Grade 8 Science Term Examination Reviewer Flashcards

Vocabulary flashcards generated from the Grade 8 Science Examination Reviewer covering Genetics, Biogeochemical Cycles, and Atomic Structure.

Genetics

Study of heredity and variation.

Heredity

Passing traits from parents to offspring.

Trait

A characteristic of an organism.

Gene

A section of DNA that controls or contributes to a trait.

DNA

Molecule that carries genetic information.

Chromosome

Structure made mainly of DNA and proteins; genes are located on chromosomes.

Allele

An alternative form of a gene.

Genotype

The genetic makeup or allele combination.

Phenotype

The observable characteristic or trait.

Dominant allele

An allele expressed when present; usually written with a capital letter.

Recessive allele

An allele generally expressed when two copies are present; written with a lowercase letter.

Homozygous

Having two identical alleles: $AA$ or $aa$.

Heterozygous

Having two different alleles: $Aa$.

Mutation

A change in DNA.

Variation

Differences among individuals of the same species.

Law of Dominance

Mendel's principle stating that a dominant allele can mask the effect of a recessive allele.

Law of Segregation

Mendel's principle stating that the two alleles for a trait separate when reproductive cells form.

Law of Independent Assortment

Mendel's principle stating that alleles for different traits are distributed independently when the genes are not linked.

Complete dominance

A type of inheritance where one allele masks another.

Incomplete dominance

A type of inheritance resulting in an intermediate phenotype.

Codominance

A type of inheritance where both alleles are expressed.

Sex-linked inheritance

Inheritance where a gene is located on a sex chromosome.

Polygenic inheritance

Inheritance pattern where many genes contribute to one trait.

Photosynthesis

Process in which plants take in $CO_2$ and use light energy to make glucose ($C_6H_{12}O_6$) while releasing oxygen ($O_2$).

Respiration

Process in which organisms break down glucose to release energy and release $CO_2$.

Decomposition

Process where decomposers break down dead organisms and waste, returning carbon to soil and atmosphere.

Combustion

Burning wood and fossil fuels, which releases $CO_2$ and uses $O_2$.

Evaporation

Liquid water changing to water vapor, occurring mainly from bodies of water due to heat from the Sun.

Transpiration

Process where plants release water vapor through tiny openings in their leaves.

Condensation

Process where water vapor cools and changes into tiny liquid droplets, forming clouds.

Precipitation

Water falling from clouds as rain, snow, sleet, or hail.

Infiltration

Process where water enters the soil.

Percolation

Process where water moves deeper through soil and rocks.

Runoff

Water flowing over land into rivers, lakes, and oceans.

Evapotranspiration

The combined term for evaporation from bodies of water and transpiration from plants.

Atom

The smallest unit of an element that retains the properties of that element.

Proton

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

Neutron

A subatomic particle in the nucleus with a charge of $0$ and a relative mass of $1$.

Electron

A subatomic particle in the electron cloud with a charge of $-1$ and a relative mass of almost $0$.

Solid-sphere model

Atomic model proposed by John Dalton picturing matter made of tiny solid sphere atoms.

Plum-pudding model

Atomic model proposed by J. J. Thomson proposing electrons embedded in positively charged matter.

Nuclear model

Atomic model proposed by Ernest Rutherford following the gold-foil experiment, showing a tiny, dense, positively charged nucleus and mostly empty space.

Bohr / shell model

Atomic model proposed by Niels Bohr stating that electrons occupy specific energy levels or shells around the nucleus.

Electron-cloud / quantum model

Modern atomic model where electrons are described as likely to be found in regions called orbitals/electron clouds rather than fixed paths.

Atomic number

The number of protons in an atom.

Mass number

The total number of protons and neutrons in an atom.

Cation

A positive ion formed when an atom loses electrons.

Anion

A negative ion formed when an atom gains electrons.

Isotopes

Atoms of the same element with the same number of protons but different numbers of neutrons.

Valence electrons

Electrons in the outermost shell that strongly influence chemical behavior.

Group 1 (Alkali metals)

Elements in Group 1 of the periodic table; very reactive metals.

Group 17 (Halogens)

Elements in Group 17 of the periodic table; reactive nonmetals.

Group 18 (Noble gases)

Elements in Group 18 of the periodic table; generally unreactive because their outer electron arrangements are stable/full.