Download Homeostasis and Cellular Transport

KEY CONCEPT The plasma membrane is a barrier that
separates the inside of a cell from the external
environment.
Objectives:
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Identify and describe the cell structures involved in transport of
materials into, out of, and throughout a cell.
Describe how the structure of the plasma membrane allows it fo
function as a regulatory structure and/or protective barrier for a
cell.
Compare the mechanisms that transport materials across the
plasma membrane (ie., passive transport – diffusion, osmosis,
facilitated diffusion; and active transport – pumps, endocytosis and
exocytosis).
Describe how membrane-bound organelles (eg. endoplasmic
reticulum, Golgi apparatus, vesicles) facilitate the transport of
materials within a cell.
Describe how organisms maintain homeostasis in order to survive
(eg. thermal regulation, water regulation and oxygen regulation).
Plasma Membrane
The plasma membrane has two major functions.
• Forms a boundary between the inside and outside of the cell
• Controls passage of materials in and out of the cell
plasma membrane
Plasma Membrane
Plasma membranes are composed of PHOSPHOLIPIDS.
• A phospholipid is made of three parts:
1. Fatty Acid – Hydrophobic Tail (Water-fearing)
2. Phosphate
3. Glycerol
Hydrophilic Head (Water-loving)
Polar Head
Non-polar Tail
Plasma Membrane
Plasma Membrane Structure
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Phospholipids bind together and form two layers (phospholipid bilayer).
There are other molecules embedded in the membrane.
• Carbohydrates – serve as ID’s so cells can tell each other apart
• Proteins – help to transport substances through the membrane
• Cholesterol – strengthens the cell membrane; helps to maintain fluidity
cell membrane
carbohydrate
chain
protein
Fluid
Mosaic
Model
cholesterol
protein
protein channel
Plasma Membrane
Fluid Mosaic Model
Plasma membrane
The “Fluid Mosaic Model” was developed from two cell membrane characteristics:
1. The plasma membrane is flexible, not rigid…it is fluid and able to move.
2. The molecules embedded in the plasma membrane make it appear like a mosaic
(a colorful tile arrangement).
Plasma Membrane
The plasma membrane is selectively permeable or semipermeable.
Which means…..
Some molecules can cross the membrane
while others cannot.
Plasma Membrane
Selective Permeability
Three things determine which molecules can cross the plasma membrane.
• The molecule’s size. (How big is the molecule?)
• The molecule’s polarity. (Is it polar or nonpolar?)
• The concentration of substances inside and outside a cell. (How many
molecules are inside the cell versus outside the cell?)
Terms to Know:
Intracellular – Located inside a cell
Extracellular – Located outside a cell
Permeable – All substances can pass through
Semi-Permeable – Some substances can pass through
Impermeable – No substance can pass through
Concentration – The amount of a substance
Concentration gradient – The difference in the concentration
(amount) of a substance from one location to another. Substances
naturally move from high to low concentration.
Molecules are transported into and out of cells by
means of active transport OR passive transport.
Passive Transport
Passive transport is the movement of molecules across a
plasma membrane without energy input from the cell.
Passive transport = NO ENERGY NEEDED
• Types of passive transport:
• Simple Diffusion – the movement of
molecules in a fluid or a gas from a
region of higher concentration to a
region of lower concentration (small
molecules – ex. O2)
• Facilitated Diffusion – the movement of
molecules from a region of high
concentration to low concentration
USING A PROTEIN CHANNEL (larger
molecules such as glucose – C6H12O6)
• Osmosis – the movement of water
molecules from a region of higher
concentration to a region of lower
concentration (ONLY WATER – H2O)
Hypertonic Solutions: contain a high concentration of solute relative to another
solution (e.g. the cell's cytoplasm). When a cell is placed in a hypertonic solution,
the water diffuses out of the cell, causing the cell to shrivel.
Hypotonic Solutions: contain a low concentration of solute relative to another
solution (e.g. the cell's cytoplasm). When a cell is placed in a hypotonic solution,
the water diffuses into the cell, causing the cell to swell and possibly explode.
Isotonic Solutions: contain the same concentration of solute as another solution
(e.g. the cell's cytoplasm). When a cell is placed in an isotonic solution, the water
diffuses into and out of the cell at the same rate. The fluid that surrounds the body
cells is isotonic.
Rules of Osmosis
Active Transport
Active transport requires energy input from a cell and enables
a cell to move a substance against its concentration gradient
from low to high concentrations.
• Active transport requires energy from the cell b/c molecules are moving
from low to high concentrations.
• Active transport is powered by chemical energy (ATP). ATP is
produced in the mitochondria.
• Active transport occurs through
transport protein pumps or by using
vesicles. There are three types of
active transport:
• Protein Pump
• Endocytosis
• Exocytosis
“Protein Pumps”
Require energy from the mitochondria to move
molecules across the plasma membrane in large
quantities (Ex. Sodium & Potassium Pumps)!
Active Transport
A cell can import and export large materials or large
amounts of material in vesicles during the processes of
endocytosis and exocytosis.
• Cells use energy (ATP) to transport material in vesicles,
therefore it is a type of active transport.
• Endocytosis is the process of
taking material into the cell by using
a vesicle.
• Phagocytosis is a type of
endocytosis in which solids
are brought into a cell.
Known as “cell eating.”
• Pinocytosis is a type of
endocytosis in which liquids
are brought into a cell.
Known as “cell drinking.”
Active Transport
A cell can import and export large materials or large
amounts of material in vesicles during the processes of
endocytosis and exocytosis.
• Cells use energy (ATP) to transport material in vesicles.
• Exocytosis is the process of
expelling material from the cell by
using a vesicle.
Transport of Materials Within a Cell
1. DNA (instructions for making proteins) is transcribed into mRNA
and mRNA leaves the nucleus.
2. mRNA attaches to a ribosome and the ribosome binds amino
acids to form a protein; the endoplasmic reticulum aids in the
production, processing and transport of proteins
3. Proteins in the ER bud off in vesicles and travel to the
Golgi apparatus, then vesicles bud off the Golgi to the plasma
membrane. Vesicles fuse with the plasma membrane releasing their
contents out of the cell = exocytosis.
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Homeostasis
• Homeostasis, the ability to maintain constant internal conditions, is essential to
all cells.
• To stay alive, a cell must exchange materials such as food, water, & wastes with
its external environment.
• The plasma membrane helps cells maintain homeostasis by controlling what
substances move into and out of a cell.
• The plasma membrane helps maintain the balance of the following factors (just
to name a few):
• Body temperature
• pH
• Blood sugar levels
• A homeostatic mechanism is a mechanism that helps regulate substances to
maintain a state of equilibrium. Homeostatic mechanisms can assist in
thermoregulation, water regulation and oxygen regulation. What homeostatic
mechanisms exist to maintain the factors above? ….sweating, shivering,
increases in breathing rate, decreases in heart rate, or release of insulin to
control blood sugar levels.