Summary Notes designed for the International Baccalaureate Diploma Programme. These notes are detailed yet concise, with all the information to achieve a 7 in IB Biology HL or SL. These notes were made using information from the IB syllabus, Oxford IB Diploma HL Biology Textbook, Bioninja and the B...
Class notes Biology Oxford IB Diploma Programme: Biology Course Companion
IBDP HL Biology - 2.2 Water Notes
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La Côte International School
IB Biology Unit 9- Plant Biology
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Unit 9.1
• Water is polar and can form hydrogen bonds.
• Cohesion is the surface tension between water molecules, and adhesion
is the surface tension between a water molecule and something else.
• Capillary action occurs when the adhesion to the walls of a vessel is
stronger than the cohesive forces between liquid molecules.
• The stomata are are pores in plant tissue which allow for gas exchange.
• The stoma are open when CO2 uptake and water loss is high, there is a high pressure in the
cytoplasm and high levels of sunlight.
• The stoma are closed when CO2 uptake and water loss is low, there is low pressure in the
cytoplasm and low levels of sunlight.
• Transpiration is the movement of water up the xylem.
• The xylem are long, dead, continuous tubes arranged end to end.
• All transport in the xylem is passive as it is dead.
• The xylem has a large lumen and no cytoplasm. It also contains spiral lignin which supports the
circular structure and stops it from collapsing under low pressures.
• The cambium is made out of stem cells.
• A vascular bundle consists of the xylem
and phloem.
• The root has many adaptations including
large surface and area and vacuoles, and
1000’s of root hair cells.
• Water is transported in the root via two pathways:
• Symplast pathway where mineral ions are actively transported through the root causing
water to follow in the cytoplasm through holes in the cell wall called plasmodesmata.
• Apoplast pathway where adhesion and cohesion are used through the cell walls.
• The casporian strip located in the endodermis cell causes water in the apoplast pathway to
travel into the symplast pathway.
• When water moves into the xylem root pressure is created pushing the water upwards.
• The pulling force generated from cohesion and adhesion creates negative pressure.
• Transpiration is measured using a potometer.
Unit 9.2
• Translocation is the active movement of sugars in the phloem.
• Glucose produced during photosynthesis is converted into sucrose as it is soluble.
• A sink cell is where sucrose might be used (roots, bud etc) whereas a source cell is where
glucose is produced (leaf etc).
• Phloem cells also have companion cells which provide them with organelles and proteins so the
phloem can have a larger lumen.
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