passive cellular transport student edition...name: ___ period: _ date:___ passive cellular...

Name: _________________________________________________ Period: ___________ Date:________________

Passive Cellular Transport Guided Notes – Student Edition

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As cells perform their functions, they need to absorb _______________ and food from their environment and remove

_______________products. Thus, cells must have mechanisms to move materials in and out of the cell through the

________ ________________ .

The Cell Membrane Lipid Bilayer

Recall that the cell membrane (shown right) is a double-layered

structure made of _______________. This is called the “lipid

bilayer”. The phospholipids in the membrane have two parts:

a _______________ (attracted to water) head

a _______________ (repelled by water) tail

Along the membrane itself, the hydrophilic heads and tails will

align so that they are orientated in the same direction along each

of the two layers. This occurs because the phospholipids heads

are attracted to the watery _______________ on the inner side

of the membrane and the watery _______________fluid outside

the cell. The hydrophobic tails are repelled by the two watery

substances on the inside and outside of the cell and are therefore found with their tails pointing

_______________towards each other.

The arrangement of these molecules ensures that certain molecules such as _______________and _______________are

able to pass through, while other molecules are kept out. Therefore, the cell membrane is referred to as “semi” or

“_______________” permeable. Other structures inside the cell which also have membranes have a similar structure

surrounding them.

Other Structures found in the Cell Membrane

Cells also need other substances such as glucose, certain ions and other macromolecules to be brought into the cell.

Many of these cannot pass directly through the membrane and therefore require assistance to be absorbed. These

include:

Cholesterol – a _______________ molecule which is found embedded in both sides of the lipid bilayer. This

molecule prevents the membrane from becoming stiff by ensuring that the phospholipids are not too closely

packed together.

Name: _________________________________________________ Period: ___________ Date:________________



Glycolipids – these molecules have a

_______________attached to a

_______________ molecule and are found

randomly dispersed on the surface of the cell

membrane. These molecules are responsible for

recognizing other cells within the organism.

Glycoproteins – in a similar way that glycolipids

contain a carbohydrate and lipid molecule,

glycoproteins contain a _______________

attached to a _______________molecule. These

structures are essential for cell to cell _______________and assist with transport of molecules through the cell

membrane.

Peripheral proteins - are found on the exterior of the membrane and are attached there with hydrogen

bonds. These proteins maintain the cell’s cytoskeleton.

Channel/Integral proteins - are inserted into the membrane and extend through the membrane. These proteins

are often called _______________proteins as they assist specific molecules with entering and exiting the cell.

Globular proteins – also act as transporters during facilitated diffusion.

Structural proteins – provide the cell with support and _______________.

Alpha helix proteins – these are able to ‘plug’ any gaps in the phospholipid bilayer, ensuring that none of the

fatty acid tails are exposed to the watery substances on either side of the membrane.

Moving Molecules into and out of the Cell

The movement of substances into and out of the cell is called _______________ _______________. When this process

occurs without requiring energy expenditure, it is called _______________cellular transport. Passive cellular transport

relies on the _______________ _______________to move substances across the cell membrane as well as the

_______________energy of the particles involved. A concentration gradient occurs when there is a greater number of

particles of the same type in one area than another. The bigger the difference in concentration, the

_______________the concentration gradient will be. A steeper concentration means that passive transport will occur at

a much _______________rate than if the concentration gradient was not as steep.

Name: _________________________________________________ Period: ___________ Date:________________



There are three types of passive transport which are used to move particles into and out of the cell.

Diffusion

Diffusion is the ________movement of small or uncharged

particles from an area of ________concentration to an area of

________concentration. Molecules and ions are in constant

motion, which means that as they collide with each other they can

spread through a medium and spread out evenly. Once the

substance has fully dispersed through the medium it is said to be

at ________________. The image to the right shows an example

of how sugar (the solute) can diffuse through a beaker of water.

The image on the left shows how molecules diffuse through the

cell membrane. Initially, there is a ________concentration of

particles ________________ the cell (in the extracellular space),

creating a steep concentration gradient. However, over time as

the particles move through the cell membrane into the cell (the

intracellular space), the concentration gradient will ________ .

Once the same number of particles are in both the extracellular

and intracellular spaces ________________is reached.

Name: _________________________________________________ Period: ___________ Date:________________



Factors which affect the Rate of Diffusion

The previous paragraphs have already discussed concentration gradient. However, several other factors also affect

diffusion rates. These are:

The ________of the molecules – smaller molecules move ________than larger ones.

