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iGCSE Biology Section 3 lesson 2
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Reproduction and Inheritance
Content Section 3 Reproduction and Inheritance Reproduction - Flowering plants - Humans b) Inheritance
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Lesson 2 Content Humans a) Reproduction – Humans
3.8 describe the structure and explain the function of the male and female reproductive systems 3.9 understand the roles of oestrogen and progesterone in the menstrual cycle 3.10 describe the role of the placenta in the nutrition of the developing embryo 3.11 understand how the developing embryo is protected by amniotic fluid 3.12 understand the roles of oestrogen and testosterone in the development of secondary sexual characteristics
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Human gametes (sex cells)
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Human gametes (sex cells)
Male sex cell = sperm
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Human gametes (sex cells)
Male sex cell = sperm
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Human gametes (sex cells)
Male sex cell = sperm The chromosomes (genetic information) are tightly packed together in the nucleus Head Tail
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Human gametes (sex cells)
Male sex cell = sperm The chromosomes (genetic information) are tightly packed together in the nucleus Head The tail lashes from side to side and propels the sperm forwards Tail
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Human gametes (sex cells)
Male sex cell = sperm The chromosomes (genetic information) are tightly packed together in the nucleus Head The tail lashes from side to side and propels the sperm forwards Tail A single ejaculate may be about 4cm3 of fluid and may contain up to 500 million sperms
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Human gametes (sex cells)
Female sex cell = egg (ovum) Membrane Nucleus containing chromosomes Cytoplasm Jelly coat
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Summary of sexual development
MALE FEMALE AT BIRTH Testes have descended into scrotal sac but they do not make sperms yet Ovaries containing immature eggs present in abdomen but they do not produce eggs yet 12-14 years PUBERTY 45-50 70-75
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Summary of sexual development
MALE FEMALE AT BIRTH Testes have descended into scrotal sac but they do not make sperms yet Ovaries containing immature eggs present in abdomen but they do not produce eggs yet 12-14 years PUBERTY PITUITARY GLAND Gonad-stimulating hormones Testes Male sex hormones (androgens) Testes start producing sperms. Secondary sexual characteristics, eg growth of body hair, breaking of voice Ovaries Female sex hormones (oestrogens) Ovaries start producing eggs. Secondary sexual characteristics, eg. growth of breasts, fat in thighs 45-50 70-75
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Summary of sexual development
MALE FEMALE AT BIRTH Testes have descended into scrotal sac but they do not make sperms yet Ovaries containing immature eggs present in abdomen but they do not produce eggs yet 12-14 years PUBERTY PITUITARY GLAND Gonad-stimulating hormones Testes Male sex hormones (androgens) Testes start producing sperms. Secondary sexual characteristics, eg growth of body hair, breaking of voice Ovaries Female sex hormones (oestrogens) Ovaries start producing eggs. Secondary sexual characteristics, eg. growth of breasts, fat in thighs 45-50 MENOPAUSE Ovaries stop producing eggs 70-75
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Summary of sexual development
MALE FEMALE AT BIRTH Testes have descended into scrotal sac but they do not make sperms yet Ovaries containing immature eggs present in abdomen but they do not produce eggs yet 12-14 years PUBERTY PITUITARY GLAND Gonad-stimulating hormones Testes Male sex hormones (androgens) Testes start producing sperms. Secondary sexual characteristics, eg growth of body hair, breaking of voice Ovaries Female sex hormones (oestrogens) Ovaries start producing eggs. Secondary sexual characteristics, eg. growth of breasts, fat in thighs 45-50 MENOPAUSE Ovaries stop producing eggs 70-75 Testes stop making sperms
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Male and female reproductive systems
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Male and female reproductive systems
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Male and female reproductive systems
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Male reproductive system
TESTES (singular testis). Sperms are manufactured here. The testes are slightly cooler than the rest of the body.
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Male reproductive system
SCROTAL SAC (or scrotum). Alters position to maintain the optimum temperature for the testes.
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Male reproductive system
SPERM TUBULES – where the sperm are actually made. Combined length of over 500 metres!
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Male reproductive system
EPIDIDYMIS – coiled tube where the sperm are stored
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Male reproductive system
URETHRA – tube which runs down the centre of the penis – dual function, carrying both urine and sperms
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Male reproductive system
PENIS – male reproductive organ. During intercourse it fills with blood to become stiff and erect. Tip of the penis, the GLANS, is protected by the foreskin.
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Male reproductive system
SEMINAL VESICLE and PROSTATE GLAND – these glands produce a fluid which keeps the sperm alive and swimming vigorously. Sperm + fluid = semen
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Female reproductive system
OVARIES (singular ovary). Two, on either side of the abdomen. Every 28 days or so an egg is released.
