B2.2 challenges of size (plant)

• active transport is the movement of particles from an area of low concentration to an area of high concentration, against the concentration gradient. This requires energy
• companion cells are the active cells of the phloem. they provide energy for the phloem to transport substances
• guard cells are the cells that control the opening and closing of the stomata
• lignin is a material that lines the xylem vessels and provides strength and support
• osmosis is the net movement of water molecules from a region of high concentration to a region of low concentration through a partially permeable membrane
• phloem is a plant tissue that transports sugars from the source to the sink
• a potometer is a piece of capillary tube that is used to investigate the rate of transpiration. Water loss from the surface is the lead is measured by the distance that th air bubble travels over a certain period of time
• root hair cells are specialised cells that provide a large surface area for the uptake of water and minerals from the soil
• sieve tubes are plant cells that have no nuclei and are connected by the cytoplasm
• the stomata are small pores in the lower epidermis of the leaf that facilitate gaseous exchange
• translocation is the process of transporting sucrose around the plant
• transpiration is the loss of water from the surface of the leaves by evaporation from the open stomata
• turgidity is when the vacuol of a plant cell becomes swollen and enlarged with water
• water potential is the measure for the tendency of water to move from one area to another area. it is represented by the sigh psi (it looks like a mini trident head)
• xylem is a specialised plant tissue that transports water and dissolved minerals from the roots to the leaves of a plant
• water is needed for photosynthesis and to maintain shape of a plant
• dissolved minerals are needed to make proteins and other molecules is leaf cells in order to grow
• sugar is needed for respiration and to make other molecules such as cellulose and starch, and to store in roots
• root hair cells are adapted by having

  • very large vacuole
  • large surface area
  • lots of mitochondria
  • low water potential
• journey of water through a plant

  1. water in the soil
  2. gets soaked up by the root hair cells
  3. goes to the root cortex
  4. transported to the xylem
  5. upwards movement through the xylem
  6. arrives at the leaves
  7. diffuses out the stomata
• when the concentration of minerals in soil is higher than inside the plant, active transport is used to absorb the minerals against the concentration gradient
• leaves are entry and exit points for the gases needed by plants
• stems connect the roots to the leaves, flowers and fruits. they contain cells specially adapted to transport minerals water and sugar (xylem and phloem)
• roots absorb minerals and water from the soil
• the structure of xylem is hollow, made up of dead cells. it has a thick cellulose wall strengthened by lignin
• the function of xylem is to transport water and minerals up the stem from the roots to shoots and leaves. Only transports upwards
• the structure of phloem is made of alive cells, arranged end to end
• the function of phloem is to carry food molecules such as glucose and amino acids from the leaves down into other parts of the plant where they can be stored or used for respiration
• vascular bundle : https://www.thesciencehive.co.uk/xylem-and-phloem-a-level
• the substances transported in?..

  • xylem -> water and minerals
  • phloem -> sugar/glucose
• substances transports from...to..?

  • xylem -> roots to stem to shoots/leaves
  • phloem -> leaves to stem to growing tissue and store tissue
• are the cells coming the tissue dead or alive?

  • xylem -> dead, hollow vessels
  • phloem -> alive
• direction of flow?

  • xylem -> upwards only
  • phloem -> upwards and downwards
• In young trees the phloem tissue is found in the ring right under the bark. Can you explain why young trees die when a deer eats a complete ring of bark?


  because the deer would eat all the phloem tissue, meaning that no glucose tissue can be transported to growing tissue
• oxygen and carbon dioxide enter the plant via the stomata
• water enters the plant via the root hair cells
• the function of chloroplast is to carry out photosynthesis
• each stoma is surrounded by two guard cells which control the opening and th closing of the stoma
• when light intensity is high, guard cells gain water and become turgid. they curve out, opening the stone and allowing carbon dioxide to enter and oxygen and water out
• low light intensity or high temperature causes the guard cells to lose water, closing the stoma