Support in Terrestrial Plants & Adaptations

Support in Terrestrial Plants Some terrestrial plants attain enormous sizes. For example the picture on the left is the giant sequoia of the west coast of North America. These trees reach over 90 m

Support in Terrestrial ant The support for the enormous trees is provided by three factors: Thickened Cellulose Cell Turgor pressure Lignified Xylem

Thickening of the cellulose cell wall. The cell wall’s of supporting tissues of plants are thickened with cellulose. Note the extra thickening of the cells towards the outer (lower) sections of this stem section. Above figure shows the cell wall’s of a stem.

Thickening of the cellulose cell wall. The photograph to the right show the thickening of the cellulose walls of the xylem

Lignified xylem vessels Lignin is a highly branched polymer. In the diagram to the far left the xylem shows a cylinder of cellulose cell wall with annular lignification in rings.

Cellulose in cell walls & Lignin in xylem act together to provide support Stem cells, including xylem cells occur in cylindrical arrangements within a plant. These act like strong rods to support plant during high winds.

Cell turgidity and plant support: Turgor Pressure: Support for plants generated by wall pressures a) Water enters the cell by osmosis from the higher osmotic potential (solute potential) to the lower osmotic potential (solute potential). b) The volume of the cell cytoplasm increases forcing the plasma membrane outwards against the cell wall. A pressure develops called the turgor pressure (pressure potential) , which is excerpted against the cell wall. c) The outward pressure is matched by an inward pressure, equal in magnitude but opposite in direction d) These pressures are called turgor pressures and provide mechanical support to the plant tissue. If a plant experiences a lack of water the cell becomes plasmolysed, wall pressure is lost and the plant wilts

9.2.10 Adaptations to reduce water loss

Xerophytic adaptation to reduce transpiration. Plants adapted to dry environments are called Xerophytes. Xerophytes are plants that have adaptations to reduce water loss or indeed to conserve water. They occupy habitats in which there is some kind of water stress. Examples of such water stress habitats include: Desert (high temp, low precipitation) High Altitude & High Latitude ( low precipitation or water locked up as snow or ice) Rapid drainage (sand dunes)

Examples of adaptations Small thick leaves Waxy leaves and cuticles Hair-like leaves Reduced number of stomata Stomata are in deep pits Become dormant during dry months Alternative photosynthetic processes CAM photosynthesis C4 photosynthesis

Light- dependent reactions Inside a Chloroplast H2O CO2 Light NADP+ ADP + P Light- dependent reactions Calvin Cycle Calvin cycle The process of photosynthesis includes the light-dependent reactions as well as the Calvin cycle. Chloroplast O2 Sugars

The Calvin Cycle C3 Plants 12 12 ADP 6 ADP 12 NADPH 6 12 NADP+ The Calvin cycle uses ATP and NADPH to produce high-energy sugars. 12 NADP+ 5-Carbon Molecules Regenerated Sugars and other compounds

CAM photosynthesis CAM: Crassulacean acid metabolism (CAM) in plants like the Stonecrop reduces water loss by opening pores at night but closing them during the day. This is a Time based alteration of biochemistry. At night carbon dioxide is combined with phosphoenol pyruvic acid (C3) to form Oxoloacetic acid (C4). Oxoloacetic acid is changed to malic acid or aspartic acid. This stores the carbon dioxide until required for photosynthesis during the day. During the day the pore is closed and the malic acid degenerates to PEP (C3) and carbon dioxide. Carbon dioxide is then used in photosynthesis A plant that utilizes the Crassulacean acid metabolism (CAM) as an adaptation for arid conditions. CO2 entering the stomata during the night is converted into organic acids, which release CO2 for the Calvin Cycle during the day, when the stomata are closed. 
Supplement CAM plants often show xerophytic features, such as thick, reduced leaves with a low surface-area-to-volume ratio, thick cuticle, and stomata sunken into pits. Cam plants utilize an elaborate carbon fixation pathway in a way that the stomata are open at night to permit entry of CO2 to be fixed and stored as a four-carbon acid (i.e. malate).Then, during the day the CO2 is released for use in the Calvin cycle. In this way, the rubisco is provided with high concentration of CO2 while the stomata are closed during the hottest and driest part of the day to prevent the excessive loss of water. CAM plants are therefore highly adapted to arid conditions. Examples of CAM plants include orchids, cactus, jade plant, etc.

