Biology Component 3 - 3.2 Plant Transport

Developed from the resources provided by Peter Symonds College

There are lots of flashcards, just to ensure that everything is covered for any eventuality in the exams

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What happens to plants at night?
They only respire and draw O2 from the atmosphere
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What is greater, the rate of photosynthesis or the rate of respiration?
The Rate of Photosynthesis is greater than the Rate of Respiration during daytime.
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What significance does large surface area have for gas exchange and photosynthesis?
Many stomata present to capture as much light as possible
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What significance does the thinness have for gas exchange and photosynthesis?
Short diffusion pathway for light penetration
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What significance does the transparent cuticle have for gas exchange and photosynthesis?
Allows light penetration to Mesophyll layers
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What significance does elongated palisade cells have for gas exchange and photosynthesis?
Accommodate a large number of cells
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What significance does palisade cells packed with chlorophyll have for gas exchange and photosynthesis?
Capture more light
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What significance does chloroplasts in mesophyll have for gas exchange and photosynthesis?
Allows movement to the best positions
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What significance do the air spaces in spongy mesophyll have for gas exchange and photosynthesis?
O2/CO2 can diffuse into cells
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What significance do stomatal pores have for gas exchange and photosynthesis?
Gas exchange in and out of cell
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Three key facts about stomata
Mostly on lower surface of the leaf; guard cells have unevenly thick walls (inside thicker than outside); can change to control gas exchange
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What does the Xylem and Phloem look like in Roots?
Xylem is central/star-shaped; Phloem between groups of Xylem cells (resists vertical stress)
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What is the position of the Xylem and Phloem in Stems?
Vascular Bundles are found on the periphery of the epidermis - Xylem closest to the centre, with Phloem behind.
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Where is the Vascular Bundle in a leaf?
Vascular tissues in the middle and in a network of veins; flexible strength and tear resistance
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Describe the structure of the Vascular Bundle in a stem (from most central to the periphery)
Xylem - Cambium - Phloem - Sclerenchyma
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What is the role of the Casparian *****?
It surrounds the cell of the endodermis and prevents water/minerals from seeping between the cells; in order to get the the vascular cylinder, water and minerals must pass through the cell membrane by selective ion uptake
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Describe how root pressure is achieved
Ammonium ions diffuse through the apoplast pathway; ions are actively transported into endodermis to lower water potential; greater for of water flows in Xylem (positive hydrostatic pressure); root pressure established
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How could nitrate ions enter the root if the concentration of nitrate ions outside the plant is less than the concentration inside a Root Hair Cell?
Active Transport
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Suggest how the Casparian ***** in the endodermis may ensure the selective absorption of ions into the Xylem of the root
Stops apoplast pathway, forcing symplast; water forced through a permeable membrane
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What is the function of the Sieve Tube?
Transports sucrose and amino acids
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What is the function of the Xylem Vessel?
Transports Water
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What is the function of the Guard Cells?
Gas Exchange
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What is the function of the Endodermis?
Selection Ion Uptake
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Explain how water enters the Root Hair Cells
Root hairs on the root increase the surface area of the root; high water content in soil and high solute concentration in the vacuole of cells; water enters via osmosis; ions can be actively transported into the root hair cell
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Name and explain three ways water moves through the root
Apoplast Pathway (80% - along cellulose cell wall); Symplast Pathway (through cytoplasm and plasmodesmata); Vacular Pathway (through vacuoles and cytoplasm)
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What is the last set of cells that water and ions pass through before the Xylem?
Pericycle layer
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Define Transpiration
The evaporation of water vapour from the leaf via the stomata
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Explain the Cohesion Tension Theory
Water travels in xylem up stem to leaf; most water evaporates in leaf (Transpiration); water loss via osmosis; as water molecules leave the leaf transpiration pull occurs as water has a large cohesive force between them
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Why do sunken stomata feature in Xerophytes?
Water vapour gets trapped - increase humidity, decrease water potential gradient, reduced air movement
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Why do hairs feature in Xerophytes?
Trap water vapour - increase humidity, decrease water potential gradient
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Why does a thick cuticle feature in Xerophytes?
Reduced water loss from lower epidermis
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Why do hinge cells feature in Xerophytes?
Hep the leaf roll to trap water vapour - increase humidity, decrease air movement, decrease water potential gradient
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Compare Mesophytes and Hydrophytes
Mesophyte - stomata close during night, stomata on lower epidermis, loss of leaves in winter, thin cuticle, lignified tissue; Hydrophytes - Poorly developed Xylem due to water surrounding, little/no lignified tissue, stomata on upper epidermis
