BIS 2C Lecture Notes - Lecture 16: Sieve Tube Element, Tracheid, Xylem
27 Apr 2018
School
Department
Course
Limitations of Non-Vascular Plants
Support
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Gamete Dispersal (swimming sperm)
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Transport
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Vascular Advantages
Received tracheids (vascular cells - xylem and phloem)
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Branching independent sporophytes (tree leaves on branches)
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Xylem
Tracheids (small tubes) and vessels (larger tubes) are essentially dead cells
Tracheids came first
○
•
Vessels are cell walls with smaller cell walls to be joined end on end so that this
scan allow for large openings for water transport
•
Dead at maturity, provide structural support, no energy required for water
movement, have thick walls with lignin
200-400 liters per day can be moved up a large tree
○
The narrower the tube, the more pressure that can be withstood
○
•
Transpiration - passive movement of water up a tree
Evaporation takes water out of stomata (pulling forces)
○
Tension/negative pressure on xylem resulting from transpiration of leaves,
○
Cohesion between water molecules and adhesion to xylem transmits
tension all the way to roots, pulling water out from ground
○
One molecule lost will be a molecule gained at the bottom
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Unidirectional from roots to shoots
○
•
Loss of water is potentially detrimental but a necessary evil because it is through
these stomata that CO2is taken up
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As xylem extends and tree grows, must keep extending roots
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Phloem
Two alive cell types
Sieve tube cells - end on end cells with pores that connect via
plasmodesmata but lack nuclei at maturity
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Companion cell - sister cell to sieve cells
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Both thin walled
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•
Source vs Sink Cells
Source: create photosynthetic through photosynthesis; leaves
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Sink: take the products of photosynthesis for own use; fruits, flowers
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Pressure Flow Model
Can be moved bidirectionally
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ATP required to move sucrose in and out of the sieve tubes from sources
and to sinks
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Sucrose imported to system, increasing pressure which causes water to flow
passively to osmotically balance system which then pushes the solution
down the phloem
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Reproductive Life Cycles
Seedless Vascular Plants (fern)
Create a haploid spermatophyte and gametes through fertilization create a
diploid embryo
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Sporophyte crated from saprophyte and then sporangium creates the
spermatophyte
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Dominant sporophyte
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•
All land plants are Embryophytes so all have multicellular embryos retained on
the haploid parents
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Evolution of Vascular Plant
Group of Rhyniophytes
Fossils; simple vascular system with dichotomous branching (small xylem
and phloem)
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No leaves or roots with water absorbing filaments called rhizoids and
anchors called rhizomes
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•
Evolution of Leaves
Microphylls are small single veins that branch through small leaves on
Lycophytes (club moss)
Sporangium loses reproduction skill and becomes a method of transport
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Also strobilus projection with small clusters of sporangium (spores here
through meiosis)
○
•
Megaphylls are multiple branching veins through leaves on pretty much
everything after Lycophytes
Dichotomous branching changes to having one dominant branch and then
flattened side branches with webbing that then became megaphylls
○
•
Different aspects of Megaphylls
Horsetails - has highly reduced leaves that circle the stem(still megaphylls
because of branching) and sometimes have reproductive shoots with
sporangium
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Ferns have small reduced leaves, many sori on bottom of leaves (leaves are
not in clusters like on strobili)
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•
Ferns vs Mosses
Ferns exhibit alternation of generations where
Sporophyte is dominant and independent
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Swimming sperm which need wet places to reproduce
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Mosses also exhibit alternation of generations where
Gametophyte is dominant
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Introduction to Vascular Plants (16-18)
Monday, February 5, 2018
12:07 PM
Document Summary
Received tracheids (vascular cells - xylem and phloem) Tracheids (small tubes) and vessels (larger tubes) are essentially dead cells. Vessels are cell walls with smaller cell walls to be joined end on end so that this scan allow for large openings for water transport. Dead at maturity, provide structural support, no energy required for water movement, have thick walls with lignin. 200-400 liters per day can be moved up a large tree. The narrower the tube, the more pressure that can be withstood. Transpiration - passive movement of water up a tree. Evaporation takes water out of stomata (pulling forces) Tension/negative pressure on xylem resulting from transpiration of leaves, Cohesion between water molecules and adhesion to xylem transmits tension all the way to roots, pulling water out from ground. One molecule lost will be a molecule gained at the bottom.
