Various concentrations of ferrous and ferric iron solutions were held at room temperature for 60 min before they were assayed for ferrous iron, which may be unstable due to oxidation. The ferrous and ferric solutions (in pH 2 HCl) were maintained as such for 60 min without the use of chelators. There was no significant oxidation of ferrous iron. Also, four different levels of each ferrous and ferric iron were injected into proximal duodenal loops of rat intestine and uptake was determined at four different time intervals. Two iron-replete rats were assigned to each of the treatments. The in situ experiments showed that iron was taken up rapidly from pH 2.0 solutions of ferrous and ferric iron. Maximum amount of iron was taken up in the first 10 min. Uptake of ferrous iron was significantly greater (p < 0.05) than uptake of ferric iron, and there were significant differences in total uptake among the four iron levels used. Uptake, absorption, and adsorption kinetics of both ferrous and ferric iron were determined in situ for both iron-replete and iron-deficient rats. Deficiency caused greater uptake and absorption, confirming a biological adaptation of these processes. Both uptake and absorption were greater for ferrous than for ferric iron and were possibly taken up by different pathways or by a ferrous-ferric pathway with preference for ferrous. Uptake and absorption kinetics were biphasic for both ferrous and ferric iron. The first phase demonstrated saturation kinetics and was followed by a nonsaturable phase at higher concentrations of luminal iron. Iron deficiency altered the uptake and absorption kinetics of ferrous and ferric iron, but not always in a similar manner, suggesting that ferrous and ferric iron were each taken up by a separate pathway. Indications were that enhanced absorption during deficiency was largely due to adaptation of ferric uptake. Iron adsorption was directly proportional to luminal iron concentration, but it was greater for ferric than for ferrous, possibly due to charge interactions. Iron deficiency caused increased adsorption of both ferrous and ferric iron, supporting the notion that adsorption acts to maintain iron in a form available for uptake.

A global increase in atmospheric CO2 and temperature is assumed to affect the marine ecosystems in numerous ways, e.g. by altering ocean circulation patterns and changing nutrient regimes. The changes are expected to impact heavily on both phytoplankton communities as well as the rest of the marine food-web. Based on previous experimental studies that have investigated the impacts of varied algae food-quality on zooplankton, this quantitative study hypothesizes that (i) the tested microzooplankton species Brachionus plicatilis (rotifer) and Euplotes sp. (ciliate) will show high population growth rates (g) when fed with Nannochloropsis sp. grown under nutrient replete conditions, (ii) that the species will show a population growth rate close to zero when fed with algae grown on phosphorous-deficient media and (iii) that microzooplankton will be negatively affected by the algae grown in nitrogen-deficient media. The study thus aims to investigate how changes in the balance of energy and several chemical elements in ecological interactions, ecological stoichiometry, affect the growth rates of algal grazers. The results show that food-independent factors had a large impact on growth rates and resulted in unexpected, deviating trends. However, as the growth rates for B. plicatilis fed with phosphorous-deficient algae were lower than those of B. plicatilis fed with nitrogen-deficient algae, there is some support for the / <p>The paper was written within the research-area of marine biology.</p>