Reproduction and variation Lesson 1 Sexual Reproduction Reproduction is one of the seven life processes. There are many ways in which organisms reproduce. One of these is sexual reproduction. Sexual reproduction is the fusing of two gametes (sex cells). Humans use sexual reproduction to produce their young, to do this the two parents (male and female) have different organs and reproductive systems to produce the two gametes. 1. Label these diagrams, 2. In your workbooks, list the function of each part of the human reproductive system. Male reproductive system Female reproductive system Males produce sperm cells, and females produce egg cells. How many usually participate? Size Number of chromosome s Mitochondria Special features Ovum (egg cell) 1 per menstrual cycle Sperm cell ~250 – 280 million per ejaculation Largest cell in the human body, diameter of ~0.12mm Half the number of chromosomes of the offspring (23 in humans) One of the smallest cells in the human body, ~50µm long Half the number of chromosomes of the offspring (23 in humans) 75 to 100 Tail for movement. Mitochondria in the middle to generate energy. Acrosome, at the very front of the sperm, contains enzymes to help it fuse with the egg. ~150,000 A special layer of jelly (called the zona pellucida) covers the cell membrane and is there to make sure only one sperm fertilises the egg. Diagram 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. Which organelle controls the cell? What is contained in this part of the cell? Why do sperm cells have mitochondria? What is the female sex cell called? Which system are sperm and egg cells part of? What is a gamete? How many chromosomes are there in gamete compared to the cells of the offspring? How many chromosomes are in an adult human cheek cell? Where are sperm cells produced? Where are egg cells produced? How does the egg cell stop more than one sperm cell fertilising it? What adaptations does a sperm cell have to help it reach the egg cell? Explain why gametes need to have half the number of chromosomes of the offspring. Lesson 2 Fertilisation Sexual reproduction is the fusing together of two gametes. In mammals (and some other animals), the gametes meet via sexual intercourse. During sexual intercourse, the man’s penis goes into the woman’s vagina. During sex, the male may ejaculate – this means release sperm into the vagina. The sperm that have been deposited in the vagina swim up towards the oviducts. The uterus and oviduct can also help move sperm closer to the egg. Usually, only one egg will have been released whilst at least 250 million sperm will have been deposited. Some will swim the wrong way, some will go down the oviduct without an egg cell in it. Despite egg cells releasing chemicals to help attract sperm towards it, only about 100 sperm will reach the egg of the 200 or so that make it to the correct oviduct. When the sperm reach the egg, they try to get through the egg cell membrane. When one gets through, the membrane of the egg cell changes so that others can’t get in. The tail of the sperm breaks off outside the egg cell. The nuclei of the sperm and egg cell join together. This is fertilisation. The fertilised egg cell is called a zygote. The fertilised egg continues its journey down the oviduct to get the uterus. The egg cell divides as it goes. Cell divisions increase the number of cells. It can take over a week to get to the uterus, and by the time it arrives it will have divided lots of times and will have over 300 cells. Once it implants into the uterus lining, it develops into an embryo. 16. 17. 18. 19. 20. 21. 22. 23. 24. Where does fertilisation take place? How are sperm cells adapted to reach the egg cell from the vagina? How does the egg cell stop itself being fertilised by more than one sperm? What happens to the nuclei of the sperm and the egg at fertilisation? What is a zygote? How many chromosomes are in a zygote? Where does the zygote travel to and how long does this take? What does the zygote do as it travels to its final destination? Annotate this diagram to explain what is happening at each stage. 25. Label this diagram. 26. In your workbook define each of the labels. 27. Challenge: By the time a zygote implants itself in the uterus, it has a new name, a blastocyst. A blastocyst forms when the zygote has divided enough to make over 200 cells. The zygote starts as single cell. If the number of cells in the zygote doubles each time there is a cell division, how many cell divisions are needed to make a blastocyst? Lesson 3 Foetal development and health In the earliest stages of development, a human baby is called an embryo. The embryo needs to get nutrients and oxygen, and to get rid of waste. It can’t do this for itself until it is born, and so the mother has to provide all the nutrition and oxygen and get rid of the embryo’s waste (like carbon dioxide). This is done through the placenta. The mother’s blood does not mix the embryo’s blood. They are kept separate in the placenta by a tissue called the placental membrane, and the nutrients and oxygen move from the mother’s blood to the embryo’s blood through this tissue. The waste products from the embryo moves from the embryo’s blood to the mother’s blood. Villi are adapted to increase the surface are for this. The umbilical cord links the placenta to the embryo. 