OCR Biology Transport in Plants 3.1.3 Revision Summary - By A* student
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Course
Transport in Plants 3.1.3 (H420)
Institution
OCR
A revision summary of OCR A level Biology Transport in Plants 3.1.3
Made by a student who achieved A* in A level Biology.
Covers all the points within the OCR Biology Specification.
Condenses 3 OCR specification books and class notes.
Need for transport system
- High metabolic rate, Small SA: V (stem), Large sizes Water transport in plants
Transport in Dicotyledonous plants Root hair cell – large SA: V, microscopic size can
Stem Root Leaf penetrate between soil particles, thin cell wall, solutes in
cytoplasm maintain conc gradient for osmosis
1. Mineral ions enter RHC, ↓ᴪ and water follows by
osmosis. Through each cell.
2. Water moves through cortex cells by osmosis (ions ↓ ᴪ
Vascular bundles Mid vein supports in adjacent cell) pulled through cohesive forces.
Vascular bundles in Apoplast – in between cell walls and does not pass
around the edge structure and
middle help plant membranes. Mineral ions are carried with water.
give strength & transports vascular
withstand tugging Symplast – enters cytoplasm, travels cell to cell
support tissue
forces through plasmodesma
Vacuolar – water enters vacuoles of cells.
Vessel Function Features 3. Endodermis cell layer (into xylem) is surrounded by
Xylem Transport Continuous column of the Casparian strip – waxy suberin forms waterproof
of water, dead cells – does not layer. Blocks apoplast pathway forcing water into
inorganic impede mass flow of water. symplast pathway. Selectively permeable CSM excludes
ions, small Cohesion & adhesion toxic solutes reaching cytoplasm.
organic Thick lignin walls – 4. Water enters vascular bundle (xylem)
molecules strength & waterproof, 5. Endodermal cells move mineral ions into xylem by
from roots layered in spiral so plant active transport. ↓ᴪ so water moves via osmosis
upwards can sway 6. Root pressure theory – initial flow into vascular
Pits – lateral flow of water tissue forces water up the stem.
Narrow – prevents water 7. Capillary action - charged water molecules attracted
column breaking to sides of xylem & are pulled up by adhesion.
Phloem Transport Sieve plates – connect 8. Transpiration pull – water molecules are attracted to
of organic sieve tubes & let contents each other by cohesion forming a continuous column.
substance flow Water is pulled upwards to replace water lost by
s from Companion cells – lots of transpiration.
source to mitochondria (ATP) for Evidence for cohesion-tension theory
sink metabolic functions. - Trees are narrower in the day during transpiration. Transpiration
(sucrose, Infoldings in CSM for ↑SA increased tension in xylem vessels causing diameter to decrease.
hormones, Plasmodesmata – link - When a stem is cut – air is drawn in and water does not leak out
products sieve tube & companion cell
of photo- for assimilates to move
synthesis through
No nucleus/ cytoplasm –
reduces friction &
maximises space
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