4A

• water in plants:

  • photosynthesis
  • support as hydrostatic pressure makes cells rigid
  • transport to move mineral ions
  • cools the plant via evaporation
• Nitrates (-NO3) are used to make amino acids and proteins, which make enzymes which are vital for life. Nitrates are also used to make DNA and hormones.

  Observations:

  • yellow leaves
  • stunted growth
  • death
• Calcium ions (-Ca 2+) are found in the middle lamella of plant cell walls, which when combined with pectin, hold the cells together. Calcium ions are important in the permeability of membranes.

  Observations:

  • growing points are black
  • young leaves are yellow and crinkly
• Magnesium ions (-Mg 2+) produce the green pigment in chlorophyll, which is vital for trapping light for photosynthesis. Magnesium also activates some enzymes and has a role in the synthesis of nucleic acids.

  Observations:

  • yellow areas on old leaves
  • slow growth
• New drugs must be:

  • effective - cures, prevents or relieves symptoms
  • safe - non-toxic with acceptable side-effects
  • stable - can be stored and used under normal conditions
  • easily taken in and removed from body - gets to its target and is excreted
  • large scale - can be manufactured cheaply in large quantities
• Drug testing:

  1. preclinical testing
  2. computer modelling
  3. tissue cultures
  4. animal testing (rodent and non-rodent)
  5. clinical trials
  6. stage 1
  7. stage 2
  8. stage 3
  9. production
• clinical trials:

  1. stage 1 - small number of healthy volunteers are given the drug to ensure that there are no dangerous side-effects
  2. stage 2 - larger number of patients are given the drug to see how it affects the disease, and the correct dosage, placebos are also used at this stage
  3. stage 3 - very large number of patients are given the drug, and it is compared to other current drugs on the market
• double blind trial


  a clinical drug trial where neither the doctor nor the patient know whether the patient is receiving the new medicine, a control medicine, or a placebo in order to ensure that the results are not effected by the placebo effect
• cell wall


  freely permeable wall around plant cells, made mainly of cellulose
• The plant cell wall is made of many layers.

  1. primary cell wall - first flexible cell wall with all of the cellulose microfibrils oriented in a similar direction
  2. secondary cell wall - cellulose microfibrils build up at different angles, making the cell wall more rigid
  3. middle lamella - mainly made of calcium pectate that binds to cellulose on adjacent cell walls, holding the cells together
• Suberin is a waterproof chemical that impregnates cellulose cell walls in cork tissues to make them impermeable. Lignin is a chemical that impregnates cellulose cell walls in wood to make them impermeable.
• Cellulose is a carbohydrate composed of long chains of b-glucose joined by 1,4-glycosidic bonds. To do this every other monomer is inverted, to form the bond between 2 -OH groups. Hydrogen bonds form between neighbouring chains, in cross-linking, making microfibrils. These are deposited in layers which are held together by hemicelluloses, which bind to each other and to the cellulose molecules. This makes the cell wall turgid.
• plasmodesmata


  cytoplasmic bridges between plant cells that allow communication between the cells
• pits


  thin areas of cell wall in plants cells with secondary thickening where plasmodesmata maintain contact with adjacent cells
• Plant cells contain a permanent vacuole, which keeps cells turgid and stores cell sap. The tonoplast is the specialised membrane that surrounds the vacuole and controls the movement of substances into and out of the cell sap, so it controls the water potential of the cell.
• Chloroplasts are responsible for photosynthesis in plants as they contain chlorophyll, and are found in green tissues.

  Features:

  • large biconcave shape
  • contain their own DNA
  • double membrane
  • folded inner membrane for increased surface for enzyme-controlled reactions
  • site of photosynthesis
  • chlorophyll which is the green pigment responsible for trapping the energy from light
• Amyloplasts are plant organelles that store starch which can be converted to glucose to provide energy when needed.
• stem function:

  • support
  • movement of materials
  • some photosynthesis
• Parenchyma are unspecialised plant cells that act as packing in stems and roots to give support. They can be modified to become suitable for storage and photosynthesis.
• Collenchyma are plant cells with areas of cellulose thickening that give mechanical strength and support to the tissues. They are found around the outside of the stem, just inside the epidermis.
• Sclerenchyma is a modified parenchyma tissue that has very thick lignified cell walls which are made of strong but flexible fibres. When the fibres are lignified, the cell contents die, so the cells can't grow and plant growth occurs higher up the stem. If they are completely impregnated with lignin, they are sclereids.
• The vascular bundle is part of the transport system of a plant, with the phloem on the outside and the xylem on the inside, which strengthens the sclerenchyma.
• The cambium is the layer of unspecialised cells that divide to form specialised cells for the xylem and the phloem.
• Xylem formation:

  1. protoxylem -first xylem a plant makes that can grow because its walls are not fully lignified
  2. cellulose fibres are arranged vertically to resist the weight of the plant
  3. more lignin is added
  4. cell stops growing
  5. tissue is stronger but cell components die
  6. metaxylem is formed - mature xylem vessels made of lignified tissue
  7. end walls between cells break down
• Water and mineral ions are transported from the roots to the leaves in the xylem using a transpiration stream. Water can move out of the xylem into other cells through specialised pits.
• The phloem is the tissue that transports organic solutes, e.g. sucrose and amino acids, around the plant. The phloem can move substances in both directions, using the active process of translocation. The walls between phloem cells are sieve plates, so that phloem sap can flow through.
• The phloem is a living cell, but it has no nucleus, so companion cells are linked to the sieve tube cells by plasmodesmata. The companion cells transport sucrose and ATP to the sieve tube cells.
• Many plants fibres have great tensile strength while being flexible, making them useful.
• fabrics:

  • cotton - spinning
  • flax - retting
  • nylon and polyester (crude oil so not sustainable)
• Wood is resistant to compression but it also has some flexibility so it doesn't crack, making it perfect for construction. It locks away carbon dioxide, can be a sustainable resource with replanting, and it is carbon neutral.
• Bioplastics are plastics made out of biological polymers so that they are biodegradable and a sustainable resource. :

  • cellulose based plastics e.g. cellophane for food packaging
  • thermoplastic starch e.g. capsules that contains drugs
  • polylactic acid e.g. computer casings, cups
  • PHB e.g. ropes, bank notes
• Bioplastics are burnt once they are no longer useful, which releases energy to generate electricity. If the plastics biodegrade, they release methane which is a greenhouse gas.
• Risks of culturing bacteria:

  • harmless cultures can become pathogenic from a mutant strain
  • contamination from pathogenic bacteria in the environment
  • bacteria from air or skin will contaminate pure cultures
• Aseptic technique is used to carry out experiments in a sterile environment to prevent contamination.
• Plants can have antimicrobial properties as they contain antiseptic compounds and antibiotics. These chemicals can be extracted and purified to make specific doses. The chemicals are often synthesised industrially to minimise plant wastage and to make the drug more effective.