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B5: Reproduction

B5: Reproduction. Miss Friedman IGCSE Science. Internal Fertilization. Where fusion of male and female gamete takes place inside the body Male gamete (sperm) are mobile and move to meet the stationary female gamete (egg)

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B5: Reproduction

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  1. B5: Reproduction Miss Friedman IGCSE Science

  2. Internal Fertilization • Where fusion of male and female gamete takes place inside the body • Male gamete (sperm) are mobile and move to meet the stationary female gamete (egg) Note: zygote does NOT necessarily grow inside body (bees deposit fertilized egg into honeycomb)

  3. External Fertilization • When fertilization takes place outside the body • Generally male and female animal are present at the same time even though fertilization is outside • Happens in a watery environment Note: frogs, clams, sea urchins, coral, starfish reproduce this way

  4. Pollination vs. Fertilization • Pollination is the transfer of male gamete (pollen) by a third-party vector. Fertilization is the joining together of the male and female gamete into a zygote. • Plants use pollination & fertilization • Pollination does NOT guarantee fertilization. • Animals use only fertilization.

  5. Insect-pollinated • Insect (bee, butterfly etc) are attracted to flower by smell, colour, nectar etc. • Pollen attaches to body of insect and is transferred to another flower (cross-pollination) when moves to the next flower • Insect is vector by which transfer of genetic material occurs

  6. Wind-pollinated • Physical force of wind carries pollen from one plant to another • Plants are smaller and do NOT smell, or have colour • Need to produce a lot of pollen

  7. Formation of seed & fruit • Once male gamete (pollen) reaches female gamete (ovule) fertilization occurs • Each ovule is fertilized begins to develop into a seed • Inside seed, zygote forms an embryo plant • As this is happening, ovary changes into a fruit • Fruit has function of containing, protecting the seeds inside and helped them be dispersed

  8. Structure of a bean seed Cotyledon: where food is stored in seed Testa: outside wall of seed (thick & hard) Micropyle: tiny hole where pollen tube entered

  9. Conditions for germination • Once seed grown to full size, it loses water and seed becomes dormant • This allows seed to survive in difficult conditions (such as very cold or dry) that would kill actively growing plant • Germination occurs when conditions are right in: • Light • Temperature • water

  10. Homework • Read pgs 203-213 • Q 12.7 pg208 • Investigation 12.2 pg 208

  11. Male reproductive system

  12. Female reproductive system

  13. Adolescence • A time during early teens when a person has a growth spurt • As well as rapid growth, rapid development takes take. • A time when a person changes from being a child to being a sexually mature person

  14. Puberty • Time when sex organs become mature • Generally happens earlier in girls • Ovaries & testis begin secreting larger amount of sex hormones, estrogen and testosterone Girls begin to release eggs, period begins, breaks develop, hips widen Boys begin to produce sperm, shoulders become broader, voice deepens, grows facial hair Both hair around sexual organs, under the arms and sweat glands become more active.

  15. Menstrual cycle

  16. Sexual intercourse • Blood pressure is increased in penis • This causes penis to become stiff & erect • It can then be inserted into the woman’s vagina • Muscular contractions force semen out of urethra, in ejaculation • Sperm is deposited at top of vagina, just below cervix

  17. Fertilization • Sperm inside semen must swim using tails towards egg, through cervix and through film of moisture lining wall of uterus • Sperm is attracted to chemical signal of egg • Egg only lives a few days after release from ovary, of if it has reached uterus by the time sperm finds it, it is too late to fertilize it • Therefore fertilization occurs in oviduct (Fallopian tubes) • Sperm has sac of enzymes at tip of head that digests way into egg, once one sperm has succeeded, a fertilisation membrane is produced stopping more sperm from getting in • Fertilization is the fusion of the nucleus of sperm and nucleus of egg together

  18. Implantation • Fertilized egg is called a zygote • Zygote is diploid (2 copies of each chromosome) • Zygote begins to divide soon after fertilization and is called an embryo • While dividing ball of cells move from oviduct towards uterus. • About 7 days after fertilization embryo sinks into soft lining of tissue called implantation • Progesterone maintains lining of uterus

  19. Amnion & Placenta Amnion: • a thin but strong sac that surrounds the fetus while it is growing inside the uterus • Secretes a fluid called amniotic fluid that supports the fetus from mechanical shock Placenta: • A projection from mother to child that allows for exchange of materials • Secretes progesterone & estrogen that keeps lining in good order, stimulates milk production, and prevents more eggs from being released from ovaries

  20. The Process of Birth • Baby ready to be born 9 months after fertilisation • A few weeks before birth baby turns over so head is downwards • Birth begins with walls of uterus contracting slowly & rhythmically • Amnion breaks releasing fluid • Cervix opens wider, baby’s head pushes out of cervix and vagina • Baby slides out, & placenta is cut • Placenta falls away from mother’s uterus and passes out of vagina

  21. HIV virus & AIDS • AIDs is caused by HIV (human immunodeficiency virus) • Virus lives in body fluids • HIV may live inside boy for many years before it produces symptoms of AIDS (acquired immune deficiency syndrome) • HIV prevents lymphocytes from defending body from disease • Eventually one or more infections (virus, bacteria etc.) cause death

  22. Methods of HIV transmission • Sexual intercourse with someone infected with the virus • Blood transfusions using blood containing the virus • Injections with needles previously used by someone with the virus

  23. Preventing transmission • Sexual intercourse is most common method of infection with HIV Use of condom can greatly decrease risk of virus passing from one person to another • Sterilize needles before use

  24. Birth Control • World population is growing rapidly and birth control can help control this growth Methods: • Natural (rhythm method) • Chemical (contraceptive pill, morning-after pill, spermicidal cream) • Mechanical (condom, IUD intra-uterine device) • Surgical (sterilization) • Condom helps prevent STDs as well as preventing pregnancy

  25. Homework • Read pgs 182-202 • Q 12.3 pg 187 • Q 12.4 pg 190 • Q 12.5 pg 198

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