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Transcript
The Cell Membrane The Master of Homeostasis Terms to Know • • • • • • Homeostasis Diffusion Osmosis Active Transport Cell membrane Plasma membrane • • • • • • Selectively permeable Gradient Dynamic equilibrium Hypotonic solution Hypertonic solution Isotonic solution Homeostasis • An organism’s regulation of its internal environment to maintain conditions suitable for survival is known as homeostasis • One of the main structures of a cell responsible for maintaining homeostasis is the cell membrane or (plasma membrane) The Cell Membrane The Cell Membrane • The cell membrane or (plasma membrane) is a flexible boundary between the cell and its environment – It is the outermost structure making the outline of the cell The Cell Membrane • The cell membrane allows certain things in, such as water and nutrients, and other things out • This ability of the cell membrane to allow certain things in or out is referred to as selective permeability Diffusion • Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration Diffusion • Click here to link to a diffusion animation online • Particles are usually moving about randomly and changing directions as they bump into one another • In diffusion, the particles in high concentration will migrate to areas of lower concentration until they fill in all of the empty space Diffusion in Cells • Movement of particles from areas of high concentration to low concentration are said to be moving with the “gradient” – The particles move until they are evenly distributed, which is called “dynamic equilibrium” • Substances in cells are in a water solution and constantly move by diffusion Osmosis • The diffusion of water molecules across a selectively permeable membrane is known as osmosis – The direction of osmosis is determined by whether the concentration of dissolved substances is higher inside of or outside of a cell membrane Osmosis • If a cell has more dissolved substances (like sugar) inside the cell than outside, this means that there is a higher concentration of water outside than inside – Remember that osmosis is the movement of WATER across a membrane – Also remember that in diffusion, particles move from areas of HIGHER CONCENTRATION TO LOWER CONCENTRATION Osmosis • Therefore the water is going to move INSIDE the cell with the gradient until dynamic equilibrium is reached • This cell is said to be in a hypotonic solution – You can remember this by using the word (HIPPO-Tonic) because the cell becomes fat and hippos are fat Osmosis • If the concentration of dissolved substances is higher outside of a cell than inside, then the concentration of water is higher inside and the water will rush outside of the cell with the gradient until dynamic equilibrium is reached – This cell is said to be in a hypertonic solution • You may think of hyper students running outside of a classroom and the classroom, or (cell) shrinks in size Osmosis • If the concentration of dissolved substances inside the cell are the same as the outside of a cell, there is no concentration gradient and water moves back and forth across the cell membrane at an equal rate – A cell in this case is said to be in an isotonic solution Active Transport • Sometimes the cell needs to get things inside and outside of the cell against the concentration gradient • This requires energy from the cell and is called active transport Cell Membrane and Homeostasis • Because of the selective permeability of the cell membrane, the cell only allows good things in and keeps bad things out of the cell. This helps the organism maintain healthy and able to survive Cell Organelles The Nuts and Bolts of a Cell Terms to Know • • • • • • • • • • Organelle Plasma membrane Cell wall Mitochondria Golgi apparatus Lysosome Vacuole Centrioles Chromatin Endoplasmic reticulum • • • • • Ribosome Cytoplasm Nucleus Nuclelous Nuclear membrane Centrioles Mitochondria Nucleus Endoplasmic Reticulum Chromatin Nucleolus Cytoplasm Nuclear Membrane Cell Membrane Ribosome Lysosome Golgi Apparatus Vacuole Cell Organelles • Like many organisms have organs within them that have specific functions, cells have organelles • Organelles are membrane-bound structures within a eukaryotic cell that have specific functions The Cell Membrane • The cell membrane, or plasma membrane, is a selectively permeable layer on the outside of the cell, which contains all of the organelles within – Remember that the plasma membrane helps maintain homeostasis within an organism • All cells have a cell membrane Cell Wall • A cell wall is a fairly rigid structure located outside the plasma membrane of plants, fungi, most bacteria, and some protists which provides support and protection • The cell wall allows the cell to become quite turgid without bursting Mitochondria • A eukaryotic membrane-bound organelle that transforms energy stored in food molecules is called mitochondria – Mitochondria have highly folded membranes that produce energy-storing molecules • Mitochondria is the powerhouse of the cell Golgi Apparatus • The Golgi apparatus is an organelle in eukaryotic cells with a system of flattened tubular membranes • It sorts and packages proteins and sends them to their appropriate destinations Lysosome • A lysosome contains digestive enzymes and is responsible for digesting excess or worn out organelles, food particles, and engulfed viruses or bacteria Vacuole • A vacuole is a membrane-bound space in the cytoplasm of cells used for the temporary storage of materials – The vacuole in a plant is very large Centrioles • In animal cells, a pair of small cylindrical structures composed of microtubules called centrioles duplicate during interphase and move to opposite ends of the cell during prophase Chromatin • Long strands of DNA found in the eukaryotic cell nucleus is known as chromatin and condenses to form chromosomes Endoplasmic Reticulum • The endoplasmic reticulum is an organelle in eukaryotic cells with a series of highly folded membranes surrounded in cytoplasm • It is the site of cellular chemical reactions – Can be rough “ER” with ribosomes attached or smooth ER without ribosomes Ribosomes • Ribosomes are non-membrane-bound organelles in the nucleus where proteins are assembled Cytoplasm • Cytoplasm is the clear, gelatinous fluid in cells that is the site of numerous chemical reactions – In eukaryotes, it suspends the organelles Nucleus • The nucleus is the central membranebound organelle that manages cellular functions and contains DNA • The nucleus is surrounded by a nuclear membrane which can dissolve or allow structures out to the cytoplasm Nucleolus • The nucleolus is found in the nucleus and produces ribosomes Review • To link to an Internet site on parts of the cell click here!
