GED Prep: Life Science (Cells, Genetics, Evolution, Ecosystems, Human Body)

GED – Life Science (Cells, Genetics, Evolution, Ecosystems, Human Body)

GED Life Science Study Guide: Cells, Genetics, Evolution, Ecosystems & Human Body

What This Is

Life Science on the GED tests your understanding of fundamental biological concepts, including cell structure, genetics, evolution, ecosystems, and human body systems. These topics appear in multiple-choice, drag-and-drop, and short-answer questions, often requiring you to interpret diagrams, analyze experiments, or apply concepts to real-world scenarios. For example, you might be asked: "A scientist observes that a population of bacteria becomes resistant to an antibiotic over time. Which process best explains this change?" This tests your knowledge of natural selection—a key concept in evolution.

Key Terms & Rules

Cells & Cell Processes

• Cell Theory: All living things are made of cells; cells are the basic unit of life; cells come from pre-existing cells.
• Prokaryotic vs. Eukaryotic Cells:
• Prokaryotic (bacteria, archaea) – No nucleus, no membrane-bound organelles.
• Eukaryotic (plants, animals, fungi, protists) – Has a nucleus and organelles (e.g., mitochondria, chloroplasts).
• Organelles & Functions:
• Mitochondria – "Powerhouse" (produces ATP via cellular respiration).
• Chloroplasts – Site of photosynthesis (plants only).
• Ribosomes – Make proteins (found in all cells).
• Cell Membrane – Selectively permeable barrier (controls what enters/exits).
• Osmosis & Diffusion:
• Diffusion – Movement of molecules from high → low concentration (no energy needed).
• Osmosis – Diffusion of water across a membrane.
• Active Transport – Requires energy (ATP) to move molecules against concentration gradient.

Genetics & Heredity

• DNA (Deoxyribonucleic Acid): Double helix structure; stores genetic information.
• Gene: Segment of DNA that codes for a protein (determines traits).
• Allele: Different versions of a gene (e.g., B for brown eyes, b for blue eyes).
• Genotype vs. Phenotype:
• Genotype – Genetic makeup (e.g., BB, Bb, bb).
• Phenotype – Physical trait (e.g., brown eyes).
• Punnett Square: Tool to predict offspring genotypes.
• Example: Bb × Bb → 25% BB, 50% Bb, 25% bb (3:1 phenotype ratio).
• Dominant vs. Recessive Alleles:
• Dominant (B) – Masks recessive allele (expressed if present).
• Recessive (b) – Only expressed if no dominant allele is present.
• Mutations: Random changes in DNA (can be harmful, neutral, or beneficial).

Evolution & Natural Selection

• Natural Selection (Darwin): Organisms with advantageous traits survive and reproduce more.
• Example: Peppered moths in England (dark vs. light coloration due to pollution).
• Adaptation: Inherited trait that improves survival (e.g., camouflage, thick fur in cold climates).
• Fossil Record: Evidence of evolution (shows changes in species over time).
• Homologous Structures: Similar structures in different species (e.g., human arm, bat wing, whale flipper) → common ancestor.
• Vestigial Structures: Remnants of organs with no current function (e.g., human appendix, whale pelvis).

Ecosystems & Ecology

• Biotic vs. Abiotic Factors:
• Biotic – Living (plants, animals, bacteria).
• Abiotic – Non-living (sunlight, water, temperature).
• Food Chain vs. Food Web:
• Food Chain – Linear sequence (e.g., grass → rabbit → fox).
• Food Web – Interconnected food chains (more realistic).
• Trophic Levels:
• Producers (plants, algae) – Make their own food (photosynthesis).
• Primary Consumers (herbivores) – Eat producers.
• Secondary Consumers (carnivores) – Eat primary consumers.
• Tertiary Consumers (top predators) – Eat secondary consumers.
• Decomposers (fungi, bacteria) – Break down dead matter.
• Energy Pyramid: Only 10% of energy transfers to the next trophic level (90% lost as heat).
• Symbiosis: Close relationship between species.
• Mutualism (+/+) – Both benefit (e.g., bees & flowers).
• Commensalism (+/0) – One benefits, other unaffected (e.g., barnacles on whales).
• Parasitism (+/-) – One benefits, other harmed (e.g., ticks on dogs).

Human Body Systems

• Homeostasis: Maintaining stable internal conditions (e.g., body temperature, blood sugar).
• Circulatory System:
• Heart – Pumps blood.
• Arteries – Carry blood away from heart (oxygen-rich, except pulmonary artery).
• Veins – Carry blood to heart (oxygen-poor, except pulmonary vein).
• Capillaries – Exchange gases/nutrients with cells.
• Respiratory System:
• Pathway: Nose → Pharynx → Larynx → Trachea → Bronchi → Lungs (alveoli).
• Alveoli – Tiny sacs where gas exchange occurs (O₂ in, CO₂ out).
• Digestive System:
• Mechanical Digestion – Chewing, stomach churning.
• Chemical Digestion – Enzymes break down food (e.g., amylase in saliva breaks down starch).
• Key Organs: Mouth → Esophagus → Stomach → Small Intestine (nutrient absorption) → Large Intestine (water absorption) → Rectum.
• Nervous System:
• Central Nervous System (CNS) – Brain & spinal cord.
• Peripheral Nervous System (PNS) – Nerves outside CNS.
• Neuron Structure: Dendrites (receive signals) → Cell body → Axon (sends signals).
• Endocrine System: Hormones regulate growth, metabolism, reproduction (e.g., insulin, adrenaline).

