Cell Transport Flashcards
Unit 1, Cell Biology
How to cells maintain homeostasis?
They need to bring in food, water, oxygen and eliminate wastes
What are two general types of transport into and out of the cell
- Passive transport, no energy required.
- Active transport, requries energy
Define brownian motion
All particles being under random movement
Define Diffusion
Movement of particles from an area of high concentration to low concentration, no energy required (Passive)
Define concentration gradient
When the concentration of something builds up in one area
Define equilibrium
Equal distribution of all particles in the area
When does diffusion occuer?
They occur until the particles have reached equilibrium
Define dynamic equilibrium
When at equilibrium the particles are still in motion but there is no net change
Define simple diffusion
When particles pass through the phospholipid bilayer from high to low concentration without energy being required
Define Osmosis
The passive movement of water from an area to low solute concentration to high solute concentration through a semipermeable membrane
Low to High
Why is the net movement of water from low [solute] to high [solute]?
Areas with high [solute] have a lower [freely movable water] than areas with a lower [solute]
Define Aquaporins
Water channels present in some cells (ie. kidney cells, plant root hair cells), greatly increase permeability of water
Categorisation of solutions
Solutions can be categorised as hypertonic, hypotonic or isotonic according to their relative solute concentrations
Define hypertonic
Solutions with relatively higher solute concentrations are categorised as hypertonic (high solute ⇒ gains water)
Define hypotonic
Solutions with relatively lower solute concentrations are categorised as hypotonic (low solute ⇒ loses water)
Define isotonic
Solutions that have equivalent solute concentrations are categorised as isotonic (same solute ⇒ no net water flow)
Define Osmolarity
A measure of solute concentration
Concentration
Amount of solute (moles) per unit volume (v-3 or dm-3) of solution
Define Osmotically active solutes
They are solutes that have intramolecular attractions between them and water
What does difference in [solute] mean?
Cell membrances are very permeable to water and less permeable to solutes so it means that water moves not solute
Is osmosis passive or active
PASSIVE
How to cells change the speed of osmosis?
They change the speed of osmosis by changing the permeability of membrane to water
Define water potential
Water potential is a measure of the potential energy of water per unit volume (symbol is ψ, unit is kPa)
What is the movement of water
Water moves from an area of higher water potential to lower water potential (minimizes potential energy)
What does having a higher concentration of dissolved solutes mean
High the concentration of dissolved particles, the lower the potential energy of water. If there are no solutes, Ψs is 0. As [solutes] increases the Ψs becomes more negative (less free water, therefore less potential kinetic energy of water)
What does having a higher pressure mean?
Higher pressure means higher potential energy of water.
Movement of water in plants
Water always moves from high potential to low potential
What happens after the water moves in the plant cell?
The Ψp increases inside the cell due to the force/pressure of the cell wall pushing back against the cell membrane (Being squashed)
What is a turgid plant cell?
Occuring of potential pressure increasing until the water potential equalts the distilled water potential. (Pressure of the cell wall pushing back against the cell membrane)
What happens to plants in hypertonic solutions?
A hypertonic solution has a more negative Ψs than inside the cell. the Ψp is 0.
Why does water move out in plant cells
The Ψp inside the cell will be higher than outside solutions due to plant cells typically being turgid
Ψ is therefore higher in the cell than out, so water will more out
What is flaccid plant cells?
When water loss of a cell reduces the pressure inside and it drops to atmostpheric pressure, the pressures are equal!
Notes/Reminder for plants in hypertonic solutiosn (NOT FOR MEMORIZATION)
The Ψs will rise due to the water loss, if it is higher than the solution’s Ψs water continues to move out
This causes the cell membrane to detach from the cell wall and shrink, this process is called plasmolysis
Once the Ψs inside and outside the cell are equal there will be no net movement of water due to equal water potentials
What happends to animal cells in hypotonic solutions?
Animal cells will swell (gain wtaer) and becuase they lack cell walls, they will easily burst
What happends to animal cells in hypertonic solutions?
Animals cells will shrink/shrivel (lose wtaer), crenations or indentations can occur.
What do unicellular organisms lacking cell walls do to prevent swelling?
They will pump water out to prevent swelling (contrctile vacuoles)
Define facilitated diffusion
Passive transport of molescules through a membrane with the help of proteins
Define channel proteins
Integral transmembrane proteins iwht a pore that has specific size to allow only certain molecules through
When does active transport occur?
It occurs during a movement against the concentration gradient (low to high) with the use of energy
How does active transport occur?
It is dont by pump proteins, only in one direction by the use of energy, most from an energy molecule called ATP
Given an example of indirect active transport
Glucose can move against its concentration graident because sodium is movign down its gradient
When [Na+] builds up it will flow down a glucose transporter from high to low, bringing glucose along with it (no energy)
Selective permeability in facilitated diffusion and active transport
They are selective in what is passing through the cell membrane, both have pump proteins that are specific to the molecules they are transporting
What happens in endocytosis?
Vesicles made by small pieces of the cell membrane being pulled away and pinched off (done by proteins, using energy)
Define endocytosis
When large substances enter the cell without crossing the membrane
Define exocytosis
When large substances (or bulk amounts of small substances) exit the cell without corssing the membrane
What happens in the process of exocytosis
During the process, it adds phospholipids to the cell membrane, replacing those lost when vesicles are formed via endocytosis
Why is exocytosis important?
It gets rid of waste or unwanted substances and to secrete cell products like hormones and enzymes
