The Darwin Centre Phase Two is designed around an iconic eight-storey "Cocoon", encased within a glass atrium.
The temperature-controlled Cocoon will house 20 million of the museum's 34 million plant and insect specimens, and laboratories for up to 200 researchers.
Visitors will watch these scientists in action cataloguing rare specimens, when the centre opens in September 2009.
Dr Michael Dixon, director of the Natural History Museum, said: "The Darwin Centre Phase Two will be a landmark new building that will allow visitors to explore the natural world in an exciting and innovative way - truly putting our science on view for the first time.
"It is the only place in the UK where visitors can interact daily with natural science experts, seeing how the collections are helping us to address issues such as the quality of our air, the causes of disease and the maintenance of delicate ecosystems around the world."
Safe from attack
The top floor will become a public gallery, featuring interactive exhibits
The second phase of the Darwin Centre is the most significant development to the Natural History Museum since it moved to South Kensington in 1881.
The £78m building, designed by C F Moller Architects, and built by HBG Construction, links the historic Waterhouse building with the existing Darwin Centre Phase One and the museum's gardens.
Phase One, which opened in September 2002, houses the museum's collection of 22 million specimens stored in spirit, including the famous giant squid, affectionately known as Archie.
Phase Two is designed to safeguard the museum's dry collections - some 28 million insects and six million plant specimens - of which 20 million will be moved in over the next 12 months.
The 30cm-thick cocoon wrapped in silk lines not only looks stunning, it also has a practical purpose - to protect the museum's delicate collections from attack by pests.
The threat of infestation comes from so-called "museum beetles", commonly known as carpet beetles, which are capable of munching through insect body armour.
The dry collection includes 28 million insects, such as Schizodactylusm
To guard against invaders, the temperature within the "silk bubble" will be restricted to 17 Celsius, while the walls and ceilings will be kept bare, to prevent any hidden infestations.
The humidity will be a constant 45% to ensure the longevity of historic specimens, such as the original cocoa plant brought from Jamaica by Dr Hans Sloane in 1689, which inspired the first recipe for drinking chocolate.
Buried within more than 3km of cabinets are rare gems collected by Charles Darwin on the voyage of the Beagle, and by Sir Joseph Banks, who accompanied Captain James Cook on his first great expedition.
Science in action
Visitors will observe and interact with the museum's 200 working scientists
The new centre is a working research facility for about 200 scientific staff at any one time, including visiting researchers from some of the 70 countries around the world with whom the museum has affiliations.
Through special glass screens, visitors to the museum will be able to view these scientists in action, creating specimen slides, and classifying species, by a technique known as "DNA barcoding".
Understanding the unique physiology of these species will help scientists to tackle urgent ecological problems, such as how climate change is affecting biodiversity.
Mosquito species studied within the museum are helping scientists to develop better controls for malaria, while the forensic identification of crop pests will help to secure global food supplies.
Neil Greenwood, programme director, Darwin Centre Phase Two, said: "The museum's botany and entomology specimens are vital for research into disease, climate change and threats to the Earth's biodiversity.
The Attenborough theatre will host public debates on topical science issues
"The controlled conditions within Darwin Centre Phase Two will keep the collections safe for future generations of scientists and visitors."
Nature-lovers will be encouraged to examine botanical specimens "hands-on", with interactive exhibits regularly updated to reflect the changing research that is taking place within the laboratories.Guests will also be invited to take part in audience debates about issues facing the natural world, in a new live communications space called the David Attenborough Studio.