Photosynthesis Flashcards
the source of energy
the sun
autotrophs
organisms that can make their own food
all green plants, some bacteria, some protists
what form of energy do autotrophs use to produce food
light energy from the sun
what form is light energy produced as food
glucose or sugar
heterotrophs
organisms that cannot make their own food
all animals and all fungi
how do heterotrophs gain energy
by consuming food
what form does energy enter the ecosystem
sunlight
what do plants use the suns energy to make
glucose
photosynthesis
- converting radiant energy (from the sun) into chemical energy (as glucose)
- convert water & carbon dioxide into high-energy sugar molecules
Name & Energy Level
ATP
- Adenosine Triphosphate
- Energy Rich
Name & Energy Level
ADP
- Adenosine Diphosphate
- Energy Poor
Structure of ATP
- Adenine, a nitrogen base
- Ribose, a 5-carbon sugar
- A chain of three phosphate groups
ADP -> ATP
Adding a phosphate
* when a cell has energy available it can store small amounts by adding a phosphate group
Storing Energy
Add a phosphate
ATP -> ADP
Removing a phosphate
* when a cell needs energy, the third phosphate will be removed
Releasing Energy
Removing a phosphate
What does ATP power?
- Photosynthesis
- Protein Synthesis
- Muscle Contractions
- Active Transport
Basic Energy Source
ATP
How much ATP is consumed & regenerated in a second?
10,000,000
waste product of photosynthesis
oxygen
What is life on earth dependent on photosynthesis for?
food & oxygen
The Photosynthesis Equation
6CO2 + 6H2O + Sunlight = C6H12O6 + 6O2
How do plants take in CO2?
Through their leaves
How do plants take in H2O?
Through their roots
What does photosynthesis require?
- water
- carbon dioxide
- light energy
- chlorophyll
electromagnetic spectrum
the range of energy radiated outward from the sun
what does the atmosphere act as?
a selective window that allows visible light to pass through while screening out a substantial fraction of other radiation
What drives photosynthesis?
the visible light from radiation
the colors of the visible spectrum are
red, orange, yellow, green, blue, indigo, violet
pigment
any substance that absorbs light
how do plants absorb the suns energy?
via pigments (light absorbing)
different pigments…
…absorb light of different wavelengths
what happens to the absorbed wavelengths?
they disappear
is there an alternate to absorbing wavelengths?
yes, reflecting them
the colors we see are being reflected by a pigment
principal photosynthetic pigment
chlorophyll
chlorophyll
a green pigment contained in chloroplasts
What can chlorophyll absorb?
All colors of the visible spectrum except for green. It reflects green.
So, its green to us
What wavelengths of light are best absorbed by chlorophyll?
~425nm and ~660nm
What wavelengths of light are least absorbed by chlorophyll?
~450nm and ~650nm
chlorophyll-a
blue-green
chlorophyll-b
yellow-green
what happens when chlorophyll absorbs light?
energy transfers directly to electrons
these high-energy electrons make photosynthesis work
major organ of photosynthesis
leaves
what are leaves the major organ of
photosynthesis
how many chloroplasts per sqmillimeter of leaf?
~500,000
Cuticle
A waxy covering on the upper & lower surface of a leaf that helps prevent water loss
Mesophyll
- central middle area
- contains palisade cells & spongy cells (both of many chloroplasts)
- the palisade layer is the primary photosynthetic layer
Stomata
- pores in the leaf (for CO2 to enter and oxygen to exit)
- the opening into the leaf
- guard cells found on either side (they’re like the doors)
- source of water loss
- usually found on the lower surface (to help reduce water loss)
vascular bundles
- contains xylem and phloem
- xylem carries water up the plant, brings water to the leaf
- phloem carries food down the plant, glucose will exit through the phloem and get carried to other parts of the plant
chloroplast membrane
double membrane - there is a space between them
thylakoids affect on the chloroplast
- make a third membrane system
- big stacks of thylakoids are called grana
- they contain chlorophyll
What is surrounding of the thylakoid?
a dense solution called, the stroma
What are Thylakoids
the structural unit of photosynthesis
what form do thylakoids take
the form of flattened sacs or vesicles
What molecules are built into the thylakoid membrane
chlorophyll molecules
what do chlorophyll molecules do?
capture light energy
where does photosynthesis take place??
in the chloroplast
What happens to pigments in the thylakoid membrane?
They are clustered together
What are clusters of pigments called?
Photosystems
Photosystems
- clusters of pigments
- light collecting units
what is the light collecting unit of the chloroplast?
photosystems
what happens when sunlight hits chlorophyll
the electrons in chlorophyll become very excited
excited electrons
electrons that have a LOT of energy
what do high energy electrons need?
a carrier
an electron carrier
a compound that can accept a pair of high energy electrons
without draining the electrons energy
electron carriers are also known as
the electron transport chain
what is the process of transporting high energy electrons called?
electron transport
example of an electron carrier
NADP+
NADP+
accepts and holds 2 high energy electrons alongside a hydrogen ion
when that happens NADP+ becomes NADPH
NADPH
NADP+ when it has 2 high energy electrons and a hydrogen ion
where do the high energy electrons go?
elsewhere in the chloroplast for chemical reactions & to build glucose molecules
where do light dependent reactions occur?
thylakoid membranes
where do light INdependent reactions occur?
in the stroma - region outside of the thylakoids
example of a light independent reaction
calvin cycle
Which photosystem comes first?
