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Flashcards in Transport in Plants Deck (45)
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Why do plants need a transport system?

Get water from the roots to the leaves

Move sugars from leaves to the rest of the plant


What is the function of the xylem?

Carry water up the plant

Provide structure


What happens to xylem cells as they mature which impacts their function?

They become lignified


What does lignin do to the xylem?

Kills the cells

Makes them waterproof

Strengthens the vessel


What is the function of the cambium?

Contains meristem cells which can divide and specialise to form new xylem and phloem cells


Give ways in which xylem is adapted to its function

Made from dead cells aligned end to end

tubes are narrow so capillary action can be effective

Bordered pits allow water to move from one vessel to another

Lignin deposited in a spiral allows the xylem to stretch as the plant grows despite being dead


What are the two types of cells that make up the phloem?

sieve tube elements

Companion cells


What is the function of the phloem?

Transport assimilates (mostly sucrose and amino acids)


How are sieve tube elements specialised to carry out their function?

Lined up end to end to make a long tube

contain no nucleus and little cytoplasm, leaving more space for mass flow to occur


What is the function of the companion cells?

To carry out metabolic processes needed to actively load assimilates into the sieve tube elements

They are needed because the little cytoplasm in the sieve tube elements means that they can't do this themselves.


How are companion cells adapted to their function?

They have a large nucleus

Dense cytoplasm

This is because they need to carry out metabolic reactions for not only themselves but the sieve tube elements also


What is a plasmodesma?

A gap in the cell wall of a cell where it connects to another cell


describe what the 3 pathways in which water can move are and how they work?

Apoplast pathway - Moves in the spaces between cells

Symplast pathway - Moves between the plasmodesmata of cells through the cytoplasm

Vacuolar pathway - Moves through the vacuoles of cells also


Where will water move in a water potential gradient?

To the area with he lowest water potential


What will happen if you put plant cells in distilled water and why does this happen?

The plant cells will take up water by osmosis and swell

This because the solutes in the plant cell cause the water potential to be lower than that of the distilled water

Water moves to the area of lowest water potential


What will happen if you put plant cells in a salt solution and why?

A salt solution will have a very low water potential

Water will move out of the plant cell into the solution down a water potential gradient

Water will move to the area of lowest water potential

Cells will shrink


What is the name of the condition whereby the plasma membrane comes away from the cell wall?



What is Transpiration?

The loss of water vapour from the upper parts of the plant- particularly the leaves


Describe the pathway of water leaving the leaf

Water enters leaf through xylem and moves by osmosis into the spongy mesophyll

Water evaporates from the cell walls of the spongy mesophyll

Water vapour moves by diffusion out of the leaf through he open stomata. This requires a water potential gradient between the leaf and the surroundings


Why is transpiration essential for a plant to survive?

As water vapour is lost it draws water up the stem as a transpiration stream, this movement:

Transports useful mineral

Maintains cell turgidity

Supplies water for growth, cell elongation and photosynthesis

Supplies water that can evaporate to cool the plant


Give 5 environmental factors that affect rate of transpiration

Light intensity
Water availability


What type of cells is the epidermis of a root made of?

Root hair cells


Where does water move from and to in the root?

Water moves from the soil into the epidermis of the root hair cells

Moves across the root cortex to the endodermis of the vascular bundle


Why can water only move through the apoplast pathway as far as the endodermis?

Because the Casparian strip blocks the apoplast pathway


Describe how the endodermis and Casparian strip act to move water into the medulla and xylem

Casparian strip blocks the apoplast pathway between the cortex and medulla

Ensures that mineral ions (especially nitrates) pass through the plasma membrane into the cytoplasm

Mineral ions are actively transported into the medulla and xylem

This creates a water potential gradient so water moves by osmosis into the medulla

The Casparian strip then blocks it from moving back out


What are the 3 processes that ensure mass flow occurs?

Root pressure
Transpiration pull
Capillary action


Describe what root pressure is.

As water moves into the roots and xylem it causes an increase in pressure

This pressure forces water up the xylem

This can push water a few meters up a stem but can't account for tall trees


Describe the process of transpiration pull

Water is lost from the top of the plant by transpiration

Hydrogen bonds cause cohesion between water molecules

Water moves up to the leaves to replace lost water and other molecules are pulled up with it


Describe the process of capillary action

The high surface tension of water causes it to stick to the sides of the xylem vessels. This is called adhesion

Because the xylem vessels are very narrow, this can pull water up the xylem.


What is the term given to plants that are adapted to survive in arid conditions?



Give an example of a Xerophyte

Marram grass


What are the adaptions of marram grass that make it a xerophyte?

Rolled leaf - increases humidity next to the stomata

Thick waxy cuticle - reduces evaporation

Stomata are on the inside of the rolled leaf - protected by the enclosed space

Hairs surround stomata - reduce air movement maintaining a water potential gradient

Dense spongy mesophyll - fewer air spaces so slower evaporation of water


What type of plant are cacti?



Give some adaptions of cacti to reduce water loss

Leaves are reduced to spines to reduce transpiration

Stem is green to perform photosynthesis (no leaves)

roots are shallow and very widespread to increase water uptake in a rain event


What is the name given to plants that can live in water?



Give some adaptions of hydrophytes

Large air spaces to keep the leaf afloat so the leaves can perform photosynthesis

Stomata on the upper epidermis to allow gaseous exchange

Stem has large air spaces to keep it afloat but also so oxygen can quickly diffuse all the way to the roots.


Where does translocation occur?

In the phloem


What is translocation?

The movement of assimilates throughout the plant


What are assimilates?

Substances made by the plant from substances absorbed from the environment.

e.g Sugars and amino acids


What is a source? (Translocation)

Somewhere where assimilates are loaded into the phloem


What is a sink?

A part of the plant where assimilates leave the phloem


Describe the process of active loading

H+ ions are actively transported out of the companion cells

A concentration gradient is formed

H+ ions diffuse back into the host cell through co-transporter proteins

These proteins only allow H+ back in that is attached to sucrose molecules

Sucrose can then diffuse into the sieve tube elements through the plasmodesmata


By what process does the sucrose move in the phloem?

Mass flow


Describe the process of mass flow

Flow is caused by a difference in hydrostatic pressure between the two ends of phloem

Water enters the tube at the source increasing hydrostatic pressure and leaves at the sink which reduces the pressure.

Therefore mass flow always goes from source to sink


Why does water enter the phloem at the source?

Because the assimilates cause the solution inside the phloem to have a low water potential

Thus, water moves in via osmosis