Plant Biology Notes

Plant Classification

  • Plant classification relies on cytological, anatomical, and morphological criteria.

Prokaryotes

  • Unicellular organisms lacking a nucleus and internal membranous organelles.
  • Reproduce through simple cell multiplication.

Eukaryotes

  • Microorganisms and complex organisms with a nucleus and internal membranous organelles.
  • Includes unicellular (protists) and multicellular organisms (animals, plants, fungi).
  • Reproduction: sexual or asexual.

Thallophytes

  • Plants with a simple thallus structure (cells with no physiological differentiation).
  • Water and mineral absorption: at the cell wall surface.
  • Variable forms: unicellular to multicellular.
  • Reproduction: spores or gametes.
Phycophytes (Algae)
  • Autotrophic organisms capable of photosynthesis.
  • Types: Chlorophycophytes (green), Chromophycophytes (brown), Rhodophycophytes (red).
Mycophytes (Fungi)
  • Thallus: mycelium filament.
  • Heterotrophic organisms (no photosynthesis).
  • Various life forms: free-living, parasitic, symbiotic.

Cormophytes

  • Multicellular higher plants with tissues organized into complex organs (cormus).
Bryophytes (Mosses)
  • Structures resemble stems and leaves but lack true roots and conducting tissues.
Pteridophytes (Ferns)
  • Possess root systems and conducting apparatus but no flowers or seeds.
Pre-Spermatophytes
  • Intermediate group between pteridophytes and spermaphytes.
  • Ovule develops on the plant, but fertilization occurs on the ground.
Spermatophytes (Phanerogams)
  • Characterized by flowers and seeds.
Gymnosperms
  • Ovules and seeds are not enclosed (naked seeds).
Chlamydosperms
  • Reproductive organs are surrounded by a simple envelope; intermediate between gymnosperms and angiosperms.
Angiosperms
  • Seeds enclosed in a container (ovary).
  • Flowering plants bearing fruits; includes dicotyledons and monocotyledons.

Plant Cell Particularities

  • Angiosperm plant cells have a geometric shape due to a rigid skeletal wall.
  • Interior: largely occupied by a vacuole; contains chloroplasts.

Cell Envelopes

  • Pectocellulosic wall: thick, rigid, mainly cellulose; maintains cell structure.
  • Cell membrane: inside the cell, encloses organelles.

Middle Lamella

  • Outer part; pectic substances for cell cohesion.

Primary Wall

  • Between middle lamella and secondary wall; pectocellulosic; extensible for cell growth.

Secondary Wall

  • Between cytoplasmic membrane and primary wall; cellulose, hemicellulose, and phenolic compounds; solid and non-extensible.

Cell Membrane

  • Plasmalemma: delimits intracellular milieu from extracellular milieu.
  • Tonoplast: membrane separating the vacuole from the cytoplasm.

Plastids

  • Cellular organelles with their own DNA and a double membrane.

Proplasts

  • Undifferentiated plastids.

Etioplasts

  • Plasts in plants lacking light.

Chloroplasts

  • Contain carotene and chlorophyll pigments; perform photosynthesis(solar energy transformed into chemical energy).

Chromoplasts

  • Contain carotene; responsible for yellow, red, or orange color.

Leucoplasts

  • Plastids without pigments; store starch (amyloplasts), lipids (oleoplasts), or proteins (proteinoplasts).

Vacuole

  • Organelle delimited by the tonoplast, filled with water, inorganic/organic molecules; storage site.
  • Vacuolar sap inside the vacuole; entire apparatus is the vacuome.

Cytosomes

  • Spherical organelles with a single membrane, containing enzymes.

Lysosomes

  • Contain lytic enzymes that break down macromolecules.

Glyoxysomes

  • Convert reserve lipids into carbohydrates.

Peroxisomes

  • Key role in photorespiration, release of CO_2.