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What features does a Xerophyte have?
Sunken stomata; rolled leaves; thick cuticle; stomata close during day; store water in stem; succulent stems; hairs around stomata; lignified tissue
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What is a Potometer used to measure?
Rate of Transpiration (actually used to measure rate of water uptake)
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Describe how you would investigate the effect of air movement on the rate of transpiration
Cut healthy shot underwater; cut shoot at slant; check apparatus full of water; insert shoot into tube; shut screw clip; remove potometer from water (airtight); dry leaves; constant conditions; acclimatise
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What effect does an increase in temperature have on the effect of transpiration?
Increase in kinetic energy of water molecules, increase in rate of evaporation
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What effect does an increase in humidity have on the effect of transpiration?
Increase in humidity = increase in water vapour in air; water potential gradient between the air and leaf decreases, less water lost by evaporation
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What effect does an increase in air movement have on the effect of transpiration?
Increase in air movement = increase in water potential gradient between leaf and air as boundary layer of air and water vapour around stomata is removed quicker
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What effect does an increase in light intensity have on the effect of transpiration?
Increased light intensity = increase in number of stomata open due to increase in exchange of CO2 to increase rate of photosynthesis, therefore greater SA of which transpiration can occur
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What is C6H12O6 transported as in plants?
Sucrose (Glucose [alpha] + Fructose)/Amino Acids
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What is Translocation?
The movement of organic molecules (i.e. Sucrose, Amino Acids, Hormones) in the Phloem
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What is a source in the plant for Translocation?
Leaf (Photosynthesis - sucrose)
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What are the sinks in a plant for Translocation?
Fruit (needs sucrose to be made sweet for seed dispersal); buds (sucrose - nector | amino acids - growth); Roots (Amino Acids for Growth); Bulb/Tuber (Storage of starch/fats)
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Define Source
The part of the plant that releases the sucrose is called the source (i.e. leaf)
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Define Sink
The part of the plant that receives the sucrose and amino acids for growth or storage are called the sink (i.e. roots, fruit, seeds, bulbs)
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What is the Xylem Vessel made up of?
Dead cells aligned; no end walls; no cell contents; lignin thickening prevents wall from collapsing and is waterproof; pits in lignified walls allow water to move sideways from one vessel to another
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What are Tracheids?
Tracheids have tapered ends which fit together and pits which allow transfer of water between
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What type of cells always accompany Phloem Tissue?
Companion Cells (dense cytoplasm, large nucleus, mitochondria [provides ATP for active transport])
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What is the Sieve Tube?
Allows for water and mineral transport (bi-directional), clear of most organelles (ease of transport), thin cytoplasm to reduce resistance
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What is the job of the Plasmodesmata in the Phloem Tissue?
Links cytoplasm of companion cell and sieve tube element (allows movement of fluid from companion cells to sieve tube for transport)
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What are the active steps in Translocation of Photosynthetic Products in the Phloem?
Hydrogen ions pumped out of companion cell into source cell by Active Transport; ions return to companion cell with sucrose down diffusion gradient (co-transport proteins)
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What are the passive steps in Translocation of Photosynthetic Products in the Phloem?
Sucrose into sieve tube via companion cells and plasmodesmata (decrease water potential); water enters sieve tube; increases hydrostatic pressure; sucrose unloads from sieve tube; water moves out of sieve tube; sucrose moves from source to sink
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Experimental Evidence for Mass Flow Hypothesis
Aphids (Stylet takes in sucrose 10,000 times faster than diffusion); bidirectional flow (carbon 14 in plant); ***** bark of a tree away and see if a bulge appears (removes phloem)
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What evidence is there against the Mass Flow Hypothesis?
Sieve plates with sieve pores would obstruct mass flow; sucrose and amino acids have been observed moving at different rates/directions in same tissue; why are there companion cells in the middle of the stem?
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What are the alternate theories to Mass Flow Hypothesis?
Cytoplasmic Streaming can be responsible for bidirectional movement along sieve tubes; protein filaments have been observed passing through sieve pores and suggest that different solutes are transported along different filaments.
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State the name of the substance in which the Carbon 14 will be transported in the stem
Sucrose
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State the general name given to areas where unloading of carbohydrates occur
Sink
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Other cards in this set

Card 2

Front

What is greater, the rate of photosynthesis or the rate of respiration?

Back

The Rate of Photosynthesis is greater than the Rate of Respiration during daytime.

Card 3

Front

What significance does large surface area have for gas exchange and photosynthesis?

Back

Preview of the front of card 3

Card 4

Front

What significance does the thinness have for gas exchange and photosynthesis?

Back

Preview of the front of card 4

Card 5

Front

What significance does the transparent cuticle have for gas exchange and photosynthesis?

Back

Preview of the front of card 5
View more cards

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