Reproduction in animals


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Reproduction in animals

  1. 1. Two types of Reproduction 1. Asexual 2. Sexual Offspring are produced by a single parent; No sperm and egg needed Involves the fusion of two cells, one from a male and the other from a female
  2. 2. Which type of reproduction produces clones? Asexual reproduction. Offspring are genetically identical
  3. 3.  Fertilisation is the fusion of the male and female gamete nuclei to form a zygote  Zygote is the first cell that forms after fertilisation
  4. 4. hermaphrodite  have both male and female sex organs Tapeworm EarthwormSnail Flower
  5. 5. Fertilisation can be: a) Internal:  in reptiles, birds & mammals b) External:  in most fish & amphibians
  6. 6. Why is internal fertilisation essential amongst land animals? No water in the animal’s immediate environment to carry the sperm cells to the eggs
  7. 7. A cod [fish] lays millions of eggs in one year but a rabbit produces only a few thousand. Question
  8. 8. External fertilisation in fish:  Not all eggs are fertilised  Young ones are not protected by the mother’s body
  9. 9. Table 1 Comparison of sexual and asexual reproduction. ASEXUAL SEXUAL 1) One parent needed Two parents needed, a male and a female 2) No gametes required (sex cells) Gametes required 3) Offspring are genetically identical (clones) Offspring are not genetically identical
  10. 10. Table 1 Comparison of sexual and asexual reproduction. ASEXUAL SEXUAL 4) Only one individual is needed to colonise a new area A male and a female are needed 5) A fast process A slow process 6) Always increases the population Does not always increase the population 7) Very common among plants and simple animals Almost all animals and plants
  11. 11. ASEXUAL SEXUAL Advantage: a good characteristic shows up in all the offspring Advantage: new varieties are produced, which may be more able to adapt to the new environment Disadvantage: a defect in the parent shows up in all offspring ; no variation occurs Disadvantage: excellent individuals cannot give identical offspring
  12. 12. Gonads & Gametes MALE FEMALE Gonads [sex organs] Testes Ovaries Gametes [sex cells] Sperm Ovum / egg Gametes are produced by a type of cell division called: Meiosis
  13. 13. The Male Reproductive System (scrotal sac) (vas deferens)
  14. 14. The male Excretory System
  15. 15. The male Excretory & Reproductive Systems bladder ureter sphincter muscle prostate gland urethra testis scrotum penis sperm duct
  16. 16. Functions of the testes: 1. Produce sperms 2. Produce the sex hormone testosterone
  17. 17. Function of the epididymis: Stores sperms for 2-3 months [6m long but coiled = 3.8cm]
  18. 18. Function of the sperm duct:  Stores sperms  A passageway for sperms from epididymis to urethra
  19. 19. Scrotum  holds testes outside the body  temperature of about 1-2C lower than body temperature  sperms only develop properly inside the testes at a slightly cooler temperature  heat can cause infertility
  20. 20.  ejaculation  is the expulsion of semen from the urethra  copulation (sexual intercourse / mating)  is when the man's penis is inserted into the woman's vagina and excited until orgasm and ejaculation occur
  21. 21. Semen = fluids + sperms Semen from a bull Semen from a dog
  22. 22. Human semen contains  90-600 million sperms in 3 cm3 of ejaculate or semen Normal sperm count Low sperm count Why are sperms produced in large numbers? Increase chance for fertilisation
  23. 23. Fluids in semen are released from the:  seminal vesicles  prostate gland
  24. 24.  semen contains:  alkali  sugars  proteins Urine is ACIDIC.  Functions of the fluid: 1. the fluid keeps the sperms alive 2. helps them to swim vigorously
  25. 25. Fig. 2 Ovum structure.
  26. 26. Fig. 3 A spermatozoon.
