Characteristics of living organisms INTRODUCTION
Δ Fig 1.1 Tiny tardigrades (about 1 mm long) are the toughest organisms known. They can survive temperatures below –200 °C, 10 days in the vacuum of space and over 10 years without water!
Sometimes it is easy to tell when something dies – an animal will stop moving around, a plant may wilt and all the green parts collapse. But does a tree die in winter, when its leaves have dropped off? Are animals ‘dead’ when they hibernate underground for months? As technology gets increasingly sophisticated, and we can create machines with ‘brains’ and new organisms from basic molecules, distinguishing between living and dead could get even more difficult. We need a set of ‘rules’ that work for most organisms, most of the time.
KNOWLEDGE CHECK ✓ Living organisms show a range of characteristics that distinguish them from dead or non-living material. ✓ Life processes are supported by the cells, tissues, organs and systems of the body. LEARNING OBJECTIVES
CHARACTERISTICS OF LIVING ORGANISMS There are seven life processes that most living organisms will show at some time during their life. • Movement: Animals may move their entire body so that it changes position or place. EXTENDED
Organisms may also move parts of their body. For example, plants may move body parts in response to external stimuli such as light, while structures in the cytoplasm of all living cells move.
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CHARACTERISTICS OF LIVING ORGANISMS
✓ EXTENDED Define the seven characteristics of living organisms. ✓ Describe each of the characteristics of living organisms. ✓ Explain that not all living organisms show every characteristic all of the time. ✓ List the features shared by all living organisms. ✓ Identify the main features of plants and animals.
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• Respiration: This is a series of chemical reactions inside living cells that break down nutrient molecules and release energy. EXTENDED
The energy released from respiration is used for all the chemical reactions that help to keep the body alive. Together, these reactions are known as metabolism. END OF EXTENDED
• Sensitivity: Living organisms are able to detect (or sense) and respond to changes in the environment around them. For example, we see, hear and respond to touch. EXTENDED
Living organisms can also detect and respond appropriately to changes inside their bodies (the internal environment). END OF EXTENDED
• Growth: This is the permanent increase in size of an organism. EXTENDED
Growth is often defined as an increase in dry mass (mass without water content) of cells or the whole body of an organism. This is because total mass can vary, depending on how much the organism eats and drinks. Dry mass only measures the amount by which the body increases in size when nutrients are taken into the cells and used to increase their number and size.
Δ Fig 1.2 Sunflowers respond to light by tracking the sun across the sky during the day.
• Reproduction: This includes the processes that result in making more individuals of that kind of organism, such as making gametes and the fertilisation of those gametes. • Excretion: This is the removal from the body of substances that are toxic (poisonous) and may damage cells if they stay in the body. Organisms also excrete substances that are in excess, where there is more in the body than is needed. EXTENDED
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Living cells produce many products from the metabolic reactions that take place inside them. Some of these are waste products – materials that the body does not use; for example, animals cannot use the carbon dioxide produced during respiration. These waste products may be toxic, so they must also be removed from the body by excretion.
CHARACTERISTICS OF LIVING ORGANISMS
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• Nutrition: This is the absorption of nutrients into the body. The nutrients are the raw materials needed by the cells to release energy and to make more cells for growth, development and repair. EXTENDED
Plant nutrition requires light, carbon dioxide, water and mineral ions, such as iron and magnesium. Animal nutrition requires organic compounds such as carbohydrates and proteins, mineral ions such as iron and sodium, and usually water. END OF EXTENDED
All these characteristics will be described in greater detail in later Topics in this book.
SCIENCE LINK
Δ Fig 1.3 Growth of a child can be measured by recording their change in height over time.
CHEMISTRY CHEMICAL REACTIONS, PARTICLE IDEAS
• respiration is an example of a chemical reaction • as with all chemical reactions, ideas about particles will make it easier to understand what changes are taking place • many processes in living things need particles to move about (for example, the circulation of blood) so particle ideas are helpful in describing or explaining how this works
PHYSICS PROPERTIES OF WAVES
• the vibrations of sound waves are used for hearing; different frequencies and amplitudes of sound waves produce the variety of sounds living things can sense
QUESTIONS 1. For each of the seven characteristics, give one example for: a) a human b) an animal of your choice c) a plant. 2. For each of the seven characteristics, explain why they are essential to a living organism.
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CHARACTERISTICS OF LIVING ORGANISMS
• in sensing their environment, many living things use the refraction of light through a lens to form an image
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