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Reproduction

  • Reproduction is the process that makes more of the same kind of an organism
  • There are two types of reproduction, asexual and sexual reproduction
Asexual Reproduction
  • The process resulting in the production of genetically identical offspring from one parent
  • It is the formation of a new organism, without the involvement of gametes or fertilization

Bacteria

  • Bacteria reproduce asexually by binary fusion
  • Inside an individual bacterium, the DNA replicates
  • Then the cell divides into two, with each daughter cell containing a copy of the parental DNA
  • Once the daughter cells have grown, they can also reproduce

Fungi

  • Fungi can reproduce asexually by producing spores, which may be formed inside a structure called a sporangium
  • When ripe, the sporangium bursts open allowing the spores to be dispersed
  • In suitable conditions, the spores germinate and grow to form new individuals

Potatoes

  • Potatoes are stem tubers
  • The parent plant photosynthesizes and stores the food produced in underground stems, which swell to form tubers
  • Each tuber contains stored starch, and there are buds in depressions in the surface known as eyes
  • In suitable conditions, the buds use the stored food to form shoots, from which roots also develop
  • Each tuber can form a new plant

The Advantages and Disadvantages of Asexual Reproduction

Sexual Reproduction
  • Sexual reproduction is a process involving the fusion of the nuclei of two gametes (sex cells) to form a zygote and the production of offspring that are genetically different from each other
  • Fertilization is the fusion of gamete nuclei
  • Nuclei of gametes are haploid and the nucleus of a zygote is diploid

The Advantages and Disadvantages of Sexual Reproduction

Sexual Reproduction in Plants

  • Reproduction in flowering plants may occur both sexually or asexually
  • Self-pollination is the transfer of pollen grains from the anther of a flower to the stigma of the same flower or different flower on the same plant
  • Cross-pollination is the transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same species
  • Fertilization occurs when a pollen nucleus fuses with a nucleus in an ovule

Parts of a Flowering Plant (Photo Credit: Homestratosphere.com)

Pollen Grains

  • Wind-pollinated Flowers
    • Pollen grains are smooth, light and very small to be easily carried by the wind
    • They are produced in large quantities
  • Insect-pollinated Flowers
    • Pollen grains are big, and with hooks to attach to insects’ legs
    • They are produces in smaller quantities

Growth of Pollen Tube

  • Pollen grain germinates and grows pollen tube
  • Pollen tube grows down style
  • It secretes enzymes to digest a pathway through the style
  • Ovule is surrounded by layers of integuments, at one end, there is a small hole called micropyle
  • Pollen tube grows throughout the micropyle and reaches the ovule
  • Tip of pollen tube breaks open
  • Male gametes travel down the pollen tube and enter the ovule
  • Male gametes fuse with female gamete and zygote is formed

Structural Adaptations of Insect-pollinated and Wind-pollinated Flowers

Environmental Conditions Affecting Germination

  • Water
    • Absorbed through the microphyle, needed to activate enzymes for converting insoluble food stores into soluble food for growth and energy production
  • Oxygen
    • Needed for respiration, to release energy for growth and chemical changes for mobilization of food reserves
  • Warmth/Temperature
    • Enzymes present in the seed get activated and work best at optimum temperature (20 – 40°C)
  • Light Intensity
    • High or very low light intensity does not allow enzymes to function normally

Sexual Reproduction in Humans

Male Reproductive System

  • Testes: Produce sperm and testosterone
  • Scrotum: A sac that keeps testes cool (its outside the body)
  • Sperm Ducts: Link testes to urethra, allows passage of semen containing sperm
  • Prostrate Gland: Produce alkaline fluid (semen)
  • Urethra: To urinate, pass semen (+ sperm) through penis
  • Penis: Becomes firm, inserted into the vagina during sexual intercourse (to transfer sperm)

Male Reproductive System (Photo Credit: True.org)

Female Reproductive System

  • Ovaries: Contain follicles, produce and store eggs, produce estrogen
  • Oviducts: Carries ovum to uterus. Fallopian tubes = site of fertilization
  • Uterus: Where the fetus develops
  • Cervix: A ring of muscles that separate the vagina from the uterus
  • Vagina: Receives sperm from an erect penis during intercourse

Female Reproductive System (Photo Credit: True.org)

Adaptive Features of Sperm

  • Tail (for motility) which propels it through the cervix, uterus, and Fallopian tube towards the egg
  • Each sperm has many mitochondria to release the energy needed for its journey
  • Acrosomes allow them to break through the cell membrane of the egg

Adaptive Features of Egg Cells

  • It has a large cytoplasm which contains the nutrients and mitochondria needed for mitosis after fertilization
  • Each egg has a special cell membrane which only allows one sperm to fertilize it

Fertilization

  • When the sperm and egg nucleus fuse together, they form a zygote
  • The zygote continues to move slowly down the oviduct
  • As it goes, it divides by mitosis
  • After several hours, it has formed a ball of cells called embryo
  • It takes several hours for the embryo to reach the uterus and by this time it will be a ball of 16 or 32 cells
  • The uterus has a thin spongy lining, and the embryo sinks into it
  • This is called implantation

Functions of the Umbilical Cord, Placenta, Amniotic Sac, and Amniotic Fluid

  • Umbilical Cord
    • Transports nutrients/excretory products
    • Attaches th placenta to the fetus
  • Placenta
    • Prevention of material and fetal blood mixing
    • Protection against mother’s immune system
    • Supply of oxygen to fetus
    • Loss of carbon-dioxide from fetus
    • Loss of urea/waste
    • Protection against pathogens
    • Transfer of antibodies
    • Supply of nutrients
    • Secretes hormones
  • Amniotic Fluid
    • Support fetus
    • Protects against damage
    • Provides constant temperature
    • Allows fetus to move
    • Needed for bone/muscle growth/development
    • Helps lungs/gut development
  • Amniotic Sac
    • Membrane from embryo cells; encloses fetus
    • Prevents entry of pathogens
    • Secretes the amniotic fluid

