Plants and Their Role in the Ecosystem

Plant Diversity Course - BIO112

• Course lecturers are Ms I. Makhura (235/225) and Prof. B. Moseki (235/244)
• Assessments include a plant diversity CA Test 1
• The Plant Diversity Manual contains all other course information

Plant Diversity - BIO112 Course Outline

• BIO112 is a survey of the plant kingdom and land plants, using an evolutionary approach.
• The course starts with simple plants and progresses to complex non-flowering and flowering plants.
• It also examines plant evolution from an aquatic to a terrestrial environment.
• The course highlights the adaptation that has led to plant survival and success on land.

Why Study Plants?

• Plants are essential to life on Earth as they are the primary producers of food.
• All life depends on photosynthesis, and only plants, algae, and cyanobacteria directly perform this function.
• Plants are the base of the food chain.
• Throughout history, thousands of plant types have been used as food.
• 12 major food crops include maize, beans, sorghum, rice, and wheat.
• Plants provide nutrients such as carbohydrates, proteins, lipids (fats), water, vitamins, and minerals.
• Plants yield spices for flavouring, beverages (e.g., beer, tea, coffee), starches (carbohydrates/sugars), oils (unsaturated fatty acids), food additives, and animal feed.
• Plants provide oxygen, absorb carbon dioxide (reducing the greenhouse effect), regulate the water cycle, and provide aesthetic value.
• Plants serve as habitats for other organisms and offer ecosystem services, including soil erosion control and nitrogen fixation by some species.
• Some plant species, such as Datura sp. and Nerium oleander, can also be poisonous.

What is a Plant?

• Plants are multicellular, photosynthetic eukaryotes.
• They produce sugars from carbon dioxide using light energy and release oxygen.
• Plants are immobile and respond to the environment differently than animals.
• Plant cells are surrounded by rigid cell walls.
• A miniature plant (embryo) within the plant body is protected.
• Plants exhibit unique development and regeneration processes.

Plant Classification

• Botanists use various systems to classify plants.
• BIO112 will follow Sadava et al., 2011, which categorizes the Plant Kingdom into two major groups.
  • Vascular plants (Tracheophytes): characterized by conducting cells (tracheids).
  • Non-vascular plants (Non-Tracheophytes): lack conducting cells.
• Sadava et al. recognize 10 groups/clades within the Plant Kingdom.

Plant Classification - Specific Groups

• Non-Vascular Plants:

  • Liverworts (Hepatophyta)
  • Hornworts (Anthocerophyta)
  • Mosses (Bryophyta)

• Vascular Plants (Seedless):

  • Club mosses (Lycopodiophyta)
  • Ferns & fern allies (Pteridophyta/Monilophyta)

• Vascular Plants (Seed Plants):

  • Gymnosperms
    • Cycads (Cycadophyta)
    • Ginkgo (Ginkgophyta)
    • Gnetophytes (Gnetophyta)
    • Conifers (Coniferophyta)
  • Angiosperms (Flowering Plants)

Plant Kingdom and Algae

• This course includes algae, though many botanists consider them a separate group.
• Sadava et al. includes algae in 'Green Plants'.
• Algae possess characteristics that fit the plant definition.

Why Algae in this Course?

• The course aims to survey the plant kingdom and how plants evolved.
• Understanding the origins and evolution of plants requires examining earlier forms, such as algae.

Why Algae?

• Algae played a key role in shaping Earth's environment, including producing the oxygen atmosphere we use today.
• Algae were instrumental in the evolution of eukaryotic cells (especially the origin of chloroplasts),
• Some algae are the ancestors of plants.
• Algae can play a significant role in an ecosystem, providing food, habitat and nutrient cycling.

Main Features of Algae

• Algae bodies aren't differentiated into roots, stems, and leaves, but into a thallus.
• Photosynthesis occurs within this thallus.
• Attachment is achieved via rhizoids (root-like structures).
• Algae lack embryos.
• Gametes fuse in open water.
• Zygotes develop directly into new plants.
• Reproductive structures lack protection.
• In contrast, Algae reproductive gametes are produced in a single cell.

Where are Algae Found?

• Algae are mostly aquatic (marine and freshwater).
• Some species are also terrestrial (wet soils).

Morphological Diversity of Algae

• Algae exist in diverse forms:
  • Unicellular
  • Filamentous
  • Colonial
  • Coenobium
  • Siphonaceous
  • Parenchymate

Types of Reproduction in Algae

• Algae reproduce both asexually (fragmentation, spore formation) and sexually (fusion of gametes).
  • Isogamy (identical gametes)
  • Anisogamy (unequal gametes: small male, large female)
  • Oogamy (large stationary female, small motile male)

Different Algal Groups

• Blue-green algae (cyanobacteria)
• Green algae (chlorophyta)
• Diatoms
• Euglenoids
• Brown algae
• Red algae

Economic Importance of Algae

• Primary producers contributing significantly to primary production in aquatic environments;
• Some algae fix nitrogen.
• Some algae are toxic, forming harmful algal blooms.
• Algae are used as food and fertilizers.
• Useful compounds (e.g., agar, carrageenan) are extracted from brown and red algae, some are used for thickening agents , cosmetics, food and microbiological media.
• Diatomaceous earth (remains of diatoms) is used for various purposes (filtration, abrasives).

Green Algae as Ancestors of Land Plants

• Green algae, particularly charophytes, are thought to be ancestors of land plants.
• Green algae and land plants share similar biochemical features (starch reserves, cellulose cell walls, similar chlorophyll).
• They also share molecular similarities (rRNA and DNA sequences) and structural characteristics, including the presence of plasmodesmata, a way plants retain eggs and protect young sporophytes, chloroplast structure (grana) and the way they grow and branch).

Test your knowledge about the importance of plants and their various functions in the ecosystem with this quiz. From food crops to environmental benefits, this quiz covers essential aspects of plant biology and reproduction. Discover the truths and myths surrounding plant life and its contributions to life on Earth.