Plasma Membranes Surround all cells Surround organelles Nucleus, chloroplasts & mitochondria have double membranes
Cell Environment Must be suitable for enzyme function Internal environment – all material contained within the cells’ plasma membrane External environment – fluid outside the plasma membrane, which supplies nutrients for the cell, and removes cell waste Plasma membrane allows these environments to be different But the plasma membrane must be able to allow this exchange – HOW?
Prokaryotes – Escherichia coli Bacterium in human large intestine Indicator of faecal contamination of beaches Plasma membrane keeps internal contents in, foreign molecules out Cell must also be able to detect & adapt to changes outside cell Cell must be able to take in wanted molecules and ions Cell must be able to excrete waste material of metabolism Relies on plasma membrane to do this
Eukaryotes – Plants and Animals Membranes have same functions as prokaryotes PLUS: (Double) Membrane-bound organelles, responsible for specialised chemical processing Mitochondria – enzymes for cellular respiration and ribosomes for protein synthesis Nucleus – contains genetic material Plants – chloroplasts, for photosynthesis Animal cell
Summary - Functions Keep cellular material inside Keep extracellular material out Surround organelles (compartmentalise for specific functions) Entry and export of substances (vesicles and vacuoles) Break and reassemble during cell division Cell communication and recognition Transport processes (channels etc)
Questions What are the main functions of plasma membranes? What are the main differences between prokaryotic and eukaryotic cells? What benefits do these differences give eukaryotic cells? How do you think cells might achieve selective movement in and out of them? BioZone questions page 88
Activity – Cheek Cells Prepare a wet prep of your cheek cells, and locate the membranes you can see under a microscope Scrape cells inside cheek with the flat side of a toothpick, and apply to a glass slide Add a drop of water, then carefully lower a coverslip so no bubbles form Add a drop of methylene blue stain on one side of the coverslip Draw the stain under the coverslip by putting paper towel on the opposite side, drawing the water out and the stain in
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