My favorite is Brainpop Jr. It's very kid friendly and it has a large variety of topics.
Parts of a plant.
Discovery Education has the largest academic videos collection available for different grades and topics.
Plants life cylcles.
With the help of a friendly scarecrow, students identify the basic needs of plants. They learn how seeds grow into plants and that the plant goes through changes called a life cycle. They witness each step as seeds germinate and grow into flowering plants which produce seeds that eventually germinate and grow again.