longer
carries water – heartwood (dark) Surrounded by sapwood – active in
fluid transport (light)
Tree Rings In spring, vascular cambium produces
light colored rings of xylem (early wood) Cells grow less as season continues,
have thicker cells walls, darker in color (late wood)
A ring = a year of growth Thick rings mean favorable weather
Formation of Bark Everything outside the vascular
cambium in a mature stem (phloem, cork cambium, cork)
Expansion leads to oldest tissue splitting Cork cambium surrounds cortex
producing a thick layer of cork to prevent water loss
Outer layers may flake off as stem thickens
Section 23-4Leaves
Anatomy of a Leaf Blade – thin, flat part of leaf –
maximum light absorption Blade attached to stem by petiole Outer covering of dermal tissue
Top and bottom covered by epidermis, tough irregular cells with thick outer walls
Covered by waxy cuticle – waterproof, prevents water loss
Anatomy of a Leaf Vascular tissues bundles into veins that
run from stem through leaf Palisade mesophyll beneath upper
epidermis – closely packed cells that absorb sunlight
Spongy mesophyll contains air spaces connected to stomata – small opening in epidermis allowing for gas exchange
Transpiration Mesophyll cell walls moist for easy
diffusion Water can evaporate from these
surfaces by transpiration May be replaced by water from xylem Cools leaves on hot days, but can
threaten survival
Gas Exchange Exchange gases between air spaces in
spongy mesophyll and exterior by opening stomata
Homeostasis If stomata were always open, too much
water would be lost to transpiration Open just enough to allow
photosynthesis Guard cells control opening and
closing of stomata, regulating movement of gases
Homeostasis When water is abundant, increaser in water
pressure in guard cells opens stoma by curving
When water is scarce, water pressure in guard cells drops and stoma closes
Stomata usually open during day, closed at night
Can be closed in bright sunlight or hot/dry conditions
Respond to environment
Transpiration and Wilting Osmotic pressure keeps leaves/stems
rigid Water loss due to transpiration can lead
to a loss of pressure in the cells
Adaptations of Leaves Pitcher plant – attract/digest insects to
obtain nitrogen Living stone (rock plant) – 2 leaves for
hot/dry conditions are round to minimize exposure to air, have very few stomata
Spruce – waxy epidermis, stomata sunken below leaf surface
Cactus – photosynthesis occurs in stems, leaves are thorns
Section 23-5Transport in Plants
Water Transport Combination of transpiration and
capillary action moves water through xylem
Water evaporates through stomata, leaf dries out, water is pulled up through xylem
How Cell Walls Pull Water Upward Water molecules
attracted to each other by cohesion – H bonds form between molecules
Water molecules bond to other substances by adhesion
How Cell Walls Pull Water Upward Capillary action is
the tendency of water to rise in a thin tube because of cohesion and adhesion
Thinner tube, higher water will rise
Putting it All Together Xylem tissue hollow, connected tubes
(tracheids and vessel elements Tubes are lined with cellulose cell walls
(adhesion) Transpiration removes water from the
exposed walls, adhesion pulls water from interior of leaf
Pull is powerful - extends down through tips of roots to the water in the soil
Nutrient Transport Pressure-flow hypothesis1. Membranes of sieve tube cells use active
transport to move sugars from cytoplasm into sieve tube itself
2. Water follows by osmosis, creating pressure at the source of the sugars
3. If a plant region has a need for sugars, they are actively pumped out of the tube and into the tissue - water leaves the tube via osmosis, reducing the pressure
Nutrient Transport Flow of nutrient-rich fluid from the
sources of sugars (source cells) to the places where sugars are used or stored (sink cells)
Flexibility in changing seasons