Cell Structure and Function
Intro to The Cell
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Cells are small and the most basic unit of life
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Cells have cell membranes
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All cells have ribosomes and cytosol(just liquid)/cytoplasm (liquid and everything in it)
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Most cells have DNA
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Red blood cells have no DNA
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Eukaryotes have a nucleus with DNA
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Prokaryotes have DNA floating around cytoplasm
Eukaryotic Cells Organelles
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Organelles: membrane bound in a cell (unique function)
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The nucleus stores DNA, nucleus pores connect to the endoplasmic reticulum
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Rough Endoplasmic Reticulum: site of protein synthesis
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Smooth Endoplasmic Reticulum: site of lipid synthesis
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Golgi Apparatus: packages proteins and molecules
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Mitochondria: makes ATP (has own DNA)
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Chloroplast: site of photosynthesis (ONLY IN ALGAE AND PLANTS)
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Vacuoles: contains enzymes, water, waste, etc.
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Lysosomes: has enzymes that break down waste
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Organelles allow complex metabolic reactions
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Eukaryotes are larger than Prokaryotes
Endoplasmic Reticulum and Golgi Apparatus
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The rough ER has ribosomes which create proteins
1. mRNA attaches to the ribosomes and is translate in the lumen (inside rough ER)
to make proteins
2. Protein “buds off” of the ER
3. Protein moves into a vesicle
4. Protein moves into the Golgi apparatus or the cell membrane
5. Protein matures in Golgi body
6. The fully-manufactured protein leaves the Golgi body
7. Protein move onto or out of cell membrane
Endomembrane System
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Organelles have membranes consisting of phospholipids
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The Golgi apparatus has enzymes that add things or tag the proteins
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Lysosomes have membranes to protect the rest of the cell from its acidic environment
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Endomembrane System: a group of organelles in eukaryotic cells that work together to
modify, package, and transfer lipids and proteins
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Endomembrane system only included lysosomes, ER, and golgi body
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Peroxisomes are similar to lysosomes but they house enzymes involved in oxidation
reactions which produce hydrogen peroxide as a by product
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It breaks down fatty acids/amino acids and detoxifies substances that enter the
body (not part of the endomembrane system\
Mitochondria
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ATP factory; provide energy for cell
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Has two membranes and own DNA
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Endosymbiosis says mitochondria was aerobic bacteria and chloroplast was
photosynthetic bacteria which came in symbiosis with a eukaryotic cell because it
provided the cell with food and energy
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Mitochondria’s membranes have imbedded proteins
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Outer membrane has pores allowing small molecules inside
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Inner membrane is called cristae; produces ATP by the electron transport chain
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In the matrix (inside inner membrane) the Krebs cycle (cellular respiration) occurs
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Mitochondria is inherited from the mother
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Red blood cells have no mitochondria
Cell Size
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The surface area to volume ratio has to be greater in order to provide enough nutrients
and get rid of waste in the cell
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As the cell gets larger it starves and slowly dies because it cant provide nutrients for the
nucleus
Cilia, Flagella, and Pseudopodia
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Cilia (small hairs) helps the cell move itself or other things around
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Flagellum is a tail that helps cells move around
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Pseudopodia (like a leg) helps amoeba attack or move around
Surface Area to Volume
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Resources are needed by the cell to survive
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The cell needs to move waste and other things out of the cell
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The cell benefits if the surface area is greater than the volume
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The cell activity decreases and becomes more difficult when volume increases
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The more folds in a cell membrane more surface area
Fluid Mosaic Model
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Phospholipids build the cell membrane
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Polar head; hydrophilic; faces outwards
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Nonpolar tail; hydrophobic; faces inwards
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Amphipathic: both hydrophilic and hydrophobic
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The cell membrane has many proteins/lipids
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The membrane moves around allowing things to move around or through the cell
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Proteins allow communication
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Cholesterol allows fluidity of the membrane at different temperatures
Cell Membrane Proteins
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Integral proteins are found throughout the entire membrane (stuck)
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Two types of integral proteins:
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Channels:
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Let molecules and ion in and out of the cell
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Requires no ATP; goes down concentration gradient
