Ch 29: Resource Acquisition, Nutrition, and Transport in Vascular Plants Flashcards
Define apoplast.
Everything external to the plasma membrane of a plant cell, including cell walls, intercellular spaces, and the space within dead structures such as xylem vessels and tracheids.
Movement of water and minerals through the xylem,
movement of sugars through the phloem.
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Plants do use oxygen, but they make more than they need, so they have extra to emit back out into the environment
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The leaves are the site of sugar production, and then need to be transported around the plant to other parts. Sugars are carried to storage organs.
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Roots still take in ______, just as all eukaryotes do. And then still emit CO2, but the net production is of more O2.
oxygen
Plants cells are connected by _______ (singular: plasmodesma) which allow materials to move from cell to cell.
plasmodesmata
At maturity, xylem is just a cell wall, like a straw.
Apoplastic route
The _________ consists of the entire mass of cytosol of all the living cells in a plant, as well as the plasmodesmata, the cytoplasmic channels that interconnect them.
symplast
In the ________ route, water and solutes move out of one cell, across the cell wall, and into the neighboring cell, which may pass them to the next cell in the same way. The transmembrane route requires repeated crossings of plasma membranes as substances exit one cell and enter the next.
transmembrane
The cell’s plasma membrane is selectively permeable.
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The physical property that predicts the direction in which water will flow is called water potential, a quantity that includes the effects of solute concentration and physical pressure. If there is no barrier to the flow of free water, it moves from regions of higher water potential to regions of lower water potential.
Water moves from high water potential –> low water potential
A water potential of 0 means there are no solutes present at all.
**Ch 5 has more info about water potential.
Figure 5.10 Water molecules can pass through pores, but sugar molecules cannot.
Water moves from an area of higher to lower free water concentration (lower to higher solute concentration).
Passive transport
d
The movement of water molecules across biological membranes is too rapid to be explained by unaided diffusion. Transport proteins called ________ (see Figure 5.9) facilitate the transport of water molecules across plant cell plasma membranes. These channels, which can open and close, affect the rate at which water moves osmotically across the membrane.
aquaporins
If a cell moves things against a concentration gradient, it has to use energy to do that (______ transport).
active
When solute concentration in a solution increases, the water potential of the solution _________
decreases.
Water and dissolved minerals located in the cell walls and intercellular spaces of the root cortex are in the __________ route of transport, and those in the ________ of cortex cells are in the symplastic route.
apoplastic
cytoplasm
The _________ route requires plasmodesmata. The __________ route is obstructed by the Casparian strip, thereby forcing water and minerals to cross the plasma membranes of endodermal cells before gaining entrance into the vascular cylinder.
symplastic
apoplastic
Solute potential is always negative.
Living cells have + turgor pressure. Dead cells have - pressure potential.
_
Xylem transports water and minerals. At maturity, xylem cells are ____ and ______.
dead
hollow
Vessel elements are found mostly in angiosperms.
Tracheids (think straws) are present in all vascular plants.
–
Pressure potential inside xylem cells is negative.
Pressure potential in xylem changes with position in the plant. trunk xylem = -0.6 MPa
Review hydrogen bonding – Concept 2.5 in text
hydrogen bonds between molecules of water (cohesion) is important
Cohesion - water molecules have surface tension between them at air/water interfaces.
ii
Adhesion - water molecules forming hydrogen bonds with other types of molecules.
adhesion - two different types of things sticking together
cohesion - two like things sticking together
How does transpiration get started?
water evaporates out of the stomata of the leaf
Cell walls aren’t solid. Microfibrils
More water from in between the microfibrils moves into the gas phase when water evaporates from the air spaces.
Surface tension increases when the gas spaces are full of evaporated molecules.
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The strong adhesion of water molecules (again by hydrogen bonds) to the __________ walls of xylem cells helps offset the downward force of gravity.
hydrophilic
The plant expends no energy to lift xylem sap by bulk flow. Instead, the absorption of sunlight drives most of transpiration by causing water to ________ from the moist walls of mesophyll cells and by lowering the water potential in the air spaces within a leaf. Thus, the ascent of xylem sap, like the process of photosynthesis, is ultimately _____ powered.
evaporate
solar
p. 620
How do materials get into the plant?
Materials can’t travel through the apoplastic route at the endodermis. There is a structure that prevents materials from traveling between cells, known as the Casparian strip.
materials that make it through the endodermis can enter the xylem.
Phloem moves sugars.
Unlike xylem, phloem cells are living at maturity. Pressure potential in phloem cells is positive. 2 kinds of cells in phloem - sieve-tube element (only cytosol, no _______), the companion cell is packed with organelles. The companion cell supplies the sieve tube with what it needs.
organelles
Translocation = transport of photosynthetic products (sugars). Photosynthesis happens in the _________
mesophyll
Sugar travels from mesophyll to phloem using _____ ________ transport (not bulk flow).
Once it gets to the phloem, it moves by bulk flow.
short distance
Phloem can carry sugars from a source cell (leaf) down to a sink cell (storage root).
This loading of sugar (most often sucrose), must be done by active transport bc the sugar is moving against a concentration gradient.
Water potential is higher in the leaf than in the phloem, so water can move by osmosis/ passive transport.
The water at the leaf pushes material down the phloem into the sink. Increased water potential at the top, pushes materials down.
Figure 29.22
3 - unloading of sugar into sink cell - happens by diffusion (down a concentration gradient)
The sink cell converts the sucrose to a polymer starch, to prevent the sucrose concentration from getting to high (which would stop diffusion).
Down near the sink cells, water moves from the phloem back over to the xylem to be recycled, moved back up the plant.
Water recycling is passive - osmosis.
