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Life Science

Study Guide

Life science makes up about 40% of the GED Science test. You need to understand cell structure, genetics, evolution, ecosystems, and how the human body works.

1Cell Structure and Function

All living things are made of cells. Plant cells have a cell wall and chloroplasts; animal cells do not. Both have a nucleus (contains DNA), cell membrane, mitochondria (energy), and cytoplasm.

Examples:

•Nucleus: control center, contains DNA
•Mitochondria: produce energy (cellular respiration)
•Cell membrane: controls what enters and leaves the cell
•Chloroplasts: found only in plant cells, perform photosynthesis
•Ribosomes: make proteins
2Genetics and DNA

DNA carries genetic information. Genes are segments of DNA that code for traits. You inherit one allele (version of a gene) from each parent. Dominant alleles (capital letter) mask recessive alleles (lowercase).

Examples:

•Genotype: the genetic makeup (Bb, BB, bb)
•Phenotype: the physical expression (brown eyes, blue eyes)
•Bb × Bb → 25% BB, 50% Bb, 25% bb (Punnett square)
•DNA → RNA → Protein (central dogma of biology)
3Natural Selection and Evolution

Evolution is the change in species over time. Natural selection is the mechanism: organisms with favorable traits survive and reproduce more, passing those traits to offspring.

Examples:

•Variation exists in every population
•Some variations are advantageous in a given environment
•Organisms with advantageous traits survive longer and reproduce more
•Over many generations, the population changes
4Ecosystems and Energy Flow

Energy flows through ecosystems: Sun → Producers (plants) → Consumers (animals) → Decomposers. Food chains and food webs show these relationships. Only about 10% of energy transfers from one level to the next.

Examples:

•Producers (autotrophs): make their own food via photosynthesis
•Primary consumers: herbivores that eat plants
•Secondary consumers: carnivores that eat herbivores
•Decomposers: break down dead organisms, recycle nutrients
5Human Body Systems

The human body has several organ systems that work together. Key systems: circulatory (heart, blood), respiratory (lungs), digestive (stomach, intestines), nervous (brain, nerves), immune (white blood cells).

Examples:

•Circulatory: transports oxygen, nutrients, and waste
•Respiratory: exchanges oxygen and carbon dioxide
•Digestive: breaks down food into nutrients
•Nervous: sends and receives signals, controls body functions
•Immune: defends against pathogens (disease-causing organisms)
Test-Taking Tips
GED science questions often include diagrams — practice reading charts, graphs, and scientific diagrams.
Focus on understanding concepts, not memorizing facts. The GED tests your ability to reason scientifically.
Know the difference between a hypothesis (testable prediction), a theory (well-supported explanation), and a law (description of a pattern in nature).
Remember: correlation does not equal causation.