Carriers:
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Change shape allowing certain things through
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Requires ATP; goes against concentration gradient
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Peripheral proteins are on top of the membrane (attached, “can move”)
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Lipid-bound proteins are inside the cell membrane (very rare)
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Proteins are meant to interact with the environment (inside/outside)
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Proteins help maintain homeostasis
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Glycoproteins are sugars attached to integral proteins that allow signaling
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Saturated fatty acids are straight and pack tightly
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Unsaturated fatty acids are bent and less packed
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Unsaturated fats stay fluid at cold temp compared to saturated fats
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Membranes have both types of fatty acids
Cell Membrane Intro
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The cell membrane is semi-permeable
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Small, nonpolar molecules can use “passive diffusion”
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Example: Gasses (Oxygen and Carbon Dioxide)
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Water and ethanol are small but polar, they can diffuse but at a slower rate
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Large and nonpolar molecules can pass through slowly
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Large and polar molecules cant pass through (unless with protein)
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Charged molecules like ions and amino acids cant pass through because of polarity
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Glycoproteins and glycolipids are on the outside of the membrane
Cell Wall
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The cell wall of plant cells provides structure and protection
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Square like shape
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Plants are given structure by the water in the cell pushing against the cell wall
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Cell wall is made up of cellulose, hemicellulose, and pectin
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Cell walls have plasmodesmata, tunnels between other cells to let certain things
inside/outside
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Middle lamella helps hold the cell walls of adjacent plant cells together
Extracellular Matrix
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Animal cells release materials in the extracellular space, creating a network of protein
and carbohydrates called the extracellular matrix
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Collagen proteins are modified by carbohydrates and when they are released from the
cell they assemble into collagen fibrils (long fibers)
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The ECM includes collagen fibrils and proteoglycans
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The ECM id directly connected to other animal cells by integrins (on membrane)
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Integrins are linked to the cytoskeleton and trigger signaling pathways
Passive and Active Transport
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Passive transport; no energy and moves along concentration gradient
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Active transport; need energy and moves against concentration gradient
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Electric gradient: the potential for two charged particles to move toward each other or
the difference in charge between two areas
Selective Permeability
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Only small, non charged molecules can pass through the cell membrane as they go along
concentration gradient by diffusion
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Large, charges molecules cant pass through the cell membrane by diffusion
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Only very few water molecules can diffuse through the cell membrane at a slow rate
because of its charge
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Diffusion: high to low concentration until equilibrium is reached, but they still move
around
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Transport proteins allow large molecule and ions to move along their concentration
gradient protecting them for the hydrophobic region
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Active transport requires assistance of carrier proteins which change when ATP
hydrolysis occurs
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Facilitated diffusion moves molecules along concentration gradient
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Active Transport moves molecules against concentration gradient
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NO CHANNEL PROTEINS IN ACTIVE TRANSPORT ONLY CARRIER
PROTEINS
Endocytosis, Phagocytosis, Pinocytosis
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Bulk Transport (require energy):
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Phagocytosis: engulfing large things for the inside of the cell by a vesicle
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Pinocytosis: engulfing liquids for the inside of the cell by a vesicle
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Exocytosis: vesicles transport large numbers of molecules out of the cell by fusing
with the cell membrane and then the contents of the vesicle are expelled
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Important for the transport of neurotransmitters
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Endocytosis is both phago/pinocytosis
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Motor proteins use ATP to move vesicles to the membrane
Receptor-Mediated Endocytosis
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Receptor proteins on the cell surface are used to capture a specific target molecule and
then using a food vesicle to move it into the cell
Facilitated Diffusion
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Channel proteins(may be gated and are faster) allow large, charges molecules through the
cell membrane, by a signal or binding of a molecule
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Specific to which molecule or ion they let in or put
Carrier Proteins(change shape and are slower) are specific and allow large, charged
molecules down their concentration gradient
Electron chemical Gradient -Secondary Active Transport
