Edexcel International A Level Biology Plant Structure PDF

Head to www.savemyexams.com for more awesome resources Edexcel International A Level Your notes Biology Plant Structure & Function Contents 4.1 Plant Cell Structure 4.2 Electron Microscopy of Plant Cells 4.3 Starch & C...

Head to www.savemyexams.com for more awesome resources Edexcel International A Level Your notes Biology Plant Structure & Function Contents 4.1 Plant Cell Structure 4.2 Electron Microscopy of Plant Cells 4.3 Starch & Cellulose: Structure & Function 4.4 Properties of Cellulose 4.5 The Vascular Structure of Plants 4.6 Core Practical 7: Identifying Tissue Types Within Stems Page 1 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.1 Plant Cell Structure Your notes Plant Cell Structure & Ultrastructure The structure of plant cells is made up of a complex system of organelles and ultrastructures Plant cells contain many of the organelles found in animal cells, along with a few other organelles that are only found in plant cells Cell wall Cell walls are formed outside of the cell membrane and offer structural support to the cell This structural support is provided by the polysaccharide cellulose Cell walls are freely permeable, and will allow most substances to enter the plant cell Middle lamella This forms the outermost layer of the plant cell and acts like glue to stick adjacent plant cells together It is mainly composed of a polysaccharide called pectin A diagram to show the cell wall and middle lamella of one plant cell Plasmodesmata Narrow threads of cytoplasm (surrounded by a cell membrane) called plasmodesmata connect the cytoplasm of neighbouring plant cells This interconnected system of cytoplasm between plant cells is known as the symplast Pits Page 2 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources These are very thin regions of the cell wall The pits in adjacent plant cells are lined up in pairs They are formed due to the absence of secondary thickening in the cell walls in the areas where Your notes plasmodesmata are present Detailed structure of plant cell wall Chloroplasts Chloroplasts are larger than mitochondria Surrounded by a double-membrane Within the chloroplast there are membrane-bound compartments called thylakoids containing chlorophyll stack to form structures called grana (singular = granum) Grana are joined together by lamellae (thin and flat thylakoid membranes) Chloroplasts also contain small circular pieces of DNA and ribosomes used to synthesise proteins needed in chloroplast replication and photosynthesis Page 3 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Chloroplasts are found in the green parts of plants - the green colour is due to the presence of the pigment chlorophyll Amyloplasts Small, membrane bound organelle containing starch granules Large numbers are found in plant storage organs, such as potato tubers Structure of an amyloplast Vacuole and tonoplast Page 4 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The vacuole is a sac in plant cells surrounded by the tonoplast (selectively permeable membrane) They are large, permanent structures in a plant cell Contains cell sap, which is a mixture of different substances such as water, minerals, waste and Your notes enzymes The concentration of the cell sap enables water to enter the vacuole by osmosis The structure of the vacuole Page 5 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Plant Cell Structure & Ultrastructure: Function The ultrastructures and organelles listed above each perform a specific function in a plant cell Your notes Cell wall The cellulose component of cell walls provides structural support to the cell Due to its rigid nature, it is responsible for the regular shape of a plant cell Middle lamella It provides stability to the plant by ensuring that adjacent plant cells are adhered together Plasmodesmata The cytoplasmic strands connect the contents of adjacent plant cells This allows substances to be transported between cells and facilitates cell to cell communication Pits Since the cell wall is very thin in these regions, it allows for the transport of substances between cells This is particularly useful in xylem vessels, where it allows for the lateral flow of water and mineral ions between adjacent vessels Chloroplasts Due to the presence of chlorophyll and thylakoids, chloroplasts are the site of photosynthesis Certain parts of the process occur in thylakoid membranes, while other parts happen in the stroma Amyloplasts They are responsible for storing starch in plants and converting it back to glucose when the plant needs it Vacuole and tonoplast Vacuoles have several functions in plant cells: They keep cells turgid, which stops the plant from wilting Store various substances, such as pigments and waste products Break down and isolate unwanted chemicals in plant cells The tonoplast controls what can enter and leave Page 6 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.2 Electron Microscopy of Plant Cells Your notes Electron Microscopy of Plant Cells It is important to be able to recognise various plant organelles from electron microscope images Chloroplast Has distinctive stacks of thylakoids Double membrane Has a roughly oval shape Larger than mitochondria Indicates the cell is a plant cell Nucleus Has a nuclear membrane and a dark nucleolus within It has a roughly spherical shape Vacuole Occupies a large space within a cell Often shows up as a very light shade (white) within an electron micrograph Indicates the cell is a plant cell Cell wall Located around the perimeter of the cell Mitochondria