Transport In Plants

Question 1

Why do multicellular plants need transport systems?

Answer 1

• Different areas of plant require certain molecules so they need to be delivered
• Plant continue to grow throughout their lives so they need to be able to move substances both up and down from the topmost leaves to the roots
• Plants overall have a relatively small SA:V and therefore cannot reply on diffusion alone as it will be too slow.

Question 2

What materials do plants exchange and transport?

Answer 2

• CO2
• O2
• Water
• Organic nutrients
• Inorganic ions
• Auxins (plants growth)

Question 3

What is photosynthesis?

Answer 3

Plants producing glucose through sunlight

Question 4

Equation for photosynthesis

Answer 4

6CO2+6H2O=C6H12O6+6O2

Question 5

What is a vascular bundle?

Answer 5

Collection of plant tissues used for transport found in the roots, stem and leaves of a plant, typically with the phloem on the outside and the xylem on the inside.

Question 6

Where are the vascular bundles in the roots?

Answer 6

Found in the middle of the roots to help the plant withstand the tugging strains that results as the stems and leaves are blown in the wind.

Question 7

Where are the vascular bundles in the stem?

Answer 7

Around the edge to give strength and support

Question 8

Where are the vascular bundles in the leaves?

Answer 8

In the midrib of leaves, which provides support and has many small, branching veins spread through the leaf functioning in both transport and support.

Question 9

What is the xylem made up of?

Answer 9

• Largely non-living tissue
• Made up of several types of dead cells
• Xylem vessels are the main structure, which are long, hollow structures made by several columns of cells fusing together.

Question 10

What are the adaptions of xylem vessel?

Answer 10

• Non-lignified pit, which allows interconnection for lateral water flow around blockages
• Strengthened by lignin to provide structural support and prevent water loss
• No end cell wall, allowing water to flow uninterrupted
• Xylem parenchyma packed around vessel, which stores food and tannin (chemical that protects plant from attack by herbivores)

Question 11

What is the phloem made up of?

Answer 11

-Made up of sieve tube elements, which are many cells joined end to end

Question 12

What are the adaptions of phloem vessels?

Answer 12

• Non-lignified
• Have plasmodesmata linking cytoplasm of companion cell to thin cytoplasm of sieve tube element
• Perforated cell walls, called sieve plates that allows phloem contents to flow through
• Don’t have a nucleus or other major organelles
• Very thin layer of cytoplasm

Question 13

How are root hair cells well adapted?

Answer 13

• Microscopic size
• Each microscopic hair has a large SA:V
• Each layer has thin diffusion pathway
• Conc. of solutes in cytoplasm of root hair cells maintain water potential gradients between soil water and cell

Question 14

How does water move from the soil into the root hair cels?

Answer 14

Soil water has a very low concentration of solutes and therefore has a high water potentials. So it moves from the soil into the root hair cells down a water potential gradients by osmosis from an area of high wp to an area of low wp.

Question 15

How does water move from the root hair cells to the xylem the SYMPLAST pathway?

Answer 15

• Water moves through the symplast, which is the continuous cytoplasm of living plant cells connected through plasmodesmata.
• Root hair cell has a higher water potential than the next cell a long
• Water will move from one root hair cell into the next by osmosis down a water potential gradient
• Process continues from cell to cell across root until xylem is reached

Question 16

How does water move from the root hair cells to the xylem the APOPLAST pathway?

Answer 16

• Water moves across the apoplast, which is the intercellular spaces between the cell’s cell walls
• Water fills spaces between loose, open network of fibres in cellulose cell wall
• As water molecules move into the next cell, more water molecules are pulled through due to the cohesive forces between them

Question 17

Water actually going into xylem?

Answer 17

• Water moves across root through apoplast and symplast pathways until it reaches the endodermis
• The endodermis has a waxy strip called the Casparian strip, made out of suberin which forces the water in the apoplast pathway to join the symplast pathway.
• Water potential of xylem cells is much lower than water potential of endodermal cells, so water moves by osmosis down a water potential gradient through the partially permeable membrane.
• Once inside the vascular bundle, water returns to the apoplast pathway to enter the xylem itself and move up the plant.

Question 18

What is transpiration?

Answer 18

The inevitable loss of water through evaporation from the leaves during gaseous exchange.

Question 19

What are the three mechanisms of water transport up the xylem?

Answer 19

• Capillarity
• Cohesion-Tension Theory
• Root pressure

Question 20

What is capillarity?

Answer 20

• Results from strong intermolecular attraction between water molecules and attraction between water molecules and side of vessels
• Although xylem vessels are extremely narrow, the maximum height is only 50mm and therefore capillarity alone cannot account for upwards transport of water.

Question 21

What is the Cohesion-Tension Theory?

Answer 21

• Water vapour lost from leaves through evaporation, which is the driving force for this tension
• Water molecules stick to sides of xylem vessel as forms H bonds with carbohydrates
• Water molecules stick to each other
• Combined adhesion and cohesion result in water exhibiting capillary action
• Process of water rising up a narrow tube against force of gravity in a continuous stream to replace water lost by evaporation.

Question 22

What is the mechanism of stomatal opening and closing?

