Chapter 4 - Cells Exchange Materials Flashcards
What is the extracellular Fluid?
Extracellular or tissue fluid is the immediate thin layer of fluid environment which surrounds a cell
There is continual exchange of materials between the cells and the tissue fluid
What is homeostasis?
Homeostasis is the constant maintained temperature and the concentration of fluids for an effective environment for all cells to function.
What is a cell membrane?
Each cell is surrounded by a plasma or cell membrane which separates the cell contents from the external environment.
It is very thin - too thin to be seen clearly with a light microscope
What is the fluid mosaic model?
Current accepted model for a cell membrane is called the FLUID MOSAIC MODEL.
Which showcases that the membrane is to ‘fluid’ because the molecules of which it is made are constantly changing position and, and it is said to be ‘mosaic’ because it is composed of different kinds of molecules giving a mosaic patter.
What is the main structure of membrane composed of?
- phospholipid molecules; which are lipid molecules (tail) containing a phosphate group (head).
They are arranged in two layers known as a bilayer. - each phospholipid has a head that is HYDROPHILIC meaning it is water loving and a HYDROPHOBIC tail, meaning water hating.
- therefore the heads face the intra and extra cellular fluids of the cell
- they drift from place to place with their heads and tails moving, keeping the membrane fluid
- embedded in the phospholipid bilayer of the membrane and cholesterol and protein molecules
- cholesterol molecules are wedged between the phospholipids
- some proteins molecules pass through the membrane from one side to the other while others are bound to the membrane surface.
- membrane proteins are also found in the cell membrane which act as channels and gates to inside/outside the cell
What are the 4 main functions of the cell
- A physical barrier- the membrane separates the cell cytoplasm and contents from the extracellular cloud around the cell. It isolates the cell from the surrounding fluid because the composition of cytoplasm and extracellular fluid are very different.
- Regulation of passage of materials - the membrane controls the movement of the materials into and out of the cell Eg. Entry of ions and nutrients, removal of wastes and release of secretions.
- Sensitivity- the cell membrane is the first part of the cell affected by any changes in the extracellular fluid. It also has receptors that are sensitive to particular molecules in its immediate environment.
- Support - the internal part of the cell membrane is attached to the microfilaments of the cytoskeleton, thus giving it support to the whole cell. There are also connections between the membranes of adjacent cells that give support to the whole tissue of which the cells are a part of.
What are the 4 main membrane proteins?
- Receptor proteins
- channel proteins
- Carrier proteins
- cell-identity markers
Proteins are large molecules 2% of the molecules in membrane = proteins, however 55% of weight is from proteins in membrane.
What it mean that cell membranes are differently permeable?
Differentially permeable membranes allow certain ions and molecules to pass through but restricts the movement of others.
Semi or selectively permeable
What are passive processes?
This means that the cell’s energy, which comes from respiration does not have to be used
What are active processes?
Active processes are which require the cell’s energy for transfer to occur.
What are the three basic processes in transport of materials into or out of the cell?
- Diffusion - a passive process resulting from the random movement of ions and molecules; Osmosis is a type. - special case of diffusion where water passes across the membrane
- Carried mediated transport- the process which requires special proteins in the cell membrane; it may be passive or active, depending on the exact nature of mechanism
- Vesicular transport - a process in which materials are moved in membrane- bound sacs; it is an active process.
What is diffusion
Diffusion is the spreading out of particles so that they are evenly 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 lines until they hit another molecule or the wall of a container.
Molecules will move away from an area in which they are concentrated in experience fewer Collisions than those moving towards a higher concentration.
Eg. Sugar in water
What is the concentration gradient?
The difference in concentration of gas and liquid particles that brings about the diffusion is called Concentration Gradient or Diffusion Gradient.
The greater the difference in concentrations, the ‘steeper’ the diffusion gradient and the faster diffusion will occur.
What is net diffusion?
The movement of liquid or gas molecules from places of higher concentration to places of lower concentration, along a diffusion gradient is more correctly called a net diffusion.
There will always be some molecules moving against the diffusion gradient because the movement of molecules are random.
What diffuses through the cell membrane?
Alcohol, steroids and other fat- soluble substances can easily enter cells because they can diffuse through the lipid portions of the membrane.
