Microorganisms, Algae, Fungi and Plant Water Transport Explained

Microorganisms: Prokaryotes and Their Reproduction

Microorganisms are microscopic organisms. Prokaryotes, such as bacteria and archaea, do not have a nucleus and reproduce asexually, mainly through binary fission.

Bacteria

Bacteria are classified as photosynthetic and non-photosynthetic:

• Photosynthetic bacteria:
  • Cyanobacteria are phototrophs that contain chlorophyll a and perform oxygenic photosynthesis.
  • Other photosynthetic bacteria have bacteriochlorophyll and perform anoxygenic photosynthesis, without releasing oxygen.
• Non-photosynthetic bacteria:
  • Chemotrophs obtain energy from chemical reactions, such as oxidation, without light.
  • Heterotrophs obtain nutrients from other organisms. Most are saprophytic (they ferment organic matter), while others are parasites causing diseases or live in symbiosis.

Archaea

Archaea live in extreme environments:

• Methanogens live in anaerobic environments and reduce CO₂ to produce methane.
• Halophiles live in extremely salty environments, with highly concentrated salt.
• Thermoacidophiles live in very hot and acidic water.

Protozoa

Protozoa are unicellular eukaryotes that are heterotrophic. Their main types are:

• Flagellates: move using one or more flagella. They have one nucleus and some are pathogenic, such as Trypanosoma gambiense, which causes sleeping sickness.
• Ciliates: move using cilia. They have one cytostome (a mouth-like opening) and two nuclei, a macronucleus and a micronucleus. Paramecium is an example.
• Rhizopods: move and capture food using pseudopods.
• Sporozoans: have no locomotor organs and are parasites, such as the agent of malaria.

Algae

Microalgae

Microalgae live in water and are autotrophic:

• Euglenophytes are unicellular with two flagella and no cell wall.
• Diatoms have a silica cell wall made of two halves and form diatomite fossils.

Macroalgae

Macroalgae are multicellular and live mainly in marine water:

• Green algae contain chloroplasts and include Ulva.
• Brown algae live in deeper waters and contain fucoxanthin. They are used in food and as natural stabilizers and thickeners, such as alginates, found in kelp.
• Red algae live at greater depths and contain phycoerythrin, which allows photosynthesis with little light. They produce agar and carrageenan.

Fungi

Fungi are uni- or multicellular. Multicellular fungi form tubular filaments called hyphae, which group together to form the mycelium. Some hyphae form reproductive structures called carpophores or fruiting bodies. Fungi absorb nutrients directly from their environment through digestion outside their bodies.

• Zygomycetes: produce zygospores and have a coenocytic structure. Examples include bread mold (Rhizopus).
• Ascomycetes: unicellular (yeasts) and multicellular forms. Examples include morels and truffles, as well as ergot (cornezuelo del centeno).
• Basidiomycetes: produce true fruiting bodies, such as mushrooms. Examples include wheat rust and corn smut.
• Deuteromycetes (imperfect fungi): include Aspergillus and Penicillium, which cause diseases and are fermentative.

Lichens

Lichens are a symbiotic association between a photosynthetic partner (the photobiont, a cyanobacterium or alga) and a fungal partner (the mycobiont, usually an ascomycete). The photobiont performs photosynthesis, while the mycobiont absorbs water and minerals and provides protection. Lichens reproduce by fragmentation or through asci grouped in apothecia, which are fruiting bodies.

Water and Mineral Transport in Plants

Nutrient Absorption

Nutrients enter plant cells through:

• Simple diffusion
• Facilitated diffusion, using carrier proteins
• Active transport, which requires energy and uses protein pumps

Water Absorption

Water enters the root by osmosis. Its absorption depends on:

• Soil water content: higher water content increases absorption.
• Soil solute concentration: high salinity reduces absorption.
• Temperature: higher temperature increases absorption.
• Aeration: good aeration favors root absorption.

Gas Exchange

Plant cells respire, consuming O₂ and releasing CO₂. During photosynthesis, plants consume CO₂ and release O₂. Gas exchange occurs by simple diffusion.

Transpiration

Transpiration is the loss of water vapor through the stomata. It depends on:

• Relative humidity: low humidity increases transpiration.
• Wind speed: wind increases transpiration.
• Temperature: higher temperature increases transpiration.

Transport of Raw Sap

Water and mineral salts travel through the xylem. Movement occurs by:

• Capillarity: water rises through narrow tubes.
• Root pressure: pressure in the roots pushes water upward.
• Tension-cohesion: water molecules stick together and are pulled upward by transpiration.

Transport of Elaborated Sap

Organic substances travel through the phloem by mass flow. Sugars move from areas of production, where solute concentration is high, to areas of consumption, where it is low. This process is called translocation.