Understanding Plants: Photosynthesis, Reproduction, and Classification
Plants are autotrophic organisms that live attached to the ground and are unable to move actively. They use water, carbon dioxide, and mineral salts to produce the organic matter they need to survive, grow, and reproduce. This transformation of inorganic substances into organic matter requires energy, which plants obtain from sunlight through a process called photosynthesis. Chlorophyll is the substance that enables plants to use light energy for photosynthesis.
Plant Organs and Their Functions
Many familiar plants produce flowers and seeds. The main vegetative organs of a plant are:
- Root: Anchors the plant in the soil and absorbs water and minerals.
- Stem: The aerial part of the plant that transports substances between the root and leaves.
- Leaves: Laminar expansions of the stem where photosynthesis takes place.
The Structure of a Flower
A flower consists of:
- Floral Stalk: Attaches the flower to the stem.
- Floral Whorls: Enclose the reproductive organs.
- Calyx: The outermost part of the flower, consisting of green leaves called sepals.
- Corolla: Made up of colored leaves called petals.
- Stamens: The male reproductive organs, consisting of a filament that holds the anther, where pollen grains are formed.
- Pistil: The female reproductive organ, with an enlarged ovary at the bottom containing the eggs, a tube-shaped style in the middle, and a flared stigma at the top.
Inflorescence
Flowers can be arranged individually on a stalk or in crowded groups called inflorescences. Examples of inflorescences include:
- Capitulum: Daisy
- Spike: Wheat
- Umbel: Fennel
Pollination and Fertilization
When flowers mature, pollination occurs, which is the transport of pollen from the anthers to the stigma. If a pollen grain lands on the stigma of a flower of the same species, it develops a tube that grows to the egg, and fertilization occurs. This process involves:
- Development of a fertilized ovum.
- Formation of the seed, which contains an embryo of the plant, including a radicle (root), plumule (shoot), and cotyledons (seed leaves) with food reserves.
- Protective seed covers derived from the walls of the egg.
- Disappearance of the flower’s structures, such as the stamens, petals, and often the sepals.
- Transformation of the ovary into the fruit, which contains the seeds and aids in seed dispersal.
Angiosperms and Gymnosperms
Angiosperms are flowering plants with seeds enclosed in a fruit.
Gymnosperms, such as pine trees, have flowers in cone-shaped inflorescences. Female cones and small, grouped male cones are present. Gymnosperms produce seeds that are not enclosed in a fruit.
Ferns and Mosses
Ferns are plants with roots, stems, and leaves but no seeds. They reproduce by spores.
Mosses are small plants that reproduce by spores and lack true organs.
Fungi
Fungi, such as mushrooms and mildew, are heterotrophic organisms that live in damp places and reproduce by spores.