ESS 2.1.2-3

• The atmosphere is the gaseous envelope surrounding Earth.
• A habitat is the environment in which a species usually lives.
• In most habitats the physical environment includes soil, moisture, temperature and sunlight whilst the biological environment is the food, mate and predators that are around. 
• The niche is the role an organism plays and the position it holds in the environment. It includes all the interactions the organism has with the abiotic and biotic environment.
• a niche refers to the way an organism fits into the ecosystem, where it lives and what it does. It describes how the organism survives and reproduces.
• Limiting factors are the resources in the environment that limit the growth, abundance and distribution of organisms/populations in an ecosystem. biotic or abiotic factors, and they will determine the carrying capacity of an area. They may be density dependent or density independent. 
• population growth: The population growth rate is affected by the number of individuals in the population.Density dependent factors are ones that affect the population only when it reaches a certain density. These include competition, disease, parasitism and predation - they tend to be the biotic factors. Disease spreads best when there are a lot of organisms for it to infect.
• Density independent factors will control populations no matter what the density of it is. They include sunlight, temperature, water and natural disasters. High density or low density the organisms still need a certain temperature range or a particular amount of sunlight and water.
• Carrying capacity is the maximum number of individuals of a species that the environment can sustainably support in a given area. 
• The J-shaped growth curve shows exponential population growth under ideal conditions with plenty of resources and limited competition. The population continues to grow until environmental resistance take effect – it could be that the organisms have used all the resources available. At that point the population will crash. Organisms that follow this type of graph generally show great fluctuation and a “boom and bust” pattern in population numbers.
• S-shaped curve is more likely when resources are limited - they are limiting factors. Exponential growth is only possible for a short period of time because as the population grows resources are depleted and the growth rate slows and will eventually plateau off.