Chapter 8
Life Science
Name ______________________________
Cell Processes
1. Cell Membrane – The cell membrane surrounds the cell. It is made from a double layer of lipids
(fats). This creates a thin fluid membrane similar to a soap bubble. The cell membrane has many
functions. They include: 1. Protecting the cell. 2. Taking in food, water, & other compounds.
3. Getting rid of waste. 4. Communication with other cells. (156)
2. Selectively Permeable – When a material allows only certain things to pass through it is
called selectively permeable. The cell membrane is selectively permeable.
3. Diffusion & Passive Transport – Movement of molecules from an area of high
concentration (many) to low concentration (few) is called diffusion. The cell uses no
energy during diffusion so it is called passive transport. It usually involves small
molecules only (water, oxygen, carbon dioxide). Heat can speed the process of
diffusion. (157)
4. Equilibrium – When molecules are spread equally on each side of the cell membrane diffusion
stops. This is called equilibrium. When equilibrium is reached molecules continue to move
around randomly but movement from high concentration to low concentration no longer
happens. (157)
5. Osmosis – The diffusion of water molecules across a cell membrane is called osmosis. If the
solution outside a cell has a higher concentration of water molecules (pure water) than the inside
more water diffuses into the cell than out. This causes the cell to swell. If a solution outside the
cell has a lower concentration of water molecules (salt water, sugar water) than inside the cell
more water will diffuse out than in. This causes the cell to shrink. (158)
Note: Plant cells can take in more water than animal cells because of their strong cell
walls.
6. Protein Channels (carrier proteins) - Larger molecules like sugar, starch and some proteins
have to diffuse into the cell through protein channels (carrier proteins). Because this is still
diffusion the cell again does not use any energy. (159)
7. Active Transport – When molecules move across the cell membrane from lower concentrations
(less) to higher concentrations (more) this is called active transport. It requires the cell to use
energy. Protein molecules (channels) in the cell membrane work as “pumps” to force the
molecules into the cell.
Note: Although sugar can diffuse it is often brought in to cells by active transport. This
will be discussed in class.(159)
8. Endocytosis & Exocytosis – Endocytosis is a form of active transport where extremely large
molecules are transported into the cell. They are engulfed by a “fold” of the cell membrane,
which then breaks off and becomes a vacuole inside the cell. In exocytosis, also a form of active
transport, a vacuole holding large particles breaks of from fuses with the cell membrane, which
then opens up and pushes the material out. Many large materials are released through the cell
membrane this way.
Note: Golgi bodies assist in these processes by transporting large molecules (such as protein)
back and forth from the inside of the cell to the cell membrane. (159)
9. Photosynthesis – Photosynthesis is he process where plants use the energy from the sun (sunlight)
to produce carbohydrates (a simple sugar called glucose). Photosynthesis happens in the
chloroplasts of the cell. Carbon dioxide and water are the reactants used in the reaction. These
reactants are changed into the products of glucose (sugar) and oxygen. Plants can then use the
glucose (sugar) for energy when they need it. (162)
Note: The carbon dioxide used in photosynthesis enters the leaf on the bottom side through openings
called stomates. Oxygen, left over after the process, is released out the same
openings into the air. Humans & all other animals can then use the oxygen for life processes.
10. Producers & Consumers – Because plants produce their own food (glucose) during
photosynthesis they are called producers. Remember that plants are also the beginning of every
food chain. Consumers are animals that have to eat other organisms (plants or animals) to get
their energy. They cannot produce their own food like a plant does.
11. Pigment – A molecule that absorbs some colors of light but reflects others is called a pigment.
(164)
12. Chlorophyll – The main pigment used in photosynthesis is the green pigment called
chlorophyll. It is the chlorophyll that allows plants to make their own food. It is found in the
chloroplasts of the cell. Chlorophyll absorbs/traps mostly blue and red light, and reflects green.
This is why most plants are green. Plants need red and blue light to grow. When the days get
shorter in the fall photosynthesis slows down and chlorophyll begins to break down. It will no
longer mask (hide) the other pigments in the leaves so the trees change color and the leaves fall.
(164)
13. Cellular Respiration & ATP – The energy releasing process in both plants and animals is
called respiration. Cellular respiration is the process in which the chemical bonds in energy-rich
food molecules are broken apart and then converted into energy. In eukaryotic cells this takes
place in the mitochondria. In the process the reactants glucose (sugar) and oxygen are converted
into the products of carbon dioxide, water, and energy. Part of the energy released is in the form
of a molecule that stores and transfers the energy within the cell. It is called ATP. Energy is also
released and lost in the form of heat. Your body is warm because of that heat. (165)
14. Respiration – The act of breathing is called respiration. When you inhale you bring in the
oxygen needed for cellular respiration. When you exhale you get rid of carbon dioxide and water
vapor produced as wastes during cellular respiration. (165)
15. Fermentation – A form of respiration that converts energy from glucose when oxygen is in
low supply is called fermentation. This process only produces small amounts of energy and
leaves behind a substance called lactic acid. Lactic acid is what makes your over-worked muscles
sore after a hard workout. Fermentation is also used to make some foods and beverages because
of the alcohol and carbon dioxide which are given off as wastes during the process. Yeast cells
are used in this process (bread, wine, & beer).
16. Metabolism – All the chemical activities & changes within the cell of an organism that allow
it to stay alive, grow, & reproduce is called the cell metabolism. Cellular respiration,
fermentation. and photosynthesis are part of a cell’s metabolism.
17. Comparing Plants and Animals – Plants use carbon dioxide and water during photosynthesis,
and produce glucose and oxygen. Animals use glucose and oxygen during cellular respiration
and produce carbon dioxide and water as wastes. This shows that we depend on each other for
the materials we need for our life processes.
Remember: Plants use small amounts of oxygen and glucose during cellular respiration just like
we do. (167)