D3.1 Reproduction

What is asexual reproduction?

• Reproduction involving one parent→ fusion of gametes

• Offspring are genetically identical to the parent and each other (except for mutations)

What is sexual reproduction?

• Reproduction involving the production of haploid gametes and the fusion of their nuclei during fertilization to produce a diploid zygote

• Involves two parents and creates genetic variation

What are the advantages of asexual reproduction

• Well suited for a stable environment (well adopted parent→ well adapted offspring)

• Only one parent needed

• Reproduction can occur quickly

• Many offspring produced in a short time

What are the disadvantages of asexual reproduction?

• Little genetic variation among offspring

• A disease or environmental change could affect the entire population

• Harmful mutations can be passed on to offspring

What are the advantages of sexual reproduction?

• Evolve in response to changing environments or disease

• Offspring with genetic variation improve survival

What are the disadvantages of sexual reproduction?

• Reproduction is often slower than asexual reproduction

• Finding a mate takes time and energy

• Each parent may contribute only some of their genes to each offspring

Outline the role of meiosis in reproduction

• Meiosis produces haploid cells containing half the chromosome number of the diploid parent cell

• In humans, meiosis produces cells with 23 chromosomes rather than 46

• Allows fertilization to restore the diploid chrosome number(46 chromosomes with 23 pairs)

• Creates genetic variation through crossing over and independnt assortment

Define fertilization

• The fusion of the nuclei of two haploid gametes(male and female sex cell) to form a diploid zygote

• the sperm nucleus (23 chromosomes) fuses with the egg nucleus (23 chromosomes), restoring the diploid number of 46

Compare male and female gametes, focusing on distance travelled, energy reserves, number produced and reproductive strategies

• Mobility of gamete

  • Male: Highly motile→must travel through female reproductive tract

  • Female: Stationary

• Size of gamete

  • Male: Small → allows for movement

  • Female: Larger→ allows for food storage

• Food reserves of gamete

  • Male: Limited

  • Female: Substantial to support embryo growh

• Quantity produced

  • Male: Millions produced to increase probability of fertalization

  • Female: One egg released per menstrual cycle

Draw and annotate diagram of male reproductive system → structure and function for annotations

• Testes: produce sperm

• Scrotum: Holds the testes and regulates their temperature for sperm production

• Epididymis: stores sperm and allows them to mature

• Sperm ducts: transports sperm during ejaculation from the epididymus towards the urethra

• Seminal vesicles and prostate gland: Provides fluids that help transport and nourish the sperm

• Urethra: Tube for transferring semen and urine

• Penis: Deposits semen into the female reproductive tract

Draw and annotate diagram of female reproductive system → structure and function for annotations

• Ovaries: produce egg cells

• Uterus: Contains and supports the developing embryo and fetus during pregnancy

• Oviducts: Collects eggs during ovulation and site of fertilization

• Cervix: narrrow opening between uterus and vagina→ protects fetus

• Vagina: Stimulates penis to cause ejaculation, receives semun, allows menstrual flow to leave the body

• Vulva: protection of reproductive system

Outline the purposes of the ovarian and uterine cycles

• Ovarian cycle: Coordinates the development and maturation of an egg, its release during ovulation, and the formation of the corpus luteum, which secretes hormones after ovulation

• Uternine cycle: prepares the uterus for possible implantation → if pregnancy does not occur, lining sheds during menstruation

Positive vs Negative feedback

• Positive feedback: amplifies or increases a change, moving the system further away from the starting point (contractions)

• Negative feedback: counteracts a change to bring the body back to a normal set point (homeostasis)

Positive feedback in the ovarian and uterine cycles, including hormones involved, location of action, and mechanism

• Hormones involved: estrogen

• Happens in hypothalamus and anterior pituitary gland

• Mechanism:

  • Follicle stimulating hormone produces a lot of estrogen→ enters bloodstream

  • hypothalamus and anterior pituitary gland are stimulated

  • The pituitary releases a lot of LH (luteinizing hormone)

  • Ovulation occurs→ egg is released from ovary

• Positive feedback because the high estrogen levels brain to increase LH release, amplifying the signal until ovulation occurs

Negative feedback in the ovarian and uterine cycles, including hormones involved, location of action, and mechanism

• Hormones involved: estrogen and progesterone

• Happens in hypothalamus and anterior pituitary gland

• Mechanism:

  • After ovulation, the remains of the follicle become the corpus luteum

  • Corpus luteum releases progesterone and estrogen into the blood

  • Hormones signal to the hypothalamus and anterior pituitary in the brain to slow down sending signals

  • Anterior pituitary releases less FSH and LH

  • With less FSH and LH, another follicle is less likely to develop fully, and another ovulation is prevented during this phase

• Negative feedback because the hormones reduce the signals that would otherwise stimulate more hormone production

Estrogen- produced by? trigger for secretion? target and role?

