Plant Resources

• Cell wall


  A rigid structure made of cellulose which provides support to the cell
• Middle lamella


  The middle lamella is found outside of the cell walls in plant cells. It is responsible for sticking plant cells together and providing stability. It is mostly made of a substance called calcium pectate
• Amyloplasts


  Plant storage granules which contain starch and are mostly found in bulbs and tubers. Amyloplasts can convert the starch back into glucose when the plant cell needs more glucose for respiration
• Vacuole


  An organelle which stores cell sap and may also store nutrients and proteins. It helps to keep plant cells turgid. Some vacuoles can perform a similar function to lysosomes and digest large molecules
• Tonoplast


  A membrane which surrounds the vacuole which functions to separate the vacuole from the rest of the cell
• Plasmodesmata


  Narrow channels of cytoplasm within the cell walls of plants. It allows two neighbouring plant cells to transport substances between them and to communicate
• Pits


  Regions of a plant cell where the cell wall becomes very thin. Pits are arranged in pairs so that the pit of one plant cell is aligned with the pit of another plant cell. Like plasmodesmata, pits allow neighbouring plant cells to exchange substances
• Cell image:

  
• Vascular bundles


  Vessels which function to transport water and sugars from one part of the plant to another
• Xylem vessels


  • Transport water and dissolved mineral ions from the roots to the rest of the plant
  • Provide structural support
• Phloem vessels


  • Transport dissolved substances, such as sucrose and amino acids, from the leaves to the rest of the plant
• Vascular bundles in the plant stem


  1. Xylem vessels are found right on the inside

  2. Phloem tissue is located in the middle

  3. Sclerenchyma fibres are found on the outside
• Xylem vessels in the centre of the stem


  Provides strength and acts like an internal 'scaffolding' to support the stem and prevent it from bending in the wind
• Vascular bundles in the root

  1. Xylem forms a cross-like structure in the centre

  2. Phloem vessels surround the xylem
• Arrangement of vascular bundles in the root


  Adds strength as the root pushes through the soil
• Vascular bundles in the leaf

  1. Xylem vessels are found towards the top

  2. Phloem vessels are found underneath
• Xylem


  Transports water and mineral ions from the roots to the rest of the plant
• Xylem vessels


  • Made up of dead, hollow cells with no end cell walls
  • Cells stacked on top of each other to form one continuous tube
  • Cells have no organelles or cytoplasm, creating more space inside the vessel for transporting water
  • Cell walls contain pits which allow water and mineral ions to move into and out of the vessel
  • Cell walls contain lignin, a tough, woody substance that strengthens the xylem vessel and provides structure and support to the plant
• Xylem vessel:

  
• Phloem


  Vessels that transport dissolved substances, such as sucrose and amino acids from parts of the plant where they are made (sources) to the parts of the plant where they are used (sinks)
• Sources


  Parts of the plant where substances are made, e.g. leaves produce glucose from photosynthesis
• Sinks


  Parts of the plant where substances are used or stored, e.g. roots and bulbs store sugar
• Phloem vessels


  • Made up of two types of cell - sieve tube elements and companion cells
  • Sieve tube elements are living cells joined end-to-end to form sieve tubes
  • Sieve tube elements have 'sieve plates' with holes to allow solutes to move from one cell to the next
  • Sieve tube elements contain no organelles and very little cytoplasm to create more space for solutes
  • Sieve tube elements are associated with companion cells which contain a nucleus and are packed full of mitochondria to provide energy for active loading of sucrose
• Sieve tube element and companion cell

  Connected through plasmodesmata (channels in the cell wall) which allow the two cells to communicate
• Phloem vessel:

  
• Sclerenchyma

  Together with xylem and phloem vessels, sclerenchyma fibres are also found within vascular bundles and provide structural support to the plant. They are made up of bundles of long, dead cells. The cells have a hollow lumen and the cell walls are thickened with lignin. The cell walls also contain more cellulose than a typical plant cell which makes sclerenchyma fibres particularly strong.
• Dissecting plant stems to view vascular bundles under the microscope

  1. Cut a thin section of the plant stem using a scalpel

  2. Place the tissue sample into water to prevent it from drying out

  3. Place the tissue sample into a small dish containing the stain (toluidine blue O)

  4. Rinse the tissue samples in water

  5. Place each one onto a microscope slide
• Toluidine blue O (TBO)


  Stain that stains lignin blue/green, enabling visualisation of xylem and sclerenchyma fibres. Phloem cells and remaining tissue will appear pink/purple.
• Take care when using the sample and remember to cut away from you.
• Plant fibres

  Plant fibres, such as cotton and hemp, are made up of long tubes of plant cells. Plant fibres are strong which makes them useful for materials such as rope or sacks. Their strength is due to two factors:

  1. The arrangement of cellulose microfibrils in the cell wall
  2. The secondary thickening of cell walls with lignin
• Cellulose microfibrils

  Cellulose is a polysaccharide made up of long chains of beta-glucose monomers joined by 1-4 glycosidic linkages. Cellulose molecules are unbranched but are bonded to each other through hydrogen bonds. This bonding between cellulose molecules forms a net-like arrangement called a microfibril. Microfibrils are in turn hydrogen bonded to other microfibrils to form larger structures called macrofibrils. The net-like arrangement and the strength of the cellulose microfibrils are what make plant fibres so strong.
• Lignin

  • Lignin is a thick, woody substance which is found in the cell walls of xylem and schlerenchyma cells and provides strength to the plant stem. Lignin forms during a process called secondary thickening this is when xylem and schlerenchyma cells which have finished growing produce a secondary cell wall between the normal cell wall and the cell membrane. This second cell wall is thicker than the first cell wall and contains a higher proportion of lignin. Secondary thickening is what makes the structural plant fibres (xylem and schlerenchyma vessels) so strong.
• Tensile strength


  The amount of weight a plant fibre can take before it snaps
• Measuring tensile strength is important to avoid injury when using fibres in things like construction or sports
• Measuring the tensile strength of plant fibres


  1. Set up a clamp stand and attach the plant fibre

  2. Tie a weight to the end of the fibre

  3. Add more weights, one at a time, until the plant fibre breaks

  4. Record the mass of weights that the fibre was carrying before it snapped

  5. Repeat with different samples of the same fibre at least three times then calculate a mean
• Control variables in the experiment


  • Length of the plant fibre
  • Temperature in the room
  • Level of humidity
• Safety measures to be considered are to stand away from the area below the weights to avoid them falling on your feet and wearing safety goggles to protect your eyes
• Sustainability


  The use of materials that meets the needs of the current generation and can be replenished so that the same resources are still available for future generations
• Materials made from


  • Plant fibres
  • Plastics obtained from fossil fuels
• Materials made from plant fibres


  • Weaker
  • Don't last as long
  • More sustainable