Biology How Scientists Work

Designing an experiment Asking a question ◦ How do new living things, or organisms, come into being? Forming a Hypothesis ◦ Spontaneous generation- a disproven hypothesis stating that life could arise from nonliving matter ◦ Hypothesis-possible explanation for a set of observations or possible answer to a scientific question.

Setting up a controlled Experiment ◦ Controlled experiment- a test of a single variable by changing it while keeping all other variables the same. ◦ Manipulated variable- the variable that is deliberately changed. ◦ Responding variable- the variable that is observed and that changes in response to the manipulated variable. Recording and analyzing results Drawing a conclusion Publishing and repeating investigations

Why are controlled experiments sometimes not possible? To learn how animals in the wild interact with others in their group. Ethical considerations

How do Theories Develop? Theory-a well-tested explanation that unifies broad range of observations. A theory enables scientists to make accurate predictions about new situations. What is your theory on why marsupial mammals are only found in Australia and nearby islands? A theory may sometimes become a dominant view among people but is never considered an absolute truth.

Characteristics of living things Living things are made up of units called cells. Living things reproduce. Living things are based on a universal genetic code Living things grow and develop Living things obtain and use materials and energy Living things respond to their environment Living things maintain a stable internal environment. Taken as a group, living things change over time. What characteristics of living things are missing from a fire?

Made up of cells Cell- a collections of living matter enclosed by a barrier that separates the cell from its surroundings. Unicellular organisms- made up of one cell Multicellular organisms – made up numerous cells, each type of cell is specialized to perform a different function. The human body alone has 85 different cell types.

Reproduction Sexual Reproduction- two cells from different parents unite to produce the first cell of a new organism Asexual reproduction- the new organism has a single parent, sometimes a single cell divides in half to form two new organisms, sometimes a portion of an organism splits off to form a new organism.

Based on a genetic code Asexual reproduction, offspring and their parents have the same traits. Sexual reproduction, offspring differ from their parents in some ways. Directions for inheritance are carried by a molecule called DNA.

Growth and Development For many organisms development includes period of rapid and dramatic change.

Needs for materials and energy What do organisms need in order to grow and develop? Metabolism- the combination of chemical reactions through which an organism builds up or breaks down materials as it carries out its life processes.

Response to environment Organisms detect and respond to stimuli from their environment. External Stimulus- A signal from the environment outside an organism, include factors such as light and temperature. Internal Stimulus- A stimulus that occurs from inside the body. What stimuli are you experiencing right now?

Maintaining internal Balance Homeostasis-a process by which organisms maintain a relatively stable internal environment. Example- When your body needs more water to maintain homeostasis, internal stimuli make you feel thirsty What are some other examples?