Unit 4 Study Guide PDF

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Summary/study guide for Unit 4 of BIO 152 with Dr. O'Quinn. ...

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Unit 4: Learning Objectives  Describe the two linked reactions that make up photosynthesis. o Light dependent reactions  The energy from sunlight is absorbed by chlorophyll and converted into chemical energy in the form of electron carrier molecules like ATP and NADPH  Take place in the thylakoid membranes of chloroplasts; comprised of photosystem 1 and 2 o Light independent reactions  aka Calvin cycle  carbohydrate molecules are assembled from carbon dioxide using the chemical energy harvested during the light-dependent reactions  takes place in the stroma  Identify the parts of the chloroplast. o Envelope: double-membrane structure comprised of an outer and inner membrane o Stroma: aqueous matric present inside of the chloroplast; internal components and several solutes are dispersed within; rich in proteins and contains enzymes vital for cellular processes o Thylakoids: internal, membrane-bound network of flattened sac-like structures inside a plant chloroplast that functions in converting light energy to chemical energy o Granum: in chloroplasts, a stack of flattened membrane-bound thylakoid discs where the light reactions of photosynthesis occur o Lumen: the space inside a thylakoid

 Describe the role chlorophyll and carotenoids in photosynthesis and what colors of light they absorb or reflect. o Chlorophyll

 Any of several closely related green pigments, found in the chloroplasts, that absorb light during photosynthesis  Absorb blue and red, reflect green o Carotenoid  Extend the range of wavelengths that can participate in photosynthesis and help to quench free radicals and protect the chlorophyll molecules from harm  Absorb blue and green, reflect yellow, orange, and red  Describe the basic structure of a photosystem and how energy and electrons are transferred within the system. o Photosystems  Present in the thylakoid membranes, they are structural and functional units for harnessing light energy  Comprised of a reaction center surrounded by light harvesting antenna complexes that contain chlorophyll, carotenoids, and other photosynthetic pigments  Antenna complex  part of a photosystem, containing an array of chlorophyll molecules and accessory pigments that receives energy from light and directs the energy to a central reaction center during photosynthesis  Resonance energy transfer: the chlorophyll absorbs the energy from a photon and an electron is excited. This energy—NOT the electron—is passed to a nearby chlorophyll molecule, where another electron is excited in response  Reaction center  centrally located component of a photosystem containing proteins and a pair of specialize chlorophyll molecules; it is surrounded by antenna complexes  Oxidation/reduction: eventually the energy from the antenna complex reaches a chlorophyll molecule in the reaction center, exciting it which results in an electron being passed to an electron acceptor  Describe how photosystem II works, where it takes place in the chloroplasts, how electrons move, any input that is needed, and the resulting output and where it is sent. 1. Electron from reaction center is transferred to an electron acceptor. 2. Electrons from that acceptor are passed to an electron carrier which shuttles the electrons to the electron transport chain. 3. The electron carrier passing the electrons to the ETC also helps transport protons from the stroma to the lumen. 4. This establishes an electrochemical gradient. The protons diffuse down their concentration gradient back into the stroma through ATP synthase, producing ATP. o Located in the interior/middle of thylakoid o Electrons move from the reaction center acceptor  carrier  ETC

o Inputs: Sunlight, water, electrons that are made from the splitting of water molecules o Outputs: ATP (which is sent to the Calvin cycle), oxygen (released into the atmosphere), protons (sent through ATP synthase to make ATP)  Describe how photosystem I works, where it takes place in the chloroplasts, how electrons move, any input that is needed, and the resulting output and where it is sent. 1. The excited electron from the reaction center gets passed to ferrodoxin (an electron acceptor). 2. Ferrodoxin transfers the electron to NADP+ reductase which produces NADPH. o Located embedded in the thylakoid membrane o Inputs: electrons and light o Outputs: NADPH (sent to the Calvin cycle)  Identify how the reaction center electrons for photosystem I and II are replenished o Photosystem II: replenished by the splitting of water o Photosystem I: replenished by photosystem II  Describe how photosystem I and II are connected o Plastocyanin, an electorn carrier, bridges the systems together  Describe the three steps of the Calvin cycle, where the Calvin cycle takes place, the molecules that go into the pathway, the molecules produced by the pathway, where those molecules produced are sent, and how the pathway is regulated. Fixation 1. CO2 reacts with ribulose bisphosphate (in the presence of rubisco, a catalyst) to produce 2 molecules of 3-phosphoglycerate. Reduction 2. 3-phosphoglycerate is phosphorylated by ATP and reduced by NADPH to form glyceraldehyde-3 phosphate. a. Some of the G3P is sent to make sucrose. The rest is stored as starch. Regeneration 3. The rest of the G3P serves a substrate where, with the input of ATP, ribulose bisphosphate is regenerated.

