LIV Biology - Reproduction

• Reproduction is when organisms produce new living

  things.
• Plants and animals reproduce to make new

  individuals of the same species.
• If organisms didn't reproduce, species would die out.
• There are two types of

  reproduction:

  
  

  1. Asexual reproduction
  2. Sexual reproduction
• In asexual reproduction there is only one parent. The new individual is genetically identical to its parent.
• Organisms can reproduce asexually in many

  different ways:

  1. Some very small organisms can

  simply divide into two e.g. bacteria

  Some organisms can reproduce by

  ‘budding’. A part of their body

  breaks

  off and grows into a new organism e.g.

  some flowering plants
• Organisms can reproduce asexually in many

  different ways:

  • Some very small organisms can

  simply divide into two (e.g. bacteria)

  • Some organisms can reproduce by 'budding'. A part of their body breaks off and grows into a new organism (e.g. some flowering plants)
• Most animals reproduce sexually. In sexual reproduction there are two parents. The parents have sex organs which produce sex

  cells or gametes. The offspring of sexual reproduction are

  genetically quite different to their parents.
• Humans use sexual reproduction to produce their

  young. In order to do this, the two parents have to have

  sex organs so that they can produce sex cells. In humans, males and females have different reproductive systems and sex organs
• In males the sex cells are called sperm. Sperm are

  produced in sex organs called testes
• In females the sex cells are called eggs. Eggs are

  produced in sex organs called ovaries.
• Human children are born with a complete set of sex

  organs, however they do not become active until

  later in life. Between 10 and 18 the testes start to make sperm

  and the ovaries start to make eggs. This time of development in their life is called puberty. As well as these changes, other physical and emotional changes may also occur.
• Puberty is the time in which a child's sexual and

  physical characteristics mature. It occurs due to hormone changes. Adolescence is the period between puberty and

  adulthood.
• Oestrogen and progesterone are secreted by

  the ovaries in females
• Testosterone is secreted by the testes in males
• Puberty in females

  Hair grows under arms

  Spots on face

  Breasts develop

  Ovaries begin to release eggs

  Periods begin

  Shoulders broaden

  Hips grow wider

  Growth of pubic hair
• Puberty in males

  Spots on face

  Hair grows under arms

  Erections occur

  Hair grows on face

  Testes and penis get bigger

  Growth of pubic hair

  Testes produce sperm

  Shoulders broaden

  Voice deepens
• The female reproductive system includes a

  cycle of events called the menstrual cycle. It lasts about 28 days, but it can be slightly less or more than this. Two hormones control the menstrual cycle: oestrogen and progesterone
• The uterus prepares for a new baby by building

  up a lining rich in blood. If an egg is not fertilised, the lining is not needed. The tissue will break down and be removed from

  the body together with a little blood. A new lining then builds up. The cycle stops while a woman is pregnant.
• The menstrual cycle lasts approximately 28 days
• Days 0 to 5: Uterus lining breaks down, known as menstruation or the period
• Days 6-13: Uterus lining grows thicker with blood vessels due to the hormone oestrogen
• Day 14: Ovulation occurs, releasing an ovum into the fallopian tube
• At ovulation, oestrogen levels drop and progesterone levels rise to maintain the uterus lining
• In the last few days of the cycle, if fertilization has not occurred, oestrogen and progesterone levels drop, leading to the breakdown of the uterus lining
• Unless a woman becomes pregnant, the cycle restarts after each period.
• Periods:

  Start – during puberty

  Stop – when pregnant (but also if malnourished,

  seriously ill or can be controlled with

  certain types of contraceptive pill)

  Finish – menopause at about 50-ish.
• Fertilisation is when a sperm from a man and an egg from a woman join together to make a new baby
• Sexual intercourse involves a man inserting his penis into

  the woman’s vagina. Before this can be done blood pressure in the tissue stiffens the penis, called an erection. Once the penis is inside the vagina, sperm may be released. This is called an ejaculation. They enter the uterus through the cervix and travel to the fallopian tubes. The fusion of the two gametes (sperm cell and egg cell) is called fertilisation. The fertilised egg divides to form a ball of cells called an embryo. The embryo implants itself in the lining of the

  uterus and begins to develop into a foetus.
• Fraternal (non identical twins):

  Occur when two fertilized eggs are implanted

  in the uterus wall at the same time

  
  

  May look similar, particularly given that they

  are the same age

  
  

  However, non-identical twins may also look

  very different from each other

  
  

  Two eggs and two sperm

  
  

  Seperate placentas
• Fertilisation; sperm cell joins with the egg cell in the oviduct and fusion of the nuclei occurs to form a zygote.
• Fertilised egg divides rapidly; it is still called a zygote at this stage. The zygote moves down the oviduct towards the uterus.
• Weeks 3-5. The embryo’s heart has started to beat. The formation of arms, legs, eyes, lips and nose has begun. The spinal cord grows faster than the rest of the body giving a tail like appearance. The placenta begins to provide nourishment for the embryo.
• Week 7. Major organs have all begun to form. The embryo has developed its own blood type. Hair follicles, knees, elbows and facial features are observable. The eyes have a retina and lens. The major

  muscle system is developed and the embryo is able to move.
• Weeks 8-12. The embryo is reactive to its environment inside the amniotic sac where it moves around. Hands and feet can be seen. By week 10 the embryonic period is over and the foetal stage begins.
• Weeks 13-16. The brain is fully developed and the foetus can suck, swallow and make irregular breathing sounds. Foetal skin is almost

  transparent. Bones are becoming harder. Eyebrows and eyelashes appear and the foetus makes active movements including kicks.
• Weeks 20-24. A protective waxy substance called Vernix and soft hair

  called lanugo covers the skin: this is gone by the birth. The foetus’ foot and fingerprints are forming. Foetus practices breathing with its

  developing lungs.
• Weeks 25-28. Rapid brain development

  occurs and the nervous system can

  control some functions. Foetus’ eyelids

  open and close.
• Weeks 29-32. There is a rapid increase in

  the amount of body fat a foetus has. The foetus sleeps 90-95% of the day
• Around week 40. The baby’s head moves down into the

  pelvis and is said to be “engaged”. The cervix relaxes, and the walls of the uterus begin to contract. The baby is born.