• Produced by ovarian follicles (sacs in the ovaries) and later the corpus luteum

• Triggered by the development of the follicles (caused by FSH)

• Target: thickens endometrium (wall of the uterus)

• Negative feedback at low levels: inhibits FSH and LH

• Positive feedback at high levels→ triggers LH surge

Progesterone- produced by? trigger for secretion? target and role?

• Produced by the anterior pituitary gland

• Triggered by the formation of the corpus luteum (caused by LH)

• Target: maintains the thickened endometrium for possible implantation (fertilized egg attatching itself to walls of the uterus)

• Slows down signals to the hypothalamus and anterior pituitary gland through negative feedback→ slows down FSH GnRH and LH secretion

  • To ensure the body doesn't start growing a new egg

Steps of fertilization

• Sperm undergo chemical changes in femal reproductive traict to gain hypermobility and reach the egg in the oviduct

• Sperm breaks through the outer follicular cells

• Sperm binds to receptors on the glycoprotein (zona pellucida)

• Fusion of sperm and egg cell membraines hardens the zona pellucida to prevent the entry of multiple sperm

• The sperm nucleus enters the egg cytoplasm, and both the male and female nuclei fuse to form a diploid zygote.

How DNA combines

• Both the sperm and egg are haploid cells containing n=23 chromosomes

• When sperm nucleus merges with egg, their chromomes pair up, resulting in the diploid 2n=46

  • 46 chromomes with 23 pairs

• Genetically unique combination of paternal and maternal alleles in the new zygote

First cell division of zygote to 2-cell organism

• mitosis occurs

• DNA replicates the single-cell zygote divides via cytokinesis to form a 2-cell embryo (blastomeres), with each cell containing an identical copy of the newly combined diploid genome

Use of hormones in the steps of IVF

• Suppression of the menstrual cycle

  • Woman takes a medication to stop the pituitary gland from secreting FSH and LH

  • Pauses the natural menstrual cycle so natural hormone peaks do not interfere with doctors timeline

• Stimulation of ovaries (superovulation)

  • The woman receives daily injections of high does of FSH for about 7 to 12 days

  • Forces the ovaries to develop multiple ovary follicles and multiple eggs at the same time instead of just one

• Maturation

  • Once the follicles are large enough, an injection of hCG or LH is given

  • Matures the eggs inside the follicles and gets them ready for collection

  • Eggs are harvested before the follicles rupture

• Supporting Implantation

  • After eggs are collcted and fertilized in a lab, the woman begins take progesterone

  • This develops and maintains a thick endometrium to help the transferred embryo impant and support early pregnancy

Define Superovulation

Process where fertility drugs containing FSH induce ovaries to produce multiple eggs in a single menstrual cycle

• Enhances chances of achieving fertilization during IVF

Sexual reproduction significance in flowering plants

• Fusion of male and female haploid gametes to form a genetically unique diploid zygote

• Introduces genetic variation through meiosis → helps populations adapt to changing environmental conditions

Gamete production in pollen grains (male)

• Formed in anthers

• In each pollen grain, nucleus undergoes mitosis, creating male gametes

• Pollen grains develop a thick, protective wall to ensure the male gametes are shielded during pollination

Gamete production in ovules (female)

• Found inside the ovule

• Diploid cell undergoes meiosis to form haploid cells

  • Develops into an embryo sac containing the female gamete

  • Only becomes one egg

Outline the process of pollination, including the development and role of pollen

• Pollination: transfer of mature pollen grains from the anther to the stigma of another flower via one of the different methods

• Pollen grains develop a thick, protective wall to ensure the male gametes are shielded during pollination

Fertilization resulting in embryo formation

• Once on the stigma the pollen grain grows a pollen tube down the style into the ovary

