A healthy ecosystem must contain:
Plants. A plant has nutrients and energy that make it possible for herbivores to eat.
Primary consumers. These consumers will feed off of the plants to maintain a stable environment. They will also provide food and energy to secondary consumers
Secondary consumers. They will maintain the the population of the primary consumers. Once they die, they provide food and habitat for decomposes and scavengers
Habitat. The ecosystem must contain shelter for the creatures in the forest.
Stable temperatures. This is for the creatures who require specific amounts of heat and cold to survive. For example snakes would thrive in a swamp, but would die in the mountains.
There are probably more attributes, but here's a healthy list :) Hope it helps!
This is the depiction of a solar eclipse
On his visit to the Galapagos Islands, Charles Darwin discovered several species of finches that varied from island to island, which helped him to develop his theory of natural selection. He defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".
Hope this helps! ;)
By interacting with the external environment, if you mean how molecules are transported outside and into the cell then there are 3 main ways of transport.
Passive transport which refers to the movement of molecules into the cell without using any energy. This includes osmosis (movement of water), diffusion (movement of small molecules like salt) and facilitated diffusion which is the movement of large molecules such as glucose via by channels on the plasma membrane.
Note, in diffuson the cell wants equilibrium which means that the cell wants the same ratio of a specific type of molecule compared to the external envionrment. In other words, it's like a a very salty cell becoming less salty because the external envionrment is less salty.
Active transport refers to the movement of molecules against the concentration gradient using energy.
Bulk transport which refers to the movement of molecules that is influenced by the plasma membrane. One of the ways is for the plasma membrane to engulf particles or expel particles. This allows cells to remove waste.
Go look it up on Khan academy.