PLANT CELL organisation

• Plant Cell Organisation


  Plant cells are organised into tissues and organs that work together
• Plant organ systems


  Organs (stems, roots, leaves) work together to transport substances around the plant
• Plant tissues

  • Epidermal tissue
  • Palisade mesophyll tissue
  • Spongy mesophyll tissue
  • Xylem
  • Phloem
  • Meristem tissue
• Leaf structure

  • Upper epidermis is transparent to let light through
  • Palisade layer has lots of chloroplasts near the top to get more light
  • Spongy mesophyll has air spaces to increase gas diffusion
  • Lower epidermis has stomata to let gases in and out
  • Xylem and phloem transport water, nutrients and food
• Phloem


  Tubes made of elongated living cells that transport dissolved sugars around the plant
• Xylem

  Tubes made of dead cells that transport water and mineral ions from roots to stem and leaves
• Phloem transports substances in both directions


  Xylem only transports things upwards
• Transpiration

  The loss of water from a plant, mainly through the leaves
• Transpiration process

  Water evaporates from leaves, creating a shortage that draws more water up from the roots through the xylem
• Guard cells


  • Control the size of stomata to regulate gas exchange and water loss
  • Open when plant has lots of water, close when plant is short of water
• A big tree can lose about a thousand litres of water from its leaves every day
• Factors affecting transpiration rate

  • Air flow
  • Temperature
  • Humidity
  • Light intensity
• Air flow


  More wind means faster transpiration as water vapour is removed from around the leaf
• Temperature


  Warmer temperatures mean faster transpiration as water particles have more energy to evaporate and diffuse out
• Humidity


  Higher humidity means less difference between inside and outside the leaf, so slower diffusion and transpiration
• Light intensity


  Brighter light means faster transpiration as stomata are open for photosynthesis
• where is meristem tissue found in a plant?

  tips of roots and shoots
• which layer of plant tissue contains lots of chloroplast?

  palisade layer
• which tube transports substances in both directions?

  phloem
• main factors that affect the rate of transpiration in plants

  • air flow
  • temperature
  • humidity
  • light intensity
• how does airflow affect transpiration rate?

  1. more windy=faster transpiration
  2. fast moving air means that water vapour around leaf is swept away
  3. higher concentration of water vapor inside the leaf compared to outside, water will diffuse out of leaf more quickly
• how does temperature affect transpiration rate?

  1. warner temp=faster transpiration
  2. due to water particles having more energy=evaporate and diffuse out of stomata faster
• how does humidity affect transpiration

  1. air is humid=lots of water in it
  2. means isn’t much of a difference between the inside and the outside of the leaf
  3. means diffusion wnot happen fast
  4. drier around leaf=faster transpiration
• how does light intensity affect transpiration rate

  1. brighter the light=greater the transpiration
  2. photosynthesis cant happen in dark so stomata close when dark
  3. when stomata close, very little water escapes
• which type of plant tissue contains air spaces for the diffusion of gases


  spongy mesophyll tissue
• which type of plant tissue forms the transparent layer covering the outside of plant?

  epidermal tissue
• phloem tubes

  • made of stretched out living cells
  • end walls between cells which have pores so cell sap can flow through
  • transport the food substances plants make in their leaves around the plant for immediate use or storage
  • transport goes in BOTH directions
  • called translocation
• xylem tubes

  • made of dead cells
  • cells joined together with hole down the middle
  • no end walls between cells
  • cells are strengthen with a material called lignin
  • carries water and mineral ions from roots to the stem and leaves
  • movement of water form roots through xylem and out of leaves=transpiration stream
• upper epidermis 


  layer is transparent

  lets light through to palisade layer
• stomata


  lets gas diffuse into and out of lead

  opened and closed in response to the environment

  controlled by guard cells