D3.3.1 Differences between sexual and asexual reproduction

Asexual:

• One parent

• Mitosis throughout life cycle

• Genetically identical offspring

• No genetic variation

Sexual:

• Two parents (one male one female)

• Meiosis used once per generation

• Genetically different offspring with new combinations of genes

D3.1.2 Role of meiosis and fusion of gametes in the sexual life cycle

• Fertilization: Fusion of male and female gametes

  • doubles the number of chromosomes

• Meiosis: Occurs in the creation of gametes

  • halves number of chromosomes

• Meiosis and fertilization produce individuals with new combinations of genetic material

D3.1.3 Differences between male and female sexes in sexual reproduction

• Male

  • travel to the female (motile)

  • Smaller

  • Less food reserve

  • More produced at once

• Female

  • Sessile

  • larger

  • More food reserve - enough for embryo

  • Few produced at once

D3.1.4 Anatomy of the human male and female reproductive systems

D3.1.5 Changes during the Ovarian and Uterine cycles and their hormonal regulation

• Ovarian cycle: Process of producing/developing eggs

• Uterine cycle: Changes occuring in the uterus lining

• Menstrual cycle: Monthly hormonal cycle that prepares the body for pregnancy

• Follicular phase: First half of the ovarian cycle

  • Follicles develop in the ovary → releases egg into oviduct

  • Hypothalamus secretes gonadotropin-releasing hormone (GnRH) → Pituitary releases follicle-stimulating hormone (FSH) and lutenizing hormone (LH)

• Day 1-13: Follicular phase

• Day 14: Ovulation

• Day 15-28: Luteal phase

• Luteal phase: Wall of follicle → corpus luteum

• Endometrium thickens with blood/nutrients in preparation for implantation of an embryo in luteal phase

  • Sheds at the end of luteal phase → menstruation → back to day 1

• FSH peaks at the end of menstrual cycle → stimulates follicle development

• Estrogen peaks at the end of follicular phase → stimulates thickening of endometrium after menstruation + increase in FSH receptors

  • High levels of FSH → estrogen inhibits secretion of FSH + stimulates LH secretion

• LH peaks at the end of follicular phase → stimulates completion of meiosis + development of corpus luteum

  • corpus luteum secretes estrogen and progesterone

• Progesterone rises at start of luteal phase then drop by the end

  • promotes thickening/maintenance of endometrium

  • Inhibits FSH and LH secretion

D3.1.6 Fertilization in humans

• Zona pellucida: Outer layer of egg cell

• First sperm to penetrate zona pellucida fuses their membranes together

  • Acrosome of sperm releases enzymes that digest the zona pellucida

  • sperm nucleus enters egg cell (fertilization)

• Zona pellucida chemically changes after fertilization to prevent other sperms from entry

D3.1.7 Use of hormones in vitro fertilization (IVF) treatment

• In vivo: inside living tissues of the body (regular fertilization)

• In vitro: Outside the body

1. woman is injected everyday for 2 weeks with drug to inhibit pituitary gland from producing FSH or LH + stop secretion of estrogen/progesterone

2. Injections of FSH daily for 7-12 days → follicle development

3. injection of human chorionic gonadotropin (hCG) → maturation of follicles

4. eggs are collected

5. Each egg mixed with thousands of sperm cells

6. One or more embryos placed in uterus + extra progesterone

7. Implantation → regular pregnancy

D3.1.8 Sexual reproduction in flowering plants

• Flowers used for sexual reproduction

• Non reproductive parts:

  • Sepals: green outermost leaf-life structures

  • Petals: brightly colored/odor to attract pollinators

• Stamens are male parts of a flower

  • Anther: produces pollen (male gametes)

  • Filament: stalk that holds anther

• Carpels are female parts of a flower

  • Stigma: receives the pollen

  • Style: tube connecting stigma and ovary

  • Ovary: Place where fetilization occurs

  • Ovules: female gametes

• Pollination: Transfer of pollen from an anther to a stigma → via wind/water or animals

• Fertilization:

  • Pollen grain germinates → tube grows down style to ovary

  • release of male gametes into ovules

D3.1.9 Features of Insect-pollinated flowers

• Large, brightly-colored petals

• Scent secreted by petals

• Pollen grains that stick to insects + food source

• Stigma is sticky → collects pollen from insects

• Nectar as a food source

  • positioned deep inside flower → forces insects to brush past anthers/stigma

D3.1.10 Methods of promoting cross-pollination

• Cross-pollination: The transfer of pollen of an anther in a flower from one plant to the stigma of a flower on another plant

