4.9 Energy Needs of Living Things
Mush!
These beautiful sled dogs are a metabolic marvel. While running up to 160 kilometres (about 99 miles) a day, they will each consume and burn about 12 thousand calories — about 240 calories per pound per day, which is the equivalent of about 24 Big Macs! A human endurance athlete, in contrast, typically burns only about 100 calories per pound (0.45 kg) each day. Scientists are intrigued by the amazing metabolism of sled dogs, although they still haven’t determined how they use up so much energy. But one thing is certain: all living things need energy for everything they do, whether it’s running a race or blinking an eye. In fact, every cell of your body constantly needs energy just to carry out basic life processes. You probably know that you get energy from the food you eat, but where does food come from? How does it come to contain energy? And how do your cells get the energy from food?
What Is Energy?
In the scientific world, is defined as the ability to do work. You can often see energy at work in living things — a bird flies through the air, a firefly glows in the dark, a dog wags its tail. These are obvious ways that living things use energy, but living things constantly use energy in less obvious ways, as well.
Why Living Things Need Energy
Inside every of all living things, energy is needed to carry out life processes. Energy is required to break down and build up molecules, and to transport many molecules across plasma membranes. All of life’s work needs energy. A lot of energy is also simply lost to the environment as heat. The story of life is a story of energy flow — its capture, its change of form, its use for work, and its loss as heat. Energy (unlike matter) cannot be recycled, so organisms require a constant input of energy. Life runs on chemical energy. Where do living organisms get this chemical energy?
How Organisms Get Energy
The chemical energy that organisms need comes from food. consists of organic molecules that store energy in their chemical bonds. In terms of obtaining food for energy, there are two types of organisms: autotrophs and heterotrophs.
Autotrophs
Autotrophs are organisms that capture from nonliving sources and transfer that energy into the living part of the ecosystem. They are also able to make their own food. Most autotrophs use the energy in sunlight to make food in the process of . Only certain organisms — such as plants, algae, and some bacteria — can make food through photosynthesis. Some photosynthetic organisms are shown in Figure 4.9.2.
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| Figure 4.9.2 Photosynthetic autotrophs, which make food using the energy in sunlight, include plants (left), algae (middle), and certain bacteria (right). |
Autotrophs are also called . They produce food not only for themselves, but for all other living things (known as consumers), as well. This is why autotrophs form the basis of food chains, such as the food chain shown In Figure 4.9.3.
A food chain shows how energy and matter flow from producers to consumers. Matter is recycled, but energy must keep flowing into the system. Where does this energy come from?
Watch the video “The simple story of photosynthesis and food – Amanda Ooten” from TED-Ed to learn more about photosynthesis:
The simple story of photosynthesis and food – Amanda Ooten, TED-Ed, 2013.
Heterotrophs
are living things that cannot make their own food. Instead, they get their food by consuming other organisms, which is why they are also called . They may consume autotrophs or other . Heterotrophs include all animals and fungi, as well as many single-celled organisms. In Figure 4.9.3, all of the organisms are consumers except for the grasses and phytoplankton. What do you think would happen to consumers if all producers were to vanish from Earth?
Energy Molecules: Glucose and ATP
Organisms mainly use two types of molecules for chemical energy: glucose and ATP. Both molecules are used as fuels throughout the living world. Both molecules are also key players in the process of .
Glucose
is a with the chemical formula C6H12O6. It stores chemical in a concentrated, stable form. In your body, glucose is the form of energy that is carried in your blood and taken up by each of your trillions of . Glucose is the end product of , and it is the nearly universal food for life. In Figure 4.9.4, you can see how photosynthesis stores energy from the sun in the glucose molecule and then how cellular respiration breaks the bonds in glucose to retrieve the energy.
ATP
If you remember from section 3.7 Nucleic Acids, (adenosine triphosphate) is the energy-carrying molecule that cells use to power most cellular processes (nerve impulse conduction, protein synthesis and active transport are good examples of cell processes that rely on ATP as their energy source). ATP is made during the first half of photosynthesis and then used for energy during the second half of photosynthesis, when glucose is made. ATP releases energy when it gives up one of its three phosphate groups (Pi) and changes to ADP (adenosine diphosphate, which has two phosphate groups), as shown in Figure 4.9.5. Thus, the breakdown of ATP into ADP + Pi is a catabolic reaction that releases energy (exothermic). ATP is made from the combination of ADP and Pi, an anabolic reaction that takes in energy (endothermic).
Why Organisms Need Both Glucose and ATP
Why do living things need glucose if ATP is the molecule that cells use for energy? Why don’t autotrophs just make ATP and be done with it? The answer is in the “packaging.” A molecule of glucose contains more chemical energy in a smaller “package” than a molecule of ATP. Glucose is also more stable than ATP. Therefore, glucose is better for storing and transporting energy. Glucose, however, is too powerful for cells to use. ATP, on the other hand, contains just the right amount of energy to power life processes within cells. For these reasons, both glucose and ATP are needed by living things.