The Growth and Development of the Fetus

Photo Credit: Dummies.com

  • The blastula develops into an embryo and some of the cells form a placenta, linking the embryo with the uterus lining
  • Organs such as the heart develop, and after 8 weeks, the embryo is called a fetus
  • Some toxins, e.g. nicotine, and pathogens, e.g. rubella virus, can pass across the placenta and affect the fetus

Antenatal Care

  •  Antenatal (before birth) care is a routine care for the healthy pregnant woman

Dietary Needs

  • Before the baby is born, it obtains all its dietary requirements from its mother through the placenta
  • The mother’s diet needs to be balanced so that the fetus receives all the materials needed for healthy growth and development
  • If the mother’s diet is deficient in any nutrients, the baby may not develop properly, so her diet should contain plenty of:
    • amino acids: healthy growth and development
    • calcium: development of the skeleton
    • iron: red blood cell formation
    • energy (carbohydrates/fats): help to move mother’s heavier body

Exercise

  • Gentle exercise (swimming, walking, etc.)
  • Special exercises

Things to Avoid

  • Drugs: aspirin, heroin
  • Smoking: Nicotine and CO
  • Alcohol drinking
  • Viruses: HIV, rubella (can pass across the placenta, risking the fetus health)

The Advantages and Disadvantages of Breast-feeding Compared with Bottle-feeding using Formula

The Processes involved in Labor and Birth

Photo Credit: MicrobeNotes.com

  • Stage 1
    • The muscular walls of the uterus start to contract slowly stretch the opening of the cervix
    • The pressure breaks the amniotic sac, releasing the amniotic fluid
    • Contraction gradually becomes more frequent, pushing the baby down towards the cervix, which become dilated to allow baby to pass through
  • Stage 2
    • The vagina stretches to allow the baby to be born
  • Stage 3
    • The baby is still attached to the placenta by the umbilical cord, so this is cut and tied
    • The placenta breaks away from the wall of the uterus and passed out (afterbirth)

Sex Hormones in Humans

  • Sex hormones are responsible for the development of secondary sexual characteristics at puberty
  • Testosterone is secreted by the testes in males
  • Estrogen is secreted by the ovaries in females
  • The sex organs become mature and start to secret hormones, making gametes (ova and sperm). This happens at about 10 -14 years

Secondary Sexual Characteristics at Puberty

Sited of Production of Estrogen and Progesterone during the Menstrual Cycle and in Pregnancy

The Menstrual Cycle

  • The menstrual cycle in women is a recurring process in which the lining of the uterus is prepared for pregnancy, and if pregnancy does not happen, the lining is shed at menstruation
  • The cycle last about 28 days

The Role of Hormones in Controlling the Menstrual Cycle and Pregnancy

Methods of Birth Control in Humans

  • There are four main groups of birth control methods: natural, chemical, mechanical, and surgical
  • Natural Methods
  • Chemical Methods
  • Mechanical Methods
  • Surgical Methods

The Use of Hormones in Contraception and Fertility Treatments

  • Fertility drugs are used when the woman is not producing enough eggs
  • She is given hormones, including FSH, and LH, that cause multiple release of eggs

Artificial Insemination (AI)

  • An artificial insemination procedure uses a thin, flexible tube (catheter) to put sperm into the woman’s reproductive tract (vagina, cervix, and uterus) around the time of ovulation
  • For some couples with infertility problems, insemination can improve the chances of pregnancy

In Vitro Fertilization

  • If the woman has a problem with blocked oviducts, the eggs are removed from her ovaries just before they are due to be released, and placed in a warm liquid in a Petri dish.
  • Some of her partner’s sperms are added, and fertilization takes place in the dish
  • Two or three of the resulting zygotes are placed into her uterus, where they develop in the usual way
  • This is called in vitro fertilization

The Social Implications of Contraception and Fertility Treatments

  • Fertility
    • Stress is associated with the difficulty of having children
    • Multiple births might occur
    • Problems with unused embryos when used with IVF
    • Issues with elderly parents
    • Religious objections to the use of fertility drugs
    • Treatment might be expensive
    • Can be used to increase population (useful in countries where birth rate is low)
  • Contraception
    • It is a widely held belief that the pill revolutionized sex for women as they no longer had to worry about pregnancy
    • It allows for population control in a way that did not exist 100 years ago
    • Religion often forbids the use of contraception

Sexually Transmitted Infections (STIs)

  • Sexually transmitted infection is an infection that is transmitted via body fluids through sexual contact
  • Human immunodeficiency virus (HIV) is an STI

How the Spread of STIs is Controlled

  • Use of condoms during sexual intercourse
  • Abstinence from sexual intercourse
  • Screening of blood for transfusions
  • Use of sterile needles
  • Use of sterilized surgical instruments

How HIV Affects the Immune System

  • HIV attacks the lymphocytes, so the number of these cells in the body decreases
  • Lymphocytes produce antibodies against infections
  • If the body cannot respond to infections through the immune system, it becomes vulnerable to pathogens that might not otherwise be life-threatening
  • As a result, the patient has little or no resistance to a wide range of diseases such as influenza, pneumonia, blood disorders, skin cancer or damage to the nervous system, which the body cannot resist

The Methods of Transmission of HIV

  • Unprotected sexual intercourse
  • Across placenta at birth or in breast milk
  • Sharing needles
  • Blood for transfusion
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