Transport in Plants (Revised)

Question 1

Function of xylem

Answer 1

• conducts water and dissolved mineral salts frm roots to stems
• mechanical support

Question 2

What xylem tissues are made up of

Answer 2

• many xylem vessels
• long hollow tube
• made up of many dead cells
• collectively need to remain turgid to keep plant upright

Question 3

How the xylem vessel is adapted for its function

Answer 3

1. inner walls thickened with lignin (hard and rigid)
   - prevents collapse of vessel
2. empty lumen w/o protoplasm
   - reduces resistance to water flowing thru

Question 4

Function of phloem

Answer 4

• conducts sucrose and amino acids frm leaves/chlorophyll-containing parts to other parts

Question 5

What phloem is made up of

Answer 5

• sieve tubes

- companion cells

Question 6

Sieve tubes (Phloem)

Answer 6

• contains sieve tube elements/cells and sieve plates
• Sieve tube cells:elongated, thin-walled living cells
• Sieve plates: cross walls with pores

Question 7

Sieve tube cell

Answer 7

• mature: thin layer of cytoplasm, no central vacuole, nucleus, most organelles
• each has a companion cell
• carries out metabolic processes to keep sieve tube cell alive
• contains many mitochondria, cytoplasm, nucleus
• provides nutrients and help STC transport sucrose and aa

Question 8

How phloem is adapted for its function

Answer 8

1. Companion cell has many mitochondria
   - provide energy needed to load sucrose and aa frm mesophyll cells into sieve tubes via active transport
2. Holes in sieve plates
   - allow rapid flow of sucrose and aa thru sieve tubes

Question 9

Pith and cortex

Answer 9

• store glucose as starch

Question 10

Cambium

Answer 10

• mitosis (divide and differentiate)
• form new xylem and phloem cells
• in between xylem and phloem
• thickens stem

Question 11

Epidermis

Answer 11

• waxy cuticle greatly reduces rate of evaporation

Question 12

Vascular bundle (stem)

Answer 12

• xylem, phloem and cambium

Question 13

Dicotyledonous root

Answer 13

• phloem and xylem alternate
• cortex of root is storage tissue
• epidermis –> piliferous layer

Question 14

Root hair cell

Answer 14

• tubular outgrowth of an epidermal cell
• thin layer of moisture surrounding it (dilute soln of mineral salts)
• sap relatively concentrated with sugars and salts (lower wp)

Question 15

How root hairs absorb ions/mineral salts

Answer 15

1. Active transport
   - conc of ions in soil soln lower than RHC
   - energy obtained frm cellular respiration in RHC
2. Diffusion

Question 16

How RHC adapted for its function

Answer 16

1. Long and narrow
   - increase SA:V, increase rate of absorption
2. Cell surface membrane prevents cell sap frm leaking out
   - sap contains glucose, aa and salts
   - lower wp than soil
   - water enter roots via osmosis
3. RHC contains many mitochondria
   - aerobic respiration releases energy for active transport of ions into cell

Question 17

Define root pressure

Answer 17

• living cells around xylem vessels in root pump ions in
• decrease wp of xylem vessels
• water moves frm living cells into vessels via osmosis, flow upwards

Question 18

Define capillary action

Answer 18

• water molecules form bonds with each other and lignified cell wall
• forces of cohesion and adhesion
• helps move water up narrow tubes

Question 19

Define transpiration

Answer 19

• loss of water vapour frm plant mainly thru stomata in leaves

Question 20

How transpiration moves water against gravity

Answer 20

• water evaporate frm stomata of leaves
• water removed frm xylem vessels
• suction force aka transpiration pull
• main force in drawing water and mineral salts up the plant

Question 21

How water is removed

Answer 21

1. Water continuously moves out frm mesophyll cells, form thin layer of moisture
2. water evaporate frm thin layer , move into intercellular air spaces
   - water vapour accumulate in sub-stomatal air spaces
3. water vapour diffuses thru stomata into drier air (transpiration)
4. water evaporate frm mesophyll cells, wp of cell sap fall, cell absorb water via osmosis frm cells deeper in leaf
   - remove water frm xylem vessels
5. transpiration pull, suction force pulls whole column of water up vessels

Question 22

Why transpiration is impt

Answer 22

1. Pulls water and mineral salts frm roots to stems and leaves
2. Evaporation of water frm cells in leaves remove latent heat of vaporization, cools plant down (wont get scorched)
3. Transported to leaves for photosynthesis
4. keep cells turgid, mechanical support, allow leaves to spread widely

Question 23

Factors that affect rate of transpiration

Answer 23

1. Humidity
2. Wind/air movement
3. Temp of air
4. Light

Question 24

Humidity

Answer 24

• intercellular air spaces normal saturated with water vapour
• less humid outside leaf, steeper concentration gradient
• vice versa

Question 25

How plants are adapted for desert-like conditions

Answer 25

1. Trichomes: tiny hairs that trap water vapour, increase humidity arnd stomata, decrease rate of transpiration
2. Sunken stomata: water vapour condense back into stomata
3. smaller SA:V of leaves (don’t say size)
4. Thicker cuticle

Question 26

Wind/air movement

Answer 26

• wind blows away water vapour accumulated outside stomata
• maintains water vapour conc gradient btwn leaf and atmosphere
• stronger wind, higher rate of transpiration (vice versa)

Question 27

Temp of air

Answer 27

• affects rate of evaporation

- high temp, higher rate of evaporation, higher rate of transpiration

Question 28

Light

Answer 28

• affects size of stomata
• sunlgiht: stomata will open and become wider
• vice versa

Question 29

Wilting

Answer 29

• turgor pressure in leaf mesophyll cells supports leaf; keeps it firm to spread out widely (why?)
• strong sunlight, rate of transpiration exceeds rate of absorption of water
• cells lose turgor
• become flaccid, plant wilts

Question 30

Advantages of wilting

Answer 30

• S:A exposed to sunlight falls as leaf folds up
• excessive loss of water, guard cells become flaccid, stomata close
• rate of transpiration falls

Question 31

Disadvantages of wilting

Answer 31

• rate of photosynthesis falls as water becomes limiting factor
• stomata closed, amt of CO2 entering leaf reduced
• CO2 becomes limiting factor for photosynthesis, cause rate of photosynthesis to fall
• folding of leaf reduces SA:V exposed to light

Question 32

Translocation

Answer 32

• Source: manufactures glucose
• SInk: need glucose
• can change depending on environment
• bi-directional

Question 33

How respiratory poison works

Answer 33

• dissolves, taken in by xylem
• assimilates into leaf, companion cells in phloem
• cannot respire (mitochondria poisoned), active transport affected
• translocation affected