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Characteristics of Life Biology 20 Life Has Organization • Life processes maintain the organization but upon death and organism breaks apart from the simplest to the most complex and include: – Atoms molecules cell organelles cells (smallest unit of life) tissue organs organ systems organism Life Acquires Materials and Energy • Living things acquire nutrient molecules that can be used as building blocks or for the organisms structure • Molecular bond energy is used in cell metabolism. Homeostasis means “Staying the Same” • The internal environment of an organism stays relatively constant compared to the external environments; for example – Body temperature fluctuates only slightly during a variable day Life Responds to Stimuli • Living things often respond to external stimuli by moving, whether an animal detects an energy and runs or plant leaves track the movement of the sum • Behaviors are directed toward minimizing injury, acquiring food, and reproducing. Life Reproduces • During reproduction, a copy of its hereditary information (genes) is passed on. • Unicellular organisms may reproduce asexually by dividing into two cells, each of which has the same genes and structures as the single parent. • Multicellular organisms may reproduce sexually. Each parent contributes one-half of the total number of genes to an offspring, which then has characteristics of both parents and may not resemble either one exactly. Life Grows and Develops • Growth is recognized by an increase in size and often in the number of cells. • Human development includes all changes that take place between conception and death. Life Adapts • Adaptations are modifications that make an organism suited to its way of life; for example, hollow bones in birds reduce weight and permit flying. • Adaptations are selected by evolution, the process where characteristics of species change through time. When new variations arise that allow certain members of the species to capture more resources, survive in higher numbers and have more offspring than poorly adapted members. Evolution explains the diversity and unity of life. Structure of the Ecosystem • Population – all the members of one species found in a specific area at the same time. • Community – a group or population of both plants and animals that live together. (Biotic only) • Ecosystem – consists of various interactions among populations and with the physical environment. (Biotic and Abiotic) • Biosphere – the narrow band around the Earth in which life can exist. – Upper boundary is higher atmosphere – Lower boundary extends into soil and ocean bottoms Humans Threaten the Biosphere • Humans modify existing ecosystems for their own purposes. • Increases in human populations threaten more ecosystem stability and diversity. • Loss of stable and diverse ecosystems in turn threatens human populations; for example, destruction of the world’s rain forest may lead to increased carbon dioxide in the atmosphere, which in turn may increase the average daily temperature. Biodiversity • From perhaps 80 million species, fewer than 2 million have been destroyed. • Extinction, which occurs naturally, has increased from human’s alteration of the environment, development, pollution and overfishing. • Modern extinction rates from human activities could exceed the five natural mass extinctions in geological history. Tropical Rain Forest Destruction • Even if you do not believe in a species existing for its own sake, the extinction of species reduces resources available to humans for food, clothing, medicines and other raw materials. – Rain forests constitute an area similar to the USA – Each year an area of rain forest 1/3 the size of Alberta is lost – Social, economic and political forces encourage poor people to convert rain forest into smaller farms, followed by logging, mining and cattle ranching. – Harvest of natural forest products might be an economic alternative that would save this ecosystem.