How Do Organisms Reproduce?

How Do Organisms Reproduce?

Why Do Organisms Reproduce?

• Reproduction is not essential for an individual’s survival, unlike eating, breathing, or getting rid of waste.
• It takes a lot of energy to reproduce.
• So, why do organisms reproduce? Discuss this in class!
• We notice organisms because they reproduce and exist in large numbers.

Do Organisms Create Exact Copies of Themselves?

• Organisms look similar because their body designs are similar.
• These body designs come from blueprints in the form of DNA in the cell nucleus.
• DNA contains instructions for making proteins, which shape our body designs.
• Reproduction involves copying DNA to create new cells.

How Do Cells Reproduce?

• Cells make copies of their DNA.
• These copies are separated into two new cells.
• New cells are similar but not always identical.
• DNA copying can have minor mistakes, leading to variations.

The Importance of Variation

• Variations help species survive changes in their environment.
• If the environment changes, some organisms with beneficial variations might survive while others die.
• For example, bacteria that can survive in warmer water will live if water temperature increases due to global warming.
• Variations help ensure the survival of species over time.

Key Points to Remember

• Reproduction helps in the continuity of species.
• DNA copying during reproduction can have minor variations.
• Variations are important for adapting to changes in the environment.

Modes of Reproduction Used by Single Organisms

Activities to Observe Reproduction:

1. Fission

• Unicellular organisms: Reproduce by dividing their cells (fission).
• Examples:
  • Amoeba: Splits into two equal halves in any plane.
  • Leishmania: Has a whip-like structure; fission occurs in a specific orientation.
  • Plasmodium: Divides into many daughter cells simultaneously (multiple fission).
• Yeast: Puts out small buds that grow further (as seen in Activity 8.1).

2. Fragmentation

• Fragmentation: Simple multicellular organisms break into fragments, each growing into a new individual.
• Example: Spirogyra (a filamentous algae).

3. Regeneration

• Regeneration: Some organisms can grow into new individuals from their body parts.
• Examples:
  • Hydra and Planaria: Can be cut into pieces, each growing into a complete organism.
• Process: Specialized cells proliferate, forming a mass of cells that develop into different cell types and tissues in an organized sequence.

Key Points:

• Unicellular organisms: Use simple methods like fission and budding.
• Multicellular organisms: Need more complex methods like fragmentation and regeneration.
• Regeneration: Different from reproduction as it usually involves specialized cells and organized development.

4. Budding

• Hydra: Uses regenerative cells for budding.
  • A bud forms as an outgrowth from repeated cell division.
  • The bud matures and detaches, becoming a new individual.

5. Vegetative Propagation

• Plants: Use parts like roots, stems, and leaves to grow new plants.
  • Methods include layering and grafting (e.g., sugarcane, roses, grapes).
  • Advantages:
    • Faster flowering and fruiting compared to seed-grown plants.
    • Useful for plants that can’t produce seeds (e.g., banana, orange).
    • Genetically similar to parent plants.

More to Know: Tissue Culture

• Tissue Culture: Growing new plants from plant tissues in artificial media.
  • Cells divide to form callus.
  • Callus transferred to growth medium with hormones.
  • Plantlets placed in soil to mature.
  • Produces many disease-free plants from one parent.

6. Spore Formation

• Bread Mould (Rhizopus): Reproduces by spore formation.
  • Hyphae: Thread-like structures (not reproductive).
  • Sporangia: Blob-on-a-stick structures containing spores.
  • Spores: Protected by thick walls, grow when in contact with moist surfaces.

Asexual Reproduction

• All modes discussed (budding, vegetative propagation, spore formation) involve creating new generations from a single individual.

Key Points

• Budding: New individuals grow from buds on the parent.
• Vegetative Propagation: New plants grow from roots, stems, or leaves.
• Spore Formation: Spores develop into new individuals.
• Asexual Reproduction: No need for another individual to reproduce.

Sexual Reproduction

What is Sexual Reproduction?

• Involves two individuals, male and female, to create a new generation.
• Examples: Bulls and cows for calves, hens and roosters for chicks.

Why the Sexual Mode of Reproduction?

Need for Variation

• Asexual reproduction creates exact copies, leading to slow variation.
• Variations help species survive changes in the environment.
• Sexual reproduction mixes DNA from two individuals, speeding up variation.

