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Life Science Structure and Function of Living Things Living things require basic needs to be met in order to perform specific life functions. Every organism is made of a complex structure and undergoes a change during the life cycle. Organisms are classified according to common criteria. Vocabulary Life cycle- the continuous sequence of changes of an organism from birth to adult Metamorphosis- a change of form from one stage to the next in the life cycle of an organism Classification- grouping of organisms according to similarities Prokaryotes- any cellular organism that has no nuclear membrane, such as bacteria and blue-green algae (archeobacteria) Eukaryotes- any organism having a cell type that contains specialized organelles; this includes all life forms except bacteria, blue-green algae, and other primitive microorganisms. Focus on Structure and Function of Living Things 1. It is important for students to understand that all living things are made of cells. Cells are the basic structure of every organism. Cells have specific jobs depending on their type and combine to make an organism. The physical characteristics of the organisms divide them into three domains: prokaryotes, eukaryotes, or archaebacteria. Further classification of commonalities breaks all organisms into six kingdoms: Animal, Plant, Fungi, Protist, Eubacteria, and Archaebacteria. 2. Living organisms go through distinct changes from life to death. The life cycles of different species are important. Students should recognize the different types of life cycles and the stages of development can be distinguished depending on the type of organism. Water, temperature, and light are some environmental conditions that can affect the development of an organism. The majority of common organisms including dogs, snakes, and fish have a simple, three-stage life cycle which includes the egg, birth of young, and then to adult. The young are similar to the parent, just smaller size. Plants also have a simple life cycle which includes the seed, seedling, and adult. The life of an insect can be categorized as either complete or incomplete metamorphosis. Complete metamorphosis is a four-stage cycle in which the young look completely different than the adult. An example of such an organism is the butterfly. The four stages include the egg, larva, pupa, and adult. Incomplete metamorphosis consists of three-stages in the life cycle: egg, larva (nymph), and adult. The dragonfly and grasshopper both have this type of life cycle.
3. Teachers should make sure students understand that living organisms have commonalities. Every living organism requires basic needs air, water, nutrition, and shelter in order to perform the basic life functions such as growth and reproduction. Things that cannot take in nutrients have no ability to grow or reproduce. Molten skins of a snake, petrified wood, or broken branches are non-living. 4. Structure and function have a direct correlation which should be explained to the science student as each system is introduced. The structure of each type of cell complements its function. The tissue in an organism provides a specific function to support its structure; some examples include muscle tissue, dermal tissue, and bone tissue. The function of an organ is specific to its structure. Organ systems function together to create a uniquely designed organism. These organ systems have a role to play in providing energy to the cells of the body, removing waste, protecting the body from harm, and maintaining homeostasis. Atoms combine to make molecules, which combine to make cells; cells combine to make tissue, which combine to make organs; these organs make up organ systems, which are the structure of every organism. Organisms merge together to form ecosystems. 5. The human body is composed of organ systems that effectively combine to provide the basic functions for life. The teacher should explain that the organ systems interact to maintain life in the organism. The students should recognize the function of all human body systems: Circulatory system: transports nutrients, water, waste, and disease fighting cells Digestive system: breaks down of food for energy Excretory: controls water and salt balances, gets rid of waste Endocrine: produces hormones and regulates the body Immune: protects and fights off diseases Integumentary: protects body from injury and bacteria, responds to stimuli and regulates temperature Muscular: movement Nervous: controls the function of the body Respiratory: takes in oxygen and removes carbon dioxide from the body Reproductive: produces offspring to continue the species Skeletal: support the body
Reproduction and Heredity Organisms pass on characteristics to their offspring, some through genetics and some are the effects of environment. Through heredity, a genetic code for specific traits are passed down and stored in the DNA of every organism. Dominant traits show up more often than those considered to be hidden, recessive traits. The understanding of genetics has impacted the outcome of genetically engineered organisms. Vocabulary Genetics- the study of traits passed down from parents to offspring Traits- a distinguishing characteristic Heredity- passing down genetic characteristics from parents to offspring through DNA Sperm- the male sex cell Egg- the female sex cell Allele- any of several forms of a gene Gamete- the fusing of a sperm and egg during the process of fertilization Meiosis- the process of gamete formation Mitosis- the nucleus of a cell separates into two parts resulting in two new cells Genotype- the genetic makeup of an organism referring to a set of traits Phenotype- the physical appearance of an organism reflecting the specific genotype Dominant- one or a pair of alleles that when present covers the characteristic of the other trait Recessive- the allele whose characteristic is masked by the dominant trait Focus of Reproduction and Heredity 1. Students need to understand that traits are passed from parent to offspring through genes. Flowering plants and animals both reproduce with reproductive structures which contain male (sperm) or female (egg) sex cells. These cells contain the key to characteristics, or genetic traits, passed from the female and male sex cells to the offspring. The traits are controlled by genes, the units of heredity. Organisms inherit a set of genetic information called alleles from each parent cell, or gamete, through the process of meiosis, creating a genetic pair. Humans have forty-six chromosomes in the nucleus of each cell, other than sex cells, which make up twenty-three pairs. The cell divides during mitosis, duplicating the cell over and over until an organism is formed. 