Possible Clues:

• Classification of plants and animals
• Duty to switch half the gloomy branch from biology
• Classification of duty levied in respect of old yacht
• Categorisation of plants or animals
• The scientific process of classifying living things
• System of classification putting duty on order, ending in dismay
• Duty on oxygen finds its way to my branch of biology
• Field of biology
• Classy type of duty to broadcast from office that's belongs to me
• Classification