Plant Biology: From Algae to Angiosperms
Chlorophytes: Green Algae
Chlorophytes are commonly known as green algae. They exhibit diverse thallus structures.
Corm and Epidermal Tissue
Epidermal tissues are the ground tissues covered with pores called stomata. The need for plants to grow upward necessitated the existence of a resilient stem or trunk to withstand their own weight.
Parts of the Leaves
- Petiole: Supports and connects the leaf to the branch.
- Lamina: The upper side of the blade is called the obverse, and the underside is the reverse. The main nerve runs through the middle.
Terrestrial Adaptation: Bryophytes and Vascular Plants
When plants conquered the terrestrial environment, two main groups emerged: bryophytes and vascular plants. Vascular plants developed specialized vessels for transport.
Chlorophyll: The Pigment of Life
Chlorophyll is the pigment that captures energy from sunlight and converts it into chemical energy.
Plant Parasites
Plant parasites obtain nutrients from other plants. There are two main groups:
- Hemiparasites: Obtain some nutrients from the host plant using specialized structures called haustoria.
- Holoparasites: Completely depend on the host plant for all nutrients.
Carnivorous Plants
Carnivorous plants are plants that consume animals. Many are tropical species.
Mosses: Primitive Land Plants
Mosses do not have a fully developed corm structure. Instead, they are formed by:
- Phyllids: False leaves
- Caulids: False stems
- Rhizoids: False roots
The sporangium is responsible for manufacturing and dispersing spores (asexual reproduction).
Pteridophytes: Ferns
Ferns are seedless vascular plants.
Reproduction of Ferns
On the underside of the fronds, there are clusters of sporangia called sori. These contain:
- Antheridia: Male organs that produce male gametes.
- Archegonia: Female organs.
Herbaceous and Woody Plants
- Herbaceous plants: Have green, tender, and small stems.
- Woody plants: Have tough, woody stems. They are divided into shrubs and trees.
Classification of Seed Plants: Angiosperms and Gymnosperms
Seed plants are divided into two groups:
Gymnosperms
Gymnosperms are woody plants. They do not have hermaphroditic flowers; all are unisexual and grouped in cone-shaped inflorescences. They are also called conifers. Pollination is always anemophilous, meaning it is always spread by the wind.
Angiosperms
Angiosperms can be evergreen or deciduous.
The Flower
The process of carrying pollen grains to the ovule is called pollination. Flowers have several key parts:
- Androecium: Contains the male reproductive organs.
- Ovary: Contains the female reproductive organ.
- Calyx: Formed by sepals.
- Nectariferous glands: Produce nectar.
A hermaphroditic flower has both male and female sexual organs. A unisexual flower has only one sexual organ, either male or female. Unisexual flowers can be:
- Monoecious: Male and female flowers are present on the same individual.
- Dioecious: Male and female flowers are found on different individuals.
The Fruit
There are two types of fruit:
- Fleshy: Like apples.
- Dry: Like almonds.
The fruit has several layers:
- Epicarp: The skin of the fruit.
- Mesocarp: The most developed part of the fruit.
- Endocarp: The innermost part of the fruit, where the seeds are located.
Cotyledons are the first leaves of the plant. If there is only one cotyledon, the plant is called monocotyledonous. If there are two, it is called dicotyledonous.
Fertilization
Once the pollen reaches the pistil of the flower, it sticks to the stigma. The pollen tube then begins to develop, passing through the style to reach the ovary. Through this tube, the two male gametes, or sperm nuclei, travel to carry out fertilization. This is a process of double fertilization. The union of a sperm nucleus with the egg results in the zygote, which develops into the future embryo.
Vegetative Reproduction
There are four main types of vegetative reproduction:
- Bulbs: A set of underground buds or shoots that originate a new plant.
- Tubers: Enlargements of underground stems.
- Rhizomes: Underground stems of variable length that grow horizontally.
- Stolons: Aerial stems that sprout from the parent plant.