2. Teachers need to compare and contrast both purebred and hybrid genetic codes to make it clear for students. For each trait, every organism has a pair of alleles for each genetic code. The prominent trait is dominant. A purebred, or homozygous, organism has like alleles for a particular trait, either dominant or both recessive (BB or bb). A hybrid, or heterozygous trait, has one of each, a dominant allele and recessive allele for a specific trait (Bb). In order for the recessive trait to show up in the offspring, there must be a purebred recessive genotype for that specific trait.
3. Teachers should explain the difference between dominant and recessive traits. Traits are passed down to offspring from the alleles, which carry the genetic information contributed by each parent. DNA in the chromosome stores and passes on genetic information from one generation to the next. The physical appearance of an organism, or phenotype, is the result of a combination of genetic makeup, or the genotype, in the DNA from each parent. A visual model for predicting the outcome of genetic crosses is known as a Punnett square. The purpose of this visual is to map the genotype of both parents and show the probability of specific traits occurring in the offspring. The traits that seem to appear more often are known as dominant traits. If the allele for a dominant trait is present, that trait will hide a recessive, less prominent trait in the offspring. Dominant genes hide recessive genes when both are inherited by an organism. For example, the dominant trait for eye color is brown (B) and the recessive trait for eye color is blue (b). If the dominant allele (B) is present in the genotype of the parent, the genotype of the offspring will be brown eyes. 4. Teachers should give examples of both acquired and inherited traits. Traits are qualities that distinguish one organism from another. Hair colors, shape of features, beak shape, or muscle structure are all traits. There are two types of traits: acquired and inherited. Acquired traits are not passed on genetically. Behaviors that help an organism survive, like where to hide and what animals to hide from are acquired traits. An example of a plant s acquired traits might include bending because of wind. Inheritable traits get passed down from generation to the next generation. This might include things like passing blonde hair down from one family member to the next. All plants and animals that reproduce pass on traits to their offspring. 5. Students need to understand that some genetic traits can be manipulated by selective breeding of desired characteristics. The information known about genetics has a tremendous impact on the environmental and genetic factors concerning traits of an organism. Breeding plants or animals that have desired traits in a particular species, or crossing two genetically different but related species, has had an impact on various species of organism. Genetic engineering has resulted in contributions to medicine, agriculture, and the desires of human nature.
Evolution and Adaptations of Organisms Living and non-living things in an environment are partners in keeping an ecosystem in balance. Living things constantly interact with their environment. Organisms can change in response to environmental conditions, and the environment can change in response to a population or group of organisms. Vocabulary Evolution- change over time Adaptation- a modification that is either inherited or acquired that make an organism better able to survive and reproduce Population- the total number of organisms in a specific habitat Extinction- the eliminating of a species Natural selection- having traits that make an organism better able to adapt to a specific environment Selective breeding- breeding two organisms intentionally to produce offspring with a desirable characteristic or to produce offspring to eliminate a specific trait Mutation- a change in a gene or chromosome Focus of Evolution and Adaptations 1. Teachers should clarify the difference between structural and behavioral adaptations. There are only a limited amount of resources to satisfy the needs of all organisms in an ecosystem. Each population must compete for the food, water, shelter, and light needed to survive. As resources diminish or change, the organism must change as well. Adaptations can be both how an organism looks and how it acts. Two kinds of adaptations have been observed in response to change in an ecosystem: Structural adaptations are changes in physical features that help the organism survive. For example, the beak of a bird changes to make it easier to get food; a change of coloration allows the organism to replicate another animal (snake coloring), blend in for survival (camouflage), or get noticed in order to make it easier to reproduce. Acclimatization to the changes in environment is also a structural adoption. Behavior adaptations are things that organisms do to naturally avoid harm. Verbal communication (mockingbird imitating another bird s sound), migration, hibernation, physiological adjustments (decision making and learning), and chemical protection (skunk spraying scent) are examples of behavior adaptations.
