Reproduction in Biology - IB HL

This array of flashcards is designed to help students review key vocabulary terms and concepts related to reproduction in biology, focusing on both sexual and asexual reproduction, gametogenesis, hormonal control, and related processes.

Sexual Reproduction

Involves two parents contributing genetic material through the fusion of specialized sex cells (gametes) to form a unique offspring (zygote), resulting in genetically diverse individuals.

Asexual Reproduction

Involves a single parent producing offspring that are genetically identical to itself and each other, without the fusion of gametes.

Gamete

A specialized haploid sex cell (e.g., sperm or egg in animals, pollen nucleus or ovum in plants) that fuses with another gamete during fertilization to form a zygote.

Haploid

A cell (like a gamete) that contains only one set of chromosomes (denoted as n), which is half the number of chromosomes found in diploid body cells (e.g., 23 chromosomes in human gametes).

Diploid

A cell (like a somatic cell or zygote) that contains two complete sets of chromosomes (denoted as 2n), one set inherited from each parent (e.g., 46 chromosomes in human body cells).

Zygote

The single diploid cell formed by the successful fusion of a male gamete (sperm) and a female gamete (egg) during fertilization; it is the first cell of a new organism.

Clones

Organisms that are genetically identical to their parent and to each other, typically produced through asexual reproduction or artificial cloning techniques.

Binary Fission

A form of asexual reproduction primarily in prokaryotic organisms (like bacteria) where a single cell divides into two genetically identical daughter cells.

Fertilization

The process involving the fusion of the male gamete's (sperm) nucleus with the female gamete's (egg) nucleus to form a diploid zygote.

Meiosis

A specialized type of cell division that reduces the chromosome number by half (from diploid to haploid) in sexually reproducing organisms, producing four haploid gametes from a single diploid cell. This process includes two rounds of division: Meiosis I and Meiosis II.

Crossing Over

A crucial event during prophase I of meiosis where homologous chromosomes exchange segments of genetic material (alleles) between non-sister chromatids, leading to increased genetic variation in the gametes.

Independent Assortment

The random orientation and separation of homologous chromosomes during metaphase I and anaphase I of meiosis, meaning that the inheritance of one gene does not affect the inheritance of another, contributing significantly to genetic diversity.

Random Fertilization

The unpredictable chance encounter and fusion of any one of millions of possible sperm with any one of potentially viable eggs, further maximizing genetic variation in offspring produced by sexual reproduction.

Primary Follicle

An immature ovum (egg cell) within the ovary, surrounded by a single layer of flattened follicular cells; it represents an early stage of egg development.

Corpus Luteum

A temporary endocrine structure formed in the ovary from the remnants of the ovarian follicle after ovulation. It secretes progesterone (and some estrogen) to prepare the uterine lining for potential embryo implantation.

FSH (Follicle-Stimulating Hormone)

A gonadotropic hormone secreted by the anterior pituitary gland that stimulates the growth and development of ovarian follicles in females and sperm production (spermatogenesis) in males.

LH (Luteinizing Hormone)

A gonadotropic hormone secreted by the anterior pituitary gland that triggers ovulation in females and stimulates the corpus luteum to produce progesterone. In males, it stimulates Leydig cells to produce testosterone.

Oestrogen

The primary female sex hormone, produced mainly by the ovarian follicles and corpus luteum. It is responsible for the development of female secondary sexual characteristics and plays a key role in regulating the menstrual cycle.

Progesterone

A female sex hormone primarily produced by the corpus luteum after ovulation, and by the placenta during pregnancy. Its main role is to prepare the uterus for pregnancy and maintain the uterine lining.

Menstrual Cycle

A recurring monthly series of hormonal and physiological changes in the female reproductive system that prepares the uterus for a potential pregnancy, culminating in either menstruation or pregnancy.

Ovulation

The process by which a mature egg (ovum) is released from the ovarian follicle into the fallopian tube, typically occurring around day 14 of a 28-day menstrual cycle.

Menstruation

The shedding of the thickened uterine lining (endometrium) and associated blood through the vagina, occurring when fertilization and implantation do not take place during the menstrual cycle.

Blastocyst

A hollow ball of cells formed approximately 5-7 days after fertilization, consisting of an inner cell mass (which will become the embryo) and an outer layer (trophoblast) that will contribute to the placenta; it implants into the uterine wall.

