Topic 7: Transport in Plants Flashcards
Definitions I:
(a) Xylem
(b) Phloem
(c) Transpiration
(a) Xylem: Tissue transporting water and minerals. (1 mark)
(b) Phloem: Tissue transporting assimilates. (1 mark)
(c) Transpiration: Water evaporation from leaves. (1 mark)
Draw a plan diagram of a dicot stem’s transverse section from a microscope slide. [2 Marks]
Circular stem, vascular bundles in ring (1 mark); Xylem inside, phloem outside, labelled (1 mark). (2 marks)
In a dicot root, describe the distribution of xylem and phloem in a transverse section. [2 Marks]
Xylem in central star shape (1 mark); Phloem between xylem arms, near pericycle (1 mark). (2 marks)
Draw and label xylem vessel elements from an electron micrograph of a leaf. [2 Marks]
Hollow tubes, lignin walls (1 mark); Label: vessel element, pits (1 mark). (2 marks)
Draw and label phloem sieve tubes and companion cells from a stem photomicrograph. [2 Marks]
Sieve tubes with plates, companion cells dense (1 mark); Label: sieve plate, companion cell (1 mark). (2 marks)
Relate the structure of xylem vessel elements to their function in a tree trunk. [2 Marks]
Lignin walls resist collapse (1 mark); Hollow for water flow to leaves (1 mark). (2 marks)
In a flowering plant, relate the structure of sieve tubes and companion cells to their roles. [2 Marks]
Sieve tubes: Porous plates for flow (1 mark); Companion cells: Load assimilates, support (1 mark). (2 marks)
State how mineral ions are transported in a plant’s root system. [1 Mark]
Mineral ions dissolve in water, move via xylem. (1 mark)
In a pea plant, describe water transport from soil to xylem via apoplast and symplast pathways. [3 Marks]
Apoplast: Through lignin/cellulose walls (1 mark); Symplast: Cytoplasm, blocked by Casparian suberin (1 mark); Enters xylem (1 mark). (3 marks)
Explain transpiration in a sunflower leaf under sunlight. [3 Marks]
Water evaporates from mesophyll (1 mark); Vapour diffuses via stomata (1 mark); Driven by sunlight (1 mark). (3 marks)
In a tall oak, explain how hydrogen bonding aids water movement in xylem. [3 Marks]
Cohesion: H-bonds pull water up (1 mark); Adhesion: Sticks to cellulose (1 mark); Transpiration pull drives (1 mark). (3 marks)
Draw an annotated transverse section of a cactus leaf showing xerophytic adaptations. [3 Marks]
Thick cuticle, sunken stomata drawn (1 mark); Reduced area, labels (1 mark); Limits water loss (1 mark). (3 marks)
State how sucrose moves from a leaf to a root tuber in phloem. [1 Mark]
Sucrose dissolves, moves from source to sink. (1 mark)
In a potato plant, explain how companion cells load assimilates into sieve tubes. [4 Marks]
Proton pumps create H⁺ gradient (1 mark); Cotransporters load sucrose (1 mark); Moves into sieve tubes via active transport (1 mark); Water enters via osmosis, increasing pressure (1 mark). (4 marks)
Explain mass flow in phloem from a leaf source to a fruit sink. [4 Marks]
High pressure at leaf source (1 mark); Low pressure at fruit sink (1 mark); Assimilates flow down gradient by mass flow (1 mark); Via sieve tubes (1 mark). (4 marks)