2. Students should be able to identify the different factors that can limit the growth of a population. The fossil record shows organisms different in appearance than the species alive today. Consequences of human interference with ecosystems can result in the decrease or extinction of various organisms. Deforestation, desertification, wetlands destruction, and pollution are examples of this negative effect. As environmental conditions change naturally or with human interference, adaptations must occur in order for the species to survive. Adaptive characteristics insufficient to enhance survival lead to a change in genetic variations or extinction of the species. Diversity of species takes time. Biological evolution accounts for the diversity of species developed through gradual processes over many generations. 3. Students should be able to explain why some organisms survive with more success than others. Reproduction of offspring is needed for a species to survive. Organisms with the most favorable traits survive in the natural environment and reproduce most successfully. The successful organisms pass on the genetic information, which enhances survival and reproduction more frequently, from generation to generation through natural selection. Natural selection will elevate organisms, making them better able to survive and reproduce under specific environmental extremes. When a different genetic trait first appears in an organism, it can be random at times as mistakes occur in the copying process of DNA. These mutations either cause harm, decreasing its chance for survival, or benefit the organism by making it more efficient. Breeders of animals and plants take advantage of the beneficial mutations and intentionally select organisms with desirable traits they would like to be passed on to the offspring. The process of selective breeding has resulted in a variety of superior organisms and those with desired traits; some examples are the new hybrid corn plants that are drought and disease resistant or designer dogs like the Labradoodle.
Organisms and their Environment Ecosystems are in a constant state of change. The interactions in any system must maintain a state of dynamic balance for the system to function and survive. To maintain this balance, ecosystems adjust in response to change. The interference from outside forces can change one small part of the system and endanger the entire balance. If this balance is destroyed, it may be impossible for the system to recover. Vocabulary Homeostasis- the tendency of an organism to maintain internal balance Habitat- the natural environment of a living organism Niche- the relationships and activities of an organism within its habitat Symbiosis- two dissimilar organisms living together Focus on Organisms and Environment 1. Students should recognize that either internal or external stimuli in the environment cause a response in the organism, which can be equated to cause and effect. Organisms live in unpredictable environments. To survive and maintain homeostasis, they must react to both external and internal stimuli as a response to environmental changes and from interactions with other species, as well as their own. 2. Organisms respond to internal stimuli, a change within themselves, and external stimuli, situations that affect them in their environment. There are two types of responses to all stimuli: learned and instinctual. Learned responses are not present at birth and must be taught, such as methods to find food and the ability to read. Instinctual responses do not have to be taught and are naturally present at birth. Fight or flight response, migration, reaction to hunger and thirst, pupil dilation, and shivering when cold are instincts that take over when a stimulus occurs. Phototropism is the natural response of a plant to grow toward the sun. 3. Students should be able to identify the difference between parasitism, commensalism, and mutualism. The close relationship among organisms in the environment and with the environment, known as symbiosis, is designed specifically to meet the organism s basic needs. Three types of symbiotic relationships exist: parasitism, commensalism, and mutualism. A parasite must have a host, which it causes harm in order to survive. A tapeworm uses the host for shelter and feeds off of the food in the organism s intestines, causing harm. There are no benefits or harm in commensalism. The relationship between a whale and the barnacles living on it provide no benefit or harm to the whale. Mutualism is a symbiotic relationship where both organisms benefit. Lichens are an example of mutualism; both the fungus and algae need one another to survive.
