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Chapter 11 Mind Map, Light-dependent reactions use this way of energy…
Chapter 11 Mind Map
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Stroma Reactions
Stroma reactions (otherwise known as the Calvin-Benson cycle or the C3 cycle) convert carbon dioxide to carbohydrates
These reactions take place in the stroma, helped by enzymes that are not bound to thylakoid membranes
In the first step, an acceptor molecule (RuBP) -which contains five carbons- reacts with a molecule of CO2
The molecule breaks apart, while still attached to the enzymes, to form 3-phosphoglycerate (PGA)
The enzyme responsible for helping with this reaction is call RuBP carboxylase (RUBISCO) which makes up about 30% of the protein in a leaf (makes it the most abundant protein on Earth!)
The first step of these reactions is carboxylation only. In the next step, ATP donates a phosphate group to 3-phosphoglycerate to form 1,3-phosphoglycerate
This molecule is then reduced to 3-phosphoglyceraldehyde (PGAL) by NADPH. A phosphate is released in this step
While the rest of the reactions are complex, it is important to realize that the PGAL molecules can be taken out of the chloroplast and used to build sugars, amino acids, and more
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General Concepts
The disorder of the universe (or entropy) is continuously increasing, however, the prokaryotes, protists, fungi, plants, and animals represent a phenomena where particles enter a more orderly state
Photoautotrophs are organisms that get their energy directly from light and use it to bring small inorganic molecules into their tissues
Heterotrophs can't make their own energy from light and instead take in organic molecules and break them down to get the energy inside of them
Tissues and organs are either photoautotrophic or heterotrophic. Tissues can, however change their type of metabolism as they go through the plant life cycle
Anabolic Metabolism
3-phosphoglyceraldehyde (PGAL) is very versatile and can be used with water, nitrates, sulfates, and minerals to construct anything that the plant needs
PGAL, for these reactions, must be rearranged or broken down in a process called anabolism (constructive metabolism) which consists of anabolic reactions
Two anabolic pathways are especially important with regard to energy metabolism: the synthetic pathways of polysaccharides
Because ATP and NADPH can't be stored for even a short amount of time, a plant must have a few other types of storage
- Short-term storage: ATP and NADPH can be used within the cell and last only briefly
- Intermediate-term storage: the simple sugar glucose and the disaccharide sucrose are stable enough to be moved from cell to cell and can last in storage for weeks of months
- Longer-term storage: starch is a large, high-molecular-weight polymer of glucose that is too large to be transported. It is more stable than glucose, can last for years, and does not cause the cell to take in water
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Environmental Factors
Light
From a plant's viewpoint, light has three important properties: quality, quantity, and duration
Quality of sunlight refers to the colors or wavelengths that the light contains. Because sunlight is white, it contains the entire visible light spectrum and allows the plant to take in what it needs
Quantity of sunlight refers to light intensity and is affected by several factors. More light is available on a clear day than a cloudy one, and the location of the plant (be it on the side of a mountain or at the equator) also determines the amount of sun
For some species of plants, specifically those that grow underwater, the plant gets less sunlight but is still able to grow 
Duration of sunlight refers to the number of hours per day that sunlight is available. At the equator, there are an even 12 hours of sunlight, every single day of the year. However, at the poles of the earth (depending on when you are recording sunlight) you may get a 24 hour period of only light or only darkness
Leaf Structure
In the most tropical areas of the world (think rain forest), leaves are open wide with a spongy root system below. This allows for excellent light and carbon dioxide absorption, but is inefficient at collecting water
In the desert areas of the world, the leaves are much more closely bunched together with a small internal surface area that minimizes water evaporation
Water
Most plants keep their stomata open during the day. This allows for the absorption of CO2 but leads to the loss of water. At night, the stomata is closed which retains water within the plant
If the soil becomes dry and water is not readily available, the plant keeps the stomata closed (even during the day). This means, however, that the plant need to find other ways to metabolize while conserving water
Photosynthesis Reactions
Photosynthesis is the process that uses light energy to synthesize something (particularly glucose). For photosynthesis to happen, water (for an electron source) and light (for an energy source) are needed
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Internal Factors
C4 Metabolism
Water use efficiency is a ratio that compares the amount of water lost for each molecule of carbon dioxide absorbed. Ideally, this ratio is low
Carbon dioxide diffuses into a leaf faster if the concentration in the air is higher or the concentration in the leaf is lower
Even with a faster diffusion of carbon dioxide, it will still be slow with a (potentially) high water loss. Under normal conditions, each molecule of RUBISCO catalyzes only 1 to 12 CO2 molecules per second (compared to the thousands that enzymes typically fix)
Molecules of phosphoglycolate (formed by RUBISCO) is transferred from the chloroplast to the mitochondria, where much of it is broken down into two molecules of CO2. This break down is called photorespiration and is an energy-wasting process
RuBP has survived for billions of years, but is starting to struggle. due to the decreasing amounts of carbon dioxide in the air. With increasing amounts of oxygen in the air, plants are losing up to 30% of their energy produced because RuBP is making phosphoglycolate
One alternative is to improve the working conditions of RuBP by compartmentalizing the enzyme in a space where carbon dioxide concentrations are high and oxygen concentrations are low
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C4 metabolism occurs in leaves with Kranz anatomy, where mesophyll cells are not spread out in the leaf, but are rather located around a chlorophyllous sheath
Mesophyll cells contain the enzyme phosphoenolpyruvate (PEP) carboxylase, which draws in carbon dioxide and never oxygen
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Differences and similarities between C3, C4, and CAM carbon dioxide processing