The bell shaped curve indicates polygenic traits. A polygenic trait is controlled by multiple alleles. Hope this makes sense :)
Structures in plant leaves that open and close to maintain homeostasis are called stomata. This is where gases would diffuse in and out of the leaf.
Benefits of living on land: Sunlight is brighter, since it doesn't have to go through water first. More carbon dioxide in the atmosphere than in the ocean. Mineral nutrients are plentiful in the soil.
Skin Pigmentation is how frogs camouflage themselves in nature