BI111 Lecture 10: BI111 – L10
BI111 – L10
Challenge 2: Competition for Light and Gravity
Why grow upwards?
oPhotosynthesis requires light
oCompetition between individuals for access to light, leads to selection for growth AND
structures that increase photosynthetic ability
Solution:
Some plant cells have secondary cell wall
oCellulose fibres anchored with lignin: stronger and more rigid
oCreates waterproof barrier (hydrophobic)
oResistant to decay and attack by microbes
Lignin not found in bryophytes or green algae
oRecently discovered in red algae
The presence of lignin in both land plants and red algae, what is the most likely due to?
oConvergent evolution
Leaves: microphylls and megaphylls
oMicrophylls - single unbranched strand of vascular tissue
Lycophytes: club mosses and scale trees
oMegaphylls - multiple, branched strand of vascular tissue
Pterophytes: ferns, horsetails, and whisk ferns
Challenge 3: Spatial Segregation and Transportation or Resources
Minerals and most water in the soil
Light and carbon dioxide for photosynthesis above ground
As plants get bigger, how do they ensure that water and nutrients get to the right places?
Primary Growth (Up and Down)
Apical meristems at root and shoot tips
oSelf-perpetuating clusters of cells
oIncreases height of shoot, and length of roots
Transportation and Support:
Root and shoot system are an integrated system with many adaptations for transport of water,
minerals and organic substances, as well as structural support
Material transport:
oShort distances between cells
oLong distances between roots and shoots parts → xylem and phloem
Rhynia - an early seedless vascular plant:
oPhloem - vascular tissue which conducts sugars through the plant body
oXylem - vascular tissue conducts water and dissolve minerals from soil to roots to shoots
Below ground:
oThe rhizoids of early plants functioned as anchors, not for support, nutrition, storage or
water absorption
oExtensive mutualisms with Mycorrhizial fungi (carbon for nutrients)
Why are they so good at extracting nutrients> → root hairs
Other Seedless Vascular Plant Characteristics:
Lycophytes (club mosses and scale trees), pterophytes (ferns, horsetails, and whisk ferns)
Sporophyte phase dominant
Mst are homosporous (some heterosporous)
oA few ferns
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Document Summary
Why grow upwards: photosynthesis requires light, competition between individuals for access to light, leads to selection for growth and structures that increase photosynthetic ability. Some plant cells have secondary cell wall: cellulose fibres anchored with lignin: stronger and more rigid, creates waterproof barrier (hydrophobic, resistant to decay and attack by microbes. Lignin not found in bryophytes or green algae: recently discovered in red algae. The presence of lignin in both land plants and red algae, what is the most likely due to: convergent evolution. Leaves: microphylls and megaphylls: microphylls - single unbranched strand of vascular tissue. Lycophytes: club mosses and scale trees: megaphylls - multiple, branched strand of vascular tissue. Challenge 3: spatial segregation and transportation or resources. Minerals and most water in the soil. Light and carbon dioxide for photosynthesis above ground. Apical meristems at root and shoot tips: self-perpetuating clusters of cells o. Increases height of shoot, and length of roots.