Step-by-Step / Process Flow

How to Answer a Genetics (Punnett Square) Question

1. Identify the parents’ genotypes (e.g., Bb × bb).
2. Set up the Punnett Square (4 boxes, one parent’s alleles on top, the other’s on the side).
3. Fill in the boxes (combine alleles from each parent).
4. Determine genotypic ratio (e.g., 2 Bb : 2 bb → 1:1 ratio).
5. Determine phenotypic ratio (e.g., 2 brown-eyed : 2 blue-eyed → 1:1 ratio).
6. Match to the answer choices (look for ratios or percentages).

How to Analyze an Evolution Question

1. Read the scenario carefully (e.g., "Finches on an island develop different beak shapes over time").
2. Identify the key concept (natural selection, adaptation, mutation).
3. Eliminate wrong answers (e.g., "acquired traits" is Lamarckism, not Darwinism).
4. Look for evidence (e.g., "beak shape changed due to food availability" → natural selection).
5. Choose the best answer (e.g., "The finches with beaks best suited to the available food survived and reproduced").

How to Interpret a Food Web Diagram

1. Identify producers (plants, algae – always at the base).
2. Trace energy flow (arrows point from food → eater).
3. Determine trophic levels (producer → primary consumer → secondary consumer, etc.).
4. Look for decomposers (usually at the side, breaking down dead matter).
5. Answer the question (e.g., "Which organism is a tertiary consumer?" → top predator).

Common Mistakes

Exam Insights

✅ Most-Tested Concepts:
- Cell organelles (mitochondria, chloroplasts, ribosomes).
- Punnett Squares & genetic inheritance (dominant/recessive, ratios).
- Natural selection & adaptations (e.g., camouflage, antibiotic resistance).
- Energy flow in ecosystems (food chains, 10% rule).
- Human body systems (circulatory, respiratory, digestive).

⚠️ Common Traps:
- Distractors with "acquired traits" (e.g., "Giraffes stretched their necks to reach leaves" – wrong, Lamarckism is not Darwinism).
- Confusing homologous & analogous structures (homologous = common ancestor; analogous = similar function, no relation).
- Misreading food web arrows (arrows point from food → eater, not the other way around).
- Assuming all mutations are harmful (some are neutral or beneficial).

? Tricky Distinctions:
- Prokaryotic vs. Eukaryotic (nucleus vs. no nucleus).
- Mitosis vs. Meiosis (mitosis = body cells, meiosis = sex cells).
- Primary vs. Secondary Succession (primary = no soil, e.g., after a volcano; secondary = soil present, e.g., after a fire).

Quick Check Questions

Question 1 (Genetics)

A pea plant with the genotype Tt (tall) is crossed with a tt (short) plant. What percentage of offspring will be tall? A) 0% B) 25% C) 50% D) 100%

✅ Answer: C) 50%
Explanation: A Tt × tt cross produces 50% Tt (tall) and 50% tt (short).

Question 2 (Evolution)

Which of the following is the best example of natural selection? A) A dog learns to sit for a treat.
B) A population of moths changes color due to pollution.
C) A lizard grows a longer tail after an injury.
D) A farmer breeds cows for higher milk production.

✅ Answer: B) A population of moths changes color due to pollution.
Explanation: Natural selection involves inherited traits that improve survival (e.g., dark moths surviving in polluted areas).

Question 3 (Ecosystems)

In a food chain: Grass → Grasshopper → Frog → Snake, which organism is the secondary consumer? A) Grass B) Grasshopper C) Frog D) Snake

✅ Answer: C) Frog
Explanation: The frog eats the grasshopper (primary consumer), making it the secondary consumer.

Last-Minute Cram Sheet

1. Cell Theory: All living things are made of cells; cells come from other cells.
2. Prokaryotic = no nucleus (bacteria); Eukaryotic = nucleus (plants, animals).
3. Mitochondria = energy (ATP); Chloroplasts = photosynthesis.
4. Osmosis = water diffusion; Active transport = requires energy.
5. Dominant (B) masks recessive (b); Punnett Squares predict offspring ratios.
6. Natural selection = survival of the fittest (e.g., antibiotic resistance).
7. 10% energy rule: Only 10% transfers to the next trophic level.
8. Arteries = away from heart; Veins = to heart.
9. Alveoli = gas exchange in lungs; Villi = nutrient absorption in small intestine.
10. ⚠️ GED traps:
11. "Acquired traits" (Lamarckism) is wrong for evolution questions.
12. Food web arrows point from food → eater.
13. Mutations aren’t always bad (can be neutral/beneficial).

Good luck—you’ve got this! ?