You need to remember what a homogeneous mixture represents. Mixtures can be classified in two categories: homogeneous, heterogeneous. Homogeneous mixture has a constant composition all over. Hence, if sugar is dissolved by water, the resulted composition is considered a homogeneous composition since it's state is liquid and there exists no solid components in it.
Lemon juice or orange juice or fruit juices are mixtures since they are composed from water, fruit juice and sugar. If the lemon juice contains fruit pulp, meaning the membranous vesicles containing the fruit juice, the composition will not be the same throughout the juice, hence, the lemon juice will become a heterogeneous mixture, which that can be filtered to obtain the homogeneous mixture, namely the lemon juice without floating particle in it.
Mixtures can be described in two ways. Homogeneous mixtures are ones that appear the be the same throughout. One would not be able to physically pick different pieces out of a homogeneous mixture. When observing lemon juice the mixture looks the same thoughout even though it is made up of sugar, lemon juice, and water. Once mixed,the sugar dissolves with the liquids and makes the mixture appear the same throughout.