Oxygen diffuses into cells because it is continually used up inside the cell for respiration. The concentration of oxygen inside the cell is therefore lower than the oxygen concentration outside the cell. Because of this concentration difference, there is net diffusion of oxygen into the cell.
Small molecules such as water are able to pass though the pores in the membrane quite easily
CO2 is continually produced inside the cell by respiration. The higher concentration of carbon dioxide inside the cell means that there will be net diffusion of carbon dioxide out of the cell.
What do channel proteins do?
Channel proteins are a membrane protein which allows the passive transfer of materials through the membrane.
The process of diffusion of water soluble molecules must pass through protein channels in the membrane. Theses channels are very small in diameter, but water and ions can easily get through them.
Larger molecules are too big to fit through the channels.
What is osmosis?
Osmosis is a type of diffusion of a solvent through a differentially permeable membrane.
Osmosis is the diffusion of water across a differentially permeable membrane from a region of ‘higher’ concentration to a ‘lower’ concentration
The concentration of water depends on how much solute is dissolved in the water
What is osmotic pressure
Osmotic pressure is the pressure that would have to be applied to a pure solvent to prevent it from passing into a given solution by osmosis, often used to express the concentration of the solution.
What is carrier mediated transport?
Carrier mediated transport is where proteins in the cell membrane bind to molecules to be transported and help their passage across the membrane.
What are some characteristics of carrier mediated transport?
- the carrier proteins are SPECIFIC ; they will only bind to a particular molecule Eg. The carrier that transports glucose will only transport glucose and not the similar simple sugars.
- Can Become SATURATED. - carries can become saturated when once all available carriers are occupied. Any increase in the concentration of molecules to be transported cannot increase the rate of movement.
- Carrier activity is regulated by substances such as hormones. Hormones are important in coordination of the activities of carrier proteins
What are the two different types of Carrier - mediated transport
Facilitated diffusion
Active Transport
Explain facilitated diffusion
Facilitated Diffusion = PASSIVE PROCESS
Substances move with the concentration gradient, from a higher concentration on one side of the membrane to a lower concentration gradient on the other side.
The molecule to be transported attaches to the binding site on the carrier. The carrier changes shape and the molecule is released on the other side of the membrane.
Substances transported are Glucose, amino acids
Explain Active Transport
Active Transport is a ACTIVE way of transfer of material.
It requires energy because substances are transported across the membrane against the concentration gradient from a lower to a higher concentration.
It is the same as facilitated diffusion but does not depend on the concentration gradient.
Using the active transport method a cell can take in or pass out substances regardless of their concentrations inside or outside the cell.
Eg. Sodium potassium pump (circle and triangle)
Certain ions, glucose and amino acids
What is Vesicular Transport?
Vesicular transport is the movement of substances across the cell membrane in membraneous bags called VESICLES.
it is an ACTIVE PROCESS because energy is required to form the vesicles.
What are the two types of vesicular transport?
Endocytosis and Exocytosis
What is Endocytosis
Endocytosis is taking liquid or solid into the cell by vesicular transport.
The cell membrane folds around a droplet of liquid or a solid particle until the droplet or particle is completely enclosed . The vesicle is pinched off and is suspended in the cells cytoplasm.
Transports; cholesterol , iron ions, Micro-organisms and cell debris but only by certain specialised cells.
What is Exocytosis
An ACTIVE PROCESS of material transport between the cell membrane
Exocytosis is when the contents of a vesicle inside the cell are passed to the outside. 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.
Transports ; Secretions, such as mucus of digestive juices
Difference between phagocytosis and Pinocytosis
When Vesicles contain liquids to transport this way it is called Pinocytosis
When Vesicles contain solids to transport this way it is called Phagocytosis
What do microtubules do?
Micro tubules are very fine tubes that help to maintain the shape of the cell and to hold the organelles in place. They also act like railway tracks, guiding organelles or molecules to particular places within the cell. Microtubules are not permanent structures but are able to be broken down or built up as needed in various parts of the cell.
Difference between hypotonic, hypertonic and isotonic
Equal amounts of fluid with the outsides and inside of cell - isotonic
More water in cell (high concentration) - is hypotonic causing cell to swell and explode
More water outside than in cell - hypertonic causing cell to shrivel and dehydrate
