Plant Diversity I: Non-Vascular and Seedless Vascular Plants

Plant Diversity I: Non-vascular and Seedless Vascular Plants

Origin and Phylogeny of Land Plants

• Land surface was largely lifeless for the first 3 billion years.
• Cyanobacteria existed on land around 1.2 billion years ago.
• Small plants, fungi, and animals emerged on land around 500 million years ago.
• There are now approximately 290,000 living species of plants.

Colonizing Land

• Moving from water to land had advantages: bright sunlight, more CO2 in air, soil rich in mineral nutrients, and less competition.
• However, it also posed challenges: scarcity of water and lack of structural support against gravity.
• Plants' diversity reflects different adaptations to these challenges.

Special Adaptations of Land Plants

• Land plants alternate between two multicellular stages: multicellular haploid and multicellular diploid organisms.
• Gametes, zygotes, and spores are protected: specialized organ for gamete production, multicellular dependent embryos, and tough and protected spores.
• Plants need to grow above and below ground, which led to the development of apical meristems.

Kingdom: Plantae

• Plants are photosynthetic organisms that have adapted to life on land, are eukaryotes, have cell walls, and are photosynthetic autotrophs.
• Life on land owes its existence to plants, which live in all but the harshest terrestrial habitats.
• There are two distinct forms of plants: vascular and non-vascular plants.

Non-vascular Plants

• Non-vascular plants (bryophytes) are primitive land plants with simple structures that require an abundance of water.
• They lack specialized conductive tissues and are represented by three phyla: Liverworts (Hepatophyta), Hornworts (Anthocerophyta), and Mosses (Bryophyta).
• There are approximately 9000 species of liverworts, which are usually small.

Biological Systems - Module 5 (Lecture 5.1)

Origin and Phylogeny of Land Plants

• For the first 3 billion years, the land surface was largely lifeless
• Cyanobacteria existed on land ≈1.2 billion years ago
• Small plants, fungi, and animals emerged on land ≈500 million years ago
• Now, there are ≈290,000 living species of plants

Adaptations of Land Plants

• Plants have adapted to life on land, with features such as:
  • Alternation of generations, including multicellular haploid and diploid organisms
  • Protection of gametes, zygotes, and spores
  • Specialized organs for gamete production (gametangia)
  • Multicellular, dependent embryos (“embryophytes”)
  • Tough and protected spores with walls resistant to drying
  • Apical meristems, allowing growth above and below ground

Kingdom: Plantae

• Plants are photosynthetic organisms that have adapted to life on land
• They are eukaryotes, have cell walls, and are photosynthetic autotrophs
• They produce their own food using sunlight, and have adapted to live in all but the harshest terrestrial habitats

Non-Vascular Plants (Bryophytes)

• Non-vascular plants are primitive land plants with simple structures
• They need an abundance of water and lack specialized conductive tissues
• They are represented by three phyla: Liverworts (Hepatophyta), Hornworts (Anthocerophyta), and Mosses (Bryophyta)

Characteristics of Non-Vascular Plants

• Bryophytes are small, herbaceous, and non-woody plants
• They have no roots, only simple rhizoids
• They reproduce by producing spores
• They need a film of water for fertilization and reproduction

Plant Organisation

• Plants are composed of cells, tissues, and organs.
• A cell is the fundamental unit of life.
• A tissue is a group of cells consisting of one or more cell types that together perform a specialised function.
• An organ consists of several types of tissues that together carry out particular functions.

Hierarchical Organisation in Plants

• Basic morphology reflects evolution as organisms that draw resources from below ground and above ground.
• Plants have three basic organs:
  • Roots: anchor, absorb water and minerals, and store products of photosynthesis (sugars).
  • Stems: elongate and orient shoot for optimal photosynthesis; elevate reproductive structures.
  • Leaves: produce sugars by photosynthesis; exchange gases; dissipate heat.

Plant Organs

• Roots:
  • Functions: anchor, absorb minerals and water, store carbohydrates and other reserves.
  • Most eudicots and gymnosperms have taproot systems.
  • Most monocots have fibrous root systems.
• Stems:
  • Functions: elongate and orient shoot to maximise photosynthesis; elevate reproductive structures.
  • Consist of alternating nodes and internodes.
  • Most growth in young shoots is concentrated in the shoot tip (apical bud).
• Leaves:
  • Main photosynthetic organ of most vascular plants.
  • Generally consist of a flattened blade and a stalk (petiole).
  • May be simple (undivided blade) or compound (leaf divided into leaflets).

Plant Tissues

• 3 basic tissue systems:
  • Dermal tissues: protective covering of the plant.
  • Vascular tissues: conduct water, minerals, and food.
  • Ground tissues: the bulk of the plant.

Dermal Tissues

• Surface of the plant is covered in a continuous layer of tightly packed cells (epidermis).
• Specialised characteristics in each organ:
  • Roots: enhance water and mineral uptake.
  • Stem and leaves: protect against water loss.
  • Leaves: increase gas exchange through stomata.

Vascular Tissues

• Conduct long-distance transport of materials between roots and shoots.
• Two vascular tissues are xylem and phloem.
• Xylem:
  • Transports water and dissolved minerals upward from roots into shoots.
  • Dead (functioning) cells.
• Phloem:
  • Transports sugars (products of photosynthesis) from where they are made to where they are needed or stored.
  • Alive cells with pores on sidewalls.

Ground Tissues

• Anything that isn't vascular or dermal is ground tissue.
• Not just filler: includes specialized cells for functions such as:
  • Storage
  • Photosynthesis
  • Support
  • Short-distance transport
• 3 types of cells:
  • Parenchyma: soft tissue, metabolic functions, alive.
  • Collenchyma: flexible structural support, alive.
  • Sclerenchyma: strong structural support, mostly dead cells ("skeleton").

Wrapping Up

• Summary of what we learned about plant organisation, organs, and tissues.