plant structure & development chapter 35. overview roots – underground shoots – leafs...
TRANSCRIPT
PLANT STRUCTURE & DEVELOPMENT
Chapter 35
Overview
Roots – Underground Shoots – Leafs & Stems 3 Tissue types in the above
Dermal, Vascular, & Ground 5 Types of Differentiated Plant Cells
Parenchyma Collenchyma Sclerenchyma Xylem Phloem
Roots
Multicellular organ Anchors plant Absorbs water & Minerals May store sugar & starches
Fibrous Roots vs. Taproots
Fibrous Roots – mat of thin roots that are spread just below the root’s surface
Taproots – 1 thick, vertical root with many lateral roots that emanate from it
Questions
Which root type is focused on absorption?
Which root type is focused on storage?
Fibrous roots are not efficient absorbers, so what structure is responsible for absorption?
Root Hairs
Located at the tips of roots Dramatically increase the
surface area Efficient absorption of H2O
and minerals
Mycorrhizae – Symbiotic relationship
Root tips & fungus – assist in absorption
Found in vast majority of plants
Mycorrhizae
Shoots
Questions
What is the advantage to a plant to only grow at the apical and axillary buds?
A tree house was built between the stem and a branch without axillary buds. The growth rate of the apical buds is 2 feet per year, the growth rate of the axillary buds is 3 feet per year, and the tree house was built at a height of 10 feet. What will be the height of the tree house in 10 years?
Plant Organs (Leaf, Stem, & Roots)
Plant Organ Tissue Types
Ground Any tissue that is neither dermal nor vascular If the Ground tissue is located inside the
vascular tissue called pith Cortex – ground tissue located outside
vascular tissue
5 Types of Differentiated Cells1. Paren(chyma) cells – Most abundant cell type
-- Present throughout the plant-- perform most of the metabolic functions of the
plant (Photosynthesis & Respiration)
2. Collen(chyma) cells-- Support growing parts of the plant-- Grouped into cylinders
3. Scleren(chyma) cells -- Occupy NonGrowing parts of plant -- Tough cell walls for structural support
4th Type of Plant Cells
4. Xylem – water conducting cells-- 2 types: Tracheids & Vessels
-- Both types are dead at functional maturity
-- Tracheids found in ALL vascular plants
-- Long thin cells with lignin
-- Water moves through the pits
-- Vessels found primarily in angiosperms (flowering plants)
-- Have pits & perforated end walls for water movement
Vessel Elements & Tracheids
5th & Final Type of Plant Cell
5. Phloem – Sugar & other organic compounds
2 Types: Sieve-tube elements & Companion Cells
-- Both types are alive at functional maturity
Sieve Tubes
-- Consist of chains of cells
-- Called sieve-tube element
-- Highly modified for transport
-- Lack nucleus, ribosomes, & vacuoles
Phloem Continued
Besides Sieve Tubes, there are also: Companion Cells
Provide for the molecular needs of the sieve-tube elements
Connected to the sieve-tube elements by plasmodesmata
Plant Growth
Plant growth is indeterminant Growth occurs throughout plant’s life Embryonic, developing, and mature organs
exist at all times during a plant’s life Animal growth is determinant
Growth ceases after a certain size has been reached
Meristems
Meristems are perpetually embryonic tissues Responsible for indeterminate growth Growth occurs only as a result of cell division in a
meristem 2 Types of Meristems
Lateral Meristem – Thickening of shoots or roots Thickening is called Secondary Growth
Apical Meristem – tips of roots and in buds of shoots Sites of cell division Allow the plant to grow and lengthen Primary Growth – when plant grows at apical meristems
Lengthening is called Primary growth
Primary Growth lengthens … Root Cap – protects
delicate meristem of the root tip as it pushes through the soil
Secretes a polysaccharide lubricant
Root Tip – contains 3 zones of cells in various stages of growth
3 Zones in root tip
Zone of cell division Root apical meristem & derivatives New root cells are produced in this region Mitotic divisions
Zone of elongation Cells elongate, sometimes significantly
Zone of maturation Differentiation and functional maturation
occurs
Roots - Primary Growth
Lateral Roots emerge from the Pericycle (lies inside the endodermis)
What about shoots?
Apical meristem – dome of dividing cells at tip of terminal bud
Primary growth (Lengthening) Accomplished by cell division and elongation
Primary Growth in Stems
How does grass continue growth after mowing?
Mowing should destroy the apical meristems, so how would grass continue to grow if there were no “growth areas”?
2 other meristems
Intercalary Primarily in monocots
(grasses) Response to grazing
pressure
Floral Flower growth Determinate growth
Lateral Meristems
Secondary growth Growth in the thickness of the shoot or root
2 Types Vascular Cambium
Adds layers of tissue called 2ndary Xylem & phloem
Cork Cambium Replaces the epidermis with the periderm (thicker
& tougher)
Secondary Growth
2 lateral meristems are responsible for 2ndary growth Vascular Cambium – produces 2ndary xylem
(wood) Cork Cambrium – produces a tough covering that
replaces epidermis Early in secondary growth
Bark – all the tissues outside the vascular cambium Includes the phloem derived from the vascular
cambium, cork cambium, & tissues derived from cork cambium
Question?
Why would the diameter of the plant have to increase as the plant grows?
Which diameter grows as a higher rate, xylem or phloem? Why?
Leaves…
Stomata interrupts the underside of the leaf
Flanked by guard cells – open/close the stomata
Ground tissue is in between upper & lower epidermis, in the mesophyll
Ground tissue is composed of parenchyma cells Site of photosynthesis are parenchyma cells
Leaf: Cross-Section
Angiosperms (Flowering Plants) Classified by years in life cycle
(germination death) Annuals – 1 year life cycle Biennials – 2 year life cycle Perennials – multiple year life cycle
Question
Why would there be spaces in the spongy mesophyll?
Why would there not be spaces in the palisade mesophyll?