BOTANY 160 MID-SEMESTER EXAM KEY OCTOBER 18, 1995 I. Definitions (Choose 5; 4 points each) Leaf Area Index - the area of leaves exposed over a unit area of land surface. Gross Primary Production - the total fixation of energy into organic matter by photosynthesis; includes that which is released by respiration. Physiognomy - outward appearance of a plant community; relates to the plants life forms and the stratification (architecture)of the community. Holism - a belief that the system is more than the sum of its parts and can only be understood by studying the whole intact system. Biome - large regional ecosystems characterized by the dominant plant life form. i.e. deciduous forests, grasslands etc. Littoral zone - the zone at the edge of a lake or pond; often delimited by the extent to which rooted plants can grow. Thermocline - layer in a thermally stratified body of water in which temperature changes most rapidly relative to the rest of the water column. Epilithic periphyton - the microbial community attached to submersed rock in aquatic systems. Insectivory - the eating of insects; occurs in a number of highly evolved aquatic and wetland plants as a means to supplement their nitrogen. Allochthonous - organic matter entering a system that is derived from outside the system. II. Short Answer (Choose 4; 10 points each) 1. What is the distinction between collective and emergent properties in community ecology? Give an example of each. Collective - properties of a community that are a composite(sum) of the lower levels of organization (individuals and populations). Examples: species diversity, community biomass and productivity. Emergent - properties of a community that are a composite (sum) of the lower levels of organization (individuals and populations) and their interactions. These properties appear only when the community is the focus of attention. Example: structure of the food web. [see your text - page 613] 2. Give two physical/chemical properties of water and for each give an example of its importance for aquatic life. viscosity - water is 'sticky' or viscous due to the polarity of the molecules and hydrogen bonding. One result is that frictional resistance of an organism moving through water is 100 times that of air. heat capacity - water is capable of storing large quantities of heat with a relatively small rise in temperature. One result is that aquatic organisms are generally stenothermal. light extinction - water absorbs certain wavelengths of light energy more so than others. This phenomenon is exponential in nature and restricts photosynthetic autotrophs to the upper layers of water. surface tension - a condition that exists at the free surface of a liquid due to inter-molecular forces about the individual surface molecules - manifested by properties resembling those of an elastic skin under tension. Some organisms have evolved to take advantage of property of water - for example the neuston, water striders etc. Also, some flying insects can become trapped in the surface tension of water and flounder on the surface. 3. What are three ways that phytoplankton have evolved to stay in the euphotic zone of lakes? 1) motility (flagellated cells) 2) morphology (form resistance to sinking) 3) storage of low density reserves (ie. diatoms store oil) 4) gas vacuoles (blue-green algae) 4. What is meant by the expression that water velocity in rivers is a double-edged sword for the organisms living there? It is both beneficial and harmful. Beneficial in that it enhances nutrient delivery and uptake by reducing diffusion resistance - harmful in that it increases shear stress or drag on attached organisms and increases the probability of being detached from the substrate and washed away downstream. 5. What are the criteria used to define a wetland? - the presence of hydrophytes (indicator plants) - hydric soils - hydrology of the site 6. What is the essence of the Raunkiaer classification of life forms? Plants are classified according to the way in which their meristems are held and protected (i.e. the position of their overwintering, perennating parts, such as buds, bulbs, seeds). 7. In soils the clay and humus components are said to have Cation Exchange Capacity. What is meant by this and what role does it play in plant growth? Ability of soil particles to absorb/exchange positive charged ions (cations) - is related to the number of negative charges on the surface of the soil particle - clay and humus have high cation exchange capacity. It is important to plant growth because through the exchange process essential nutrients such as Calcium, Potassium etc. are stored and released to the roots of plants. 8. In the Northern Coniferous Forest biome the dominant plants are xerophytes. What are xerophytes and why do they dominate in this biome? Xerophytes are plants that have evolved adaptations to dry environments. The northern coniferous forests experience "physiological drought" for an extensive period of the year when water is frozen and therefore unavailable. Plants such as conifers have a number of adaptations to minimize water loss (sunken stomata, thick cuticles etc.) III. Essay Question (CHOOSE 1; 40 points) 1. Contrast and compare a typical river aquatic ecosystem to that of a lake. Bring into your discussion the structure and function of these systems, including the evolutionary adaptations of the dominant plants and algae, and the current paradigms of energy flow and nutrient cycling in these systems. For full credit your answer should have addressed the essential differences between these two systems, such as water velocity, stratification, nutrient spiraling, river continuum, trophic dynamics and also have contrasted the adaptations of the lotic periphyton relative to the phytoplankton. OR 2.(A)Diagram the essential components of an ecosystem emphasizing the structural and functional aspects of ecosystems in general. (B)Using the above diagram as a framework discuss the essential differences between the Northern Coniferous Forest and the Eastern Deciduous Forest biomes. For full credit your diagram should have included the following: an open boundary, the input of light energy and the output of heat energy, the three functional kingdoms of life (producers, consumers and decomposers) linked via energy flow and nutrient cycling. Your comparison should have addressed the boundaries of these two biomes, differences in the dominant primary producers with regards to physiognomy, life form and productivity, production of litter, decomposition rates etc.