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Pathogen

A microorganism that causes disease.

Bacteria

Single-celled organisms; some cause disease.

Virus

Tiny infectious particles that need a host cell to reproduce.

Fungus

Organisms like yeast or mold that can cause infections.

Protozoa

Single-celled organisms that can infect humans.

Primary defense

First barriers like skin and mucus that block pathogens.

Sebaceous glands

Glands in the skin that produce oils to stop pathogen growth.

Mucous membranes

Tissues that trap pathogens in sticky mucus.

Blood clotting

Process that stops bleeding by forming a clot.

Platelets

Small cell fragments that help form blood clots.

Clotting factors

Proteins in blood that help form clots.

Prothrombin

Inactive protein that changes into thrombin during clotting.

Thrombin

Enzyme that converts fibrinogen to fibrin.

Fibrinogen

A blood protein that changes into fibrin during clotting.

Fibrin

Sticky threads that form a mesh to seal a wound.

Innate immunity

Fast, general defense you're born with.

Adaptive immunity

Slower, targeted defense that improves with exposure.

Phagocyte

White blood cell that engulfs and digests pathogens.

Macrophage

Large phagocyte that eats pathogens and shows antigens.

Lymphocyte

White blood cell involved in adaptive immunity.

Antibody

A protein made by lymphocytes to fight specific pathogens.

Antigen

A molecule that triggers an immune response.

Specific immune response

A targeted attack on a particular pathogen.

ABO blood group

Classification of blood based on antigens (A, B, AB, O).

Agglutination

Clumping of cells, often by antibodies.

Hemolysis

Breaking down of red blood cells.

Helper T lymphocyte

White blood cell that activates other immune cells.

B lymphocyte

White blood cell that produces antibodies.

Plasma cell

Activated B cell that makes lots of antibodies.

Clonal selection

Process of selecting and copying immune cells that recognize an antigen.

Memory cell

Immune cell that stays in the body to respond faster to future infections.

Immunity

The ability to resist disease.

HIV

Virus that attacks the immune system.

AIDS

Condition caused by HIV where the immune system fails.

Antibiotic

Medicine that kills or stops bacteria.

Antibiotic resistance

When bacteria evolve to survive antibiotics.

Zoonosis

Disease that spreads from animals to humans.

Immunization

Giving a vaccine to protect against disease.

Vaccine

A weak or dead pathogen used to stimulate immunity.

Herd immunity

Protection for unvaccinated people when most of the population is immune.

R₀ (R-naught)

Number showing how many people one sick person can infect.

Percentage change

How much a value increases or decreases in percent.

Percentage difference

How much two values differ compared to their average.

Sexual reproduction

Reproduction involving two parents and the joining of gametes.

Asexual reproduction

Reproduction involving one parent; offspring are identical copies.

Meiosis

Cell division that makes gametes with half the usual number of chromosomes.

Fertilization

The joining of a sperm and an egg to form a zygote.

Gamete

A sex cell (sperm or egg) with half the chromosomes.

Zygote

A fertilized egg cell.

Motility

The ability to move.

Testis

Organ in males that makes sperm.

Scrotum

Skin sac that holds the testes outside the body.

Epididymis

Coiled tube where sperm mature and are stored.

Sperm duct

Tube that carries sperm from the epididymis to the urethra.

Seminal vesicle

Gland that adds fluid to sperm to make semen.

Prostate gland

Adds more fluid to semen.

Urethra

Tube that carries semen or urine out of the body.

Penis

Male reproductive organ that delivers sperm.

Ovary

Organ in females that produces eggs and hormones.

Uterus

Organ where a fertilized egg develops into a baby.

Vulva

The external female genital area.

Vagina

Muscular canal leading from the cervix to the outside of the body.

Cervix

Opening between the uterus and vagina.

Oviduct

Tube where fertilization usually occurs; connects ovary to uterus.

Ovarian cycle

Monthly changes in the ovary that lead to egg release.

Uterine cycle

Monthly changes in the uterus to prepare for pregnancy.

Menstrual cycle

The full cycle of changes in ovaries and uterus (~28 days).

FSH (Follicle-stimulating hormone)

Hormone that helps eggs mature in the ovary.

LH (Luteinizing hormone)

Hormone that triggers ovulation.

Estrogen

Hormone that builds up the uterine lining.

Progesterone

Hormone that maintains the uterine lining.

Corpus luteum

Structure in the ovary that makes progesterone after ovulation.

In vitro fertilization (IVF)

Fertilization that happens outside the body in a lab.

In vivo fertilization

Fertilization that happens inside the body.

Oestradiol

A type of estrogen important in the menstrual cycle.

Pollination

Transfer of pollen to the female part of a flower.

Fertilization (plant)

Joining of a sperm (from pollen) and an egg in a flower.

Petal

Colored part of a flower that attracts pollinators.

Sepal

Leaf-like part that protects the flower bud.

Stamen

Male part of the flower that makes pollen.

Anther

Tip of the stamen that makes pollen.

Filament

Stalk that holds up the anther.

Carpel

Female part of the flower.

Stigma

Sticky part of the carpel where pollen lands.

Style

Tube that connects the stigma to the ovary.

Ovary (flower)

Bottom part of the carpel that holds ovules.

Ovule

Structure inside the ovary that becomes a seed after fertilization.

Cross-pollination

Pollen from one plant fertilizes a flower on a different plant.

Self-incompatibility

A plant's ability to avoid fertilizing itself.

Seed dispersal

Spreading seeds away from the parent plant.

Germination

When a seed starts to grow.

Gibberellin

Plant hormone that helps seeds germinate.

Haploid

A cell with one set of chromosomes (like gametes).

Diploid

A cell with two sets of chromosomes (like most body cells).

Genetic cross

A diagram showing the possible offspring from parents.

P generation

The parent generation in a genetic cross.

F1 generation

The first generation of offspring from the parents.

F2 generation

The second generation, or offspring of the F1 generation.

Allele

A version of a gene (e.g., the gene for eye color can have a blue or brown allele).

Homozygous

Having two of the same allele for a gene.