How Living Things Obtain Matter and Energy for Growth
The biggest difference between plants and animals is how they get the matter and energy they need for growth. Animals have to eat other living things to get their food, but plants can produce their own food. Plants absorb sunlight and use that energy to make glucose from carbon dioxide and water during the process of photosynthesis; glucose is the food plants can use as a source of energy or matter for growth.
As you can see from the following list, plant structures are specialized to help plants get what they need for photosynthesis:
- The shoot system helps plants capture energy from the Sun. Shoots grow upward, bringing leaves toward the Sun. Branches spread leaves out so they can absorb light over a wider area, and many leaves are flat so they have the most surface area possible for light absorption.
- The root system absorbs water and minerals from the soil. Water is needed for photosynthesis and basic plant functioning. Minerals perform the same function for plants as they do for you — they improve general metabolism by helping enzymes function properly. Also, plants absorb nitrogen-containing compounds from the soil and use them, along with the carbohydrates made during photosynthesis, to construct plant proteins.
- Stomates in the leaves allow plants to take carbon dioxide from the atmosphere and return oxygen to it. The carbon dioxide provides the carbon and oxygen atoms plants need to build carbohydrates. Also, photosynthesis produces oxygen when the hydrogen and oxygen atoms in water are separated. Oxygen gas leaves plants through their stomates.
Plants extract energy from food molecules the same way animals do — by cellular respiration. When plants do cellular respiration, they produce carbon dioxide and use oxygen just like animals do. During the day, however, photosynthesis absorbs so much carbon dioxide and releases so much oxygen that plant respiration isn’t detectable. If you were to measure gas exchange around a plant in the dark, the plant would be exchanging gases just like you.