  27. 27. Function of the TAIL: to swim towards the ovum
  28. 28. Function of the NUCLEUS: Fuses with ovum nucleus to produce the offspring
  29. 29. Function of the MITOCHONDRIA: releases energy for tail to move
  30. 30. releases enzymes to penetrate ovum Function of the ACROSOME:
  31. 31. [Old term]
  32. 32. Question: JUNE 1998 What are the main differences between a sperm and an ovum? (4 marks) SPERM OVUM 1. Small Large 2. Has a tail No tail 3. Has an acrosome No acrosome 4. No food reserves Has food reserves
  33. 33. Question: SEP 2006 The female egg and the male sperm are two specialized cells. Compare the egg and the sperm in each of the following characteristics: i) size (2 marks) ii) numbers produced (2 marks) iii) movement. (2 marks)
  34. 34. Fig. 4 The human female reproductive system. Endometrium (uterus lining) Uterus Cervix Vagina Ovary Fallopian tube (oviduct) ‘womb’ – common term for uterus
  35. 35. TWO separate openings in female. Vagina Urethra
  36. 36. Ovulation  the release of an ovum from the ovary  occurs once every 28 days Developing follicles Mature follicle Corpus luteum /yellow body Ovulation Graafian follicle
  37. 37. Ovulation caught on camera: takes 15 minutes Ovum Follicle Ovary Surgical instrument
  38. 38. An ovum develops inside a:  fluid-filled Graafian follicle
  39. 39. What happens to an egg if it is not fertilised? If not fertilised within a day or so it will die
  40. 40. Vagina Cervix Ovary Fallopian tube Ovum Uterus Sperm cells deposited in vagina Fertilisation
  41. 41. What happens during menstruation?
  42. 42. Functions of: Ovary: 1. Produces ova (eggs) 2. Produces sex hormones
  43. 43. Functions of: Fallopian tubes: 1. Pathway for sperms to reach the ovum 2. Fertilisation occurs inside it 3. Has cilia and is muscular to move ovum towards uterus
  44. 44. Functions of: Uterus: 1. An embryo attaches to the uterus lining (becomes implanted) 2. An embryo develops inside it 3. Muscles in uterus contract to give birth implantation
  45. 45. Functions of: Cervix: 1. To allow menstrual blood to flow into the vagina 2. To direct the path of sperm into the uterus so fertilisation may occur 3. Becomes blocked by mucus when pregnant to avoid infections
  46. 46. Functions of: Vagina: 1. Penis is inserted to deposit semen 2. Passageway for menstrual blood 3. Serves as the birth canal
  47. 47. Side view of female reproductive system
  48. 48. Question: MAY 2012 Describe the role of each of the following in a female: i) vagina; (3) ii) oviduct; (1) iii) ovary; (3) iv) uterus. (2)
  49. 49. Question: MAY 1999 Trace the path of the male gamete, from its site of origin until it reaches the female gamete in a mammal. Diagrams are not expected, but detail of how and what helps the male gamete to reach the female gamete at the site where fertilisation usually takes place, are important. (10 marks)
  50. 50. Testis, epipidymis, sperm duct, urethra Top of vagina, cervix, uterus, fallopian tube
  51. 51. Question What are the functions of the following? MALE FEMALE UTERUS URETER URETHRA
  52. 52. MALE FEMALE UTERUS Absent Where embryo develops URETER URETHRA
  53. 53. MALE FEMALE URETER Urine flows from kidney to bladder Urine flows from kidney to bladder
  55. 55. MALE FEMALE URETHRA Semen & urine flow to exterior Urine flows to exterior
  56. 56. How long does an ovum & a sperm survive once released?  12–24 hours  1-3 days in the presence of fertile mucus
  57. 57. How long is the fertile period?
  58. 58. Can you predict with certainty when the fertile period is going to be? NO
  59. 59. In a short cycle of 21 days, ovulation will occur around day 7 and there will be no pre-ovulatory infertile days.