4. Students should be able to distinguish between a food chain and a food web and explain how energy flows from one organism to the next. Energy travels through an ecosystem from producers to the consumers and then to decomposers. This flow is a network of feeding relationships and at each level of the cycle, some energy is lost. Organisms are classified by how they get their food. Producers make their own food using nutrients in the soil and energy from the sun. Consumers and decomposers have to get their food from another source. Consumers depend on producers to provide the nutrients they need for energy. Decomposers break down dead organisms for food and return important materials back to the soil and water. The flow of energy through the ecosystem from producer to consumer is followed in a series from one organism to another called a food chain. There are a number of organisms in an ecosystem that are linked by food and energy relationships. These overlapping food chains from producer to consumer to decomposer are represented in a diagram known as a food web. 5. Teachers should show the relationship between the needs of the organism and the resources in the ecosystem. Ecosystems can only sustain the population as long as resources and favorable living conditions are available. As the population grows, so must available resources. When an ecosystem is at its capacity, it cannot support exponential growth, rapid and unchecked growth, without affecting the population of organisms or the environmental conditions unfavorably. Exponential growth continues until specific conditions limit or level off the growth. Several factors create logistic growth: limiting resources, temperature, weather or other conditions, and competition among organisms. 6. Students should recognize how competition for resources is a natural occurrence, unless organisms coexist by sharing resources. Competition arises when species compete for a short supply of resources and these resources are used by organisms at the expense of others. Competition occurs between members of the same species and between different species. The exclusion of a species occurs when, as a result of the competition for resources, one species is eliminated from the community by another species or non-living conditions. The more competitive species survive and reproduce while the less competitive species do not reproduce as successfully. Several species can coexist by rationing or dividing and sharing resources. 7. Students should understand that everything an organism does and everything it needs in its environment is defined by the organism s relationship to its physical and biological environment, or niche. When defining a niche three factors are considered for survival and reproduction: physical factors (sunlight, soil composition, ph, temperature, and humidity), biological factors (competitors, parasites, prey, and predators), and behavior factors (diurnal patterns, movement, and social organization). Competition exists between organisms that have the same needs water, food, types of shelter, etc. When an area is populated with species that require the same things, competition for that resource is inevitable. For example, both chipmunks and squirrels compete for acorns. Competition between species occurs. Squirrels compete within their species for nesting sites, acorns and mates. Therefore the competition is stronger among the same species and resource availability is reduced.
PRACTICE QUESTIONS The following are 240Tutoring Life Science questions taken from our PRAXIS II Elementary Education: Content Knowledge practice questions. These and many others can be found in our PRAXIS II Elementary Education: Content Knowledge Study Guide. Please find the answers and explanations after the practice questions. 1. A species of rabbit has alleles for black (B) or white (b) fur. The gene for black fur (B) is dominant. If a black (Bb) rabbit and a white (bb) rabbit mate, what percentage of their offspring can be expected to have black fur? a. 25% b. 50% c. 75% d. 100% 2. During the summer, flies and ticks live off of bison causing them harm; particularly in the spring and summer. The cattle egret is a bird that sometimes eats the flies and ticks that live on bison. What symbiotic relationship exists between the bison and the egret? a. Mutualism b. Parasitism c. Commensalism d. Symbolism 3. Which one of the following is true of grass in an ecosystem? a. It gets its food from the microorganisms in the water it absorbs b. It is non-living and does not need to make food c. It makes its own food using nutrients from the soil and the energy from the sun d. It makes its own food by taking the carbon out of the air and converting it to nitrogen 4. While Susan is viewing cells under a compound microscope, she notices that the cells do not appear to have any specialized organelles. These cells are most likely which of the following? A. Animal cells B. Plant cells C. Eukaryotic cells D. Prokaryotic cells 5. Which of the following correctly sequences the levels of organization for all living things?
A. Cell tissue organ organ system organism B. Cell organ system organ organism tissue C. Cell tissue organism organ system organ D. Organ organ system cell organism tissue 6. Which of the following systems in the human body functions as the system responsible for transporting food and water waste? A. Immune system B. Digestive system C. Endocrine system D. Circulatory system 7. All living organisms are classified into one of the six kingdoms used in the modern day classification system. The kingdoms are: A. atoms, cells, tissues, organs, organ systems, organisms. B. animals, plants, fungi, protists, eubacteria, archaebacteria. C. worms, fishes, birds, reptiles, amphibians, mammals. D. classes, phyla, orders, families, genus, species. 8. If P represents the trait for purple flowers and p represents the trait for white flowers, which of the following genotypes would be considered to be a hybrid? A. PP B. Pp C. pp D. Both PP and pp 9. Gregor Mendel, the Father of Genetics studied different traits of pea plants. One of the traits he studied that followed the Law of Dominance was the height of pea plants. He discovered that a purebred short plant had which of the following characteristics? A. A pair of alleles for tall height B. One short allele and one tall allele C. No alleles for height D. A pair of alleles for short height 10. What inference could you make if the genotypes of two parents did not show the recessive phenotype, but the recessive trait was visible in their offspring?
