In humans, following formation of a small cluster of cells, tissues begin to form. During the first three months, organs begin to form. All organs and body features develop by the sixth month. During the last three months of pregnancy, organs and features develop well enough to function after birth. All organisms must be able to obtain and use resources, grow, reproduce, and maintain stable internal conditions while living in a constantly changing external environment.
Organisms respond to internal or environmental stimuli.
Performance Indicator 5.2 Describe the importance of major nutrients, vitamins, and minerals in maintaining health and promoting growth, and explain the need for a constant input of energy for living organisms. 5.2a Food provides molecules that serve as fuel and building material for all organisms. 5.2b Foods contain a variety of substances which include carbohydrates, fats, vitamins, proteins, minerals, and water. Each has a vital purpose at the cellular level. 5.2c Metabolism is the sum of all chemical reactions in the body.