Gas exchange in plants

• What is the main function of stomata in plants?

  Gas exchange
• How do guard cells control the opening of stomata?

  By becoming turgid or flaccid
• What happens to stomata when guard cells are flaccid?

  They close to reduce water loss
• What are the similarities between gas exchange in plants and terrestrial insects?

  • No living cell is far from external air
  • Diffusion occurs in the gas phase
  • Both avoid excessive water loss
  • Diffusion through pores in outer covering
• What are the differences between gas exchange in plants and terrestrial insects?

  • Insects create mass air flow; plants do not
  • Insects have smaller surface area to volume ratio
  • Insects have specialized structures for gas diffusion
  • Plants interchange gases between respiration and photosynthesis
• Why is it advantageous for plants to control stomata opening and closing?

  To control water loss by evaporation
• What adaptations do insects have to limit water loss?

  Small surface area to volume ratio
• Why is a small surface area to volume ratio not feasible for plants?

  Plants need large surface area for photosynthesis
• What are xerophytes?

  Plants adapted to limit water loss
• What are the main tissues found in the leaf of a plant?

  Epidermal tissues, mesophyll tissues (palisade and spongy), and vascular tissues (xylem and phloem)
• What are the three main ways in which an insect's tracheal system is adapted for efficient gas exchange?

  Diffusion gradients, mass transport, tracheole water
• What is the function of the guard cells surrounding each stoma?

  Guard cells turgid - pore open to allow gas exchange, guard cells flaccid - pore closed to reduce water loss
• Why is it important for plants to have a large surface area to volume ratio?

  To maximize light absorption and gas exchange with the external environment
• What is the main adaptation that both plants and insects share to reduce water loss?

  Waterproof coverings and the ability to close the openings of the gas-exchange system
• Why is a small surface area to volume ratio not a feasible way for plants to limit water loss, unlike insects?

  Because plants need a large surface area to volume ratio to maximize light absorption and gas exchange for photosynthesis
• What are two reasons why plants growing on sand dunes need to have xerophytic features even though there is plentiful rainfall?

  The rain rapidly drains through the sand, out of the reach of the roots, and sand dunes are usually found in windy conditions which increases the water potential gradient and water loss
• Why do salt marsh plants have difficulty obtaining water, despite having plenty around their roots?

  The soil solution is very salty (has a low water potential) which makes it difficult for the root hair cells to obtain water by osmosis
• How does the structure of a leaf help it carry out photosynthesis efficiently?

  • Large, flat surface area to maximize light absorption
  • Leaves arranged to form an optimal leaf mosaic
  • Network of veins to support the leaf blade
  • Thin leaf to allow efficient gas exchange
  • Stomata on lower epidermis to allow gas exchange while reducing water loss
  • Large air spaces between cells for gas diffusion
  • Transparent, waxy cuticle to reduce water loss
  • Cylindrical palisade cells arranged perpendicular to upper epidermis
  • Large number of chloroplasts in cells
  • Chloroplasts can move around the cell to optimize light absorption
  • Thin cell walls and narrow air spaces for large gas exchange surface area
• What are the key adaptations of xerophytic plants to reduce water loss?

  • Thick, waxy cuticle on leaves to reduce evaporation
  • Leaves with hairs that trap moist air near the leaf surface
  • Stomata located in pits or grooves to reduce water potential gradient
  • Leaves that are small and cylindrical to reduce surface area
  • Lower stomatal density to limit unnecessary water loss
• Which of the following is the main way that plants exchange gases with the environment?

  Stomata
• How do the gas exchange needs of plants differ from those of animals?

  Plant cells carry out both respiration and photosynthesis, so they need to exchange both oxygen and carbon dioxide with the environment, while animal cells only need to exchange oxygen and carbon dioxide for respiration
• What is the main advantage of plants being able to control the opening and closing of their stomata?

  It helps them control water loss by evaporation/transpiration
• What is the name given to plants that have adaptations to survive in habitats with high water loss and limited water supply?

  Xerophytes
• If you wanted to observe the detailed external features of a cell, which type of microscope would you use?

  Scanning electron microscope
• How does the structure of a leaf help it maximize light absorption for photosynthesis?

  The leaves are arranged in an optimal leaf mosaic to maximize light absorption, and the palisade cells are cylindrical and oriented perpendicular to the upper epidermis to efficiently capture light
• What is the purpose of the network of veins containing xylem and phloem in a leaf?

  To help support the leaf blade
• What is the formula to calculate the area of a circle?

  $A =$$\pi r^2$
• How do the gas exchange needs of plants differ from those of animals?

  • Plant cells carry out both respiration and photosynthesis, so they need to exchange both oxygen and carbon dioxide with the environment
  • Animal cells only need to exchange oxygen and carbon dioxide for respiration
  • The volumes of gases exchanged by a plant leaf depend on the rates of photosynthesis and respiration
  • When photosynthesis is occurring, the leaf takes in CO2 and releases O2
  • When photosynthesis is not occurring, the leaf takes in O2 and releases CO2 through respiration
• What is the name given to the waxy, waterproof layer covering the epidermis of leaves?

  Cuticle
• How does a thick cuticle on leaves help xerophytic plants conserve water?

  The waxy cuticle reduces water loss by evaporation through the leaf surface
• How do hairy leaves on xerophytic plants help them conserve water?

  The hairs trap moist air next to the leaf surface, reducing the water potential gradient and slowing evaporation
• How do stomata located in pits or grooves on xerophytic plant leaves help conserve water?

  The pits or grooves trap moist air close to the leaf surface, reducing the water potential gradient and slowing evaporation
• How does having leaves that roll up help xerophytic plants conserve water?

  Rolling up the leaves protects the lower epidermis where the stomata are located, trapping a region of still, moist air and reducing the water potential gradient
• What is the term for plants that have adaptations to survive in habitats with high water loss and limited water supply?

  Xerophytes
• How does having a reduced surface area to volume ratio in the leaves of xerophytic plants help them conserve water?

  It reduces the overall surface area from which water can evaporate, while still providing enough surface area for photosynthesis
• What is the term for having a lower density of stomata on the leaves of xerophytic plants?

  Lower stomatal density
• How does having a lower density of stomata on the leaves of xerophytic plants help them conserve water?

  Reducing the number of stomata lowers the chances for unnecessary water loss through transpiration
• What are the key adaptations of xerophytic plants to reduce water loss?

  • Thick, waxy cuticle on leaves to reduce evaporation
  • Leaves with hairs that trap moist air near the leaf surface
  • Stomata located in pits or grooves to reduce water potential gradient
  • Leaves that are small and cylindrical to reduce surface area
  • Lower stomatal density to limit unnecessary water loss
• If you wanted to observe the detailed external structure of a cell, which type of microscope would you use?

  Scanning electron microscope
• How does the arrangement of palisade cells in the leaf help maximize light absorption for photosynthesis?

  The cylindrical palisade cells are arranged perpendicular to the upper epidermis to efficiently capture light