Exchange And Transport In Plants

Question 1

Describe the uptake of water and minerals in dicotyledonous plants. (Write it out)

Answer 1

Water from the soil is drawn in through the root hair cells via osmosis, across its partially permeable membrane. There are also lots of mitochondria for active transport in order to uptake minerals. In addition, root hair cells are long, which increase its surface area. This increases the area in which water can move from an area of higher water potential to an area of lower water potential.

Question 2

Why do plants require a transport system?

Answer 2

• Metabolic demands
• Size
• SA:V

Question 3

What is a dicotyledonous plant?

Answer 3

A plant that contains two cotyledons - organs that act as food stores while the embryo plant develops.
- Usually woody, with lignified tissues and a long life cycle.

Question 4

What is the function of translocation?

Answer 4

• Transport or organic material (e.g. sugars)

- Sugar is transported in the form of sucrose

Question 5

What plant vessel does translocation take place in?

Answer 5

Phloem

Question 6

What is the purpose of transporting sugar in the form of sucrose?

Answer 6

• Glucose doesn’t get used up in respiration
• Less reactive than glucose
• Less osmotic effect
• More energy efficient

Question 7

What is a source?

Answer 7

A source is where sucrose is being transported from and loaded into the phloem.

Question 8

What are examples of sources?

Answer 8

Photosynthetic tissues and leaves

Question 9

What is a sink?

Answer 9

Where sucrose is being transported to and unloaded from the phloem.

Question 10

What are examples of sinks?

Answer 10

Roots, meristematic tissues, any growing regions

Question 11

What are two pathways in which sucrose can enter the phloem?

Answer 11

• Symplastic pathway

- Apoplastic pathway

Question 12

What type of process is the symplastic pathway?

Answer 12

Passive process

Question 13

What type of process is the apoplastic pathway?

Answer 13

Active pathway

Question 14

Describe the symplastic pathway in translocation?

Answer 14

Sucrose moving through the cytoplasm of the mesophyll cells by diffusion, through plasmodesmata.

Question 15

Describe the apoplast pathway in translocation

Answer 15

• Sucrose travelled through the cell walls and intercellular spaces to the companion cells

Question 16

How does sucrose reach the companion cell?

Answer 16

1. ATP is broken down, it is turned into ADP + P, which releases energy.
2. Hydrogen ions are then able to be pumped out of the companion cells, via a proton pump.
3. This creates a steep hydrogen concentration gradient outside the cell.
4. In order for hydrogen ions to return to companion cell, they must have a cotransporter - sucrose.
5. Sucrose is now present in the companion cell and then can be loaded into the phloem.

Question 17

How does sucrose move along the phloem?

Answer 17

1. Sucrose is loaded into the sieve tube element, which reduces water potential.
2. Water follows by osmosis and increases hydrostatic pressure.
3. Water moves down sieve tube down from higher hydrostatic pressure at source to lower hydrostatic pressure at sink.
4. Sucrose is removed from the sieve tube by the surrounding cells, which increases the water potential.
5. Water moves out of sieve tube and reduces the hydrostatic pressure.

Question 18

What is a xerophyte?

Answer 18

Plants that live in hot and dry conditions

Question 19

How do xerophytes allow for water conservation and survival?

Answer 19

Reduced transpiration:

• Thick waxy cuticle
• Reduced numbers of stomata
• Reduced leaves
• Leaf loss
• Root adaptions:
  Long deep roots to reach water table
  Shallow wide roots to collect water from large surface area

Creation of microclimates (reduces water potential gradient - reducing transpiration):

• Hairy leaves
• Sunken stomata
• Curled leaves

Question 20

What are hydrophytes?

Answer 20

Plants that live in extremely wet conditions

Question 21

What is an example of a xerophyte?

Answer 21

Marram grass

Question 22

What is an example of a hydrophyte?

Answer 22

Water lilies

Question 23

How do hydrophytes allow for survival in wet conditions?

Answer 23

• Very thin waxy cuticle - more transpiration
• Always open stomata
• Wide, flat leaves - more photosynthesis
• Small roots
• Air sacs - allows leaves to float

Question 24

How do succulents allow xerophytes to survive in dry conditions?

Answer 24

• Contain special parenchyma tissue in stems and roots.

- Have a swollen appearance and can be used in a time of drought.

Question 25

How does aerenchyma allow hydrophytes to survival in extremely wet conditions?

Answer 25

Contains parenchyma tissues which contain air spaces that provide buoyancy

Question 26

How does water move INTO the roots?

Answer 26

- Soil water has a high water potential (due to its low number of solutes), however root-hair cells have a low water potential. - As a result, water moves in via osmosis, down the water potential gradient. - Minerals require active transport to be transported into the root hair cells.

Question 27

How are root hair cells adapted for water uptake?

Answer 27

- Microscopic size to penetrate roots. - Large SA:V - tiny hairs. - Thin surface layer - Concentration of solutes maintains water potential gradient.

Question 28

What pressure is created as a result of water moving into the plant via the root hair cells?

Answer 28

Root pressure.

Question 29

What 2 pathways can water move across the root?

Answer 29

Symplast pathway | Apoplast pathway

Question 30

Describe the symplastic pathway across the root.

Answer 30

- Water moves through continuous cytoplasm (connected by plasmodesmata) - Movement by osmosis due to differences in water potential in adjacent cells.

Question 31

Describe the apoplast pathway across the root

Answer 31

- Water moves through cell walls and intercellular spaces, filling spaces between an open network of cellulose fibres. - As water moves through the xylem, cohesive forces create a tension force, pulling water molecules through the apoplast pathway.

Question 32

What is the purpose of the Casparian strip?

Answer 32

- Forces water into the apoplast pathway into cytoplasm of cells, joining the symplast pathway. - As the water will now have to cross a selectively permeable membrane, this excludes any potential toxic solutes from reaching living tissues.

Question 33

What is the casparian strip?

Answer 33

A band of waxy material called Suberin found on the endodermal cells, forming a water proof layer.

Question 34

What is root pressure?

Answer 34

Pressure created due to active pumping of mineral ions into the xylem, through active transport, alongside water transporting down the water potential gradient, via osmosis into the xylem.

Question 35

Why is the transpiration stream necessary?

Answer 35

- Photosynthesis in the leaves (requires water) - Maintain/regulate temperature (homeostasis) - Maintain turgidity (water in cells) - Growth and elongation of cells - To transport minerals

Question 36

What are the 3 ways that water movement can occur up the transpiration stream?

Answer 36

- Cohesion tension theory - Adhesion - Root pressure

Question 37

How does adhesion cause water movement up the stream?

Answer 37

Water’s adhesive properties allow it to form hydrogen bonds with the carbohydrates in the walls of narrow xylem vessels. This results in water rising up the xylem against the force of gravity.

Question 38

How does the cohesion tension model allow water to move up the transpiration stream?

Answer 38

- Water evaporates from spongy mesophyll layer into air spaces. - Diffuses into surrounding air via diffusion. - Loss of water by evaporation leads to a reduced water potential, leading to water moving into the cell. - Due to water’s cohesive properties, hydrogen bonds are formed between water molecules, meaning there’s a CONTINUOUS COLUMN of water. - This will create a “transpiration pull” when evaporation occurs.

Question 39

What factors affect rate of transpiration?

Answer 39

- Light intensity (high light=high rate) - Relative humidity (high humidity=low rate) - Air movement (high air movement=high rate) - Temperature (high temp.= high rate)