Question

3. Explain dendrochronology. How do these researchers evaluate historical climate?

4. Explain the bulk flow process in plants. In your answer, be sure to describe bulk flow driven by negative pressure and bulk flow driven by positive pressure.

5. Explain the mutualistic relationships that are important for proper plant nutrition using the relationship between bacteria and roots as an example.

6. How does acid rain influence cation absorption by plant roots?

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Answer 1

3- Dendrochronology is the science or technique of dating events , environmental affects and artefacts of archaeology by analysing the growth rings or annual rings pattern in tree trunk . Dendrochronology helps in studying environmental factors as each growth ring tells the weather conditions about that particular year when it was formed. As trees are highly sensitive to climate change , slight change in climate can affect the growth ring pattern . For example - rings grow wider in warm , wet year but grow thinner in cold and dry years.

4- Bulk flow is movement of water and solutes together due to a pressure gradient . Bulk flow can be due to negative pressure or positive pressure .For example - in transpiration, a negative pressure is created at surface of stomatal opening pulling bulk flow of water from xylem Sap to stomata . Similarly , pressure flow hypothesis for sugar loading and unloading from source to sink is due to positive pressure. Loading sugar from photosynthetic leaf cells create high positive pressure pushing it through phloem tube.

5- Mutualistic relationships are adapted by plants for better nutrition . For example - Nitrogen is present in atmosphere in free form. Plants are not able to fix nitrogen . So , some plants like leguminous plant root form symbiotic association with bacteria Rhizobium . Rhizobium along with legume roots form a structure called nodules in which nitrogen fixation takes place . Here , atmospheric nitrogen is converted to ammonia by enzyme nitrogenase.

6- Plants derive their nutrition primarily from elements like calcium , magnesium and potassium that are present in soil . Organic matter and clay matter in soil tend to be negatively charged , hence, they hold positively charged captions and prevent leaching of them. Plants absorb these elements through roots . But acid rain adds hydrogen ions in the soil which leads to process of leaching . Leaching means either ions are washed deeper into subsoil or washed out of the top soil . It means these ions will no longer be able to plants affecting their growth .