How Energy Flows Through Living Things
The flow of energy through living organisms begins with photosynthesis. This process stores energy from sunlight in the chemical bonds of glucose. By breaking the chemical bonds in glucose, cells release the stored energy and make the ATP they need. The process in which glucose is broken down and ATP is made is called .
Photosynthesis and cellular respiration are like two sides of the same coin. This is apparent in Figure 4.9.6. The products of one process are the reactants of the other. Together, the two processes store and release energy in living organisms. The two processes also work together to recycle oxygen in the Earth’s atmosphere.
4.9 Summary
- Energy is the ability to do work. It is needed by all living things and every living to carry out life processes, such as breaking down and building up molecules, and transporting many molecules across cell membranes.
- The form of that living things need for these processes is chemical energy, and it comes from food. Food consists of organic molecules that store energy in their chemical bonds.
- Autotrophs make their own food. Plants, for example, make food by . Autotrophs are also called .
- s obtain food by eating other organisms. Heterotrophs are also known as .
- Organisms mainly use the molecules and for . Glucose is a compact, stable form of energy that is carried in the blood and taken up by cells. ATP contains less energy and is used to power cell processes.
- The flow of energy through living things begins with photosynthesis, which creates glucose. In a process called , organisms’ cells break down glucose and make the ATP they need.
4.9 Review Questions
- Define energy.
- Why do living things need energy?
- Compare and contrast the two basic ways that organisms get energy.
- Describe the roles and relationships of the energy molecules glucose and ATP.
- Summarize how energy flows through living things.
- Why does the transformation of ATP to ADP release energy?
4.9 Explore More
Learn Biology: Autotrophs vs. Heterotrophs, Mahalodotcom, 2011.
Energy Transfer in Trophic Levels, Teacher’s Pet, 2015.
Attributions
Figure 4.9.1
Three Airmen participate in dog-sled expedition by U.S. Air Force photo by Tech. Sgt. Dan Rea is released into the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 4.9.2
- Plant [photo] by Ren Ran on Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Green Algae by Tristan Schmurr on Flickr is used under a CC BY 2.0 (https://creativecommons.org/licenses/by/2.0/) license.
- Cyanobacteria by Argon National Laboratory on Flickr is used under a CC BY-NC-SA 2.0 (https://creativecommons.org/licenses/by-nc-sa/2.0/) license.
Figure 4.9.3
Biomass_Pyramid by Swiggity.Swag.YOLO.Bro on Wikipedia is used and adapted by Christine Miller under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.
Figure 4.9.4
Photosynthesis and respiration by Christine Miller is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) license.
Figure 4.9.5
Photo synthesis and cellular respiration by Lady of Hats/ CK-12 Foundation is used under a CC BY-NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/) license.
References
LadyofHats/CK-12 Foundation. (2016, August 15). Figure 5: Photosynthesis and cellular respiration [digital image]. In Brainard, J., and Henderson, R., CK-12’s College Human Biology FlexBook® (Section 4.9). CK-12 Foundation. https://www.ck12.org/book/ck-12-college-human-biology/section/4.9/
Mahalodotcom. (2011, January 14). Learn biology: Autotrophs vs. heterotrophs. YouTube. https://www.youtube.com/watch?v=eDalQv7d2cs
Teacher’s Pet. (2015, March 23). Energy transfer in trophic levels. YouTube. https://www.youtube.com/watch?v=0glkXIj1DgE&feature=emb_logo
TED-Ed. (2013, March 5). The simple story of photosynthesis and food – Amanda Ooten. YouTube. https://www.youtube.com/watch?v=eo5XndJaz-Y&feature=youtu.be
The ability to do work.
The smallest unit of life, consisting of at least a membrane, cytoplasm, and genetic material.
Any substance consumed to provide nutritional support for an organism.
Created by CK-12 Foundation/Adapted by Christine Miller
Case Study: Trying to Conceive
Alicia, 28, and Victor, 30, have been married for three years. A year ago, they decided they wanted to have a baby, and they stopped using birth control. At first, they did not pay attention to the timing of their sexual activity in relation to Alicia’s menstrual cycle, but after six months passed without Alicia becoming pregnant, they decided to try to maximize their efforts.
They knew that in order for a woman to become pregnant, the man’s sperm must encounter the woman’s egg, which is typically released once a month through a process called ovulation. They also had heard that for the average woman, ovulation occurs around day 14 of the menstrual cycle. To maximize their chances of conception, they tried to have sexual intercourse on day 14 of Alicia’s menstrual cycle each month.