A. Both parents were hybrids and carried one recessive allele for the recessive trait B. Both parents were purebred. One carried two of the recessive alleles and the other carried two dominant alleles C. Neither parent had the recessive allele D. One parent had two of the dominant alleles and the other one was heterozygous for that trait Answer and Explanations 1. B Correct Answer B: (B)If the alleles of two rabbit parents combine. The possible outcomes of those genetic traits are: (Bb) (bb) (Bb) (bb). The trait for black fur is dominant and white fur is recessive. For the fur of the offspring to be white, the genotype must be purebred or both recessive (bb). As a result of the cross between these parents, 50% are expected to have black offspring. (A/C) It is not possible for only 25% or 75% of the offspring to have black fur if the parents have this specific genotype, because the trait for black fur (B) is dominant. 2. A - Correct Answer A: (A) The cattle egret and the bison have a symbiotic relationship of mutualism, where both organisms benefit. The cattle egret gets the food from ticks and fleas, and as the bison provides that food, it gets the parasites off of its body. (B) Parasitism could only exist as the symbiotic relationship if the bird caused harm to the bison. (C) Commensalism cannot be the symbiotic relationship represented in this example because there is a direct benefit to both organisms. 3. C Correct Answer C: Plants are living organisms known as producers, which make their own food from nutrients in the soil and energy from the sun. Photosynthesis does not convert food from carbon and nitrogen. 4. D Correct Answer D: (D) Prokaryotic cells do not contain specialized, membrane bound organelles (ex: bacteria, blue-green algae and other primitive microorganisms). (A) Animal cells are eukaryotic cells which contain specialized, membrane-bound organelles. (B) Plant cells are eukaryotic cells which contain specialized, membrane-bound organelles. (C) Eukaryotic cells all contain specialized organelles which are membrane-bound (ex: plants, animals, fungi, etc). 5. A Correct Answer (A): All living things are composed of cells. Cells make up tissues, tissues make up organs, organs make up organ systems, and organ systems make up organisms.
6. D Correct Answer (D): (D) The circulatory system is responsible for transporting nutrients and water waste. (A) The immune system is responsible for protecting the body and fighting off diseases. (B) The digestive system is responsible for breaking down food to provide the body with energy. (C) The endocrine system is responsible for producing hormones used by the body. 7. B Correct Answer (B): (B) These are the six kingdoms. (A) These are the levels of organization of all living things. (C) These are all classes of animals. (D) These are all taxonomic groups. 8. B Correct Answer (B): (B) A genotype of Pp is a hybrid because it has two different alleles. (One is P and the other is p.). (A) A genotype of PP is not a hybrid. It is purebred because both alleles are the same (P, P). (C) A genotype of pp is not a hybrid. It is purebred because both alleles are the same (p, p). (D) These genotypes are both purebreds because their alleles are the same (P, P and p, p). 9. D Correct Answer D: (D) Two short alleles would result in a short plant. (tt) (A) Two tall alleles would result in a tall plant. (TT) (B) One short allele and one tall allele would result in a tall plant. (Tt) (C) Every trait has two alleles. 10. A Correct Answer A: (A) A Tt hybrid x a Tt hybrid would not show the recessive trait, but 25% of their offspring could have a genotype of tt and the recessive trait would be visible. (B) If one parent carried two of the recessive alleles (tt) and the other carried two of the dominant alleles (TT), all of their offspring would have a genotype of Tt. None of them would have the recessive trait. (C) If neither parent had the recessive allele, it would be impossible for their offspring to show the recessive trait. (D) If one parent had two of the dominant alleles (TT) and the other one was heterozygous (Tt) none of their offspring would show the recessive trait.