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...
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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