Module 3: Section 3- Transport in plants

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what are the two types of tissue involved in transport in plants?
The xylem and phloem tissue
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what does the xylem tissue transport?
water and mineral ions (in solution)
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what direction do these substances move in?
up
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what does the phloem tissue transport?
sugars (in solution)
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what direction do these substances move in?
both up and down the plant
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what do the xylem and phloem make up?
the vascular system
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what is the xylems other function?
support for the roots, stems and leaves
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how are the xylem vessels adapted for these functions? part 1
--> there are no end wall on the cells, which means that the xylem vessel can be 1 long tube for water to move through easily. --> the walls contain lignin, which provides support and allows the vessels to be waterproof.
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how are the xylem vessels adapted for these functions? part 2
--> they have bordered pits in their side walls (contain no lignin) to allow lateral movement of water. --> the cells are deadand contain no cytoplasm, allowing water to pass through easily.
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how is the phloem tissue adapted for transporting solutes?
they contain phloem fibres and parenchyma (both for support), sieve tube elements and companion cells
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describe the sieve tube elements part 1
living cells that form the tube for transorting solutes through the plant, contain sieve plates at the end walls which allow solutes to pass through.
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describe the sieve tube elements part 2
They contain NO nucleus and have few organelles and a thin layer of cytoplasm which is connected to the cytoplasm of adjacent cells through the sieve plate holes.
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describe the companion cells
there is a companion cell for each sieve tube element as they carry out their living functions as well as their own, e.g. provide energy for active transport of solutes.
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how does the water enter the root hair cells?
by osmosis
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how is a water potential gradient maintained?
water moves from high water potential to areas of lower water potential, therefore the leaves have a lower water potential than the roots, and the roots have a lower water potential than the soil=water moves into the root hair cells form soil.
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what are the 2 pathways that the water moves through?
the symplast and apoplast pathway.
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describe the symplast pathway
goes through the cytoplasm by osmosis. The cytoplasm connects to neighbouring cells through the plasmodesmata (small channels in the cell walls).
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describe the apoplast pathway
goes through the cell walls, water can simply diffuse through the walls.
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what happens when the water reaches the endodermis cell layer?
water in the apoplast pathway is blocked by a waxy layer called the casparian *****.
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why is this a good thing?
It is good because the water has to take the symplast pathways through the partically permeable membrane, which can control the substances that pass through.
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what are the 3 mechanisms that help water move against gravity?
cohesion, tension and adhesion
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what is cohesion and tension?
by the water evaporating at the top of the xylem, it creates TENSION (suction), which pulls more water into the leaf. Water molecules are cohesive, which means they stick together, so when they are pulled into the leaf others follow.
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what is adhesion?
adhesion is where water molecules are attracted to the walls of the xylem vessels, which helps water to rise up.
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what is transpiration?
the evapouration of water form the plants surface (leaves).
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how is transpiration a consequence of gas exchange?
the plant has to open its stomata to let in CO2 for photosynthesis, there is a higher concentration of water in the leaf than outside, so it diffuses out by osmosis.
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what are the 4 main factors that affect transpirition rate?
light, temperature, humidity, wind.
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how does light affect transpirition rate?
the lighter it is the faster the transpirition rate, this is becuase the stomata open when its light.
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how does temperature affect transpirition rate?
the higher the temp the faster the transpirition rate, because this provides the water molecules with more energy so they evaporate from the cells inside the leaf faster.
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how does humidity affect transpirition rate?
the lower the humidity the faster the transpirition rate, if the air around the leaf is dry it increases the water potential gradient between leaf and air.
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how does wind affect transpirition rate?
the windier it is the faster the transpirition rate, lots of air movement blows away the water molecules from around the stomata, increaseing the water potential gradient.
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what piece of equipment is used to measure the transpirition rate?
a potometer
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what is the name of the plants that are adapted to reduce wtaer loss?
Xerophytes
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what adaptions do the xerophytes have to prevent them loosing too much water by transpiration? part 1
*stomata that are sunk in pits, so they are sheltered from the wind. *has a layer of hairs on the epidermis which traps moist air around the stomata
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what adaptions do the xerophytes have to prevent them loosing too much water by transpiration? part 2
*rolled leaves which traps moist air and reduces surface area for losing water. *thick waxy layer on epidermis, its waterproof meaning water can't move through it.
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what adaptions do the xerophytes have to prevent them loosing too much water by transpiration? part 3
*spines instead of leaves, reducing surface area for water loss. *closing their stomata at the hottest time of day.
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what is the name of the plants that are adapted to survive in water?
Hydrophytes
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what adaptions do the hydrophytes have to help them cope with low oxygen levels?
>air spaces in tissues can be used as oxygen stores and to help plants float(increasing the amount of light they recive) >stomata are on upper surface of floating leaves, which maximises gas exchange. >flexible leaves & stems=prevent damage by water
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what is translocation?
translocation the the movement of dissolved substances e.g. sugars like sucrose and amino acids
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where does translocation happen?
the phloem
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what is a source?
where a substance is made
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What is a sink?
where a substance is used up
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What is an example of a source and a sink of sucrose?
the leaves is where sucrose is made and the sinks would be areas of growth (meristems) in roots, stems and leaves or food storage organs.
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Some parts of the plant can be both source and sink, why?
Sucrose can also be store in the roots during the growing season and then transported to the leaves to provide energy for growth. Therefore, the roots are the sourse and the leaves are the sink.
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(Mass flow hypothesis) How are solutes loaded into the sieve tubes of the phloem at the source?
active transport is used to activley load the solutes.
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What does this do?
this lowers the water potentialinside the sieve tubes, so water enters by osmosis from the xylem and companion cells.
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What happens to the pressure?
this creates a high pressure in the sieve tubes at the source end.
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What happens at the sink end?
solutes are removed from the phloem to be used up, this increases the water potential inside the sieve tubes so water leaves by osmosis, thus lowering the pressure.
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What does this process result in?
the result is a pressure gradient from the source end to the sink end.
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what is the name of the process of loading sucrose into the phloem?
active loading
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in the companion cell what binds to a co-transport protein?
H+ ion and sucrose
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what provides energy for the H+ ions to move into the sieve tube?
ATP
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what does the H+ion take with it when it moves into the sieve tube?
sucrose
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what does this do to the water potential?
it lowers the water potential.
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what does this cause?
water to move into the sieve tube by osmosis from the xylem.
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what does this do to the pressure?
this creates a higher pressure inside the sieve tubes at the source end
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what is happening at the sink end at this time?
at the sink end sucrose is being used up and so the water potential increases and wtaer moves out by osmosis.
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what does this create?
a pressure gradient
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what happens to the solutes(sucrose) and water at the source?
It all moves down to the sink end by Mass flow
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Card 2

Front

what does the xylem tissue transport?

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water and mineral ions (in solution)

Card 3

Front

what direction do these substances move in?

Back

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Card 4

Front

what does the phloem tissue transport?

Back

Preview of the front of card 4

Card 5

Front

what direction do these substances move in?

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