Challenges of Life in the Sea: Salinity, Osmosis, Temperature, Surface-to-Volume Ratio, Prokaryotes

1. Challenges of Life in the Sea • Salinity • Diffusion and Osmosis • Diffusion problematic – leads to loss of important ions • Selectively permeable cell membrane limits movement of certain molecules (large, electrically charged) but allow movement of small molecules, e.g. water • Osmosis – Diffusion of water across selectively permeable membrane • Water diffuses from region of higher water concentration (lower salt concentration) to region of lower water concentration • Possible to move molecules against concentration gradient by using energy to power active transport

2. Fig. 4.13

3. Challenges of Life in the Sea • Salinity • Regulation of Salt and Water Balance • Osmoconformers • Energetically inexpensive • Limits distribution to areas with stable salinity (Where?) • Osmoregulators • Expend energy to maintain body fluid composition • Less constrained by salinity in habitat • Euryhalinevs.Stenohaline

4. Fig. 4.14

5. Fig. 4.15

6. Challenges of Life in the Sea • Temperature • Rates of metabolic reactions double for each 10 oC increase in temperature • Most marine organisms adapted to specific temperature range • Species distributions often based on temperature of water • Polar • Cold temperate • Subtropical (warm temperate) • Tropical • Eurythermalvs.Stenothermal

7. Fig. 4.16

8. Challenges of Life in the Sea • Temperature • Ectotherms – Body temperature essentially determined by temperature of environment • Often poikilotherms (“cold blooded”) • Some species warm certain tissues to improve performance (tuna, billfish, some sharks) • Endotherms – Maintain elevated internal body temperature • Usually homeotherms (“warm blooded”) • Energetically expensive • Insulation may help to conserve heat • Blubber • Feathers • Hair

9. Challenges of Life in the Sea • Surface-to-Volume Ratio • Organisms exchange heat and substances across body wall • Nutrients • Gases • Waste products • Rate of exchange depends on S/V ratio • Ratio decreases as organism size increases, if shape stays the same • Smaller organisms exchange materials by diffusion • Larger organisms have special systems to exchange materials Fig. 4.17

10. Prokaryotes • Bacteria • Many shapes - spheres, coils, rods, rings • Very small cells (usually less than 1 μm across) • Little known until second half of 20th century • Exceptions - 570 to 750 μm diameter in sediments (filamentous) and fish guts • Rigid cell walls • May reach very high densities under favorable conditions • Heterotrophic Bacteria • Most are decomposers (break down organic material) • Important in nutrient recycling • Important components of organisms’ diets, especially for benthic organisms

11. Prokaryotes • Bacteria • Autotrophic Bacteria • Photosynthetic (Photoautotrophic) • Obtain energy from sunlight • Contain chlorophyll or other photosynthetic pigments • Important primary producers in open ocean • Chemosynthetic (Chemoautotrophic) • Obtain energy from chemical compounds - Hydrogen - Hydrogen sulfide - Ammonia Fig. 4.7

12. Prokaryotes • Bacteria • Cyanobacteria (Blue-green) • Photosynthetic • Contain chlorophyll + phycocyanin & phycoerythrin • Some form filaments or mats • Some similarities to eukaryotic algae • Contain chlorophyll a • Produce gaseous O2 • May have been first photosynthetic organisms on earth • Fossil stromatolites from 3 billion years ago • Calcareous mounds containing sediment and cyanobacteria

13. http://www.fossilmall.com/Science/About_Stromatolite.htm

14. http://www.fossilmall.com/Science/About_Stromatolite.htm

15. Prokaryotes • Bacteria • Cyanobacteria (Blue-green) • Occur in a variety of habitats • Polar bear hair • Endolithic (inside calcareous rocks and coral skeletons) • Rocky shorelines (black crusts) • Epiphytic (on algae or plants) • Endophytic (inside algal or plant cells) • Many carry out nitrogen fixation • Very important process • Some forms have lost ability to photosynthesize • Live as heterotrophs