| What does Phloem transport? [Translocation] | They transport food substances up and down the stem for growing purposes. This is called Translocation. |
| What is the Phloem made up of? | It is made from living cells in columns called sieve tube elements. The Phloem has perforated end-plates, to allow stuff to flow through.
The cells have no nucleus so therefore they have a companion cells to do its 'living' for the cell. |
| What does the Xylem transport? | Water and minerals. They take them up to the leaves, into the transpiration stream. |
| What is the Xylem made off? | It is made from dead cells joined end to end with no walls between them. The hole in the middle is called the Lumen. It has quite thick side walls, made from cellulose which is strong and stiff which therefore gives the plant support. They are also coated with Lignin, a material which doesn't rot the wall. |
| What is Transpiration? | Transpiration is the loss of water from the plant |
| How does water get lost? | It is mainly caused from evaporation and diffusion from a plants surface. It mainly happens in the leaves. So the water comes from the Xylem and diffuses/evaporates out the plant as the outside has a lower concentration of water. This makes a Transpiration stream. |
| What are the good things about Transpiration? | The constant stream of water keeps the plant cool
Photosynthesis carrys on
The water makes turgor pressure, which supports the plant and stops it witling
Minerals are also transported with water |
| What factors affect Transpiration? | Light Intensity: The brighter the light is, the greater the transpiration rate is. It also increases Photosynthesis as the stomata lets CO2 in. When its dark, the stomata closes as Photosynthesis cant happen without light. This also means water cant escape.
Temperature: The warmer it is, the faster transpiration happens. This is because the water particles have more energy and can evaporate and diffuse quicker
Air Movement: If its more windy, transpiration happens faster. This is because the water vapor is carried away therefore making the outside still being less concentrated. However if there is no wind, the water vapor will stay there and balance out the concentration gradient which will therefore slow down transpiration. [Diffusion] |
| How do plants adapt against water loss? | Leaves usally have a Waxy Cuticle which is above the Upper Epidermis. This makes the top surface waterproof. The stomata where water vapor diffuses out is at the bottom where its darker and cooler which therefore will slow down the rate of diffusion. Plants also limit the amount of stomata as the quantity can affect diffusion rates. |
| How does the Stomata close and open? | The Stomata closes when the water supply drys up. The Guard Cells which surround the stomata closes if its goes flaccid or open when its turgid. They have thin outer walls and thick inner walls to ensure the open/close feauture works.
They are also sensitive to light. They open in the day, close in the night. |
| Why do Stomata close at night? | Photosynthesis can not happen without light. So diffusing water out for no reason is a waste of resources and time. |
| What is a Potometer? | This is something that can estimate the Transpiration rate but it doesn't. It really just measures the water uptake by the plant. |
| How would you measure the rate of Transpiration? | Distance Moved
------[Divide]---- = Transpiration Rate
Time Taken |
