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26 Cards in this Set
- Front
- Back
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Why do multicelluar plants need a transport system? |
Every cell in a multicelluar plant needs a regular supply of water and nutrients. There are many cells that are too far away from the edge to get these by diffusion so they need a transport system |
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What is the distribution in the xylemand pholem in leaves, stesms and roots? |
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What is the structure of xylem vessels? |
Xylem tissue consists of tubes to carry the water and dissolved minerals, fibres to help support and living parenchyma cells. The tubes are narrow it has lignified walls with pits in which allows the water to move sidewards. Lignin is deposited in spiral, annular or reticulate patterns. |
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What is the structure of Seive tubes elements? |
They contain very little cytoplasm and no nucleus. They are lined up end-to-end to form a tube. This tube contains cross walls at intervals, these are called sieve plates. The sieve tubes have very thin walls |
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What is the structure of companion cells? |
They have a large nucleus and dense cytoplasm. They have numerous mitochondria to produce the ATP needed for active processes. The cytoplasm of the companion cell and the sieve tube is linked through many plasmodesmata. |
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What is the function of xylem vessels? |
To transpor water and minerals from the roots up to the leaves and other parts of the plant. |
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What is the function of seive tube elements? |
They line up end to end to form a tube that can transport sucroe. The cross walls allow sap to flow |
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What is the function of companion cells? |
They carry out the metabolic action needed by the seive tube elements. This includes using ATP as a source of energy to load sucrose into the sieve tubes. |
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What does the term transpiration mean? |
The loss of water by evaporation from the aerial parts of a plant |
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Why is transpiration a consequence of gaseous exchange? |
Water enters the leaves and pases to the mesophyll cells by osmosis the water evaporated from the surface of them to form water vapour mesophyll cells have large spaces that help it diffuse through the leaf, the water potential rises as more and more water vapor is collected. then water will diffuse outside the leaf |
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Names 8 things that affect transpiration rates |
number of leaves number, size and position of the stomata presence of cuticle light temperature relative humidity air movement of wind water availability |
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How is a potometer used to estimate transpiration rates? |
Water lost by the leaf is replaced from the water in the capillary tube. The movement of the meniscus at the end of the water column can be measured |
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Explain the movement between plant cells and their enviroment and other plant cells |
When plant cells are touching each other, water molecules can pass from one cell to another. The water molecules will move from the cell with the higher water potential to the cell with the lower water potential |
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How is water transported in the apoplast pathway? |
The cellulose wlls have many water filled spaces between the cellulose molecules. Water can move through these spaces. The water does not pass through any plasma membranes. |
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How is water transported in the symplast pathway |
Water enters the cell through the plasma membrane. It can then pass through the plasmodesmata from one cell to the next. The plasmodesmata are gaps that have a thin strand of cytoplasm. Once inside the cytoplasm water can move through the continuous cytoplasm cell to cell |
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How is water transported through the vacuolar pathway? |
Similar to the symplast pathway but the water is not confined to the cytoplasm of the cell. It is able to pass through the vacuoles as well. |
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What is the role of the casparian strip? |
It blocks the apoplast pathway between the cortex and the xylem this ensures water and dissolved ions pass into the cell cytoplasms There are transporter proteins in cell membranes Nitrate can be actively transported from the cytoplasm to the xylem this lowers the water potential in the xylem so water from cortex cells follows into the xylem by osmosis once the water has entered the xylem it cannot pass back into the cortex as the apoplast pathway of the endodermal cells is blocked |
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what is the route of water? |
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What is adhesion? |
The attraction of molecueles to the walls of the xylem |
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What is cohesion? |
The attraction of water molecules for one another |
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How are the leaves of some xerophytes adapted to reduce water loss by trasnpiration? |
-smaller leaves -densely packed mesophyll (reduces the cell surface area that is exposed to the air inside the leaves( -thicker waxy cuticle -closing the stomata where water availability is low -Hairs on the surface on the leaf that traps air -pits containing stomata can become saturated with water vapour which reduced diffusion -rolling the leaves -some plants have low water potential inside their leaf cells |
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Explain translocation as an energy requiring proced |
Sucrose is loaded into the phloem by ATP, it is used by the companion cells to transport hydrogen ions out of their cytoplasm and into the surrounding tissue This sets up a diffusion gradient and the hydrogen ions diffuse back into the companion cells. the diffusion occurs through special cotransporter proteins. |
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What are sources and sinks? |
Sugers made in photosyntesis are converted into sucrose and loaded into the phloem. In early spring when the leaves need energy this energy is supplied from the stores in other parts of the plants and the leaves act as a sink other sources include roots which can also be a sink at other times. |
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The movement of sucrose along the phloem |
1. sucrose is actively loaded into the sive tube elemnt and reduces water potential 2. water follows by osmosis and increases the hydrostatic pressure in the sieve tube element 3. water moves down the sieve tubes from higher hydrostatic pressure at the source to lower hydrostatic pressure at the sink 4. Sucrose is removed from the sieve tube by the surrounding cells and increases the water potential in the sieve tube 5. water moves out of the sieve tube and reduced the hydrostatic pressure |
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Evidence for the energy requiring mechanism of translocation |
-ringing a tree to remove phloem results in sugers collecting above the ring -an aphid feeding on a plant stem can be shown that the mouthparts are taking food from the phloem -companion cells have many mitochondria -the rate of flow of the sugars in the phloem is so high that energy must be needed to drive the flow |
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Evidence agaisnt the energy requiring mechanism of translocation |
-not all solutes in the ohloem sap move at the same rate -sucrose is moved to all parts of the plant at the same rate rather than going more quickly to areas with a low concentration -the role of sieve plates in unclear |
