plants

• root hair cells are adapted for what?

  for efficient uptake of water --> osmosis

  for efficient uptake of mineral ions --> active transport
• what are root hairs?

  single-celled extensions of epidermic cells in the root
• root hairs are long and thin. why?

  so they can penetrate between soil particles and absorb water and minerals from the soil.

  root hairs increase the surface area to volume ratio, which increases the uptake of water and mineral ions.
• how does osmosis in root hair work?

  high proportion of dissolved minerals and sugars in the cytoplasm of the root hair cells gives it a low water potential.

  as the soil has a higher water potential than the cytoplasm, water moves into the root hair cell.
• how does active transport work in the root hair?

  the concentration of mineral ions in the soil is much lower than the root hair cell cells.

  • they need to move into the cell against the concentration gradient which requires energy.
• what are the 2 specialist transport vessels that plants possess?

  xylem and phloem
• what is transpiration?

  The process by which plants lose water through their leaves.

  • caused by the evaporation and diffusion of water from surface of plant.
• water travels up the xylem from the roots into the leaves of the plant to replace the water that has been lost due to transpiration.
• how is a constant transpiration stream created in the xylem?

  as the evaporation and diffusion of water creates a net loss of water in the lead, water is drawn up through the xylem to replace it.

  consequently, more water is absorbed by the roots.

  this creates a constant transpiration stream.
• what direction does movement take place in xylem?

  upwards. from the root to leaves
• transpiration is also a side effect of how leaves are adapted to maximise gas-exchange for photosynthesis.

  • plants contain tiny pores called stomata that allow for gas exchange
• what is the role of stomata and guard cells?

  to control gas exchange and water loss
• how are stomata formed?

  by 2 kidney-shaped guard cells which open and close the stomatal pore.

  • stomata can be opened or closed depending on the conditions the plant is in.
• guard cells:

  have cell walls with unevenly distributed cellulose - the inner wall is thicker and the outer well is thinner to aid opening and closing of the stomata.
• • When the availability of water is high, guard cells become turgid as a result of osmosis
  • This causes the stomatal pore to open which allows gases to diffuse in and out of the leaf
  • Water is consequently lost via transpiration
  • When less water is available, the guard cells lose water by osmosis and become flaccid, pulling them together
  • This closes the stomatal pore and reduces water loss via transpiration
• how do stomata conserve water?

  they are sensitive to light

  they open in the day and close in the night

  this allows water to be conserved whilst no photosynthesis is occuring
• The guard cells control the opening and closing of the stomata

  A) turgid

  B) open

  C) flaccid

  D) closed

  
• what is translocation?

  the transport of soluble products of photosynthesis (mainly sucrose) in the plant
• what type of process is translocation and why?

  an active process because it requires energy
• where are sucrose and amino acids transported?

  phloem tubes
• how are the xylem and phloem arranged?

  vascular bundles
• what does the xylem do?

  transports water and minerals from the roots to the stem and leaves in the transpiration stream
• key features of xylem:

  made of dead cells joined end to end with no end walls between them

  this creates a hole down the middle which forms a hollow tube.
• how are xylem cells strenghtened?

  by a woody material called lignin which makes the cell walls strong, waterproof and stiff
• structure of xylem.

  A) lignin

  B) broken

  C) cells

  D) continuous

  
• what does the phloem tube do?

  transport nutrients like dissolved sugars like sucrose and amino acids both up and down the stem.

  • nutrients are transported to new growing and storage tissue in a process known as translocation
• key features of phloem tube:

  • made of columns of living cells called sieve-tube elements which are joined end to end.

  --> sieve tube elemnts contain end plates with holes (sieve plates)

  --> allows sugars and amino acids to flow easily through

  • sieve tube elements are supported by companion cells that carry out the living functions for the sieve tube elements.

  --> this is because the sieve tube elements contain no nucleus so cant survive on their own
• phloem cell!

  A) sieve plates

  B) companion cell

  
• fill in this table.

  A) water and mineral ions

  B) sucrose and amino acids

  C) transpiration stream

  D) translocation

  E) one-way

  F) all

  G) dead

  H) living

  
• what are the 4 factors affecting transpiration?

  air movement, humidity, temperature and light intensity
• how does high air movement affect transpiration?

  higher rate of transpiration.

  good airflow removes water vapour surrounding the leaf, which sets up a concentration gradient between the leaf and the air, increasing water loss.
• how does high humidity levels affect transpiration?

  decreases transpiration.

  when the air is saturated with water vapour, the concentration gradient is weaker, so less water is lost.
• how does high light intensity affect transpiration?

  increases rate of transpiration

  guard cells are responsive to light intensity: when it is high they are turgid and the stomata open allowing water to be lost
• how does temperature affect transpiration?

  increases it

  higher temperature, particles have more kinetic energy so transpiration occurs at a faster rate as water molecules evaporate from the mesophyll and diffuse away faster
• what does a potometer measure?

  the uptake of water by a stem as a measure of the amount of water that is being lost by evaporation consequently pulling water up through the stem to replace it.
• label the aparatus for investigating the effect of environmental factors on the rate of transpiration.

  A) cut shoot

  B) reservoir

  C) capillary tube

  D) air bubble

  E) beaker

  F) volume

  
• rate of transpiration?

  distance moved by air bubble (m)

  --------------------------------

  time (min)
• why do we cut the shoot underwater in the potometer experiment?

  to prevent air entering the xylem
• steps for experiment:

  1. remove the capillary tube from water so single air bubble can form and then place back into water
  2. set up a lamp 10cm from the leaf
  3. allow plant to adapt for 5 mins
  4. record starting location of air bubble
  5. leave for 30 minutes
  6. record the end location of air bubble
  7. change the light intensity
  8. reset bubble by opening tap below reservoir
  9. repeat experiment
  10. calculate rate of transpiration
• how could we investigate airflow using the potometer experiment?

  set up a fan or hairdryer to blow air over the plant

  • set the fan at different distances or different fan-speed settings