Semester One Life Science Revision Flashcards

Comprehensive vocabulary flashcards covering Biology (DNA, genetics, evolution) and Environmental Science (ecosystems, nutrient cycles, climate change) as outlined in the Year 10 Semester One Revision Pack.

DNA

Deoxyribonucleic acid; the double helix structure that carries genetic information and is organized into chromosomes within cells.

Nucleotide

The basic building block of DNA, consisting of a deoxyribose sugar, a phosphate group, and one of four nitrogenous bases.

Nitrogenous bases

The four types of bases in DNA: adenine ($A$), thymine ($T$), guanine ($G$), and cytosine ($C$).

Complementary base pairs

The specific pairing arrangement in DNA where adenine always pairs with thymine ($A=T$) and guanine always pairs with cytosine ($G=C$).

Double helix

The twisted-ladder shape of the DNA molecule.

Antiparallel

A term describing the opposite orientations of the two strands in a DNA double helix.

Gene

A section of DNA which codes for a particular set of instructions to produce a specific protein.

Chromosome

A thread-like structure made of DNA and proteins, found in the nucleus, which carries genetic information.

Chromatid

One of the two identical halves of a duplicated chromosome.

Centromere

The region of a chromosome where two sister chromatids are joined together.

RNA

Ribonucleic acid; a single-stranded nucleic acid containing the nitrogenous base uracil ($U$) instead of thymine ($T$).

Transcription

The first stage of protein synthesis occurring in the nucleus, where DNA unzips and a complementary mRNA strand is created.

Translation

The second stage of protein synthesis occurring in the cytoplasm at the ribosome, where mRNA codons are used to assemble amino acids into a protein.

mRNA

Messenger RNA; copies the genetic code from DNA in the nucleus and carries it to the ribosomes.

tRNA

Transfer RNA; brings specific amino acids to the ribosome during translation by matching its anticodon to the mRNA codon.

Codon

A sequence of three nitrogenous bases on mRNA that codes for a specific amino acid.

Anticodon

A sequence of three bases on tRNA that is complementary to a codon on mRNA.

Amino acid

The building blocks of proteins, bonded together during translation.

Somatic cells

General body cells that are diploid, meaning they contain two sets of chromosomes.

Gametes

Sex cells (sperm and eggs) that are haploid, meaning they contain only one set of chromosomes.

Diploid

A cell containing two complete sets of chromosomes ($2n$); in humans, this number is $46$.

Haploid

A cell containing a single set of chromosomes ($n$); in humans, this number is $23$.

Interphase

The stage of the cell cycle where DNA replication takes place.

Mitosis

Cell division resulting in two genetically identical diploid daughter cells, used for growth and repair.

Meiosis

Cell division resulting in four genetically unique haploid gametes.

Allele

An alternative form of a gene located at the same position on a chromosome.

Genotype

The genetic makeup of an organism, represented by pairs of alleles (e.g., $TT$, $Tt$, or $tt$).

Phenotype

The observable physical characteristics or traits of an organism, determined by its genotype and environment.

Homozygous

An individual having two identical alleles for a particular gene (e.g., $GG$ or $gg$).

Heterozygous

An individual having two different alleles for a particular gene (e.g., $Gg$).

Mutation

A change that occurs at the DNA level within a gene or chromosome that is inheritable.

Mutagen

An agent, such as radiation (X-rays, UV) or chemicals (tobacco, benzene), that causes genetic mutations.

Karyotype

An image of a person's chromosomes arranged in order of size used to identify chromosomal abnormalities.

Natural Selection

The process where individuals with favorable traits are more likely to survive and reproduce, passing those alleles to the next generation.

Evolution

The process by which species change over time through mechanisms like natural selection, mutation, gene flow, and genetic drift.

Speciation

The evolutionary process by which new and distinct species are formed.

Homologous structures

Organs or skeletal elements of animals and organisms that, by virtue of their similarity, suggest connection to a common ancestor.

Analogous structures

Structures that look similar and have similar functions but evolved separately due to similar selection pressures, not a common ancestor.

Divergent evolution

When two or more species sharing a common ancestor become more different over time.

Convergent evolution

When unrelated species evolve similar traits because they occupy similar environments or face similar selection pressures.

Ecosystem

A system of living organisms (biotic) interacting with one another and with their non-living (abiotic) surroundings.

Abiotic factors

Non-living components of an ecosystem, such as temperature, light intensity, rainfall, and pH.

Biotic factors

The living components of an ecosystem, including all organisms and biological waste.

Producer (autotroph)

An organism that harnesses the Sun's energy through photosynthesis to create its own food.

Consumer (heterotroph)

An organism that eats other organisms to obtain energy.

Decomposer

An organism, like bacteria or fungi, that breaks down the dead remains of organisms and cycles nutrients.

Carrying capacity

The maximum population size of a species that an ecosystem can sustainably support.

Eutrophication

A process where nutrient-rich water (often from fertilizers) causes excessive algal growth, depleting oxygen and harming aquatic life.

Natural Greenhouse effect

A natural process where greenhouse gases like $CO_2$ and methane trap heat in the atmosphere, keeping Earth warm enough for life.

Enhanced Greenhouse effect

Global warming caused by human activities (burning fossil fuels, deforestation) that results in increased levels of greenhouse gases trapping more heat.