28. Name five organs of the digestive system and state their function. 29. How are red blood cells adapted to carry oxygen? 30. What features of the small intestine make it good at getting digested food into the blood stream? 31. Describe the gas exchange of oxygen and carbon dioxide in your lungs. 32. Where is the egg cell fertilised? 33. What is a tissue? 34. Suggest how the mother gets rid of the embryo’s waste. 35. Label the following diagram of an embryo, including definitions with your labels. The fluid that surrounds the embryo is called amniotic fluid, and one its main purposes is to protect and cushion the developing embryo. After the first eight weeks of pregnancy, a human embryo is then called a foetus. At this stage the foetus has all the main features you would expect to see in a child. The foetus continues to develop and grow inside its mother’s uterus for a total of 40 weeks. It is not just nutrients and oxygen that can cross the placenta from the mother, drugs (legal and illegal) can cross the placenta as well. Therefore pregnant women have to be careful with the medicines they take, as some can affect the embryo. Alcohol and chemicals from cigarettes can cross the placenta and harm the developing embryo, which is why pregnant women are advised to avoid alcohol and cigarettes during pregnancy. This graph shows data for the UK. 36. What is happening to the number of women known to be smokers at birth? 37. The UK target is to reduce the number of women who smoke in pregnancy to 6% by 2022/23. Do you think this target will be met? Explain your answer Average reduction in birth mass/g All smokers Fewer than 10 cigarettes per day 10 to 19 cigarettes per day 20 or more cigarettes per day 38. Plot a graph to show the effect of smoking on birth mass. 39. Describe the trends seen in the graph. 142 96 183 200 Lesson 4 Birth and early years After about 40 weeks, the foetus is ready to be born. This happens in stages. Stage 1: Contractions gradually dilate (open up) the cervix and push the baby down the birth canal. This is the longest stage of labour and can last from 5 to 15 hours, sometimes as long as 36 hours. The cervix needs to dilate to 10cm before the woman can begin to push. The “waters will break” which means the baby’s head breaks the amnion and the amniotic fluid will come out. Stage 2: This is where the baby is pushed through the birth canal, caused by contractions from the muscles of the uterus. Stage 3: This is where the placenta (sometimes called the after birth) is delivered. 40. 41. 42. 43. 44. 45. 46. 47. How are the sperm and egg adapted for reproduction? Where are the sperm and egg produced? How does an embryo get the oxygen and nutrients it needs? Why do pregnant women need to be careful with the medicines they take? What is one of the effects of smoking on a foetus? Describe the changes that happen during stage 1 of labour Describe how the baby is born. Use the words contraction, uterus, push, cervix, vagina. What happens after the baby is born? Reproduction in other organisms. The gestation period is how long an organism is pregnant for. In mammals, usually the higher the body mass of the adult mammal, the longer the gestation period. However, not all organisms have gestation periods, because the embryo does not develop inside the body, it develops outside the body, for example, in an egg. Some animals use internal fertilization for reproduction and the unborn offspring develops inside the mother. Some animals use external fertilization – laying unfertilized eggs outside the mother for the father to fertilise. Look at the data below, which shows reproductive data for several different animals. Number of young Fertilization Survival rate 48. 49. 50. 51. Black rat snake 20 Bullfrog Cod Gorilla Tiger Salmon 5000 3000 1 3 200 Internal External External Internal Internal External 50% 1% 2% 60% 50% 15% Explain the difference between internal and external fertilisation. Describe the patterns shown by the data. Use numbers to help you make your points. Explain why the bullfrog and cod have thousands of young at one time. Suggest how organisms could increase the survival rate of their offspring. Lesson 5 Growth and puberty Puberty is when a child's body begins to develop and change as they become an adult. Girls develop breasts and start their periods. Boys develop a deeper voice and facial hair will start to appear. The average age for girls to begin puberty is 11, while for boys the average age is 12. But it's different for everyone, it's completely