Life Science: Standard 3- Flow of Matter and Energy
Section 1: Photosynthesis & Cellular
Respiration
Photosynthesis and cellular respiration are the two main processes by which organisms
acquire energy and release energy. These processes are complementary to one another.
Photosynthesis
Photosynthesis occurs within the chloroplast of a cell.
Chloroplasts are cellular organelles that are shaped like flattened discs. They contain stroma
and stacks of thylakoids, and they are the site of photosynthesis. Chloroplasts are found in
the cells of plants and other eukaryotic, photosynthetic organisms.
During photosynthesis, light energy is converted to chemical energy when green plants
capture sunlight and use it to build sugars out of carbon dioxide and water.
The process of photosynthesis can be generally expressed by the equation:
carbon dioxide + water + light energy sugar + oxygen
During photosynthesis, plants absorb water from the soil through their roots and carbon
dioxide from the air through stomata in their leaves. Then, they convert the water and
carbon dioxide into sugar and oxygen within their chloroplasts.
The sugar (food) that is produced through photosynthesis may be used immediately by the
plant for its normal life functions, or it can stored by the plant for later usage. If an animal
eats the plant, then the sugar from the plant may be used to nourish the animal.
Section 2: Carbon-Oxygen Cycle
Carbon and oxygen are necessary for all organisms. These elements move between
producers, consumers, and the atmosphere in a continuous biogeochemical cycle.
The carbon and oxygen cycles are sometimes discussed separately. However, these cycles
can also be addressed together since they are dependent upon each other for proper
operation. This combined, interdependent cycle is known as the carbon-oxygen cycle.
There are several processes that either store carbon dioxide or release it into the
environment.
Processes that Release Carbon Dioxide into
the Atmosphere
◦Cellular respiration is a natural process in which substances are broken down to create
energy.
◦Decay is a natural process in which organic matter, like dead organisms, decomposes or
breaks down.
◦Volcanic activity is a natural process involving the eruption of hot gases and rock material
from within the Earth.
◦Weathering is the process by which stones at the Earth's surface are broken down, either
physically or chemically.
◦Combustion is a reaction in which a substance burns in oxygen.
•It can be natural, such as a forest fire started by lightning.
•It can be man-made, such as burning wood and fossil fuels.
◦Degasification is the release of carbon dioxide, once dissolved in water, into the air. It is a
natural process, but it has increased due to higher global temperatures. Warm water can
hold less dissolved gases than cooler water. This is why a can of soda goes flat when it gets
warm.
Processes that Store Carbon Dioxide
◦Photosynthesis is a natural process in which carbon dioxide and water are converted into
sugar.
◦Sedimentation is a natural process in which pieces of rock and other matter settle out of
water and are buried.
◦Dissolution is a natural process in which carbon dioxide from the atmosphere dissolves into
water.
Photosynthesis & Respiration
The two most important natural processes that drive the carbon-oxygen cycle are
photosynthesis and cellular respiration. Each of these processes must take place in order for
the cycle to function properly. This is because the end products of one process are starting
materials for the other.
Photosynthesis:
carbon dioxide + water → sugar + oxygen
The end products of photosynthesis are sugar and oxygen. These substances are the
starting materials of cellular respiration.
Cellular Respiration:
sugar + oxygen → carbon dioxide + water
The end products of cellular respiration are carbon dioxide and water. These substances are
the starting materials of photosynthesis.
Section 3: Gas Exchange
Organisms require the exchange of gases with their environment for various life processes,
such as respiration. There are a few structures which allow organisms to release and absorb
the gases they need to survive.
Respiration
During respiration, glucose molecules are broken down to releases energy. The chemical
reaction of the breakdown of glucose is summarized as follows:
glucose + oxygen → carbon dioxide + water + energy
The reactants of this reaction are glucose and oxygen, and the products are carbon dioxide,
water, and energy.
The energy needs of an organism is constant, so respiration is always occurring. This
requires a constant exchange of oxygen and carbon dioxide, where oxygen is absorbed into
the body and carbon dioxide is released.
Structures for Gas Exchange
There are several structures or means used to obtain oxygen, and they differ for different
types of organisms. The main methods of gaining oxygen in animals are as follows:
•Lungs – animals with lungs breathe in oxygen from the air and it is exchanged into the
bloodstream in the lungs. Examples include all mammals, birds, and most reptiles and
amphibians.
•Gills – fish and some amphibians have gills that allow them to absorb oxygen from water.
These are internal gills. Some insects and amphibians have external gills. These extend
outside of the body and absorb oxygen from the water.
•Skin - some small animals that do not require a lot of oxygen get their oxygen by
absorbing it through their skin. Flatworms and earthworms are two examples.
Plants obtain oxygen through:
•Stomata – during the process of respiration, plant leaves take in oxygen through openings
called stomata. The oxygen is then used to break down sugars to release energy. Also, the
carbon dioxide and water that are produced during plant respiration are released through
the plant's stomata