Ch.3-Cells Flashcards
Describe structure of cell membrane(plasma membrane).
Lipids and proteins are the primary substances that make up cell membranes, usually formed as a double layer of phospholipid molecules(phospholipid bilayer), this is wall between inside and outside of cell.
Phospholipids organise as a bilayer in order to hide their fatty acid/hydrophobic tail regions(non-polar), forming the inner surface, thus exposing the phosphate/hydrophilic region(polar) to the water found in both intracellular and extracellular fluids.
These polar/non-polar interactions stop molecules moving from one half of the bilayer to the other.
Cholesterol in the inner cell membrane maintains stability by spacing or connecting the phospholipids during changes of environment, eg.temp.
Approx. half of cell membrane mass made up of integral and peripheral proteins that are responsible for specialised membrane functions.
Cell membrane proteins form receptors for hormones and growth factors, transport substances across the cell membrane, and form selective channels that determine which types of ions can enter/exit the cell.
Similar to olive oil in consistency, constantly changing, molecules moving side to side, parallel with the membrane surface.
Describe function of cell membrane.
Encloses the cell, its nucleus,various organelles,and its cytoplasm.
It controls movement of substances into/out of the cell.
Allows selective communication between intracellular and extracellular compartments whilst aiding in cellular movement.
Gives form to the cell.
Site of much of cell’s biological activity.
Adheres to other cells during formation of tissues
Can be semipermeable(selectively permeable)-allow only certain substances to pass through.
Or
Differential permeable-allowing passage of smaller molecules but not of larger ones.
List the processes that transport substances across plasma membrane.
Passive cell mechanisms - Diffusion, Osmosis, Filtration.
Active cell mechanisms - Active Transport, Endocytosis, Exocytosis.
Describe the Passive cell mechanism-Diffusion.
The process by which substances spontaneously move from regions of higher concentration to regions of lower concentration.
Describe the Passive cell mechanism-Osmosis
Special type of diffusion that occurs when water molecules diffuse from an area of higher water concentration to an area of lower water concentration.
Describe the Passive cell mechanism-Filtration.
Forces molecules through membranes.
Describe the Active cell mechanism-Active Transport.
The movement of particles through membranes from regions of lower concentration to regions of higher concentration.
Describe the Active cell mechanism-Endocytosis.
Involves a secretion from the cell membrane moving particles too large to enter the cell by other processes within a vesicle of the cell.
Describe the Active cell mechanism-Exocytosis.
The opposite process of Endocytosis, in which a substance stored in a vesicle is secreted from the cell.
Compare Passive and Active cell mechanisms.
Differences:
Passive transport does not require energy, whilst active transport requires metabolic energy(ATP).
Passive transport moves molecules WITH the concentration gradient(high to low), while active transport moves molecules AGAINST the concentration gradient(low to high).
Similarities:
They both allow cells to maintain homeostasis by maintaining an equilibrium of substances inside and outside of the cell.
They both involve moving materials across or through the cell membrane.
