6 Flashcards
Diffusion across cell membrane
Cell membrane is the boundary between inside & outside…
and it separates cell from its environment
Can it be an impenetrable boundary?
NO!
Why it cannot be an impenetrable boundary?
Because cell needs materials in & products or waste out.
What are the substances inside of the cell membrane?
Food such as
carbohydrates,
sugars,
proteins,
amino acids,
lipids,
salts,
O2,
H2O
What are the substances outside of the cell membrane?
Waste such as
ammonia,
salts,
CO2,
H2O, and
products
Permeability of the Plasma Membrane
Differentially (selectively) Permeable
Allows some materials to pass.
- Water, oxygen, carbon dioxide
Prevents others from passing.
- Proteins, carbohydrates
Permeability of the Plasma Membrane
Factors that determine how a substance may be transported across a plasma membrane:
Size
Polar or Nonpolar
charge
PASSIVE DIFFUSION
2nd Law of Thermodynamics
governs biological systems
– universe tends towards disorder (entropy)
is a measure of disorder or randomness in a system, often interpreted as the tendency for energy to disperse and systems to move toward equilibrium
Entropy
is the movement of molecules across a membrane without the need for energy input, occurring naturally from an area of high concentration to an area of low concentration. This process helps equalize concentrations on both sides of the membrane, allowing substances like oxygen, carbon dioxide, and small uncharged molecules to move freely.
Passive diffusion
PASSIVE DIFFUSION
Only ____, relatively ____ molecules are able to diffuse across a _______ at significant rates by using passive diffusion.
small
hydrophobic
phospholipid bilayer
Passive Diffusion
Molecules have to _______ in lipid interior.
dissolve
Molecules have to dissolve in lipid interior. Molecules such as?
- Gases (oxygen, carbon dioxide)
- Water molecules (rate slow due to polarity)
- Lipids (steroid hormones)
- Lipid soluble molecules (hydrocarbons, alcohols, some
vitamins) - Small noncharged molecules (NH3)
Water molecules has slow rate due to?
polarity
Why large polar molecules (e.g glucose) and charged molecules (e.g amino acids and ions) cannot pass through the plasma membrane?
Because the membrane is composed of a lipid bilayer, which is hydrophobic (water-repelling). This structure prevents these molecules from dissolving in or diffusing through the lipid layer. Instead, they often require specific transport proteins or channels to facilitate their movement across the membrane.
Why is diffusion important to cells and humans?
Because it allows essential substances, like oxygen and nutrients, to move into cells while enabling waste products to exit, maintaining cellular function and homeostasis.
Why is diffusion important to cell respiration?
Oxygen diffuses into cells for aerobic respiration, while carbon dioxide, a waste product, diffuses out.
Why is diffusion important to Alveoli of lungs?
Oxygen from inhaled air diffuses into the bloodstream, and carbon dioxide diffuses from the blood into the alveoli to be exhaled.
Why is diffusion important to Capillaries?
Nutrients and oxygen diffuse from the blood into surrounding tissues, while waste products diffuse from tissues into the blood.
Why is diffusion important to Red Blood Cells?
Oxygen binds to hemoglobin for transport, and carbon dioxide diffuses into red blood cells to be carried back to the lungs.
Why is diffusion important to Medications: timerelease capsules?
Drugs diffuse slowly through the capsule membrane, allowing for gradual absorption into the bloodstream over time.
What is Facilitated Diffusion?
Facilitated diffusion is the process by which molecules move across a cell membrane through specific transport proteins, allowing substances that cannot easily pass through the lipid bilayer (such as large polar or charged molecules) to enter or exit the cell. This process still occurs along the concentration gradient and does not require energy.
Facilitated Diffusion
Is a diffusion through protein channels which do not interact with hydrophobic interior.
Facilitated Diffusion
Diffusion through protein channels which do not interact with hydrophobic interior
- For biological mol unable to dissolve in hydrophobic interior.
– No energy needed.