B2 - Plant Tissues and Organs

• 1. waxy cuticle 
  • reduces water loss
• 2. upper epidermal 
  • protective covering
  • thin so allows light to pass through for photosynthesis
• 3. palisade mesophyll 
  • photosynthesis occurs in this layer
  • contains lots of chloroplasts
• 4. spongy mesophyll
  • photosynthesis occurs in this layer
  • contains air spaces for movement of gases
• 5. stomata (lower epidermal)
  • surrounded by guard cells
  • gas exchange - co² goes in, o² goes out

during the day:

guard cells are open, letting carbon dioxide enter for photosynthesis, and water and oxygen exit

at night:

no light, so no photosynthesis occurs. therefore the stomata do not need to be open

animal cells differentiate very early during the development stage. plant cells have the ability to change once they have specialised. 

meristem tissue contains stem cells which can develop into several other tissues and organs in plants.

parts of a plant:

• shoots = anything above ground (stems/flowers/leaves)
• roots = anything below ground (roots/tuba)

making identical copies of plants:

• take a cutting. this cutting contains meristem tissue
• once planted, this meristem tissue has changed shoot into roots
• two identical plants have now been grown

root har cells:

• large surface area to absorb water and minerals 
• magnesium needed for chlorophyll, nitrates needed to make proteins

xylem tubes

• job: transporting water and mineral ions to the shoots through the transpiration stream
• movement: one direction - upwards towards the shoots from the roots
• structure: hollow tubes made from dead cells
• adaptations: lignin strengthens and makes it waterproof. hollow tubes make transportation more efficient

phloem tubes

• job: transports sugars for immediate use or storage as starch to the shoots or roots through translocation
• movement: both directions, travels to the growing parts of the plant
• structure: living, elongated cells that are not hollow. cells are stacked end to end and contain pores.
• adaptations: pores allow sugar to pass through from cell to cell

transpiration is the evaporation of water from areal parts of a plant like the leaves. the rate of transpiration is increased in warm, dry, and windy conditions.

1. water is absorbed from the soil into the roots 

2. water is transported up the xylem

3. water is lost from the underside of the leaf, through the stomata. this is transpiration.

stomata are found on the underside of the leaf as it is cooler, which results in less evaporation and less water loss

the transpiration stream is the process of water being transported through the xylem of a plant and evaporating from the leaves and other areal parts 

stomata

• during the day
  • stomata are open to allow carbon dioxide to enter for photosynthesis 
  • water vapour is lost
• at night
  • stomata are closed because photosynthesis is not taking place
  • reduces water vapour loss

plant adaptations - cactus

• thick stem to store more water 
• spikes instead of leaves to reduce the surface area so less transpiration occurs 
• deep root system to absorb ground water 
• shallow root system to absorb surface water