9.1 - Transport in Dicots

Question 1

What are reasons for the need of plant transport systems?

Answer 1

METABOLIC DEMAND - Green parts of plant photosynthesis and make their own glucose, however internal and underground plants don’t and need glucose transported to them - Mineral ions must be transported from roots to rest of plants to make proteins for enzymes and cell structure - Hormones must be transported - Waste cell metabolism products must be removed SIZE - Large perennial plants need effective transport systems to move substances up and down plant (roots to leaves) SA:V RATIO - Leaves have large SA:V, but stems trunks/roots make plants overall ratio small.

Question 2

What are herbaceous dicots?

Answer 2

Soft tissue plants with short life span (leaves and stems that die down at the end of growing season)

Question 3

Define vascular system.

Answer 3

Series of transport vessels that run through leaves, roots and stem of a dicot plant.

Question 4

Define vascular bundle.

Answer 4

The vascular system of herbaceous dicots comprising of xylem and phloems.

Question 5

Draw and label the structure of the stem

Answer 5

• Parenchyma - In the middle, packing and supporting tissue Phloem vessel on outside - for translocation
• Xylem vessel on inside - for transpiration
• Vascular cambium - new xylem and phloem cells divide from it.
• In a stem the vascular bundles around the edge provide structural support.

Question 6

Draw and label the structure of a root (dicot)

Answer 6

• Root hair on the outside protruding
• From root hair
• Exodermis, epidermis, cortex, endodermis Phloem as 4 dots Xylem as a cross

Question 7

Draw and label the structure of a leaf (dicot)

Answer 7

Midrib of the leaf gives structural support as it is the main vein carrying the vascular tissue through the organ

Xylem and phloem

Palisade mesophyll - main photosynthetic tissue

Question 8

What is the function and structure of a xylem?

Answer 8

• End walls removed forming a long tube
• No cytoplasm or organelles - non-living tissue
• Cell walls lignified (impregnated with lignin)
  
  • Makes wall waterproof and prevents xylem collapsing
• Spiral, annular (ring-like) and reticulate (mesh-like) thickening to strengthen walls and prevent collapsing
• Bordered pits to allow lateral water flow between xylem vessels
  
  • E.g. if the xylem has an obstruction, water can still flow but in another xylem vessel

Question 9

What is the role of xylem parenchyma?

Answer 9

• Surrounds xylem vessels
• Stores food as contains tannin
  
  • Tannin: bitter-tasting to deter herbivorous attack

Question 10

What is the function of a phloem vessel and what are its components?

Answer 10

• Transports assimilates actively by mass flow - involves 2 cells
  
  • Sieve Tube Elements (STE) - long sieve tubes transporting assimilates
  • Companion Cells - supports metabolic function of STE, also involved in actively loading the phloem

Question 11

What are the adaptations of the sieve tube element?

Answer 11

• Few organelles and no nucleus - long hollow tubular structure
• Has end walls with sieve plates (perforated walls)
• Thin layer of cytoplasm
• Not lignified as the cell is not under tension

Question 12

What are the adaptations of companion cells?

Answer 12

• Closely linked to STE
• Connected to STE by plasmodesmata
  
  • microscopic channels of cytoplasm through cellulose cell walls linking cytoplasm to adjacent cells
• Dense cytoplasm with many mitochondria and a large nucleus
  
  • Mitochondria gives energy to move sucrose into STE