Unit Four

4.1 Stimulus and Response

Vocabulary

auxin: plant hormone that speeds up the rate at which plant cells grow

geotropism: plant growth in response to gravity

homeostasis: keeping conditions constant inside the body

hormone: a chemical that affects an organisms growth and development

negative tropism: plant growth away from stimulus

phototropism: plant growth in response to light

positive tropism: plant growth toward stimulus

response: an action or change in behavior that occurs as a result of a stimulus

stimulus: any change in the environment that affects the activity of an organism. Examples include changes in light, sound, temperature and odor.

thigmotropism: plant tendrils can respond to the touch of a nearby limb and grow around the structure entwining like a vine

tropism: plant growth in response to a stimulus

turgor pressure: the pressure exerted by the water in a cell against the cell wall

wilt: the bending over of a plant due to lack of water

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4.2 Characteristics of Life

Vocabulary

accommodations: something supplied for convenience or to satisfy a need

astronaut: a person trained to be part of a spacecraft crew

atmosphere: the entire mass of air that surrounds the Earth made up of 78% nitrogen, 21% oxygen, and trace amounts of other gases

filter: a device through which a gas or liquid is passed that removes unwanted material

gravity: the force of attraction that pulls objects toward each other; the force that controls the motion of our solar system

International Space Station: space station that floats in orbit about 200 miles above Earth’s surface

microgravity: the almost complete absence of the feeling of gravity that can only be found in space or freefall

ozone: molecule made up of three atoms of oxygen

ozone layer: a thin concentration of ozone high in Earth’s atmosphere; protects life on Earth by absorbing ultraviolet radiation that causes sunburn, skin cancer, and cataracts in humans

proximity: closeness

spacesuit: also known as an extravehicular mobility unit; designed to regulate temperature and pressure, and provide oxygen and protection from the environment

vacuum: nearly empty of particles

4.3 Cells

Vocabulary

animal cell: eukaryotic cell, enclosed by a plasma membrane and containing a membrane-bound nucleus and organelles

cell: basic unit of structure and function in living things

cell membrane: structure that surrounds the cytoplasm of the cell

cell theory: idea that cells are the basic unit of structure in every living thing and that all cells come from other living cells.

cell wall: stiff outer barrier of a plant cell, outside the cell membrane, which is made mostly of cellulose

chloroplast: structure in a plant cell that contains chlorophyll; sugar molecules are made in chloroplasts through the process of photosynthesis

cytoplasm: gel-like fluid that takes up most of the space inside a cell

eukaryote: organisms made up of cells that have a membrane-bound nucleus and other organelles

homeostasis: keeping conditions constant inside the body, as in keeping a steady body temperature

mitochondria: structures in the cell that transform the energy in food into a form cells use to carry out their activities

nucleus: structure near the center of a cell that contains the cell’s DNA

organ: structure made of two or more different tissues which has a specialized function; for example the lungs

organ system: group of organs that work together to do a specific job for an organism, such as a digestive system

organism: a living thing

plant cell: eukaryotic cell enclosed by a cell wall for structure. Plant cells depend on chlorophyll and chloroplast for energy production.

prokaryote: one-celled organism that does not have a membrane-bound nucleus or organelles; includes all bacteria

tissue: in plants and animals, a group of cells that work together to do a specific job

vacuole: fluid-filled structure that holds waste products or substances needed by a cell

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