Biology: Life Processes, Environments, and Heredity
Life processes and environments
Know the cell as the unit of life: nucleus (hereditary information), cytoplasm, cell membrane, and - in plant cells - cell wall, chloroplast, and vacuole. Photosynthesis makes glucose and oxygen from carbon dioxide and water using light, while respiration releases energy from glucose and oxygen and occurs day and night in every living cell. Enzymes break food into absorbable molecules; the small intestine absorbs nutrients, the liver stores and processes them, the kidneys filter wastes, and the heart drives blood with arteries leaving it and veins returning.
In ecosystems, energy flows from producers to consumers along food chains: arrows point in the direction energy travels (eaten → eater), and decomposers return mineral nutrients to the soil. Populations are limited by light, water, food, and predators, so removing one species reshapes the whole web.
Continuity of life
Cells divide by mitosis for growth and repair; gametes form by meiosis, halving the chromosome number, which fertilization restores. Genes on chromosomes carry traits, and a dominant trait masks a recessive one, producing the familiar 3 : 1 ratio in the second generation of a monohybrid cross.
Traps: claiming veins carry "deoxygenated blood" (the pulmonary vein carries oxygen-rich blood); implying plants respire only at night; drawing food-chain arrows backwards; confusing growth with reproduction.
Worked example. Cross pure-bred tall with pure-bred short: all F₁ are tall, so tall is dominant. Crossing two F₁ plants yields about 3 tall : 1 short.