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Female reproductive system
OVIDUCTS (also known as the Fallopian tubes) carry the eggs from the ovaries to the uterus. Fertilisation occurs here.
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Female reproductive system
UTERUS – if the egg is fertilised by the sperm, then it develops here into the baby during which time it is known as the womb)
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Female reproductive system
CERVIX – the neck of the uterus. Becomes dilated (opens up) just prior to the birth of the baby.
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Female reproductive system
VAGINA – the birth canal. Like the lining of the uterus, the vagina secretes a lot of mucus.
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Female reproductive system
CLITORIS – the female equivalent of the penis, can become erect during sexual intercourse
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Sexual intercourse The erect penis is inserted into the vagina. Drops of fluid, secreted by the male’s glands, emerge from the tip of the penis and serve as a lubricant, as does the mucus lining of the vagina.
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Sexual intercourse Rhythmical movement of the penis eventually results in ejaculation – semen is forcibly expelled from the penis into the vagina. The feelings experienced during ejaculation are known as orgasm. Female orgasm is usually brought about by stimulation of the clitoris.
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Fertilisation Once inside the vagina,the sperm swim up through the uterus and in to the oviducts. If an egg is present in the oviduct then one sperm will enter the egg and fuse with the female nucleus – this is known as fertilisation.
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Fertilisation Once inside the vagina,the sperm swim up through the uterus and in to the oviducts. If an egg is present in the oviduct then one sperm will enter the egg and fuse with the female nucleus – this is known as fertilisation.
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Fertilisation Once inside the vagina,the sperm swim up through the uterus and in to the oviducts. If an egg is present in the oviduct then one sperm will enter the egg and fuse with the female nucleus – this is known as fertilisation.
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Fertilisation After fertilisation has occurred, the egg divides repeatedly into a ball of cells which moves down the oviduct to the uterus. It now sinks into the soft lining of the uterus and becomes implanted. The woman is now pregnant.
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Lesson 2 Content Humans a) Reproduction – Humans
3.8 describe the structure and explain the function of the male and female reproductive systems 3.9 understand the roles of oestrogen and progesterone in the menstrual cycle 3.10 describe the role of the placenta in the nutrition of the developing embryo 3.11 understand how the developing embryo is protected by amniotic fluid 3.12 understand the roles of oestrogen and testosterone in the development of secondary sexual characteristics
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Lesson 2 Content Humans a) Reproduction – Humans
3.8 describe the structure and explain the function of the male and female reproductive systems 3.9 understand the roles of oestrogen and progesterone in the menstrual cycle 3.10 describe the role of the placenta in the nutrition of the developing embryo 3.11 understand how the developing embryo is protected by amniotic fluid 3.12 understand the roles of oestrogen and testosterone in the development of secondary sexual characteristics
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“Approximately once a month from puberty to the menopause, the human female experiences a menstrual cycle. This is part of a cycle of events which occurs inside her body”
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Uterus lining develops
The Menstrual Cycle Menstruation Graafian follicle Ovulation Uterus lining develops
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Uterus lining develops
The Menstrual Cycle Menstruation Graafian follicle Ovulation Uterus lining develops
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The Menstrual Cycle The cycle starts with menstruation. During this time the uterus lining breaks down and passes out through the vagina. This is known as menstrual bleeding, or having a ‘period’.
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Uterus lining develops
The Menstrual Cycle Menstruation Graafian follicle Ovulation Uterus lining develops
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The Menstrual Cycle Thousands of immature eggs are present in the ovaries. Following menstruation, one develops within a protective structure called the Graafian follicle. Development takes about 14 days.
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Uterus lining develops
The Menstrual Cycle Menstruation Graafian follicle Ovulation Uterus lining develops
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The Menstrual Cycle After about 14 days the follicle moves to the edge of the ovary and the mature egg pops out into the oviduct. This process is called ovulation.
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Uterus lining develops
The Menstrual Cycle Menstruation Graafian follicle Ovulation Uterus lining develops
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The Menstrual Cycle During the time the lining of the uterus has been thickening, with many blood vessels. If the egg has been fertilised then it will become embedded in the lining and the pregnancy will continue. If not, then menstruation occurs ….
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The Menstrual Cycle The whole menstrual cycle is controlled by hormones (special chemical messengers in the blood).
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The Menstrual Cycle The pituitary gland, at the base of the brain, releases a hormone (FSH, or follicle stimulating hormone), which causes the follicle to develop in the ovary.
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The Menstrual Cycle The ovary produces oestrogen which causes the lining of the uterus to re-build after menstruation.
