Mission 1: Cellular Respiration
Mission Objectives. You should be able to...
1. Describe and explain the process of cell respiration.
2. Identify the molecule that gives a cell its energy.
3. Differentiate between aerobic and anaerobic respiration.
Mission Objectives. You should be able to...
1. Describe and explain the process of cell respiration.
2. Identify the molecule that gives a cell its energy.
3. Differentiate between aerobic and anaerobic respiration.
Recall that energy is stored in the bonds between atoms within molecules. When these bonds are broken, the energy is released. Each time a bond is broken, a small amount of energy is released. The ultimate objective is to release energy in a controlled manner in the form of ATP molecules. Respiration is the process by which glucose is converted to ATP and it occurs inside the cell, within the mitochondria.
Image courtesy of freelearningchannel.org
Image courtesy of freelearningchannel.org
Aerobic Respiration. There are three steps:
Glycolysis: Takes place outside the mitochondria, within the cytoplasm. Glucose is broken down into two molecules of pyruvate (which are 3-carbon molecules). For every glucose molecule used, 2 molecules of ATP are produced. A compound called NADH is also produced. The pyruvate then diffuses into the mitochondrion, within the matrix, and forms a complex that converts the pyruvate into an enzyme called acetyl CoA, which is a 2-carbon molecule. Acetyl CoA moves into the second phase, the Krebs Cycle, and the remaining carbon is given off in the form of carbon dioxide. So the end products of glycolysis are two pyruvate and two ATP.
Image courtesy of science leadership academy.
Glycolysis: Takes place outside the mitochondria, within the cytoplasm. Glucose is broken down into two molecules of pyruvate (which are 3-carbon molecules). For every glucose molecule used, 2 molecules of ATP are produced. A compound called NADH is also produced. The pyruvate then diffuses into the mitochondrion, within the matrix, and forms a complex that converts the pyruvate into an enzyme called acetyl CoA, which is a 2-carbon molecule. Acetyl CoA moves into the second phase, the Krebs Cycle, and the remaining carbon is given off in the form of carbon dioxide. So the end products of glycolysis are two pyruvate and two ATP.
Image courtesy of science leadership academy.
Krebs Cycle: The acetyl CoA that resulted from glycolysis is now within the mitochondrion. It is metabolized further and the carbons turn into carbon dioxide, which diffuses out of the mitochondrion. Two more ATP are produced from each original pyruvate, and more energy is added to NADH. NADH has high energy electrons that go to the ETC. The Krebs cycle then repeats.
Electron Transport Chain. The energy that was in glucose is now in NADH and another molecule called FADH. They transfer their electrons to the electron transport chain. The electrons move through a series of proteins and the energy of the proteins are used to pump hydrogen ions into the inter membrane space within the mitochondrion. The electrons are added to other protons and the oxygen we breathe in combine to make water. A lot of energy is produced during the ETC.
Anaerobic Respiration. This is what happens when there is no oxygen present (or there are no mitochondria). Glycolysis shuts down when NAD+ transfers all available electrons to NADH. What happens as a result is called lactic acid fermentation, which takes place in muscle cells. Glucose is converted to pyruvate, which is then further converted into lactic acid. The lactic acid accepts the electrons so that more NAD+ can be formed, and NAD+ can be recycled. Each time this happens, 2 ATP are produced. However, lactic acid (sometimes called lactate) builds up in muscles like a toxin. Oxygen is required to oxidize the lactate, and this process is called lactic acid fermentation.
This is why your muscles are sore after intense exercise, and why it is important to warm up and cool down properly before and after exercising. Your muscles need the oxygen to remove the lactate so that you won't be sore.
Alcoholic fermentation works the same as LAF. This occurs in some bacteria. Pyruvate is broken down into ethanol, which accepts electrons to recycle NAD+. The difference is that carbon dioxide is produced instead of lactic acid. This is how wine and beer are made.
Image courtesy of leavingcertbiology.net
Electron Transport Chain. The energy that was in glucose is now in NADH and another molecule called FADH. They transfer their electrons to the electron transport chain. The electrons move through a series of proteins and the energy of the proteins are used to pump hydrogen ions into the inter membrane space within the mitochondrion. The electrons are added to other protons and the oxygen we breathe in combine to make water. A lot of energy is produced during the ETC.
