33 terms

Bio 8

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sun
-original source of energy for all living things on Earth
-provides energy for photosynthesis
- although our eyes see it as "white" light, it is actually a mixture of different wavelengths known as the visible spectrum
-non-visible light (such as radio waves) can't be used for photosynthesis
- the optimum wavelength is 680 nanometers for photosystem II
Autotrophs
- organisms that make their own organic molecules (food) from inorganic (non-living) molecules & energy through the process of photosynthesis
-most plants are these
- nearly all life on Earth, including us, depends on the ability of autotrophs to capture energy from sunlight and store it in molecules to make food
Heterotrophs
- organisms that obtain food by consuming other living things
- can obtain food by eating plants, eating plant-eating animals, or even absorbing nutrients from decomposing organisms in the environment (ex. mushrooms)
ADP
(Adenosine Diphosphate)
-molecule of energy that's involved in energy reactions
-it's like a rechargeable battery that powers the cell because it can be fully charged by adding a phosphate group to make ATP
- consists of adenine, a 5-carbon sugar (ribose), and 2 phosphate groups
ATP
(Adenosine TRIphosphate)
-molecule that's the energy "currency" of the cell because it powers the functions of the cell
-made of adenine, ribose, & 3 phosphate groups
-releases energy when a phosphate group is removed
- one of the most important compounds that cells use to store and release ENERGY, which all organisms require energy to carry out life processes.
-made-up of the same compounds as ADP, but it has 3 phosphate groups instead of 2
- consists of adenine, a 5-carbon sugar (ribose), and 3 phosphate groups (DIphosphate has 2 phosphate groups)
- can easily release and store energy by breaking and re-forming the bonds between its phosphate groups
- powers many processes including active transport (powering sodium and potassium pumps), movement of the cell, synthesis of proteins, and can be used to produce light
- it is unstable and hard to store so cells do keep a supply of it but store energy in other ways
Photosynthesis
- in this process, plants convert the energy of sunlight into chemical energy stored in the bonds of carbohydrates
- the process by which autotrophs use carbon dioxide, water, & the energy of sunlight to produce oxygen and high-energy carbohydrates - sugars and starches - that can be used as food and to produce proteins & lipids
-in the 3rd stage carbon-containing molecules are made from carbon atoms from CO2 in the air & hydrogen atoms from NADPH
-removes carbon dioxide from the atmosphere
- we get the carbon to form our DNA from the CO2 taken in by plants during this process
Photosynthesis Equation
In symbols:
6CO2 + 6H20 + sunlight --> C6H12O6 + 6O2

In words:
6CarbonDioxides + 6Waters + sunlight --> 1Sugar + 6Oxygens

In both "light" should be written above the arrow, because the energy from light is used to convert

