Protists: Characteristics and Types

Protists

• An informal term for eukaryotes that are not plants, animals, or fungi
• Characteristics:
  • Have a nucleus and membrane-enclosed organelles
  • Most are unicellular, but some are multicellular
  • Nutritionally diverse (photoautotrophs, heterotrophs, mixotrophs)
• Endosymbiosis: a relationship between two species where one organism lives inside the cell or cells of the other
• 4 groups:
  • Excavata (Trypanosoma, Euglena)
  • SAR (Diatoms, brown algae, water molds, Dinoflagellates, Plasmodium, Paramecium)
  • Archaeplastida (red and green algae, Charophytes, Volvox)
  • Unikonta (Amoeba, slime mold)

Fungi

• Heterotrophs that absorb nutrients from outside their bodies
• Characteristics:
  • Mostly multicellular, but some are unicellular (e.g., yeast)
  • Cell walls made of chitin
  • Sexual and asexual reproduction
• Body structure:
  • Hyphae: tubular cell walls strengthened with chitin, divided into cells by septa
  • Mycelium: an interwoven mass formed by hyphae, maximizing surface area for absorption
• Roles:
  • Decomposers
  • Mutualists
  • Pathogens (e.g., ringworm, yeast infection)
  • Medicine (e.g., penicillin)

Mutualism of Fungi

• Mycorrhiza: mutually beneficial relationships between fungi and plant roots
• Lichen: symbiotic associations between photosynthetic microorganisms and fungi
• Fungus-farming ants: some fungi share digestive services with animals

Plant Diversity

• Role of plants: oxygen production, food sources, habitat for land organisms
• Similarities between plants and green algae:
  • Multicellular, eukaryotic, photosynthetic autotrophs
  • Cellulose cell walls
  • Chloroplasts
• Differences:
  • Alternation of generations
  • Walled spores produced in sporangia
  • Apical meristems
  • Cuticle and stomata unique to plants

Evolution of Plants

• From cyanobacteria to green algae to land plants
• Four groups of plants:
  • Nonvascular plants (Bryophytes, Mosses)
  • Seedless vascular plants (ferns)
  • Gymnosperms (naked seeds)
  • Angiosperms (flowers, double fertilization, nearly 90% of living plants)

Seed Plants

• Sporophyte-dominated life cycle
• Characteristics:
  • Reduced gametophytes
  • Heterospory
  • Ovules
  • Pollen
• Pollination: transfer of pollen to ovules
• Seeds:
  • Consist of embryo and nutrients surrounded by a coat
  • Can remain dormant for years
  • Can be transported long distances by wind or animals
• Gymnosperms:
  • Naked seeds exposed on sporophylls (e.g., conifers)
• Angiosperms:
  • Seed plants with reproductive structures called flowers and fruits
  • 90% of all plants

Plant Structure

• Hierarchical organization: cell – tissue – organ – organism
• Plant organs:
  • Roots (root system)
  • Stems and leaves (shoot system)
• Root functions:
  • Anchoring the plant
  • Absorbing minerals and water
  • Storing carbohydrates
• Stem functions:
  • Elongating and orienting the shoot
  • Maximizing photosynthesis
• Leaf functions:
  • Main photosynthetic organ
  • Exchanging gases
  • Defending against herbivores and pathogens

Plant Tissues

• Dermal tissue: protective outer coating
• Vascular tissue: facilitates transport of materials and provides mechanical support
• Ground tissue: specialized cells for storage, photosynthesis, and support
• Meristem tissue: for growth and development

Plant Cells

• Parenchyma: performs most metabolic functions
• Collenchyma: provides flexible support
• Sclerenchyma: rigid cells with secondary cell walls containing lignin
• Water-conducting cells of the xylem: tracheids, vessel elements
• Sugar-conducting cells of the phloem: sieve-tube elements, companion cells

Resource Acquisition and Transport

• Xylem: transports water and minerals from roots to shoots
• Phloem: transports photosynthetic products from where they are made to where they are needed
• Stomata: pores necessary for CO2 diffusion into photosynthetic tissues
• Mycorrhizae: fungal associations increase surface area for absorbing water and minerals
• Aquaporins: transport proteins facilitating water passage across cell membranes

Soil and Plant Nutrition

• Essential elements: 17 chemical elements required for plant life cycle
• 9 macronutrients: required in large amounts
• 8 micronutrients: required in small amounts
• Plant mutualism with soil bacteria: rhizobacteria and endophyte
• Nitrogen fixation: required for plants to acquire nitrogen as nitrate

Angiosperm Reproduction

• Angiosperm anatomy:
  • Flowers: reproductive shoots of the angiosperm sporophyte
  • Four parts of flowers: carpels, stamens, petals, sepals
• Angiosperm life cycle:
  • Gametophyte development
  • Sperm delivery by pollen tubes
  • Double fertilization
  • Seed development
• Pollination: transfer of pollen from anthers to stigma
• Double fertilization: fusion of gametes
• Fruits: mature ovary of a flower, protects seeds and aids in seed dispersal

Eukaryotic Groups

• Excavata group consists of Trypanosoma and Euglena
• Trypanosoma infects humans, causing sleeping sickness
• Euglena has one or two flagella and is mixotrophic

SAR Group

• Diatoms are unicellular algae with a unique glass-like wall of silicon dioxide
• Brown algae are the largest and most complex multicellular algae, with some being edible seaweeds
• Dinoflagellates are marine and freshwater phytoplankton with two flagella, often causing toxic red tides
• Plasmodium is a parasite that causes malaria
• Paramecium uses cilia to move around and feed on bacteria or other protists

Archaeplastida Group

• Charophytes are a type of green algae, most closely related to plants

Unikonta Group

• Amoeba has pseudopodia
• Slime mold resembles fungi due to convergent evolution

Eukaryotic Groups

• Eukaryotes are divided into four groups: Excavata, SAR, Archaeplastida, and Unikonta.

Excavata

• Includes Trypanosoma and Euglena.
• Trypanosoma infects humans, causing sleeping sickness.
• Euglena have one or two flagella and are mixotrophs.

SAR (Stramenopila, Alveolata, and Rhizaria)

• Includes Diatoms, brown algae, water molds, Dinoflagellates, Plasmodium, and Paramecium.
• Diatoms are unicellular algae with a unique glass-like wall of silicon dioxide.
• Brown algae are the largest and most complex multicellular algae, with some species being edible seaweeds.
• Dinoflagellates are marine and freshwater phytoplankton, characterized by two flagella, and often cause toxic red tides.
• Plasmodium is a parasite that causes malaria.
• Paramecium use cilia to move around and feed on bacteria or other protists.

Archaeplastida

• Includes red and green algae, as well as Charophytes.
• Charophytes are a type of green algae, most closely related to plants.

Unikonta

• Includes Amoeba and slime mold.
• Amoeba have pseudopodia.
• Slime mold resembles fungi due to convergent evolution.

Learn about the characteristics and types of protists, including their nutrition, structure, and relationships with other organisms. Covers endosymbiosis and the four groups of protists.