Transcript
JULIA COOKE
Glucose, C6H12O6, is a sugar ubiquitous in nature as a way of storing energy. It takes energy to assemble the molecule, and this stored energy is what is useful to living things. Glucose is a carbohydrate because it contains only carbon, hydrogen and oxygen. And the hydrogen and oxygen are in a ratio of two to one. Glucose can occur in a linear or cyclic form.
Autotrophs, including plants, make their own food using energy from sunlight to assemble glucose. They make glucose from non-living ingredients, water, and carbon dioxide. Autotrophs are also called ‘producers’.
Heterotrophs consume other living things as food sources. A caterpillar, for example, eats a leaf to get energy, including glucose, and a bird will eat a caterpillar is its energy source. Heterotrophs are also called ‘consumers’.
Plants store glucose as starch, and animals store it as glycogen, both by chemically linking glucose molecules together. Starch and glycogen are similar but have different branching patterns. They are useful ways to store glucose because, unlike glucose, they’re not soluble. When needed, both are broken down by breaking the chemical bonds to form glucose.
Regardless of where the glucose came from, all living things obtain energy by breaking glucose back into carbon dioxide and water again in a process called ‘cellular respiration’. This releases the energy used to assemble glucose initially, and the energy is used to sustain life. Respiration occurs in heterotrophs such as the caterpillar and us. We take in oxygen and breathe out carbon dioxide. Autotrophic plants both respire and photosynthesise.
Living things use energy to grow and reproduce and some is lost in waste, not able to be used by the organism. Living things use energy to do work, such as moving and lifting, and use energy to produce heat, and in maintenance. It takes energy to assemble the molecules of life.
We can look at how much glucose an oak leaf uses for growth and maintenance. Research has determined that, in a single day, a young leaf of an oak tree used 1.3 grams of glucose for each gram of growth. It used 27 milligrams of glucose to maintain each gram of leaf. That’s nearly 50 times as much glucose to use for growth compared to maintaining the tissue.
Getting enough energy or glucose contributes to some of the patterns we see in nature. Plants can only grow where they can get enough sunlight to power photosynthesis. Animals can only survive where there is enough of the right kind of food to sustain them. A butterfly, for example, will lay its eggs away from other eggs to increase chances that there is enough food for the larvae and food which locations are sought after. Many distribution patterns and behaviours are driven by the need for glucose, the molecule that stores energy.