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69 Cards in this Set
- Front
- Back
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Why do plants need a transport system (refer to size, metabolic rate and SA:V ratio) |
Larger plants have a smaller SA:V ratio Not very active so demand for oxygen is low, however demand for sugars and water are high Need a system to move water and minerals from roots to leaves And sugars from leaves to rest of plant |
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What does vascular tissue consist of |
Xylem and phloemwhat |
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What are dicotyledonous plants |
Plants with two seed leaves and a branching pattern of veins in the leaf |
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What may vascular tissues also contain |
Collenchyma and sclerenchyma for support |
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Where is the vascular bundle found in a young root |
The centre |
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What is the shape of the xylem core and where is the phloem found |
X shape, phloem found between the arms of the X |
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What two cells surround the vascular bundle and state their function |
Endodermis- getting water into xylem vessels Meristem cells- able to divide |
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What is the layer of meristem cells called |
Pericyle |
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Where are the vascular bundles found in a stem |
Near the outer edge |
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What is the difference in distribution of the vascular bundle in woody and non-woody plants |
Non-woody- bundles are separate Woody- separate in young stems but form a continuous ring in older stems |
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Why do woody plants have a ring of vascular tissue |
Provides strength and flexibility to withstand the bending forces to which stems and branches are exposed to |
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State the composition of these vascular bundles |
Xylem found towards the inside Phloem found towards outside Layer of cambium found in between |
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Where are the xylem and phloem found in a dicotyledonous leaf |
In the veins at the central midrib |
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Which cell is located on top |
The xylem is found above the phloem |
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What does xylem tissue consist of and state their functions |
Vessels to carry water and dissolved mineral ions Fibres to help support plant Living parenchyma cells which act as packing tissues to separate and support the vessel |
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What is a xylem vessel |
A long column of dead cells with no contents |
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What does lignin do to the xylem walls |
Makes them waterproof Kills the cells Strengthens vessel walls and stops them from collapsing |
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Why does lignin form patterns in the cell wall |
Prevent the vessel from being too rigid |
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What happens when lignification is not complete |
Leaves gaps in the cell walls |
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What are these gaps called and what are their function |
Bordered pits, the pits in two adjacent vessels are aligned to allow water to leave one vessel and enter the other |
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Adaptations of xylem vessels |
Made from dead cells, aligned end to end to form a continuous column Tubes are narrow, so water column does not break easily and capillary action is effective Bordered pits Lignin deposited in patterns |
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Why is the flow of water not impeded |
No cross walls No cell contents, nucleus or cytoplasm Lignin thickening prevents wall from collapsing |
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What cells does phloem tissue consist of |
Sieve tube elements and companion cells |
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Structure of sieve tube elements |
Elongated and lined end to end to form sieve tubes Contain no nucleus and little cytoplasm |
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Why do sieve tube elements contain no nucleus and little cytoplasm |
Leave space for mass flow of sap |
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What are found at the ends of each sieve tube element |
Cross walls called sieve plates |
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Why do sieve plates contain holes |
To allow movement of sap from one element to the next |
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Main functions of sieve plates |
Support the tube, keep lumen open Block sieve tube after an infection |
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Where are companion cells found |
In between the sieve tubes |
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What do companion cells contain |
Large nucleus, dense cytoplasm, numerous mitochondria |
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Main function of companion cells |
Carry out metabolic processes needed to load assimilates actively into the sieve tubes |
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What are plasmodesmata |
Gaps in the cell wall containing cytoplasm that connects two cells |
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Name the 3 pathways water can take |
Apoplast, symplast and vacuolar |
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Apoplast pathway |
Passes through spaces in cell walls Water moves by mass flow |
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Symplast pathway |
Water enters cell cytoplasm through plasma membrane Then pass through plasmodesmata from one cell to next |
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Vacuolar pathway |
Similar to symplast but water passes through vacuole aswell |
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Why is the water potential in plant cells always negative |
Cytoplasm contains mineral ions and sugars |
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Typical pathway taken by most water leaving the leaf |
Water enters leaf through xylem and moves by osmosis into spongy mesophyll. May also pass along the apoplast pathway Water evaporates from cell walls of spongy mesophyll Water vapour moves by diffusion out of the open stomata |
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Importance of transpiration (stream) |