Acrosome Reaction

A crucial event during fertilization where the acrosome (a cap-like organelle on the sperm head) releases hydrolytic enzymes that digest components of the egg's outer layers, primarily the zona pellucida, allowing the sperm to penetrate the egg.

Polyspermy

A condition in which an egg is fertilized by more than one sperm. This is typically prevented by rapid block mechanisms (like the fast block and slow block to polyspermy) to ensure normal embryonic development.

In Vitro Fertilization (IVF)

A complex reproductive technology where eggs are retrieved from a woman's ovaries and fertilized by sperm in a laboratory setting ("in vitro"). The resulting embryos are then transferred into the woman's uterus.

Seed Dispersal

The ecological process by which seeds are moved away from the parent plant, often carried by wind, water, or animals, to reduce competition with the parent and increase the chances of survival and colonization in new areas.

Germination

The process by which a plant embryo, encased within a seed, breaks dormancy and begins to grow into a seedling. It typically requires specific environmental conditions such as water, oxygen, and a suitable temperature.

Hormone Replacement Therapy (HRT)

A medical treatment used to alleviate menopausal symptoms and prevent certain long-term conditions (like osteoporosis) by replacing hormones, primarily estrogen and sometimes progesterone, that are no longer produced in sufficient amounts by the ovaries.

Human Chorionic Gonadotropin (hCG)

A hormone secreted by the trophoblast cells of the developing embryo (and later the placenta) shortly after implantation. It signals the corpus luteum to continue producing progesterone, thus maintaining the uterine lining and preventing menstruation during early pregnancy.

Testosterone

The primary male sex hormone (an androgen) produced mainly by the Leydig cells in the testes. It is vital for the development of male primary and secondary sexual characteristics, sperm production, and libido.

Oogenesis

The rigorous process of female gamete (ovum/egg) formation, which begins during fetal development and continues cyclically from puberty until menopause, resulting in one mature egg and polar bodies from each primary oocyte.

Spermatogenesis

The continuous process of male gamete (sperm) formation, occurring in the seminiferous tubules of the testes from puberty onwards, producing millions of mature, motile sperm cells.

Interstitial Cells

Also known as Leydig cells, these are endocrine cells located in the connective tissue between the seminiferous tubules in the testes. They are responsible for producing and secreting testosterone.

Sertoli Cells

Also called "nurse cells," these large cells located within the seminiferous tubules provide structural support, nourishment, and regulatory signals to developing sperm cells during spermatogenesis.

Umbilical Cord

A flexible, tube-like structure containing blood vessels that connects the developing fetus to the placenta, facilitating the transport of oxygen and nutrients from the mother to the fetus and waste products from the fetus to the mother.

Placenta

A temporary organ that develops in the uterus during pregnancy, serving as the interface between the maternal and fetal blood supplies for nutrient, gas, and waste exchange, and also producing essential hormones.

Amniotic Fluid

The clear, yellowish fluid found within the amniotic sac that surrounds and protects the developing fetus in the uterus, providing cushioning against physical impact, temperature regulation, and allowing for fetal movement.

Self-Pollination

The transfer of pollen grains from the anther (male part) to the stigma (female part) of the same flower or to another flower on the same plant. This leads to reduced genetic variation.

Cross-Pollination

The transfer of pollen grains from the anther of one flower to the stigma of another flower on a different plant of the same species. This increases genetic diversity.

Endometrium

The mucous membrane lining the inner wall of the uterus, which undergoes cyclic changes during the menstrual cycle, thickening in preparation for embryo implantation and shedding during menstruation if pregnancy does not occur.

Acrosome

A specialized organelle located on the head of a sperm cell, containing a variety of hydrolytic enzymes (e.g., hyaluronidase, acrosin) that are released during the acrosome reaction to aid in penetrating the egg's outer layers.

Zona Pellucida

A thick, extracellular glycoprotein layer that surrounds the plasma membrane of an oocyte (egg cell). It plays a vital role in protecting the egg, mediating species-specific sperm binding, and preventing polyspermy.

Gametogenesis

The general biological process of forming mature haploid gametes (sperm and egg cells) from diploid precursor cells through meiosis, occurring in the gonads (testes in males, ovaries in females).

Follicle Cells

Specialized cells that surround and provide support, nourishment, and hormonal signals to the developing oocyte within an ovarian follicle.

Hormonal Control

The regulation of various physiological processes, including reproduction, growth, metabolism, and mood, by the secretion and action of hormones released from endocrine glands.

