Biology of Unicellular Algae

Plant Classification

• The most common method for classifying plants is based on their descent or phylogenetic relationships.
• Phylogenetic classification systems are based on evolutionary relationships between various organisms.
• This assumes that organisms belonging to the same taxa share a common ancestor.
• Approximately 3,000,000 plant species are identified and classified into four main divisions: Thallophytes, Bryophytes, Pteridophytes, and Spermatophytes.

Thallophytes

• Thallo = plant body without roots, stems, or leaves
• Phyta = a plant
• Thallophytes include Algae, Fungi, Bacteria and Lichens.
• Thallophytes are primarily aquatic organisms.
• Thallophytes are unicellular, colonial or multicellular.
• Thallophytes reproduce mainly asexually.
• Thallophytes are also termed Cryptogamae.

Algae

• Algae are pond scums, fresh and marine phytoplanktons.
• Algae are relatively undifferentiated and lack true roots and leaves.
• The "green algae is the most diverse group of algae."
• There are over 7000 species found in many habitats.
• Algae contain the green pigment chlorophyll that uses sunlight energy to produce food through photosynthesis.
• Algae can be unicellular, colonial or multicellular.
• Algae reproduce asexually through fragmentation or by producing zoospores.
• Algae reproduce sexually through isogamy.
• Algae have different cell walls(e.g Cellulose, algin, cellulose, agar, pectin, silica).
• Different types of algae occupy different depths in water.

Fungi

• Fungi are eukaryotic organisms that can be unicellular or in multicellular form (mushrooms).
• Fungi are heterotrophs.
• Fungi have cell walls made of chitin.
• Fungi reproduce asexually through fragmentation, budding, or spores.
• Fungi reproduce sexually by producing spores in fruiting bodies like mushrooms.
• Fungi cause plant diseases including rusts, smuts, and leaf, root, and stem rots.

Lichens

• A lichen is a composite organism that develops from algae or cyanobacteria and fungus.
• Lichens come in different colours, sizes and shapes, but they are not plants.
• Lichens produce their own food by photosynthesis
• Lichens do not grow as parasites on plants, but use plants as substrate for growth.
• Lichens reproduce asexually by soredia.

Bryophytes

• Bryophytes include mosses and liverworts.
• Bryophytes are also known as the 'amphibians of the plant kingdom' and are found typically in moist, shaded areas in the hills.
• They have no vascular system.
• They need water for sexual reproduction.

Mosses

• Mosses are the simplest plants.
• Mosses do not have roots, vascular tissues (no transport), simple stems and leaves, but they have rhizoids for anchorage.
• Mosses reproduce by producing spores in capsules.
• Mosses reproduce asexually by fragmentation or budding in secondary protonema

Liverworts

• Liverworts are found in moist, shady habitats.
• Liverworts reproduce asexually by fragmentation, or by gemmae formation.

Spermatophytes

• Spermatophytes encompass all seed-bearing plants divided into Gymnosperms and Angiosperms.

Gymnosperms

• These are naked seed plants.
• They include trees with needle-shaped leaves and cones that have naked seeds located in the female cones.
• They do not produce fruit because they lack ovaries.

Angiosperms

• These produce seeds in an enclosed structure, a fruit.
• They include trees, herbs, shrubs, water plants, and grasses.
• Two types of angiosperms are Monocots (one cotyledon) and Dicots (two cotyledons).

Plant Reproduction

• Plants reproduce asexually or sexually.
• Asexual reproduction happens when no gametes are required and only one parent is needed.
• Sexual reproduction requires two parents and involves gametes(male and female gametes)
• Types of asexual reproduction include fission, budding, fragmentation, and spore formation.
• Types of sexual reproduction include stages like pollination, fertilization, seed formation, seed dispersal and germination.
  • There are three types of flowering plant life cycles: annuals, biennials, and perennials.
  • Annuals complete their life cycle in one year.
  • Biennials complete their life cycle in two years.
  • Perennials live for several years.

Classification of Plant Reproduction

• Monocarpic plants: are those that flower, set seeds and die.
• Plant reproduction can be classified by the time the plant species take to complete life cycle and flowering such as annuals, biennials and perennials.
• Parts of a complete flower: sepals, petals, carpel, stamen

Seed Dispersal

• Dispersal of seeds is carried by wind, animals, water, and plant bursting.
• Examples: wind (dandelion, maple), animals (edible fruits, hooked fruits), water (water lilies), and bursting seed pods (some plants).