Organisms Capture & Store Free Energy for Use in Biological ...
Organisms Capture & Store Free Energy for Use in Biological Processes Photosynthesis & Cellular Respiration Anabolic pathway Catabolic pathway Heterotrophs -Capture
free energy present in carbon compounds produced by other organisms. Have the ability to metabolize carbohydrates, lipids, and proteins by hydrolysis as sources
of free energy. Autotrophs Capture free energy from physical sources in the environment. - Chemosynthesis
can occur in the absence of oxygen Lets look at Photosynthesis 1st Plants & other photosynthetic organisms produce foods that begin food chains. The sun is a constant energy source. Must be converted into a chemical energy in order to be useful to all non-photosynthetic organisms.
Most common chemical energy is glucose which is also the most common fuel organisms use for cellular respiration (more on that later) Where in the plant does photosynthesis occur? Outer Membrane Inner Membrane
Stroma Thylakoid Chloroplasts are said to have been bacteria that had a symbiotic relationship with a eukaryotic cell after the ancient eukaryotic cell engulfed it
CHLOROPLAST STRUCTURE & FUNCTIONS Chloroplast Chloroplaststructure structure Function Functionallowed
allowed Extensive membrane Thylakoids surface area of the thylakoids Extensive membrane surface area allows greater absorption of light by photosystems
Small Smallspace space(lumen) (lumen)within withinthe thethylakoids thylakoids
Allows faster accumulation of protons to create a concentration gradient Stroma region similar Stroma to cytosol of the cell Region similar to cytosol of the cell. Allows an area to form the enzymes necessary for
the Calvin cycle to work Double membrane on the outside outside= chloroplast envelope Isolates the working parts & enzymes of the chloroplast from the surrounding cytosol.
Where do plants get the resources they need to make their own food? The s un , air , an
d so il What does each resource offer the plant? Sun is the energy source used to drive anabolic/endergonic synthesis of glucose. Air provides the carbon necessary for glucose production .
Soil water and trace elements come from here. What are the by-products of photosynthesis? Oxygen and water If plants, bacteria & other autotrophs did not make glucose from air & sunlight, , how would the earths heterotrophs be
affected? They would all die once everything on earth had been eaten, since only autotrophs can make food. Overall Process of Photosynthesis How does the water get to the chloroplast?
How does the CO2 get to the chloroplast? Houses most of the chloroplasts Lets Look at some stomata Go on a hunt for leaves.
Try to find 3 different leaves Make sure each type of leaf has a width Stay away from pine like leaves. All arrows are pointing to stomata Post Lab Questions
How do guard cells open & close stomata? At what time of day might more stomata be closed & justify your answer. Usually plants open most of their
stomata during the day. In drier, hotter regions, plants usually have more of their stomata open at night in order to reduce loss of water vapor. Why does the lower epidermis usually have more stomata than the upper epidermis?
Many plants are adapted to an environment where the upper surface is exposed to strong sunlight and higher temperatures and/or where water is more limited compared to a watery environment. =more stomata on the bottom than the top What about other plants? Underwater plants are in 100 percent humidity; transpiration does not
occur. So there is no need for water vapor. = zero stomata Plants adapted to an environment where only the upper side of the leaf is exposed to air; thus, only one surface can exchange water vapor with the environment. = lots of stomata on the upper side of the leaves Why does the density of stomata differ among plants?
It depends on the environmental conditions, such as: Amount of sunlight Amount of atmospheric carbon dioxide concentrations Amount of humidity in the environment Define transpiration Transpiration is the process by which moisture is carried through plants from roots to the stomata, where it changes to vapor and is released to the
atmosphere. evaporation of water from plant leaves. Transpiration also includes a process called guttation, which is the loss of water in liquid form from the uninjured leaf or stem of the plant, principally through water stomata. What 2 gases move in & out of the
leaf stomata? What does a larger number of leaf stomata indicate about the growing climate of that plant? A large number of stoma indicate that there is an excess rate of transpiration from the leaves which is an indication that the plant is in excess water supply
What pigments do leaves have? chlorophyll a, chlorophyll b, carotene, an xanthophyll LETS CHECK THEM OUT!!! ACTION AND ABSORPTION SPECTRA OF PHOTOSYNTHESIS
Various pigments in photosynthesis absorb photons of light from specific wavelengths of the visible spectrum. Why do leaves change colors in the fall? History of Photosynthesis Originated in
prokaryotes. Scientific evidence supports that prokaryotic photosynthesis was responsible for the production of an oxygenated atmosphere.
