What are the factors influencing grasshopper population changes, the nutrients involved in tooth hardening, arthropod classes with body trunks, and why ecosystems are self-sustaining?

Here are the answers to your questions:

11. (b) Give two factors that could lead to change in grasshopper population between the first and the second capture

1. Natality (births): New grasshoppers hatching or being born into the population.
2. Mortality (deaths): Grasshoppers dying due to predation, disease, or other environmental factors.
3. Immigration: Grasshoppers moving into the study area from outside.
4. Emigration: Grasshoppers moving out of the study area to another location.

24. Name the vitamin and mineral ion involved in tooth hardening

• Vitamin: Vitamin D
• Mineral ion: Calcium ion ($\text{Ca}^{2+}$) or Fluoride ion ($\text{F}^{-}$)

25. Name the two classes under phylum Arthropoda whose members are characterised by possession of body trunk

1. Chilopoda (centipedes)
2. Diplopoda (millipedes)

26. Why is an ecosystem referred to as a self-sustaining system?
An ecosystem is self-sustaining because it has a continuous flow of energy (primarily from the sun) and efficient recycling of nutrients within its boundaries. Producers convert solar energy into organic matter, which is then transferred through consumers, and decomposers break down dead organic material, returning essential nutrients to the environment for reuse by producers. This continuous cycling and energy flow allow the system to maintain itself without constant external input of matter.