Notes on Seaweed and Marine Plants

Seaweed and Marine Plants.

Seaweeds

Seaweeds are eukaryotic, multicellular algae

• They are also known as macrophytes or macroalgae

There importance of Seaweed:

• They are autotrophs
• They convert sunlight energy into chemical energy, which can be a very useful source of food for heterotrophs
• They produce oxygen for organisms 
• They are source of shelter for many organisms
• They have economic importance
• Many people harvest seaweed, especially for food
• Seaweeds produce gelatinous chemicals called phycocolloids
• One example of phycocolloids is agar

Types of Seaweed: Green Algae, Brown Algae, Red Algae

General Structure of seaweed

• Seaweeds lack the true roots, leaves and stems of plants
• The seaweed can be a giant kelp, filament structure, or thin leafy sheet
• The complete structure of the seaweed is called thallus
• Many seaweeds have leaf-like structures called blades
• Blades do not have veins, so they are not considered as true leaves
• Blades also have identical structures on both the upper and lower surfaces
• Blades have large surface area, and it is the main site of photosynthesis
• Blades have pneumatocysts, which are gas filled bladders that help the blades be close to the sea surface
• Being close to the sea surface allows for more exposure to sunlight
• The stem-like structure of the seaweed is called the stipe
• Stipe provides support for the seaweed
• Blades are connected from the stipe
• Stipes lack specialized tissue, which are essential in true plants for water and nutrient transport
• The root-like structure of the seaweed is called holdfast
• Holdfast attach the thallus to the bottom
• Unlike the roots in true plants, holdfast do not absorb water and nutrients

Reproduction of Seaweed

• Seaweed can reproduce sexually or asexually
• Some seaweeds produce spores
• Seaweeds can produce haploid spores or gametes through meiosis
• 4 ways of reproduction

  1. Alternation of generation

• This is the most common way of reproduction for seaweeds

2. Alternation of three generations

• This occurs to red algae only

3. No alternation of generations

• This occurs in some green algae and some brown algae

4. Reproduction that occurs in some green algae

• Haploid dominant thallus produces haploid gametes

  • The gametes form diploid zygote upon fertilization

    • The zygotes then result in haploid spores from meiosis

      • The haploid spores develops into haploid individuals

 

Marine Flowering Plants (also known as angiosperms)

• The flowering plants that live in the sea are like the plants that live on land because they have specialized tissue and true leaves, roots and stems
• Flowering plants are eukaryotic and multicellular
• They are bottom dwelling organisms
• Reproduction involves alternation of generation that includes dominant sphorophyte (sphorophyte dominates over gametophyte)
• Seagrasses, mangroves and salt-marsh grasses are marine flowering plants

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