bio mass transport in plants

• give the parts of the leaf structure

  upper epidermis, lower epidermis, waxy cuticle, palisade mesophyll, spongy mesophyll, guard cell, stomata
• give three things that happen at stomata

  oxygen diffuses out

  carbon dioxide diffuses in

  close at night to reduce water loss as no photosynthesis occurs
• what is a xerophytic plant

  adapted to survive in environments with limited water
• list the adaptations of xerophytes

  curled leaves

  hairs

  sunken stomata

  thicker cuticle

  longer roots
• why is curve leaves an advantage for xerophytes

  to trap moisture and increase humidity which reduces the water potential gradient from in to out so less evaporation
• why is hairs an advantage for xerophytes

  trap moisture to increase humidity reduce the water potential gradient so less evaporation
• why is a sunken stomata advantageous to xerophytes

  trap moisture and increase humidity, reduces water potential gradient and less evaporation
• why is a thicker cuticle advantageous for xerophytes

  to prevent evaporation
• why is longer roots advantageous for xerophytes

  so can reach more water
• what is transpiration

  loss of water vapour from the stomata by evaporation
• what are the four factors which affect transpiration

  light intensity

  temperature

  humidity

  wind
• how does light intensity affect transpiration

  positive correlation

  more light causes more stomata to open therefore larger surface area for evaporation
• how does temperature affect the rate of transpiration

  positive correlation

  more heat means more kinetic energy so faster molecules so more evaporation
• how does humidity affect the rate of transpiration

  negative correlation

  more water vapor in the air will make water potential more positive outside leaf therefore reduces water potential gradient
• how does wind affect the rate of transpiration

  positive correlation

  more wind will blow away humid air containing water vapour therefore maintaining water potential gradient
• where is the most negative water potential on a tree

  at the top
• what three things cause movement water up the xylem

  cohesion

  adhesion

  root pressure
• explain cohesion in cohesion tension theory

  water is polar so forms hydrogen bonds

  means that the water molecules stick together in one continuous column
• explain adhesion in cohesion tension theory

  water molecules stick to other molecules, at the xylem wall

  the narrower the wall= greatest impact
• explain root pressure in cohesion tension theory

  water moves in by osmosis

  increases volume and pressure

  forces water up (positive pressure)
• explain movement of water up xylem

  1. water evaporates out of stomata creating low pressure
  2. more water is pulled up the xylem to replace (negative pressure)
  3. water molecules create column due to cohesion and their hydrogen bonds
  4. water molecules adhere to the walls
  5. as column of water is pulled up the xylem it creates tension so the xylem is narrower