4.6.2Additional lessons
Sexual Reproduction — IB Biology SL Revision Notes & Topical Questions
5 min read 5 parts Lesson 117 of 142
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 5Meiosis and Fertilisation
In humans meiosis takes place in the testes and ovaries; in flowering plants it takes place in anthers and ovules.
1
Gamete-producing cells are diploid and have homologous pairs, one chromosome of each pair from each parent.
2
During meiosis I, homologous chromosomes pair up and non-sister chromatids exchange segments by crossing over.
3
Pairs line up randomly at the equator, then separate, so each daughter cell receives only one chromosome from each pair.
4
Meiosis II separates chromatids, giving four haploid cells that differ genetically from each other.
5
At fertilisation a sperm nucleus and egg nucleus fuse, restoring the diploid number in the zygote and creating a new allele combination.
Part 2 of 5Comparing Gametes
Sperm size
- Sperm size A sperm is tiny and has little cytoplasm, which keeps it light so it can swim a long distance.
Sperm structure
- Sperm structure A flagellum drives movement, many mitochondria supply ATP, and the acrosome holds enzymes for entering the egg.
Egg size
- Egg size The egg cell is large and contains stored food and cytoplasm that supports the early embryo.
Egg structure
- Egg structure It is non-motile and surrounded by a protective jelly-like layer, the zona pellucida, with cortical granules beneath the membrane.
Numbers
- Numbers Millions of sperm are produced continuously, but usually one egg is released at a time in the human female.
| Feature | Sperm | Egg |
|---|---|---|
| Motility | Motile | Non-motile |
| Size | Very small | Large |
| Food reserves | Almost none | Yes |
| Production | Millions, continuous | Usually one per cycle |
Part 3 of 5Male Reproductive System
Male Reproductive System
Testis
- Testis Produces sperm in seminiferous tubules and secretes testosterone, which controls male sex characteristics.
Epididymis
- Epididymis A coiled tube on the testis where sperm mature and are stored before ejaculation.
Sperm duct
- Sperm duct Carries sperm from the epididymis towards the urethra during ejaculation.
Seminal vesicle and prostate
- Seminal vesicle and prostate These glands add fluids containing nutrients and alkaline substances, forming semen with the sperm.
Urethra
- Urethra Passes through the penis and carries semen, and also urine, out of the body at different times.
Part 4 of 5Female Reproductive System
Female Reproductive System
Ovary
- Ovary Produces egg cells and secretes oestrogen and progesterone.
Oviduct
- Oviduct The tube that receives the released egg;
- cilia and muscle move it along, and fertilisation normally happens here.
Uterus
- Uterus A muscular organ whose lining, the endometrium, receives and supports the embryo.
Cervix
- Cervix A ring of muscle at the base of the uterus that keeps the uterus closed during pregnancy.
Vagina
- Vagina Receives semen during intercourse and forms the birth canal.
Part 5 of 5Exam Checklist & Tips
4.6.2 – Key Points for the Exam
- Gamete A haploid sex cell, such as a sperm or egg.
- Zygote The diploid cell formed when two gametes fuse.
- Acrosome Vesicle at the tip of the sperm head containing digestive enzymes.
- Zona pellucida Glycoprotein layer around the egg that sperm must penetrate.
- Crossing over Exchange of chromatid segments between homologous chromosomes during meiosis I.
Common Mistakes
- Labelling the sperm duct as the urethra; the urethra is the common exit tube.
- Saying that fertilisation happens in the uterus; it usually happens in the oviduct.
- Claiming that sperm contain no mitochondria; they have many in the midpiece to supply ATP.
- Describing meiosis as producing identical cells; the four cells are genetically different.
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