Reproduction in Humans and Plants - Notes (1)

Contents

• Asexual Reproduction

• Sexual Reproduction

• Sexual Reproduction in Plants

• Sexual Reproduction in Humans

• Sexual Hormones in Humans

• Sexually Transmitted Infections

Asexual Reproduction

• Does not involve sex cells or fertilization.

• Only one parent is required, leading to no fusion or genetic mixing of gametes.

• Offspring are genetically identical (clones).

• Defined as the process resulting in genetically identical offspring from one parent.

• Examples:

  • Bacteria: Binary fission resulting in exact genetic copies.

  • Plants: Asexual reproduction through bulbs and tubers, producing new plants from food storage organs.

Advantages & Disadvantages of Asexual Reproduction

• Wild Species:

  • Advantages:

    • Rapid population growth.

    • Efficient exploitation of suitable environments.

    • More time and energy-efficient; faster reproduction.

  • Disadvantages:

    • Limited genetic variation, leading to vulnerability to environmental changes (e.g., temperature changes, droughts).

    • Disease can affect the whole population due to lack of genetic variation.

• Crop Plants:

  • Advantages:

    • Can produce desired characteristics (e.g., high yield, disease resistance).

    • Uniform characteristics for commercial sale.

    • Faster production time compared to sexual reproduction.

  • Disadvantages:

    • Lack of adaptation to changing climates if reproduced asexually.

    • If a diseased parent plant is used, offspring will also be diseased.

    • Production efficiency may be reduced due to vulnerability to disease or pests.

Sexual Reproduction

• Involves the fusion of gametes (sex cells) to form a zygote, leading to genetically varied offspring.

• Gametes:

  • Male (sperm) and female (ovum in animals; pollen nucleus and ovum in plants).

  • Gametes have a haploid nucleus (half the chromosome number of normal cells).

  • Fusion of male and female gametes results in a zygote with a diploid nucleus.

Advantages & Disadvantages of Sexual Reproduction

• Advantages:

  • Increased genetic variation, making crops more resilient to environmental changes.

• Disadvantages:

  • Variability can lead to unsuccessful offspring with poor growth or yield.

Sexual Reproduction in Plants

• Insect Pollinated Flowers:

  • Flowers are reproductive organs that facilitate gamete fusion.

  • Pollination is the transfer of pollen from male to female flower parts; can be assisted by insects or wind.

• Flower Structures:

  • Key structures: sepals, petals, stamens (with filaments and anthers), carpel (with style, stigma, ovary, ovules).

Wind Pollinated Flowers**

• Adaptations for pollen dispersal through wind:

  • Anthers and stigmas hanging outside the flower.

  • Light, small pollen grains for airborne dispersal.

Pollination vs Fertilisation

• Pollination: Transfer of pollen grains from anther to stigma.

• Fertilisation: Fusion of pollen nuclei with ovum nuclei, resulting in seed formation.

Factors Affecting Seed Germination

• Three Required Factors:

  1. Water (for enzyme activation).

  2. Oxygen (for energy release).

  3. Warmth (optimal temperatures aid growth).

  • Experiment: Cress seeds germinated under different moisture, temperature, and oxygen conditions.

  • Findings: All three factors necessary for successful germination.

Self- & Cross-Pollination

• Cross-Pollination: Transfer of pollen between different plants of the same species, enhancing genetic variation.

• Self-Pollination: Pollen from a flower lands on its own stigma, leading to reduced genetic diversity.

  • Risks lack of variation under changing environmental conditions.

Sexual Reproduction in Humans

• Male Reproductive System Key Structures:

  • Prostate gland, sperm duct, urethra, testis, scrotum, and penis.

  • Functions: Production and transportation of sperm and hormones.

• Female Reproductive System Key Structures:

  • Oviduct, ovary, uterus, cervix, vagina.

  • Functions: Fertilisation, egg maturation, and development of the fetus.

Fertilisation in Humans

• Fusion of male sperm and female egg cells, typically in the oviduct.

• Adaptive Features of Human Gametes:

  • Sperm: Contains a tail (flagellum) for mobility, many mitochondria for energy, and enzymes for penetrating the egg.

  • Egg: Contains energy reserves and a jelly-like coating to prevent multiple sperm from entering after fertilisation.

Pregnancy and Development

• Zygote divides and embeds in the uterus lining over about three days.

• Development phases: implantation, organ development, and growth into a fetus.

• Placenta facilitates nutrient exchange and waste removal between mother and fetus, while acting as a barrier to some toxins.

Sexual Hormones in Humans

• Primary vs Secondary Characteristics:

  • Primary: Differentiation of reproductive organs in the uterus.

  • Secondary: Changes during puberty controlled by hormones (e.g., testosterone and oestrogen).

• Menstrual Cycle: Average duration of 28 days, with ovulation occurring around day 14; involves hormonal regulation by FSH, LH, oestrogen, and progesterone.

Sexually Transmitted Infections (STIs)

• STIs, including HIV, spread through unprotected sex, sharing needles, and from mother to child.

• HIV Effects:

  • Infects lymphocytes, weakens immune response, leading to AIDS.

• Control Strategies for STIs:

  • Limiting sexual partners, using condoms, testing, and educational programs.