Temperature – temperature increases the ________energy of the molecules, making them move faster.

Membrane thickness – a thicker membrane means that molecules will take a lot ________to move through than

if the membrane was thinner.

The surface area of the cell – the ________the surface area of the cell, the more area is available for diffusion to

occur.

Surface Area to Volume Ratio

The surface area of a cell is defined as the area that is in contact with the ________________space. As the cell increases

in size, it's surface area will also ________________accordingly, allowing for greater diffusion. However, this change in

size also changes the cell’s ________________. In fact, increasing the size of the cell has a much greater effect on the

volume of the cell than it does on its surface area. If a cell becomes too large, substances are unable to reach the parts

of a cell that need them. The surface area to volume ratio of a cell is defined as the area on a cells

________________compared to the area inside the cell. Smaller cells have a much ________________ surface area to

volume ratio which allows for the efficient diffusion of substances throughout the entire volume of the cell.

Surface area to volume ratio can be used to justify the shape of many cells and cell surfaces. For example:

folds inside the mitochondria or the flat pancake-like structures inside chloroplasts provide a greater surface

area on which specific reactions can occur

folds in the lining of the human stomach or the tiny, finger-like projections that extend out from the intestinal

wall both act to increase the surface area without increasing the overall size or volume of the organ

Calculating Surface Area to Volume Ratio

Cells are often depicted as cubes for surface area to volume calculations, with their dimension in centimeters. For a ‘cell’

with sides of 1 cm in length, the ratio can be calculated as follows:

Surface area = 6 x area of a single side = ________________________

Volume = width x depth x height = ________________________

Surface area to volume ratio (SA:V) = ________________

Name: _________________________________________________ Period: ___________ Date:________________



Osmosis

___________is the diffusion of water through the

___________permeable membrane from a region of high

concentration to a region of low concentration. ___________

___________ are completely permeable to water, and the amount

of water in the environment has a large effect on the survival of a

cell. Water cannot be compressed and the pressure it creates when

inside the cell helps to keep the cell firm (or ___________).

There are 3 types of solutions that involve water, each of which

affects the cell differently:

1. Hypertonic Solutions

In a hypertonic solution, there is a ___________concentration of water inside the cell than outside the cell. A

hypertonic solution has ___________solute (salt, sugar, etc.) than the cell, which causes there to be

___________water in the solution. Water flows from an area of high concentration to an area of low concentration

and leaves the cell. This loss of water causes the cell to ___________.

In animal cells, the shriveling is called ___________. In plant cells, ___________ occurs, and the cell membrane

shrinks away from the cell wall. Death will result in both cells.

Name: _________________________________________________ Period: ___________ Date:________________



2. Hypotonic Solutions

In a hypotonic solution, the solution contains a higher

concentration of ___________than the cell. A hypotonic solution

has less ___________than the cell, and this causes the solution to

have ___________water than the cell. When a cell is placed in a

hypotonic solution, water flows from an area of

___________concentration to an area of

___________concentration and rushes into the cell. This causes the cell

to expand and possibly burst.

In animal cells, the cell bursts or will lyse, killing the cell. This is because

animal cells lack a cell wall to ___________the cell membrane. In plant

cells, the cell membrane is pressed up against the cell wall, but the cell

wall does not allow the cell to expand anymore and the plant cell does

not die.

3. Isotonic Solution

In an isotonic solution, there is the ___________concentration

of water on the outside of the cell as the inside of the cell. An

isotonic solution has the same amount of ___________as the

inside of the cell. Water moves at a constant rate into and out of

the cell, and the cell maintains its original shape.

In animal and plant cells, the cell keeps its shape when in an

isotonic solution. Most cells live in an isotonic environment, and

are able to maintain their water levels and survive.

Name: _________________________________________________ Period: ___________ Date:________________



Facilitated Diffusion

Some molecules, such as ___________are too large to pass through the cell membrane by simple diffusion. These

molecules require the assistance of other molecules such as ___________or carrier proteins which are found embedded

in the cell membrane. This process is called facilitated diffusion and is the movement of ___________ ___________from

an area of high concentration to an area of low using ___________in the cell membrane.

Glucose enters our cells from the bloodstream by ___________diffusion. These molecules are too large to pass through

the phospholipid bilayer and therefore require the assistance of a protein channel to help them enter the cell. These

protein “helpers” are extremely important; without them, our cells would not have glucose they need to carry out

cellular respiration.

passive cellular transport student edition...name: _____ period: _____ date:_____ passive cellular...

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