STAAR Organisms and the environment Middle School Science

Genetic traits Genes- a segment of DNA on a chromosome that contains information for specific genetic traits. Genes are passed from parents to offspring. Genetic trait- a characteristic passed on from a parent to offspring. Genetic traits that help organisms to survive in their environment are called adaptations. Adaptations can be either physical characteristics or behaviors.

How are genes passed from parents to offspring? During reproduction, the parents’ genes in the sex cells (egg & sperm) will create the new organism. This is called sexual reproduction. In sexual reproduction, both parents pass the genes for traits on to their offspring. Half the genes come from the male and half come from the female. Sexual reproduction results in genetic diversity due to the large number of gene combinations that may occur.

How are genes passed from parents to offspring? In Asexual reproduction, offspring arise from a single organism, and inherit the genes of that parent only; the offspring will be exact genetic copies of the parent.

Genes combine to produce different traits Each parent has genes that occur in pairs and only one of the alleles of a gene pair will be in each sex cell. Alleles are forms of the same gene. So the offspring receive one allele of a gene from the mother and one from the father. Alleles occur in two forms: dominant and recessive. If a dominant allele of a gene is present, the dominant trait will appear in the organism. A capital letter is used to show a dominant allele. For a recessive trait to be expressed, both alleles of the gene must be recessive. A lowercase letter is used to show a recessive trait. A pea plant will have purple flowers if it receives a dominant allele from one or both parents (Pp or PP). A plant will have white flowers only when both parents contribute an allele for the recessive trait (pp).

Ecosystem – includes the living & nonliving parts of an environment. Abiotic (Nonliving)- water, soil, light, air Biotic (Living) - plants, animals & other living organisms (makes up the community) Community – a group of different types or populations or plants, animals, & other organisms living & interacting with one another in an environment. Each population in a community lives in a particular part of that environment called a habitat. A habitat is the specific place in which an organism makes its home. As you move up the diagram, each level is more complex.

Each part of the community has its own function, but together they form the entire pond ecosystem. Organisms are connected by the energy that flows through the pond community. Both plants & animals require energy. This flow begins with the plants using energy from the sun and continues through all the organisms in an ecosystem.

Plants change radiant energy from the sun into chemical energy. Carbon dioxide and water are converted into sugar and oxygen. (Sugar is very important in an ecosystem- it’s food for plants & for other organisms. When plants are eaten, the energy in the plant matter is passed on to other organisms in the food chain.)

Chemical energy passes from plants to animals through a food chain Producers- (plants) organisms that make their own food Primary consumers- animals that get their energy from eating plants Secondary (second-order) consumers- animals that eat primary consumer animals.

Animals can be both a primary & secondary consumer.

Types of consumers  Herbivores- animals that eat only plants  Carnivores- animals that eat only other animals  Omnivores- animals that eat both plants & other animals

Decomposers Organisms that feed on dead plants & animals. This releases the chemical energy and nutrients in the dead plants and animals back into the environment. Decomposers play an important role in recycling nutrients & energy.

Food Chain- shows the flow of energy from one organism to another to yet another.

Food Chains The arrows show the direction of energy flow. The arrows point from what is being eaten to what is eating it.

Food Web A complex system of energy flow through overlapping food chains. Energy passes in many different directions through all the organisms.

Succession Succession can happen in any environment where change occurs. Other examples: a plowed farm field, a burned forest, or a grassland that gradually receives less rainfall. Rebuilding of populations in a community or ecosystem that has been changed.

Ecological Succession

A. possible gene combinations. A.Possible offspring traits are predicted based on combinations of the parents' genes for an individual trait. Use a _______ _______ to show the results of possible gene combinations. Punnett Square Glossy leaves are smooth and shiny. What percent of offspring from the cross shown will have glossy leaves? A.0% B.25% C.50% D.100% Gg gg Gg gg

When a trait has two forms and one trait or gene is expressed or shown over the other, the trait that shows this is said to be A. A.recessive. B. B.homozygous. C. C.dominant. D. D.pure. The hidden or masked trait in a gene combination is A. A.recessive. B. B.homozygous. C. C.dominant. D. D.pure. A capital letter written in a gene combination indicates that the gene is A. A.recessive. B. B.homozygous. C. C.dominant. D. D.pure.

The growth of weeds on rock exposed by a recent landslide is an example of A.competition B.adaptation C.succession D.mutualism

Why do you think decomposers play an important role in the cycling of matter through the ecosystem? A.The decomposers’ excreta are full of nutrients that enrich the soil. B.Decomposers’ remains mix with the soil to enrich it with nutrients. C.Decomposers break down remains of living things and release nutrients back into the ecosystem. D.Decomposers add nutrients to the air and soil through breathing.

Which of the following is a biotic factor in a typical lake environment? A.water B.sunfish C.mud D.sunlight

Light is an essential abiotic factor that can strongly influence the health of an ecosystem. In stands of fir trees, the dense foliage of these trees blocks light from reaching the forest floor. Which of the following organisms would be affected first? A.primary consumers B.producers C.decomposers D.secondary consumers