After several months of trying this method, Alicia is still not pregnant. She is concerned that she may not be ovulating on a regular basis, because her menstrual cycles are irregular and often longer than the average 28 days. Victor is also concerned about his own fertility. He had some injuries to his testicles (testes) when he was younger, and wonders if that may have caused a problem with his sperm.
Alicia calls her doctor for advice. Dr. Bashir recommends that she try taking her temperature each morning before she gets out of bed. This temperature is called basal body temperature (BBT), and recording BBT throughout a woman’s menstrual cycle can sometimes help identify if and when she is ovulating. Additionally, Dr. Bashir recommends she try using a home ovulation predictor kit, which predicts ovulation by measuring the level of luteinizing hormone (LH) in urine. In the meantime, Dr. Bashir sets up an appointment for Victor to give a semen sample, so that his sperm may be examined with a microscope.
As you read this chapter, you will learn about the male and female reproductive systems, how sperm and eggs are produced, and how they meet each other to ultimately produce a baby. You will learn how these complex processes are regulated, and how they can be susceptible to problems along the way. Problems in either the male or female reproductive systems can result in infertility, or difficulty in achieving a successful pregnancy. As you read the chapter, you will understand exactly how BBT and LH relate to ovulation, why Dr. Bashir recommended that Alicia monitor these variables, and the types of problems she will look for in Victor’s semen. At the end of the chapter, you will find out the results of Alicia and Victor’s fertility assessments, steps they can take to increase their chances of conception, and whether they are ultimately able to get pregnant.
Chapter Overview: Reproductive System
In this chapter you will learn about the male and female reproductive systems. Specifically, you will learn about:
- The functions of the reproductive system, which includes the production and fertilization of gametes (eggs and sperm), the production of sex hormones by the gonads (testes and ovaries), and, in females, the carrying of a fetus.
- How the male and female reproductive systems differentiate in the embryo and fetus, and how they mature during puberty.
- The structures of the male reproductive system, including the testes, epididymis, vas deferens, ejaculatory ducts, seminal vesicles, prostate gland, bulbourethral glands, and the penis.
- How sperm are produced, how they mature, how they are stored, and how they are deposited into the female.
- The fluids in semen that protect and nourish sperm, and where those fluids are produced.
- Disorders of the male reproductive system, including erectile dysfunction, epididymitis, prostate cancer, and testicular cancer — some of which predominantly affect younger men.
- The structures of the female reproductive system, including the ovaries, fallopian tubes, uterus, cervix, vagina, and external structures of the vulva.
- How eggs are produced in the female fetus, and how they then mature after puberty through the process of ovulation.
- The menstrual cycle, its purpose, and the hormones that control it.
- How fertilization and implantation occur, the stages of pregnancy and childbirth, and how the mother’s body produces milk to feed the baby.
- Disorders of the female reproductive system, including cervical cancer, endometriosis, and vaginitis (which includes yeast infections).
- Some causes and treatments of male and female infertility.
- Forms of contraception (birth control), including barrier methods (such as condoms), hormonal methods (such as the birth control pill), behavioural methods, intrauterine devices, and sterilization.
As you read the chapter, think about the following questions:
- Why might sexual intercourse on day 14 of Alicia’s menstrual cycle not necessarily be optimal timing to achieve a pregnancy?
- Why is Alicia concerned about her irregular and long menstrual cycles? How could tracking her BBT and LH level help identify if she is ovulating and when?
- Why do you think Victor is concerned about past injuries to his testes? How might analysis of his semen help assess whether he has a fertility issue and, if so, the type of issue?
Attributions
Figure 18.1.1
Couple by Md saad andalib on Flickr is used under a CC BY 2.0 (https://creativecommons.org/licenses/by/2.0/) license.
Figure 18.1.2
Basal_Body_Temperature by BruceBlaus on Wikimedia Commons is used under a CC BY SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organisms' activities.
Image shows a diagram of how non-steroid hormones affect cell processes. The non-steroid hormone binds to a receptor embedded in the cell membrane. The bound receptor then activates an enzyme with acts as a secondary messenger, effecting a specific cellular function.
Image shows a labelled diagram of the human reproductive system. This includes components that hang below the pelvic cavity including the testes and epididymes, which are enclosed in the scrotum. The vas deferens is a tube than runs up into the pelvic cavity from each testes. These two vas deferens merge and empty into the urinary urethra, which runs along the length of the penis.
Organisms that eat organisms from a different population in order to satisfy their energy needs.
Glucose (also called dextrose) is a simple sugar with the molecular formula C6H12O6. Glucose is the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using energy from sunlight.
The simplest form of sugar and the most basic units of carbohydrates, also called simple sugars.
A complex organic chemical that provides energy to drive many processes in living cells, e.g. muscle contraction, nerve impulse propagation, and chemical synthesis. Found in all forms of life, ATP is often referred to as the "molecular unit of currency" of intracellular energy transfer.
A set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP).
