Reproduction in Plants

Green plants are autotrophs because they synthesize their own food using inorganic raw materials from the environment:

$$\mathbf{6\text{CO}_2 + 6\text{H}_2\text{O} \xrightarrow[\text{Chlorophyll}]{\text{Sunlight}} \text{C}_6\text{H}_{12}\text{O}_6 \ (\text{Glucose}) + 6\text{O}_2 \uparrow}$$

• Chlorophyll: Green pigment in chloroplasts that absorbs solar energy.
• Stomata: Tiny microscopic pores on leaf undersides flanked by kidney-shaped guard cells that regulate gas exchange ($\text{CO}_2$ in, $\text{O}_2$ out).
• Starch Storage: Excess glucose is converted into starch; testing with iodine solution produces a distinctive blue-black color!

• Xylem Tissue: Continuous tubes of dead, hollow cells running from root tips to leaf veins. Transports water and dissolved mineral ions strictly upward (unidirectional).
• Phloem Tissue: Living sieve tubes that transport synthesized carbohydrates (sucrose) from leaves to roots, storage fruits, and growing buds bidirectionally (translocation).

Plants absorb huge volumes of water through root hairs, but use only about $1-2\%$ for photosynthesis. The remaining water evaporates through stomata into the atmosphere as water vapor. This process is called Transpiration.

• Vegetative Propagation: New plants grow from vegetative vegetative organs:
  • Stem: Potato tubers with "eyes" (buds), ginger rhizomes, rose stem cuttings.
  • Leaves: Bryophyllum develops buds along leaf margins that drop and sprout.
  • Roots: Sweet potato and dahlia.
• Budding: A bulb-like projection (bud) grows out of a single parent cell and detaches (e.g. Yeast).
• Fragmentation: Algae like Spirogyra break into two or more fragments when mature, each growing into a complete ribbon.
• Spore Formation: Fungi and ferns produce microscopic tough-walled asexual spores that float through air.

The flower is the reproductive organ of a plant:

• Stamen (Male Organ): Consists of the anther (producing yellow pollen grains containing male gametes) and the supporting filament.
• Pistil / Carpel (Female Organ): Consists of sticky stigma (receives pollen), style (stalk), and basal swollen ovary (containing one or more ovules housing female egg cells).
• Pollination: Transfer of pollen grains from anther to stigma (Self-pollination within same flower; Cross-pollination between different flowers by wind, water, or insects).
• Fertilization: The fusion of the male gamete with the female egg cell inside the ovule to form a zygote. The zygote becomes an embryo, the ovule becomes a seed, and the ovary swells to become the fruit!