Biology: Cells, Body Systems, Inheritance and Ecosystems
Biology questions in Tottori often ask you to connect structure to function and to interpret data from a cross or a food web. The strands are 生物の体のつくりとはたらき, 生命の連続性, 遺伝, 生態系 and 細胞.
Cells and body systems
Cells are the basic unit of life. Plant cells have a cell wall, chloroplasts and a large vacuole; animal cells lack these. Photosynthesis in chloroplasts uses light, CO₂ and water to produce glucose and O₂. Respiration in mitochondria releases energy from glucose. Digestion breaks polymers into monomers: starch → glucose, protein → amino acids, fat → fatty acids and glycerol. Villi increase absorption area. Blood transports oxygen bound to hemoglobin; arteries carry blood away from the heart, veins return it.
Reproduction and genetics
Meiosis halves the chromosome number and makes gametes; fertilization restores the diploid number. Alleles separate during meiosis. A dominant allele masks a recessive one in heterozygotes. A cross Aa × Aa gives genotypes 1 AA : 2 Aa : 1 aa and phenotypes 3 dominant : 1 recessive.
Ecosystems
Producers capture energy; consumers transfer it; decomposers recycle nutrients. Energy flows one way and about 90% is lost at each level, so food chains are short. Matter cycles.
Worked example
Tall (T) is dominant to short (t). Cross Tt × Tt. Reasoning: a Punnett square gives TT, Tt, Tt, tt. Phenotypes are 3 tall : 1 short; genotypes are 1 TT : 2 Tt : 1 tt. The recessive phenotype appears only in tt.
Traps
- Confusing genotype ratio with phenotype ratio.
- Saying energy cycles instead of flows.
- Forgetting that meiosis halves the chromosome number.
- Swapping arteries and veins.
- Thinking plants respire only at night.