Transcript Chapter 36 - BelvilleApBio

Chapter 36
By Tom Tessitore, Hannah Turk,
and Allie Duca
-36.1: Land plants acquire resources both above
and below ground
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Live above ground and below ground
Algae absorbs CO2, water, and minerals from water
Competition for light, water, and nutrients
Taller plants have advantage
Natural selection favored the production of multicellular,
branching roots
• Natural selection favors plants capable of transporting
nutrients, water, and minerals over a long distance
• Plant success depends on photosynthesis
• Many mechanisms have been developed to acquire light,
CO2, and water
• Arrangement and size of leaves on a stem = phyllotaxy
• Determined by the shoot apical meristem and specific
species
• Most angiosperms have alternate phyllotaxy (spiral
around stem)
• Each leaf max light and reduces shading by other leaves
(lower)
• Features reduce self-shading increase light absorbed
• Leaf area index: the ratio of the total upper leaf surface
of a single plant divided by the surface area of the land
it’s growing on
• Higher than 7 is not helpful
 Add more leaves means respire not photosynthesize
 Programmed cell death, leaves and branches shed =
self-pruning
 Leaf orientation affects light capture
• Variation in shoot architecture because plants have finite
amount of energy for it
• Allows to grow tall and prevent shading by other plants
• Natural selection shoots to optimize light absorption
• Vary in stem thickness
• The stronger the plant, the stronger the root system
• Taproot = anchored tall plant
• Fibrous root systems do not anchor tall as strongly
• Mycorrhizae = specialized mutualistic assosiations
between roots and fungi
• The elongation, branching, and mycorrhizae help roots
obtain water and minerals
-36.2: Transport occurs by short-distance diffusion
or active transport and by long-distance bulk flow
• Diffusion and active transport of solutes
• Diffusion is the spontaneous movement down
concentration gradients
• Diffusion if facilitated by aquaporins
• Transport proteins help diffusion across membranes
• Proton pumps generate an H+ gradient used to transport
solutes
• Diffusion of water (osmosis)
• Osmosis = spontaneous movement of free water down
its concentration gradient
• Water flows across membranes from regions with higher
water potential to regions with lower water potential
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Solutes decrease
When plants lose water the become flaccid
Greater solute becomes turgid
Wilts with loss of water
Protoplast shrinks and pulls away from cell wall =
plasmolysis
• External solution has lower water potential and water
diffuses out of cell
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3 major pathways of transport:
the apoplastic-moving in the spaces between cells
Symplastic-moving through the cells themselves
transmembrane routes-a combination of both apoplastic
and symplastic routes
 cytoplasmic channels = plasmodesmata
 bulk flow due to pressure differences at opposite ends
36.3- Water and minerals transported from roots to shoots
• Absorption of water and minerals by root cells
• most of the water and mineral absorption occurs at the
roots
• epidermal cells are permeable to water
• root hairs are a type of epidermal cells that account for
much of the absorption of water by roots
• the soil solution the root hairs absorb consists of water
and mineral ions
• although soil solution usually has a low mineral
concentration, active transport helps roots obtain
essential minerals
• Transport of water and minerals into the Xylem
• Water cannot be transported to the rest of the plant until
they enter the xylem of the stele, or vascular cylinder.
• Endodermis- the innermost layer of cells in the root
cortex, surrounds the stele and functions as the last
checkpoint for the passage of minerals into the vascular
tissue.
• Casparian Strip- a “dead-end” that blocks minerals from
reaching the stele. It forces water and minerals that are
passing moving to cross the plasma membrane.
• Bulk Flow Driven by Negative Pressure in the Xylem
• Transpiration lowers water potential in the leaf by
producing negative pressure (tension)
• Low water potential draws from the xylem
• Xylem Sap- the water and dissolved minerals in the
xylem
• At night- root cells continue pumping mineral ions into
the xylem of the stele.
• Root pressure- a push of xylem sap.
• Guttation- water pushed out of leaves; happens when
more water enter the leaves than is transpired.
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Material can be moved:
Upward by positive pressure from below
Downward by Negative Pressure above.
Transpirational pull depends on
Adhesion
Cohesion
Surface Tension
Cohesion and adhesion help transportation by bulk flow
Cohesion is due to hydrogen bonding- can pull xylem
sap without the water breaking
• Adhesion is also due to hydrogen bonds- bonds to
hydrophilic cell walls to slow the force of gravity.
• Xylem sap ascent by bulk flow: a review
• Transpiration maintains movement of xylem sap against
gravity
• The water potential gradient is essentially a pressure
gradient.
• Plants do not use energy to lift xylem by bulk flow.
36.4- Stomata help regulate the rate of
transpiration.
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Plants control loss of water from their leaves using stomata
Stomata open and close using guard cells
Potassium ions are transported through the plasma and vascular
membranes and causes the guard cells to become more turgid
when the water enters
when it becomes more turgid, it opens
when the potassium ions leave, it closes
generally stomata open during the night and close during the day
Plants know that it is dawn because:
1. Light
2. Carbon Dioxide
3. an internal clock
some plants called xerophytes are adapted to regions of little
moisture.
CAM plants photosynthesize differently than other plants.
36.5-Transportation of Sugars
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Transpiration only pulls water from the roots up
Instead, sugar moves from a sugar source to a
sugar sink
– Sugar source-a plant organ that makes sugar
(Ex:a fully developed leaf)
– Sugar sink-organ that consumes sugar
(Ex:growing roots, fruit)
Sugar sinks use nearest sugar source
Sugar moves both apoplasticly and symplasticly
into the phloem
Building up of sap at a sugar source gives it the
pressure to move quickly to sugar sinks
36.6-The Dynamic Symplast
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Plasmodesmata were once thought to be rigid
In fact, they are actually fluid and changing
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Plants are able to dilate plasmodesmata to
allow proteins to pass through
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Viruses make proteins that cause the
plasmodesmata to open, allowing the viruses to
move from cell to cell
– The symplast allows proteins and RNA molecules to
coordianate development between cells
• It also allows electric signals to pass through it,
triggering different systems
– These include change in gene transcription,
respiration, photosynthesis, and hormone
levels
– This allows the phloem to act as a pseudonerve