Anaerobic Respiration. This is what happens when there is no oxygen present (or there are no mitochondria). Glycolysis shuts down when NAD+ transfers all available electrons to NADH. What happens as a result is called lactic acid fermentation, which takes place in muscle cells. Glucose is converted to pyruvate, which is then further converted into lactic acid. The lactic acid accepts the electrons so that more NAD+ can be formed, and NAD+ can be recycled. Each time this happens, 2 ATP are produced. However, lactic acid (sometimes called lactate) builds up in muscles like a toxin. Oxygen is required to oxidize the lactate, and this process is called lactic acid fermentation.
This is why your muscles are sore after intense exercise, and why it is important to warm up and cool down properly before and after exercising. Your muscles need the oxygen to remove the lactate so that you won't be sore.
Alcoholic fermentation works the same as LAF. This occurs in some bacteria. Pyruvate is broken down into ethanol, which accepts electrons to recycle NAD+. The difference is that carbon dioxide is produced instead of lactic acid. This is how wine and beer are made.
Image courtesy of leavingcertbiology.net
Mission 2: Photosynthesis
Mission Objectives. You should be able to...
1. Describe and explain the process of photosynthesis.
2. List the wavelengths of light used in photosynthesis.
3. Describe and explain the factors that limit photosynthesis.
Mission Objectives. You should be able to...
1. Describe and explain the process of photosynthesis.
2. List the wavelengths of light used in photosynthesis.
3. Describe and explain the factors that limit photosynthesis.
Recall that photosynthesis is the process by which plants convert carbon dioxide and water into glucose and oxygen. It is the reverse process of respiration that takes place in plant chloroplasts. The pigment chlorophyll absorbs sunlight.
Image courtesy of brittanica.com
Image courtesy of brittanica.com
We can see a portion of the electromagnetic spectrum as visible light, and even though chlorophyll absorbs most of the light wavelengths except green, we will focus on the red end, the blue end, and the green middle. When light energy is absorbed, it may be used. When energy is reflected, we see it at a particular wavelength as color. When all colors are reflected, we see white. When all colors are absorbed, we see black. So again, we see green because chlorophyll reflects it, but all other wavelengths are absorbed.
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Photosynthesis occurs in two stages: the light-dependent and light-independent. Light-dependent reactions (LDR) obviously involve the sun. Light energy is converted into ATP and split water into hydrogen and oxygen (called photolysis). The oxygen is released as a waste product (which we need to breathe). So the products of LDR are hydrogen and ATP. Light-independent reactions (LIR) do not necessarily require sunlight in order to take place. The ATP and hydrogen are used as forms of chemical energy to convert carbon dioxide and water into useful molecules for the plant. It takes six carbon dioxide molecules to form one glucose molecule.
Fixation is the process by which this happens. Carbon dioxide and water are fixed into glucose and oxygen is produced as a waste product. Fixation requires energy, which comes from the ATP and hydrogen created in the LDR, which came from sunlight.
The rate of photosynthesis is dependent upon environmental factors, such as intensity of light and air temperature. During the daytime, the rate may be very high for a particular plant. At night, the rate of photosynthesis may drop to zero. Measuring the rate of oxygen production or carbon dioxide intake is an indicator of photosynthetic rate as long as a correction is made for cell respiration.
The rate of photosynthesis is dependent upon environmental factors, such as intensity of light and air temperature. During the daytime, the rate may be very high for a particular plant. At night, the rate of photosynthesis may drop to zero. Measuring the rate of oxygen production or carbon dioxide intake is an indicator of photosynthetic rate as long as a correction is made for cell respiration.
From the Pearson (2014) text:
Cellular Respiration Questions
Photosynthesis Questions
Cellular Respiration Questions
- Which stage of cellular respiration is common to all types of cell respiration?
- Where does this stage of cell respiration occur in a cell?
- Why does that make sense?
- Why do we inhale oxygen and exhale carbon dioxide?
Photosynthesis Questions
- Plants produce sugars via photosynthesis. What do plants do with the sugars after that?
- Why do most plants produce an excess of sugars in some months of the year?