mod 1.2 - cell function Flashcards
What does the permeability of a cell membrane refer to?
Its ability to allow the cell to exchange liquids and materials between the cell’s internal environment and the external environment.
Why is the movement of materials in and out of a cell is critical to its function and survival?
It allows essential materials to enter while keeping waste materials out. It also allows cells to communicate with other cells.
What is it called when the cell membrane is selective about the materials that it allows in and out of the cell?
This characteristic is known as being semipermeable.
What are cell membranes permeable to?
Small molecules and lipid-soluble molecules that can move freely through the phospholipid bilayer.
Small, uncharged molecules:
Oxygen and carbon dioxide.
Lipid-soluble, non-polar molecule:
Alcohol, chloroform, steroids.
Small, polar molecule:
Water, urea.
Small ion:
Potassium ion, sodium ion, chloride ion. –> impermeable; ion travels through protein channels.
Large, polar, water-soluble molecule:
Amino acid, glucose. –> impermeable; molecule travels through protein channels.
What are cell membranes impermeable to?
Most water-soluble molecules, ions (atoms or molecules with charged regions but no overall charge), polar molecules (molecules with charged regions but no overall charge).
Where do impermeable substances pass through?
Specific protein channels in the cell membrane.
What is diffusion?
Diffusion is the net movement of molecules, passively (does not require energy because it occurs from the concentration gradient), along a concentration gradient (from a region of high concentration to a region of low concentration).
Solute:
Material dissolved in the solvent to form a solution.
Solvent:
Substance that dissolves the solute to form a solution (eg: water is a common solvent)
Solution:
Solution: a mixture in which a solute is dissolved in a solvent.
What are the two types of diffusion across membranes?
Simple diffusion and facilitated diffusion.
What is simple diffusion?
A form of diffusion that does not require the assistance of membrane proteins; small non-charged molecules or lipid soluble molecules pass between the phospholipids to enter or leave the cell, moving from areas of high concentration to areas of low concentration.
What is facilitated diffusion:
A form of diffusion that DOES require the assistance of membrane proteins; because the substances are impermeable.
What is the term when transport proteins become fully occupied as the concentration of the transported substances increases?
Saturation.
In facilitated diffusion, are the membrane transport proteins specific for particular particles?
Yes, transport is selective; some particles are transported and others are not.
What are the two main types of membrane transport involved in facilitated diffusion?
Channel proteins and carrier proteins.
What are channel proteins?
Channel proteins don’t usually bind with molecules being transported; they function like pores that open and close to allow the passage of specific molecules.
Channel proteins are mainly involved in the passage of water-soluble polar particles, such as ions. (eg: Na+, K+ and Cl-)
What are carrier proteins?
Carrier proteins bind the molecules being transported.
This causes the protein to undergo a change in shape (or conformation) that allow specific molecules to be transported across the membrane.
After the molecule has crossed the membrane, the original shape of the protein is restored.
What is osmosis?
Osmosis refers to the net diffusion of water molecules across a semipermeable membrane. (passive)
What is the osmotic gradient?
The net diffusion of water occurs through a semipermeable membrane from a diluted to a concentrated solution along its own concentration gradient.
What is osmotic pressure?
The pressure causing the water to move along this osmotic gradient.
What is high turgor?
Plant cells with high internal fluid pressures.
What are the terms used to describe the differences between solutions? (osmosis)
Isotonic, hypotonic and hypertonic
What are isotonic solutions?
The solutions being compared have equal concentration of solutes.
What are hypertonic solutions?
The solution with a higher concentration of solute (hence lower concentration of free water molecules).
What are hypotonic solutions?
The solution with a lower concentration of solute (hence higher concentration of free water molecules).
What are halophiles? (give eg)
Bacteria that are adapted to extremely salty environments, such as the pink salt lakes in NSW.
They survive by retaining much higher ion concentrations within their cells; and they also produce small, osmotically active molecules to reduce the osmotic gradient, which prevents the loss of water to their salty environments.
Their proteins are also specialised to function normally, despite the high concentration of salts in the cytosol.
Describe osmosis in RBC.
If red blood cells are placed in freshwater, the cells absorb so much water by osmosis that they swell and may eventually burst, releasing red pigment into the water. Conversely, if red blood cells are placed in a solution that is more concentrated than their cytosol, water leaves the red blood cells by osmosis, causing them to shrink.
What is passive transport? (give eg)
Diffusion, facilitated diffusion and osmosis are examples of passive transport, as they don’t require energy to move particles across the cell membrane..
What is active transport?
Active transport involves the cell using energy to transport particles across the membrane.
What is selectivity in cell membranes?
Means that some substances are transported but others aren’t.
What is saturation in cell membranes?
Means that there is no increase in the rate of transfer when all transport molecules are open.
What is competitive inhibition in cell membranes?
Means that one substance can inhibit the transport of another substance by using the same transport protein.
Compare facilitated diffusion and active transport.
Unlike facilitated diffusion (which occurs through either channel or carrier proteins), active transport only occurs through carrier proteins.
