Transport across cell membranes

Where does the energy from which active transport occurs come from?

ATP produced during respiration is used up in order to proceed with active transport. Cells in which a lot of active transport takes place have large numbers of mitochondria.

What proteins does facilitated diffusion make use of

Carrier and channel proteins

What are co-transport proteins?

Carrier molecules that only transport glucose in the presence of sodium ions. Each time a sodium ion is transported into the cell, so is a glucose molecule. - This part involves facilitated diffusion.

How does a thin exchange surface affect the rate of diffusion?

Diffusion is only efficient over very short distances. E.g. the epithelium of the intestine is just one cell thick.

What are surfaces through which diffusion takes place known as?

Exchange surfaces

How does surface area affect the rate of diffusion?

Greater the surface area of the exchange surface, the faster the total rate of diffusion due to more exchange surface.

Why is facilitated diffusion necessary?

Large, water soluble molecules such as those of glucose cannot pass directly though the phospholipid bilayer of a cell surface membrane.

How is the concentration gradient for facilitated diffusion maintained for co-transport

Maintained by actively transporting sodium ions out of the cell into the blood. (With the use of active transport.) The glucose molecules can then pass from the inside of the cells into the blood by facilitated diffusion.

How does temperature affect the rate of diffusion?

Molecules move faster at higher temperatures, the higher the temperatures, the faster the rate of diffusion.

What is a situation in which active transport is needed?

Plant cells contain mineral ions that are present in very small concentrations in the surrounding cell. They take these minerals up by active transport.

What are the 5 different ways movement across the membranes occurs?

Simple diffusion Facilitated diffusion Osmosis Active transport Co-transport

What factors affect the rate of diffusion?

Temperature Surface area Difference in concentration on either side of the exchange surface Thin exchange surface

How do carrier proteins work?

The diffusing molecules bind to a carrier proteins binding site (which has a specific shape). For example, a glucose carrier has a binding site onto which only glucose molecules will fit. The protein then changes shape and takes the molecules through the membrane. Different sorts of cells have different carrier proteins so not all cells take glucose molecules etc.

How does difference in concentration affect the rate of diffusion?

The greater the difference, the faster the rate of diffusion. If the products are being continually transported away from the exchange surface then the concentration gradient is increased and the rate of diffusion is faster.

What is osmosis?

The net movement of water molecules from a solution with a higher water potential to a solution with a lower water potential through a selectively permeable membrane.

What is active transport?

The process by which a cell takes up a substance against a concentration gradient.

What is diffusion?

The random movement of ions or atoms or molecules that make up a substance from where they are at a high concentration to where they are at a lower concentration. Particles diffuse down a concentration gradient.

How do channel proteins work?

These proteins contain a water filled centre which water-soluble molecules and ions can diffuse through. Some channel proteins have gates the open and close Relies on the kinetic energy of the molecules, therefore it is described as a passive process.