Plant Biology SL Unit 2 Transport Past Paper 2024-2025 PDF

Unit 2 Transport SL Biology M 2026 Plant Biology Transport of Gases and Water in Plants. B 3.1.7 Adaptations of gas exchange in leaves. B 3.1.8 Distribution of tissues in a leaf The leaf is the plant organ where gas exchange occurs....

Unit 2 Transport SL Biology M 2026 Plant Biology Transport of Gases and Water in Plants. B 3.1.7 Adaptations of gas exchange in leaves. B 3.1.8 Distribution of tissues in a leaf The leaf is the plant organ where gas exchange occurs. The top and bottom of the leaf are covered by a single layer of cells, the epidermis, and the inner part of the leaf contains mesophyll tissue and vascular tissue in a system of vascular bundles. The vascular bundles in leaves are referred to as veins. B 3.1.7 Adaptations of gas exchange in leaves. B 3.1.8 Distribution of tissues in a leaf B 3.1.7 Adaptations of gas exchange in leaves. B 3.1.8 Distribution of tissues in a leaf Structure of the leaf pdf B 3.1.7 Adaptations of gas exchange in leaves. B 3.1.8 Distribution of tissues in a leaf Epidermis: The cells located above the mesophyll cells and below the spongy mesophyll cells.It provides protection for the mesophyll cells and are transparent to allow light to pass through. Waxy cuticle: The waxy cuticle covers the epidermis cells and reduces the evaporation of water from the leaf. Stomata are on the bottom surface of the leaf, this area receives less light, so as a result, the temperature is lower than on the upper side. This minimises water loss from the pores and the plant, so the lower epidermis has a thinner cuticle than the upper epidermis. B 3.1.7 Adaptations of gas exchange in leaves. B 3.1.8 Distribution of tissues in a leaf Palisade mesophyll is located in the upper portion of the leaf, where light is most available. The cells of this region are chloroplast rich, to allow maximum photosynthesis. Veins are distributed throughout the leaf to transport raw materials and products for photosynthesis. The veins occur roughly in the middle of the leaf so that they are near all the leaf cells. They contain xylem and phloem, carrying water,minerals and nutrients respectively. The spongy mesophyll is located just above the stomata, to allow continuous channels of gas exchange.The irregular shape of spongy mesophyll cells increase surface area for gas exchange. They are surrounded by air spaces. B 3.1.7 Adaptations of gas exchange in leaves. B 3.1.8 Distribution of tissues in a leaf Structure of the leaf pdf Using the information from the video and the next slide, complete page 4 of the notepack B 3.1.7 Adaptations of gas exchange in leaves. B 3.1.8 Distribution of tissues in a leaf Explain how the cells of the leaf help to carry out its functions. B 3.1.8 Distribution of tissues in a leaf Draw and label a plan diagram to show the distribution of tissues in a transverse section of a dicotyledonous leaf B 3.1.8 Distribution of tissues in a leaf Plan diagram of the distribution of tissues in a leaf. You don’t have to draw cells, only distribution of tissues. B 3.1.9 Transpiration is a consequence of gas exchange in leaves. Review Leaves are the primary organ for photosynthesis and it involves synthesis of carbohydrates using light energy. Carbon dioxide is the raw material and oxygen is one of the products. Exchange of the two gases must take place to sustain photosynthesis. The epidermis of the leaf has a waxy cuticle and it has a very low permeability to carbon dioxide so pores called stomata( stoma) are found in the lower epidermis of the leaf. B 3.1.9 Transpiration is a consequence of gas exchange in leaves. The problem for plants is that the stoma that lets carbon dioxide in will usually allow water vapour to escape. The loss of water vapour from the leaves and stems of plants is called transpiration. Fun fact! A single corn plant loses between 135 and 200 L through transpiration during the growing season. B 3.1.9 Transpiration is a consequence of gas exchange in leaves. Plants minimise water losses through stomata using guard cells. These are the cells that are in found in pairs, on one either side of a stoma. B 3.1.9 Transpiration is a consequence of gas exchange in leaves. Light: Guard cells close the stomata in darkness, so transpiration is much greater in light ,open Factors that stomata increases the rate of diffusion of CO2 affect the rate of transpiration. needed for photosynthesis but also increasing transpirational water loss through stomata. Temperature: Rate of transpiration (water loss) through stomata is doubled for every 10°C increase in temperature. B 3.1.9 Transpiration is a consequence of gas exchange in leaves. Wind: Removes water vapor from leaf, reducing water potential around leaf thus increasing the water potential gradient between the leaf and its surroundings and therefore Factors that increasing the rate of transpirational water loss. affect the rate of Humidity: transpiration. As humidity increases, water potential around leaf is increased thus decreasing the water potential gradient between the leaf and its surroundings and therefore decreasing the rate of transpirational water loss  B 3.1.9 9.1 Transpiration S 1 Measurement is a consequence of transpiration of gas rates using exchange in potometers. leaves. Measurement of transpiration rates using potometers. What does a potometer do? This is a device used to measure water uptake in plants. B 3.1.9 Transpiration is a consequence of gas exchange in leaves. Vernier Lab. B 3.1.10 Stomatal density Lab Students should use micrographs or perform leaf casts to determine stomatal density. Stomatal density is the number of stomata per unit area of leaf Guided Inquiry to surface. Microscopy To find the density, the number of stomata in a known area must be Page 7. counted. Guard cells