There are two major stages The Light-Dependent Reaction The Light-Independent Reaction (Calvin Cycle) Write a one-sentence summary, describe what happens in each of these phases.
Light Dependent Reactions The photon energy of sunlight is captured and converted to molecules that can be used to power the second phase; specifically NADPH & ATP. Light Independent Reactions (Calvin Cycle) The molecules from the light dependent
reactions are used to build carbon chains from carbon dioxide Lets start with the Light Reactions How does a satellite dish bring more TV stations & better reception to your TV?
The larger the parabola, the more signals it can gather & bounce on to a single focus point before it sends the signal to your TV. How are the pigments like a satellite dish? Accessory pigments in the thylakoid membranes train the collected energy onto a focal point so that the sum total of its strength is used to excite the electrons on chlorophyll a.
Which pigments are at the focal point? Which pigments are accessory pigments surrounding the chlorophyll a? What are these central chlorophyll a molecules called? Photosystems PS I and PS II Chlorophyll a
Chlorophyll b & carotenoids Modern-day plants have 2 photosystems Chlorophylls absorb free energy from light, boosting electrons to a higher energy level in photosystems I & II Photosystem I Most efficient at absorbing wavelengths at 700nm
Photosystem II Most efficient at absorbing wavelengths at 680nm Light Dependent Reaction Occurs in the thylakoids or grana of chloroplast. Light is absorbed in the pigments (chlorophylls and carotenoids) which are organized on the membranes of the thylakoids.
The regions of organization are called photosystems which include: Chlorophyll a molecules Accessory pigments A protein matrix The reaction centre is the portion of the photosystem that contains: A pair of cholorophyll molecules
A matrix of protein A primary electron acceptor Photosystems I & II are connected by the transfer of higher free energy electrons through an electron transport chain (ETC). If an atoms electrons are energized, then they can get so excited they will leave the orbital & jump off the
atom/molecule in a state of high energy At what point does the electron have the greatest potential energy? When the electron is in its excited state PHOTOSYSTEM II These electrons are captured by the primary acceptor of the reaction center. Chlorophyll a is a strong oxidizing agent when
it has lost its electron. What will the chlorophyll a molecule do now that it is missing an electron from its orbital? Water is split by an enzyme to produce electrons, hydrogen ions, and an oxygen atom. This process is driven by light energy & is called photolysis. The electrons are supplied one by one to the chlorophyll a molecules of the reaction center.
The leftover oxygen will find another broken water molecule & become O2 gas (a by-product of photosynthesis). Electron Transport Chain (ETC) Electrons are transferred between molecules in a sequence of reactions as they pass through the ETC. An electrochemical gradient of
hydrogen ions (protons) is established across the thylakoid membrane The excited electrons pass from the primary acceptor down an electron transport chain (ETC) losing energy at each exchange.
The energy lost from the electrons moving down the ETC drives chemiosmosis to bring about phosphorylation of ADP to produce ATP Movement of ions down their electrochemical gradient through a selectively permeable membrane. The Calvin cycle needs 18ATP molecules and 12 NADPH molecules for every molecule of glucose produced.
