3.1.3 Transport in Plants COMPLETE

Question 1

Why plants need a transport system

Answer 1

• Plants are multicellular so not all in direct contact with the environment
• Allows metabolic reactions to occur and the removal of waste.
• So plants continue growing, allows them to become large, water transported a long way
• Their large size means they have a small SA:V

Question 2

What plants need to transport

Answer 2

• Water & Minerals from soil to cells via roots
• CO2 during daytime
• O2 for respiration
• Assimilates such as sucrose and amino acids
• Plant Hormones to where they’re needed

Question 3

Xylem

Answer 3

Transport water and mineral ions up the plant

Vascular Tissue

Question 4

Phloem

Answer 4

Transports assimilates such as sucrose up and down the plant

Vascular Tissue

Question 5

How substances are transported around the plant

Answer 5

Diffusion, osmosis, active transport, bulk transport

Question 6

Vascular Tissue in a young root

Answer 6

Xylem forms a cross in the centre, contains an
Endodermis- sheath surrounding the vascular bundle to help get water in
Pericycle- Layer of meristem which is undifferentiated

Question 7

Vascular Tissue in young stem

Answer 7

Multiple bundles circle around a pith in the centre, contains
Cambium- Layer of undifferentiated meristem
Parenchyma- Packing and support
Collenchyma- provide structure for growth in shoots and leaves

Question 8

Distribution of vascular tissue in the leaf

Answer 8

Vascular bundles form the midrib (main vein) and the side veins, the branched network helps to support the leaf. Airspaces are of photosynthesis

Question 9

Structure of the Xylem Vessels

Answer 9

Starts as a column of live cells which lay down lignin, this makes them waterproof, the cell dies along with its contents. No endplates mean theres a continuous column, there are gaps in the lignin called pits these let water move across

Question 10

Adaptions of the Xylem Vessels

Answer 10

• Continuous column with no contents so the flows not impeded
• Lignin prevents walls collapsing and allows adhesion of water
• Pits allow lateral sideways movement

Question 11

Xylem Parenchyma

Answer 11

Living cells that form packaging tissues and stores food, bitter tasting to prevent attack

Question 12

Structure of the Phloem Tissue

Answer 12

Consists of more than one cell:

• Sieve tube elements
• Companion Cells
• Parenchyma Cells
• Scleroid’s and fibres

Question 13

Sieve Tube Elements

Answer 13

Contains a thin layer of cytoplasm, mitochondria and endoplasmic reticulum. No nucleus or ribosomes. Thin non lignified walls with perforated edges forming sieve plates

Question 14

Companion Cells

Answer 14

Linked to the STE by plasmodesmata, have dense cytoplasm with large nucleus, contain more mitochondria and ribosomes than usual and have no large permanent vacuole.

Question 15

Transporting water up Plants

Answer 15

1. Water uptake near roots
2. Water enters the xylem
3. Water moves up the xylem
4. Water moves from the xylem to leaf cells via pits
5. Evaporation of water into leaf airspaces
6. Transpiration of water vapour through open stomata

Question 16

Water Potential

Answer 16

The tendency of water molecules to leave a solution, the more solute in a solution the lower the water potential

Question 17

Turgid

Answer 17

Water enters as a higher water potential outside the cell, this prevents the plant wilting

Question 18

Plasmolysed

Answer 18

Water moves out the cell as a lower water potential outside

Question 19

Mineral ion and water uptake from the soil

Answer 19

The epidermis has root hair cells to increase SA, Mineral ions are absorbed by active transport alongside amino acids and sugar. These lower the water potential of the cytoplasm so water follows via osmosis.

Question 20

Movement of water across a root

Answer 20

1. Apoplast pathway
2. Symplast Pathway
3. Vacuolar Pathway

Question 21

The Apoplast Pathway

Answer 21

The cellulose cell wall is fully water permeable so water and dissolved minerals move through them. It doesn’t go through the cell membrane as is not osmosis. As the water moves up and is cohesive theres a continuous flow.
Stops at the endodermis

Question 22

The Symplast Pathway

Answer 22

Water travels through the cytoplasm, plasmodesmata connect the cells and they’re made of thin strands of cytoplasm. Not osmosis as there’s no barrier

Question 23

The Vacuolar Pathway

Answer 23

Similar to the symplast pathway but can also travel through vacuoles.

