What property of water allows it to form continuous columns in xylem vessels?
Cohesion
Hydrogen bonding between water molecules maintains an unbroken column.
What is the main driving force for water movement up the xylem?
Transpiration pull
Evaporation at leaves creates tension drawing water upward.
What term describes the movement of water vapour out of leaves through stomata?
Transpiration
Occurs down a water vapour concentration gradient.
Outline the pathway of water from soil to xylem in roots.
soil → root hair → cortex → endodermis → xylem
Includes apoplast and symplast pathways.
Fill in the blank:
Water moves into root hair cells by _____ due to a lower water potential inside the cell.
osmosis
Water potential gradient is created by mineral ion uptake.
What structure forces water into the symplast pathway before entering the xylem?
Casparian strip
Waterproof band in endodermis blocks apoplast route.
True or False:
Transpiration increases when humidity is high.
False
High humidity reduces the water vapour gradient.
Explain how evaporation from mesophyll cells contributes to water transport.
Creates tension
Water loss lowers water potential, pulling more water into leaves.
What tissue transports water and mineral ions in plants?
Xylem
Dead cells forming hollow tubes for mass flow.
Describe the cohesion-tension theory in simple steps.
evaporation → tension → cohesion → upward pull
Explains continuous water column movement.
What is translocation in plants?
Movement of assimilates
Transport of sugars and organic molecules in phloem.
Which molecule is mainly transported in the phloem?
Sucrose
Non-reducing sugar suitable for transport.
Fill in the blank:
The movement of sugars in phloem is explained by the _____ _____ hypothesis.
Mass flow
Also called pressure flow hypothesis.
Describe how sucrose is loaded into phloem sieve tubes at the source.
Active transport
Uses ATP to move sucrose into companion cells.
What happens to water potential in the phloem at the source?
It decreases
High sucrose concentration draws water in by osmosis.
True or False:
Translocation only occurs upwards in plants.
False
Can occur in both directions depending on source and sink.
Explain how pressure differences drive translocation.
high → low pressure
Created by sucrose loading and unloading.
What is meant by a “sink” in plant transport?
Region of storage/use
e.g. roots, fruits, growing tissues.
What experimental evidence supports translocation in phloem?
Ringing experiments
Removing bark stops sugar transport below the ring.
Why is ATP required for translocation?
Active loading/unloading
Maintains concentration gradients in phloem.
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1: Biological Molecules138
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1: Enzymes & Digestion16
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1: Cells & Ultrastructure52
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1: Transport Across Membranes20
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1: Cell Division20
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2: Exchange & Transport Systems76
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2: Plant Transport20
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2: Immune System36
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3: DNA & Protein Synthesis27
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3: Genetic Diversity14
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3: Biodiversity & Classification32
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3: Investigating Diversity12
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4: Natural Selection & Evolution42
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4: Populations & Ecosystems24
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4: Energy Transfer in Ecosystems35
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5: Photosynthesis23
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5: Respiration17
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5: ATP & Energy Transfer11
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6: Homeostasis57
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6: Nervous Coordination53
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6: Stimuli & Response62
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6: Muscles14
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7: Inheritance12
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7: Populations (Hardy–Weinberg)15
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8: Gene Mutations & Expression58
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8: Gene Technologies & Genomics46
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8: Disease24
