Lesson Notes By Weeks and Term v4 - SHS 1
MOVEMENT OF SUBSTANCES IN LIVING ORGANISM S
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MOVEMENT OF SUBSTANCES IN LIVING ORGANISM S
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Subject: Biology
Class: SHS 1
Term: 1st Term
Week: 20
Grade code: 1.2.1.LI.3
Strand code: 2
Sub-strand code: 1
Content standard code: 1.2.1.CS.1
Indicator code: 1.2.1.LI.3
Theme: LIFE IN THE FUNDAMENTAL UNIT
Subtheme: MOVEMENT OF SUBSTANCES IN LIVING ORGANISM S
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This lesson explores the fascinating ways cells, the basic units of life, get the substances they need to survive and get rid of waste. Every living thing, from the smallest bacteria to the mighty *Odum* tree and ourselves, depends on this constant traffic of materials across the tiny but powerful cell membrane. Understanding this topic is crucial because it explains many everyday biological processes: why we feel thirsty after eating salty *koobi*, how plants absorb water from the soil to grow our food like yam and cassava, how we breathe, and how our bodies absorb medicine.
A. The Cell Membrane: The Gatekeeper of the Cell Before we discuss how things move, we must understand the "gate" they have to cross. The cell membrane (or plasma membrane) is a thin layer surrounding every living cell. Key Feature: It is selectively permeable (or semi-permeable). Analogy: Think of it like a security guard at a school gate. The guard allows students and teachers in (the substances the cell needs) but stops strangers or troublemakers from entering (harmful substances). It also allows students to leave at the end of the day (waste products). It doesn’t just let anything and everything pass through. This control is vital for the cell's survival. B. Types of Movement Across the Cell Membrane Movement is categorized into two main types based on whether the cell uses its own energy (ATP). Passive Transport: No energy required from the cell. Substances move "downhill" from an area of high concentration to an area of low concentration. Active Transport: Requires energy (ATP) from the cell. Substances are moved "uphill" against their concentration gradient, from low to high concentration.
C. Detailed Look at Passive Transport Diffusion Definition: The net movement of particles (molecules or ions) from a region of their higher concentration to a region of their lower concentration. Mechanism: It happens because particles are in constant, random motion. Where there are more particles, they are more likely to bump into each other and spread out into the less crowded space. Example: When someone sprays perfume in one corner of the classroom, the scent particles gradually spread until everyone can smell it. The particles moved from a high concentration (near the person who sprayed) to a low concentration (the rest of the room).
Factors Affecting the Rate of Diffusion: Concentration Gradient: The steeper the gradient (i.e., the bigger the difference in concentration), the faster the rate of diffusion. *Example:* If you drop a sugar cube into tea, it dissolves and spreads. If you drop ten sugar cubes, the "push" to spread out is much stronger and faster. Temperature: Higher temperatures increase the kinetic energy of particles, making them move faster. *Example:* A drop of ink spreads much faster in a beaker of hot water than in a beaker of cold water. In our bodies, our constant warm temperature (37°C) helps diffusion happen efficiently. Surface Area: A larger surface area allows for more particles to cross at the same time, increasing the rate. *Example:* The alveoli in our lungs are folded into millions of tiny air sacs to create a massive surface area (like a tennis court!) for oxygen to diffuse quickly into our blood. Size of Particles (Molecular Weight): Smaller, lighter particles move faster than larger, heavier ones. *Example:* Oxygen molecules (O₂) diffuse faster than larger glucose molecules (C₆H₁₂O₆). Diffusion Distance: The shorter the distance the particles have to travel, the faster the rate. *Example:* The walls of our capillaries and alveoli are only one-cell thick to ensure a very short diffusion path for gases. Osmosis Definition: A special type of diffusion. It is the net movement of water molecules across a selectively permeable membrane from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution). Key Idea: Think of it as water moving to where there is more "stuff" (solute like salt or sugar) dissolved in it. A concentrated salt solution has less "free" water molecules than pure water, so water moves into the salt solution to try and balance things out.
Osmosis in Action (Tonicity): Isotonic Solution: The concentration of solutes outside the cell is the *same* as inside. Water moves in and out at an equal rate. The cell remains normal. Hypotonic Solution: The concentration of solutes outside the cell is *lower* than inside. Water will move *into* the cell. Animal Cell (e.g., Red Blood Cell): It will swell and burst (lysis) because it has no cell wall. Plant Cell (e.g., Yam Cell): It will swell, but the strong cell wall prevents it from bursting. It becomes firm and stiff, or turgid. This is how plants stay upright. Hypertonic Solution: The concentration of solutes outside the cell is *higher* than inside. Water will move *out of* the cell. Animal Cell: It will shrink and shrivel (crenation). Plant Cell: The cell contents pull away from the cell wall. The cell becomes flaccid and then plasmolysed. This is why plants wilt when they don't get enough water or if the soil is too salty.