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Electrochemical gradient allows charged ions to move down their concentration
gradient
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Ions want to move away from themselves because they repel
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Symporters (secondary active transport) use ions charge to move other things
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When moving an ion against its concentration gradient active transport is need
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Now the cycle of the ions begins again because they want to move away from ions like
itself, this is a type of potential energy
Symporters, Uniporters, Antiporters
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Primary Active transport are the Sodium/Potassium pump(animal cells), which breaks
ATP for energy, another form is the proton pump(plant cells), which reaks ATP for
energy to move against concentration gradient
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Primary active Transport allows Secondary Active Transport (uses electrochemical
gradient)
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Symporters (same direction) use the energy of a ion or molecule moving down their
concentration gradient to move another ion or molecule against their concentration
gradient
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Antiporters (opposite side) use the energy from a ion or molecule moving down their
concentration gradient to power another molecule against their concentration gradient
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The inside of the cell is very negative
Sodium-Potassium Pump
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Sodium out of the cell, Potassium in cell
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Steps:
1. Pump faces inside of cell and has a high affinity for sodium(takes three)
2. Sodium binds triggering the pump to hydrolyze(break down) ATP, one phosphate
group is attached to the the pump, ADP is released as a by product
3. Phosphorylation makes the pump change shape(to extracellular space), now the
pump doesn't like sodium ions so lets the three go
4. The pump now has an affinity for potassium(takes two), the phosphate group is
released
5. The release of the phosphate group changes the pumps shape towards the
interior of the cell
6. The pump doesn't like the potassium anymore letting go of the two, now the
cycle can begin again
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This pump generated a membrane potential
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Since the outside of the cell is positive these ions(positive) will use these pumps to move
away towards the negative interior of the cell
Diffusion and Osmosis
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Solvent- what is dissolving
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Solute - what is dissolved
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Diffusion: high concentration to low concentration
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Concentration can be molar
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Solvent moves to lower concentration
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Hypertonic(more) Solution - against concentration gradient
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Hypotonic (less) Solution- down concentration gradient
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Water tends to be the typical solvent, if a solute cant pass through the semipermeable
membrane, the solvent will move where there is a lowers solvent concentration
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If a cell has more solvent it will have less solute, so more solute will move in
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If a cell has more solute it will have less solvent, so the solute will move out
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Hypertonic and hypotonic can be applied or oth the solvent and the solute
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Osmosis: water dissolving through a semipermeable membrane
Osmosis
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Water moves to a higher solute concentration
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If solute molecules are blocking the pores water wont move in any direction
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Water moves towards charged ions/molecules
Hypertonic, Isotonic, Hypotonic Solution
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Hyposmotic: solution has less solute, but the cell has more solute making it hypertonic,
so solute will move in
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Isosmotic: both the solution and the cell have the same concentration of solute, meaning
equilibrium, both are isotonic
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Hypoosmotic: solution has more solute, but the cell has less solute making it hypotonic,
so solute will move out
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Hypertonic:
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Bad for plant cells, will lose water and lose structure (hypotonic cell)
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Bad for animal cells, will lose water and shrivel up, plasmolysis (hypotonic cell)
Isotonic:
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Bad for plant cells, will lose turgor pressure
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Good for animal cells, will keep shape (isotonic cell)
Hypotonic:
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Good for plant cells, will keep turgor pressure helping cell wall keep plants
structure (hypertonic cell
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Bad for animal cells, solution will rush in the cell causing it to burst (hypertonic
cell)
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Osmolarity: total concentration of solutes in a solution
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Tonicity: an extracellular solutions ability to move water in or out of a cell by osmosis
Water Potential
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𝞇=𝞇p+𝞇s
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Open beaker = pressure 0
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𝞇s= -iCRT
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- : as long as solute is solution
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i : # ions the solution breaks in (more ions, lover 𝞇s
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C : molar concentration
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R : 0.0831 (L-bars/mol*k or LMPa/mol*k)
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T : temperature in Kelvin (273.15) + temperature in Celsius
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On graph 0, on x-axis, represents the same water potential of the solute and
solvent
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Distilled water has 𝞇 of 0 bars
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Water moves to a system with lower 𝞇