Jessica Biel says motherhood is ''an amazing, amazing experience.''

The 'Spark' actress, who has five-month-old son Silas with husband Justin Timberlake, thinks her little boy is ''wonderful,'' but admits being a parent is ''the hardest job in the world.''

Asked how she is adapting to having a child, the 33-year-old star said: ''He's wonderful. He's just a joy. It's an amazing, amazing experience.

''[It's] incredibly hard, the hardest job in the world and I've never been more thankful and grateful to my own mother. Oh, my gosh I'm going to call her right after this actually and just thank her. What you have to do for your kid -- it's an amazing responsibility and the biggest joy ever.''

The brunette beauty is also grateful to 'Mirrors' hitmaker Justin, 34, for getting up in the middle of the night to feed and take care of Silas.

She told the 'Today' show: ''He is doing it all. He is in there, deep.''

Jessica and her friend Saundra Pelletier's new online sex education video series launched this week on website Funny or Die and the 'Total Recall' actress thinks it was the best platform to reach as many people as possible.