Chapter 29: Plant Structure & Function
(of roots, stems, & leaves)Pages 582-607Targets: 18-24
Name: Hour:
Plant Unit Notes 4 of 5
2
Review of Main Plant Cell Parts:• Large fluid-filled vacuole - provide turgor
pressure for support & store water for dry spells
• Plastid: pigment containing organelles
• Thick cell wall - made of cellulose for support, that surrounds the cell membrane
3
Plants are made up of 3 types of cells• Parenchyma Cells
– Thin flexible cell walls, cube-shaped– Large central vacuole– Function: photosynthesis, storage, & healing– Ex: flexible green stems, & fleshy fruit (Apples)
• Collenchyma Cells– Thicker cells walls; irregular shape– Function: support for growing plant parts– Ex: areas still lengthening (Celery stalks)
• Sclerenchyma Cells– Thickest/rigid cell wall– Function: strength & support for non growing
plant parts; usually dies at maturity– Ex: a frame to support the plant (shell on nut)
4
3 Types of Plant Tissue Systems
Location
Function in
Roots
Function in
Stems
Function in
Leaves
Dermal
Tissue(epidermis)
outer most layer
-cuticle-stomata
absorption;
protection
gas exchange
; protecti
on
gas exchange; protection
Ground
Tissue
b/w dermal & vascular
support; storage
support; storage Photosynthe
sis
Vascular
Tissue
Tubes throughou
t plant
transport; support
transport; support
transport; support
5
Vascular Plant Tissue:Xylem:
- Dead at maturity- Transports water- 2 Cell Types
- Tracheid: tapered ends;
pits to allow water to pass through
- Vessel Elements: larger holes at top & bottom
http://www.sirinet.net/~jgjohnso/plants.html
Phloem:- living at maturity-Transports organic material- 2 Cell Types
- Sieve Tube: filters- Companion Cell:
assists in transport along sieve tube
http://www.sirinet.net/~jgjohnso/plants.html
6
• Meristems: where plant growth originates (cells continually divide)
1. Apical Meristems: increase length @ tips• Location: Tips of stem & root
2. Intercalary Meristems: increase length b/w nodes• Location: b/w tip and base of stem & leaves
*why grass can regrow after being mowed
3. Lateral Meristems: increase diameter• Location: outsides of stems & roots• 2 Types:
– Vascular cambium (b/w xylem & phloem)– Cork cambium (outside phloem = makes cork)
• Primary Growth: growth in length (apical & intercalary)• Secondary Growth: growth in width (lateral)
Plant Growth:
7
Concept Check1. What is the function of a plant vacuole?
- provide turgor pressure for support & store water for dry spells
2. Name the 3 types of plant tissues- dermal, vascular, ground
(a 4th could be meristematic)
3. Name the 3 types of cells found in plants- Parenchyma Collenchyma
Sclerenchyma
8
Plant Organs: Roots (typically grow underground)
Function: anchor in place, transport water & mineral nutrients, and storage of water & organic compounds
Types of roots:– Taproot: 1st root is the largest; generally not deep
rooted• Ex: Carrot, radish
– Fibrous Root System: numerous roots develop & branch
• Ex: Grass
– Adventitious: grow roots from above ground parts (stems & leaves); prop roots of corn & aerial roots of vines
9
Root Structures– Root cap : protects apical meristem, produces “oil”
– Root hairs: increase surface area for water absorption (mycorrhizal fungi)
– Cortex: ground tissue just inside of epidermis
– Endodermis: ground tissue found inside the cortex; has a waterproof substance to control water & mineral movement
– Vascular Tissue: innermost core of roots.– Dicot: “X” shaped xylem with pockets of phloem– Monocot: pith in the middle with alternating
xylem & phloem in a ring
– Pericycle: outer layer of vascular tissue; produces lateral roots
10
Plant Organs: Stems (typically above ground, upright & woody or non-
woody)
Function: support leaves, transport material, provide storage
Special Types of stems: (due to adaptations to the environment)
• Stolons: grow along soil to produce new plants
• Tubers: underground; modified for storing energy as starch
• Fleshy stems: store water and carry out photosynthesis
11
Stem Structures–Node: where a leaf is attached to a stem–Internodes: space between the nodes–Bud: where a new shoot can grow (stem or leaf)–Bud scales: cover buds; leave scars after opening
Primary Growth-Pith: forms in center of stem in dicots; separates from cortex-Vascular Tissue:
-Monocots: xylem/phloem in scattered bundles
-Dicots: xylem in/phloem out; form a ring in the cortex
-Look at extra picture handouts!
12
Stem Structures - ContinuedSecondary Growth: stems increase in thickness due to
division of vascular cambium cells (b/w xylem & phloem)
–Wood: secondary xylem–Heartwood: darker wood; older, does not transport water–Sapwood: lighter wood; still transports water
–Bark: phloem near outside of stem; for protection (made of cork, cork cambium, and phloem)
–Springwood: wood cells wide & thin walled; more water present–Summerwood: wood cells small & thick walled; lack of water–Annual Ring: created by difference in appearance (not seen in tropical plants, why?)
13
Transport of sugar through phloem (translocation)• From source to sink by Pressure Flow Hypothesis
– Source: where sugar is made or stored– Sink: where sugar will be stored or used
*sugar mainly made in leaves - moved to rest of plant
Transport water & dissolved minerals through xylem (transpiration)
• Water pulled up by Cohesion-Tension Theory– Water molecules stick together; cohesion– Water molecules stick to xylem; adhesion– Water evaporates through stomata & pulls others along
• Storing water and nutrients– Large amount of parenchyma cells to store:
• Water; cactus / Sucrose; sugar cane / Starch; potatoes
Stem Function: transport, storage, support leaves
14
Plant Organs: Leaves (typically thin & flat)
Function: Capture sunlight for photosynthesis
Types of leaves:- Tendrils: used to support & climb- Spines: protection; non-photosynthetic- Food traps: plants with poor soil nutrients
Structure:– Blade: broad flat portion of leaf– Petiole: stalk-like attachment to stem– Simple leaf: single blade– Compound leaf: blade is divided into leaflets
• Can be doubly compound; leaflets divided
15
• Epidermis: Outside layer of cells– Cuticle: waxy covering; prevent water loss– Hairs: protect against insects & sun– Stomata: tiny air pores, areas for gas exchange;
number & location vary on plants•Guard cells: regulate the size of the stomata
• Mesophyll: Ground tissue; chloroplast-rich– Palisade: under upper-epidermis; tightly packed– Spongy: under palisade layer; loosely packed, air
spaces
• Veins: bundles of vascular tissue (parallel vs. branched)
Leaf Structures
16
Concept Check1. What is the function of the root cap?
- protects apical meristem, produces “oil”
2. What are the main differences b/w xylem & phloem?
- xylem: dead at maturity; transports water; specialized cells: tracheid/vessel elements
- phloem: alive at maturity; transports food; specialized cells: companion/sieve tube
3. What difference b/w the stomata & the guard cells?
- stomata = space; gas (O2/CO2) passes through- guard cells = cells; swell/shrink to control size of
space
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