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Lecture 2

BIOB38H3 Lecture Notes - Lecture 2: Light-Independent Reactions, Light-Dependent Reactions, Symplast

Biological Sciences
Course Code
Connie Soros

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BIOB38H3 – Lecture 2: Plant Cells and Physiology
Plant cells
Most plant cells have a large vacuole
Plants have cell walls so they are able to stay in one place; to be rigid,
What plant cells have different than animal cells:
oPlasmodesmata: channels that allow movement of molecules and
ions to get through cell wall
oPlasma Membrane: phospholipid bilayer that is permeable to
diffusion of some molecules like water and other small molecules.
The larger molecules go through transport proteins by active
transport in the plasma membrane.
Chromoplasts- have pigments of yellow, orange, blue, etc. to
attract pollinators and animals
E.g: Amyoplasts for starch storage
Chloroplasts- site of photosynthesis by their chlorophyll
(green pigment) that absorbs photons of light
NOTE: most cells are actually clear or white looking, not coloured unless they
have pigments.
oInternal membranes: Rough ER, Golgi apparatus
oMitochondria: The energy factories of the cell that carry out the
Krebs cycle in the fluid filled matrix.
oPrimary cell wall: thatched proteins and cellulose like a plant
Pectin allows rigidity but flexibility
oSecondary cell wall: waterproof, sits over the primary cell wall
towards to outside of the plant
Lignin allows for strength, not flexible though
These cells are xylem and are what are only in woody plants
Plant Physiology
Passive Transport: requires no energy, “goes with the flow”
Active Transport: requires energy
Cell Osmosis
Isotonic cell: gains or losses net water, the cell is at equilibrium of water
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Hypotonic cell: more water is flowing into the cell so the cell is bigger
Water flows in because there are too many solutes inside, and it wants to
return to equilibrium
Water goes into the vacuole and pushes against the cell wall
Hypertonic cell: too much water flows out of the cell and the cell is smaller
Water flows out of the cell because there are more solutes outside of the
cell and its trying to maintain equilibrium
Turgor pressure: so much water in cell and in central vacuole making it rigid
Wilting happens when a plant is losing too much water than is can gain.
It plasmolysis
Pathways of Water in Roots
Apoplastic pathway: water moving through non-living part of cell, between the
cell walls
Symplastic pathway: water moving through living part of cell; the inside of cell by
going through the cell wall. Plant controls this movement, and it is just larger
molecules that use this pathway.
Casparian Strip: a strip wrapped around each cell which forces apoplastic water
to symplast because it blocks the apoplastic pathway between the cell walls.
Xylem Transport (Adhesion-Cohesion Theory)
Cohesion: strong double bond between hydrogen and hydrogen of two water
molecules (H=H)
Adhesion: Hydrogen bonds to the walls of the xylem cells such as vessel
elements and tracheids
Adhesion-Cohesion Theory: there is a continuous source of H2O that can
evaporate in intracellular spaces of the leaf and transpire through stomata, the
cohesive force on them is so strong that any force or pull on one H2o molecule
acts on all of them resulting in bulk flow of water within the plant.
So water molecules are pulling as they are attached to eachother
(cohesion), and also being pulled by the walls of cells (adhesion).
Xylem Transport (Transpiration-Cohesion Theory)
Transpiration: water loss from leaves
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