Topic 6 – Plant structures and their functions

• Photosynthetic organisms are the main producers of oxygen and food.
• photosynthesis in plants and algae is an endothermic reaction that uses light energy to react carbon dioxide and water to produce glucose and oxygen.
• What are the main limiting factors of photosynthesis?

  Light intensity, carbon dioxide concentration, and temperature.
• What is the effect of temperature on photosynthesis?

  If the temperature is too low, the enzymes work at a slower rate. The optimum temperature for enzymes is usually 25C.
• What is the effect of carbon dioxide concentration on photosynthesis?

  Increasing the concentration of CO2 increases the rate of Photosynthesis. CO2 is needed for photosynthesis to happen.
• What is the effect of light on the rate of photosynthesis?

  As you increase light intensity the rate of photosynthesis increases.
• How do you investigate light intensity on the rate of photosynthesis?

  1. Aerate Water:

  • Bubble air to keep oxygen in bubbles.

  1. Illuminate Plant:

  • Well-lit for photosynthesis enzymes.

  1. Setup in a dark place so the plant does not photosynthesise:

  • pondweed in 1% sodium hydrogen carbonate.

  1. Clean Stem Cut:

  • Pondweed stem cut before boiling tube.

  1. Measure Gas:

  • Record gas volume over 5 mins, vary light source, and plot results.

  
• light intensity is inversely proportional to 1/distance squared, so the light intensity at a distance of 100m is 1000 times greater than at 1m.

  
• How are root hair cells adapted to their function?

  Root hair cells have a lot of microscopic hair cells that give a large surface area to absorb water and minerals.
• How is the phloem adapted to its function?

  The phloem transports food substances (mainly sucrose) made in the leaves to the rest of the plant. Phloem tubes are made out of small pores in the end walls to allow stuff to go through. This process is called TRANSLOCATION and it occurs both up and down and requires energy from respiration.

  
• What is transpiration?

  Transpiration is the process by which plants release water vapor into the atmosphere through their leaves. More water is replaced through the xylem vessels. This means that there is a constant transpiration stream.

  
• How is the Xylem adapted to its function?

  Xylem tubes are made out of dead cells and are supported with lignin. They carry water and mineral ions from the roots to the stem and leaves. This is called the transpiration stream.

  
• What is a Stomata?

  Pores on the surface of plant leaves that allow for gas exchange. When the guard cells are turgid, the guard cells make the stomata open. When the guard cells are flaccid, the guard cells make the stomata close. They allow oxygen and CO2 to diffuse directly into the leaf but also allow water vapour to escape during transpiration.
• What is the structure of the leaf?


  Waxy cuticle, upper epidermis, palisade mesophyll tissue, xylem and phloem, spongy mesophyll and lower epidermis.
• What are the adaptations in the functions of the leaf?

  The palisade layer contains a lot of chloroplasts. The upper epidermis is transparent which allows light to pass through. The waxy cuticle helps prevent water loss. The lower epidermis has a lot of stomata which helps during gas exchange.
• How do environmental factors affect the rate of transpiration?

  Light intensity: The higher the light intensity, the higher the rate of transpiration as the stomata are open which releases water while allowing CO2 to enter.

  Temperature: When it's warm, particles have more energy to evaporate meaning that they can diffuse more easily.

  Airflow: The stronger the wind, the easier the vapour is swept away from the leaf.
• To work out transpiration rate, you divide the distance travelled by the time taken.
• How are some plants adapted to live in extreme environments?


  Drought tolerance, deep root systems, and thick waxy leaves. Spikes and the ability for cactus to store water and inflate.
• What are auxins?


  Plant hormones that regulate growth and development. Auxins are involved in the growth responses of plants to light (phototropism) and gravity (gravitropism).
• Shoots are positively phototropic, meaning they grow toward the light. When a shoot is in the shade, it grows towards the light because auxin is found in that area which makes the cells elongate faster. By bending towards light, the shaded area will be able to absorb light for more photosynthesis. Shoots are negatively gravitropic.

  
• Auxin moves through the cell walls via diffusion. It causes the cells on one side to stretch and become longer than those on the other side. As a result, the stem curves away from the source of auxin.
• Roots are negatively phototropic (they are gravitropic), meaning they grow away from the light. This means roots avoid growing into bright sunlight where there may not be enough moisture or nutrients. Roots also need to anchor the plant so they don’t get blown over.

  
• auxins are used in weedkillers and rooting powders.
• gibberellins are used in germination, fruit and flower formation, and the production of seedless fruit.
• Ethene is used in fruit ripening.