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7th Grade Science Benchmark Study Guide
End of 3rd Quarter
Investigation & Experimentation
 Information obtained from government or education Web sites is usually the most reliable.
 A scientific theory is an explanation of things or events that is based on knowledge gained from many
observations and investigations.
 A lab report should include a problem, hypothesis, materials, procedure, data, and conclusion.
 To view the smallest organisms, an electron microscope is the best tool.
Cells
 The cell theory states that:
1. All new cells come from preexisting cells.
2. The cell is the smallest unit of life.
3. All organisms are made of one or more cells.
 Organelles that are common to both plant and animal cells include the cell membrane, cytoskeleton, nucleus,
ribosomes, ER, and Golgi apparatus.
 Genetic information is stored in chromosomes, which are located inside the nucleus of plant and animal cells.
 The organelles that release energy for cell functions are the mitochondria.
 The organelles that use sunlight energy to make food are the chloroplasts.
 Label the plant cell diagram to the right.
A
A. central vacuole
B. chloroplast
C. nucleus
C
B
Reproduction
 Multicellular organisms grow when their number of cells increases.
 The cell cycle includes SIX phases: interphase, prophase, metaphase, anaphase, telophase, cytokinesis
 MITOSIS includes these FOUR phases: prophase, metaphase, anaphase, telophase
 The levels of organization from MOST complex to LEAST complex are:
organism  organ system  organ  tissue  cell
 A group of cells that work together to perform a function is called a tissue.
 In mitosis, division of the nucleus and cytokinesis happens once, producing two daughter cells.
 In meiosis, division of the nucleus and cytokinesis happen twice, producing four daughter cells.
 If a diploid cell has 20 chromosomes, its sex cells will have the haploid number, which is 10 (half of 20).
 In a flower, the female reproductive part is the pistil, which is made up of the stigma, style, and ovary.
 In a flower, the male reproductive part is the stamen, which is made up of the anther and filament.
 In a flower, after fertilization occurs, the ovary becomes fruit surrounding the seed.
Genetics
 A dominant allele is a genetic factor that blocks another genetic factor.
 A recessive allele is a genetic factor that is hidden by the presence of a dominant factor.
 Examples of each of the following genotypes:
 homozygous recessive = tt
 homozygous dominant = TT
 heterozygous = Tt
 Incomplete dominance involves alleles that produce a phenotype that is a blended form of the parents’
phenotypes.
 Multiple alleles involves a situation when more than two alleles are found on a gene.
 Polygenic inheritance is a situation when multiple genes determine the phenotype of a trait.
Evolution and its Evidence
 Natural selection is the process that allows for only some individuals to survive when there are limited
resources, such as food, water, and habitat.
 Natural selection acts on genetic variation of individuals in a population.
 Evolution can take place when two things are present in a species: genetic variation and environmental factors
 Inherited traits that increase an organism’s chance of surviving and reproducing in a particular environment are
called adaptations.
 Extinction occurs when all the individuals of a particular species die off.
 Fossils are the remains or traces of once-living organisms.
 The depth of a fossil in the rock layer tells us approximately how old it is.
 The fossil record is the history of all known fossils and their placements in the formation of rocks and positions
in time.
 The fossil record tells us:
1. Species have evolved through natural selection.
2. Most species that lived on Earth are extinct.
3. Environmental conditions on Earth have changed much.
4. In Earth’s early history, life was less complex.
 The wings of insects and birds are examples of analogous structures.
 The bone structure of human forearms and cat forearms are examples of homologous structures.
 Homologous structures can indicate how closely species share a common ancestor.
 The human appendix and the whale pelvis are examples of vestigial structures.
 The classification hierarchy (from largest to smallest): domain, kingdom, phylum, class, order, family, genus,
species.
 The movement of lithospheric plates can lead to the evolution of a new species because of the changing
environmental conditions it creates.
 The rock cycle is a process that includes heating, melting, cooling, uplift, weathering, and increasing pressure.
 Relative age is an estimation of age made by comparing position or characteristics of two objects.
 Absolute age is a more specific way of determining age and the process of radiometric dating is used.
 Scientists estimate that the Earth and its moon are approximately the same age: 4.6 billion years old.