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Biology LibreTexts

25.15: Glossary: O

  • Page ID
  • obesity

    disease in which the body mass index (BMI) is greater than 30.0 kg/m2


    anything that is detected through human senses or with instruments and measuring devices that enhance human senses

    observational study

    type of nonexperimental scientific investigation in which the researcher measures characteristics in a sample but does not attempt to manipulate or control variables of interest

    occipital lobe

    part of each hemisphere of the cerebrum that is dedicated almost solely to vision

    old age

    last stage of human adulthood that lasts from the mid-60s until death

    olfactory receptor

    chemoreceptor in the nasal passages that detects chemicals in the air


    consumer that eats both plants and animals


    process of producing eggs in the ovaries of a female fetus

    oogonium (plural, oogonia)

    diploid stem cell in an ovary that undergoes mitosis to begin the process of oogenesis


    drug derived from the opium poppy or a synthetic version of such a drug, including heroin and painkillers such as codeine, morphine, or OxyContin

    opportunistic disease

    disease that rarely occurs except in people with a compromised immune system, such as people infected with HIV


    structure composed of more than one type of tissue that performs a particular function, such as the brain, kidney, or heart


    structure within the cytoplasm of a eukaryotic cell that is enclosed within a membrane and performs a specific job

    organic compound

    compound found in or derived from living things that contains mainly carbon


    individual living thing


    process in which organs develop in an embryo

    organ system

    group of organs that work together to do a certain job


    diffusion of water molecules across a membrane


    process in which cartilage is changed into bone


    joint disorder that results from the breakdown of joint cartilage and bone, most often due to wear and tear on joints


    type of bone cell that makes and mineralizes bone matrix


    endocrine hormone secreted by bone cells that helps to regulate blood glucose and fat deposition


    type of bone cell that breaks down bone, dissolves its minerals, and releases them into the blood


    type of bone cell that helps regulate the formation and breakdown of bone tissue

    osteogenic cell

    type of stem cell that can divide and differentiate to form new bone cells


    disorder that generally occurs in older adults in which bones lose minerals, become brittle, and break easily

    ovarian cycle

    events of the menstrual cycle that occur in the ovaries, including maturation of a follicle, ovulation, and development of the corpus luteum

    ovarian follicle

    functional unit of an ovary that consists of a nest of epithelial cells surrounding an egg


    one of a pair of female reproductive organs that produces eggs and secretes estrogen


    use of a natural resource at an unsustainable rate, such as over-fishing or overly intensive use of soils for farming


    condition in which population size is too large to be supported by available resources without damaging the environment


    release of a secondary oocyte from an ovary about half way through the menstrual cycle


    endocrine hormone secreted by the pituitary gland that functions during childbirth to stimulate uterine contractions