2- Cell transport mechanisms

All cells and organelles are surrounded by a partially permeable membrane, what is this composed of?

A sea of phospholipids with protein molecules between phospholipid molecules.

What type of proteins can be in a membrane?

Transport proteins, receptor proteins, enzymes, structural and recognition proteins.

What is the main function of the membrane?

Controlling the movement of substances in and out of the cell/organelle.

And contains receptors for other molecules such as hormones, and enables adjacent cells to stick together.

Why are membranes structure called the fluid mosaic model?

The fluidity of the membrane (proteins and lipids are free to move) and the mosaic arrangement of the proteins give the structure of the membrane its name.

Why does the movement of molecules through cell membranes use different types of movement?

It depends on the properties of the molecule as well as the requirements of the cell.

What are the different types of movement?

1. Diffusion

2. Facilitated diffusion

3. Active transport

4. Osmosis

5. Endocytosis and Exocytosis

Define diffusion

The passive movement of small, non-polar molecules such as CO2 and oxygen.

From an area of high concentration to an area of low concentration. The molecules move directly through the phospholipid bilayer.

When/ why can the diffusion rate become faster?

When the surface area increases, diffusion distance decreases and the diffusion/ concentration gradient becomes steeper.

What is facilitated diffusion?

This requires a channel protein in the cell membrane to transport polar, charged and water-soluble molecules across the membrane.

Define active transport

The movement of molecules through carrier proteins from an area of low concentration to an area of high concentration.

This process requires energy in the form of ATP. The hydrolysis of ATP provides an accessible store of energy for biological processes.

What is the general definition for endocytosis and exocytosis?

The movement of large particles into and out of cells via the formation of vesicles.

Define endocytosis

Particles are enclosed in vesicles made from cell surface membrane and transported into the cell.

Define exocytosis

Vesicles containing large particles fuse with the cell surface membrane and are transported out of the cell.

Define osmosis

The movement of water molecules from an area of high water potential to an area of low water potential across a partially permeable membrane (more dilute to less dilute).

In animals what does water potential =

osmotic potential

What is turgor pressure?

Inward pressure exerted by the plant cell wall on the protoplasm as the protoplasm expands and pushes out.

In plants, turgor pressure is also a factor.

It is generated because water moves in by osmosis, causing the protoplasm to swell and push against the cell wall, generating hydrostatic pressure. This generates a reactive force pushing inwards. A combination of these forces is turgor pressure and it prevents water moving into a cell.

When does the cell become turgor?

When turgor pressure is balanced with osmotic potential.

What is the equation for plants becoming turgor?

Water potential = osmotic pressure + turgor pressure (P)