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Photosynthesis, Cellular
Respiration, & Nutrient Cycles
What is energy?
• energy is the ability to do work
– ex. energy allows humans to run, write, talk
on the phone, etc.
• ALL ORGANISMS (living things) NEED
ENERGY TO LIVE!
Where do organisms get the energy
they need to live?
• nearly all organisms get their energy either
directly or indirectly from the sun
HOW?
• We know that the sun gives off LOTS of
ENERGY (light, heat)
!plants get their energy directly from the sun by
converting light energy to food (glucose)
!animals get their energy indirectly from the sun
by eating plants or by eating animals (which
have fed on plants)
Photosynthesis
! plants harness the sun’s light energy and
convert it into chemical energy (glucose) or
food—this process is called photosynthesis
Chemical Equation for Photosynthesis:
CO2 + H2O + light energy
O2 + C6H12O6
carbon
dioxide
water
reactants: CO2, H2O, light energy
products: O2 , C6H12O6
oxygen
glucose
(sugar)
Where does photosynthesis occur?
! in the chloroplasts of plant cells (most of the
chloroplasts are in the leaves)
! the chloroplasts contain pigments such as
chlorophyll that absorb and harness the light
from the sun
! chloroplasts convert LIGHT energy into
chemical energy (glucose)
autotroph (auto = “self”, troph = “feeding”):
organisms that make or synthesize their own
food (sugar), such as PLANTS
Why is photosynthesis important?
! photosynthesis is responsible for the majority
of oxygen gas in our atmosphere
! oxygen is a waste product of the reactions of
photosynthesis
! most organisms on Earth need oxygen to
survive
! Do plants need oxygen to survive?
! Yes, they need it for cellular respiration just like
people do. However, plants only need very small
amounts of oxygen compared to people. If plants
do not rid themselves of excess oxygen, they can
become damaged or die.
Where do we (animals) get our energy from?
• from the food we eat
heterotroph (hetero= “other”, troph= “feeding”): an organism that
cannot make or synthesize its own food and must eat other
organisms to obtain energy
examples: humans, cats, guinea pigs, caterpillars,
fungi, amoebas
HOW much energy is in our food?
! we can find out by looking at food labels to find out
how many kilocalories are in the food (labeled as
Calories on the labels in the US)
! in simple terms, a Calorie is a measure of how much
energy is in our food
Nutrition Label for 1 Potato
How much energy can
you get from eating one
potato?
! 100 calories
Where is the energy in the food we eat?
• it is stored in the chemical bonds in our
food
• the cells in our bodies break the chemical
bonds in our food, releasing the energy—
we convert this energy into ATP
• ATP = adenosine triphosphate, the energy
currency of cells, a nucleotide
• the process for converting food energy
into energy stored in ATP is called
CELLULAR RESPIRATION
Cellular Respiration
The Chemical Equation:
O2 + C6H12O6
oxygen
glucose
CO2 + H2O + ATP
carbon
dioxide
water
reactants: oxygen, glucose
products: carbon dioxide, water, ATP
! cellular respiration occurs in the mitochondria
of cells
! the mitochondria are called the “powerhouses”
of cells because they use food to make ATP for
the cell
Do Plants use Cellular Respiration?
! Heck YES!
! plants need to convert their food into ATP just
like you do
! plants have mitochondria
mitochondrion
plant cell
Ecology Terms to Know
ecology—the science that studies the
relationships between organisms and their
environments
population—a group of individuals of the same
species living in a particular area
community—many different populations of
different species that all live in a particular area
ecosystem—consists of all biotic (living) and
abiotic (nonliving) parts of a community
ex. an aquarium is an example of an ecosystem
Food Chain
• shows a transfer of energy through trophic levels (levels of
feeding/obtaining energy)
Trophic levels:
• producers—photosynthetic autotrophs; they get their
energy from the sun (ex. plants)
• primary consumers—herbivores (plant eaters),
heterotrophs (ex. caterpillar, deer)
• secondary, tertiary, quaternary consumers—
carnivores (meat-eaters, heterotrophs, includes
omnivores); examples include humans, snakes,
raccoons, dogs
• decomposers—organisms that break down dead or
decaying organisms (ex. fungi, bacteria)
omnivores—organisms that feed both on plants and
animals (ex. humans)
Feeding Ecology: Trophic Levels in Two Food Chains
• not all food chains
have tertiary and
quaternary consumers
• What trophic level is
not in these food
chains?
– decomposers
• food web: food chains linked together with arrows in a “web” to
show feeding interactions among food chains
• think of the arrows pointing into the mouth of what is eating that organism
Energy Transfer Between
Trophic Levels
• usually less than 20% efficient
• the amount of energy transferred to the
next trophic level is the amount of
chemical energy in a consumer’s food that
is converted to its biomass (growth &
development)
Energy efficiency of a caterpillar
• less than 17% of the caterpillar’s food is used
for growth (new biomass)
Trophic Efficiency: Food/Trophic Pyramids
• food pyramids are used to show how much energy
is passed upwards through the different trophic
levels
Another
Food Pyramid
•B, 10%
10,000kcal/1000kcal =10
10% of 10,000 is 1000
10% of 1000 is 100
10% of 100 is 10
Reasons to be a Vegetarian
• when people eat meat, much more energy is used than when
people do not eat meat
• feeding and raising the meat uses lots of energy and is not as
energy efficient for the planet as being a vegetarian
• vegetarians are using fewer of the planet’s valuable resources
to feed themselves
The Water Cycle
transpiration—
evaporation from
plants
condensation
evapotranspiration
condensation—water
vapor (a gas) is
converted into
liquid water
The Carbon Cycle
• the burning of fossil fuels
(ex. coal, oil) and cellular
respiration from plants
and animals releases CO2
gas into the air
• plants take in the CO2 from
the air, and using
photosynthesis they
incorporate the carbon into
sugars and other
macromolecules (proteins,
lipids, nucleic acids)
• decomposition of
organic matter also
releases carbon dioxide
into the atmosphere
The Importance of Nitrogen
! nitrogen is essential to life because it is found in proteins and
DNA
! nitrogen is also an essential nutrient for plants
! most of the air we breathe (80%) is nitrogen gas (N2)
! plants can only use nitrogen if it is in the forms of ammonium
(NH4+) or nitrate (NO3-)
! plants and people cannot use N2 gas
! atmospheric N is fixed by bacteria in the soil: incorporated
into other molecules (ammonium and nitrate) in order for
organisms to use it to make proteins and DNA
! legume plants (bean plants) have nitrogen-fixing bacteria
living in their root nodules
! plants also obtain nitrogen from sedimentary rocks in the soil
The Nitrogen Cycle