Comprehensive 9th Grade Biology & Chemistry Key Concepts

Characteristics of Life

Cellular organization, reproduction, metabolism, homeostasis, growth and development, response to stimuli, and adaptation/evolution.

Unicellular

An organism made of one cell.

Multicellular

An organism made of many cells.

Cell specialization

When cells develop structures and functions suited for specific jobs.

Tissue

A group of similar cells working together.

Organ

A structure made of different tissues working together.

Organ system

A group of organs working together to perform major functions.

Organelle

A specialized structure inside a cell that performs a specific function.

Plant cell

Usually has a cell wall, cell membrane, cytoplasm, nucleus, chloroplasts, mitochondria, ribosomes, and a large central vacuole.

Animal cell

Usually has a cell membrane, cytoplasm, nucleus, mitochondria, ribosomes, ER, Golgi apparatus, lysosomes, and smaller vacuoles.

Plant vs animal cells

Plant cells have a cell wall, chloroplasts, and usually a large central vacuole; animal cells do not.

Prokaryotic cell

Small, simple cell without a nucleus; DNA is located in the nucleoid region.

Eukaryotic cell

Cell with a nucleus and membrane-bound organelles.

Cell membrane function

Controls what enters and leaves the cell and helps maintain homeostasis.

Surface-area-to-volume ratio

The amount of cell surface compared with its internal volume; it decreases as a cell gets larger.

Diffusion

Particles move from high concentration to low concentration until equilibrium is reached.

Osmosis

The movement of water across a selectively permeable membrane from higher water concentration to lower water concentration.

Equilibrium

A condition in which particles are evenly distributed and there is no net movement.

Hypertonic

A solution with a higher solute concentration than another solution.

Hypotonic

A solution with a lower solute concentration than another solution.

Isotonic

A solution with equal solute concentrations on both sides of a membrane.

Endocytosis

A cell takes material into the cell by forming a vesicle from its membrane.

Exocytosis

A cell releases material by fusing a vesicle with the cell membrane.

ATP

Energy-rich molecule cells use to power many cellular processes.

Photosynthesis purpose

To convert light energy into chemical energy stored in glucose.

Photosynthesis equation

6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂.

Glycolysis

The first stage of cellular respiration; glucose is split into smaller molecules.

Krebs cycle

A series of reactions that helps extract energy from fuel molecules.

Electron transport chain

A series of proteins that helps produce large amounts of ATP.

Fermentation

An anaerobic process that allows cells to keep producing small amounts of ATP when oxygen is unavailable.

DNA shape

DNA has a double-helix structure.

DNA base pairing

A pairs with T; C pairs with G.

Central dogma

DNA → RNA → protein.

Mutation

A change in DNA.

Substitution

A mutation in which one DNA base is replaced by another.

Insertion

A mutation in which one or more bases are added.

Deletion

A mutation in which one or more bases are removed.

Frameshift mutation

An insertion or deletion that shifts the reading frame of codons.

Mutations can be

Beneficial, harmful, or neutral.

Genetic variation

Differences in DNA among individuals of a population.

Cell cycle

The series of events a cell goes through as it grows and divides.

G1 phase

Cell grows and performs normal functions.

S phase

DNA is copied.

G2 phase

Cell continues growing and prepares for division.

M phase

Cell division occurs.

Mitosis

Division of the nucleus that produces two genetically identical nuclei.

Prophase

Chromosomes condense and the spindle begins forming.

Metaphase

Chromosomes line up in the middle of the cell.

Anaphase

Sister chromatids separate.

Telophase

New nuclei form around the separated chromosomes.

Cytokinesis

The cytoplasm divides to form separate cells.

Mitosis purpose

Growth, repair, replacement, and asexual reproduction in some organisms.

Meiosis

Cell division that produces genetically different haploid sex cells.

Haploid

A cell containing one set of chromosomes.

Diploid

A cell containing two sets of chromosomes.

Crossing over

The exchange of DNA between homologous chromosomes during meiosis.

Why is meiosis important?

It produces gametes with half the chromosome number and increases genetic variation.

Mitosis vs meiosis

Mitosis produces 2 genetically similar diploid cells; meiosis produces 4 genetically different haploid cells.

Dominant allele

An allele that can determine the phenotype when at least one copy is present.

Recessive allele

An allele whose phenotype is generally expressed only when two copies are present.

Homozygous

Having two identical alleles for a gene.

Heterozygous

Having two different alleles for a gene.

Punnett square

A diagram used to predict possible offspring genotypes and phenotypes.

Monohybrid cross

A genetic cross involving one trait.

Probability

The likelihood that a particular outcome will occur.

Genotype ratio

The ratio of different genetic combinations predicted from a cross.

Phenotype ratio

The ratio of observable traits predicted from a cross.

Incomplete dominance

Neither allele completely masks the other, producing an intermediate phenotype.

Codominance

Both alleles are fully expressed in the phenotype.

Sex-linked trait

A trait controlled by a gene located on a sex chromosome.

Pedigree

A diagram used to track a trait through a family.

Genetic disorder

A condition caused by changes in genes or chromosomes.

Natural selection

Individuals with advantageous inherited traits tend to survive and reproduce more successfully.

Variation

Differences among individuals in a population.

Fitness

An organism's ability to survive and reproduce in its environment.

Selective pressure

An environmental factor that affects survival or reproduction.

Adaptation

An inherited characteristic that improves survival or reproduction.

Artificial selection

Humans choose which organisms reproduce based on desired traits.

Evidence for evolution

Fossils, comparative anatomy, embryology, molecular evidence, and biogeography.

Homologous structures

Structures with similar underlying anatomy because of common ancestry.

Analogous structures

Structures with similar functions but different evolutionary origins.

Vestigial structure

A reduced structure inherited from ancestors that has little or no current function.

Common ancestor

An ancestral organism shared by two or more groups.

Speciation

The formation of new species.

Population genetics

The study of how allele frequencies change in populations.

Ecology

The study of interactions between organisms and their environment.

Biosphere

The parts of Earth where life exists.

Habitat

The place where an organism normally lives.

Niche

An organism's role and position in its ecosystem.

Producer

An organism that makes its own food.

Primary consumer

An organism that eats producers.

Secondary consumer

An organism that eats primary consumers.

Tertiary consumer

An organism that eats secondary consumers.

Decomposer

An organism that breaks down dead material and returns nutrients to the environment.

Energy pyramid

A diagram showing energy available at different trophic levels.

10% rule

Approximately 10% of energy is transferred from one trophic level to the next.

Carbon cycle

The movement of carbon through organisms, atmosphere, water, and Earth.

Nitrogen cycle

The movement of nitrogen through the atmosphere, soil, and living organisms.

Water cycle

The continuous movement of water through evaporation, condensation, precipitation, and collection.

Greenhouse effect

The warming of Earth's surface caused by gases that absorb and re-emit infrared radiation.