Chapter 4Cells and their Environment

Mrs. Cook

Biology

Cell Structure Cont.• Cell Membrane

- primarily made of lipids- makes a barrier that separates the

outside of the cell from the inside of the cell- it allows only certain substances in the

environment to pass through, “selectively permeable”

Lipid Bi-layer-phosolipids are arranged in a double

layer-non-polar tails make up the interior of

the bi-layer. - “Hydrophobic” -polar heads make up the outside of the

bilayer. - “Hydrophilic”

Cell Structure cont. • Phospholipid bi-layer contains several types of

Membrane Proteins1. Marker Proteins- attached to carbohydrate on

cell surface and advertise cell type- heart cell, liver cell, etc.

2. Receptor Proteins- recognize and bind to substances outside the cell. Ex: hormones

3. Enzyme- assist in chemical reactions inside the cell.

4. Transport Proteins- move substances into and out of the cell.

Fluid Mosaic Model http://www.youtube.com/watch?v=Rl5EmUQdkuI

Homeostasis • http://www.youtube.com/watch?v=gxoDUz_UMMg

Homeostasis

• Your body responds to external conditions to maintain a stable internal condition.

• When an organisms adjusts internally to changing external conditions they are maintaining Homeostasis.

• How cells maintain homeostasis is by controlling movement of substances across their cell membrane.

• Water

• CO2

• O2

• Na+

• K+

Homeostasis

• Either by transporting substances using energy- called active transport.

• Or with out the use of energy- called passive transport.

Passive Transport

-When substances enter or leave a cell without the use of any energy.

•1st type of Passive Transport is Diffusion-

-is the movement of molecules from an area of higher concentration to an area of lower concentration

https://www.youtube.com/watch?v=VY0mZUDvbH4

Passive Transport- Diffusion cont

• This difference in the concentration of molecules across a distance is called a concentration gradient

• Is driven by the molecules’ kinetic energy. Molecules are constantly in motion because they have kinetic energy.

• Moving from an area of high to low is called “moving down” the concentration gradient

• Like swimming with the current

Passive Transport- Diffusion cont• Diffusion will eventually cause the molecules to be in

equilibrium when the concentration of molecules will be equal throughout the space they share.

• Diffusion across a membrane, if molecules are small enough to pass is call simple diffusion.

http://www.youtube.com/watch?v=6yMPpDeNwqQ

Passive Transport- Osmosis

• 2nd Type of Passive Transport is Osmosis-

-Is the diffusion of water molecules - Osmosis is the passive transport of water!- The direction of Osmosis does NOT REQUIRE

ENERGY!!

Passive Transport- Osmosis

• Solute- A substance dissolved in another substance creating a solution.

• Solvent- as substance that dissolves a solute, can be a liquid or a gas- is usually water.

Example:- sugar dissolved in water• Sugar is the solute• Water is the solvent

- salt water• Salt is the solute• Water is the solvent

Passive Transport- Osmosis

• The cell membrane• Remember it is selectively permeable! This

means it is only going to allow certain substances in and out of the cell.

• Water can move by passive transport in and out of the cell depending on the concentration of solute either inside or outside the cell.

http://www.youtube.com/watch?v=sdiJtDRJQEc

Passive Transport- Osmosis cont.

• When the concentration of solute molecules outside the cell is LOWER than the concentration in the cytosol, the solutions outside is HYPOTONIC to the cytosol; water will diffusion into the cell until equilibrium is reached.

Water outside the cell.

Sugar and water inside the cell

Water moves into the cell

http://www.youtube.com/watch?v=5FMLz_qmg9Y

Passive Transport- Osmosis cont.

• When the concentration of the solute molecules outside the cell is HIGHER than the concentration in the cytsol, the solution outside is HYPERTONIC to the cytosol; water will diffuse out of the cell until equilibrium is reached.

Water inside the cell.

Sugar and water outside the cell

Water moves out of the cell

http://www.youtube.com/watch?v=Ym1rvwP-po4 Hypertonic RBCs

Passive Transport- Osmosis cont.

• When the concentration of solutes outside and inside the cell are EQUAL, the outside solution is said to be ISTOTONIC to the cytosol and there is no net movement of water molecules.

Sugar and water outside the cell

Sugar and water inside the cell

Water moves in and out of the cell

http://www.youtube.com/watch?v=7-QJ-UUX0iY&feature=youtu.be

How Cells Deal with Osmosis

• Many animals live in hypotonic environments. If they take in too much water their plasma membrane could burst!

• To deal with this they have an adaptation called a contractile vacuole.

