Chapter 8 Flashcards
what is the plasma membrane
The outer boundary of the cell that separates if from other cells and the external environment. Determines which substances get into or out of a cell
what does selectively permeable mean
allows some substances but not others to pass across it
what is the structure of cell membranes
is a fluid mosaic model composed of phospholipid molecules which are arranged in two layers, know as a bilayer. Each phospholipid molecule has a head that is hydrophilic and a tail that is hydrophobic. Arranged with heads on the outside and tails on the inside. Embedded in the bilayer of the membrane are cholesterol and protein molecules. Many of these proteins are involved in the movement of substances from one side of the membrane to another. DRAW DIAGRAM
Define Hydrophilic
water loving
Define Hydrophobic
Water hating
what are adhesion proteins
membrane proteins that help link cells together
what are transport proteins
protein that carriers molecules across membranes
what are receptor proteins
protein that binds hormones and other signal molecules
what are recognition proteins
Identifies the cell as ‘self’ to prevent attack by the body’s immune system
What is an example of transport proteins allowing specific substances to move across the membrane
Rapid movement of ions when a nerve is stimulated. Causes a dramatic change in the differences in positive and negative charges across the membrane and explains how the electrical charge of a nerve impulse is transmitted along nerve cells
what is a passive process
When the cells energy, which comes from respiration, is not required
What is an active process
Process that require the cells energy for the transfer to occur
what is diffusion
- The spreading out of particles so that they are eventually distributed over the space available.
- Occurs in gases and liquids because the molecules of gases and liquids are constantly moving.
- They move in random directions and in straight line until they hit an obstacle.
- Molecules moving away from an area in which they are concentrated won’t collide as much as those moving towards the high concentration.
- Therefore stay on straight paths for longer, evenly spreading over the space available
what is the difference between diffusion and concentration gradient
Diffusion is the net movement of particles from a region of high concentration to low concentration. The difference in the particle concentration between the two regions is the concentration gradient
Why does a sugar cube dissolve in a beaker of water
When the sugar cube is first placed into the water, there is a lower concentration of water in the sugar cube and higher concentration of water else where in the beaker. Therefore there is a diffusion gradient for the water but is in opposite direction to that for the sugar.
what are the two types of diffusion and what substances undergo them
- Diffusion (O2, H2O, CO2 and other small uncharged particles)
- Facilitated Diffusion (charged particles like sodium and large molecules like glucose)
what is facilitated diffusion
a form of diffusion that requires the substance to be attached to a specific carrier molecule to move across the membrane
what is the difference between carrier and channel
proteins in facilitated diffusion
- Carrier proteins bind to specific molecules on one side of the membrane, change shape and release the substance on the other side
- Channel proteins form narrow passageways through which small ions can diffuse rapidly from a high to low concentration. only ions of specific size and shape can pass through a channel protein
Explain the role of cholesterol in a plasma membrane
in animal cells, cholesterol interferes with interactions between the lipid tails, making the membrane more flexible. In plant cells, it is phytosterol (not cholesterol)
what is a solvent
a substance in which another substance can be dissolved to create a solution (eg water)
what is a solute
a substance that can be dissolved in another substance (eg salt)
what is osmosis
the diffusion of water across a semipermeable membrane from an area of high water concentration (low solute) to an area of low water concentration (high solute)
define hypertonic
a solution with higher solute concentration compared with another solution (Hyper = ‘higher’)
define hypotonic
a solution with lower solute concentration compared with another solution (Hypo = ‘lower’)
define isotonic
describes fluid with equal solute concentration to another fluid (iso = ‘same’)
why must red blood cells remain in an isotonic solution?
if the plasma surrounding blood cells becomes hypertonic, water will move out of the cells by osmosis and will shrink and become crinkled. if the blood plasma is diluted by water, the blood cells will swell and burst
what happens to plant cells in a hypotonic solution
when a hypotonic solution surrounds a plant cell, water molecules diffuse into cytoplasm and then into vacuole. The vacuole swells, pushing the cytoplasm and plasma membrane against the cell wall. The tough cell wall prevents the cell from bursting.
what is endocytosis
the movement of solids or liquids into a cell from the environment via vesicle formation
what is exocytosis
the movement of solids or liquids from a cell to the environment via vesicle formation
what is pinocytosis
Taking liquids into the cell during endocytosis
what is phagocytosis
Taking solids into the cell during endocytosis
what are the physical factors that effect transport, give examples
size and shape. small molecules like water, oxygen and carbon dioxide are able to slip between the phospholipids
what are the chemical factors that effect transport, give examples
Charged ions such as Na+, K+ and Ca+ which are hydrophilic cannot cross gthe hydrophobic interior of the membrane
why are cells so small
As a cell grows, its ability to exchange enough materials to support its increasing volume is diminished because the volume increases at a greater rate than the surface area. A large cell could not support itself because it would not have enough surface area to absorb the nutrients required and remove wastes produced
