Biochemistry End of Unit Test is Tuesday, December 9th.

Lesson 2

Structure of the Cell Membrane

Learning Intention

Students will be able to discover how the structure of the cell membrane makes it selectively permeable.

Success Criteria

Review diffusion key concept and vocabulary through regents questions.
Determine the direction of diffusion based on the concentration.
Apply my knowledge of the cell membrane structure.
Demonstrate my knowledge of concentration gradient by answering regent questions.

Reminders:

Tutoring after-school Wednesdays with Mr. Pinho in A-301

Agenda

Activity 1: Warm-Up

Activity 2:

Activity 3:

Activity 4:

Activity 5:

NGSS Standard

Each cell is covered by a membrane that performs a number of important functions for the cell. These include: separation from its outside environment, controlling which molecules enter and leave the cell, and recognition of chemical signals. The processes of diffusion and active transport are important in the movement of materials in and out of cells. (1.2g)

Activity 1

Warm-Up

sc1 (10 min)

Q1

Q2

Q3

Q4

Activity 2

See, Think, Wonder

sc 2 - (5 min)

Activity 3

Discovery Learning

sc3- (10 min)

Essential Question: How is the cell membrane structured and what is the purpose of these structures?

The Cell Membrane

Every cell is surrounded by a cell membrane, which acts like a selective barrier between the inside of the cell and its environment. The cell membrane helps protect the cell and controls what enters and leaves. This allows the cell to maintain balance, or homeostasis, even when conditions outside the cell change.

The cell membrane is made mostly of phospholipids, arranged in a double layer. This structure allows small nonpolar molecules like oxygen to pass directly through the membrane, while many other substances cannot cross on their own. Because of this, the cell depends on proteins to help with transport and communication.

Embedded within the cell membrane are protein structures that perform important functions. Some proteins act as channel proteins, forming passageways that let certain molecules or ions move into or out of the cell. Other proteins help transport larger molecules, like glucose, that cannot fit through the membrane by themselves.

Another important type of membrane protein is the cell receptor. Receptors help cells receive messages from the environment. Many hormones and neurotransmitters cannot enter the cell, so they bind to receptors on the surface instead. Receptors follow a lock-and-key model, where each receptor has a specific shape (the “lock”) that fits only one type of signaling molecule (the “key”). When the correct molecule binds, it triggers a response inside the cell, such as starting a reaction or telling the cell to change its activity.

While receptors are used for communication, another type of membrane protein is used for water movement: the aquaporin. This is a different structure with a different purpose. Aquaporins are protein channels that allow water to move rapidly across the cell membrane. Although water can pass through the membrane slowly on its own, aquaporins make this process much faster. Cells rely on aquaporins to prevent swelling, shrinking, and other water-balance problems that could damage the cell. These channels are especially important in tissues such as red blood cells, plant roots, and the kidneys.

Through all these structures—phospholipids, channel proteins, receptors, and aquaporins—the cell membrane stays flexible, protective, and highly selective. These features allow the cell to survive and function in a constantly changing environment.