Understanding Plant Nutrient Transport and Membrane Diffusion, Summaries of Physics

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Moving Materials Through Plants

Plants make sugars in their leaves and then must move those sugars throughout the plant in order to provide sugar to all of the plant cells. Likewise, water and minerals are taken up by the plant roots and then must be transported to all the plant cells. Once the circulating materials arrive at plant cells, they must be moved into the cells.

Introduction

Movement of Molecules

Moving Across Membranes

The plasma membrane controls what can enter and exit each plant cell. Whether or not a molecule will cross a membrane, and which way it will go, depends on three things.

Moving Across Membranes

The concentration of the molecule on either side of the membrane. If molecules are allowed to move freely, they will move from areas where they are more concentrated to areas where they are less concentrated. In other words, they’ll move until they are evenly spread out, or in equilibrium, over an area. This type of movement is called diffusion.

Moving Across Membranes

Whether or not the membrane contains a transport protein for the molecule. Although some small hydrophobic molecules can cross membranes by themselves, most molecules need the help of a transport protein. If a plant plasma membrane doesn’t have a protein to transport a particular molecule, it won’t be able to cross in or out of the plant cell.

Diffusion

Diffusion

1. A chemical starts out more concentrated on one side of a membrane, but its molecules can cross the membrane freely.
2. The molecules bounce around due to kinetic energy and gradually become equal in concentration on both sides of the membrane.
3. If you measure the overall movement of the chemical, you can see that its molecules moved from the side of the membrane where they were more concentrated to the side where they were less concentrated.

Diffusion

Simple diffusion occurs when molecules diffuse across a membrane all by themselves.

Facilitated diffusion occurs when molecules diffuse across a membrane with the help of a membrane protein.

Diffusion

Active transport

Plant cells often need to move molecules from areas where the molecules are less concentrated to areas where they are more concentrated, a process called active transport. In other words, plant cells need to move molecules against their concentration gradient.

Active transport

Active transport requires the input of energy from the cell. Active transport is like rolling molecules up the hill of their concentration, going from where they’re less piled up to where they’re more piled up. If a cell is going to move something up a hill, it’s going to have to put some energy into the process.

Active transport

As an example, a plant cell that stores energy for the plant may have lots of glucose inside the cell, but it may still need to bring in more. This cell could use active transport to continue bringing glucose molecules in against their concentration gradient.

Osmosis

Water moves across membranes by diffusion. The diffusion of water across membranes is called osmosis. During osmosis, water moves from an area where water is more concentrated to an area where water is less concentrated.