 Describe what happens to the sugar produced by photosynthesis. o If photosynthesis is occurring…  Slowly: the sugar produced by photosynthesis powers cellular respiration  Rapidly: the sugar is converted to starch and serves as a temporary storage product  Describe the structures and basic anatomy of the leaf. Understand the different types of specialized structures and cells present in the leaves, including the vascular bundles, cuticle, epidermis, stomata, guard cells, mesophyll, and photosynthetic cells. o Vascular bundles: comprised of xylem and phloem o Cuticle: in leaves, a protective layer of a waxy substance secreted by epidermal cells that limits water loss o Epidermis: in plants, the outermost layer of cells in leaves, young stems (lacking secondary growth), and roots o Stomata: pores in the epidermis of a leaf that regulate the diffusion of gases between the interior of the leaf and the atmosphere o Guard cells: one of two cells surrounding the central pore of a stoma o Mesophyll: a leaf tissue of loosely packed photosynthetic cells o Photosynthetic cells: specialized plant cells that are central to food production by taking energy from the sun and converting it to make carbohydrates o Bundle sheath: a cylinder of cells that surrounds each vein in C 4 plants in which carbon dioxide is concentrated in bundle sheath cells, suppressing photorespiration

 Describe the advantages and disadvantages of the cuticle and stoma with regards to gas exchange and water loss. o Cuticle  Advantages: reduces water loss  Disadvantages: inhibits CO2 diffusion

o Stoma  Advantages: CO2 can diffuse in  Disadvantages: water vapor can diffuse out very quickly  Describe the mechanism used to open and close the stomata; understand the triggers that can cause this opening or closing. o Each stoma is comprised of 2 guard cells which can shrink or swell, changing the size of the central pore. o Opening and closing is dependent on the volume of the guard cells, which is caused by the movement of solutes and water into and out of the cell. o When solutes enter the cell, the concentration increases with water entering by osmosis, causing the cells to swell and the stoma opens. o When solutes leave the cell, water leaves as well, shrinking the cells and the

stoma closes.  Describe the changes to the photosynthetic pathway (to the extent described during lecture) in CAM plants. Explain how these changes in photosynthesis in CAM plants helps it survive in dry environments. o CAM plants only open their stomata at night to reduce the loss of water vapor. o System to store CO2 overnight by converting it to a non-diffusible form. o Live in dry environments 1. CO2 diffuses in through the open stomata. 2. It is converted into bicarbonate HCO3- by carbonic anhydrase. 3. PEP carboxylase, an enzyme, combines HCO3- and PEP to make a 4 carbon organic acid. 4. The 4 carbon organic acid gets stored in the cell’s vacuole. 5. The stomata close to conserve water when the sun comes up. 6. Simultaneously, the 4 carbon organic acid is transported from the vacuole to the chloroplast. 7. The 4 carbonic organic acid is then decarboxylated back to CO2 and PEP.

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The CO2 is sent to the Calvin cycle The PEP is converted to starch and stored until the sun goes down Greatly increases the amount of CO2 gained per unit of water lost Drawbacks: carbohydrate production is slower and only a limited amount of acid can accumulate and be sequestered overnight

 Describe the changes to the photosynthetic pathway (to the extent described during lecture) in C4 plants. Explain how these changes in photosynthesis in C4 plants helps it survive in hot environments. o live in hot, sunny environments o must have a way to suppress photorespiration—utilize bundle sheath and mesophyll cells 1. Capture CO2 in mesophyll cells via PEP carboxylase. 2. Combine bicarbonate HCO3- ions and PEP to make a 4 carbon organic acid. 3. Organic carbons diffuse through the plasmodesmata into bundle sheath cells. 4. Once inside the bundle sheath cells, the 4 carbon organic acid is decarboxylated to CO2 and 3 carbon molecule. o The CO2 is sent to the Calvin cycle. o The 3 carbon molecule diffuses back into the chloroplasts of the mesophyll cells where ATP is used to reform PEP o Increases the efficiency of the Calvin cycle by allowing high rates of photosynthesis in the bundle sheath cells by putting CO2 in direct contact with rubisco. o Lose less water because they can maintain a high concentration of CO2 in the bundle sheath cells