Active transport requires energy (ATP), meaning that it can move against the concentration gradient (from low to high concentrations), unlike facilitated diffusion which can only move down the concentration gradient.
What is endocytosis?
Active transport; where cells take in materials in bulk by forming new vesicles from the cell membrane.
During endocytosis, a small area of the cell membrane sinks inwards to form a pocket; and as this pocket deepens, materials near the cell membrane are enclosed by the membrane, which then pinches off to form a vesicle.
The vesicle then transports the substance to where it is required within the cell.
What are the three types of endocytosis?
Phagocytosis, pinocytosis and receptor-mediated endocytosis.
What is phagocytosis?
When a cell engulfs a solid material by wrapping temporary cytoplasmic extensions called pseudopodia around it. This forms a membrane-bound structure called a phagosome. The material will then be digested when the food vacuole fuses with a lysosome that contains enzymes.
What is a phagosome?
When temporary cytoplasmic extensions called pseudopodia wraps around solid material forming a membrane-bound structure called a phagosome.
What is pinocytosis?
When the cell membrane engulfs liquid that contains dissolved molecules.
What is receptor-mediated endocytosis?
A type of pinocytosis that engulfs specific substances. Protein receptors located on the surface of the cell membrane respond to particular molecules, binding to the molecule and triggering the engulfment of the substance into the cell.
What is exocytosis?
Active transport; a process by which the contents of a cell vacuole are released to the exterior through fusion of the vacuole membrane with the cell membrane.
What is the process of exocytosis?
When a secretory vesicle membrane and the cell membrane come into contact, specific proteins alter the arrangement of the phospholipids in the phospholipid bilayer.
The fluid and dynamic nature of the cell membrane then enables the two membranes to fuse.
Once the membranes have fused, the contents of the secretory vesicle are released out of the cell → this process is exocytosis (ayo epic?)
The vesicle membrane becomes a permanent part of the cell membrane; the cell membrane is continually recycled as vesicles fuse during exocytosis, and are conversely formed and released during endocytosis.
What is exocytosis used for?
In addition to being used for secreting proteins, exocytosis is also involved in the release of cellular waste and the breakdown products from lysosomes.
What are factors affecting the rate of diffusion?
Concentration: the greater the difference in concentration gradient, the faster the rate of diffusion. When the concentration is equal on both sides of the membrane, the net diffusion is zero, even at high temperatures.
Temperature: the higher the temperature, the higher the rate of diffusion, as increasing temperature increases the speed at which molecules move.
Particle size: the smaller the particles, the faster the rate of diffusion.
Why do larger cells have smaller SA?
Larger cells have greater metabolic needs, so they need to exchange more nutrients and waste with their environment; however, as the size of a cell increases, the SA:V of the cell decreases.
Because of this SA:V relationship, larger cells don’t have a proportionally larger surface area of cell membrane for the efficient exchange of nutrients and waste.
Smaller cells can exchange matter with their environment more efficiently.
THIS IS WHY CELLS DIVIDE.
What are the three ways of increasing SA:V?
Three ways of increasing the membrane surface area of cells without changing cell volume are: cell compartmentalisation, a flattened shape and cell membrane extensions.
How does cell compartmentalisation increase SA:V?
Allows organelles to have the right conditions and concentration of enzymes and reactants for a particular function, making processes in the whole cell highly efficient.
Cell compartmentalisation also allows eukaryotic cells to be much bigger than prokaryotic cells, because it:
Reduces the amount of exchange that needs to occur across the cell membrane to maintain an environment suitable for all cell functions.
Creates more space for membrane-bound enzymes, allowing increased activity in the cell.
How does a flattened shape increase SA:V?
As a cell increases in volumes, the distance from the centre of the cell to the cell membrane also increases.
The rate of chemical exchange (diffusion) from the centre of the cell to the surrounding environment may then become too low to maintain the cell.
One way to counteract this effect is to be flatter. eg: red blood cells and lung epithelium
How does cell membrane extensions increase SA:V?
Cells involved in absorbing nutrients or secreting wastes counteract the SA:V problem by extending the surface area of their cell membranes. eg: microvilli in some animal cells and root hairs in plants.
Why would a flattened shape not be useful for cells involved in absorbing nutrients or secreting wastes?
Because they require an increased surface area in particular regions of the cell.
What are the two groups organisms can be divided into depending on the strategies they use to obtain organic compounds (source of energy)?
Autotrophs and heterotrophs.
What are autotrophs?
They make their own organic compounds from inorganic compounds found in the soil and the atmosphere.
The conversion of inorganic compounds into organic compounds is called carbon fixation; as the autotroph ‘fixes’ inorganic carbon into organic molecules, such as glucose.
Also called producers, autotrophs include all of the green plants that carry out photosynthesis.
What are heterotrophs?
They obtain organic compounds by consuming other organisms.
Also called consumers, heterotrophs consist of all animals and fungi.
What are organic compounds?
Characteristic complex compounds that contain carbon and hydrogen that organisms produce.
