CB6 - Plant & Functions (Leaf & plant adaptations)

• How are leaves adapted for photosynthesis?

  1. Leaves are BROAD and flat so theres are large surface area exposed to light.

  2. On top of leaves have the waxy cuticle layer to conserve water

  3. Below the waxy layer theres lots of tightly packed chloroplasts (/w chlorophyll) in the palisade tissue to absorb sunlight.

  4. Then theres a spongy tissue layer containing ait spaces allowing for easier diffusion.

  5. Below the leaf theres little holes called STOMATA that open and close to let gases like CO2 and O2 in and out.

  ~ Leaves are thin for easier gas exchange
• What is the stomata and how does it work?

  ~ The stomata are tiny poes underneath the leaf.

  ~ This is where CO2 will enter for photosynthesis and where O2 will exit (gas exchange). Also transpiration takes place too as water particles would exit.

  ~ The stomata has guard cells that would open and close during the day based on water levels and environmental conditions.
• Why is the stomata located under the leaf?

  ~ To prevent excessive water loss as direct sunlight and wind could increase transpiration.

  ~ To prevent potential cell damage so guard cells aren't damaged from direct sunlight.
• How does light intensity affect the opening & closing of the stomata?

  ~ The more light, the more the stomata will be open as that indicates for photosynthesis and the need for CO2 to diffuse in.

  ~ The guard cells would detect this through their photoreceptors.

  ~ Then when theres less light, the stomata would close as photosynthesis doesnt take place and gas exchange isn't needed.
• How does water levels in the plant affect the opening & closing of the stomata?

  ~ When theres plenty of water, the plant cells become turgid (swollen), opening the stomata and allowing for transpiration.

  ~ When theres less water, the plant cells become flaccid (shrunk), closing the stomata and pausing transpiration.
• How do the guard cells become turgid (swollen) in optimal environmental conditions?

  ~ They become turgid as potassium ions from neighbouring cells enter the vacuole of the guard cells.

  ~ This creates a lower water concentration difference compared to surrounding cells, which stimulates the release of more water molecules into the vacuole via osmosis which swells up the cell and changes its shape to bow outwards, creating an opening.
• What is transpiration?

  The movement of water vapour through a plant from the roots & out of the stomata.

  ~ Its passive so it doesn't need energy.
• Why does transpiration take place?

  ~ The water potential in the cell is higher than the water potential in the air around them, creating a water potential gradient.

  ~ Cools the plant down as the water absorbs the heat energy and its taken outside the plant
• 4 factors affecting transpiration?

  ~ Light intensity

  ~ Wind intensity

  ~ Temperature

  ~ Humidity
• How would light intensity affect the rate of transpiration?

  ~ The more light, the wider the stomata would be open that allows more water vapour to escape.

  ~ The photoreceptors in the guard cells causes the stomata to open as it takes in CO2 but it also looses water vapour in the process.
• How would wind intensity affect the rate of transpiration?

  The more wind, the quicker it removes water vapour from leaf surfaces, creating a bigger concentration gradient so more water diffuses from the leaf.
• How does temperature affect the rate of transpiration?

  The higher the temperature, the more kinetic energy the water molecules will have so they would diffuse quicker out of the plant.
• How does humidity affect the rate of transpiration?

  The higher the humidity, the lower the rate of transpiration because there would be lots of water molecules in their air, lowering the concentration gradient.
• Why would the rate of transpiration be lower in higher temperatures like 45 degrees?

  Because higher temperatures would cause the stomata to close to prevent excessive water loss from evaporation and transpiration.
• How can the rate of transpiration be measured?

  Using a potometer
• How can you use a potometer to measure the rate of transpiration? (CORE PRACTICAL)

  1. Set up - making sure there's no gaps around the plant.

  2. Note starting position of bubble.

  3. Start stopwatch.

  4. Record distance moved by bubble at set time.

  ~ Speed of the bubble movement gives the estimate of the rate.

  ~ Can add something to measure of how (factor) affects rate.

  
• What would you add to the potometer to measure how (factor) affects rate of transpiration?

  ~ Temperature - UV Light

  ~ Light intensity - Lamp

  ~ Wind speed - Fan

  ~ Humidity - N/A

  
  

  ONLY CHANGE ONE VARIABLE AT A TIME
• How do you calculate the rate of transpiration according to results

  distance moved / time taken
• Why does the bubble move along the capillary tube?

  Because water is pulled along the capillary tube to replace the water being lost from the plant.
• What are root hair cells?

  Cells on the epidermis of plant roots, which grow into long "hairs" that stick out into the soil - usually for water and nutrient absorption
• How are root hair cells adapted for water & nutrient absorption?

  ~ Long extension allows for larger surface area to absorb water & nutrients.

  ~ Active transport causes mineral ions to move into the cytoplasm of cell using energy.

  ~ Osmosis also causes water to be absorbed (reason later).

  ~ Larger vacuole for storage of minerals and water.

  ~ Tiny tubes joining cytoplasm of some cells together allow water & minerals to diffuse between cells and take it up the plant.

  ~ Thinner cell wall allows for a shorter diffusion pathway.
• Explain why active transport is needed to take mineral ions into the cytoplasm of the root hair cell

  Theres a higher concentration of ions inside the cell than outside so active transport would use energy to diffuse the ions in against the concentration gradient.
• Why would a cell need a higher concentration of ions and minerals than outside?

  Because they may need a store of it for growth and function of the cell.
• How would osmosis cause water to be absorbed into the root hair cell?

  ~ Active transport would increase the conc. of mineral ions and other nutrients in the cell.

  ~ Due to the high potential of them, it creates a situation where the water potential in the cell is lower compared to the outside environment, creating a conc. gradient

  ~ This stimulates osmosis as water molecules will move from the outside of the cell (like the soil or surrounding cells) to the inside through the the semi-permeable membrane.

  ~ It equalises the water potential on both sides of the membrane.

  ~ This would also regulate water movement between cells.
• What is a xylem vessel?

  ~ The vascular tissue that transports water and dissolved minerals from the roots, up through the plant and out the leaf stomata in one direction.
• Describe the structure of the xylem

  ~ Made up of dead cells

  ~ Lack of cell walls for a continuous flow

  ~ Thick walls made out of lignin for support

  ~ Tiny pores to allow water and minerals to enter & leave

  ~ Cells have no cytoplasm - Space to flow

  
• What is translocation?

  The movement of sugars through a plant in phloem
• What is the phloem vessel?

  The vascular tissue that transport sugars like sucrose from the leaves to the roots
• Describe the structure of the phloem

  ~ Made up of living cells

  ~ Contains sieve tubes - specialised for transport and have no nuclei. Each sieve tube has a perforated end so its cytoplasm connects one cell to the next.

  ~ Companion cells that contain mitochondria to provide energy for the movement of sucrose.

  ~ Little cytoplasm and nucleus for more flow space.
• Describe the similarities between the xylem and phloem

  Similarities:

  ~ Both (transpiration and translocation) transport substances around the plant

  ~ The cells form tube like structures.

  ~ Both work to support the overall growth and development of the plant eg. the xylem provides water for photosynthesis while the phloem transport sugars for the plant
• Describe the differences between the xylem and phloem

  ~ Transpiration occurs in the xylem while translocation occurs in the phloem.

  ~ Transpiration in the xylem is passive while translocation in the phloem is active (requires energy).

  ~ Transpiration in the xylem is uni-directional as water and minerals move from the roots & through to leaves while translocation in the phloem is bi-directional as sugars move from leaves through to roots and vice versa.