Biology chapter 4
CAM (crassulacean acid metabolism
)Energetically expensive photosynthesis in which the stomata are open only at night to admit CO2, which is bound to a holding molecule and released to enter the Calvin cycle to make sugar during the day. In this type of photosynthesis, found in many fleshy, juicy plants of hot, dry areas, water loss is reduced because the stomata are closed during the day.
chlorophyll
A light-absorbing pigment molecule in chloroplasts. [Gk., chloros, pale green + phyllon, leaf]
C4 photosynthesis
A method (along with C3 and CAM photosynthesis) by which plants fix carbon dioxide, using the carbon to build sugar; serves as a more effective method than C3 for binding carbon dioxide under low carbon dioxide conditions, such as when plants in warmer climates close their stomata to reduce water loss.
light energy
A type of kinetic energy made up of energy packets called photons, which are organized into waves.
chemical energy
A type of potential energy in which energy is stored in chemical bonds between atoms or molecules.
stroma
In the leaf of a green plant, the fluid in the inner compartment of a chloroplast, which contains DNA and protein-making machinery. [Gk., stroma, bed]
What are the three inputs for photosynthesis? What are the two outputs?
Photosynthesis is the process through which the inputs of sunlight, water, and carbon dioxide are converted into the outputs of sugar and oxygen.
photon
The elementary particle that carries the energy of electromagnetic radiation of all wavelengths. [Gk., phos, light]
pyruvate
The end product of glycolysis.
Describe the three steps in the Calvin cycle.
The first step of the Calvin cycle is carbon fixation, in which carbon dioxide molecules are attached to organic molecules. The next step is sugar creation, in which these organic molecules are modified into sugars. The third and final step is regeneration, where some of these sugars are used to regenerate the original organic molecules.
What are the three main pigments present in plant leaves? What do they do?
The primary photosynthetic pigment is chlorophyll a, but the pigments chlorophyll b and carotenoids also help absorb a wider range of wavelengths of light. The pigments capture packets of light energy called photons.
chlorophyll a
The primary photosynthetic pigment. Chlorophyll a absorbs blue-violet and red light; because it cannot absorb green light and instead reflects those wavelengths, we perceive the reflected light as the color green.
cellular respiration
The process by which all living organisms extract energy stored in the chemical bonds of molecules and use it for fuel for their life processes.
fermentation
The process by which glycolysis occurs in the absence of oxygen; the electron acceptor is pyruvate (in animals) or acetaldehyde (in yeast) rather than oxygen.
photosynthesis
The process by which some organisms, including plants and some protists and bacteria, are able to capture energy from the sun and store it in the chemical bonds of sugars and other molecules. [Gk., phos, light + syn, together with + tithenai, to place or put]
electromagnetic spectrum
The range of wavelengths that produce electromagnetic radiation, extending (in order of decreasing energy) from high-energy, short-wave, gamma rays and X rays, through ultraviolet light, visible light, and infrared light, to very long, low-energy, radio waves. [Lat., specere, to look at]
Krebs cycle
The second step of cellular respiration, in which energy is extracted from sugar molecules as additional molecules of ATP and NADH are formed. [From the name of the discoverer, Hans Adolf Krebs, 1900-1981]
Can you slow their demise?
Yes. Plants are able to take up sugar in the vase water and use it as an energy source for cell activities. So adding a bit of sugar to the vase is like putting fuel in their tank.
adenosine triphosphate (ATP)
A molecule that temporarily stores energy for cellular activity in all living organisms. ATP is composed of an adenine, a sugar molecule, and a chain of three negatively charged phosphate groups.
chlorophyll b
A photosynthetic pigment similar in structure to chlorophyll a. Chlorophyll b absorbs blue and red-orange wavelengths and reflects yellow-green wavelengths.
first law of thermodynamics
A physical law that states that energy cannot be created or destroyed; it can only change from one form to another.
second law of thermodynamics
A physical law that states that every conversion of energy is not perfectly efficient and invariably includes the transformation of some energy into heat.
rubisco
An enzyme (ribulose 1,5-bisphosphate carboxylase/oxygenase) involved in photosynthesis; it fixes carbon atoms from CO2 in the air, attaching them to an organic molecule in the stroma of the chloroplast. This fixation is the first step in the Calvin cycle, in which molecules of sugar are assembled. Rubisco is the most abundant protein on earth.
What are C4 and CAM photosynthesis? What are some disadvantages of both methods?
C4 and CAM photosynthesis evolved to combat water loss through evaporation in very hot and dry climates. Plants that use either C4 or CAM photosynthesis limit the opening of their stomata (small pores on the underside of leaves). Both methods require plants to expend extra energy, and because CAM photosynthesis requires plants to close their stomata by day, the amount of carbon dioxide they can take in is reduced, resulting in slower growth than non-CAM plants.
