Transcript Cell Transport 2014

Transport of Materials Across
Cell Boundaries
Part I
Cell Boundaries
• All cells are in a liquid environment
• Cytoplasm is a solution of many substances
• Cell Boundaries help maintain constant stable
environment inside cell = homeostasis
• Must regulate substances moving into & out of cell
• Cell Membrane: Thin flexible barrier that
surrounds all cells (phospholipid bi-layer)
– Regulates what enters and leaves the cell
– Provides protection and support
– Hydrophyllic = water-loving
– Hydrophobic = water-fearing
Cell Membrane
• Cell Membranes also contain other embedded molecules with
specific jobs
• Protein channels for transport (doorways)
• Carbohydrate receptors (security guard)
• Cell Wall: Strong supporting layer around
the cell membrane in plant cells and
prokaryotes
– Provides support and protection for the cell
– Porous enough to allow some substances to
pass through
• Solution: Mixture of 2 or more substances
– Solute: Dissolved substances
• Example = Kool-Aid
– Solvent: Dissolving substance
• Example = Water
• Dissolved particles (solute) move around in space to
reach equilibrium
– Diffusion: Movement of particles from an area of
high concentration to an area of low concentration
– Equilibrium: Concentration of the solute is the
same throughout the system
Concentration Gradient
Low Concentration
High Concentration
Diffusion
• Depends on random particle movement down a
concentration gradient (cg)
– CG = Measurement of concentration change over
a distance
• Requires no energy = passive transport
• Small particles = able to pass through cell membrane
Permeability
• Permeable: A substance can pass across it
• Impermeable: A substance cannot pass across it
• Most cell membranes are semi or selectively
permeable
– Some substances can pass through
• Cells regulate water exchange to maintain
homeostasis
– Osmosis: The diffusion of water through a
selectively permeable membrane
– Water will move across the membrane until
equilibrium is reached = isotonic
• Isotonic: Equal concentration
– Same strength
– Water moves
equally
– Cell stays the same
Hypertonic: Higher concentration of solute
outside the cell
– “Above Strength”
– Water moves out
of the cell
– Cell shrinks
Hypotonic: Lower concentration of solute
outside the cell
– “Below strength”
– Water moves into
the cell
– Cell expands
Osmotic Pressure
• Pressure difference across a membrane
caused by different concentrations of particles
in and out of the cell
Facilitated Diffusion
• Molecules that are too large to cross
the cell membrane must use
special “doorways”
• Protein Channels – designed
to allow specific molecules
to diffuse across the
membrane easily
• Example - Glucose
Transport of Materials Across
Cell Boundaries
Part II
• What if a cell needs to move particles
against a concentration gradient?
– From low to high concentration
– Allows cells to concentrate molecules in a
particular location regardless of concentration
gradient
– Requires energy = Active Transport
• Examples
– Transport proteins
– Endocytosis
– Exocytosis
• Transport Protein: Transmembrane
protein that helps a certain class of
substances cross the membrane
– Think of them like doors
• Endocytosis: Materials are moved into
the cell via folds in the cell membrane
– Endo = Within
– Two examples
• Phagocytosis: Extensions of cytoplasm surround
a particle and package it within a food vacuole
• Pinocytosis: Tiny pockets form along the cell
membrane, fill with liquid, and pinch off to form
vacuoles within the cell
• Phagocyte: “Eating Cell”
– Important white blood cell
– Consumes and destroys cellular debris &
pathogens (germ)
Endocytosis
• Exocytosis: Materials are moved out of
the cell via folds in the cell membrane
– Exo = Outside
Cell
Differentiation
& Life
Organization
Ch. 7
Section 4
In
Textbook
Cell Differentiation
In unicellular organisms the single cell will
develop the structures necessary to live its
life.
Some may grow appendages for movement:
1) Cilia – tiny hairs on cell surface that move to
allow mobility of the cell
2) Flagella – whip-like appendage used for
movement
What about multi-cellular eukaryotes?
Some cells develop differently than others for
specific jobs:
1) Muscle Fiber Cells:
Highly developed cytoskeleton for movement
(remember actin?)
2) Pancreatic Cells:
Need to produce enzymes for digestion so the
Rough ER and Ribosomes are more highly
developed
3) Red Blood Cells: No nucleus, oxygen
transport