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
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Biology
Class: SHS 1
Term: 1st Term
Week: 18
Grade code: 1.2.1.LI.2
Strand code: 2
Sub-strand code: 1
Content standard code: 1.2.1.CS.1
Indicator code: 1.2.1.LI.2
Theme: LIFE IN THE FUNDAMENTAL UNIT
Subtheme: MOVEMENT OF SUBSTANCES IN LIVING ORGANISM S
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This lesson explores the dynamic and essential process of how substances move in and out of living cells. The cell membrane acts as a gatekeeper, controlling what enters and leaves, which is fundamental to life itself. We will investigate how a plant like kontomire (cocoyam leaves) wilts in the sun and becomes firm again when placed in water, why salted fish (momoni or koobi) can last for a long time without spoiling, and how our bodies fight diseases. Understanding these processes is crucial for comprehending health, agriculture, and the environment around us.
Introduction: The Cell Membrane as a 'Border Control'
Every living cell is surrounded by a cell membrane. Think of it like the border of a country. It is selectively permeable (or semi-permeable), meaning it allows some substances to pass through freely, while others are blocked or need special assistance. This control is vital for the cell to maintain a stable internal environment (homeostasis), take in nutrients, remove waste, and communicate. The structure responsible for this is the Fluid Mosaic Model, where a double layer of phospholipids has various proteins embedded in it, acting as channels and pumps. A. Passive Transport: Movement Without Energy
Passive transport is the movement of substances across the cell membrane *without* the cell using any of its own energy (ATP). The movement happens naturally down a concentration gradient – from an area of high concentration to an area of low concentration. Simple 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: The particles simply move through the phospholipid bilayer. This works for small, uncharged molecules. Effect/Importance: Gas Exchange: In our lungs, oxygen (high concentration) diffuses from the air sacs into the blood (low concentration). Carbon dioxide (high concentration in blood) diffuses out. The same happens in the leaves of plants. Everyday Example (Ghana): When someone is roasting plantain or groundnuts on the street, the scent (volatile chemical particles) spreads through the air by diffusion, moving from the source (high concentration) to your nose (low concentration). Osmosis: The Special Case of Water Diffusion Definition: The net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution) across a selectively permeable membrane. Key Idea: It's all about the concentration of water. Pure water has the highest water potential. Adding solutes (like salt or sugar) lowers the water potential. Water always "wants" to move to the area with less water (more solutes). Effects of Osmosis on Cells: On Animal Cells (e.g., Red Blood Cells): In a Hypotonic Solution (less solute, more water outside): Water enters the cell by osmosis. The cell swells and may burst because it has no cell wall. This bursting is called haemolysis or lysis. (e.g., Red blood cell in pure water). In an Isotonic Solution (equal solute concentration inside and out): There is no net movement of water. The cell maintains its normal shape. (e.g., Red blood cell in blood plasma). In a Hypertonic Solution (more solute, less water outside): Water leaves the cell by osmosis. The cell shrinks and shrivels. This is called crenation. (e.g., Red blood cell in very salty water). On Plant Cells (e.g., Onion Epidermal Cells): In a Hypotonic Solution (less solute, more water outside): Water enters the cell's vacuole by osmosis. The vacuole swells and pushes the cytoplasm and cell membrane against the strong cell wall. The cell becomes firm or turgid. This turgor pressure is what keeps plants upright and leaves firm. In an Isotonic Solution (equal solute concentration): There is no net water movement. The cell is neither turgid nor shrunken; it is called flaccid. In a Hypertonic Solution (more solute, less water outside): Water leaves the cell vacuole by osmosis. The vacuole and cytoplasm shrink, pulling the cell membrane away from the cell wall. This process is called plasmolysis, and the cell is plasmolysed. This is why plants wilt. B. Active Transport: Movement Requiring Energy Definition: The movement of substances across a cell membrane *against* their concentration gradient (from a region of low concentration to a region of high concentration). Mechanism: This process is "uphill," so it requires energy in the form of ATP (Adenosine Triphosphate), which is produced during respiration. It also requires specific carrier proteins in the membrane to act as pumps. Effect/Importance: Mineral Absorption in Plants: Soil water often has a lower concentration of mineral ions (e.g., nitrates, phosphates) than the root hair cells of a plant. Plants use active transport to pump these essential minerals into their roots, enabling them to grow even in poor soil. Nerve Impulses: Active transport pumps are crucial for maintaining the ion gradients needed for our nerves to send signals. C. Bulk Transport: Moving Large Materials
Sometimes cells need to transport very large particles (like bacteria) or large quantities of fluid that cannot pass through the membrane via diffusion or protein channels. This is done by a process that involves the folding of the cell membrane itself and requires energy (ATP). Endocytosis (Bringing things IN) Definition: The process by which a cell takes in large substances by enclosing them in a portion of its cell membrane, which then pinches off to form a vesicle inside the cell. Types of Endocytosis: Phagocytosis ("Cell Eating"): The cell engulfs large solid particles. Effect/Example: A white blood cell (phagocyte) in our blood engulfs a harmful bacterium or a malaria parasite to destroy it. An Amoeba also feeds this way. Pinocytosis ("Cell Drinking"): The cell takes in droplets of extracellular fluid containing dissolved substances. Exocytosis (Sending things OUT) Definition: The process by which a cell releases large substances. A vesicle containing the substance moves to the cell membrane, fuses with it, and then releases its contents to the outside. Effect/Importance: Secretion of Hormones: Cells in the pancreas produce the hormone insulin and package it into vesicles. They release it into the bloodstream via exocytosis to control blood sugar. Secretion of Enzymes: Cells in the salivary glands secrete digestive enzymes into our mouths using exocytosis. Release of Neurotransmitters: Nerve cells release chemical signals at synapses via exocytosis.