Plant Structure

• function = to transport water and mineral ions up the plant, and provide support
• very long, tube-like structures fromed from dead cells joined end to end (the tubes are found together in bundles)
• the cells are longer than they are wide - the have a hollow lumen (doesn't contain any cytoplasm)
• they don't have end walls, making an uninterrupted tube which allows water and mineral ions the pass up the middle easily
• walls are thickened with a woody substance called lignin which helps support the plant
• water and mineral ions move into and out of the vessels through pits in the walls where there's no lignin
• found throughout the plant, but particularly around the centre of the stem where they group together with other vessels to form vascular bundles

• function = to provide support
• made of bundles of dead cells that run vertically up the stem (like xylem vessels)
• the cells are longer than they are wide
• have a hollow lumen 
• have end walls
• cell walls are thickened with lignin
• they have more cellulose than other plant cells
• usually associated with the vascular bundles

• cells get energy from glucose (plants store excess glucose as starch - when they need more glucose for energy they break down starch to release the glucose
• starch is a mixture of two polysaccharides of alpha-glucose:
  
  • amylose = a long unbranched chain of alpha-glucose. the angles of the glycosidic bonds give it a coiled structure - this makes it compact and good for storage as you can fit mor into a small space
  • amylopectin = a long branched chain of alpha-glucose. its side branches allow the enzymes that break down the molecule to reach the glycosidic bonds easily, meaning glucose can be released quickly
• starch is insoluble in water, so it doesn't cause water to enter cells by osmosis (which would make them swell) this makes it good for storage

• is made of long, unbranched chains of beta-glucose, joined by glycosidic bonds
• the glycosidic bonds are straight, so the cellulose chains are straight
• between 50 and 80 cellulose chains are linked together by a large number of hydrogen bonds to from strong threads called microfibrils
• the microfibrils mean cellulose provides structural support for cells (strengthening plant cell walls)

• made up of long tubes of plant cells
• are strong, making them useful for making things e.g. ropes or fabrics like hemp
• strong because of:
  • the arrangement of microfibrils = the cell wall contains cellulose microfibrils in a net-like arrangement
  • secondary thickening = when some structural plant cells (sclerenchyma) have finished growing, they produce a secondary cell wall between the normal cell wall and the cell membrane which is thicker and contains more lignin than the normal cell wall - this is called secondary thickening

Tensile strength = mamximum load it can take before it breaks

• attach the fibre to a clamp stand and hang a weight from the other end
• keep adding weights, one at a time, until the fibre breaks
• record the mass needed to break the fibre (the hgher the mass, the higher the tensile strength)
• repeat the experiment with different samples of the same fibre
• the fibres being tested should be the same length
• all other variables (like temperature and humidity) should be kept constant
• safety measures - goggles to protect eyes, leave weith drop are clear so they won't drop on feet