o  Describe the similarities and differences between the photosynthetic pathways for C3, CAM and C4 plants. Basis for C3 Pathway C4 Pathway CAM Comparison Such plants whose The plants which Plants that convert Definition store the energy from first product after the sunlight energy into the sun and then C4 carbon molecule carbon assimilation or oxaloacetice acid, convert it into energy from sunlight is 3during night follows which takes place carbon molecule or the CAM pathway. before the C3 cycle. 3-phosphoglyceric This is more efficient acid for the production of energy. than the C3 pathway. It is most commonly used by plants. Cells Involved

Mesophyll cells.

Mesophyll cell, bundle sheath cells.

Example

Sunflower, spinach, beans, rice, cotton. All photosynthetic plants. Present in high rate.

Sugarcane, maize, sorghum. In tropical plants.

Can be seen in Photorespiration

Not easily

Both C3 and C4 in same mesophyll cells. Cacti, orchids. Semi-arid condition. Detectable in the

For the production of glucose First stable product

12 NADPH and 18 ATP required. 3-phosphoglycerate (3PGA).

detectable. 12 NADPH and 30 ATP required. Oxaloacetate (OAA). (4 carbon acid)

Optimum temperature for photosynthesis

15-25 °C

30-40°C

afternoon. 12 NADPH and 39 ATP required. Oxaloacetate (OAA) at night, 3PGA at daytime. > 40°C

 Describe the structures and functions of xylem tissue. Identify how tracheids and vessel elements are different, and how this affects the flow of fluid through each type. o Xylem: conducts water and dissolved ions from the root system to the shoot system o Water can flow very easily through it due to its structure. o Cells that make up the xylem are dead at maturity. So, the cells have a cell wall, but lack cytoplasm or membranes, creating a hollow center for water to flow. o The walls are thick and contain lignin which increases the strength and prevents water from passing through the cell wall. o Water enters and exits the xylem cells though pits—no lignin is present. o Tracheids  Unicellular  5-50 micrometers in diameter  Less than 1 cm long  Water enters and exits through the pits, and will flow from one cell to another at their adjacent overlapping parts. o Vessels  Multicellular  10-500 micrometers in diameter  Can be several meters long  Water enters and exits through pits. The vessel elements have perforations that connect them and allow for continuous flow.  Because they’re longer and wider than the tracheids, plants with them achieve greater rates of water transport.  Describe how solute potential and pressure potential contribute to water potential and how these two factors combined determine water movement. Be able to predict water movement with given pressure and water potentials. o Water potential: the potential energy of water in a certain environment compared with the potential energy of pure water at room temperature and atmospheric pressure; in living organisms, water potential equals the solute potential plus the pressure potential; (Ψw) = Ψs + Ψp o Water flows from areas of high water potential to low water potential.

o Solute potential: a component of the potential energy of water caused by a difference in solute concentrations at two locations; can be zero (pure water) or negative  The addition of ANY solute will make the solute potential negative o Pressure potential: a component of the potential energy of water caused by physical pressures on a solution; can be positive or negative  Turgor pressure: the outward pressure exerted by the fluid contents of a living plant cell against its cell wall  Wall pressure: the cell wall pushing back against the turgor pressure  Positive: “pushing”, results in an increase in pressure potential  Negative: “pulling”, results in a decrease in pressure potential

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Describe the water-potential gradient along a tree—i.e. where is water potential highest and lowest.

 Describe the two routes water can take to the xylem and how the Casparian strip might impede this movement. o Apoplast: in plants, the region outside the plasma membranes consisting of the porous cell walls and the intervening extracellular air space o Symplast: in plants, the region inside the plasma membrane; the symplast of adjacent cells is often connected through the plasmodesmata o Casparian strip: in plant roots, a waxy layer containing suberin, a water-repellant substance that prevents the movement of water through the endodermal cells, thus blocking the apoplastic pathway of water and ion movement into the vascular tissue; acts as a filter with the endodermal cells allowing useful ions to pass and harmful or unneeded ones from reaching the xylem  Water moving via the apoplastic route has to detour to the symplastic route in order to pass through the Casparian strip.