  60. 60. Sexual Development Puberty
  61. 61. Puberty  is the stage of the beginning of sexual maturity In girls: 12-15 years In boys: 13-17 years
  62. 62. Primary sexual characteristics  appear in the growth and enlargement of the reproductive organs  In boys:  sperm production  ejaculation starts  In girls:  ovulation starts
  63. 63. Secondary sexual characteristics  appear as changes in body shape and appearance
  64. 64. Secondary sexual characteristics  Boys: 1. grow hair on the face, armpits and pubic regions
  65. 65. Secondary sexual characteristics  Boys: 2. voice deepens 3. limb and chest muscles develop
  66. 66. Secondary sexual characteristics  girls: 1. develop hair on the armpit and pubic regions 2. pelvic girdle widens
  67. 67. Secondary sexual characteristics  girls: 3. breasts develop 4. fat deposits under the skin
  68. 68. Sex hormones are:  testosterone in males  secreted by:  oestrogen in females  secreted by:
  69. 69. Menopause Occurs in females [45-50 years] What happens:  ovaries stop producing eggs  menstrual periods stop Reason for menopause:  female stops producing sex hormones in sufficient amounts
  70. 70. What about males?  go on producing sperm throughout life  however the amount of testosterone gradually falls
  71. 71. The Menstrual Cycle The first day of menstruation is day 1 of the cycle.
  72. 72. Fig. 5 Development of follicles inside the ovary. (Yellow body)
  73. 73. The menstrual cycle  is controlled by 4 hormones 1. FSH (follicle stimulating hormone) 2. LH (luteinising hormone) 3. Oestrogen 4. Progesterone
  74. 74. Where is each hormone produced? 1. FSH 2. LH pituitary gland
  75. 75. Fig. 6 Summary of the main events during the menstrual cycle. 3. Oestrogen 4. Progesterone
  76. 76. 3. Oestrogen 4. Progesterone
  77. 77. Control of the menstrual cycle Hormone Function FSH Causes ovary follicles to develop LH Causes ovulation; Causes corpus luteum to form from follicle Oestrogen Causes repair of the uterus lining before ovulation Progesterone Causes uterus lining to remain thick after ovulation
  78. 78. Changes in uterus lining Breaks down: progesterone falls Repaired: oestrogen risesRemains thick: progesterone rises
  79. 79. Fig. 7 Changes in hormones during the menstrual cycle.
  80. 80. Changes which occurred in the thickness of the lining of the uterus of a woman over 84 days. With reference to the graph : What took place during days 0 to 5 and days 28 to 33? Menstruation
  81. 81. What event occurred on day 14 and day 42? Ovulation
  82. 82. What event occurred shortly after day 42? Pregnancy
  83. 83. Development and Pregnancy
  84. 84. Fig. 8 Fertilisation in oviduct.
  85. 85. Fig. 9 Formation and implantation of embryo.
  86. 86. How is it possible for only ONE sperm to penetrate the ovum?  a fertilisation membrane forms around the ovum to act as a barrier soon after a sperm enters
  87. 87. Fig. 12 Embryo developing inside uterus.
  88. 88. Fig. 12 Embryo developing inside uterus.
  89. 89. The Placenta  is shaped like a plate  forms a close association between the embryo and the mother
  90. 90. The Placenta has many Villi  which stick into blood spaces in the wall of the uterus  the mother’s blood circulates through these spaces
  91. 91. Fig. 11 The mother’s blood and that of the foetus come close together in the placenta, but do not mix.
  92. 92. Placenta Glucose Water Salts Amino acids Vitamins Antibodies Fatty acids GlycerolUrea Carbon dioxide
  93. 93. From embryo to foetus a developing human from usually two months after conception to birth
  94. 94. 8 week human foetus in palm of hand
  95. 95. Functions of the Placenta 1. produces the hormones oestrogen and progesterone which stop menstruation and prevent further eggs being produced by the ovaries 2. allows food and oxygen to enter the foetus 3. helps to remove wastes like urea and carbon dioxide from foetus
  96. 96. No mixing of blood at the placenta
  97. 97. Question: MAY 2010 IIB List TWO ways how a sexually transmitted disease (STD) can be transmitted from a pregnant mother to the baby. (4) 1. Microbes can cross the placenta and infect the baby before birth. 2. Microbes can be transmitted from mother to baby during the delivery as the baby passes through the birth canal. 3. During breastfeeding as is the case of HIV.
  98. 98. List TWO precautions that can reduce the incidence of STDs. (4)  Use of latex condoms for vaginal, anal and oral sex during sexual contact/  If you have an STD do not have sex until treated and cured/  Avoid multiple sex partners/avoid casual encounters/abstain (do not have sex)/ ask partner about STD/regular check up Any TWO or equivalent 4 marks Do not award any mark if students mention contraception (unless condoms are specifically mentioned)/ more sexual education. If students mention protection award 1 mark only.