• Pollen tube is created for pollen to move down and go into the ovary and ovules

  • Pollen enters the middle where the egg cell is and releases the male gamete

  • Male gamete fuses with female game creating the diploid zygote

How do Hermaphroditic Plants participate in sexual reproduction

• Hermaphroditic plants have both male and female reproductive structures in the same flower

  • Allows for self-pollination or cross pollination

Structures and functions of a plant

Petal: Large, brightly colored, scented to attract insect pollinators

Anther: location of pollen production

Stigma: loc of pollen deposit

Style: holds stigma up high

Ovule: location of female gamete

Filament: holds anther uo

Sepal: protects and supports

Peduncle: structural

adaptations in insect-pollinated flowers that facilitate effective pollination

• Bright Petals & Nectar Guides: Visual cues that direct insects straight toward the reproductive organs

• Sticky/Spiked Pollen: Unlike lightweight, smooth wind-pollinated pollen, insect-pollinated pollen is barbed or sticky so it easily clings to an insect's body

• Enclosed Anthers and Stigmas: Positioned safely inside the flower petals so brushing insects are guaranteed to contact them

Define cross-pollination and contrast it with self-pollination

• Cross pollination: between 2 different plants of the same species→ increases genetic diversity

• Self pollination: Transfer of pollen from the anther to the stigma of the same flower or another flower on the same plant

  • Possible as many plants are hermaphroditic→ reduces genetic diversity

Describe mechanisms that promote cross-pollination

• Timing: anthers mature and release pollen before stigmas of the same flower become receptive or vise versa

• Physical/structural barriers that prevent self-contact (anthers positioned lower than a stigma)

• Entirely separate male and female plants→ cross-pollination mandatory

• Wind/animal/insects

  • Act as delivery agents for picking up pollen and carrying it to the stigma of the next flower

  • Wind randomly disperses pollen grains from anthers

• All of these promote genetic diversity→ reduces the expression of harmful mutations, increases species ability to adapt

Define self-incompatibility

• Prevents self-fertilization and inbreedig

• Pollen from the same plant or identical plant cannot successfully germinate or grow a pollen tube

• Plants have genetic mechanisms to prevent his from happening

Genetic mechanisms to prevent self-incompatibility

• If the s1 and s2 alleles in the pollen grain match both in the stigma→ genetic info is too similar and pollen tube fails to develop

• Half grain compatible→ partrially compatible one pollen tube develops

• If all are different than they are all compatible and all pollen tubes develop

Consequences of Self-Pollination

• Inbreeding: homozygous recessive mutations, lower fertility, weaker offspring

• Reduced genetic diversity: Makes populations highly vulnerable to sudden environmental changes, pathogens, or climate shifts

• By filtering out similar pollen, offspring exhibit enhanced growth, resilience, and reproductive success

Distinguish between seed dispersal and pollination

• Pollination is the transfer of pollen to the stigma

• Seed Dispersal is the transport of mature seeds away from the parent plant to new locations

Methods of seed dispersal

• Wind: Lightweight seeds with wings or hair-like structures (e.g., dandelion, maple).

• Animals: Fleshy, sweet fruits eaten and excreted elsewhere (endozoochory) or hooked burrs clinging to fur (epizoochory).

• Water: Buoyant seeds floating on rivers, streams, or ocean currents (e.g., coconut).

• Self-Dispersal (Bursting): Seed pods drying out and forcefully splitting open to fling seeds away (e.g., touch-me-nots)

Stages of Seed Germination

• Water uptake: dry seeds absorb water, rehydrating tissues and triggering metabolic acitivy

• Food Reserve Mobilization: Stored starches are broken down into soluble sugars to fuel cellular respiration and growth

• Embryo Growth: The embryonic root (radicle) emerges first, followed by the shoot

Environmental Factors Required

• Water: To rehydrate enzymes and drive cell expansion.

• Oxygen: For aerobic cellular respiration to generate ATP.

• Suitable Temperature: Optimal warmth for specific enzyme kinetics

Adaptive Advantages of seed Dispersal

• Reduces direct competition for sunlight, water, and soil nutrients between the parent plant and its offspring.

• Prevents mass destruction of an entire family line by localized pathogens or herbivores and allows colonization of new habitats