  • benefits: healthy offspring (genetic variation)

• Hermaphrodites: Produce male and female gametes → self-pollination is possible

• Methods

  • adaptations for pollination via outside agent (wind/water/animals)

  • Separation of anthers and stigmas in the same plant

  • Maturation of anthers and stigmas at different times

D3.1.11 Self-incompatibility mechanisms to increase genetic variation within a species

• Self-pollination is generally avoided because of the lack of genetic variation + inability to adapt to change

• Self-incompatibility: The rejection of self proteins/cells

  • Plants with the same self-incompatibility alleles cannot successfully pollinate with each other

D3.1.12 Dispersal and germination of seeds

• Seed dispersal: when seeds travel long distances from parent plant

  • Dry and explosive

  • Fleshy and attractive for animals to eat

  • Feathery/winged to catch the wing

  • Covered in hooks that can catch onto coats of animals

• Seeds germinate into new plants

D3.1.13 Control of developmental changes of puberty by gonadotropin-releasing hormone and steroid sex hormones

• Puberty: The developmental changes that form the transition between childhood and sexual maturity

• Gonadotropin-releasing Hormone (GnRH) controls puberty progress

  • Secretion of GnRH starts about 10 weeks after fertilization until baby is 4-6 months old

  • Hypothalamus resumes secretion at time of puberty

    • stimulates FSH and LH via pituitary gland

• Puberty in males:

  • FSH → testis growth

  • LH → testosterone secretion

    • enlargement of penis

    • growth of pubic hair

    • deepening of voice

• Puberty in females:

  • FSH → follicle development → secretes estradiol

  • LH → corpus luteum development → secretes estradiol + progesterone

    • enlargement of uterus

    • breast development

    • growth of pubic hair

    • mammary glands + lactation

D3.1.14 Spermatogenesis and Oogenesis in humans

• Gametogenesis involves mitosis, cell growth, two rounds of meiosis, and differentiation

• Spermatogenesis: Production of sperm

  • Occurs in testes

  • Produces four haploid cells per meiosis → differentiate into sperm

  • millions per day

  • released during ejaculation

• Oogenesis: Production of eggs

  • occurs in ovaries

  • 4-5 months old → first division of meiosis

  • Only further develop after puberty

  • releases one egg from meiosis

  • one per month usually

  • released at ovulation (day 14 of cycle)

D3.1.15 Mechanisms to prevent polyspermy

• Polyspermy: More than one sperm fertilizing the egg

  • Detrimental → death of the zygote

• The acrosome reaction

  • Sperm bind to glycoproteins of zona pellucia → release acrosomal enzymes → digest zona pellucida

• Cortical reaction: After fertilization, cortical granules release enzymes → toughening of zona pellucida - impermeable to other sperm

D3.1.16 Development of a blastocyst and implantation in the endometrium

• Blastocyst: The product of rapid cell division in the zygote (hollow ball of cells)

  • Inner cell mass → embryo

  • Outer cell layer grows into endometrium

    • exchange materials with mother’s blood

D3.1.17 Pregnancy testing by detection of human chorionic gonadotropin secretion

• Human chorionic gonadotropin (hCG) is produced by embryo’s trophoblast cells

  • stimulates corpus luteum development and progesterone secretion → maintain uterus lining

• Trophoblast cells in placenta continue to secrete hCG

• Pregnancy tests detect hCG in urine

  • Monoclonal antibodies: Laboratory-made proteins made to bind to specific targets in the body

  • antibodies bind to hCG

D3.1.18 Role of the placenta in fetal development inside the uterus

• The placenta transfers nutrients and substances between the fetus and the mother’s blood

• Selectively permeable placental barrier → direct diffusion/selective diffusion of nutrients/substances between the mother and fetus

• Fetal blood → maternal blood

  • CO2, Urea, Water

• Maternal blood → fetal blood

  • Oxygen, glucose, antibodies, water

D3.1.19 Hormonal control of pregnancy and childbirth

• Placenta secretes estradiol and progesterone to maintain pregnancy

• Progesterone inhibits secretion of oxytocin and contractions

• End of pregnancy: fetus produces hormones that signal placenta to stop secreting progesterone

• Oxytocin stimulates contractions → more oxytocin (positive feedback)

  • cervix dilation

D3.1.20 Hormone replacement therapy and risk of coronary heart disease

• HRT relieves menopausal symptoms

  • increases estrogen and progesterone levels

• Positively correlated with increased risk of coronary heart disease (CHD) (not actually proven)