DNA and Variation

• DNA copying isn’t perfect, causing small variations.
• Variations from two different individuals combine to create new, unique combinations.
• This increases the chance of beneficial traits.

Problem of DNA Doubling

• Combining DNA from two parents doubles the DNA in the new generation.
• Too much DNA can disrupt cell functions.

Solution: Meiosis

• Multi-cellular organisms use meiosis to create germ-cells with half the DNA.
• When germ-cells combine, they restore the normal amount of DNA.

Specialized Germ-Cells

• Germ-cells in complex organisms have different roles:
  • Male gamete: Smaller, motile (moves around).
  • Female gamete: Larger, contains food stores.

Differences in Reproductive Organs

• The need for different gametes leads to different male and female reproductive organs.
• In some cases, it also causes differences in the bodies of males and females.

Key Points:

• Sexual reproduction involves two parents.
• It increases variation, helping species adapt and survive.
• Meiosis ensures the right amount of DNA is passed on.
• Male and female gametes have specialized roles.

Sexual Reproduction in Flowering Plants

Flower Parts and Their Functions

• Reproductive Parts: Stamens (male) and Pistil (female)
• Non-reproductive Parts: Petals and Sepals
  • Petals: Attract pollinators
  • Sepals: Protect the flower bud

Types of Flowers

• Unisexual Flowers: Have either stamens or pistil (e.g., papaya, watermelon)
• Bisexual Flowers: Have both stamens and pistil (e.g., Hibiscus, mustard)

Structure and Function of Stamens and Pistil

• Stamen (Male Part)
  • Produces yellow pollen grains
• Pistil (Female Part)
  • Ovary: Swollen bottom part containing ovules
  • Style: Middle elongated part
  • Stigma: Sticky top part where pollen lands

Fertilisation Process

• Pollination: Transfer of pollen from stamen to stigma
  • Self-Pollination: Pollen transferred within the same flower
  • Cross-Pollination: Pollen transferred to a different flower
• Agents of Pollination: Wind, water, animals

Post-Pollination Steps

• Pollen Tube: Grows from pollen grain through the style to ovary
• Fertilisation: Fusion of male germ-cell (pollen) with female gamete (egg cell) in ovule
• Zygote Formation: Zygote forms and develops into an embryo

Seed and Fruit Formation

• Seed Development: Ovule becomes a seed
  • Embryo: Future plant inside the seed
• Fruit Formation: Ovary ripens into fruit
  • Non-reproductive parts (petals, sepals, stamens, style, stigma) fall off

Importance of Seed Formation

• Germination: Seed grows into a new plant under suitable conditions

Reproduction in Human Beings

Human Reproduction

• Humans use a sexual mode of reproduction.

Body Changes During Growth

• General Growth: Increase in height, new teeth (milk teeth replaced).
• Puberty: Special changes in early teenage years.
  • Changes are not just body enlargement but new body features and sensations.

Common Changes in Boys and Girls

• Hair Growth: Thick hair in armpits and genital areas, thinner hair on legs, arms, and face.
• Skin: Becomes oily, pimples may appear.
• Awareness: Increased consciousness of own and others’ bodies.

Specific Changes in Girls

• Breasts: Increase in size, nipples darken.
• Menstruation: Begins around this time.

Specific Changes in Boys

• Facial Hair: Growth on the face.
• Voice: Begins to crack.
• Penis: Occasional enlargement and erection.

Timeline of Changes

• Changes happen slowly over months and years.
• Not at the same time or exact age for everyone.
• Individual Differences: Variations in patterns of hair growth, size and shape of breasts or penis.

Sexual Maturation

• Reason for Maturation: Creation of germ-cells for reproduction.
• Growth vs. Reproduction: Body focuses on growth first, then reproductive tissues mature as growth slows.
• Puberty: Period when reproductive tissues mature.

Linking Changes to Reproduction

• Germ-cells Joining: Sexual reproduction needs germ-cells from two individuals.
  • External Release: As in plants.
  • Internal Transfer: Bodies join for internal transfer of germ-cells, as in animals.
• Signals of Maturation: Changes like hair growth signal sexual maturity.

Special Organs for Reproduction

• Penis: Capable of erection for germ-cell transfer.
• Female Reproductive Organs and Breasts: Mature to carry and feed a baby.