• Contractile Vacuoles are organelles, which remove water by pumping it out of the cell. This pumping is different than osmosis or diffusion because it does require ENERGY from the cell.

http://www.youtube.com/watch?v=9Ynm5ZOW59Q

http://www.youtube.com/watch?v=-6cNX-DpVJw

How Cells Deal with Osmosis

• Some animals cells do not have contractile vacuoles, such as red blood cells. If they take in too much water they will eventually burst.

• The bursting of cells is called cytolysis.

Which solution will cause cytolysis?

http://www.youtube.com/watch?v=psUt9zrACL8

How Cells Deal with Osmosis

• Plant cells have cell walls strong enough to resist the water pressure, called TURGOR PRESSURE.

• When Plants are in HYPERTONIC environments and lose water they also lose their Turgor Pressure and wilt. This process is called plasmolysis.

http://www.youtube.com/watch?v=VK-_YHakvho

http://www.youtube.com/watch?v=gWkcFU-hHUk

3rd Type of Passive Transport is Facilitated Diffusion• When molecules CAN NOT MOVE through cell

membranes even when there is a concentration gradient they go through FACILITATED DIFFUSION.

• The molecules are assisted through the membrane through proteins called carrier proteins.

• Carrier proteins still move molecules from an area of high to low concentrations and therefore do not use energy.

• Carrier proteins are used to transport specific substances such as amino acids and sugars.

Facilitated Diffusion occurs in 4 steps

1. A molecule binds to a carrier protein on one side of the cell membrane.

2. The carrier protein changes shape, shielding the molecule from the interior of the membrane.

3. The molecule is released on the other side of the membrane.

4. The carrier protein then returns to its original shape.

Step 1.

Step 2

Step 3

Step 4

http://www.youtube.com/watch?v=OV4PgZDRTQw

http://www.youtube.com/watch?v=I4123hUU8xo

http://www.youtube.com/watch?v=faXBWOETTb4

Diffusion through Ion Channels

• Another type of transport involves membrane proteins known as ION CHANNELS.

• They transport ions such as sodium (Na+), potassium (K+), calcium (Ca+), and Chloride (Cl-) from areas of HIGH to LOW concentrations.

• Ion Channels are for specific ions

• Some are always open and others have “GATES” that open or close.

Active Transport

• When energy is required to move substances into or out of the cell.

• Uses energy molecule ATP (adenosine triphosphate)• Molecules are moving from LOW to HIGH concentrations

or “UP” (or “against”) their concentration gradients.

- like swimming against the current

Active Transport- Sodium-Potassium Pump

• Sodium Potassium Pump-• Active transport in animal cells involving a carrier

protein• Transports Na+ ions and K+ ions up their

concentration gradients because higher concentrations are needed.

Active Transport- Sodium-Potassium Pump

• Creates an electrical gradient across the cell membrane • Outside becomes positively charged and inside becomes

negatively charged • This is important for sending electrical signals by nerve

cells.

Active Transport- Sodium-Potassium Pump

• FOUR STEPS to active transport

1. THREE sodium ions inside the cell bind to the sodium-potassium pump. ATP is used for energy and loses a phosphate to become ADP (adenosine diphosphate.

Active Transport- Sodium-Potassium Pump

2. The pump changes shape, transporting the three sodium ions across the cell membrane.

Active Transport- Sodium-Potassium Pump

3. Two potassium ions, K+, bind to the pump and are transported across the cell membrane.

Active Transport- Sodium-Potassium Pump

4. The phosphate group and the two potassium ions are released inside the cell.

Active Transport- Sodium-Potassium Pump

34

3 Na+ bind to the pump

Pump transports Na+ out of the cell

2 K+ bind to the pump

K+ realeased into the cell

http://www.youtube.com/watch?v=GTHWig1vOnY

http://www.youtube.com/watch?v=9CBoBewdS3U

Movement in Vesicles

• Many substances, such as proteins and polysaccharides, are too big to be transported by carrier proteins.

• These substances are moved across the cell membrane by vesicles.

Movement in Vesicles- Endocytosis

• Endocytosis-- Is the process by which cells ingest external fluid,

macromolecules and large particles, including other cells.

- Uses vesicles to move their particles into the cell

Two Types of Endocytosis:

1. Pinocytosis: involves the transport of solutes or fluids.

2. Phagocytosis: involves the transport of large particles or whole cells.

Particles to be transported into the cell

A vesicle is formed around the particles

The particles are carried across the membrane and into the cell

Movement in Vesicles- Exocytosis

• Exocytosis-- Is the process by which a substance is released from

the cell though a vesicle

- Is basically the reverse of endocytosis

- May be used to release large molecules such as proteins, waste products, or toxins that would damage the cell if released in the cytosol.

A vesicle is formed around the molecules

The vesicle attached to the cell membrane

The molecules are released from the cell

http://www.youtube.com/watch?v=4gLtk8Yc1Zc

http://www.youtube.com/watch?v=FJmnxbYBlr4

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