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Bio Chapter 8

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How is ATP useful to cells
ATP can easily release and store energy by breaking and re-forming the bonds between its phosphate groups. This characteristic of ATP makes it exceptionally useful as a basic energy source for all cells
ATP and ADP
One of the most important compounds that cells use to store and release energy is adenosine triphosphate ATP
ATP consists of adenine a 5 carbon sugar called ribose and three phosphate groups.
Adenosine diphosphate ADP looks almost like ATP except that it has two phosphate groups instead of three. ADP contain some energy but not as much as ATP
When a cell has energy available it can store small amounts of it by adding phosphate groups to ADP producing ATP
Cells can release the energy stored in ATP by breaking the bonds between the second and third phosphate groups
Because a cell can add or subtact these phosphate groups it has an efficient way of storing and releasing energy as needed
ATP funtions
Many cell membranes contain sodium potassium pumps. ATP provides the energy that keeps these pumps working, maintaining a balance of ions on both sides of the cell membrane
ATP powers movement providing the energy for motor proteins that contract muscle and power the movement of cilia and flagella.
Energy from ATP powers the synthesis of proteins and responses to chemical signals at the cell surface
ATP is not a good molecule for storing large amounts of energy over the long term
It is more efficient for cells to keep only a small supply of ATP on hand
Cell can regenerate ATP by using the energy in foods like glucose.
Photosynthesis
In the process of photosynthesis plants convert the energy of sunlight into chemical energy stored in the bonds of carbohydrates
Heterotrophs
Some heterotrophs get their food by eating plants
Other obtain food from plant eating animals
Some get energy from eating decomposing things
Autotrophs
Organisms that make their own food are called autotrophs
Plants algae and some bacteria are able to use light energy from the sun to produce food. The process by which autotrophs use the energy of sunlight top produce high energy carbs that can be used as food though photosynthesis
What roles do pigments play in photosynthesis
Photosynthetic organisms capture energy from sunlight with pigments
Sunlight waves
Sunlight is a mixture of different wavelengths, many of which are visible to our eyes and make up the visible spectrum
Our eyes see the different wavelengths of the visible spectrum as different colors, red, orange, yellow, green, blue, indigo and violet.
chlorophyll
Plants gather the suns energy with light absorbing molecules called pigments
The plants principle pigment is chlorophyll
The two types of chlorophyll found in plants in Chloro A and Chloro B absorbs light very well in the blue violet and red regions of the visible spectrum but not in the green region.
This is why plants look green as they reflect green light
Plants also contain red and orange pigments such as carotene that absorb light in other regions of the spectrum.
Most of the time the green color of the chlorophyll overwhelms the other pigments but as temperatures drop and chlorophyll molecules break down, thread and orange pigments may be seen
Chloroplasts
Photosynthesis takes place inside organelles called chloroplasts
Chloroplasts contain saclike photosynthetic membranes called thylakoids which are interconnected and arranged in stack known as grana.
Thylakoid membranes
Pigments are located in the thylakoid membranes
The fluid portion of side of the thylakoids is called the stroma
Because light is a form of energy and compounds that absorbs light absorbs energy. Chlorophyll absorbs visible light especially well
When the chlorophyll absorbs light a large friction of the light energy is transferred to electrons. These high energy electrons make photosynthesis work.
Electron molecules
An electron carrier molecules is a compound that can accept a pair of high energy electrons and transfer them along with most of their energy to another molecule.
The high energy electrons produced by chlorophyll are highly reactive and require a special carrier.
Plants use electron carrier to transport high energy electrons from chlorophyll to other molecules
NADP+ and NADPH
NADP+ is a carrier molecule
NADP+ accepts and hold two high energy electrons along with a hydrogen ion H+. in this way it is converted to NADPH
The NADPH can then carry the high energy electrons to chemical reactions elsewhere in the cell
Products of photosynthesis
Photosynthesis the energy from the sunlight to convert water and carbon dioxide into high energy sugars and oxygen.
Photosynthesis uses the energy sunlight to convert water and carbon dioxide into high energy sugars and oxygen

