Name:_______________________________________________________________________ Block:__________ Date:______________________ Student #:________

Cell Membrane & Cell Transport

Read the passage below. Then answer the questions that follow.

A cell membrane is made of a double layer of phospholipid molecules. Each layer is a mirror image of the other layer. The structure is called a lipid bilayer.

Located within the lipid bilayer of the cell membrane are proteins of different types. Each type of membrane protein plays a vital role in the life of a cell. Cell-surface markers are membrane proteins that are attached to a carbohydrate on the cell’s surface. Together, the protein and carbohydrate help other cells recognize the cell type—liver cell or heart cell, for example. Receptor proteins are membrane proteins that recognize and bind to specific substances outside the cell. When this happens, the inside of the cell changes, as well. In this way, receptor proteins help cells detect and change in response to things in the environment outside the cell. Enzymes are proteins that change the rate of chemical reactions. Various enzymes in the cell membrane are involved in important biochemical reactions inside the cell. Many substances needed inside the cell cannot pass through the cell membrane on their own. Transport proteins are membrane proteins that aid the movement of these substances through the lipid bilayer of the cell membrane. In this way, transport proteins help carry a variety of substances into and out of the cell.

SKILL: USING CONTEXT CLUESRead each question, and write your answer in the space provided.

1. The prefix bi- means “two.” Why is the term lipid bilayer a good name for a cell membrane?

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2. Why are the proteins described in the second paragraph classified together in a group referred to as membrane proteins?

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SKILL: ORGANIZING INFORMATION The second paragraph of this passage identifies four different types of proteins found in the cell membrane. Complete the table below by listing each type of protein and its function in the spaces provided.

Type of protein Function

3. 4.

5. 6.

7. 8.

9. 10.

Use chapter 7 section 3 from your textbook to answer the following questions.Compare/Contrast Table Use a compare/contrast table when you want to see the similarities and differences between two or more objects or processes. Select words or phrases from the box to complete the table comparing passive and active transport.

Passive Transport Active Transport

Passive TransportDiffusion is the movement of particlesfrom an area of high concentration toan area of low concentration. Osmosisis the diffusion of water through aselectively permeable membrane.Study the beakers at the right. Thearrows between beakers tell youwhat process is occurring.

11. In the beakers on the right,draw the result of the describedprocess. Draw changes in waterlevels. Draw changes in the numberof solute particles. Remember todraw on both sides of themembrane.

12. Look at the top left beaker. Whatwould happen if the membrane did

diffusion energy required exocytosis osmosis endocytosis energy not required facilitated diffusion protein pumps

water movement

Osmosis

solute particle movement

Diffusionof

SoluteParticles

membrane

soluteparticles

water

not allow water or solute particlesto pass through it?

Use chapter 7 section 3 from your textbook to answer the following questions.Active TransportFacilitated diffusion takes place when a substance diffuses across the cell membrane through a protein channel. Active transport takes place when the cell uses energy to carry a substance across the cell membrane against a concentration difference.

Follow the directions.

13. Label each diagram as either facilitated diffusion or active transport.

Answer the questions. Circle the correct answer.

14. Which process can move molecules from a lower concentration solution on one side of the membrane to a higher concentration solution on the other side?

Moleculebeing carried

Energy

Molecule tobe carried

Glucose molecules

A B

active transport facilitated diffusion

15. Which process does not require energy?active transport facilitated diffusion

16. What does the word facilitated mean in facilitated diffusion ?hindered helped