Phytoplankton is the collective term covering the small photosynthetic organisms which are part of aquatic ecosystems - Leaving Cert Biology - Question 15 - 2014

Nutrient levels are typically high in winter due to reduced phytoplankton activity and decomposition processes releasing nutrients into the water. However, as temperatures rise in spring and sunlight increases, phytoplankton growth accelerates, utilizing available nutrients, leading to a sharp drop in nutrient levels.

A common inorganic nutrient necessary for phytoplankton growth is nitrate (or nitrogen).

The graph for zooplankton should show a corresponding rise following the peak in phytoplankton numbers. This reflects the food relationship between phytoplankton and zooplankton, where an increase in phytoplankton provides more food for zooplankton, causing their numbers to rise. However, as the phytoplankton population declines in late autumn, zooplankton numbers are also expected to decrease.

In late autumn, environmental factors such as lower temperatures and reduced light intensity can hinder phytoplankton growth, leading to a natural decline in their population. Additionally, changes in nutrient availability can also contribute to this decline.

One method to estimate rabbit numbers is the capture-recapture technique. This involves capturing a number of rabbits, marking them, and releasing them back into their habitat. After some time, a second sample is captured, and the proportion of marked to unmarked rabbits is used to estimate the total population size using the formula:

$ext{Population size} = \frac{(\text{Number of marked in second sample} \times \text{Total in first sample})}{\text{Number of marked in second sample}}$

The initial rapid increase in the rabbit population can be attributed to the lack of natural predators in the new environment, allowing the population to grow unchecked.

1. The extinction of a plant species may lead to a decrease in herbivore populations that relied on it for food, disrupting the food chain.
2. It may also result in reduced habitat availability for other organisms that depend on that plant for shelter or breeding.

Advantage: Biological control can effectively manage pest populations without the use of harmful chemicals.
Disadvantage: There is a risk that the biological control agent may become invasive itself or fail to specifically target only the pest species.

Rabbit numbers may have recovered due to a decline in the Myxoma virus's effectiveness or the development of immunity in the rabbit population.

1. Birth rate
2. Death rate
3. Migration patterns

1. Advances in medicine and healthcare have led to lower mortality rates.
2. Improved agriculture and food distribution methods have decreased famine and malnutrition.

As human populations grow, biological diversity may decrease due to habitat destruction, pollution, and over-exploitation of species, leading to extinction.

1. Reduce waste generation
2. Reuse materials
3. Recycle waste

Pollution is the introduction of harmful substances or products into the environment, causing adverse effects on ecosystems and human health.

Microorganisms can break down pollutants and organic waste through processes such as decomposition, helping to purify water and restore the balance in ecosystems.

Plants play a vital role in the Nitrogen Cycle by absorbing nitrates from the soil and incorporating them into their biomass. In the Carbon Cycle, plants absorb carbon dioxide during photosynthesis, converting it into organic matter and releasing oxygen as a byproduct.

Animals contribute to the Nitrogen Cycle by consuming plants and respiring, which returns nitrogen to the soil through waste products. In the Carbon Cycle, animals release carbon dioxide during respiration, which is then utilized by plants for photosynthesis.