Topic 1 Cell Membrane

• What is the cell theory?

  • Cells are the structural and functional units of life
  • Cells come from pre-existing cells
  • Cells are the smallest independent unit of life
• What is the function of the cell membrane?

  Controls what enters and exits the cell, to maintain homeostasis
• What is the structure of the cell membrane?


  Phospholipid bilayer with phosphate heads and lipid tails
• Where are the phosphate heads and lipid tails located.

  Phosphate heads are outside (hydrophilic) while lipid tails are inside (hydrophobic) the bilayer
• What do proteins do in the cell membrane?

  Embedded in the membrane and allow for transport of substances in and out of the cell
• What do glycoproteins do in the cell membrane?

  Made up of carbohydrate chains attached to proteins, for cell recognition and adhesion
• What does cholesterol do in cell membrane?

  Found within the bilayer, and regulated the fluidity of the membrane
• Why is the structure given the name fluid mosaic model?

  Proteins embedded in the bilayer resemble a mosaic.

  Individual molecules can move freely (fluid structure)
• What is cellular transport?

  Substances such as nutrients, oxygen, wastes, etc need to pass through the cell membrane
• What is the lipid bilayer permeable to?

  Small substances and lipid-soluble substances, such as oxygen, some water, urea
• what is the lipid bilayer impermeable to?

  water-soluble substances, ions, and larger molecules such as glucose and amino acids
• What is passive transport?

  Doesn't use cellular energy, and relies on the kinetic energy all particles naturally posses
• What are the types of passive transport?

  Diffusion, Osmosis, Facilitated diffusion
• What is diffusion?

  Diffusion is the movement of molecules from an area of high conc. to an area of low conc. until equilibrium is reached
• What molecules can cross the membrane through diffusion?

  Small and lipid-soluble molecules
• What is osmosis?

  Osmosis is the diffusion of water across a selectively permeable membrane, from an area of high conc. of water to an area of low conc. until equilibrium is reached
• What does hypotonic mean?

  low concentration of solute compared to water
• What does hypertonic mean?

  High concentration of solute compared to water
• When does osmosis occur?

  When the membrane is impermeable to a specific solute
• What happens when cells are placed in water?

  Water enters the cell
• What happens to plant cells when water enters?

  The vacuole enlarges, puts turgor pressure on the cell wall
• What happens when water enters animal cells?

  The cytoplasm swells, leading to the cell membrane rupturing
• What is facilitated diffusion?

  Substances diffuse across the membrane through proteins
• What molecules cross the membrane through facilitated diffusion?

  Larger molecules and lipid-soluble molecules
• What transport proteins are involved for facilitated diffusion?

  Protein channels and Carrier proteins
• What is active transport?

  Cells use energy (usually ATP) as the molecules are being moved against their concentration gradient
• What are the types of active transport?

  Protein pumps, endocytosis, exocytosis
• What is endocytosis?

  Material is engulfed in bulk, by infolding of the membrane. Food vesicle forms and transports the material
• what is phagocytosis and pinocytosis?

  Cell eating and cell drinking
• What is exocytosis?

  A vesicle containing the larger molecule will move to the membrane, merge and release its contents
• Why are cells so small?

  Cells need to have the largest surface area to volume ratio to allow for the most efficient exchange of materials.
• Why is a smaller surface area to volume ration more efficient?

  Smaller overall movement of material, faster diffusion, greater relative movement of particles
• how does a large organism change to ensure it is efficient?

  Adaptations including specialised organs and circulatory system increase their efficiency for exchange processes