Key Takeaways
- Living things: cells, growth, reproduction, response, energy use, adaptation
- Plant cells have cell walls and chloroplasts; animal cells do not
- Food chain: Producers → Consumers → Decomposers
- Heredity = passing traits through genes/DNA
- Body systems work together (circulatory transports, respiratory exchanges gases)
Last updated: January 2026
4.2 Life Science
Life Science covers about 33% of the Science subtest, including living things, ecosystems, and the human body.
Characteristics of Living Things
All living things:
- Are made of cells
- Grow and develop
- Reproduce
- Respond to their environment
- Use energy (metabolism)
- Adapt over time
Cell Structure
Plant vs. Animal Cells:
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell wall | Yes | No |
| Chloroplasts | Yes | No |
| Large central vacuole | Yes | Small vacuoles |
| Shape | Rectangular | Round/irregular |
Basic cell parts:
- Nucleus: Control center, contains DNA
- Cell membrane: Controls what enters/exits
- Cytoplasm: Gel-like fluid
- Mitochondria: "Powerhouse" - produces energy
Ecosystems
Key terms:
| Term | Definition |
|---|---|
| Ecosystem | Community of organisms + their environment |
| Habitat | Place where an organism lives |
| Niche | Organism's role in the ecosystem |
| Population | All organisms of one species in an area |
| Community | All populations in an area |
Food Chains and Webs:
- Producer: Makes own food (plants, algae)
- Consumer: Eats other organisms
- Herbivore: Eats plants
- Carnivore: Eats animals
- Omnivore: Eats both
- Decomposer: Breaks down dead organisms (fungi, bacteria)
Energy Flow: Sun → Producers → Primary Consumers → Secondary Consumers → Decomposers
Heredity and Adaptation
Heredity: Passing of traits from parents to offspring
- Gene: Unit of heredity
- DNA: Genetic material
- Trait: Characteristic (eye color, height)
Adaptation: Characteristics that help organisms survive
- Camouflage
- Mimicry
- Structural adaptations (thick fur, webbed feet)
- Behavioral adaptations (migration, hibernation)
Human Body Systems
| System | Function | Key Organs |
|---|---|---|
| Circulatory | Transport blood, nutrients, oxygen | Heart, blood vessels |
| Respiratory | Gas exchange (O2 in, CO2 out) | Lungs, diaphragm |
| Digestive | Break down food, absorb nutrients | Stomach, intestines |
| Skeletal | Support, protection | Bones |
| Muscular | Movement | Muscles |
| Nervous | Control body, process information | Brain, nerves |
Test Your Knowledge
Which cell structure is found in plant cells but NOT in animal cells?
A
B
C
D
Test Your Knowledge
In a food chain, what is the role of decomposers?
A
B
C
D
Test Your Knowledge
Which body system is responsible for transporting oxygen throughout the body?
A
B
C
D