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Chapter 5
The Cell in Action
Section 1: Exchange with
the Environment
 A cell must be able to obtain energy
and raw materials and get rid of
wastes
 This exchange of materials takes
place at the cell’s membrane
What is Diffusion?
 Matter is made up of tiny particles
 Particles of matter are always moving
and colliding with each other
 Particles naturally travel from areas where
they are crowed to areas where they are
less crowded - diffusion
 Diffusion - the movement of particles
from an area of high concentration to an
area of low concentration
Diffusion of Water
 All organisms need water to live
 Cells are surrounded by and filled with
fluids (mostly water)
 The movement (diffusion) of water
through the cell membrane is called
osmosis
 Because osmosis is diffusion, water moves
from areas of high concentration to areas of
low concentration
 Like animal cells, plant cells also
take in and release water by osmosis
 What would happen to a grape if
you placed it in a dish of pure
water?
 What would happen to it if you
placed it in water mixed with a large
amount of sugar?
Moving Small Particles
 Many particles are too large to “slip”
past the molecules of the cell
membrane
 i.e. amino acids and sugars must pass
through protein “doorways” located
within the membrane
 They can travel through these
proteins either by passive or active
transport
 Passive transport - is the diffusion of
particles through membrane
proteins
 This does not require energy
 Active transport - is the movement
of particles through membrane
proteins against the normal direction
of diffusion
 This requires energy (ATP)
Moving Large Particles
 The cell can also move particles into
and out of the cell that are too large
to pass through membrane proteins
 Endocytosis - when the cell
membrane surrounds a particle and
encloses it in a vesicle
 Exocytosis - vesicles are formed
carrying particles to the cell
membrane to be removed
Section 2: Cell Energy
 Why do you get hungry?
 Feeling hungry is your body’s way of
telling you that your cells need energy
 FROM SUN TO CELL
 All energy that fuels life comes from the
sun
 Plants are able to capture the energy
of the sun and store it in sugars
(glucose)
Photosynthesis
 The process of capturing light energy and
changing it into food is called photosynthesis
 Photosynthesis means “made by light”
 Plants have molecules in their cells that
capture light - pigments
 Chlorophyll - the main pigment found in plant
cells
 Chlorophyll is found in the chloroplasts
http://www.hsv.k12.al.us/schools/middle/wtms/student/cell/cell_energy.html
 Plants use the energy captured by
chlorophyll to change carbon
dioxide (CO2) and water (H20) into
food (C6H12O6) and oxygen (O2).
 Glucose (C6H12O6) is a carbohydrate.
 The glucose can be used by the
plant or stored as energy in the form
of other carbohydrates or lipids.
Getting Energy from Food
 Cells get energy from the food you
eat
 But they can’t get it directly from a
banana or a piece of pizza
 All organisms must break down food
molecules in order to release energy
 There are two ways to do this:
 1) Cellular Respiration
 2) Fermentation
Cellular Respiration
 Most organisms use cellular
respiration to obtain energy that is
stored in food
 C.R. breaks down glucose, in the
presence of oxygen, into carbon
dioxide and water, which releases
energy
This energy is then converted and stored as
ATP, which is eventually used by the cells
 Does the equation for respiration
remind you for the equation for
photosynthesis?
 Let’s take a look
Fermentation
 Have you ever run so far or fast that your
muscles start to burn?
 This happens because your muscle cells can’t
get the O2 it needs to produce ATP by cellular
respiration
 Your body then uses fermentation
 Fermentation leads to the production of a
small amount of ATP
 There are two types:
 1) Lactic Acid - occurring in your muscles
 2) Alcoholic - occurring in bacteria and yeast
Section 3: The Cell Cycle
 In the time it takes you to read this
sentence, your body will have
produced a millions of new cells!
 Producing new cells allows you to
grow and replace cells that have
died
 i.e. The environment in your stomach is
so acidic that the cells lining it have to
be replaced every week!
The Life of a Cell
 Cell cycle - the life cycle of a cell
 The cell cycle begins when the cell is
formed and ends when the cell divides
to form a new one
 Before a cell divides it must make an
exact copy of all its DNA and
organelles
 DNA in a cell is organized into structures
called chromosomes
Making More Prokaryotic
Cells
 Prokaryotic cells (bacteria) and their
DNA are not very complex
 Bacteria have ribosomes and a singular
circular DNA
 Because of this division of bacteria
cells is simple - binary fission
 Binary fission means “splitting in two”
Eukaryotic Cells and Their
DNA
 Eukaryotic cells are much larger and
more complex than prokaryotic cells
 Because of this eukaryotic cells have a lot
more DNA
 The total number of chromosomes in
eukaryotic cells varies from organism to
organism
 i.e fly - 8, potato - 48, and human - 46 (23
pairs)
 Pairs of similar chromosomes are called
homologous chromosomes
Making More Eukaryotic
Cells
 The eukaryotic cell cycle has three main
stages
 In the first stage, the cell grows and
copies its organelles and chromosomes
(DNA)
 After each chromosome is duplicated, the
two copies are held together at a region
called the centromere and are called
chromatids
 In the second stage, the chromatids
separate
 The complicated process of
chromosome separation is called
mitosis
 Mitosis ensures that each new cell
receives a copy of each chromosome
 Mitosis can be divided into four
phases
 In the third stage of the cycle, the
cell divides and produces two cells
that are identical to the original cell
Mitosis and the Cell Cycle
 Although mitosis is a continuous
process, it can be divided into four
phases;
 Phase 1 - prophase
 Phase 2 - metaphase
 Phase 3 - anaphase
 Phase 4 - telophase
Before Mitosis
 Before mitosis begins, the
chromosomes, organelles, and
centrioles are copied.
 Each chromosome now consists of
two chromatids
Mitosis Phase 1
 The nuclear membrane breaks
apart
 The two centrioles move to opposite
sides of the cell
 Fibers form from the centrioles and
attach to the centromeres
Mitosis Phase 2
 The chromosomes line up in the
middle (equator) of the cell
Mitosis Phase 3
 The chromatids separate and are
pulled to opposite sides of the cell
by the fibers attached to the
centrioles
Mitosis Phase 4
 A nuclear membrane forms around
each set of chromosomes
 The fibers disappear
 Mitosis is complete
Cytokinesis
 In eukaryotic cells that do not have a cell
wall, division of the cytoplasm begins at
the cell membrane
 The cell membrane will eventually pinch
all the way through the cell until there are
two
 In eukaryotic cells with a cell wall, a cell
plate forms in the middle of the cell and
becomes the new cell membranes that
will separate the cell.
 Once the cell is split a new cell wall forms
 http://bhs.smuhsd.org/bhsnew/aca
demicprog/science/vaughn/Studen
t Projects/Paul &
Marcus/Cell_Replication.html