Transcript Plasma Membranes1 Year 11 biology

Plasma Membranes
1. Function
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
Animal cell
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
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