Menopause

The natural biological transition in a woman's life, typically occurring between the ages of 45 and 55, marked by the permanent cessation of menstrual cycles and the end of reproductive capability due to the ovaries ceasing to produce eggs and significantly reducing hormone production.

Secondary Sexual Characteristics

Physical features that develop during puberty under the influence of sex hormones (e.g., testosterone in males, estrogen in females) that distinguish males from females but are not directly involved in reproduction (e.g., breast development, facial hair, deeper voice).

Leydig Cells

Cells in the connective tissue between the seminiferous tubules in the testes that produce and secrete testosterone in response to LH.

Testis

The primary male reproductive organ (gonad), located in the scrotum, responsible for producing sperm (spermatogenesis) and synthesizing male sex hormones, primarily testosterone.

Ovary

The primary female reproductive organ (gonad), located in the pelvic cavity, responsible for producing ova (eggs) through oogenesis and secreting female sex hormones, mainly estrogen and progesterone.

Sperm Duct

Also known as the vas deferens, this is a muscular tube that transports mature sperm from the epididymis to the ejaculatory duct during ejaculation.

Urethra

A tube that extends from the bladder to the outside of the body. In males, it serves as a passageway for both urine and semen; in females, it only carries urine.

Seminal Vesicle

A pair of glands located behind the bladder in males that secrete a fluid rich in fructose (for sperm nutrition), prostaglandins, and other substances that contribute to the volume and viability of semen.

Prostate Gland

A gland located below the bladder in males that secretes a milky, slightly acidic fluid containing citrate (a nutrient for sperm), enzymes, and prostate-specific antigen (PSA), which contributes to semen volume and helps activate sperm.

Genetic Variation

The diversity in genetic sequences and allele frequencies within a population or species, arising from mutations, gene flow, and sexual reproduction via processes like crossing over and independent assortment. It is the raw material for natural selection.

Natural Selection

The evolutionary process in which individuals with heritable traits that enhance their survival and reproduction in a specific environment tend to produce more offspring, leading to an increase in the frequency of those advantageous traits in the population over generations.

Endocrine System

The body's system of glands (e.g., pituitary, thyroid, adrenal, gonads) that secrete hormones directly into the bloodstream to regulate various bodily functions, including metabolism, growth, and reproduction.

Hormonal Feedback Loops

Regulatory mechanisms involving hormones where the output of a pathway (e.g., hormone secretion) acts as a stimulus to either increase (positive feedback) or decrease (negative feedback) earlier components of the pathway, maintaining homeostasis.

Parthenogenesis

A form of asexual reproduction in which an egg develops into an embryo without fertilization by a sperm. This occurs naturally in some insects, fish, and reptiles.

Polyandry

A unique mating system in which one female mates and forms pair bonds with multiple males during a breeding season, while each male typically mates with only one female.

Polygyny

A common mating system in which one male mates with multiple females during a breeding season, while each female typically mates with only one male.

Gestation Period

The duration of pregnancy, referring to the time interval between conception (fertilization) and birth, during which the embryo and fetus develop inside the mother's uterus.

Oviparous

Animals that reproduce by laying eggs (e.g., birds, reptiles, most amphibians, insects). The embryonic development occurs outside the mother's body, nourished by the yolk within the egg.

Viviparous

Animals that give birth to live young, where the embryo develops internally within the mother's reproductive tract and receives nourishment directly from the mother (e.g., most mammals, some reptiles and fish).

Fleshy Fruits

Fruits characterized by a soft, often sweet, and edible pericarp (fruit wall) at maturity (e.g., berries, drupes, pomes). They are typically adapted for seed dispersal by animals.

Dehiscent Fruits

Dry fruits that naturally split open at maturity along seams or pores to release their seeds (e.g., peas, beans, poppies).

Indehiscent Fruits

Dry fruits that do not split open at maturity to release their seeds; instead, their seeds are typically dispersed with the entire fruit (e.g., acorns, sunflower seeds, grains).

Biological Diversity

The variety of life on Earth at all levels, encompassing genetic diversity within species, species diversity (number of different species), and ecosystem diversity (variety of habitats and ecological communities).

Lifespan

The typical or maximum length of time an organism is expected to live, which varies greatly among species and can influence reproductive strategies and life history patterns.

Pheromones

Chemical signals released by organisms into the environment that affect the behavior or physiology of other individuals of the same species, often playing a crucial role in mate attraction, territory marking, and social communication.