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The Menstrual Cycle At the time of ovulation the ovary produces another hormone, progesterone, which causes the uterus to become thicker and full of blood vessels.
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The Menstrual Cycle If the egg is not fertilised then production of the two hormones stops, and menstruation continues.
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The Menstrual Cycle If the woman becomes pregnant then the ovary continues to produce progesterone and the lining remains intact and builds up further. The periods will stop during pregnancy.
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Lesson 2 Content Humans a) Reproduction – Humans
3.8 describe the structure and explain the function of the male and female reproductive systems 3.9 understand the roles of oestrogen and progesterone in the menstrual cycle 3.10 describe the role of the placenta in the nutrition of the developing embryo 3.11 understand how the developing embryo is protected by amniotic fluid 3.12 understand the roles of oestrogen and testosterone in the development of secondary sexual characteristics
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Pregnancy Placenta Umbilical cord Amniotic sac Amnion Foetus
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Pregnancy Search ……. “What is the amnion and the amniotic cavity (sac)?”
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Pregnancy The amnion is a thin membrane that surrounds the developing embryo.
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Pregnancy The membrane encloses a cavity called the amniotic cavity, filled with a watery amniotic fluid.
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Pregnancy The amniotic fluid protects the foetus from bumping and damage as the mother moves around
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Pregnancy Search ……. “How is the foetus kept alive?”
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Search ……. “How is the foetus kept alive?”
Pregnancy Search ……. “How is the foetus kept alive?”
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Pregnancy Search ……. “How is the foetus kept alive?”
The foetus is connected to the placenta by the umbilical cord.
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Search ……. “How is the foetus kept alive?”
Pregnancy Search ……. “How is the foetus kept alive?” The umbilical cord brings to the foetus oxygen and food, and takes away carbon dioxide and waste.
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Pregnancy The placenta is attached to the lining of the uterus. It has numerous finger-like projections called villi.
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Pregnancy The placenta is attached to the lining of the uterus. It has numerous finger-like projections called villi. Blood space Placenta Capillary in villus Umbilical artery Umbilical vein Foetus
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Pregnancy The foetus’s blood and the mother’s blood never mix. Instead, they come very close, and are separated by a very thin membrane. At birth, the placenta is delivered shortly after the baby. Blood space Placenta Capillary in villus Umbilical artery Umbilical vein Foetus
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Pregnancy After about nine months the uterus (womb) will undergo contractions. This is called labour. The amniotic sac will become ruptured (breaking of the waters) and shortly afterwards the baby will be born.
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Lesson 2 Content Humans a) Reproduction – Humans
3.8 describe the structure and explain the function of the male and female reproductive systems 3.9 understand the roles of oestrogen and progesterone in the menstrual cycle 3.10 describe the role of the placenta in the nutrition of the developing embryo 3.11 understand how the developing embryo is protected by amniotic fluid 3.12 understand the roles of oestrogen and testosterone in the development of secondary sexual characteristics
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Summary of sexual development
MALE FEMALE AT BIRTH Testes have descended into scrotal sac but they do not make sperms yet Ovaries containing immature eggs present in abdomen but they do not produce eggs yet 12-14 years PUBERTY PITUITARY GLAND Gonad-stimulating hormones Testes Male sex hormones (androgens) Testes start producing sperms. Secondary sexual characteristics, eg growth of body hair, breaking of voice Ovaries Female sex hormones (oestrogens) Ovaries start producing eggs. Secondary sexual characteristics, eg. growth of breasts, fat in thighs 45-50 MENOPAUSE Ovaries stop producing eggs 70-75 Testes stop making sperms
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Secondary sexual characteristics
MALE FEMALE 12-14 years PUBERTY PITUITARY GLAND Gonad-stimulating hormones Testes Male sex hormones - testosterone Testes start producing sperms. Pubic hair develops in the genital region. Penis gets larger. Voice breaks. More muscular Hair starts growing on the legs, chest and face. Ovaries Female sex hormones oestrogens Ovaries start producing eggs. Periods begin. Breasts develop Fat laid down in the thighs.
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Reproduction in Humans
3.8 describe the structure and explain the function of the male and female reproductive systems 3.9 understand the roles of oestrogen and progesterone in the menstrual cycle 3.10 describe the role of the placenta in the nutrition of the developing embryo 3.11 understand how the developing embryo is protected by amniotic fluid 3.12 understand the roles of oestrogen and testosterone in the development of secondary sexual characteristics
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End of Section 3 Lesson 2 In this lesson we have covered:
Human gametes (sex cells) Male and female reproductive systems Intercourse and fertilisation The Menstrual Cycle Pregnancy
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