View
1
Download
0
Category
Preview:
Citation preview
Name: _________________________________________________ Period: ___________ Date:________________
Passive Cellular Transport Guided Notes – Student Edition
Copyright © iTeachly.com 1
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:________________
Passive Cellular Transport Guided Notes – Student Edition
Copyright © iTeachly.com 2
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:________________
Passive Cellular Transport Guided Notes – Student Edition
Copyright © iTeachly.com 3
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:________________
Passive Cellular Transport Guided Notes – Student Edition
Copyright © iTeachly.com 4
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:________________
Passive Cellular Transport Guided Notes – Student Edition
Copyright © iTeachly.com 5
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:________________
Passive Cellular Transport Guided Notes – Student Edition
Copyright © iTeachly.com 6
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:________________
Passive Cellular Transport Guided Notes – Student Edition
Copyright © iTeachly.com 7
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.
Recommended