Transports useful mineral ions up plant Maintains cell turgidity Supplies water for growth, cell elongation and photosynthesis Supplies water that keeps plant cool when evaporated |
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Environmental factors of transpiration (5 answers) |
Light intensity, temperature, relative humidity, air movement, water availability |
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What are the 3 ways a high temperature will increase the rate |
Increase the rate of evaporation from cell surfaces so water-vapour potential in leaf rises Increase the rate of diffusion through stomata because water molecules have more kinetic energy Decrease the relative water vapour potential in air, allowing more rapid diffusion of molecules out of leaf |
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What devices measured the rate of water uptake |
Potometer |
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Precautions to make sure results are valid in potometer experiment (5 answers) |
Set it up under water to make sure there are no air bubbles Ensure shoot is healthy Cut stem under water to prevent air entering xylem Cut stem at an angle to provide a large surface area in contact with water Dry leaves |
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What is adhesion |
Attraction between water molecules and walls of xylem vessels |
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What is cohesion |
Attraction between water molecules caused by hydrogen bonds |
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Describe the movement of water and minerals across a root |
Water and minerals absorbed by root hair cells Water moves across root cortex down water potential gradient in symplast pathway towards endodermis Water moves into medulla and xylem by osmosis |
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Role of the casparian strip found on endodermis |
Blocks apoplast pathway between cortex and medulla Ensure water and dissolved mineral ions have to pass into cell cytoplasm through plasma membranes |
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Role of endodermis |
Active process that moves water along root Plasma membrane contains transport proteins, which actively pump mineral ions from cytoplasm of cortex cells into medulla and xylem |
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What three processes help move water up the stem by mass flow |
Root pressure Transpiration pull Capillary action |
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Describe root pressure |
Action of endodermis moving minerals into medulla and xylem by active transport draws water into medulla Pressure in root medulla builds up and forces water into xylem, pushing the water up the xylem by a few metres |
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Describe transpiration pull |
Water molecules attracted to each other by cohesion. These forces are strong enough to hold the molecules together in a long chain So when water is lost at top of column, the rest of the chain is pulled up |
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Describe capillary action |
Xylem vessels are narrow so adhesion forces pulls the water up the sides |
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What are hydrophytes |
A plant adapted to living in water or where the ground is very wet |
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What is a xerophyte |
Planted adapted to living in dry conditions |
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Adaptations of terrestrial plants to reduce water loss |
Waxy cuticle Stomata found on the under-surface of leaves, reduces evaporation due to direct heating Most stomata closed at night |
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Adaptations of marram grass |
Leaf rolled longitudinally so air is trapped inside- air becomes humid, which reduces water loss from leaf Thjck waxy cuticle on outer side of rolled leaf Stomata on the inner side of rolled leaf, protected by the enclosed air space Spongy mesophyll very dense, with few air spaces so less surface area for evaporation of water |
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Adaptations of cacti |
Succulents- store water in stems which become fleshy and swollen Leaves are reduced to spines- reduces surface area so less water loss by transpiration Stem is green for photosynthesis Roots are widespread or taproots |
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Issues faced by hydrophytes |
Getting oxygen to submerged tissues and keeping afloat Need to keep leave in sunlight |
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Adaptations of water lily |
Many large air spaces in leaf, keeps leaves afloat and in sunlight Stomata in upper epidermis so exposed to air to allow gaseous exchange to occur Leaf steam has many large air spaces- helps with buoyancy and also allows oxygen to diffuse quickly to roots for aerobic respiration |
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What is the name of the structure that releases water droplets when transpiration is unavailable |
Hydathodes |
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What are assimilates |
Substances that have become a part of the plant |
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What is translocation |
Movement of assimilates throughout plant |
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What is the source of a plant |
Part of the plant that loads assimilates into phloem sieve tubes |
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What is the sink |
Part of the plant that removes assimilates from phloem sieve tubes |
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Describe active loading |
H+ ions actively pumped out of companion cells using energy from ATP H+ ions diffuse back into companion cell through facilitated diffusion, however the cotransport proteins will only let them in if they have a sucrose molecule Increasing concentration of sucrose in companion cell causes it to diffuse into sieve tube through plasmodesmata |
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What does sap consist of |
Sucrose, amino acids and other assimilates |
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Through what process does sap move along the phloem |
Mass flow |
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Why does the sap move from source to sink |
Source- sap enters cells, reducing water potential resulting in water entering increasing the hydrostatic pressure Opposite occurs at sink resulting in a pressure gradient |
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Adaptations of guard cells |
Unevenly thickened cell wall Chloroplasts Ability to bend |