Roughly oval-shaped Double membrane Sometimes observed with visible cristae (foldings of the inner membrane) Page 7 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes TEM electron micrograph of a plant cell showing key features Page 8 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.3 Starch & Cellulose: Structure & Function Your notes Starch Starch: structure Starch is the storage polysaccharide of plants It is stored as granules in plastids (e.g. chloroplasts) and amyloplasts (small, membrane-bound organelles containing starch granules) Due to starch molecules being large polymers consisting of thousands of glucose monomers, starch takes longer to digest than glucose Starch is constructed from two different polysaccharides: Amylose (10 - 30% of starch) Unbranched helix-shaped chain with 1,4 glycosidic bonds between α-glucose molecules The helix shape enables it to be more compact and thus it is more resistant to digestion Amylose - one of the two polysaccharides present in starch Amylopectin (70 - 90% of starch) 1,4 glycosidic bonds between α-glucose molecules (as found in amylose) but also 1,6 glycosidic bonds form between glucose molecules creating a branched molecule Page 9 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The branches result in many terminal glucose molecules that can be easily hydrolysed for use during cellular respiration or added to for storage Your notes Amylopectin - the other polysaccharide present in starch Starch: function Starch is a storage polysaccharide because it is: Compact (so large quantities can be stored) Insoluble (so will have no osmotic effect, unlike glucose which would cause water to move into cells, meaning cells would then have to have thicker cell walls to withstand the increased internal water pressure) Page 10 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Cellulose Cellulose: structure Your notes Cellulose is a polymer consisting of long chains of β-glucose joined together by 1,4 glycosidic bonds As β-glucose is an isomer of α-glucose, consecutive β-glucose molecules must be rotated 180° to each other in order to form the 1,4 glycosidic bonds To form the 1,4 glycosidic bond between two β-glucose molecules, the glucose molecules must be rotated to 180° to each other Due to the inversion of the β-glucose molecules many hydrogen bonds form between the long chains, giving cellulose it’s great strength Page 11 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Cellulose is used as a structural component due to the strength it has from the many hydrogen bonds that form between the long chains of β-glucose molecules Cellulose: function Cellulose is the main structural component of cell walls due to its strength, which is a result of the many hydrogen bonds found between the parallel chains of microfibrils The high tensile strength of cellulose allows it to be stretched without breaking which makes it possible for cell walls to withstand turgor pressure The cellulose fibres and other molecules (e.g. lignin) found in the cell wall form a matrix which increases the strength of the cell walls These strengthened cell walls provide support to plants Page 12 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.4 Properties of Cellulose Your notes Plant Fibres Sclerenchyma fibres and xylem vessels are made of long, hollow plant cells These cells are hollow due to the fact that their cell contents died (often due to the lignification of the cell wall, which makes it almost impossible for substances to enter or leave the cell) These fibres have great strength, which is a property that is often exploited by humans They are useful in making rope and certain fabrics are made from plant fibres (e.g. cotton and hemp) Their strength is due to certain factors affecting the cell wall: The arrangement of cellulose microfibrils in a mesh-like pattern Secondary thickening, which results in a thick secondary cell wall developing which often contains lignin Page 13 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The arrangement of cellulose microfibrils, along with secondary thickening, are the main reasons why plant fibres are very strong Page 14 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.5 The Vascular Structure of Plants Your notes The Vascular Structure of Plants Plant stems have two main functions in a plant They provide support They transport various materials around the plant Support Leaves are attached to stems and are responsible for carrying out photosynthesis Stems ensure that leaves are positioned in order to receive maximum levels of sunlight to perform this task It also supports flowers in a way that will attract the attention of pollinators Plant stems need to be strong, but also flexible, in order to withstand the forces of nature (wind, rain etc.) Transport Leaves require water and mineral ions in order to photosynthesise and carry out other important functions The transport tissue in stems provide a route for these substances to travel from the roots to the leaves The products of photosynthesis also need to be transported from the tissue where photosynthesis happens to where these substances are needed Stems provide a transport route for this to occur Vascular structure of plants Plant stems are made up of different types of plant tissue The focus will be on the following tissue types: Xylem Phloem Sclerenchyma Xylem and phloem are collectively known as vascular tissue They are responsible for transporting various substances around the plant Sclerenchyma fibres are associated with the vascular bundles and provide additional