9.1 Transport Systems in Dicotyledonous Plants

Question 1

What 3 factors influence the need for transport systems in plants?

Answer 1

• METABOLIC DEMANDS
• SIZE (tall plants)
• SA:VOLUME (required when large)

Question 2

Why may plants need transport systems?

Answer 2

• High METABOLIC DEMAND
  
  • ​Underground cells do not photosynthesise
    
    • Require glucose + oxygen transported, + waste removed
  • Hormones transported from site of production ⟶ site of effect
  • Mineral ions ​transported from roots ⟶ cells
• LARGE SIZE/TALL
  
  • ​Tall plants transport substances from roots ⟶ leaves over larger distance
• Low SA:VOLUME (usually due to trunks + stems)
  
  • Cannot rely on simple diffusion alone to meet demand

Question 3

What is the arrangement of vascular bundles in the leaf of a dicotyledonous plant?

What is the benefit of this arrangement?

Answer 3

Vascular bundles branch out from midrib vein >> structural support + transport

Question 4

What is the arrangement of vascular bundles in the stem of a dicotyledonous plant?

What is the benefit of this arrangement?

Answer 4

ring around edges of stem >> provides support

Question 5

What is the arrangement of vascular bundles in the root of a dicotyledonous plant?

What is the benefit of this arrangement?

Answer 5

middle >> withstand tension

Question 6

What is xylem?

Answer 6

plant transport tissue

transporting water + mineral ions_(aq)

up from roots ⟶ leaves

as a result of physical forces

Question 7

What is the structure of xylem?

Answer 7

non-living tissue, composed of dead hollow cells, fused end-to-end to form column called xylem vessel.

• Lined with lignin in spirals/pits
  
  • bordered pits for water to enter/exit laterally
  • waterproofs vessels + provides support
• No end walls

Question 8

What is the function of xylem?

Answer 8

Transport water + mineral ions_(aq)

up plant

from roots ⟶ leaves

Question 9

What is lignin?

Answer 9

a complex organic polymer,

deposited in the cell walls of plant cells.

Increases rigidity + support.

Question 10

What are the functions of lignin in xylem?

Answer 10

• Waterproofs vessel
• Provides support

Question 11

Why is lignin present in xylem as rings/spirals?

Answer 11

provides support, whilst maintaining flexibility

Question 12

What is phloem?

Answer 12

transport tissue

transporting assimilates (products of photosynthesis)

to all plant cells

Question 13

What is the structure of phloem?

Answer 13

living tissue, composed of living hollow cells, fused end-to-end to form sieve tube element.

• FEW ORGANELLES + COMPANION CELLS
  
  • ∴ phloem cells rely on companion cells linked to sieve tube elements by plasmodesmata
    
    • ​contain organelles to carry out cell functions for sieve tube members
• SIEVE END PLATES
  
  • ​perforations in cell wall, allow flow of contents
• NO LIGNIN

Question 14

What is the function of phloem?

Answer 14

Transport assimilates (products of photosynthesis)

up + down the plant

from photosynthesising cells ⟶ all cells

Question 15

Why do sieve tube elements contain few organelles?

Answer 15

maximise area for translocation

Question 16

Compare the structure + function of xylem and phloem:

Answer 16

XYLEM ⏐ PHLOEM

dead cells ⏐ living cells

lignin ⏐ no lignin, but structural fibres

no companion cells ⏐ companion cells

no end walls ⏐ sieve plates

hollow vessel/column

made from cells fused end-to-end

transports substances up ⏐ transports substances up + down

transports H₂O + mineral ions_{<span>(aq)</span>} ⏐ transports assimilates