Human Biology (Diffusion, Osmosis, Cell Transport) Flashcards
Homeostasis
Maintenance of a constant, optimal internal environment. The inside of the cell must be separated from the outside so that homeostasis can be maintained.
The human body has an optimal temperature of 37°C.
Intracellular Fluid
Fluid inside the cell – e.g. cytoplasm, nucleoplasm
Extracellular fluid
Fluid outside of the cell (between cells) e.g. blood plasma
Cell Membrane
Is the protective double layer that is responsible for allowing materials to enter and leave the cell. The structure is too small so ‘models’ are used to describe structure.
Fluid Mosaic Model
The accepted model for the structure of the cell membrane.
Fluid because the molecules constantly change position
Mosaic because it is like a lattice of many different molecules.
What is the Cell Membrane made of?
Composed of two layers of chemicals called ‘phospholipids’. Because there are two layers its structure is described as a phospholipid bilayer.
Compartments of phospholipids
A ‘head’ made of phosphate. They are hydrophilic (water loving/attracting)
A ‘tail’ made of fatty acids (lipids). They are hydrophobic (water hating/repelling)
Arrangement of the phospholipid bilayer
Hydrophilic heads are on the outside hydrophobic tails are on the inside.
Cholesterol Molecules
Embedded in the phospholipid bilayer, and aid in the stability of the membrane.
What do proteins do in the cell membrane?
Embedded in the membrane and may serve as hormone receptors, channel proteins for transport and cell-identity markers.
Selectively Permeable
Allows some materials to pass through it but not others, usually based on size.
Passive and Active (and some transports)
Passive processes are processes that do not require energy. They include – Diffusion, osmosis, facilitated diffusion
Active processes are processes that do require energy. They include – Active transport, Vesicular transport
Concentration Gradient
The difference in concentration between the two areas. The greater the difference in concentration, the greater the concentration gradient.
High to low concentration term
Follow the concentration gradient.
Low to high concentration term
Against the concentration gradient.
Diffusion
The net movement of molecules from an area of high concentration to an area of low concentration until equilibrium is established.
A passive process.
e.g. Small particles like oxygen and carbon dioxide are able to enter an leave the cell via diffusion.
Osmosis
The net movement of water molecules from an area of low concentration to high concentration, across a semi-permeable membrane, until equilibrium, is established.
A passive process.
e.g. Plants take water and mineral from roots with the help of Osmosis.
Facilitated Diffusion
Method of passive transport through the cell membrane for large molecules that cannot fit in the gaps. Materials move from an area of high concentration to an area of low concentration, using channel or carrier proteins.
A passive process.
e.g. Amino acids or glucose.
How does facilitated diffusion work?
The substance binds to a specific carrier protein causing it to change shape and allows the substance to cross the cell membrane.
Active Transport
Carrier proteins use energy from ATP to move substances from low concentration to high concentration. The molecule of ATP binds to the protein and converts to ADP (leaving a phosphate), releasing energy in the process.
This energy causes the carrier protein to change shape, and move the substance across the cell membrane.
Active transport is an active process.
e.g. Ions such as sodium are transported via active transport.
Vesicular transport
Energy is used to move enclosed vesicles containing substances such as water or enzymes into or out of the cell.
It may go from high to low concentration or low to high.
Exocytosis (Example, Description, Statement)
When vesicles are used to remove substances it is termed exocytosis.
A vesicle that is formed inside the cell migrates to the cell membrane and fuses with the membrane. The contents of the vesicle are then pushed out into the extracellular fluid.
e.g. Mucus and digestive enzymes
Endocytosis
When vesicles are used to bring substances into the cell, it is termed endocytosis.
The cell membrane folds around a droplet of liquid or a solid particle until the droplet or particle is completely enclosed. The vesicle formed then pinches off and is suspended in the cell’s cytoplasm.
e.g. Cholesterol uptake is an example of receptor-mediated endocytosis.
Two forms of endocytosis
Endocytosis involving liquids is termed pinocytosis.
e.g. Water
Endocytosis involving solids is termed phagocytosis.
e.g. Micro-organisms
Why do we need so many cells?
Because the bigger an organism is the more reactions are needed to take place to stabilise metabolism.
Since more reactions occur, the cell needs to bring more reactants and secrete more waste.
What does the surface area to volume of the cell determine?
How much material can move in and out of the cell. The surface area must be large enough for transport to complete chemical reactions.
As the surface area and volume increase what occurs to the surface area to volume ratio?
the comparison ratio of surface area to volume decreases, as the volume increases much more rapidly than the surface area.
How does the amount of cells, affect the surface area and volume?
By being made of billions of small cells, larger organisms can still have a large surface area compared to their volume (SA:V).
This allows for an efficient exchange of materials, to keep up with the cell’s metabolic requirements
Factors that affect the rate of diffusion
- Concentration Gradient
- Surface Area
- Particle Size
- Temperature
Concentration Gradient Effect on Rate of Diffusion
If there is a greater difference of concentration in the two areas, then there will be a greater rate of diffusion.
Temperature effect on rate of diffusion
If the particles are at a higher temperature then they will move faster because heat is a form of energy.
Effect that particle size has on the rate of diffusion
If the particle size of the molecules are larger it will be harder for them to fit through the membrane therefore slowing down the rate of diffusion
Effect that surface area has on the rate of diffusion
If there is a greater surface area to move through there will be a greater area of space for particles to diffuse, which will increase the rate of diffusion.
What is a disadvantage of facilitated diffusion?
That there is a limited number of proteins that work, therefore there will be a constant rate of diffusion in the full use of all the proteins.
What is important about the cell membrane in relation to cellular fluids?
Separates the intracellular and extracellular fluid.