  99. 99. Functions of the amniotic fluid:- 1. acts as a shock-absorber 2. keeps a constant temperature 3. keeps the embryo buoyant and free to grow 8 weeks
  100. 100. Twins Identical twins Fraternal twins [non identical]
  101. 101. Question: SEP 2002 Copulation in humans may result in fertilization. When fertilization occurs, it may result in the formation of a single zygote, identical twins, or fraternal twins. Explain clearly what happens when fertilisation results in the formation of: (I) a single zygote; (II) identical twins; and (III) fraternal twins. (2, 3, 2 marks)
  102. 102. Question: MAY 2012 1. List TWO physical changes that can indicate that a female is pregnant. (2) a. Breasts enlarge b. Weight is gained
  103. 103. Question: MAY 2012 2. During the ninth month of pregnancy, the female undergoes shortness of breath. Give a reason for this observation. (1) Uterus expands and lungs get compressed.
  104. 104. BIRTH
  105. 105.  gestation  the period from fertilisation to birth  labour  the uterus begins to undergo occasional contractions which become steadily more frequent and powerful
  106. 106.  oxytocin  a hormone made by the pituitary gland What causes the uterus to contract? Uterus between contractions Uterus during contractions
  107. 107. Stages in birth
  108. 108. Afterbirth  the placenta comes away from the wall of the uterus and passes out of the vagina TWINS!!
  109. 109. During pregnancy the cervix is blocked by a mucus plug. Why?  To prevent infection  The mucus plug comes out as the cervix dilates in labour or shortly before
  110. 110. Question: MAY 2011 6a.The following diagram shows the four stages of the human menstrual cycle. i) Briefly describe the changes taking place at each stage 1, 2, 3 and 4. (10)
  111. 111. b. During gestation the placenta develops into a large disc bearing many finger-like villi. i) Explain how the placenta is joined to the foetus. (1) By means of the umbilical cord which contains blood vessels.
  112. 112. ii) Explain why in dizygotic (non-identical) twins there are two placentas. (3) Two eggs/ova and two sperms were needed to produce non-identical twins. Each egg/ovum was fertilised and two separate zygotes formed. Each zygote produced a different individual. iii)What happens to the placenta after birth? (2) The uterus contracts to expel the placenta. This is called afterbirth.
  113. 113. Parental Care involves 1. feeding the baby (lactation)  mammary glands secrete milk 2. keeping baby clean 3. warm
  114. 114. Breast-feeding  allows close contact between the mother and her baby, which is good for both of them, physically and emotionally
  115. 115. The mother’s milk is perfect food for the baby because it contains: 1. all the necessary nutrients 2. the mother’s antibodies which makes the baby immune from disease during the first few months of life
  116. 116. A newborn baby cannot take in solid food because:  no teeth to chew  the digestive system cannot deal with solid food
  117. 117. Colostrum:  is produced by the breasts beginning during pregnancy and continuing through the early days of breastfeeding
  118. 118. Colostrum:  is yellow to orange in colour and thick and sticky  is low in fat, and high in carbohydrates, protein, and antibodies to help keep the baby healthy Colostrum Breast milk
  119. 119. Colostrum:  is extremely easy to digest, and is therefore the perfect first food for the baby  has a mild laxative effect, helping the baby to egest for the first time  has white blood cells in it to protect baby from viruses and bacteria
  120. 120. Pregnancy Test
  121. 121. Birth control or Contraception
  122. 122. Birth control or Contraception  contraception is any procedure which prevents fertilisation  Three groups: 1. stop sperms reaching the egg 2. stop the eggs being produced 3. stop the fertilised egg from developing in the uterus [not in syllabus]
  123. 123. Birth control methods can be:  Natural e.g.  temperature (thermal) method  the mucus Billings method  Artificial e.g.  use of the:  Condom  Diaphragm  Contraceptive pill
  124. 124. None of the contraceptive methods is 100% effective.
  125. 125. What is the MOST effective method of avoiding pregnancy?
