Unit 2 Cell Structure and Function Module 10 Membrane Transport

Using the numbers 1-3, list each step in the correct order of a secondary active transport mechanism.

2__ A gradient is created by an excess of protons outside the cell. 3__ A transport protein uses the proton electrochemical gradient to move a different molecule out of the cell against its gradient. 1__ Protons are pumped across a membrane by primary active transport.

Describe two important components of active transport

Active transport is the uphill movement of substances against a concentration gradient, and requires cellular energy in the form of ATP.

Identify molecules that cannot cross the membrane on their own and cite examples.

Large, polar, or charged molecules cannot cross on their own, including ions, proteins, polysaccharides.

Identify molecules that can easily cross the cell membrane, and cite examples.

Nonpolar, uncharged, and small molecules can cross the membrane on their own. These include oxygen, carbon dioxide, nitrogen, and nonpolar molecules such as lipids.

Identify two substances that move into or out of cells through simple diffusion.

Oxygen, carbon dioxide

Describe primary active transport and give an example.

Primary active transport uses ATP energy directly to move a substance across the membrane, against a concentration gradient. The sodium-potassium pump is a form of primary active transport. It is a transmembrane protein that actively moves sodium ions out of the cell and potassium ions into the cell, using the energy stored in the bonds of ATP.

As diffusion occurs, the rate of diffusion blank. Molecules continue to move randomly, in both directions, a condition called blank

Slows, dynamic equilibrium

Define vesicles

Small spherical organelles that travel between organelles of the endomembrane system in eukaryotic cells.

Describe the meaning of "selectively permeable" in reference to cell membranes.

The cell membrane lets some molecules in and out freely. It lets others in and out under certain conditions, and it prevents some molecules from passing through at all.

passive transport

The movement of molecules across a membrane by diffusion.

Describe how transport proteins are critically important to secondary active transport.

Transport proteins, which are fueled by ATP, pump charged ions across a membrane, creating a concentration gradient on one side of the membrane. This concentration gradient stores energy that can be harnessed to drive the movement of other molecules across the membrane against their concentration gradient. As molecules at the higher gradient move down their gradient, the coupled molecule is moved against its gradient ("uphill"), and ATP is not directly needed.

Describe how endocytosed materials move in the cell and how this affects eukaryotic cell growth.

Vesicles and the molecules they carry are carried by molecular motors associated with the cytoskeleton. This moves nutrients and signaling molecules at much greater speeds, allowing eukaryotic cells to grow to larger sizes.

aquaporins

Water channels that allow water to enter or exit the cell by facilitated diffusion.

Describe two ways vesicles exhibit membrane transport

When a vesicle fuses with the cell membrane, its contents are released outside in a process called exocytosis. Conversely, when a membrane invaginates (or pulls inward), it encloses material from the outside into a vesicle in a progress called endocytosis.

Describe two types of transport proteins used in facilitated diffusion.

a. Channel proteins provide an opening between the inside and outside of the cell through which certain molecules can pass, depending on their shape and charge. b. Carrier proteins bind to and transport specific molecules across the membrane.

Identify four properties of a molecule that can affect its transport across a membrane into a cell.

a. Size b. Charge c. Concentration d. Polarity

As diffusion occurs, the concentration gradient

a. increases. b. decreases.

The difference in the distribution of particles in solutions is called a blank

concentration gradient

In a proton pump, protons move is from regions of higher to lower concentration, but other molecules move from regions of lower to higher concentration.

higher to lower lower to higher

Facilitated diffusion is diffusion across a cell membrane through a blank

transport protein

Diffusion

Diffusion is the net movement of molecules from areas of high to low concentration due to random motion of molecules.

Explain how materials can enter the cell without having to cross the membrane.

Endocytosis and exocytosis move materials through vesicles, pinching off the membrane with them.

Simple diffusion does not require cellular blank and only works from blank to blank concentrations.

Energy, high, low

Cells in the intestine use transport proteins to move blank from gut into cells lining the gut.

Glucose