Plant structures

• How is the glucose produced in photosynthesis used?

  - used in respiration to release energy

  - can be converted into other food, like lipids, or combined with nitrates to create amino acids

  - stored as starch as an energy source
• What is the word equation for photosynthesis?

  Carbon dioxide + water -> glucose + oxygen
• What is this part of the leaf called?

  palisade layer

  
• What is the symbol equation for photosynthesis?

  6CO2 +6H2O -> C6H12O6 +6O2
• What are the three limiting factors for photosynthesis?

  CO2 concentration, light intensity and temperature
• How does temperature affect the rate of photosynthesis?

  • If the temperature is too low, the rate will be slow as it is far from the enzyme's optimums.
  • If the temp is at the optimum, rate will be fast.
  • If it is above the optimum, the enzymes' active sites will denature.
• What is the equation for light intensity?

  Light intensity = 1/(distance from light)^2
• How does light intensity affect the rate of photosynthesis?


  • At first, as light intensity increases, so does the rate, as more light can be used in photosynthesis.
  • Then the graph plateaus - even as light intensity increases, rate won't, because temperature of CO2 concentration is the new limiting factor.
• How does CO2 concentration affect the rate of photosynthesis?

  As Co2 concentration increases, so does rate, until light intensity or temperature becomes the limiting factor, at which point, rate will stop increasing
• How to investigate the effect of light intensity on photosynthesis?

  - pondweed (or algae), and water can be added to a conical flask with a bung. Through the bung, a tube connected to a gas syringe is set up. This apparatus can be placed a measured distance away from a light source, and then left for a set amount og time.

  - Oxygen released will collect in the syringe, and rate of 02 production can be calculated by volume/time. You can repeat at a range of distances, and then see which is fastest
• How are root hair cells adapted to their functions?

  - they absorb water and mineral ions from the soil.

  - long hairs increase the surface area for max absorption

  - lots of mitochondria to provide energy needed for active transport
• How is water absorbed by root hair cells?

  osmosis
• How are mineral ions absorbed by root hair cells?

  active transport
• What do phloem tubes do?

  They transport food - mainly sucrose, made in the leaves for immediate use (eg in growing regions) or for storage.
• What is translocation, and which tubes does it involve?

  - the movement of glucose (transported as sucrose) produced in photosynthesis to all other parts of the plant for respiration

  - phloem tubes
• What is the structure of phloem tubes?

  • sieve tubes- long, thin cells with perforated end plates to enable sugar flow
  • companion cells- contain a dense cytoplasm, nucleus, mitochondria to provide energy
• What do Xylem tubes do?

  Xylem tubes transport water and minerals from the root to the rest of the plant e.g the leaves.

  They are strengthened with a material called lignin
• What is the transpiration stream?


  The movement of water from the roots through the xylem and out of the leaves
• What is the structure of xylem tubes?

  • dead cells form a long, hollow column
  • no end walls
  • thick cell wall strengthened with lignin for support
• How does the transpiration stream work?


  Water is lost from the leaves through evaportation and diffusion, meaning there is a shortage of water in the leaves, so more is drawn up the plant through the xylem vessels to replace it, meaning that more water is drawn up again through the roots, so there is a constant stream of water through the plant. This carries mineral ions dissolved in the water along with it.
• What are stomata and what is their function?

  Stomata are pores on the underside of the leaf. They can open and close when necessary to help the plant maintain moisture. They allow CO2 and O2 to diffuse in and out of the plant, as well as allowing water to leave the plant during transpiration.
• How do stomata open and close?

  They are surrounded by two guard cells.

  When water enters the guard cells they become turgid and the stomata opens.

  When water leaves the guard cells they change shape and close the stomata
• What are the three factors which affect transpiration rate?

  Light intensity, temperature and air movement
• How does light intensity affect the transpiration rate?

  Brighter the light -> faster rate.

  Stomata close as it gets darker (no light for photosynthesis, no need for CO2), so as they are closed very little water can escape
• How does temperature affect transpiration rate?

  Warmer -> faster rate

  Warmer = particles have more energy to evaporate and diffuse out of the stomata.
• How does air flow affect transpiration rate?

  - better air flow (eg stronger wind) -> faster rate

  - if air flow is poor, water that evaporate will linger around the leaf, causing the concentration gradient to be less steep, meaing diffusion occurs more quickly

  - if there is good air flow and the water vapour is swept away quickly, there will be a steeper concentration gradient, so diffusion will happen more quickly
• What equipment can be used to estimate transpiration rate?

  potometer
• How can you estimate transpiration rate using a potometer?

  Record the distance that the air bubble moved per unit time - speed of bubble movement gives an estimate for the rate
• How are leaves adapted for photosynthesis?

  -Leaves are BROAD so theres are large surface area exposed to light

  -Leaves contain lots of CHLOROPHYLL in chloroplasts to absorb sunlight

  -Leaves have little holes called STOMATA. That open and close to let gases like CO2 and 02 in and out. They also allow water vapour to escape which is known as transpiration.
• How is the upper epidermis adapted for photosynthesis?

  It is made of transparent cells to allow light through so that it can reach the palisade layer
• How is the palisade layer adapted for photosynthesis?

  It contains lots of chloroplasts, so they are near the top of the leaf to reach and collect more light
• How is does the waxy cuticle help photosynthesis?

  Helps to reduce water loss by evaporation
• How do the xylem and phloem tubes help leaf structure for photosynthesis?

  - provide water and take away glucose

  - support the structure of the leaf
• How is the spongy mesophyll layer adapted for photosynthesis?

  Lots of air pockets to allow gases to easily flow through, increasing rate of diffusion in and out of the the cells
• How is the lower epidermis adapted for photosynthesis?

  Lots of stomata to allow gases and water to enter and leave the leaf
• What are auxins, what do they do, and how to they travel through the plant

  - plant hormones

  - control growth at the tips of the roots and shoots

  - move through the plant is solution
• What do auxins do to growth in the roots and shoots?

  They promote growth in the shoots, but inhibit growth in the roots
• Where are auxins produced?

  tips of shoots and roots, and diffuse backwards to stimulate the cell elongation process which occurs just behin the tips
• Are shoots positively or negatively phototropic?

  positively - they grow towards light
• What happens when one side of a shoot is exposed to light, in relation to auxins?

  More auxins accumulate on the shaded side, meaning cells elongate more quickly on that side, so the shoot bends toward the light, allowing it to absorb more light for photosynthesis, allowing the plant to grow. (taller shoots have better chances of finding light)