B2.13 Plant Cell Organisation

• What are the different levels of organization in plants?

  Cells, tissues, organs, organ systems
• What is the function of the organ system formed by leaves, stems, and roots?

  Transport of substances around the plant
• What is the primary function of leaves?

  Site of photosynthesis
• What do leaves require to make sugars during photosynthesis?

  Carbon dioxide and water
• What is meristem tissue and where is it found? 

  • Stem cells
  • Tips of shoots and roots 
• How does water reach the leaves of a plant?

  Transported by roots and xylem
• What are stomata?

  Little holes for gas exchange
• Where are stomata primarily located on a leaf?

  Scattered through the lower epidermis
• What is the spongy mesophyll tissue's role in leaves?

  Facilitates gas diffusion
• Where does most photosynthesis occur in a leaf?

  Palisade mesophyll layer
• What do palisade cells contain that is crucial for photosynthesis?

  Chloroplasts
• What is the function of phloem in plants?

  Transport sugars to the rest of the plant
• How does the waxy cuticle help leaves?

  Reduces water loss
• Why do leaves need to balance stomata opening and closing?

  Maximize carbon dioxide absorption, minimize water loss
• What happens to guard cells when a plant has plenty of water?

  They become turgid, enlarging the gap
• What occurs to guard cells when a plant is short of water?

  They become flaccid, closing the stomata
• Why do most stomata exist on the underside of leaves?

  To reduce water evaporation
• What is meristem tissue in plants?

  Plant form of stem cells
• Where is meristem tissue found in plants?

  At the growing tips of roots and shoots
• What are the main functions of leaves in plants?

  • Site of photosynthesis
  • Gas exchange through stomata
  • Transport of sugars via phloem
  • Water conservation through cuticle
• What adaptations do leaves have to minimize water loss?

  • Waxy cuticle on the upper surface
  • Stomata primarily on the underside
  • Guard cells regulate stomata opening
• What is the process of photosynthesis in leaves?

  1. Absorption of sunlight by chlorophyll
  2. Uptake of carbon dioxide through stomata
  3. Water transport from roots via xylem
  4. Production of sugars in palisade mesophyll
• What is the role of guard cells in stomata function?

  • Control the opening and closing of stomata
  • Respond to water availability
  • Sensitive to light conditions
• At night time, when photosynthesis can't take place, are the stomata normally open or closed? Why?

  • Closed
  • At night time there is no light for photosynthesis, so plants don't need to absorb carbon dioxide. This means they can close their stomata and conserve water.
• If there is plenty of water in the leaf, guard cells become turgid, which opens the stomata. This allows carbon dioxide to enter the leaf, but also allows water to escape. 
• Which structures help to minimise water loss?

  • Guard cells which can close stomata
  • Waxy cuticle 
• The upper epidermis is transparent so that light can pass through it. This means that as much light as possible can reach the palisade mesophyll cells below, and be used in photosynthesis. 
• Stomata

  
• Guard Cells

  
• Lower epidermis

  
• Spongy mesophyll layer

  
• Palisade mesophyll layer

  
• Waxy cuticle

  
• The palisade mesophyll layer is an example of a: 

  Tissue
• A guard cell is an example of a: 

  Cell
• The root, stem, and leaves, together make up an: 

  Organ system
• The leaf is an example of an: 

  Organ
• The four levels of plant organisation are:

  cells ➔ tissues ➔ organs ➔ organ systems