Life Science
What to Know
Life Science focuses on cells, heredity, evolution, and ecosystems. Cells are the basic unit of life; plant cells have cell walls and chloroplasts, while animal cells do not. Photosynthesis stores energy (CO2 + water + light → glucose + oxygen), and cellular respiration releases energy (glucose + oxygen → CO2 + water + ATP). DNA carries genetic information; genes are sections of DNA, alleles are versions of a gene, genotype is genetic makeup, and phenotype is observable traits. In sexual reproduction, meiosis produces gametes with half the chromosome number, while mitosis produces identical body cells. Natural selection requires variation, inheritance, and differential survival and reproduction. In ecosystems, producers make food, consumers eat it, and decomposers recycle nutrients; food webs show energy flow, and energy decreases at each trophic level.
Traps
- Swapping the photosynthesis and respiration equations.
- Confusing mitosis with meiosis.
- Mixing genotype and phenotype.
- Assuming dominant alleles are more common in a population.
- Treating food chains as if energy cycles rather than flows.
- Forgetting that decomposers are not the same as consumers.
Worked Example
Cross two heterozygous pea plants (Tt × Tt) for tallness, where T is dominant. A Punnett square gives TT, Tt, Tt, tt: 3 tall : 1 short, or 75% tall. Rule of thumb: meiosis halves chromosome number; mitosis keeps it the same.