The oxygen produced comes from the water.
light
-light from the sun has wavelengths from all different colors of the spectrum (red, orange, yellow, green, blue, indigo and violet)
Chloroplasts
See picture on p. 231
- organelles where photosynthesis takes place
-have the pigment chlorophyll in them
-have a membrane around them and stroma, thylakoids, and grana in them
Thylakoids
- saclike photosynthetic membranes that are highly folded in the chloroplast
-looks like a coin
-arranged in stacks called grana and in a fluid called stroma
- pigments, including chlorophyll, are located in their membranes
-where light-dependent reactions occur
-active and passive transport allow protons to move across the thylakoid membrane during photosynthesis
granum
-membrane that's a stack of thylakoids in the chloroplast
-looks like a "stack of coins"
Stroma
-fluid/cytoplasm portion of the chloroplast that surrounds the thylakoids/grana
-where Calvin cycle occurs & produces sugar
Pigments
- light-absorbing molecules that can absorb energy from sunlight
Chlorophyll
- the plant's main light-absorbing pigment found in the thylakoid membrane
- 2 types, a and b, that absorb light very well in the blue-violet and red regions of the spectrum
-doesn't absorb green light wavelengths well so they're reflected, which is why plants look green (it also reflects so read and orange pigments but the green dominates)
- does not absorb radio waves because the wavelengths are too long to be useful to the plant
-absorbs visible light well and transfers that energy to electrons, which become more energized
Photosystems
- clusters of chlorophylls (light-absorbing pigments) and proteins in the thylakoids
-found in the thylakoid membrane
-absorb sunlight to make high-energy electrons
-water supplies the electrons for Photosystem I, and then they are replaced by electrons in Photosystem II
Photosystem II: Light-dependent reactions
AKA "light reactions"
-reactions of photosynthesis that capture sunlight & convert it to chemical energy
- require the direct involvement of light, with the optimal being 680 nanometers
- the light reactions begin when the electrons in the pigments in Photosystem II absorb light & the electrons' energy levels increase
-the high-energy electrons are passed down the electron transport chain, which are electron carrier proteins that carry the high-energy electrons
- use energy from sunlight to convert ADP and NADP+ into the energy carriers ATP and NADPH and oxygen
- take place in the thylakoid membranes
- water is required as a source of electrons & H+ ions because enzymes in the thylakoid break each water molecule into 2 electrons, 2 H+ ions, and 1 oxygen atom
-the 2 electrons from the water replace the 2 high-energy electrons lost on the electron transport chain
-produces energy & oxygen (which provides oxygen for the atmosphere and other forms of life)
steps of light-dependent reactions
-high-energy electrons move through the electron transport chain
-pigments in photosystem II absorb light
-ATP synthase allow H+ ions to pass through the thylakoid membrane
Electron carrier
- a compound that can accept a pair of high-energy electrons and transfer them, along with most of their energy and an H+ hydrogen ion, to another molecule
(Think oven mitt carrying a hot potato)
-NADP+ does this in photosynthesis
-NADP+ combines with the H+ ion to make NADPH, which holds the energy from sunlight in chemical form
-the NADPH carries the high-energy electrons to other parts of the cell so they can be used to build molecules that the cell needs, such as carbohydrates like glucose
Electron transport chain
- a series of electron carrier proteins that shuttle high-energy electrons during ATP-generating reactions
-the high-energy electrons produced in Photosystem II are used as energy for the proteins to pump H+ ions from the stroma into the thylakoid space
- electrons are continuously taken from water molecules (H+) (the O is then released which is the source of nearly all oxygen in Earth's atmosphere), moved to Photosystem I and then to Photosystem II
Photosystem I: Light-dependent reactions
AKA "light reactions"
-second light-dependent reaction
-electrons have less energy since some has been used to pump H+ ions across the thylakoid membrane
-pigments in Photosystem I use energy from light to reenergize the electrons
-the electrons go through a 2nd small electron transport chain
-NADP+ molecules in the stroma pick up the high-energy electrons & H+ ions to become NADPH
-H+ ions that accumulated in the thylakoid space during Photosystem II were left behind at the end of the electron transport chain or pumped in from the stroma & make the stroma negatively charged, in comparison to the thylakoids
-the difference between the charge and H+ ion concentration provides the energy to make ATP
NADP+
-molecule that carries high-energy electrons from chlorophyll to other molecules
- it accepts and holds 2 high-energy electrons & combines it with a hydrogen ion (H+), converting it to NADPH
NADPH
-molecule that is a form of chemical energy formed during the light-dependent reactions
-carries the electrons that were produced by light absorption to chemical reactions elsewhere in the cell
-makes sugars during the Calvin cycle
ATP synthase
- a protein located in the thylakoid membrane that spans the membrane and allows H+ ions to cross because they couldn't do it on their own
-H+ ions pass through and cause it to rotate and bind ADP and a phosphate group to make ATP (called chemiosmosis)
Where cells get ATP
- comes from the chemical compounds that we call food
- nearly all food energy ultimately comes from the SUN
Light-independent reactions
AKA "dark reactions" AKA Calvin Cycle
-reactions of photosynthesis that allow a plant to store chemical energy in the form of sugars
-don't need light (but can happen during the day)
- the light reactions produced a lot of chemical energy (ATP and NADPH) and oxygen, but it isn't naturally stable enough to be stored for a long time - the Calvin Cycle fixes that problem
-use energy from ATP & NADPH produced during the light-dependent reactions to build stable high-energy macromolecules like lipids, proteins & complex carbohydrates that can be stored for a long time
-CO2 enters the plant from the atmosphere
-an enzyme in the chloroplast combines every six CO2 molecules with six 5-carbon compounds to make twelve 3-carbon compounds
-two of the twelve 3-carbon molecules are set aside to help the plant make sugars & the other ten 3-carbon molecules are converted back into six 5-carbon molecules that combine with the next six CO2 molecules to start the cycle again
-the energy produced from the light-dependent reactions is used to keep the cycle going
-the sugars the plant makes help the plant store energy that it uses to build macromolecules, like lipids, proteins & complex carbohydrates
- no light necessary (but can happen during the day)
How plants use energy-rich sugars produced by Calvin Cycle
- to produce macromolecules needed for development and growth, including lipids, proteins, and complex carbohydrates
- when other things eat plants, they can use the energy and raw materials stored in these compounds
2 sets of reactions that occur during photosynthesis
1. light-dependent reactions (convert sunlight, ADP & NADP+ into ATP, NADPH & oxygen gas)
2. light-independent reactions
They work together.
The light reactions trap the energy in sunlight in chemical form, and the Calvin Cycle use that chemical energy to produce high-energy sugars from carbon dioxide and water
Stomata
- pores through which most water in a plant is lost
- these pores are also how gases would enter a leaf
Organisms get energy by...
-breaking-down food molecules and capturing their chemical energy
biochemical pathway
-series of link chemical reactions where the product of one chemical reaction becomes the reactant of the next chemical reaction, like a domino effect in photosynthesis
3 Environmental Factors that Affect the Rate of Photosynthesis
Light Intensity - high intensity speeds it up but then plateaus when it reaches its max rate

Availability of Water - shortage of water can slow or even stop photosynthesis; desert plants have adaptations to make photosynthesis more efficient under dry conditions

Temperature - functions best between 0 and 35 degrees Celcius - If temps too low or high, photosynthesis can slow down and stop
C4 Plant
- one group of plants that has adapted to bright, hot conditions
- have special pathway that allows them to capture even tiny amounts of carbon dioxide
- makes compounds from 4 carbon atoms
-the C4 pathway allows photosynthesis to keep going even under intense light and high temperatures
-requires extra ATP to function
Ex. corn, sugar cane
CAM Plant
- another group of plants that has adapted to bright, hot conditions
-helps the plant get carbon dioxide while not losing much water
- only let air into their leaves at night, minimizing water loss by keeping stomata closed during the day
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- open their stomata to admit air only at night
- Ex. Pineapple, cactus