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Cells. Chapter 3. Plasma Membrane . Transport Across the Plasma Membrane. Fluids in average body = ~60% ICF -- inside the cell (cytosol) ECF – outside the cell Interstitial fluid (between cells of tissues) Plasma (blood vessels) Lymph (lymphatic vessels)

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Chapter 3

transport across the plasma membrane
Transport Across the Plasma Membrane
  • Fluids in average body = ~60%
  • ICF -- inside the cell (cytosol)
  • ECF – outside the cell
    • Interstitial fluid (between cells of tissues)
    • Plasma (blood vessels)
    • Lymph (lymphatic vessels)

Materials dissolve into these body fluids; direction of movement dependent upon concentration (amount of solute in solution) 

concentration gradients
Concentration Gradients
  • Differences between ICF and ECF in solute concentration

3% salt solution 5% salt solution

??? Water ??? Water


High to low Low to high

No energy needed Energy needed

concentration gradients1
Concentration Gradients
  • Differences between ICF and ECF in solute concentration

3% salt solution 5% salt solution

97% Water 95% Water


High to low until dynamic equilibrium reached

Down concentration gradient

No energy needed

two types of diffusion
Two types of diffusion
  • Simple diffusion: lipid-soluble substances, simple cross membrane down the gradient
  • Facilitated diffusion: ions, through pores of ion channels of integral proteins
  • Net movement of water down the gradient; lower solute concentration to higher solute concentration through
    • Lipid bilayer
    • Integral proteins

20% sucrose

80% water

osmotic pressure
Osmotic Pressure
  • Exerted on cell membrane due to a solution containing solute particles that cannot pass through membrane
    • Higher solute concentration = higher osmotic pressure
    • Lower solute concentration = lower osmotic pressure
  • Volume of cell remains the same, why???
osmotic solutions
Osmotic Solutions
  • Isotonic solution: cells maintain normal shape and volume; concentration of solutes equal on both sides of membrane
  • Hypotonic solution: higher concentration of water outside; higher concentration of solutes than cytosol inside cell
    • Water molecules will enter cell faster than they leave it = cell will swell, eventually burst
      • Bursting of red blood cells referred to as hemolysis
  • Hypertonic solution: higher concentration of water inside; lower concentration of solutes than cytosol inside cell
    • Water molecules will leave cell faster than they enter it = cell will shrink
      • Shrinkage of red blood cells referred to as crenation
short video review
Short Video Review


passive or active
Passive or Active?
  • Have I been talking about passive, active, or passive and active transport?
active transport
Active Transport
  • From low to high concentration; ‘up the gradient’
  • Requires the use of energy
    • Comes from splitting of ATP molecule
    • Changes shape of transporter protein, called a pump
    • Transports ions: Na+, K+, H+, Ca+2, I-, Cl-
    • 40% of a cell’s ATP expended on active transport
  • Drugs like cyanide can turn off ATP production--FATAL
  • Cyanide can be a colorless gas, such as hydrogen cyanide (HCN) or cyanogen chloride (CNCl), or a crystal form such as sodium cyanide (NaCN) or potassium cyanide (KCN).
  • Cyanide sometimes is described as having a “bitter almond” smell, but it does not always give off an odor, and not everyone can detect this odor.
  • You could be exposed to cyanide by breathing air, drinking water, eating food, or touching soil that contains cyanide.
  • Cyanide enters water, soil, or air as a result of both natural processes and industrial activities. When present in air, it is usually in the form of gaseous hydrogen cyanide.
  • Smoking cigarettes is probably one of the major sources of cyanide exposure for people who do not work in cyanide-related industries.
transport in vesicles
Transport in Vesicles
  • Vesicles small sacs formed by budding off of membranes
    • Transport substances within the cell from one structure to another
      • Energy source again is ATP
    • Take in substances from ECF and transport substances out to ECF
      • Endocytosis: materials moved into cell
        • Phagocytosis  ‘to eat’ - solids
        • Bulk-phase endocytosis(pinocytosis)  liquids
      • Exocytosis: materials moved out of cell
  • Endocytosis: capturing substance or particle from outside the cell by engulfing it within membrane folds from the cell membrane and releasing it into cytosol. There are two main kinds of endocytosis:
    • Phagocytosis ”cellular eating,” dissolved materials enter the cell. The plasma membrane engulfs solid material, forming phagocytic vesicle or pseudopod.
      • Occurs only in phagocytes (certain white blood cells and macrophages), cells specialized to engulf and destroy bacteria, viruses, aged dying cells, and foreign matters protecting body from disease
    • Bulk-phase endocytosis (pinocytosis) ”cellular drinking,” plasma membrane folds inward, forms a channel allowing dissolved substances to enter the cell. When the channel is closed, the liquid is encircled within a pinocytic vesicle.
      • Takes in tiny droplets of ECF fuses with lysosomes to degrade solutes (ex: to amino acids, fatty acids) then released for reuse
  • Exocytosis: process of vesicles fusing with the plasma membrane and secretes their contents to the outside of the cell.
    • All cells do exocytosis process, but most important in:
      • Secretory cells
        • Release digestive enzymes, hormones, mucus, and other secretions
      • Nerve cells
        • Release neurotransmitters
cytoplasm nucleus
Cytoplasm & nucleus
  • Functions and identification of the organelles are your responsibility since this a total biology review area
    • Information found on pages 52-60 of your textbook
  • May contain up to 60 different digestive enzymes
  • Recycle the cell’s own structures  autophagy
  • May destroy own cell  autolysis
    • This cause tissue deterioration after death
    • Faulty lysosomes can contribute to certain diseases, i.e. Tay-Sachs disease
releasing energy from food
Releasing Energy From Food
  • Recall ultimate source of all energy on Earth comes from the sun
  • Plants capture and store energy as food (glucose)
  • Glucose is converted to ATP during cellular respiration in order to store chemical energy for later release
  • ATP is broken down to ADP to release stored chemical energy

A—P~P~P enzyme A –P~P + P + energy

  • Released energy is used for:
    • Movement (warmth)
    • Chemical reactions
    • Electrical impulses
    • Active transport
cellular respiration
Cellular Respiration
  • Glycolysis anaerobic process in cytoplasm
    • Glucose + 2ATP  pyruvic acid + 4ATP + NADH
  • Followed by aerobic process in mitochondria (Kreb’s cycle)
    • Pyruvic acid enters cycle changes releasing CO2 and creates NADH, FADH2, and ATP
    • ETC >>> NADH and FADH2 from glycolysis and Kreb’s used to make additional 36 ATP…