4-2 Cell Energy
From Sun to Cell
§ Nearly all
energy that fuels life comes from the sun
§ Plants capture
energy from the sun and change into food
§ This process is
called photosynthesis
§ Food, that
plants make, supplies them with energy
§ Food also
becomes a source of energy for the organisms that eat the plants
Photosynthesis
§
Plant cells have molecules that absorb light energy
§
These molecules are called pigments
§
Chlorophyll is the main pigment used in photosynthesis, which
gives plants their green color
§
Chlorophyll is found in chloroplasts
§
Plants use energy captured by chlorophyll to change carbon dioxide
and water into food
§
Food is the form of the simple sugar glucose
§
Glucose is a carbohydrate
§
Making glucose, plants have to convert the sun’s energy into a
form of energy that can be stored
§
Energy in glucose will be used by the plant’s cell
§
Photosynthesis also produces oxygen
Getting Energy from Food
§
Animal
cells have different ways of getting energy from food
§
One
way, uses oxygen to break down food
§
This
is called cellular respiration
§
Many
cells can get energy without using oxygen
§
This
process is called fermentation
§
Cellular
respiration will release more energy from a given food than fermentation will
Cellular Respiration
§
Respiration means “breathing”, but cellular respiration is
different from breathing
§
Breathing supplies the oxygen needed for cellular respiration
§
Breathing also removes carbon dioxide, which is a waste product of
cellular respiration, which is a waste product of cellular respiration
§
BUT, cellular respiration is a chemical process that occurs in
cells
§
Most complex organisms, such as plants and animals, obtain energy
through cellular respiration
§
During cellular respiration, food (such as glucose) is broken down
into CO2 (carbon dioxide) and H2O (water), and energy is
released
§
In animals, most of the energy released maintains body temperature
§
Some energy is used to form adenosine triphosphate (ATP)
§
ATP supplies energy that fuels cell activities
§
Most of the process of cellular respiration takes place in the
cell membrane of prokaryotic cells
§
BUT, in the cells of eukaryotes, cellular respiration takes place
mostly in the mitochondria
Connection
between Photosynthesis and Respiration
§ Photosynthesis transforms energy form the sun into glucose
§ During photosynthesis, cells use CO2 (carbon dioxide) to make glucose, and the
cells release O2 (oxygen)
§ During cellular respiration, cells use O2 to
break down glucose and release energy and CO2
§ Each process makes the materials that are needed for the other process to
occur elsewhere
Fermentation
§
When
muscle cells can’t get the oxygen needed for cellular respiration, they use the
process of fermentation to get energy
§
One kind
of fermentation happens in your muscles and produces lactic acid
§
This
buildup of lactic acid contributes to muscle fatigue and causes a burning
sensation
§
This
kind of fermentation also happens in the muscle cells of other animals and in
some fungi and bacteria
§
Another
type of fermentation occurs in some types of bacteria and in yeast, like bread
§
Yeast
forms carbon dioxide during fermentation. The bubbles of CO2 gas cause
the dough to rise and leave small holes in bread after it is baked.
4-1 Exchange
with the Environment
What is Diffusion?
§
What
will happen if you pour dye on to of a layer of gelatin?
§
It
is easy to see at first that the dye ends up where the gelatin begins
§
BUT,
over time, the line between the two layers will blur, as shown
§
This
is because everything, including the gelatin and the dye, is made up of tiny
moving particles
§
Particles
travel form where they are crowded to where they are less crowded
§
This
movement from areas of high concentration (crowded) to areas of low
concentration (less crowded) is called diffusion
§
Dye
particles diffuse from where they are crowded (near the top of the glass) to
where they are less crowded (in the gelatin)
§
Diffusion
also happens within and between living cells
§
Cells
do not need to use energy for diffusion
Diffusion of Water
§
Cells
of organisms are surrounded by and filled with fluids that are made mostly of
water
§
Diffusion
of water through cell membranes is very important to life processes
§
This
diffusion of water through cell membranes is given a special name----osmosis
§
Water
is made up of particles that are called molecules
§
Pure
water has the highest concentration of water molecules
§
Mixing
things, such as food coloring, sugar, of salt, with water, will lower the
concentration of water molecules
§
The
image on the left shows how water molecules move through a membrane that is
semipermeable
§
Semipermeable
means that only certain substances can pass through
§
The
image on the right shows liquids that have different concentrations of water
§
As
time goes by, the water molecules move from the liquid with the high
concentration of water molecules to the liquid with the lower concentration of
water molecules
The Cell and Osmosis
§
Osmosis is important to cell functions
§
Example: red blood cells are surrounded by plasma (made up of
water, salts, sugars, and other particles)
§
If red blood cells are in pure water, water molecules would flood into
the cells and cause them to burst
§
If red blood cells are put into a salty solution, the concentration of
water molecules inside the cell is higher than the concentration of water
outside which would make them shrivel up
§
Osmosis also occurs in plant cells
§
When a wilted plant is watered, osmosis makes the plant firm again
Moving Small Particles
§
Small particles, such as sugars, cross the cell membrane through
passageways called channels
§
Channels are made up of proteins in the cell membrane
§
Particles travel through channels by either passive or active transport
§
Movement of particles across a cell membrane without the use of energy by
the cell is called passive transport
§
During passive transport, particles move from an area of high
concentration to an area of low concentration
§
Diffusion and osmosis are examples of passive transport
§
The process of transporting particles that requires the cell to use
energy is called active transport
§
Active transport usually involves the movement of particles from and area
of low concentration to an area of high concentration
Moving Large Particles
§
Small particles cross the cell membrane by diffusion, passive transport,
and active transport
§
Large particle move into and out of the cell by processes called
endocytosis and exocytosis
Endocytosis
§
The active transport process by which a cell surrounds a large particle,
such as a large protein, and encloses the particle in a vesicle to bring the
particle into the cell is called endocytosis
§
Vesicles are sacs formed from pieces of cell
membrane
Exocytosis
§
When large particles, such as wastes, leave the cell, the cell uses an
active transport process called exocytosis
§
During exocytosis, a vesicle forms around a large particle within the
cell
§
The vesicle carries the particle to the cell membrane
§
Then the vesicle fuses with the cell membrane
and releases the particle to the outside of the cell
