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Cell Membrane Transport — Reading Comprehension

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MS-LS1-2

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This middle school science reading passage explores how cell membranes regulate the movement of substances in and out of cells, aligning with NGSS MS-LS1-2. Students will learn about passive transport (diffusion, osmosis, facilitated diffusion) and active transport (energy-requiring pumps) using real-world examples such as oxygen exchange and nutrient absorption. The passage emphasizes the importance of these mechanisms for maintaining homeostasis and supporting life processes, integrating scientific thinking about the evidence and discoveries behind these concepts. Glossary terms, a simplified version for accessible reading, Spanish translations, comprehension questions, graphic organizers, and writing prompts are included. Audio integration supports diverse learners. This resource is ideal for grades 6-8, supporting science literacy and critical thinking. Keywords: cell membrane, passive transport, active transport, diffusion, osmosis, biology, NGSS.

CONTENT PREVIEW

Cell membranes play a crucial role in maintaining the internal balance of living things. Every cell relies on its membrane to control what enters and exits, directly influencing health and survival. Researchers have observed that cells must allow in essential materials, such as oxygen and nutrients, while keeping out harmful substances. The movement of molecules across the cell membrane is called cell membrane transport. This process involves different mechanisms, which help cells respond to their environments and function efficiently.

How Substances Move: Passive Transport

One major way that substances move across the cell membrane is through passive transport. In passive transport, molecules move from areas of high concentration to areas of low concentration, and this does not require energy from the cell. The most common type is diffusion, where molecules like oxygen naturally spread out to fill available space. For example, oxygen moves from the lungs (where its concentration is high) into body cells (where its concentration is lower), allowing cells to perform cellular respiration. Another form is osmosis, which specifically refers to the movement of water molecules across the membrane. Water moves to balance concentrations on both sides. Sometimes, molecules are too large or charged to cross directly, so they use facilitated diffusion. In this case, special protein channels in the membrane help these substances pass through without using energy.

Active Transport: Moving Against the Gradient

Not all substances can move freely across the membrane. Sometimes, cells need to move molecules from low concentration to high concentration, which is the opposite of passive transport. This process is called active transport and requires the cell to use energy, usually from ATP (adenosine triphosphate). Active transport uses specialized protein pumps in the membrane to move substances against their concentration gradient. One important example is the sodium-potassium pump in nerve cells, which maintains the electrical balance necessary for nerve impulses. Another example is the absorption of nutrients in the intestines, where cells use active transport to take in nutrients even when their internal concentration is already high.

Interactions and Real-World Connections

Cell membrane transport is vital for homeostasis, which is the ability of organisms to keep internal conditions stable. Disruption of these processes can lead to serious health problems, such as dehydration or nerve disorders. Scientists have studied cell membranes using electron microscopes and discovered that the lipid bilayer and embedded proteins are essential for selective transport. Modern research continues to reveal new details, like how certain diseases result from faulty transport proteins. Understanding these mechanisms helps in developing medical treatments and advancing biotechnology.

In summary, cell membrane transport is a system of processes that allows cells to exchange materials, maintain balance, and respond to their environment. These transport methods—passive and active—are interconnected and essential for life. By learning how substances move in and out of cells, we gain insight into larger biological systems and the principles of life itself.

Interesting Fact: The human body contains about 37 trillion cells, and every single one uses its membrane to regulate what goes in and out, every moment of your life!

What is the main function of the cell membrane?

To control what enters and exits the cellTo create energy for the cellTo store genetic informationTo make proteins

Which type of transport does NOT require energy from the cell?

Passive transportActive transportProtein pumpingCellular respiration

What is diffusion?

Movement of molecules from high to low concentrationMovement of water onlyMovement of molecules from low to high concentrationA type of active transport

Why do cells use active transport?

To move substances against the concentration gradientTo move water onlyTo avoid using energyTo let oxygen diffuse

Based on the passage, which is an example of facilitated diffusion?

Large or charged molecules passing through protein channelsOxygen moving into cells by diffusionWater moving by osmosisNutrients being pumped into the intestines

What does 'homeostasis' mean as described in the passage?

Keeping internal conditions stableMoving water out of the cellProducing more cellsBreaking down nutrients

What does the word "osmosis" mean in the passage?

Water moving across a membrane to balance concentrationsAny movement of moleculesMovement of oxygen onlyProtein channels helping molecules

What is the role of protein pumps in active transport?

They use energy to move substances against the gradientThey allow water to pass freelyThey help molecules move from high to low concentrationThey store energy

True or False: Passive transport moves substances from low to high concentration.

TrueFalse

True or False: Problems with cell membrane transport can lead to health issues.

TrueFalse