normal for puberty to begin at any point from the ages of 8 to 14. The process can take up to 4 years. These changes can be emotional and can bring about mood swings. It is important to talk to someone you can trust if you are worried about puberty. First signs Later signs Girls - The first sign of puberty in girls is usually that their breasts begin to develop. - It's normal for breast buds to sometimes be very tender or for one breast to start to develop several months before the other one. - Pubic hair also starts to grow, and some girls may notice more hair on their legs and arms. - Girls' breasts continue to grow and become fuller - Around 2 years after beginning puberty, girls usually have their first period - Pubic hair becomes coarser and curlier - Underarm hair begins to grow – some girls also have hair in other parts of their body, such as their top lip, and this is completely normal - Girls start to sweat more - Girls often get acne – a skin condition that shows up as different types of spots, including whiteheads, blackheads and pus-filled spots called pustules - Girls have a white vaginal discharge - Girls go through a growth spurt – from the time their periods start, girls grow 5 to 7.5cm (2 to 3 inches) annually over the next year or two, then reach their adult height - Most girls gain weight (which is normal) as their body shape changes Boys - The first sign of puberty in boys is usually that their testicles get bigger and the scrotum begins to thin and redden - Pubic hair also starts to appear at the base of the penis - The penis and testicles grow and the scrotum gradually becomes darker (read more about penis health) - Pubic hair becomes thicker and curlier - Underarm hair starts to grow - Boys start to sweat more - Breasts can swell slightly temporarily – this is normal and not the same as "man-boobs" - Boys may have "wet dreams" (involuntary ejaculations of semen as they sleep) - Their voice "breaks" and gets permanently deeper – for a while, a boy might find his voice goes very deep one minute and very high the next - Boys often develop acne – a skin condition that shows up as different types of spots, including whiteheads, blackheads and pusfilled spots called pustules - Boys go through a growth spurt and become taller by an average of 7 to 8cms, or around 3 inches a year, and more muscular After about four years 52. 53. 54. 55. 56. 57. – Girls develop more body fat along their upper arms, thighs and upper back; their hips grow rounder and their waist gets narrower - Breasts becomes adult-like - Pubic hair has spread to the inner thigh - Genitals should now be fully developed - Girls stop growing taller - Genitals look like an adult's and pubic hair has spread to the inner thighs - Facial hair begins to grow and boys may start shaving - Boys get taller at a slower rate and stop growing completely at around 16 years of age (but may continue to get more muscular) - Most boys will have reached full adult maturity by the age of 18 Describe the three stages of labour. What is the relationship between adult body mass and gestation length? Where does fertilisation occur in humans? How does an embryo get the oxygen and nutrients it needs? Why do organisms use external fertilisation tend to have more offspring? What changes happen in both girls and boys at puberty? The changes during puberty are caused by hormones. Hormones are chemical messengers that travel in the blood and trigger different processes. They cause the changes you see and feel in your body during puberty. An important part of puberty for girls is the beginning of their monthly cycle. This is known as the menstrual cycle. The menstrual cycle involves the preparation of the uterus lining so that it is able to receive a fertilized egg. If an egg is fertilized, it can implant itself in the prepared uterus lining. If it is not fertilized, the lining of the uterus breaks down and is lost from the body. This is called menstruation or a period. 58. 59. 60. 61. When does ovulation take place? How long is the average menstrual cycle? How long does menstruation last? A sperm can survive for up to 3 days in the uterus and the egg (ovum) lives for about 36 hours. If a woman ovulates on day 14 of her menstrual cycle, on which days will she be fertile? Lesson 6 Reproduction in plants Plants use sexual reproduction too. This means they have male and female sex cells, each of which provides half of the genetic information for the offspring. Wind or insects (depending on the type of plant) help move the male sex cell (pollen) to different plants to allow cross pollination. Pollination is the transfer of pollen from the male part of the plant to the female part of either the same plant or a different one. When the pollen gets to the female parts, a pollen tube grows so that fertilisation can take place. 