Genetic Engineering

The direct manipulation of an organism's genes using biotechnology to alter its genetic makeup, typically by introducing new DNA, deleting genes, or altering gene expression, often with the aim of introducing new traits or correcting genetic defects.

Cloning

The precise process of creating a genetically identical copy of a gene, cell, or organism. In reproductive cloning, it involves creating a new organism that is an exact genetic replica of another.

Biotechnology

The application of biological processes, organisms, or systems to develop or create new products, technologies, or services, often involving genetic engineering or the use of living systems for industrial or medical purposes.

Inbreeding

The mating of closely related individuals within a population. While it can quickly fix desired traits, it increases homozygosity and the likelihood of expressing deleterious recessive alleles, potentially leading to inbreeding depression.

Outcrossing

The mating of unrelated individuals within a species, or individuals of different populations or varieties. This typically increases genetic diversity and heterozygosity, often leading to increased vigor and reduced expression of recessive diseases.

Genetic Drift

A random evolutionary process that causes changes in allele frequencies within a population purely by chance, especially pronounced in small populations. It can lead to the loss of genetic variation.

Adaptive Radiation

An evolutionary process in which a single ancestral species rapidly diversifies into many new species, each adapted to exploit different ecological niches, often following the colonization of a new habitat or the extinction of competitors.

Hybridization

The process of interbreeding between two individuals of different species or genetically distinct populations, resulting in a hybrid offspring that combines genetic material from both parents.

Epididymis

A coiled tube located on the posterior side of each testis where sperm mature and are stored before ejaculation.

Seminiferous Tubules

Highly coiled tubes located within the testes where spermatogenesis (sperm production) takes place.

Fallopian Tube (Oviduct)

A pair of slender tubes extending from the uterus to the ovaries, which serve as the pathway for the egg to travel from the ovary to the uterus and are the typical site of fertilization.

Uterus

A hollow, muscular, pear-shaped organ in the female pelvis where a fertilized egg implants and develops into a fetus during pregnancy.

Vagina

A muscular, elastic canal that extends from the cervix to the outside of the body; it receives the penis during intercourse, serves as the birth canal, and provides a passageway for menstrual flow.

Cortical Reaction

A slow block to polyspermy that occurs after a single sperm has fertilized an egg, involving the release of cortical granules to modify the zona pellucida, making it impenetrable to other sperm.

Implantation

The process by which the blastocyst attaches to and embeds itself into the endometrium (lining) of the uterus, typically occurring 6-12 days after fertilization, marking the beginning of pregnancy.

Gastrulation

A critical stage of early embryonic development immediately following blastulation, during which the single-layered blastula reorganizes into a multi-layered structure called the gastrula, forming the three primary germ layers (ectoderm, mesoderm, endoderm).

Organogenesis

The process of organ formation during embryonic development, in which the three primary germ layers differentiate and develop into the various organs and organ systems of the body.

Amnion

An innermost membrane that surrounds the embryo and later the fetus, eventually forming the amniotic sac which encloses the amniotic fluid.

Chorion

The outermost extraembryonic membrane that surrounds the embryo and other membranes, contributing to the formation of the placenta and mediating nutrient and waste exchange.

Budding

A form of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site, detaching from the parent organism (e.g., yeast, hydra).

Fragmentation

A form of asexual reproduction where a whole new organism grows from a piece or fragment of the parent organism (e.g., starfishes, some worms).

Vegetative Propagation

A form of asexual reproduction in plants where new plants grow from fragments of the parent plant or specialized reproductive structures like stems, roots, and leaves, without seeds or spores (e.g., runners, tubers, bulbs).

Stamen

The male reproductive part of a flower, typically consisting of a filament supporting an anther.

Anther

The part of the stamen that contains microsporangia, where pollen grains are produced.

Pistil (Carpel)

The female reproductive part of a flower, typically consisting of the stigma, style, and ovary.

Stigma

The receptive tip of a carpel, which protrudes and often has a sticky or feathery surface to catch pollen during pollination.

Ovary (Plant)

The enlarged basal part of a pistil, containing ovules, which develops into the fruit after fertilization.

Ovule (Plant)

A structure within the plant ovary that contains the female gametophyte (embryo sac) and, after fertilization, develops into a seed.

Pollination

The transfer of pollen from the anther (male part) to the stigma (female part) of a flower, which is a prerequisite