Oxygen in the presence of sunlight
Multicellular organisms do this by assigning specific roles to specific cells. This enables various cells within a larger organism to collaborate in order to preserve homeostasis. Since they are made up of just ONE type of cell, unicellular organisms do not need cell specialization to maintain homeostasis.
Answer:
The first line of defence (or outside defence system) includes physical and chemical barriers that are always ready and prepared to defend the body from infection. These include your skin, tears, mucus, cilia, stomach acid, urine flow, 'friendly' bacteria and white blood cells called neutrophils.
Explanation: