plant structures and their functions

• what are photosynthetic organisms?


  the main producers of food and therefore biomass
• What kind of reaction is photosynthesis in plants?

  endothermic reaction
• What is the equation for photosynthesis?

  reaction uses light energy to react carbon dioxide and water to produce glucose and oxygen
• how do we measure the rate of photosynthesis?

  the rate of oxygen production (number of bubbles or volume of oxygen gas given off in a set time),

  the rate of carbon dioxide uptake and

  the rate of glucose production
• what factors affect the rate of photosynthesis?

  light intensity, carbon dioxide concentration and temperature
• Core Practical: Investigate the effect of light intensity on the rate of photosynthesis

  
• method


  To investigate the effect of light intensity on the rate of photosynthesis.

  
  

  A lamp with an LED bulb is set up at different distances from the plant in a beaker of water:

  an LED bulb is best as this will not raise the temperature of the water

  sodium hydrogen carbonate (NaHCO3) is added to the water to supply the reactant carbon dioxide to the plant

  the light intensity is proportional to distance - it will decrease as the distance away from the bulb increases.

  The bubbles produced over one minute periods are recorded. The rate of photosynthesis is the number of bubbles produced per minute.
• independent variable


  distance from the light source/light intensity
• dependent variable


  the number of bubbles produced per minute
• control variables


  concentration of sodium hydrogen carbonate solution, temperature, using the same piece of pondweed each time
• is the rate of photosynthesis inversely or directly proportional to light intensity?

  directly
• is the rate of photosynthesis inversely or directly proportional to the distance from a light source?

  inversely

  
• what is the inverse square law formula for photosynthesis?

  
• explain how the structure of the root hair cells is adapted to absorb water and mineral ions

  root hair cells absorb mineral ions by active transport, they are adapted by having a large surface area to increase the rate of absorption.
• explain how the structures of the phloem are adapted to their function in the plant

  living cells in phloem using energy to transport sucrose around the plant
• explain how the structures of the xylem are adapted to their function in the plant

  lignified dead cells in xylem transporting water and minerals through the plant
• What is transpiration?

  Loss of water from the plant.
• What is transpiration caused by?

  It is caused by the evaporation and diffusion of water from a plant's surface. It mostly happens in the leaves.
• What does evaporation create in the plant?


  Slight shortage of water in the leaf, so more water is drawn up from the rest of the plant through the xylem vessels to replace it.
• Why do leaves have stomata?

  so gases can be exchanged easily because there is more water inside the plant than in the air outside so the water escapes from the leaves through the stomata by diffusion.
• What is transpiration affected by?

  light intensity, temperature, wind speed/air flow, humidity.
• How does light intensity affect the rate of transpiration?

  Brighter the light, greater the transpiration rate. Stomata close cause it's dark. They don't need to be open to let co2 in. Very little water can escape.
• How does the temperature affect the rate of transpiration?

  warmer, faster transpiration happens. When warm the water particles have more energy to evaporate and diffuse out of the stomata.
• How does the wind speed/air flow affect the rate of transpiration?

  stronger winds mean faster rate of transpiration, vapour is swept away, wind speed around a leaf is low then water vapour surrounds the leaf meaning stomata cannot release water vapour
• how does humidity affect the rate of transpiration?

  the drier the air the faster transpiration happens. Diffusion happens slower if the air is humid.
• What does the xylem do?

  Carries water and mineral salts from the roots up the shoot to the leaves in the transpiration stream.
• What does the phloem do?

  Transports sugars eg sucrose and amino acids from where they are made in the leaves to other parts of the plant.
• What is a potometer?


  apparatus used to estimate transpiration rate. Measures water uptake by a plant .
• How can you change the light intensity?

  Use a lamp to increase the intensity- increase transpiration rate. Decrease it put potometer in cupboard.
• How can you change the temperature?

  Increase/decrease by putting potometer in a room that's warmer or colder than where you did the control experiment. Inc temp,inc transpiration rate.
• How can you change the humidity?

  Increase humidity of air by spraying a little water into clear plastic bag before sealing it around the plant. -decrease transpiration rate.
• How can you change the wind speed?

  use fan to increase the wind speed around the plant-increase transpiration.
• What are the adaptations of a xylem cell?

  no nucleus, no cytoplasm, large lumen, thick lignin walls.
• What are the adaptations for a phloem cell?

  living, no nucleus, cells arranged end to end (sieve tubule), sieve plate between phloem cells has pores which allow cytoplasm and other substances to flow from cell to cell.
• What happens when the stomata is open?

  H20 enters cell guard cell by osmosis. cell becomes turgid and curved. stomata opens.
• What happens when the stomata is closed?

  H20 leaves the gc by osmosis. cell becomes flaccid and flat. stomata closes.
• What are the functions of the transpiration stream?

  supply water for photosynthesis, provide water to ensure cells are turgid - support, carries essential minerals dissolved in the water, allows evaporation from leaf-leaf cools down.
• What does a weight potometer measure?

  mass of : plant pot + soil + water + plant: at the start, mass after a given time.
• describe how sucrose is transported around the plant by translocation

  phloem are columns of elongated living cells with small pores in the end walls to allow stuff to flow through, they transport food substances mainly sucrose made in the leaves to the rest of the plant for immediate use or for storage. this is called translocation and it requires energy from respiration, transport goes both ways
• Explain how the structure of a leaf is adapted for photosynthesis and gas exchange-stomata

  They are adapted for photosynthesis by having a large surface area, and contain openings, called stomata to allow carbon dioxide into the leaf and oxygen out.