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Cellular Transport
Bynum-Biology
Tuesday, September 8, 2015
Objective: SWBAT…
 Explain how the process of diffusion, passive transport, and active transport
occur and why they are important to cells.
 Predict the effect of a hypotonic, hypertonic, or isotonic solution on a cell.
Essential Questions:
1. Can you distinguish the difference between osmosis and diffusion with
respect to cellular function and ATP for removal of material?
2. Can you compare and contrast the two types of cellular transport?
Vocab you should know!
Osmosis isotonic
hypertonic
hypotonic
passive transport
facilitated diffusion active transport
endocytosis
exocytosis
Warm-up & Daily Writing
Tuesday, September 8, 2015
Writing Assignment
Excitement that never ends: Describe the last thing you got really excited about – the
butterflies in the stomach, giggling, can’t wait excited.
1.
2.
3.
4.
5.
6.
Warm-Up
In order for a cell to survive, what substances might need to get into a cell or out of
a cell?
Do you think it would be easier for you to get to a place by walking with the wind or
against the wind? Why?
Draw and label a phospholipid.
What is the most important characteristic of the cell membrane?
What is diffusion?
What is osmosis?
Homeostasis in a Cell
 Remember: Homeostasis is maintaining a stable internal balance.
 The cell membrane is structured with phospholipids that have proteins
embedded in them to help regulate homeostasis in a cell.
 The cell membrane is a semi-permeable (allowing certain things to
enter and exit the cell) barrier that surround the cells.
 The cell membrane is the cell organelle in ALL cells that regulate
homeostasis for the cell.
Osmosis: Diffusion of Water
 Recall: Diffusion is the movement of particles from an area of higher
concentration to an area of lower concentration.
 In a cell, water ALWAYS tries to reach an equal concentration on both sides
of the membrane.
 The diffusion of water across a selectively permeable membrane is called
osmosis.
 Regulating the water flow through a plasma membrane is an important factor
in maintaining homeostasis within the cell.
Osmosis: Diffusion of Water
 If you add sugar to water the water becomes sweeter. The number of sugar
molecules will increase and the number of water molecules will decrease.
 If two solutions of high sugar molecules and lower sugar molecules are
separated by a selectively permeable membrane that only allows water to
diffuse across, water flows to the side of the membrane where the water
concentration is lower.
During osmosis, water diffuses across a selectively permeable membrane. Notice that
the number of sugar molecules did not change on each side, but the number of water
molecules did.
Osmosis: Diffusion of Water
 The water will continue to diffuse until it is at equal concentration on both
sides of the membrane.
 Therefore, we know that the unequal distribution of particles
(concentration gradient) is one factor that controls osmosis.
Cells in an isotonic solution
 Most cells (unicellular and multicellular) are subject to osmosis because they
are surrounded by water solutions.
 In an Isotonic solution, the concentration of dissolved substances in the
solution is the same as the concentration of dissolved substances inside the
cell.
 The concentration of water is the same both inside the solution and inside
the cell.
 Cells that are in isotonic solutions do not experience osmosis and they
maintain normal shape.
Cells in an Hypotonic solution
 In an Hypotonic solution, the concentration of dissolved substances is
lower in the solution outside the cell than the concentration inside the cell.
 Therefore, there is more water outside the cell than inside.
 Cells in a hypotonic solution experience osmosis that causes water to move
through the plasma membrane to the inside of the cell.
 This causes the cell to swell and its internal pressure increases.
 In animal cells If the solution is extremely hypotonic the plasma membrane
maybe unable to withstand the pressure and can burst.
 Because plant cells contain a cell wall, they do not burst in a hypotonic
solution. Where does this occur at in daily life?
Cells in an Hypertonic solution
 In an Hypertonic solution, the concentration of dissolved substances
outside the cell is higher than the concentration inside the cell.
 Meaning, the concentration of water is higher on the inside of the cell.
 Cells in hypertonic solution experience osmosis that causes water to flow
out.
 In animal cells, hypertonic solutions shrivel because of the decreased
pressure in the cells. (This is why you should not salt meat – it will cause the
water to leave the meat leaving it dry & tough)
 Plant cells, in hypertonic environment mainly loose water from the central
vacuole. The plasma membrane will shrink away from the cell wall. The loss
of water will result in a drop of pressure – explaining why plants wilt.
Passive Transport
 Water and lipids are some of the substances that can pass through the
membrane via diffusion.
 The cell uses no energy to move these particles. Therefore, this movement
of these particles by diffusion is called passive transport – because it
requires no energy to move the particles.
 Particles that move via passive transport are moving WITH the gradient.
 Proteins can move substances through the membrane via transport
proteins. These proteins function in variety of ways to transport molecules.
 The passive transport of materials across the membrane with the aid of
transport proteins is called facilitated diffusion.
Active Transport
 A cell can move particles from a region of lower concentration to a region of
higher concentration, but it will require energy to counteract the force of
diffusion that is moving from the opposite direction.
 The movement of particles against the concentration gradient (from low
concentration to high concentration) is called active transport and it
requires energy from the cell.
 Some cells can take in large molecules, groups of molecules, or even whole
cells.
 Endocytosis, is a process by which a cell surrounds and takes in material
from its environment. This material does not pass through the membrane
instead it is engulfed and enclosed by a portion of the membrane. That
portion of the membrane breaks away and the resulting vacuole with its
contents move inside the cell.
 Exocytosis, is the expulsion or secretion of materials from a cell. Cells use
exocytosis to expel waste and secrete substances, such as hormones
produced by a cell.
Concept Check On a separate piece
of paper – answer the following questions for class work
1. What factors affect the diffusion of water through a membrane by osmosis?
2. How do animal cells and plant cells react differently to osmosis in hypotonic
and hypertonic solutions.
3. Compare and contrast active and passive transport.
4. Draw a cell that is in a isotonic, hypertonic, and hypotonic solution. Draw
what the cell is like before and after diffusion. Be sure to include labels for
the direction of the flow of water.
5. Compare and contrast endocytosis and exocytosis. Why would a cell use
either of these processes?