What are the two inputs for cellular respiration? What are the three outputs?
Cellular respiration is the process through which the inputs of sugar and oxygen are converted into the outputs of water, carbon dioxide, and energy in the form of ATP.
lipid
Dietary lipids are broken down into their two constituent parts: a glycerol molecule and fatty acids. The glycerol is chemically modified into one of the molecules produced during glycolysis. It enters the glycolysis pathway at that step and is broken down to yield energy. The fatty acids, meanwhile, are chemically modified into acetyl-CoA, at which point they enter the Krebs cycle.
What molecules are formed during glycolysis?
During glycolysis, glucose is broken down into two pyruvate molecules. Energy is captured and stored in the high-energy molecules ATP and NADH.
t three types of energy-rich molecules are formed during the Krebs cycle?
During the Krebs cycle, in which the two pyruvate molecules formed during glycolysis are broken down into carbon dioxide, energy is captured and stored in the high-energy molecules ATP, NADH, and FADH2.
What is the ultimate fate of the electrons passed through the electron transport chain?
Energy is released from electrons while they travel through the electron transport chain, which ultimately leads to the formation of most of the ATP needed by the cell. These low-energy electrons are ultimately combined with oxygen and hydrogen ions to form water.
Compare and contrast fermentation in animals and in yeast.
Fermentation involves the partial breakdown of glucose in the absence of oxygen. Both processes produce energy in the form of ATP without oxygen. This results in the production of lactic acid in animals and the production of ethanol and carbon dioxide in yeast.
biofuels
Fuels produced from plant and animal products.
fossil fuels
Fuels produced from the decayed remains of ancient plants and animals; include oil, natural gas, and coal.
Does the conversion of ADP to ATP require or release energy?
How about the conversion of ATP to ADP? Energy is required to convert ADP into high-energy ATP molecules, whereas energy is released when these high-energy ATP molecules are converted back into ADP.
glycolysis
In all organisms, the first step in cellular respiration, in which one molecule of glucose is broken into two molecules of pyruvate. For some organisms, glycolysis is the only means of extracting energy from food; for others, including most plants and animals, it is followed by the Krebs cycle and the electron transport chain. [Gk., glykys, sweet + lysis, releasing]
primary electron acceptor
In photosynthesis, a molecule that accepts excited, high-energy electrons from chlorophyll a, beginning the series of electron handoffs known as an electron transport chain.
pigment
In photosynthesis, molecules that are able to absorb the energy of light of specific wavelengths, raising electrons to an excited state in the process. [Lat., pigmentum, paint]
Sugars.
In the case of dietary carbohydrates, many are polysaccharides—multiple simple sugars linked together—rather than solely the simple sugar glucose. Before they can be broken down by cellular respiration, the polysaccharides must first be separated by enzymes into glucose or related simple sugars.
thylakoids
Interconnected membranous structures in the stroma of a chloroplast, where light energy is collected and converted to chemical energy in photosynthesis. [Gk., thylakis, dim. of thylakos, bag]
Give two examples of kinetic energy and potential energy.
Kinetic energy is the energy of moving objects, such as legs pushing bike pedals or a bird flapping its wings. Heat and light are also forms of kinetic energy. Heat results from lots of molecules moving rapidly, and light is created through the movement of high-energy particles. Potential energy is stored energy, such as water behind a dam, a snowboarder at the top of a hill, and a concentration gradient within a cell.
Is it that easy?
No. Putting sugar—a molecule with lots of energy stored within its chemical bonds—in the vase water is like offering a free lunch. And many, many organisms are looking for a free lunch. Unfortunately, when you add sugar, bacteria on the flower stems can grow rapidly, blocking the water-conducting tubes in the stems. This slows the flow not just of sugar, but of water as well.
carotenoids
Pigments that absorb blue-violet and blue-green wavelengths of light and reflect yellow, orange, and red wavelengths of light. [Lat., carota, carrot]
Q: How do plants get the energy they need to stay alive?
Plants use photosynthesis to harness light energy, converting it to sugar molecules that serve as their food.
Proteins.
Proteins are chains of amino acids. After consumption, the chains are broken down chemically, then each amino acid is broken down into (1) an amino group that may be used in the production of tissue or excreted in the urine, and (2) a carbon compound that is converted to one of the intermediate compounds in glycolysis or the Krebs cycle, allowing the energy stored in its chemical bonds to be harnessed.
potential energy
Stored energy; the capacity to do work that results from an object's location or position, as in the case of water held behind a dam. [Lat., potentia, power]
What are the two regions of the chloroplast in which the two main portions of photosynthesis take place?
