No, but their happier with it and without it they don't grow to much.
No they do not breathe under water. They have lungs. Aquatic turtles such as the red - eared slider can hold their breath for 3 - 4 hours.
Yes, red-eared sliders need a dry area to get out of the water. Above this area should be a turtle basking lamp. Aquatic turtles will bask daily. Basking keeps the turtle's skin and shell health from fungus while the UV in the light is needed for the turtles growth. Without a dry area and a basking light your turtle will not be healthy and happy.
Fresh water, with a strong filter. Change water once every month.
They are semi-aquatic. They need a basking light and a basking area such as a floating log or basking platform so that they can climb out of the water to bask. This is essential to their health. If a red eared slider doesn't have an area to bask and can't get out of the water, it's shell will get soft and it will eventually die. They need UVA and UVB light in order to process their food. Heat and light are essential for these turtles. Keep them in water around 70 degrees and provide a basking area and a basking light that has both UVA and UVB rays or two lights, including one UVA and one UVB bulb.
Red Eared Sliders are water turtles so they need water but sand can be in their tank with them. Sand tends to clog filters though, so gravel would be a better option.
Aquatic turtles need to live in water. How deep depends on the species. Turtles like painted turtles or slider turtles need water to be as deep as possible. Turtles like musk and snapping turtles need shallower water. They have to have land too, a turtle need to be able to completely dry off when ever they want to. Tortoises or box turtles need a shallow, easy to climb in, dish that is big enough for then to fit in so they can sit in it and drink when ever they want.
Every 6 months you should take the Red Eared Slider Turtle to the vet
For a land tortoise, you will need a UV light (that provides artificial sunlight), Vegetables, substrate (dirt), and a hiding place. For water turtles You will need all this + bugs and water.
All animals need water to live. Turtles are animals.
All turtles need to have mated in order to lay eggs, unlike birds who will lay infertile eggs, turtles won't.
Red Eared Sliders are water turtles so they need water but sand can be in their tank with them. Sand tends to clog filters though, so gravel would be a better option.
Any normal filter will work. Chacha on!!