and stomata can be seen under the microscope. D 2.3 Water Potential. Review D 2.3.4 Changes due to water movement in plant tissue bathed in hypotonic and those bathed in hypertonic solution. Osmolarity lab Lab Skills- Mathematical tools Descriptive Statistics You require at least 5 repeats if you are to calculate standard deviations. Standard deviation or standard error can be calculated to determine the range of values, which is an indication of the reliability of the data collected. Calculated standard deviation or standard error values can be used to construct error bars on graphs. Error bars can be used to determine if there is likely to be a significant difference between data points on a graph. Lab Skills- Mathematical tools Either the SD or SE can be used to draw error bars. Not testable for SL HL Content D 2.3.6 Effects of water movement of cells with a cell wall High pressures can build up inside a plant cell due to the entry of water by osmosis because the cell wall is strong enough to prevent bursting. A cell that is pressurized in this way is called turgid. Turgid plant tissue can provide support because of its strength under compression. Not testable for SL HL Content D 2.3.6 Effects of water movement of cells with a cell wall If plant cells lose water, the pressure in the cytoplasm decreases. If it drops to atmospheric pressure, the plasma membrane no longer pushes against the cell wall and the cell is not turgid. Further water loss causes the plants cells to become flaccid meaning limp or floppy. This is called wilting as is seen in plants that have lost water by transpiration in hot weather or droughts. The plants avoid further water loss by closing stomata. Not testable for SL HL Content D 2.3.6 Effects of water movement of cells with a cell wall When a plant cell is bathed in a hypertonic solution, the water moves out of the plant cell and the volume of cytoplasm decreases, and plasma membrane is pulled away from the cell wall. This is called plasmolysis and leads to cell death. When seawater floods lands as a result of high tides or tsunami, this can happen naturally. Not testable for SL HL Content D 2.3.6 Effects of water movement of cells with a cell wall When a plant cell is bathed in hypotonic solution, water enters the cell, moves into the vacuole and pushes the cytoplasm and plasma membrane against the cell wall,creating a turgor pressure. Water continues to move into the cell until the turgor pressure equals the pressure exerted by the cell wall. The cell is then fully turgid. D 2.3.11 Water potential and Not testable for SL HL Content water movement in plant tissues. If a plantʼs roots are bathed in a hypertonic environment ( which has a higher solute concentration ), there will be higher water potential inside the roots than outside. The solute potential outside the cell will be lower (more negative) that the solute potential inside the cell. Overall, the water potential will be lower outside the cell. In this case, water moves out of the roots into the hypertonic solution.  Not testable for SL HL Content D 2.3.11 Water potential and water movement in plant tissues. If a plantʼs roots are bathed in a hypotonic environment ( which has a lower solute concentration ), there will be lower water potential inside the roots than outside. The solute potential inside the cell will be higher than the solute potential outside the cell. Overall, the water potential will be higher outside the cell. In this case, water moves into the roots from the hypotonic solution. Not testable for SL HL Content D 2.3.11 Water potential and water movement in plant tissues. Pressure potential is also involved when plants are placed in hypertonic and hypotonic environments. The effect of a high pressure potential inside a cell is to decrease or stop water flow into the cell. Not testable for SL HL Content D 2.3.11 Water potential and water movement in plant tissues. When a plant is placed in a hypotonic environment, water moves in until the pressure potential is high enough to stop this inward movement of water. At this point the cell is isotonic with the surrounding fluid; the water potentials are the same. There is no net movement of water. D 2.3.9 Movement of water from higher to lower water potential. The soil has a higher water potential (-0.3 MPa) than the roots (-0.6 MPa), so water moves from the soil, into the roots. The water molecules then move upwards in the xylem since the tree trunk has a lower water potential (-0.8 MPa) than the roots (-0.6 MPa). The leaves have an even lower water potential (-0.9 MPa) than the tree trunk (-0.8 MPa), so water molecules move from the tree trunk into the leaves. The string of water molecules is pulled upwards and out of the leaves because of a large difference in water potential between the leaves (-0.9 MPa) and the atmosphere (-95.0 MPa). B 3.2.7 Transport of water from roots to leaves during transpiration. Transpiration and Water Potential - Lab Xchange For a quick refresher on transpiration and water potential. Complete the questions on the notepad for a more thorough understanding. B 3.2.7 Transport of water from roots to leaves during transpiration. Water molecules cling together by hydrogen bonds between the molecules. This is know as cohesive forces and helps water to to be pulled through the plant. Along with the adhesive forces of water molecules to the xylem walls, a strong tension force (pulling force) is created within the xylem vessel. B 3.2.7 Transport of water from roots to leaves during transpiration. As long as there is a continuous column of water in a xylem vessel, these tensions are transmitted from the leaf to the roots. This is called transpiration pull and is strong enough to move water upwards against the force of gravity to the top of the tallest tree. B 3.2.7 B 3.2.7 Transport Transport of of water water from from roots roots to to leaves leaves during during transpiration. transpiration. The cohesive property of the water provides an unbroken column of water in the xylem throughout the plant. Failure to have the cohesive property would stop all flow of water through the xylem vessels. B 3.2.7 Transport of water from roots to leaves during transpiration. Exam Question ❏ the cell walls of xylem vessels are charged, attracting water molecules. Describe how ❏ the adhesive attraction of water to xylem the adhesive vessel walls moves them up the stem property of against gravity water helps transport of ❏ adhesion is important when sap starts to rise water during in plants that were leafless through the transpiration. winter ❏ adhesion also helps prevent the column of water-filled xylem vessels from breaking. B 3.2.7 Transport of water from roots to leaves during transpiration. Not on notepack - Review 1. Water molecules adhere to hydrophilic xylem wall through hydrogen bonding which causes an upward force on transpiration stream. 2. Water molecules leave xylem and move through the cytoplasm of the spongy mesophyll cell. B 3.2.7 Transport of water from roots to leaves during transpiration. The adhesive property of water and evaporation generate tension forces in leaf cell walls. 3. Water leaves the spongy mesophyll tissue into the air spaces. 4. Water vapour is lost from air spaces through the stomata due to different concentration of water vapour between air spaces and air surrounding the leaf. B 3.2.7 Transport of water from roots to leaves during transpiration. The adhesive property of water and evaporation generate tension forces in leaf cell walls. 4. Water loss through the stomata is replaced by evaporation of water from spongy mesophyll cells. 6. Evaporation from mesophyll cells and adhesion to xylem walls generates tension and creates an upward pulling force on the transpiration stream. B 3.2.8 Adaptations of xylem vessels for transport of water Xylem is the tissue in plants that is used to transport water. It is a long continuous tube. Water is absorbed by roots and lost from leaves in transpiration, so the main flow of water is from to roots to the leaves. Xylem vessels are normally filled with xylem sap, which consists of water with relatively low concentration of potassium, chloride and other ions. In a transpiring leaf, water is lost by evaporation from the cell walls of spongy mesophyll cells and then diffusion of water vapour out through the stomata. B 3.2.8 Adaptations of xylem vessels for transport of water The xylem is made of many cell types. The two cell types largely involved in water transport are tracheids and vessel elements. Tracheids are dead cells that taper at the ends and connect to one another to form a continuous column. Vessel elements ( are called vessels) are the most important xylem cells involved in water transport. They are also dead cells, and have thick, lignified secondary walls. These secondary walls are often interrupted by areas of primary wall. These primary wall areas also include pits or pores that allow water to move laterally. B 3.2.8 Adaptations of xylem vessels for transport of water B 3.2.8 Adaptations of xylem vessels for transport of water 1. No end walls in the cells so the xylem forms a long continuous, hollow tube to allow water to flow up. 2. Lignin provides support and strength to the cell walls of xylem and prevent it from collapsing due to low atmospheric pressure inside the plant. 3. Pits or pores which allows water to flow between cells 4. Non living- no cell contents, which allow for water to flow without easily. B 3.2.9 Distribution of tissues in a transverse section of the stem of a dicotyledonous plant. Plan diagrams The distribution of tissues in stems show the areas of and roots of dicotyledonous plants tissues, but not is different. individual cells. You are expected to know to draw The lines indicate the plan diagrams of both the stem the junction and root of a dicot plant between tissues..  B 3.2.9 Distribution of tissues in a transverse section of the stem of a dicotyledonous plant. Epidermis cambium Phloem cortex Xylem pith B 3.2.9 Distribution of tissues in a transverse section of the stem of a dicotyledonous plant. Tissue Main function in stems Xylem Transport of water from roots to leaves Phloem Transport of sugars from leaves to roots Cambium Production of more xylem and phloem Epidermis Waterproofing and protection Cortex Support and photosynthesis Pith Bulking out the stem. B 3.2.10 9.2 S 2 Identifying Distribution of of xylem tissues andinphloem a transverse in microscope section of images the root of of stem a dicotyledonous and root. plant. All the vascular tissue is grouped in the centre of the roots, with xylem in a star shaped area and the phloem between the points of the star. The xylem vessels can be identified by their large size, thick walls and rounded shape in transverse section. Xylem walls may be stained red in microscope images because they are lignified. B 3.2.10 9.2 S 2 Identifying Distribution of of xylem tissues andinphloem a transverse in microscope section of images the root of of stem a dicotyledonous and root. plant. Other cells in the root are unlignified and are usually stained blue. Phloem cells are smaller than xylem with thinner wall. The outer layer of cells in the root is epidermis with small cells that may have root hairs protruding. Between the vascular tissue and the epidermis there is cortex with relatively large and thin walled cells. B 3.2.10 Distribution of tissues in a transverse section of the root of a dicotyledonous plant. B 3.2.9 Distribution of tissues in a transverse section of the root of a dicotyledonous plant. Time to Practice Monocot and Dicot Plants. Not Tested