Download Chapter 8 - Holden R-III School District

Chapter 8
Cellular Transport &
the Cell Cycle
8.1 Cellular Transport-Osmosis
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Diffusion- the movement of particles from
an area of higher concentration to an area
of lower concentration (review)

Osmosis-the diffusion of water across a
selectively permeable membrane
The water will move from the area of higher water
concentration to an area of lower water
concentration
 The difference in concentrations across the semipermeable membrane is called a concentration
gradient

8.1 Osmosis & Solution Types
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Isotonic Solution- a solution in which the
concentration of dissolved substances outside
the cell is the same as the concentration of the
dissolved substances in the cell
Hypotonic solution- a solution in which the
concentration of dissolved substances outside
the cell is lower than the concentration of the
dissolved substances in the cell
Hypertonic Solution- a solution in which the
concentration of dissolved substances outside
the cell is higher than the concentration of the
dissolved substances in the cell
8.1 Cell Response

The cell will respond differently depending on
the type of solution it is in:
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In an isotonic solution, there will be no visible
changes because water is moving in both directions
across the membrane at the same rate
In a hypotonic solution, the water will move into the
cell, causing the cell to increase in size
In a hypertonic solution, the water will move out of
the cell, causing the cell to decrease in size
8.1 Passive Transport

Passive transport is the movement of substances
across the cell membrane without the use of
energy
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Water moving across the plasma membrane is
considered to be simple diffusion and is classified as
passive transport
In facilitated diffusion, carrier or channel proteins
move substances across the membrane with the
concentration gradient and is also considered passive
transport
8.1 Active Transport

Active transport is the movement of materials
across a membrane that requires energy

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Carrier proteins that move substances across a
membrane against the concentration gradient are
exhibiting active transport
In this process, carrier proteins bind to the substance,
then change shape in order to release the substance
on the other side, before returning to their original
shape.
8.1 Transport of Large Particles

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Cells can also absorb or release
substances without using the plasma
membrane to do so:
Both are considered to be active transport,
as they require energy


Endocytosis: a process by which a cell
surrounds and takes in a material from its
environment
Exocytosis: a process by which materials are
expelled or secreted from a cell
8.2 Cell Growth & Reproduction
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Most cells are between 2 and 200
micrometers (1 micrometer = 1 millionth
of a meter)
Cell efficiency is related to cell size

Larger cells are less efficient

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This is because they have a smaller surface area to
volume ratio
Smaller cells are more efficient

This is because they have a larger surface area to
volume ratio
8.2 Cell Size

The amount of DNA can limit the size of a
cell

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If there is not enough DNA to support the
needs of the cell, the cell does not grow
As a cell gets bigger, the plasma
membrane has to move exponentially
increasing amounts of substances into and
out of the cell

Eventually, the plasma membrane won’t be
able to keep up
8.2 Cell Division

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Cells will divide before they get too big in
order to prevent the problems associated
with being too big
Cell division is the process by which new
cells are produced from one cell

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It results in 2 cells that are identical to the
first cell
Cell division must take place in order to
replace the cells that are dying
8.2 Chromosomes

Chromosomes were first observed as short,
stringy structures that appeared suddenly and
vanished right after cell division
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These structures contain DNA, which is copied and
passed from generation to generation
Most of the time, they are chromatin, strands of DNA
wrapped around histones, a type of protein
The chromatin must organize before cell division can
occur
8.2 The Cell Cycle

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The cell cycle is the sequence of growth
and division of a cell
There are 2 general phases in the cell
cycle

Interphase- when a cell grows and carries on
metabolism

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Interphase occurs during most of a cell’s lifespan
Mitosis- cell division when 2 daughter cells are
formed

The cytoplasm divides after mitosis to separate the
2 new cells
8.2 Interphase
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Interphase is divided into 3 parts:
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The cell grows rapidly and produces lots of
protein
The cell copies its chromosomes (DNA
synthesis & replication)
The cell manufactures organelles, and
Centrioles replicate
8.2 Mitosis
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When cells reach their maximum size,
they undergo mitosis
Mitosis has 4 phases:
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Prophase
Metaphase
Anaphase
Telophase
8.2 Prophase
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Prophase is the 1st phase of mitosis (and the
longest)
In prophase:

The chromatin coils into chromosomes, which have 2
halves, called sister chromatids, held together by a
centromere
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The nucleus, nucleolus, and nuclear envelope begin
to disappear
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Sister chromatids contain 2 exact copies of the DNA
By the end of prophase, they are gone
In animal cells: centrioles move to opposite ends of
the cell and the spindle forms between them
In plant cells: the spindle forms without the presence
of centrioles
8.2 Metaphase
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Metaphase is the 2nd phase of mitosis
In metaphase:

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The doubled chromosomes attach to the
spindle fibers by the centromeres
The chromosomes line up at the middle of the
spindle with one sister chromatid pointing to
each side of the cell
8.2 Anaphase

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Anaphase is the 3rd phase of mitosis
Anaphase starts with the separation of the
sister chromatids
In anaphase:

The centromeres split apart and the
chromatid pairs separate

They are pulled apart due to the shortening of the
microtubules in the spindle fibers
8.2 Telophase
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Telophase is the 4th phase of mitosis
In telophase:
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It starts when the chromatids reach the opposite
sides of the cell
The chromosomes unwind
The spindle disappears
The nucleolus reappears and the nuclear envelope
starts forming around each set of chromosomes
A new membrane starts to form between the 2 new
nuclei
8.2 Cytokinesis
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Following telophase, the cell undergoes
cytokinesis, when the cell’s cytoplasm
divides
In plants: a cell plate forms in telophase
and forms new cell walls
In animals: the plasma membrane folds in
to touch in the center
8.2 Results of Mitosis
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In unicellular organisms: after mitosis,
they remain as single cells
In multi-cellular organisms: after mitosis,
cell growth and reproduction results in the
specialization of cells to form tissues,
which form organs, which work together
to form organ systems, which are
necessary for multi-cellular organisms
8.3 Regulating the Cell Cycle
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The cell cycle is regulated by a
combination of enzymes, called cyclins,
and proteins that are activated when they
attach to the cyclin
The cell cycle can run out of control if the
body does not produce the right enzymes,
produces too much or too little of a certain
enzyme, or produces enzymes at the
wrong time
8.3 Cancer
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Cancer is the result of uncontrolled cell division
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Scientists believe that one or more of the genes that
produce the enzymes or proteins involved in the cell
cycle changes
This uncontrolled cell division usually starves
surrounding cells of their nutrients
While scientists can’t pinpoint a cause of cancer, it
appears to be a combination of environmental and
genetic factors

They do agree, however that a diet low in fats and high in
fiber can reduce the risk