Understanding Plant Reproduction and Biological Concepts

Androecium

The androecium is the male reproductive part of a flower. It is composed of stamens, each consisting of a filament and a capsule called the anther. Inside the anther are a series of chambers called pollen sacs, where pollen grains (male gametes) are formed.

Gynoecium

The gynoecium is the female reproductive part of a plant. It consists of carpels, which are sets of fused leaves that form a cavity where the ovules reside. The carpels are called the pistil. The bottom part of the pistil is the ovary (containing the eggs), the middle part is the style, and the top part is the stigma.

Types of Pollination

• Self-Pollination

  Self-pollination occurs when pollen from the same flower or from different flowers on the same plant fertilizes the ovules.

• Cross-Pollination

  Cross-pollination occurs when the pollen grain comes from flowers located on different plants.

Pollen Transport

• Anemogamous Pollination

  In anemogamous pollination, pollen transport is carried out by the wind.

• Entomogamous Pollination

  In entomogamous pollination, pollen transport is carried out by animals. This form of transport is more reliable and effective than wind pollination.

Plant Classification

• Monocot Plants

  In monocot plants, the embryo has a single cotyledon (e.g., wheat, barley, corn).

• Dicotyledonous Plants

  In dicotyledonous plants, the embryo has two cotyledons, and the albumen can join them. In other plants, the albumen is arranged around the embryo, and the cotyledons have few reserves.

Types of Life Cycles

• Diplontic

  In a diplontic life cycle, the adult is diploid, and gametes are the only haploid stage. Meiosis occurs during the formation of gametes (e.g., animals).

• Haplontic

  In a haplontic life cycle, the adult is haploid, and the zygote is the only diploid stage. Meiosis is the first division of the zygote (e.g., fungi).

• Diplohaplontic

  In a diplohaplontic life cycle, there are multiple adult stages, both haploid and diploid. Meiosis occurs at an intermediate point in the cycle (e.g., plants).

Species

• Typological Concept

  A typological species is a group of organisms that are different from other species and whose members resemble each other.

• Biological Concept

  A biological species is a group of natural populations that interbreed, either actually or potentially, and are reproductively isolated from other such groups.

Gene

A gene is a sequence of nucleotides that carries genetic or inheritable information. The presence of a particular gene will determine the possibility of an organism exhibiting a particular trait.

Genetic Variation

Genetic variation arises from:

• Mutations

  Mutations are the sudden appearance of a new characteristic. If mutations occur in the genes or chromosomes of germ cells, the mutation will be heritable. Causes include spontaneous occurrences or induction by ionizing or non-ionizing radiation, or certain chemicals.

• Sexual Reproduction

  Sexual reproduction contributes to genetic variation through:

  • Gamete Formation: The distribution of pairs of homologous chromosomes and crossing-over, which occurs in the prophase of the first meiotic division.
  • Fertilization: A random process.

Ecosystem and Habitat

• Ecosystem

  An ecosystem is a community of organisms and their physical environment interacting as a unit.

• Habitat

  A habitat is the place where an organism or species lives.

Lamarckism

Lamarckism, also known as the theory of acquired characteristics, proposes that organisms necessarily change over time, and changes acquired during this time are transmitted to offspring (the function creates the organ).

Critique: There is no evidence of any inherent drive in organisms for change, and even if there were, it would not necessarily lead to increased complexity. Characteristics acquired during an individual's lifetime are not inherited, as these changes do not affect the germ cells.