A: No, and the rules differ significantly. But there are some guidelines that generally apply to different types of business entities.
If a business operates as a sole proprietorship, the owners must report income and expenses of the business on their individual tax returns. For federal tax purposes, financial information with respect to the business is usually detailed on a Schedule "C." From one perspective, reporting everything on one tax return can simplify matters a bit. However, it's inevitable that an audit of your individual tax returns will likewise result in an audit of your business, and vice versa. (One of the reasons to consider operating through a corporation or another type of business entity is that the tax consequences of the business would be reflected on separate tax returns.)
If you operate your business through a general partnership, the partnership itself should file a tax return. A key point to understand with a partnership, though, is that it is a tax-reporting entity rather than a tax-paying entity. The partnership reports income and expenses, which are then passed through to the partners in accordance with their ownership interests. Every year, a partner should receive a Form K-1 that reflects the partner's share of income and expenses. Each partner should then reflect this information on the partner's own income tax return.
In contrast to a partnership, a corporation can be a tax-paying entity, but this is not always the case. Federal law generally provides that an incorporated entity would be taxed on net income as a "C" corporation (with this reference coming from subchapter "C" of the Internal Revenue Code) unless you elect to be treated differently. Under certain circumstances, a corporation can elect to be treated as a partnership for tax purposes (and thereby be called an "S" corporation (with this reference being to subchapter "S" of the Internal Revenue Code).
As another alternative, it is sometimes possible for a corporation to be organized as a nonprofit entity. The best-known type of non-profit business entity is probably a public charity with tax-exempt status under Internal Revenue Code section 501(c)(3), but there are plenty of other examples. Even here, though, a nonprofit corporation may still be subject to taxation with respect to "unrelated business income" that is earned on activities unrelated to its tax-exempt purpose.
The limited liability company "LLC") (or a variation known as a "limited liability partnership") is another type of a business entity that is basically a hybrid between a partnership and a corporation. It has many of the limited liability characteristics of a corporation, but for tax purposes is generally treated as a partnership. So an LLC is required to file a tax return for tax-reporting purposes, but the actual tax consequences are passed through to the owners (called "members"). Like a partnership, the members should receive a Form K-1 every year that reflects any income or losses that they are required to report on their own tax returns.
As distinct from federal law under the Internal Revenue Code, each state has different tax rules and regulations. While these rules usually parallel federal tax laws in many respects, there are always significant differences. In many states, for example, a minimum franchise tax is due and payable annually by business entities, regardless of whether they made or lost money.