Grade 8 Science Reviewer: Photosynthesis, Respiration, Cycles in Nature, and Atomic Model

A comprehensive vocabulary review of key scientific concepts including photosynthesis, cellular respiration, natural cycles, experiment design variables, atomic model developments, and atomic structure.

Photosynthesis Equation

The chemical equation represented by $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$, using light energy and chlorophyll.

Respiration Equation

The chemical equation represented by $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP}$.

Chloroplasts

Organelles in plant cells where photosynthesis occurs, consisting of an outer membrane, inner membrane, thylakoid (grana), and stroma.

Mitochondria

Organelles in plant and animal cells where cellular respiration occurs, consisting of an outer membrane, inner membrane, cristae, and matrix.

Thylakoid (grana)

Structures located inside chloroplasts where parts of photosynthesis take place.

Stroma

The fluid-filled space surrounding the thylakoids inside a chloroplast.

Cristae

The folds of the inner membrane of a mitochondrion.

Matrix

The space enclosed by the inner membrane of a mitochondrion.

Evaporation

The stage in the water cycle where liquid water turns to vapor.

Condensation

The stage in the water cycle where clouds form from water vapor.

Precipitation

Rain or snow falling to the earth in the water cycle.

Transpiration

The process in the water cycle where plants release water vapor into the air.

Soda Lime

A substance used in photosynthesis experiments to absorb carbon dioxide ($CO_2$).

Iodine Solution

A chemical solution used to test leaves for starch, which turns a blue-black color if starch is present.

Independent Variable (Investigation)

The factor intentionally changed in an experiment, such as the amount/availability of $CO_2$.

Dependent Variable (Investigation)

The factor measured for changes in an experiment, such as the presence of starch.

Democritus

Greek philosopher (c. 400 BCE) who proposed that matter is made of tiny, indivisible particles called atomos.

John Dalton

Scientist (~1803) who developed the first modern atomic theory and proposed the Solid Sphere Model, stating atoms are solid, indivisible, and unique to each element.

J. J. Thomson

Scientist (~1897) who discovered the electron and proposed the "plum pudding model" featuring electrons inside a positively charged sphere.

Ernest Rutherford

Scientist (1911) who conducted the Gold foil experiment and proposed the Nuclear Model, showing a small, dense, positive nucleus and mostly empty space.

Niels Bohr

Scientist (1913) who proposed the Bohr Model, stating that electrons move in specific energy levels or shells around the nucleus.

Modern Atomic Model

The Electron Cloud Model (~1926-Present), which states that electrons are found in regions of probability called electron clouds.

Proton ($p^+$)

A subatomic particle located in the nucleus with a relative mass of $\approx 1$ and a positive charge of $+1$.

Neutron ($n^0$)

A subatomic particle located in the nucleus with a relative mass of $\approx 1$ and no charge ($0$).

Electron ($e^-$)

A subatomic particle located in electron shells outside the nucleus with a relative mass of $\approx 1/1836$ and a negative charge of $-1$.

Nucleus

The dense central structure of an atom that contains protons and neutrons.

Electron Shells

Regions outside the nucleus where electrons are located.