support to a stem Xylem and phloem are arranged in structures known as vascular bundles The arrangement of xylem and phloem differs in the different plant organs In a stem, the xylem vessels are always located towards the middle of the stem, while the phloem can be found closer towards the outside of the stem Page 15 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 16 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The arrangement of vascular tissue (xylem and phloem) in roots, stems and leaves Your notes Sclerenchyma Sclerenchyma fibres are not involved in the transport of substances, they provide support They consist of bundles of dead cells which form long, hollow tubes, but they do have end walls present Lignification of cell walls occur, which provides structural support to allow the plant to bear the load of its own mass They have more cellulose in their walls compared to other plant cells Page 17 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Xylem Xylem vessels Your notes The functions of xylem tissue in a plant are: Vascular tissue that transports dissolved minerals and water around the plant Structural support Their cell walls contain lignin, which enables the vessels to withstand the pressure created by the moving column of water Xylem vessels form long, hollow straw-like structures that are formed by dead cells (due to lignification of cell walls) This means that they do not contain any cytoplasm or organelles that could slow down the flow of water There are small regions in the walls that are not lignified, known as pits, which allows for lateral movement of water and minerals between xylem vessels Page 18 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Images of xylem vessel elements: A = photomicrograph (drawing) in longitudinal section (lignin is stained red), B = scanning electron micrograph (drawing) in transverse section, C = microscope image (drawing) in transverse section (lignin is stained purple) Page 19 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Structure and Function of Xylem Vessels Table Your notes Page 20 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Phloem Phloem tissue Your notes The functions of phloem tissue in a plant are: Transport organic compounds (assimilates), particularly sucrose, from sources (e.g. leaves) to sinks (e.g. roots). The transport of these compounds can occur up and down the plant This is known as translocation Phloem has no support function in a 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 Page 21 of 30 © 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 below drawing) of a sieve tube element and companion cell in transverse section, B = photomicrograph image (and below drawing) of a sieve tube element and companion cell in longitudinal section Page 22 of 30 © 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 Sieve tube elements Sieve tube elements line up end to end to form a continuous tube Phloem Sieve Tube Elements Structure & Function Table Page 23 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes 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 sieve tube elements Phloem Companion Cells Structure & Function Table Page 24 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes 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, have sieve plates and companion cells that contain nuclei and cytoplasm. Page 25 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.6 Core Practical 7: Identifying Tissue Types Within Stems Your notes Identifying Tissue Types Within Stems In order to identify tissue types within stems, a permanent pre-prepared slide could be used Alternatively, a section of a plant stem could be cut and stained before preparing a temporary slide Apparatus Plant stem Scalpel Suitable stain Microscope slide Cover slip Forceps Dissecting needle Light microscope Gloves Method 1. Cut a very thin cross-section of the stem using a scalpel 2. Carefully transfer each section into a dish containing a suitable stain and leave for one minute A stain such as toluidine blue O (TBO) will make xylem and sclerenchyma fibres appear blue-green, while phloem will appear pinkish purple 3. Rinse off each section in water and mount onto a microscope slide, before adding a cover slip (take care to lower the coverslip slowly over the sample from one side to the other to avoid trapping air bubbles, which can then be mistaken for plant tissues/structures) 4. View under a microscope and adjust the focus to form a clear image 5. Make a labelled drawing of the positions of the xylem vessels, phloem sieve tubes and sclerenchyma fibres Page 26 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Light microscope image showing tissue types (sclerenchyma fibres, phloem sieve tubes and xylem vessels) found within plant stems and their locations relative to one another Plan diagrams When drawing tissue plan diagrams 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 (no sketching) 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 lines 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 that are requested Page 27 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes A tissue plan diagram of a dicotyledonous root indicating different tissue types Page 28 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes A tissue plan diagram of a dicotyledonous stem indicating different tissue types Page 29 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes A tissue plan diagram of a dicotyledonous leaf indicating different tissue types Page 30 of 30 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers