CIE AS Biology 7.1 Structure of Transport Tissues PDF

Head to www.savemyexams.com for more awesome resources CIE AS Biology Your notes 7.1 Structure of Transport Tissues Contents Plant Transverse Sections Xylem & Phloem Distribution Xylem Vessels Elements...

Head to www.savemyexams.com for more awesome resources CIE AS Biology Your notes 7.1 Structure of Transport Tissues Contents Plant Transverse Sections Xylem & Phloem Distribution Xylem Vessels Elements Phloem Sieve Tube Elements Page 1 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Plant Transverse Sections Your notes Transverse Sections: Stems, Roots & Leaves Dicotyledonous (dicots) plants Dicotyledonous (dicots) plants have: Seeds that contain two cotyledons (seed leaves) Network of veins Leaves that typically have broad blades (leaf surface) and petioles (stalks) Tap root with lateral branches Herbaceous dicots have a relatively short life cycle (one growing season) and non-woody tissue Transport systems Plants need transport systems to meet their metabolic demands (glucose, hormones, mineral ions are required for various processes within plants), to efficiently move substances up and down, e.g. Glucose from photosynthesis needs to be transported to parts of the plant that cannot photosynthesise Water from the roots needs to be transported to the upper parts of a plant Plants may store glucose in storage organs, e.g. tubers, and need to release this glucose and transport it to metabolically active parts of the plant Plants consist of many layers of cells and so cannot rely on diffusion from cell to cell to supply all their needs, as this would be too slow Plants therefore have a vascular system which involves a network of vessels (vascular tissue) running through the leaves, stem and roots. These three parts are the main organs involved in transport The vascular system is comprised of two distinct types: Xylem transports water and mineral ions from the roots to the rest of the plant Phloem transports substances from the source (e.g. a leaf) to the sink (e.g. root) The xylem and phloem are arranged together in vascular bundles The bundles are laid out differently in the leaves, stem and roots Dicotyledons Plan Diagrams Page 2 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 3 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 4 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Tissue plan diagrams of a dicotyledonous leaf, stem and root Page 5 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Worked example Your notes The micrograph below shows a transverse section of root tissue. Draw a plan diagram of this section of root tissue. Electron micrograph of transverse root tissue Step 1 Draw the outlines of each section Use a sharp pencil with no shading or sketching Use a continuous line Step 2 Add in a few required cells or structures As this is to be a drawing of an image at high power you can add some simple details to distinguish between sections such as the xylem tissue at the centre of the root Step 3 Add labels Use a ruler to draw horizontal lines to each structure of interest Label clearly with correct spelling Step 4 Add magnification (if present on micrograph or question) Page 6 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Plan diagram of transverse root tissue So, the 'before-and-after' images look like this side-by-side: Page 7 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Examiner Tip Your notes When drawing tissue plan diagrams (which is common in the practical paper 3) you need to: Read the instructions carefully Draw a large diagram Use a sharp pencil and do not shade (including the nucleus) Use clear, continuous lines When using an eyepiece graticule, use it to ensure you have correct proportions or if you are not using a microscope then endeavour to keep the proportions between tissues to scale If drawing from a low-power image: Do not draw individual cells Read the question carefully as you may only have to draw a portion of the image Include the magnification on the drawing If drawing from a high-power image: Draw only a few of the required cells Draw the cell wall of the plant cells Include the magnification on the drawing When labelling, remember: Use a ruler for label lines (and scale line if appropriate) Label-lines should stop exactly at the structure (do not use arrows) Don't cross label-lines over each other Label all tissues and relevant structures (those requested) Page 8 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Xylem & Phloem Distribution Your notes Xylem & Phloem Distribution Xylem The functions of xylem tissue in a plant are: Vascular tissue that carries dissolved minerals and water up the plant Structural support Food storage Xylem tissue is found, along with phloem tissue and other tissues, in vascular bundles The location of the vascular bundles is dependent on which organ they are in as the different organs are under different stresses: In the roots the vascular bundle is found in the centre and the centre core of this is xylem tissue. This helps the roots withstand the pulling strains they are subjected to as the plant transports water upwards and grows In the stems the vascular bundles are located around the outside and the xylem tissue is found on the inside (closest to the centre of the stem) to help support the plant In the leaves the vascular bundles form the midrib and veins and therefore spread from the centre of the leaf in a parallel line. The xylem tissue is found on the upper side of the bundles (closest to the upper epidermis) Phloem The function of phloem tissue in a plant is to: Transport organic compounds, particularly sucrose, from the source (e.g. leaf) to the sink (e.g. roots) The transport of these compounds can occur up and down the plant Phloem is a complex tissue also made up of various cell types The largest part is sieve tube elements, which are the main transport cells Companion cells are attached to each sieve tube and provide energy for the movement of substances within the sieve tube elements Parenchyma for storage Strengthening fibres The location of the vascular bundles is dependent on which organ they are in, as the different organs are under different stresses: In the roots the vascular bundle is found in the centre; on the edges of the centre core is the phloem tissue In the stems, the vascular bundles are located around the outside; the phloem tissue is found on the outside (closest to the epidermis) In the leaves, the vascular bundles form the midrib and veins and therefore spread from the centre of the