Question 24

Casparian Strip

Answer 24

Made from waxy Suberin, blocks the apoplast pathway and forces water into cells via symplast pathway. Water then has to pass through the cell surface membrane which is selectively permeable. Active transport moves the mineral ions.
water cannot pass back into the apoplast pathway

Question 25

How does water get pulled up the stem

Answer 25

1. Root pressure 2. Transpiration Pull 3. Capillary Action

Question 26

Root Pressure

Answer 26

Water is forced up through the stem when mineral ions are moved into the xylem by active transport. Metabolic poison, temp and O2 conc affect it. Cannot support really tall trees

Question 27

Transpiration Pull

Answer 27

Cohesive forces attract water, this forms a large column in the xylem. When water is lost via transpiration more water is pulled up. This creates tension, lignin prevents collapse. If one column breaks water can move through pits into another

Question 28

Capillary Action

Answer 28

Adhesive forces between water and the narrow walls of the xylem help pull it up, allows water to move against gravity, narrower container means more contact so greater adhesive forces.

Question 29

Transpiration

Answer 29

The loss of water vapour from the upper parts of the plant, especially the leaves Water evaporates into the air spaces and then leaves by diffusion out of the stomata This maintains the water potential gradient

Question 30

Measuring rate of transpiration

Answer 30

Easiest way is to measure water uptake as they'll roughy be the same. Fill apparatus up with waterhen put a freshly cut shoot in it, seal joints with vaseline, dry the leaf, and then measure how much water is moving under constant conditions

Question 31

Factors affecting Transpiration rate

Answer 31

- Number of leaves - Number of stomata - Presence of a waxy cuticle - Light - Temperature - Relative Humidity - Wind - Water availability

Question 32

Xerophytes

Answer 32

Plants that are adapted to dry conditions such as marram grass

Question 33

Features of Xerophytes

Answer 33

- Spikes to reduce SA - Hairs and rolled leaves to create a microclimate of humid air - Succulents store water in special parenchyma tissues - Thick waxy cuticle minimise diffusion - Long tap roots to access water

Question 34

Hydrophytes

Answer 34

Plants that live in water, either submerged or on the surface. They need to ensure enough O2, and maintain transpiration for mineral ions

Question 35

Features of Hydrophytes

Answer 35

- Wide leaves to capture more light - Air spaces for buoyancy - Stomata on the upper surface for gas exchange - No waxy cuticle as plenty of water - Reduced structure as water supports them

Question 36

Translocation

Answer 36

The movement of assimilates (product of photosynthesis) up and down the plants phloem. Glucose is converted into sucrose

Question 37

Sources

Answer 37

Where sugars are produced, and assimilates are loaded. Is an active process in the STE and water follows by osmosis increasing hydrostatic pressure e.g. in germinating seeds

Question 38

Sinks

Answer 38

Where the assimilates are removed from the phloem and the sugars are used. Sucrose leaves STE by diffusion water potential increases in sap and water follows down the gradient, decreasing hydrostatic pressure. e.g. in the meristem or growing roots

Question 39

Mass Flow

Answer 39

Water moves in at the source and out at the sink provides a pressure difference forcing the sap to move

Question 40

Loading sucrose into phloem

Answer 40

Either via the symplast route where it moves through the plasmodesmata or the apoplast route where it passes through the cell walls

Question 41

Movement of H ions

Answer 41

ATP is used to pump hydrogen ions out of the companion cells, this leads to a higher concentration outside. They move back into the companion cells from STE with a co transporter protein, these also carry sucrose with them.

Question 42

Supporting evidence: How do we know the Phloem is used

Answer 42

RADIOACTIVE CARBON is incorporated into carbohydrates, aphids drink phloem sap, head snapped and sample can be taken to see if its present. TREE RINGING is when bark is removed (phloem) the tree dies due to lack of energy

Question 43

Supporting evidence: How do we know it needs metabolic energy

Answer 43

Lots of mitochondria in the companion cells, when metabolic poisons used translocation is stopped

Question 44

Supporting evidence: How do we know translocation uses this mechanism

Answer 44

The pH of the sap is 8 which is expected as H ions are being pumped out, also more negative inside as H+ are outside . Theres also a higher concentration of sucrose in the source than sink,

Question 45

Supporting evidence: Against this mechanism for translocation

Answer 45

Not all solutes move at the same rate, sucrose moves at a constant rate regardless of concentration. Its also unclear what the role of the sieve plates is