Protists and Seedless Plants
Protists
General Characteristics of Protists
Classification: Protists are predominantly eukaryotes, meaning they have complex cells with a nucleus.
Cellularity: Mostly single-celled, but some forms are multicellular (e.g., certain algae).
Reproduction: Reproduce both sexually and asexually, depending on the species.
Nutrition: Can be autotrophs (photosynthetic) or heterotrophs (consume organic matter).
Size: Generally microscopic, with some exceptions being larger algae.
Diseases Caused by Protists
Certain protists are responsible for human diseases, including:
Malaria: Caused by Plasmodium spp., transmitted by mosquito bites.
Amoebic Dysentery: Caused by Entamoeba histolytica.
Sleeping Sickness: Caused by Trypanosoma brucei, transmitted by tsetse flies.
Ecological Importance of Protists
Role in Ecosystem:
Serve as primary producers, especially in aquatic ecosystems (e.g., phytoplankton).
Contribute to nutrient cycling and energy flows in ecosystems.
Environmental Contributions:
Provide oxygen through photosynthesis.
Serve as food sources for various organisms, including fish and zooplankton.
Classification Issues
Distinction from Other Organisms:
Protists cannot be classified as plants, fungi, or animals due to their diverse characteristics and evolutionary lineages.
Their cellular structures, reproductive methods, and modes of nutrition differ significantly from these kingdoms.
Definition of Algae
The term “algae” broadly refers to a diverse group of photosynthetic organisms that can be found in various environments, primarily aquatic.
Modes of Movement for Protists
Movement Mechanisms:
Cilia: Short hair-like structures that beat in coordinated waves, helping to propel the organism.
Flagella: Long, whip-like structures that enable movement through the rotational or wave-like motion.
Pseudopodia: Extensions of the cytoplasm that allow for crawling-like movement, common in amoebas.
Seedless Plants
Definition and Characteristics of Plants
Definition: Plants are defined as multicellular, autotrophic organisms that typically possess cell walls made of cellulose.
Alternation of Generations
Concept: This is a reproductive cycle that occurs in many plants, involving two distinct forms:
Haploid Stage (Gamete Stage): Produces gametes (sperm and eggs).
Diploid Stage (Sporophyte Stage): Produces spores through meiosis.
Cycle: It is a continuous cycle, where the haploid generation gives rise to the diploid generation and vice versa.
Definitions of Key Terms
Haploid: A cell or organism having a single set of chromosomes (n).
Diploid: A cell or organism having two sets of chromosomes (2n).
Importance: Understanding these terms is crucial for grasping the alternation of generations and the reproductive strategies of plants.
Adaptations of Land Plants
Survival Adaptations: Various adaptations help land plants thrive:
Development of waxy cuticles to reduce water loss.
Stomata for gas exchange that can be closed to prevent water loss.
Root systems for anchorage and nutrient uptake.
Benefits: These adaptations enhance survival by conserving water and supporting structural integrity.
Vascular vs. Non-Vascular Plants
Vascular Plants: Have specialized vascular tissues (xylem and phloem) for transporting water, nutrients, and food.
Non-Vascular Plants: Lack vascular tissues, relying on diffusion for substance movement.
Structures: Vascular plants possess roots, stems, and leaves, unlike non-vascular plants such as mosses.
Dominance of Generations
Sporophyte Dominance: In most vascular plants, the sporophyte is the dominant phase of the lifecycle, meaning it is the most prominent and longest-lasting stage.
Gametophyte Dominance: In non-vascular plants, the gametophyte stage is often dominant, being longer-lived and more conspicuous than the sporophyte stage.