  126. 126. Temperature (Thermal) method  the body temperature rises slightly at the time of ovulation
  127. 127. Temperature (Thermal) method  the body temperature is taken every morning and a graph is plotted
  128. 128. Digital fertility thermometer
  129. 129. If pregnant:  no menstruation  the body temperature remains up throughout pregnancy The temperature is low until ovulation, after which it rises for 10-16 days, and drops back with onset of period.
  130. 130. Two Australian doctors: The mucus Billings method Dr Evelyn & Dr John Billings
  131. 131. The mucus Billings method  helps to determine the time of ovulation
  132. 132. Why is mucus produced at the cervix?  to protect the sperm from the acidity in the vagina  to allow sperm to move freely through the cervix
  133. 133. Days with & without mucus during the menstrual cycle Pre-ovulation: no mucus Post-ovulation: no mucus
  134. 134.  Pre-Ovulation  Dry at first  Gradually, more mucus will accumulate – yellow, cloudy, or white in color and sticky to the touch. Texture of mucus changes
  135. 135.  Approaching Ovulation  the cervical mucus will increase  first, there will be a moistness or stickiness to the mucus, as well as a white or cream-colored appearance.
  136. 136.  During Ovulation  mucus = large amount ; resembles “egg whites”, often semitransparent.  mucus = increasingly slippery and ‘stretchable’. This is the most fertile time.
  137. 137.  Following Ovulation  Mucus = less slippery ; becomes sticky and cloudier
  138. 138. Sperms cannot swim through thick mucus INFERTILE FERTILE Sperms can swim through thin mucus
  139. 139. Watery
  140. 140. Combined with temperature: On its own: The mucus method
  141. 141. Question: MAY 2010 Compare the cervical mucus in the female reproductive system at ovulation and after ovulation. (2) At ovulation, cervical mucus gets very wet, stretches between the fingers for an inch or more, and resembles raw egg white. After ovulation, cervical mucus becomes sticky and cloudier and dryness may also result.
  142. 142. The sheath (condom)  is worn by the male over the erect penis  forms a barrier to sperms
  143. 143. The sheath (condom)  is quite reliable if used properly; best to use it with a spermicide  disadvantage:  can tear  slip off
  144. 144. The cap or diaphragm (fig. 17)  is worn by the female just before sex  a barrier to sperms  disadvantage:  can slip out of place
  145. 145. Question: SEP, 2010 Explain how the use of a diaphragm by a female prevents fertilisation. (1)
  146. 146. Spermicides kill sperms
  147. 147. Spermicides  unreliable on their own, but improve efficiency of the diaphragm and sheath
  148. 148. The oral contraceptive pill:  taken by the female to prevent any eggs being produced in the ovary  it stops ovulation  one tablet is taken daily throughout the menstrual cycle except for about a week during menstruation
  149. 149. The oral contraceptive pill:  contains chemical substances identical to oestrogen and progesterone  very effective  Disadvantages: 1. can raise blood pressure 2. cause an increase in weight
  150. 150. Sterilisation:  the person has an operation which prevents conception permanently Vasectomy: Sterilisation of a man  about 1 in 2,000 men can become fertile again after a vasectomy
  151. 151. Tubal ligation: Sterilisation of a woman  more than 99% effective  1 in 200 women will become pregnant after being sterilised
  152. 152.  there is a slightly higher risk of ectopic pregnancy after tubal ligation
  153. 153. As a last note: ever hear of viagra?
  154. 154. Question: MAY 2012 A young female had a contraceptive implant in which tubes of progestin (a form of progesterone) were implanted under the skin. Name TWO hormones that are not released from the pituitary gland as a consequence of this. (2) FSH LH
  155. 155. Question: MAY 2009 Describe each of the following processes and explain the benefits of each: vasectomy; (3) Vasectomy is a form of relatively permanent birth control method/contraception in males. The sperm ducts are cut and tied in a surgical operation to prevent sperms from being ejaculated.
  156. 156. Question: MAY, 2010 1) Explain why a male still continues to have a deep voice after he undergoes a vasectomy? A deep voice is due to the effect of testosterone. This sex hormone is still produced in the body. 2) Explain why after a vasectomy the seminal fluid contains no sperm. (3) As the sperm ducts are cut and tied and sperms cannot move into the urethra.
  157. 157. THE END