CAM photosynthesis A plant that utilizes the Crassulacean acid metabolism (CAM) as an adaptation for arid conditions. CO2 entering the stomata during the night is converted into organic acids, which release CO2 for the Calvin Cycle during the day, when the stomata are closed. 
Supplement CAM plants often show xerophytic features, such as thick, reduced leaves with a low surface-area-to-volume ratio, thick cuticle, and stomata sunken into pits. Cam plants utilize an elaborate carbon fixation pathway in a way that the stomata are open at night to permit entry of CO2 to be fixed and stored as a four-carbon acid (i.e. malate).Then, during the day the CO2 is released for use in the Calvin cycle. In this way, the rubisco is provided with high concentration of CO2 while the stomata are closed during the hottest and driest part of the day to prevent the excessive loss of water. CAM plants are therefore highly adapted to arid conditions. Examples of CAM plants include orchids, cactus, jade plant, etc.

CAM PLANTS

C4 Photosynthesis C4 is open during the day, but they absorb CO2 more rapidly than other plants C4: A C4 compound is temporarily stored in the spongy mesophyll (which lack Rubisco for carbon fixation) carbon dioxide is stored in the mesophyll layer by combining with the PEP (C3) to form oxoloacetic acid and malic acid as seen before in the CAM plants. This breaks down to provide the palisade layer (RUBISCO) with more carbon dioxide. Therefore pores can remain open for a reduced time. A plant that utilizes the C4 carbon fixation pathway in which the CO2 is first bound to a phosphoenolpyruvate in mesophyll cell resulting in the formation of four-carbon compound (oxaloacetate) that is shuttled to the bundle sheath cell where it will be decarboxylated to liberate the CO2 to be utilized in the C3 pathway. A C4 plant is better adapted than a C3 plant in an environment with high daytime temperatures, intense sunlight, drought, or nitrogen or CO2 limitation. Most C4 plants have a special leaf anatomy (called Kranz anatomy) in which the vascular bundles are surrounded by bundle sheath cells. Upon fixation of CO2into a 4-carbon compound in the mesophyll cells, this compound is transported to the bundle sheath cells in which it is decarboxylated and the CO2is re-fixed via the C3 pathway. The enzyme involved in this process is PEP carboxylase. In this mechanism, the tendency of rubisco (the first enzyme in the Calvin cycle) to photorespire, or waste energy by using oxygen to break down carbon compounds to CO2, is minimized. Examples of C4 plants include sugarcane, maize, sorghum, amaranth, etc.

It is named for the 4-carbon molecule present in the first product of carbon fixation in the small subset of plants known as C4 plants, in contrast to the 3-carbon molecule products in C3 plants. C4 fixation is an elaboration of the more common C3 carbon fixation and is believed to have evolved more recently. C4 and CAM overcome the tendency of the enzyme RuBisCO to wastefully fix oxygen rather than carbon dioxide in what is called photorespiration. This is achieved by using a more efficient enzyme to fix CO2 in mesophyll cells and shuttling this fixed carbon via malate or aspartate to bundle-sheath cells. In these bundle-sheath cells, RuBisCO is isolated from atmospheric oxygen and saturated with the CO2 released by decarboxylation of the malate or oxaloacetate. These additional steps, however, require more energy in the form of ATP. Because of this extra energy requirement, C4 plants are able to more efficiently fix carbon in only certain conditions, with the more common C3 pathway being more efficient in other conditions.