2A Flashcards
How does surface area to volume ratio affect transport of molecules?
The lower the surface area to volume ratio, the further distance molecules need to travel to reach all parts of the organism. Diffusion alone is not sufficient, so specialised gas exchange surfaces are required.
Name three features of an efficient gas exchange surface.
“1. Large surface area, e.g. folded membranes in mitochondria.
2. Thin/short diffusion distance, e.g. wall of capillaries.
3. Steep concentration gradient, maintained by blood supply or ventilation, e.g. alveoli.”
What is Fick’s law? Give the corresponding equation.
rate of diffusion = (proportional to) surface area x difference in concentration / diffusion distance
How is the mammalian lung adapted for gas exchange?
“● Alveoli provide a large surface area.
● Good blood supply and ventilation maintains a steep concentration gradient.
● Capillary and endothelium only one cell thick, providing a short diffusion distance.”
Describe the structure of a cell membrane?
“● Phospholipid bilayer
● Transmembrane proteins- channel proteins and carrier proteins
● Surface proteins and glycoproteins”
What is meant by the fluid mosaic model?
Phospholipids can move in the plane, and have a mosaic-like arrangement of proteins.
What evidence led to development of the fluid-mosaic model?
“● Phospholipids naturally form bilayers in water.
● Microscope images show proteins on membrane surface.
● Lipid-soluble substances pass more easily in and out of cells than water-soluble.”
Describe the structure of a phospholipid
One hydrophilic head with two fatty acid tails
What is the function of a channel protein?
Allow small charged particles/polar molecules to move through the membrane.
What is the function of a carrier protein?
To move large molecules across the membrane by facilitated diffusion or to move any particle against the concentration gradient.
Define osmosis.
The movement of free water molecules from an area of high concentration of water (dilute) to an area of low concentration of water (concentrated), across a partially permeable membrane.
Define passive transport and give examples of this.
The movement of particles down a concentration gradient (high to low), meaning no energy is required. Diffusion, facilitated diffusion, and osmosis are all passive.
Define diffusion.
The movement of small non-polar, lipid-soluble molecules from an area of high concentration to an area of low concentration.
Give three examples of particles that move by simple diffusion
Oxygen, carbon dioxide, some water
Define facilitated diffusion
The movement of large and or charged molecules across the cell membrane from an area of high concentration to an area of low concentration
Give three examples of particles that move by facilitated diffusion using channel proteins
sodium, chloride and magnesium ions
Give an example of particle that moves by facilitated diffusion using a carrier protein
Glucose
Define active transport.
The movement of molecules against a concentration gradient (low to high), meaning energy in the form of ATP is required. Also uses carrier proteins.
How are large molecules such as proteins moved across a cell membrane?
Endocytosis or exocytosis
Decribe exocytosis
Vesicle formed in the golgi apparatus fuses with cell membrane to release contents from cell.
Describe endocytosis
Cell membrane forms a vesicle and engulfs the material, which enters the cytoplasm.