Photosystem II
What is a photosystem?
a collection of pigment molecules that serve as the light collecting unit
embedded in the thylakoid membranes
what do pigments in photosystem II do?
absorb light
what does the light energy absorbed by the electrons do?
increase their energy level
what happens when electrons are lost?
they get replaced
what do enzymes break apart in the thylakoid membrane?
water molecules into 2 electrons, 2 H+ ions, and 1 oxygen atom
what is considered a waste product?
photosystems
oxygen
what is responsible for nearly all the oxygen in our atmosphere?
the splitting apart of water
what ion is released into the thylakoid?
hydrogen
protein molecules use the energy from high-energy electrons to create what?
ATP
what does chlorophyll do in photosystem I?
absorb energy and use it to re-energize the electrons
What is the purpose of light dependent reactions?
produce ATP and NADPH for the light independent reactions
Where do light dependent reactions take place?
Thylakoid membrane
What do light dependent reactions do?
pass electrons from water to NADPH
The two photosystems work together to produce what?
ATP and NADPH
Where are thylakoids found?
inside the chloroplasts
what are big stacks of thylakoids called?
grana
what are grana?
big stacks of thylakoids
what is the thylakoid space
the middle of the thylakoid
what is in the middle of the thylakoid?
the thylakoid space
what is a collection of chlorophylls and carotenoids called?
pigments
what do pigments do?
absorb light energy from the sun
what strikes the surface of the leaf?
sunlight
what increases the energy level of electrons in chlorophyll?
light energy
What is the energy from high energy electrons used for?
to transport hydrogen ions from the stroma into the thylakoid space
what gets released inside the thylakoid
hydrogen ions
what gets released into the air?
oxygen
what does photosystem I receive from photosystem II?
electrons
What is the energy absorbed from the sun by chlorophyll molecules in photosystem I used for?
re-energizing electrons
What does NADP+ join with in light dependent reactions?
1 hydrogen atom and 2 electrons
NADPH is formed when?
NADP+ joins with 1 hydrogen ion and two electrons
what is the area outside the thylakoid called?
the stroma
what is the stroma?
a dense liquid surrounding the thylakoids
from where to where do hydrogen ions move in the chloroplast?
flow from high concentration (in the thylakoid) to low concentration (in the stroma)
what is hydrogen flowing through?
ATP synthase, a protein enzyme
What does ATP synthase do when hydrogen flows through it?
Rotates like a turbine
What does ATP synthase do while rotating?
Binds a phosphate to ADP (forms ATP from ADP)
How does the concentration of hydrogen stay high inside the thylakoid?
Hydrogen ions are actively pumped back into it
What is formed for use in the Calvin Cycle?
NADPH & ATP
What is the purpose of light dependent reactions?
Produce high-energy compounds
What are high-energy compounds?
ATP & NADPH
What are high-energy compounds used for?
Calvin Cycle
The Calvin Cycle is also known as…
the Light Independent Reactions
Where does the Calvin Cycle occur?
In the Stroma
What is the purpose of the Calvin Cycle?
to take CO2 and high-energy products of the light dependent reaction to make glucose
How does the Calvin Cycle obtain CO2?
via the atmosphere
What does CO2 enter leaves through?
the stomata
5-carbon sugar called
RuBP or ribulose biphosphate
carbon fixation
carbon (from CO2) combining with 5-carbon sugar (RuBP)
What does Carbon Fixation form?
An unstable 6-carbon compound
What does the unstable 6-carbon compoud break apart into?
2 molecules of PGA (a three-carbon compound)
how does PGAL form?
a series of reactions involving ATP & NADPH convert PGA into PGAL
What could happen to the PGAL?
- the two PGAL molecules combine and form glucose
- the PGAL is converted into RuBP for the reaction to occur again
What is the number one problem land plants face?
Dehydration
Why is dehydration a problem?
Plants must open their stomata, to let in CO2, which causes excessive water loss
What do plants do on a hot dry day?
Close the stomata to conserve water
Consequences of having the stomata closed?
Slows down photosynthesis
What are the 2 pathways for carbon fixation?
- the four-carbon pathway
- the CAM pathway
What is special about the C4 Pathway?
Prefaces the Calvin Cycle with an additional step
Additional step of C4 Pathway
converts CO2 into a 4-carbon compound to save it until it is needed
REVERSABLE
C4 Plant Examples
Corn, Sugar Cane, Crab Grass
What is special about the CAM pathway?
Stomata is only open at night
CAM Pathway Plant examples
Cacti & Pineapples
What is REQUIRED in light dependent reactions?
water
…and light
how is water obtained for photosynthesis?
via the roots of plants
what does a shortage of water do?
slow or stop photosynthesis
what is done to prevent water loss?
plants are covered with a waxy cuticle