Answer 22

• During daylight, blue light activates ATPase, which catalyses hydrolysis of ATP
• ATP generates energy required to operate a proton pump
• H+ ions pumped out of guard cells and then re-enter simultaneously carrying Cl- ions into guard cell
• Increased ions conc. causes lower water potential so water moves into cell, causing stomatal pore to swell and open.

Question 23

What does the potometer measure?

Answer 23

The rate of water uptake

Question 24

What is a potometer used for?

Answer 24

To indirectly measure to rate of transpiration and how different factors can affect the rate

Question 25

What are some precautions that need to be taken when using the potometer?

Answer 25

• Cut leafy shoot underwater to minimised risk of air entering xylem vessel
• Submerge potometer into water and move it around until all the air bubbles have gone
• Apply vaseline to all joint to make apparatus air-tight
• Make sure start of ruler is lined up with the bubble

Question 26

What kind of change could you make for the factors?

Answer 26

Bright light
Humid atmosphere
Fan/Hairdryer

Question 27

Limitations of potometer practical

Answer 27

• Introducing air bubbles isnt easy
• Leafy shoot may not remain fully alive for as long as wanted
• Any change in outside temp may affect position of air bubble in capillary tube

Question 28

How does light intensity affect transpiration?

Answer 28

Increased light intensity= more stomata open= increased rate of diffusion of water vapour= Increased rate of transpiration

Question 29

How does relative humidity affect transpiration?

Answer 29

Higher humidity means a reduced water vapour potential gradients between inside and outside of leaf, which reduces the rate of transpiration.

Question 30

How does air movement affect transpiration?

Answer 30

Wind increase causes diffusion shells to be removed so there is a steeper water diffusion gradient so more water evaporates and transpiration increases.

Question 31

How does soil-water availability affect transpiration?

Answer 31

If soil is very dry, plant will be under water stress and rate of transport will be reduced and vice versa

Question 32

How does temperature affect transpiration?

Answer 32

Increase in temp= Increase KE of water molecules= Increased rate of evap=Increased rate of transp
OR
Increase in temp=Increased conc. of water vapour external air can hold before it become saturated, which decreases relative humidity and increases water p gradient and increases transp

Question 33

What is a xerophyte?

Answer 33

Plants which are adapted to live in extremely dry conditions

Question 34

What are the biotic factors affecting transpiration?

Answer 34

• Stomatal pore size
• Stomatal frequency and distribution
• SA:V of whole plant
• Nature of circle

Question 35

What are the adaptions of xerophytes?

Answer 35

• Thick epidermis to decrease light intensity
• Leaves may be reduce to spines to minimise area of leaf exposed to light
• Stomata are often only present on bottom of leaf surface
• Stomata surrounded by hairs to trap moisture
• Extensive and deep root systems to tap into underwater deep water reserves and/or superficial rain
• Thin cortex so there is a small distance between soil water and the xylem

Question 36

Examples of xerophytes?

Answer 36

Cactus, Marram Grass

Question 37

What are hydrophytes?

Answer 37

Plants that are adapted to live in water, either submerged, on the surface or at the edge of bodies of water

Question 38

What are some adaptions of hydrophytes?

Answer 38

• Very thin or no waxy cuticle
• Many always-open stomata on upper surface of leaf to maximise gaseous exchange
• Large surface area of stems and roots underwater to maximise area for oxygen to diffuse into submerged plants
• Air sacs to help plants float
• Aerenchyma (specialised parenchyma with large air spaces caused by apoptosis) makes leaves and stems bouyant and forms a low resistance pathway for movement of substances such as oxygen to tissues below water.

Question 39

What is translocation?

Answer 39

The movement of sugars, amino acids and other organic molecules up and down the phloem

Question 40

What is a source?

Answer 40

The area of the plant where the assimilates are produced and loaded onto the phloem from reactions/storage.

Question 41

What is a sink?

Answer 41

The area of the plant where the assimilates are unloaded from the phloem and used in various processes.

Question 42

Why is sucrose transported instead of glucose?

Answer 42

Because glucose would be used up in respiration

Question 43

How is sucrose loaded into the phloem?

Answer 43

Hydrogen ions are pumped out of the cell, requiring ATP, they return to the companion cell through transmembrane protein and the H+ ions are binded to sucrose. The sucrose then diffuses into the sieve tube element.

Question 44

What is the mass flow hypothesis?

Answer 44

1. Sucrose moves from c. cells to s.t elements by active transport
2. Reduces water potential of s.t element
3. Water moves into phloem by osmosis, increasing hydrostatic pressure
4. High hydrostatic pressure near source and low hydrostatic pressure near sink
5. Solutes move down pressure gradient towards sink end of phloem
6. Solutes move into sink
7. Removal of solutes causes high water potential at sink causing water to move out of the phloem by osmosis.

Question 45

What is evidence for mass flow?

Answer 45

1. When you cut the stem, the sap flows out of the phloem
2. Carbon 14 is radioactive so you can trace the carbon from the leaf all the way to the phloem
3. Use a metabolic inhibitor which stops ATP production which stops respiration and therefore translocation stops as there is no energy for the active process.

Question 46

What is root pressure?

Answer 46

Proposes that water is pushed through the stem due to pressures exerted by the roots
Results from active secretion of ions across endodermal cells of the root and subsequent osmotic flow of water
Pressure is too small to be solely responsible