Answer: "To move substances against a concentration or electrochemical gradient, a cell must use energy. Active transport mechanisms do just this, expending energy (often in the form of ATP) to maintain the right concentrations of ions and molecules in living cells."
Although nitrogen gas makes up 78% of the atmosphere, we can't use it because nitrogen atoms must be broken apart first before. This nitrogen is very much packed and bonded with its atoms and would be useless to use since it can't be used for plants.
The correct answer is: B) flesh of another animal
The shape of teeth is tightly connected with the food that animal eats.Examples:
• Herbivores (plant eaters) have flat teeth specialized for the grass chewing.
• Carnivores (flesh eaters) have long and sharp teeth for meat cutting.
• Omnivores (eat meat and plants) such as humans have various types of teeth with different functions.
There are four main types of teeth: incisors (at the front, sharp for cutting), canines ( to grip and tear food), premolars (flat surface for food crushing), molars (the biggest with flat biting surface, to chew).