Male Reproductive System

• Main Functions: Producing and delivering germ-cells (sperms).
• Testes: Produce sperms and hormone testosterone.
  • Located in the scrotum (outside the abdominal cavity) for lower temperature.
  • Testosterone: Regulates sperm formation and puberty changes in boys.
• Sperm Pathway:
  • Vas Deferens: Transports sperms.
  • Urethra: Common passage for sperms and urine.
  • Glands (Prostate and Seminal Vesicles): Add secretions to sperm for easier transport and nutrition.
• Sperms: Tiny bodies with genetic material and a long tail for movement.

Female Reproductive System

• Main Functions: Producing eggs and certain hormones.
• Ovaries: Produce eggs (germ-cells) and hormones.
  • At birth, contain thousands of immature eggs.
  • At puberty, eggs start maturing; one egg released each month.
• Egg Pathway:
  • Oviduct (Fallopian Tube): Carries egg from ovary to the uterus.
  • Uterus: Elastic, bag-like structure where embryo develops.
  • Cervix: Connects uterus to the vagina.
• Fertilisation Process:
  • Sperms enter through the vaginal passage during intercourse.
  • Travel to the oviduct where they may meet the egg.
  • Zygote Formation: Fertilized egg divides into an embryo.
  • Embryo Implantation: Embryo implants in the uterus lining.
• Embryo Development:
  • Uterus lining thickens with blood to nourish the embryo.
  • Placenta: Provides nutrients and oxygen from mother to embryo and removes waste.
  • Development Duration: Approximately nine months.
  • Childbirth: Rhythmic contractions of uterine muscles.

What Happens When the Egg is Not Fertilised?

• Unfertilised Egg: Lives for about one day.
• Uterus Preparation: Every month, the uterus lining thickens for a possible fertilised egg.
• Menstruation:
  • If no fertilisation, the lining breaks down.
  • Comes out through the vagina as blood and mucus.
  • Cycle takes place roughly every month, lasting 2-8 days.

Reproductive Health

• Sexual Maturation: Gradual process; body and mind may not be ready for sex or children despite physical changes.
• Pressures: Friends, family, and society can influence decisions about sex and reproduction.

Health Consequences of Sexual Activity

• Sexually Transmitted Diseases (STDs):
  • Bacterial infections: Gonorrhoea, syphilis.
  • Viral infections: Warts, HIV-AIDS.
  • Prevention: Condoms can help prevent transmission.

Preventing Pregnancy

• Contraceptive Methods:
  • Mechanical Barriers: Condoms, vaginal coverings.
  • Hormonal Methods: Pills that prevent egg release; may cause side effects.
  • Devices: Loop or copper-T in the uterus; can cause irritation.
  • Surgical Methods:
    • Vasectomy: Blocking vas deferens in males.
    • Tubal Ligation: Blocking fallopian tubes in females.
    • Risks: Surgery can cause infections and other issues.
  • Abortion: Surgical removal of unwanted pregnancies; risk of misuse for sex-selective abortions.

Population and Society

• Population Size:
  • Affects living standards.
  • Expanding population can make improving living standards difficult.
  • Inequality in society is a major reason for poor living standards, not just population size.

Chapter Summary:

• Reproduction is not essential for the life of an individual organism.
• Reproduction involves creating a DNA copy and additional cellular apparatus.
• Different organisms use different modes of reproduction based on their body design.
• In fission, bacteria and protozoa divide into two or more daughter cells.
• Hydra can regenerate if broken into pieces and can also form buds that mature into new individuals.
• Roots, stems, and leaves of some plants can develop into new plants through vegetative propagation.
• Asexual reproduction creates new generations from a single individual.
• Sexual reproduction involves two individuals to create a new individual.
• DNA copying mechanisms create variations useful for species survival.
• Sexual reproduction allows for greater variation.
• Reproduction in flowering plants involves pollination and fertilisation.
• Puberty brings body changes like breast size increase in girls and facial hair growth in boys, indicating sexual maturation.
• The male reproductive system includes testes, vas deferens, seminal vesicles, prostate gland, urethra, and penis.
• The female reproductive system includes ovaries, fallopian tubes, uterus, and vagina.
• Sexual reproduction in humans involves the introduction of sperm into the female’s vagina and fertilisation in the fallopian tube.
• Contraception methods include condoms, oral pills, copper-T, and other methods.