Cell Transport Mechanisms

1. In passive transport, what determines the direction of movement of small particles? The direction of movement of particles in passive transport is determined by the concentration gradient (diffusion) between the cytoplasm and the extracellular fluid. 2. Why do the molecules in facilitated diffusion need help moving across the plasma membrane? Likely, the molecules are too large to pass unaided through the plasma membrane with the concentration gradient; they need to pass through special transport proteins.

A major determinant of diffusion in a biological system is membrane permeability. Small, uncharged molecules pass through cellular membranes easily, while most and/or charged molecules cannot pass through the membrane. The movement of water across a selectively permeable membrane, like the plasma membrane

A cell needs to perform diffusion in order to survive. Substances, including water, ions, and molecules that are required for cellular activities, can enter and leave cells by a passive process such as diffusion. Diffusion is random movement of molecules in a net direction from a region of higher concentration to a region of lower concentration order to reach equilibrium. Diffusion does not require any energy input. Diffusion is needed for basic cell functions - for example, in humans, cells obtain oxygen via diffusion from the alveoli of the lungs into the blood and in plants water

Explain the effect that increasing the Na+ Cl- concentration has on osmotic pressure and why it has this effect. How well did the results compare with your prediction?

What happens to the urea concentration in the left beaker (the patient)? It mixes with the water to balance out the structure.

The purpose of these experiments is to examine the driving force behind the movement of substances across a selective or semiperpeable plasma membrane. Experiment simulations examine substances that move passively through a semipermeable membrane, and those that require active transport. Those that move passively through the membrane will do so in these simulations by facilitated diffusion and filtration. The plasma membrane’s structure is composed in such a way that it can discriminate as to which substances can pass into the cell. This enables nutrients to enter the cell, while keeping unwanted substances out. Active

All cells contain membranes that are selectively permeable, allowing certain things to pass into and leave out of the cell. The process in which molecules of a substance move from an area of high concentration to areas of low concentration is called Diffusion. Whereas Osmosis is the process in which water crosses membranes from regions of high water concentration to areas with low water concentration. While molecules in diffusion move down a concentration gradient, molecules during osmosis both move down a concentration gradient as well as across it. Both diffusion, and osmosis are types of passive transport, which do not require help.

Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration. The rate at which molecules diffuse can be determined by the relationship of molecular weight and that rate of diffusion through a membrane. Hypothesis of this experiment is that the fluid with higher molecular weight will diffuse at a slower rate and distance.

Diffusion, the spontaneous movement of molecule from an area of higher concentration to an area of lower concentration, and

Cells are always in motion, energy of motion known as kinetic energy. This kinetic energy causes the membranes in motion to bump into each other, causing the membranes to move in another direction – a direction from a higher concentration of the solution to a lower one. Membranes moving around leads to diffusion and osmosis. Diffusion is the random movement of molecules from an area of higher concentration to an area of lower concentration, until they are equally distributed (Mader & Windelspecht, 2012, p. 50). Cells have a plasma membrane that separates the internal cell from the exterior environment. The plasma membrane is selectively permeable which allows certain solvents to pass through

2.1. Diffusion is the spontaneous kinetic movement by which molecules move from an area of a high concentration to an area of low concentration. Diffusion continues until it reaches equilibrium. Osmosis is similar to Diffusion but it’s the process in which water moves across a semi-permeable membrane and goes to the higher concentration of solute.1

The diffusion across a cell membrane is a process of passive and spontaneous net movement of small lipophilic molecules. The molecules move from a high concentration to a low concentrated region along the concentration gradient. The result being a point of equilibrium, this is where a random molecular motion continues but there is no longer any net movement. However, there are things that can affect the rate of diffusion, these being temperature, surface area, concentration, size of the molecule, permeability, diffusion distance and concentration difference. Osmosis is a type of diffusion as it is the movement of water molecules through a semipermeable membrane into a region of higher solute concentration. Equilibrium is reached when the solute concentration is equal on both sides. Water potential is measured in kiloPascals, it is the measuring of the concentration of free water molecules that are able to diffuse compared to pure water, which is 0 kilopascals. It is a measure of the tendency of free water molecules to diffuse from one place to another. The result being, the more free water molecules, the higher the Water Potential. However, Water potential is affected by two factors: pressure and the amount of solute.

The movement of molecules have two forms of transport through the plasma membrane: active transport and passive transport. Active processes require energy, such as ATP, in order for the molecules to be transported. In active transport, the cell administers ATP.i Within passive processes no energy is required and changes n pressure and concentration are the driving forces. Processes such as simple diffusion, facilitated diffusion, osmosis, and filtration are characterized as passive transport, while solute pumps are a form of active transport. Each of these form of transports occur in the cells of all living organisms and are essential to life.

If the solution in the left beaker contained both urea and albumin, which membrane(s) could you choose to selectively remove the urea from the solution in the left beaker? How would you carry out this experiment?

Diffusion is an automated process by where the levels of oxygen, water and carbon dioxide pass over a ‘semi-permeable membrane’ between the walls of the cells and blood vessels to create a level environment. This membrane only allows these three elements to pass whilst retaining other elements such as blood cells, hence semi-permeable. The high concentration on one side of the cells transfers through this membrane until the level is equal on both sides.