The "photo" portion of photosynthesis occurs in the thylakoids of the chloroplasts, while the "synthesis" portion of photosynthesis occurs in the stroma of the chloroplasts.
Are there reasons to question the validity of the NADH supplement study's findings? Explain.
The book notes that a for-profit corporation, which markets and sells the NADH supplements, conducted the research. Although this does not invalidate the study (because it was well designed and controlled), it does raise questions about possible researcher bias. Replication of the study and results could increase our confidence in the researchers' conclusions.
energy
The capacity to do work, which is the moving of matter against an opposing force. [Gk., energeia, activity]
ethanol
The end product of fermentation of yeast; the alcohol in beer, wine, and spirits. [Contraction of the full chemical name, ethyl alcohol]
What molecules are produced in the "photo" portion of photosynthesis?
The energy in sunlight is captured and stored in ATP and NADPH molecules. When water molecules are split to provide electrons for this process, oxygen molecules also are formed.
kinetic energy
The energy of moving objects, such as legs pushing the pedals of a bicycle or wings beating against the air. [Gk., kinesis, motion]
What are the two possible fates of an excited electron in a chlorophyll molecule?
The excited electron may release energy while returning to its resting state, with some of this released energy used to excite electrons in a nearby molecule. Alternately, this excited electron itself could be transferred to another molecule.
Organisms on earth capture only about 1% of the energy from the sun. Use the two laws of thermodynamics to explain this.
The first law of thermodynamics states that energy can neither be created nor destroyed. So the energy that is not captured does not disappear. The second law of thermodynamics states that every conversion of energy is not perfectly efficient and includes the transformation of some energy to heat. The rest of the energy from the sun is transformed into heat, which is reflected into space or absorbed by the land, oceans, and atmosphere of earth.
chloroplast
The organelle in plant cells in which photosynthesis occurs. [Gk., chloros, pale green + plastos, formed]
electron transport chain
The path of high-energy electrons moving from one molecule within a membrane to another, coupled to the pumping of protons across the membrane, creating a concentration gradient that is used to make ATP; occurs in mitochondria and chloroplasts.
thermodynamics
The study of the transformation of energy from one type to another, such as from potential energy to kinetic energy. [Gk., thermē, heat + dynamis, power]
photosystems
Two arrangements of light-absorbing pigments, including chlorophyll, within the chloroplast that capture energy from the sun and transform it first into the energy of excited electrons and ultimately into ATP and high-energy electron carriers such as NADPH. [Gk., phos, light + systema, a whole compounded of parts]
What should you do?
With the addition to vase water of both sugar and an antibacterial chemical such as chlorine bleach, you can feed and protect your cut flowers, significantly increasing their longevity.
Can plants still photosynthesize once they're in a vase in your house?
Yes, but humans don't make it easy. Once cut, plants generally cannot produce sufficient sugar through photosynthesis. Light levels in houses tend to be a bit too low, and the loss of many or most plant leaves reduces the number of chloroplasts in which photosynthesis can occur. So they're starving to death.
broken down in the Krebs cycle.
e Modification 1. Each pyruvate molecule passes a pair of its high-energy electrons (and a proton) to the electron-carrier molecule NAD+, building two molecules of NADH. Modification 2. Next, a carbon atom and two oxygen atoms are removed from each pyruvate molecule and released as carbon dioxide. The CO2 molecules diffuse out of the cell and, eventually, out of the organism. In humans, for example, these CO2 molecules pass into the bloodstream and are transported to the lungs, from which they are eventually exhaled. Modification 3. In the final step in the preparation for the Krebs cycle, a giant compound known as coenzyme A attaches itself to the remains of each pyruvate molecule, producing two molecules called acetyl-CoA. Each acetyl-CoA molecule is now ready to enter the Krebs cycle.
stomata (sing. stoma)S
mall pores, usually on the undersides of leaves, that are the primary sites for gas exchange in plants; carbon dioxide (for photosynthesis) enters and oxygen (a by-product of photosynthesis) exits through the stomata. [Gk., stoma, mouth]
The metabolic machinery
of a cell is able to extract energy from what types of molecules besides glucose? Other carbohydrates, proteins, and fats also can be broken down to yield energy. This breakdown is accomplished by either converting these molecules into glucose or converting them into some intermediate molecule in glycolysis or the Krebs cycle.
NADPHA molecule (nicotinamide adenine dinucleotide phosphate)
that is a high-energy electron carrier involved in photosynthesis, which stores energy by accepting high-energy protons. It is formed when the electrons released from the splitting of water are passed to NADP+.