NADPH is an energy storage/shuttle molecule. We have just discussed how ATP is generated. How do you think NADPH is generated? PS I captures light energy (nearly the same manner PS II captured light to generate ATP) & generates an NADPH molecule. Chlorophyll a molecule from PS I replaces its missing electrons with the electrons that came from the electron transport chain
following PS II. Photophosphorylation High-energy electrons derived from light activation of chlorophyll molecules -no carbon fuel source necessary -Final electron acceptor is
NADPH NADPH is not made from a chemiosmotic gradient in the thylakoids, but instead the electron pair is given to NADP+ directly to be used in the form of NADPH. What does the Light Dependent Reactions Do Overall? The production of:
NADPH (Nicotinamide Adenine Dinucleotide Phosphate Hydrogen) ATP (Adenosine Tri-Phosphate) Oxygen is given off as a waste product (lucky for us ). ). NADPH & ATP supply the chemical energy for the light independent reactions (aka Calvin cycle).
Cyclic Photophosphorylation (Cyclic Electron Flow) Since the Calvin Cycle uses more ATP than NADPH sometimes this type of electron flow is necessary. The accumulation of NADPH will trigger the shift from non cyclic to cyclic photophosphorylation Now for the Light Independent Reactions AKA Calvin Cycle
Occurs within the stroma of the chloroplast Light Independent Reactions AKA: Calvin Cycle This reaction uses the ATP and NADPH produced by the light dependent reaction. We are synthesizing sugar in this reaction.
What are the starting molecules and the ending molecules? The process begins with CO2 binding to ribulose bisphosphate After three turns of the Calvin cycle, half a glucose molecule, called G3P, is produced.
How much energy is used to fuel this anabolic process? Calvin Cycle Song Ribulose Biphosphate Each reaction in this multi-step process is catalyzed by a reactantspecific enzyme. The 1st enzyme performs a critical step of
capturing CO2 & fixing it so that its committed to entering the Calvin cycle. Name this 1st enzyme: Rubisco is the enzyme that binds carbon to ribulose biphosphate. How does the Calvin cycle regenerate the starting molecule
ribulose bisphosphate (RuBP)? The cycle uses a series of reactions and 3 molecules of ATP to regenerate RuBP. Light-dependent Light-independent/ Calvin Cycle
Occurs in the thylakoids Occurs in the stroma Uses light energy to form ATP & NADPH Uses ATP & NADPH to form glyceraldehyde 3 phosphate (triose phosphate). Splits water (photolysis) to provide Returns ADP, inorganic phosphate & NADP +
replacement electrons and H , & to release to the light-dependent reaction. oxygen Includes ETC photosystems I & II Involves the Calvin cycle Its time for a simulation!!!!
Summarize the simulation. What is limiting the Calvin cycle? What is produced in excess? The amount of ATP produced. NADPH
How can the stroma accumulate more ATP? By running through the 1st electron transport chain of the light reactions more often, rather than running through both electron transport chains an equal number of times. Rubisco...friend with a bad habit Rubisco is so important to plants that it makes up 30% or more of the soluble protein in a typical plant leaf.
But rubisco also has a major flaw (bad habit): instead of always using CO2, as a substrate, it sometimes picks up O2instead. What happens if O2 hooks up with Rubisco? Photorespiration occurs. O2 binds to RuBP (which has a greater affinity to oxygen) and enters the Calvin cycle.
The oxygen splits carbon chains glucose is not produced by this process. ATP is consumed. Plants can lose as much as 50% of their fixed carbon through photorespiration. What determines which molecule is "chosen"?
Two key factors: the relative concentrations of O2, & CO2 the temperature. When a plant closes its stomatafor instance, to reduce water loss by evaporation, O2 from photosynthesis builds up inside the leaf.
Photorespiration increases due to the higher ratio of O 2 to CO2 Rubisco has a higher affinity for O2, when temperatures increase. How can you explain the evolution of photorespiration when this process appears to be expensive and counterproductive to the survival of
the plant? Develop a supporting hypothesis to this question. Hypothesis currently favored by the scientific community: It is assumed that rubiscos flaw is due to the fact that during the evolution of this ancient
process the amount of oxygen was either nonexistent or very low. The bottom line is that hot, dry conditions tend to cause more photorespiration. What about plants in areas that are always like this?
Through the process of natural selection. Beneficial features that showed up CAM plants such as pineapples & cacti CAM (crassulacean acid metabolism): at night, they open their stomata, allowing CO2 to diffuse into the leaves.