Plants use the sugars generated by photosynthesis to produce complex carbohydrates such as starches and to provide energy for the synthesis of other compounds including proteins and lipids
Light dependant reactions
The first set of reactions is known as light dependent reactions because they require the direct involvement of light and light absorbing pigments.
The light dependent reactions use sunlight to produce ATP and NADPH
These reactions take place in the thylakoid membranes of the chloroplasts
Plants absorb carbon dioxide from the atmosphere and complete the process of photosynthesis by producing sugars and other carbohydrates
Light independant reactions
During light independent reactions ATP and NADPH molecules produce in the light dependent reactions are used to produce high energy sugars from carbon dioxide.
No light is required to power the light independent reactions
They take place in just the stroma.
What happens during the light-dependent reactions?
The light-dependent reactions use energy from sunlight to produce oxygen and convert ADP and NADP+ into the energy carriers ATP and NADPH.
The light-dependent reactions encompass the steps of photosynthesis that directly involve sunlight. The light-dependent reactions occur in the thylakoids of diloroplasts.
Thylakoids contain clusters of chlorophyll and proteins known as photosysterns.
Photosystems absorb sunlight and generate high-energy electrons that are then passed to a series of electron carriers embedded in the thylakoid membrane.
Light energy is absorbed by electrons in the pigments within photosystem 11, increasing the electrons' energy level.
The high-energy electrons are passed to the electron transport chain, a series of electron carriers that shuttle high-energy electrons during ATP-generating reactions.
The thylakoid membrane provides new electrons to chlorophyll from water molecules.
Enzymes of the inner surface of the thylakoid break up water molecules into 2 electrons, 2 H+ ions, and 1 oxygen atom.
The 2 electrons replace the high-energy electrons that have been lost to the electron transport chain.
Oxygen is released into the air. This reaction is the source of nearly all of the oxygen in Earth's atmosphere.
The H+ ions are released inside the thylakoid.
Energy from the electrons is used by proteins in the electron transport chain to pump H+ ions from the stroma into the thylakoid space
At the end of the electron transport chain, the electrons pass to photosystem 1.
Because some energy has been used to pump H+ ions across the th-ylakoid membrane, electrons do not contain as much energy as they used to when they reach photosystem 1.
Pigments in photosystem I use energy from light to reenergize the electrons.
At the end of a short second electron transport chain, NADP+ molecules in the stroma pick up the high-energy electrons and 11+ ions at the outer surface of the thylakoid membrane to become NADPH.
H+ ions accumulate within the thylakoid space from the splitting of water and from being pumped in from the stroma. The buildup of H+ ions makes the stroma negatively charged relative to the space within the thylakoids.
This gradient, the difference in both charge and H+ ion concentration across the membrane, provides the energy to make ATP.
H+ ions cannot directly cross the thylakoid membanc. However, the thylakoid membrane contains a protein called ATP synthase that spans the membrane and allows H+ ions to pass through it.
Powered by the gradient, H+ ions pass through ATP synthase and force it to rotate.
As it rotates, ATP synthase binds ADP and a phosphate group together to produce ATP.
This process, called chemiosmosis, enables light-dependent electron transport to produce not only NADPH (at the end of the electron transport chain), but ATP as well.
The light-dependent reactions produce oxygen gas and convert ADP and NADP+ into the energy carriers ATP and NADPH.
ATP and NADPH provide the energy needed to build high-energy sugars from low-energy carbon dioxide.
What happens during light independant reactions
During the light-independent reactions, ATP and NADPH from the light-dependent reactions are used to produce high-energy sugars.

During the light-independent reactions, commonly referred to as the Calvin cycle, plants use the energy that ATP and NADPH contains to build stable high-energy carbohydrate compounds that can be stored for a long time.

Carbon dioxide molecules enter the Calvin cycle from the atmosphere.
An enzyme in the stroma of the chloroplast combines carbon dioxide molecules with 5-carbon compounds that are already present in the organelle, producing 3-carbon compounds that continue into the cycle.
For every 6 carbon dioxide molecules that enter the cycle, a total of twelve 3-carbon compounds arc produced.
Other enzymes in the chloroplast then convert the 3-carbon compounds into higher-energy forms in the rest of the cycle, using energy from ATP and high-energy electrons from NADPH.
At midcvcle, two of the twelve 3-carbon molecules are removed from the cycle.
These molecules become the building blocks that the plant cell uses to produce sugars, lipids, amino acids, and other compounds.
The remaining ten 3-carbon molecules are converted back into six 5-carbon molecules that combine with six new carbon dioxide molecules to begin the next cycle.
F
The Calvin cycle uses 6 molecules of carbon dioxide to produce a single 6- carbon sugar molecule.
The energy for the reactions is supplied by compounds produced in the light-dependent reactions.
The plant uses the sugars produced by the Calvin cycle to meet its energy needs and to build macromolecules needed for growth and development.
When other organisms eat plants, they can use the energy and raw materials stored in these compounds.

The two sets of photosynthetic reactions work together—the light-dependent reactions trap the energy of sunlight in chemical form, and the light-independent reactions use that chemical energy to produce stable, high-energy sugars from carbon dioxide and water.
In the process, animals, including humans, get food and an atmosphere filled with oxygen.
What factors affect photosynthesis?
Among the most important factors that affect photosynthesis are temperature, light intensity, and the availability of water.
The reactions of photosynthesis are made possible by enzymes that function best between O'C and 35°C.
Temperatures above or below this range may affect those enzymes, slowing down the rate of photosynthesis or stopping it entirely.
High light intensity increases the rate of photosynthesis.
After the light intensity reaches a certain level, however, the plant reaches its maximum rate of photosynthesis, as is seen in the graph.
Because water is one of the raw materials in photosynthesis, a shortage of water can slow or even stop photosynthesis. Water loss can also damage plant tissues.
Plants that live in dry conditions often have waxy coatings on their leaves to reduce water loss. They may also have biochemical adaptations that make photosynthesis more efficient under dry conditions.
In order to conserve water, most plants under bright, hot conditions close the small openings in their leaves that normally admit carbon dioxide.
This causes carbon dioxide within the leaves to fall to very low levels, slowing down or even stopping photosynthesis.
CA and CAM plants have biochemical adaptations that minimize water loss while still allowing photosynthesis to take place in intense sunlight.
C4 plants have a specialized chemical pathway that allows them to capture even very low levels of carbon dioxide and pass it to the Calvin cycle.
The name TA plant" comes from the fact that the first compound formed in this pathway contains 4 carbon atoms. The C4 pathway requires extra energy in the form of ATP to function.
C.4 organisms include crop plants Like corn, sugar cane, and sorghum.

Members of the Crassulacae family, like the ice plant shown, incorporate carbon dioxide into organic acids during photosynthesis in a process called Crassulacean Acid Metabolism (CAM).
CAM plants admit air into their leaves only at night, where carbon dioxide is combined with existing molecules to produce organic acids, "trapping" the carbon within the leaves.
During the daytime, when leaves are tightly sealed to prevent water loss, these compounds release carbon dioxide, enabling carbohydrate production.
CAM plants include pineapple trees, many desert cacti, and the "ice plants" shown.