Chapter 7 Flashcards
Factors effecting transpiration:
- Humidity.
- Wind speed.
- Light intensity.
- Very dry conditions.
Humidity:
If the water potential gradient between the air spaces in the leaf and the air outside becomes steeper, the rate of transpiration will increase. In conditions
of low humidity, the gradient is steep, so transpiration takes place more quickly than in high humidity.
Wind speed and temperature:
Transpiration may also be increased by an increase in wind speed or rise in temperature.
Light intensity:
In most plants, stomata open during the day and close at night. Most transpiration takes place through the stomata (although a little water vapour can escape through the epidermis if the
cuticle is thin), so the rate of transpiration is almost zero at night. Stomata must be open during the day to allow carbon dioxide to diffuse into the leaf for photosynthesis. This inevitably increases the rate of transpiration. Closing at night, when photosynthesis is impossible, reduces unnecessary water loss.
Very dry conditions:
In especially dry conditions, when the water potential gradient between the internal air spaces and the external air is steep, a plant may have to compromise by partially or completely closing its stomata to prevent its leaves drying out, even if this means reducing the rate of photosyn photosynthesis.
Photo-autotroph:
A plant that obtains energy from sunlight to convert inorganic materials into organic materials for use in cellular functions such as biosynthesis and respiration. They can convert carbon dioxide, water and “närsalter” into carbohydrates, proteins and lipids.
Chemi-autotrophs:
Derive energy for their life functions from inorganic chemicals. They feed on chemicals that are good electron donors, such as hydrogen sulfide, sulfur, or iron. They take atoms of carbon from inorganic compounds, such as carbon dioxide, and using it to make organic compounds such as sugars, proteins, and lipids. Chemoautotrophs are commonly found in environments where plants cannot survive, such as at the bottom of the ocean, or in acidic hot springs.
Heterotroph:
Need to consume organic substances to get energy, for example by eating either autotrophs or other heterotrophs that live or have been killed.
There are two tissue systems in the vascular tissue system:
- Xylem and phloem.
Xylem:
To conduct liquid, water, minerals salts, everything that’s liquid. Helps the liquid to transport from the ground to the leaves. It’s made of tracheids and vessel elements.
Phloem:
To conduct the food materials, mainly carbohydrates. Is made up of sieve tube elements and companion cells.
Parenchyma cells:
- Have thin primary walls and usually remain alive after they become mature.
- Rich in chlorophyll, found underneath epidermis, active in photosynthesis, always alive, function in storage.
Collenchyma cells:
- Have thin primary walls with some areas of secondary thickening.
- Provides extra mechanical and structural support, particularly in regions of new growth.
- Functions in sport and storage.
Sclerenchyma cells:
- Have thick secondary walls and often dies when mature.
- Provides the main structural support to a plant.
- Cells become lignin, firm and hard cells, function is giving support (mechanical and structural) to plants.
Transpiration:
The transport of soluble products of photosynthesis to other parts of plant through phloemation is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers.