Helps plants conserve water. Take up CO2 oxaloacetate by PEP carboxylase (the same step used by C4) Store the organic acid in vacuoles until morning CO2 is taken out of the malic acid & sent to the Calvin cycle. CAM
plants C4 plants & photosynthetic adaptations The light-dependent reactions and the Calvin cycle are physically separated. The light-dependent reactions occurring in the mesophyll cells the Calvin cycle occurring in special cells
around the leaf veins. These cells are called bundle-sheath cells C4 plants & photosynthetic adaptations C4: a spatial separation of light and dark reactions . Use 2 different cells
Fixes carbon with the help of PEP carboxylase which has only an affinity towards CO2 Makes oxaloacetate a 4 C molecule C4 plants
Because the mesophyll cells constantly pump CO2 into neighboring bundle-sheath cells in the form of malate, theres always a high concentration CO2 relative to O2 right around rubisco. This strategy minimizes photorespiration. Summarize the difference between C4 and CAM Plants C4 plants minimize photorespiration by separating CO2, fixation and the Calvin cycle in space, performing these
steps in different cell types. Crassulacean acid metabolism (CAM) plants minimize photorespiration and save water by separating these steps in time, between night and day. Determine the answers to the following questions. Why are C4 and CAM photosynthesis considered to be coping mechanisms used by plants living in
arid climates? Describe 3 specific differences in the processes of C4 and CAM compared to the processes that occur in C3 photosynthesis. Do you think C4 and CAM plants photorespirate? Support your opinion with a scientific argument. Why are C4 and CAM photosynthesis considered to be coping mechanisms used by plants living in arid
climates? C4 plants use PEP to fix carbon, which has a much higher affinity to carbon dioxide than rubisco. This allows C4 plants to keep their stomata closed or partially closed without losing the ability to fix carbon. CAM plants keep their stomata closed during the day to minimize water loss when the sun is hottest.
Describe 3 specific differences in the processes of C4 and CAM compared to the processes that occur in C3 photosynthesis. C4 plants use PEP rather than rubisco to fix carbon. C4 plants have a spatial separation of carbon fixation & the Calvin cycle. C4 plants use 2 distinct types of mesophyll cells- mesophyll cells for carbon fixation and bundle sheath cells for the Calvin cycle. C4 plants store carbon as oxaloacetate. CAM plants store carbon as an organic acid until it is needed by the Calvin
cycle. CAM plants have a temporal separation of carbon fixation and the Calvin cycle. CAM plants open their stomata during the night and close them during the day. Do you think C4 and CAM plants photorespirate? Support your opinion with a scientific argument. C4 plants are less likely to photorespirate because photorespiration takes
place when rubisco is in the presence of higher concentrations of oxygen & low concentrations of carbon dioxide. In C4 plants the Calvin Cycle occurs in bundle-sheath cells where the carbon dioxide levels are kept high. CAM plants are unlikely to lose much of their energy to photorespiration because these plants maintain a high level of carbon dioxide by fixing adequate amounts of carbon in organic acids during the night. Because we see C4 plants and CAM plants dominating arid environments where photorespiration would normally be very high, it can be assumed that these plants have more successfully adapted to this particular type of
environmental stress. How would you determine if a plant was a C3, C4, or CAM plant? What about plants in hot environments today? Besides having a problem with rubisco because of the hot
temperatures, what other problems do they face? What type of challenges do you think this plant might face in its native habitat? dehydration What do plants lose when
their stomata are open, collecting CO2 ? water What part of photosynthesis would stop if water were unavailable? Chlorophyll a would not have an electron donor, so ATP would not be made and the Calvin cycle, in turn, would stop.
How has this plant evolved to conserve water? It has a thicker, waxier cuticle
It has leaves modified to be spines so that its surface to volume ratio is reduced. Many cacti have clear hairs on their surfaces to reflect sunlight and make an insulated layer of humidity around the plant.
Cacti are able to expand greatly when it rains in order to store water for times of drought.
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