Defense Against Freezing
Not all plants react to freezing temperatures the same way. Native plants that originated in ______ climates have adaptations to survive typical winter conditions. Plants that originated in more ________ locations have fewer _________ against freezing temperatures.
What Happens Inside
Most plants contain more than 85% water. As water freezes, it ________. When this happens, cell walls and other parts of the plant can rupture. Frozen water between cells can also draw water out of the cells, causing them to ________ and _______. Hard ice crystals that form between or within the cells cause the most ___________. The _________ can be like miniature needles, piercing cell walls inside in the plant.
Water and Plants
There are many _______ of cells inside the ______ and stem of a plant. Winter-hardy plants have some _________ against freezing. Water inside the cells isn't pure water. The water in the living parts of cells contains dissolved salts, sugars, and other substances that act like anti-freeze. These substances lower the temperature at which the water freezes. This "anti-freeze water" can still ______ if temperatures drop suddenly or extremely.
If a plant is to survive freezing __________, it needs to protect cells from ice crystals, or prevent crystals from growing too big. Here are some cool plant adaptations:
- Seeds: Plants that only have an annual cycle get through the winter by making dry seeds which can __________ freezing.
- Toughening/"Anti-freeze": Some plants toughen up or become _______ in the fall in response to slowly decreasing temperatures. Most produce _______ and ______ that prevent ice crystals from forming or growing large. They also gradually lose water; the drier tissues are less likely to freeze.
- Leaf Loss: Some plants simply lose their leaves altogether and store energy in their _______. Others, such as spruce trees, have needle-like leaves with waxy coatings; these prevent water loss and cold damage.
- Controlling Water Location: Some plants keep ______ in cell walls, but move it out of the living part of the cell where ice could kill the plant.
- Underground Storage: Some plants, like tulip bulbs, store energy in underground structures. At planting depth, temperatures ________ fall much below 30 degrees Fahrenheit. The sugars in a hardy bulb, just like salt on a winter sidewalk, lower the temperature at which water freezes.
If you have a spring snow or freeze, what will happen to your tulips? The plants should be fine at 20 or 25 °F. Below those temperatures, any ______ part of the plant will be damaged and not able to make food for next year's bulb. If a tender flower bud freezes, it probably won't _________.
The process of thawing out can be more dangerous than freezing! Water can flow back to a damaged cell and cause it to ______. You can see evidence of this process when you look at leaves after taking them out of the freezer and watch what happens as they thaw.
Even a hardy plant can suffer or die under certain winter conditions. These include the following:
- When temperatures fall below a plant's maximum low-temperature limit even after it has acclimated or toughened up
- When early freezes occur before the plant has ___________ in the fall
- When unusually late freezes occur in the spring after the plant has emerged