Reproduction in Humans and Plants - Notes (1)

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.

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.

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:
- Increased genetic variation, making crops more resilient to environmental changes.
Disadvantages:
- Variability can lead to unsuccessful offspring with poor growth or yield.

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).

Adaptations for pollen dispersal through wind:
- Anthers and stigmas hanging outside the flower.
- Light, small pollen grains for airborne dispersal.

Pollination: Transfer of pollen grains from anther to stigma.
Fertilisation: Fusion of pollen nuclei with ovum nuclei, resulting in seed formation.

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.

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.

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.

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.

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.

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.

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.