62. Use the labels on the diagram to explain how pollination and fertilisation happen in plants. Key words : pollen, tube, nuclei, fertilisation, stigma, ovary Practical: • Use the scalpels to carefully dissect the flower the way you were shown by your teacher. • Identify as many parts of the flower as you can, but you must at least identify the anthers, stigma and style. • Cut into the style and see if you can find the ovules in the ovary. 63. Label this diagram, giving definitions for each label. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. What is the function of the flower in a plant? What is the ‘male’ sex cell in a plant called? What two ways is this gamete moved from one plant to another to allow pollination? What name would we give to the ‘embryo’ that is formed in a plant after fertilisation? Why do plants form fruits around their seeds? How long is the gestation period in humans? Briefly describe what happens in the three stages of labour. How many chromosomes are in a human gamete? Name three plant organs. Order these from smallest to largest: Cell, Organ, Organ System, Organelle, Organism, Tissue Lesson 7 Seed dispersal Seed dispersal is how a plant spreads its seeds. Different plants do this in different ways – by air, water or other organisms. 74. Explain what is meant by the following terms: a) Independent variable b) Dependent variable c) Control variable You are going to make a model of a seed from paper and investigate how long it takes to fall. For your independent variable choose one of the following: the number of paper clips; the length of the wings. 75. In your books write a method for investigating your independent variable. You must identify the dependent variable and control variable as well. 76. Draw a suitable results table to record your results. 77. Draw a graph of your results. 78. Write a conclusion – explain how the the independent variable affected how long it took the seed to drop. 79. Some people say that sexual reproduction must involve sex. They are wrong. Explain why. Lesson 8 Variation within a species Tigers and octopuses look very different. They are clearly different species. Lions and tigers however are more similar, but both are still quite different. They are clearly both cats, but they are different species of cat. If we got two tigers, they would both look different too, but they would be the same species. A species is defined as a group of organisms that are similar enough that they can reproduce with each other and produce fertile offspring. Fertile offspring are organisms that can themselves go on to have offspring of their own. Lions and tigers can breed with each other, but the offspring are infertile because they do not have functioning reproductive systems. Members of the same species are all similar but do show differences. Humans are a species, and each of us looks different – eye colour, height and shoe size are all examples of the differences between individuals. Even identical twins have different fingerprints! The scientific term for these differences is “variation”. Variation is group into two types: Continuous variation and discontinuous variation. Continuous variation is for things like height, weight or hand span. They are characteristics that change gradually over a range of values, and the value could fall anywhere within a range. Continuous variation is usually caused by both inheritance and your environment. A graph of continuous variation often has this classic shape known as a bell curve. Discontinuous variation is for things like blood group, sex (male or female) or ability to roll your tongue. These variations take one of only a limited number of possible values. Discontinuous variation is usually only caused by inheritance. 80. Describe the differences between continuous and discontinuous variation. 81. Plot a line graph of the data below. Height category (cm) Less than 130 130 to less than 135 135 to less than 140 140 to less than 145 145 to less than 150 150 to less than 155 155 to less than 160 160 to less than 165 165 to less than 170 170 to less than 175 175 or more Number of people in category 1 5 13 26 31 34 32 25 13 5 1 82. Suggest why the peoples’ heights were grouped into categories instead of using each individual’s actual height. 83. What causes continuous variation? 84. The same group of people above had their blood group recorded. Draw a bar graph of the data table below. Blood group Number of people in category A 78 B 7 AB 19 O 82 85. What causes discontinuous variation? 86. For each of the following, identify if it is continuous or discontinuous variation. a) How deep into the ground the roots of a cactus go. b) Peppered moths can either be light in colour, or dark in colour. c) Snap dragon petals can be red, white or pink. d) How much milk a cow can produce in litres. e) Hand span (this is a measure of the distance between the tip of someone’s little finger and their thumb, when their hand is stretched out). f) Length of giraffe necks. g) The colour of a jelly baby.