 Describe the three different forces that are involved in moving water up a tube. o Adhesion: a molecular attraction among unlike molecules; the water interacts with the cell walls of the tracheids or vessel elements; as water molecules bond to each other and to the side of the tube, they are pulled upward—capillary action o Cohesion: molecular attraction among like molecules, such as the H bonding that occurs among molecules of water; the upward pull of adhesion is transmitted to the rest of the water column because of cohesion, allowing water to rise against gravity o Surface tension: a force that exists among water molecules at the air-water interface; these molecules share stronger attractive forces because they can only H bond with molecules beside and below them; this results in tension that minimizes surface area and exerts a pull against gravity, resisting deformation of the liquid’s surface

o Cohesion tension theory: states that water is pulled to the tops of trees along a water potential gradient, via forces generated by transpiration at leaf surfaces

 Describe in step-by-step detail how xylem pulls water through its cells, from roots to shoots, and how environmental conditions such as humidity, wind, and temperature might influence this water movement. 1. A steep water gradient is created when the stoma open and humid air inside the leaf is exposed to the drier atmosphere, causing water vapor to diffuse out. 2. As water exits the leaf, the humidity of the spaces inside the leaf drops, causing water to evaporate from the menisci that exist at the air-water interfaces. 3. The tension generated at the air-water interface is transmitted though the water outside of the leaf cell, to the water in the xylem, to the water in the vascular tissues of roots, and finally to the water in the soil. o The transmission of forces from the leaf surface to the roots is possible thanks to the continuous column of water and cohesion o This movement of water is a passive process, powered by solar energy o Humidity  High relative humidity: the atmosphere contains more moisture than the interior of the leaf, so transpiration is reduced  Low relative humidity: the atmosphere is less moist, so it’s a greater driving force for transpiration o Temperature  Warmer air: increase driving force for transpiration; causes stoma to open  Colder air: decrease driving force for transpiration; causes stoma to close o Soil water  Adequate soil moisture: plants will normally transpire at high rates bc the soil provides the water to move through the plant

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 Inadequate soil moisture: plants cannot transpire without wilting if the soil is very dry o Wind  Wind: increases the rate of transpiration o “The cohesion-tension theory explains how water moves up through the xylem. Inside the leaf at the cellular level, water on the surface of mesophyll cells saturates the cellulose microfibrils of the primary cell wall. The leaf contains many large intercellular air spaces for the exchange of oxygen for carbon dioxide, which is required for photosynthesis. The wet cell wall is exposed to the internal air space and the water on the surface of the cells evaporates into the air spaces. This decreases the thin film on the surface of the mesophyll cells. The decrease creates a greater tension on the water in the mesophyll cells, thereby increasing the pull on the water in the xylem vessels. The xylem vessels and tracheids are structurally adapted to cope with large changes in pressure. Small perforations between vessel elements reduce the number and size of gas bubbles that form via a process called cavitation. The formation of gas bubbles in the xylem is detrimental since it interrupts the continuous stream of water from the base to the top of the plant, causing a break (embolism) in the flow of xylem sap. The taller the tree, the greater the tension forces needed to pull water in a continuous column, increasing the number of cavitation events. In larger trees, the resulting embolisms can plug xylem vessels, making them non-functional.” Describe the two potential ways in which xylem tissue could fail, and be unable to move water along. o 1. Pathogens or other organisms that destroy the absorptive surface area in the soil. o 2. Drought can cause roots to shrink. o 3. The occurrence of a cavitation which causes a gas bubble to form and fill the conduit, blocking water movement. Can be caused by freezing or drought. o ^^^ I didn’t have this in my notes, so I just googled it. Describe the difference between a carbohydrate source and sink in a plant. Explain how a sink at one point in time could be a source at a different time. o Source: tissue where sugar enters the phloem, where sugar is produced o Sink: tissue where sugar exits the phloem, where sugar is needed  During the growing season…  Sources: mature leaves and stems that are actively photosynthesizing  Sinks: developing leaves and flowers, developing seeds and fruits, and storage cells in roots  Early in the growing season, right after a plant resumes growth after the winter or dry season…  Sources: storage cells in roots and seeds  Sinks: developing leaves Describe the functions and structures of phloem tissue in plants. Ident...