Organisation in plants

• Tissues in leaves


  Leaves are organs because they contain many tissues that work together to perform photosynthesis
• Waxy cuticle


  • Makes the leaf waterproof
• Stomata


  Tiny openings in the undersides of leaves that allow gases to move into and out of the leaf
• Upper epidermis


  • Single layer of cells
  • Protects against water loss
  • Transparent to allow light to pass through
• Palisade mesophyll


  • Tightly packed cells
  • Lots of chloroplasts to absorb light for photosynthesis
• Spongy mesophyll


  • Spherical cells
  • Lots of air spaces to allow gases to diffuse quickly
  • Large surface area-to-volume ratio to increase gas exchange
• Lower epidermis


  • Tiny openings on the lower surface of the leaf that allow gases to move into and out of the leaf
• Guard cells


  Control the opening and closing of the stomata
• Stomata are tiny openings in the undersides of leaves-this placement reduces water loss through evaporation
• How stomata control gas exchange and water loss

  1. Allowing diffusion of carbon dioxide into the plant for photosynthesis

  2. Allowing diffusion of oxygen out of the plant

  3. When a plant has plenty of water, the guard cells become turgid and the stoma opens

  4. When a plant is flaccid, the guard cells become flaccid and the stoma closes
• Transpiration


  Water is lost through the stomata by evaporation, pulling water up from the roots through the xylem
• Importance of transpiration


  • Provides water to cells to keep them turgid
  • Provides water to cells for photosynthesis
  • Transports mineral ions to leaves
• Translocation


  The movement of dissolved sugars from the leaves to the rest of the plant through the phloem
• Importance of translocation


  • Moves dissolved sugars made in the leaves during photosynthesis to other parts of the plant for respiration, growth, and glucose storage
• Xylem


  • Specialised tissues for one-way transport of water and minerals
  • Made of dead cells, joined together with no end walls between them
  • Thick walls stiffened with lignin
• Phloem


  • Specialised tissues for transport of water and dissolved sugars in both directions
  • Cells have end walls with small holes to allow substances to flow through
  • Walls stiffened with lignin
• Factors affecting the rate of transpiration

  • Temperature
  • Humidity
  • Wind speed
  • Light intensity
• Higher temperatures


  Increase the rate of transpiration
• Lower humidity


  Increases the rate of transpiration
• More wind


  Increases the rate of transpiration
• Higher light intensity


  Increases the rate of transpiration
• Root hair cells


  • Increase absorption of water and mineral ions into the root by increasing the root surface area
  • Contain lots of mitochondria to transfer energy, which is used to take in mineral ions by active transport
• Waxy cuticle

  makes the leaf waterproof
• Upper Epidermis

  single layer of cells

  protects against water loss

  transparent to allow light to pass through
• Palisade Mesophyll

  tightly packed cells

  lots of chloroplasts to absorb light for photosynthesis
• Spongy Mesophyll

  spherical cells

  lots of air spaces to allow gases to diffuse quickly

  large surface are to volume ratio to increase gas exchange
• Guard Cells

  control the opening and closing of the stomata
• Stomata

  tiny openings on the lower surface of the leaf that allow gases to move into and out of the leaf.
• Transpiration

  water is lost through the stomata by evaporation.

  pulls water up from the roots through the xylem - transpiration.

  constant movement of water up the plant - transpiration stream.
• Transpiration

  provides water to cells to keep them turgid

  provides water to cells for photosynthesis

  transports mineral ions to leaves
• Translocation

  movement of dissolved sugars from the leaves to the rest of the plant through the phloem
• Translocation

  moves dissolved sugars made in the leaves during photosynthesis to other parts of the plant.

  this allows for respiration, growth, and glucose storage.
• Temperature effect on transpiration

  higher temperatures increases the rate of transpiration because water evaporates faster in higher temperatures.
• Humidity effect on transpiration

  lower humidity increases the rate of transpiration because the drier the air, the steeper the concentration gradient of water molecules between the air and leaf.
• Wind speed effect on transpiration

  more wind increases the rate of transpiration because wind removes the water vapour quickly, maintaining a steeper concentration gradients.
• Light intensity effect the rate of transpiration

  higher light intensity increases the rate of transpiration because stomata open wider to let more carbon dioxide into the leaf for photosynthesis.
• Root hair cells

  increase absorption of water and mineral ions into the root by increasing the root surface area.
• Root hair cells

  contain lots of mitochondria to transfer energy, which is used to take in mineral ions by active transport.
• Why is a leaf an organ?

  there are many tissues inside the leaf that work together to perform photosynthesis.
• How is the upper epidermis adapted for its function?

  singer layer of transport cells allow light to pass through

  cells secrete a waxy substance that makes leaves waterproof