Plant Biology: Photosynthesis, Structure, and Reproduction

Plants: An Introduction

Plants are living, autotrophic organisms, meaning they produce their own food. They are not fixed to the substrate and are capable of moving actively. The primary substance that allows plants to use solar energy is called chlorophyll. Plants incorporate water, carbon dioxide, and mineral salts, which serve to reproduce them. They transform inorganic substances into organic energy, and this process requires sunlight. This process is called photosynthesis.

Plant Organs

• Root: The part that anchors the plant into the soil and absorbs water and mineral salts.
• Stem: The aerial part of the plant where substances circulate from the root to the leaves.
• Leaves: Expansions that grow from the stem, where photosynthesis primarily occurs.
• Flowers: The reproductive structures of the plant.

Flower Structure

Flowers contain the reproductive organs of the plant. Hermaphroditic flowers contain both male and female organs and are called complete flowers. A complete flower consists of:

• Peduncle: Found at the base and connects the flower to the stem.
• Receptacle: Surrounds the reproductive organs and includes:
  • Calyx: The outermost part of the flower, formed by sepals.
  • Corolla: Formed by petals.
• Reproductive Organs: Protected by the receptacle:
  • Stamens: Male reproductive organs, formed by a filament and an anther.
  • Pistil: Female reproductive organ. The ovary and egg are found in the inferior part.

Not all flowers are complete. Some are incomplete, lacking either male or female organs. When flowers are grouped together on the same stem, they form an inflorescence, such as a chapter, umbel, or spike.

Fruits and Seeds

If a pollen grain reaches the stigma (a process called pollination) of the same species, a tube develops to the egg. This process has three phases:

1. Fertilization
2. Development of the fertilized egg and the formation of the seed
3. Disappearance of some flower structures

The ovary then transforms into the fruit, which encloses the seed. Plants with flowers whose seeds are enclosed in a fruit are called angiosperms.

Plants Without Flowers and Seeds

• Ferns: Plants with roots, stems, and leaves but no seeds. They reproduce by spores.
• Mosses: Small plants that reproduce by spores and lack true organs.

Plants and the Environment

Aquatic Environment

In aquatic environments, water is not lacking, and gases and salts are dissolved in it. However, plants cannot live at the bottom of deep water due to lack of light.

Terrestrial Environment

In terrestrial environments, light is abundant, but water is often a limiting factor. Plants have adapted to this environment in several ways:

• Roots collect water.
• Stems contain vascular systems for transporting sap.
• Leaves have a waxy covering that makes them waterproof.

Fungi

Fungi are not animals or plants. They are fixed to the substrate they live on and reproduce by spores. They have heterotrophic nutrition, and their body is called a mycelium. According to their environment, fungi can be:

• Decomposers: Living on the remains of other living beings, transforming them into inorganic materials useful for plants.
• Parasites: Living at the expense of living animals or plants, causing disease.
• Symbiotic: Associated with other living beings without causing harm, such as lichens.