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