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Plasma Membranes

Plasma Membranes. 4. Membrane Transport Active Transport Cell size and shape. Active Transport. Moving molecules or ions against a concentration gradient (one way) Energy required – high numbers mitochondria Occurs in intestines to absorb as much of the nutrient molecules as possible

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Plasma Membranes

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  1. Plasma Membranes 4. Membrane Transport Active Transport Cell size and shape

  2. Active Transport • Moving molecules or ions against a concentration gradient (one way) • Energy required – high numbers mitochondria • Occurs in intestines to absorb as much of the nutrient molecules as possible • Occurs in cells to keep high K+ inside and high Na+ outside, and to expel metabolism wastes (eg H+) • Plants also do this eg seaweed example

  3. Bulk Transport • Occurs when cells need to move large quantities of materials into or out of the cytoplasm at one time • Too large to pass out of the pores in the plasma membrane • Large amounts of energy required • Two forms: Endocytosis Exocytosis

  4. Endocytosis • Engulf solid and liquid particles by extending cytoplasm around the particle, forming vesicles Phagocytosis • WBC’s (macrophages) engulf bacteria/foreign bodies to defend against disease • Digested by lysosome enzymes • Selective eg Amoeba & food Pinocytosis • Cell’s plasma membrane engulfs extracellular fluid • Eg fat droplets in small intestine after a meal

  5. Exocytosis • Used by secretory cells to export products eg glands • Used by cells to remove harmful waste • Used to release transmitter chemicals from nerve cells • Exocytotic vesicles often come from Golgi apparatus

  6. Diffusion, Cell Size and Shape • Many different cell types with different functions • Cell size is small • As it grows, volume (cytoplasm) to surface area (membrane) ratio increases • Volume of cytoplasm determines waste removal and supply requirements • Removal of wastes and supply of nutrients is dependent on surface area size • So cell is limited in the size to which it can grow • Some cells have adapted to have multiple folds to increase surface area • When cell size is too big for its input and output needs, it has to divide

  7. Cell Size & Shape Activity • In small groups (4-6), create 3 different sized cubes • The lengths of the sides (of each cube) must differ by at least 5cm • Calculate the surface area and volume of each cube • Calculate the surface area:volume ratio of each cube • What is occuring with increasing size of cube? • Would this continue to occur? • How does this relate to cell size and shape?

  8. Small Intestine Villi • Have massively increased surface area to maximise absorption of nutrients from the small intestine • Disease conditions that damage villi cause malabsorption and nutrient deficiencies • Plants have also adapted in this way (root systems)

  9. Whole Class Activity • Measurement of Na and K concentration inside and outside red cells in blood • Outside cells – blood plasma • Inside cells – lysed red blood cells • Using a POCT device • How different are you expecting the results to be? How would you explain any differences?

  10. Questions • What applications are there for this information in real-life situations? • What advantages are there to many small cells rather than one large one? • Review questions (active transport) • BioZone questions (active transport)

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