leaf in a parallel line. The phloem tissue is found on the lower side of the bundles (closest to the lower epidermis) Xylem and Phloem Diagram Page 9 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The distribution of xylem and phloem tissue in the roots, stem and leaves in a herbaceous dicotyledonous plant Examiner Tip In roots and stem, the xylem tissue is found on the inside – however, in leaves, xylem is found above phloem tissue. Page 10 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Xylem Vessels Elements Your notes Xylem Vessel Elements: Structure & Function The functions of xylem tissue in a plant are: Vascular tissue that transports dissolved minerals and water around the plant Structural support Food storage Xylem tissue is made up of four cell types that function together: 1. Tracheids (long, narrow tapered cells with pits) 2. Vessel elements (large with thickened cell walls and no end plates when mature) 3. Xylem parenchyma 4. Sclerenchyma cells (fibres and sclereids) Most of the xylem tissue is made up of tracheids and vessel elements, which are both types of water- conducting cell Xylem tissue micrographs Page 11 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Micrographs of xylem vessels allow structural lignin to be seen in both longitudinal section (A) and transverse section (B) Page 12 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Drawing Xylem Tissue Diagram Your notes Biological drawing conventions can be applied to the drawing of xylem vessels from micrographs Relating structure to function in xylem vessel elements table Structure Function Adds strength to withstand hydrostatic Lignified cell walls pressure so vessels do not collapse. Impermeable to water Allows for mass flow of water and dissolved solutes as cohesive (between water No end plates molecules) and adhesive (between water molecules and xylem wall) forces are not impeded No protoplasm (cells are dead when Does not impede the mass flow of water and mature) dissolved solutes Pits in walls (in non-lignified sections) Lateral movement of water allows for continuous flow in case of air bubbles forming Page 13 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources in the vessel Small diameter of vessels (although larger Helps prevent the water column from than tracheids) breaking Your notes Also see Comparison of xylem & phloem tissue table in Phloem Sieve Tube Elements Examiner Tip You must be able to recognise the xylem vessel elements in images, so look for a thicker cell wall and a larger diameter. You should be able to draw xylem vessel elements from micrograph images. For more detail on how to make biological drawings see our revision notes here. Page 14 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Phloem Sieve Tube Elements Your notes Phloem Sieve Tube Elements & Companion Cells: Structure & Function The function of phloem tissue in a plant is to: Transport organic compounds (assimilates), particularly sucrose, from the source (e.g. leaf) to the sink (e.g. roots). The transport of these compounds in phloem tissue can occur up and down the plant The organic compounds are dissolved in water to form sap Phloem is a complex tissue made up of various cell types Its bulk is made up of sieve tube elements which are the main conducting cells and companion cells Other cell types of phloem tissue also include parenchyma for storage and strengthening fibres Mature phloem tissue contains living cells, unlike xylem tissue Phloem Diagram Page 15 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Structure of phloem tissue. (a) Microscope slide image and drawing of a sieve tube element and companion cell in transverse section (TS), (b) photomicrograph image and drawing of a sieve tube element and companion cell in longitudinal section (LS). Page 16 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Structure of phloem tissue. (c) Transmission electron micrograph image and drawing of a sieve tube element and companion cell in transverse section (TS) Sieve tube elements Sieve tube elements line up end to end to form a continuous tube They transport sugars and nutrients up and down the plants in sieve cells Phloem sieve tube elements structure & function table Structure Function Allows for continuous movement of organic Sieve plates with sieve pores substances Strengthens the wall to withstand the Cellulose cell wall hydrostatic pressures that move assimilates Page 17 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources No nucleus, ribosomes or vacuole in Maximises space for movement of assimilates mature cells Your notes Reduces friction to facilitate movement of Thin cytoplasm assimilates Companion cells Each sieve tube element has a companion cell associated with it as companion cells control the metabolism of their associated sieve tube member They also play a role in loading and unloading of sugars into the phloem Phloem companion cells structure & function table Structure Function Provides metabolic support to sieve tube Nucleus and other organelles present elements and helps with loading and unloading of assimilates Moves assimilates into and out of sieve tube Transport proteins in plasma membranes elements Provides ATP for the active transport of Large numbers of mitochondria assimilates The link to sieve tube elements, allowing Plasmodesmata (channels in cell wall) organic compounds to move from the companion cells into the sieve tube elements Comparing Xylem and phloem Xylem and phloem are similar in some ways but there are key differences that ensure they can carry out their separate functions in transport around the plant Comparison of xylem & phloem tissue table Xylem Phloem Living cells No (hollow cells) Yes (companion cells) Organic Substances transported Water and mineral ions compounds/assimilates Page 18 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Process of transportation Transpiration Active translocation Your notes One way / upwards (roots to Two ways / up and down (source Direction of flow leaves) to sink) Presence of end walls No Yes (sieve plates) Cell wall material Lignin and cellulose Cellulose Examiner Tip Understand the difference between sieve tube elements and companion cells, and how they are different to xylem tissue. Remember that mature xylem tissue is dead, so there is no evidence of organelles, and they have lignified cell walls, whereas sieve tube elements have no lignin, do have sieve plates, and their companion cells contain nuclei and dense cytoplasm. Page 19 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers