Red Algae and Endosymbiosis

• Primary endosymbiosis occurred when eukaryotes engulfed a prokaryote
• Secondary endosymbiosis describes when red algal and green algal chloroplasts were transferred to other protists

Rhodophyta (Red Algae)

• Red algae includes 6000+ species
• They range in size from microscopic to organisms with blades 2m long
• Many red algae are reef-building
• Red algae have different accessory pigments
• Accessory pigments include chlorophyll a and phycoerythrins
• They live in the ocean where yellow and orange wavelengths of light can penetrate
• Nori is a seaweed made from red algae
• Yellow and orange wavelengths are lower-energy light waves, and travel deeper in water
• Red algae have chlorophyll A, a pigment for photosynthesis
• Red algae have phycoerythrin, which absorbs yellow and orange light, and reflects red light
• Red algae can photosynthesize at deeper depths because of phycoerythrin
• Some red algae and dinoflagellates help form the foundation of coral reefs by producing calcium carbonate structures
• Carotenoids is an accessory pigment that appears orange/red
• Chlorophyll breaks down during fall season, and carotenoids become present, which is why trees/leaves turn orange/yellow or red

Green Algae

• Green algae are a likely paraphyletic group that totals about 7000 species
• Green algae are strictly aquatic
• Green algae possess chlorophyll a & b
• Charophytes were considered sister to all land plants
• Zygnematophytes (conjugating algae) have been shown to be the sister group, based on new molecular evidence
• Both are essential for photosynthesis

Types of Green Algae

• Charophytes (stoneworts) accumulate calcium carbonate, which makes them rough or stony
• Charophytes are found in freshwater environments
• They serve as an indicator species; if they are found in a body of water, it is clean and healthy
• Conjugating algae (Zygnematophyceae) is closely related to land plants

Similarities Between Green Algae and Land Plants

• Both contain chlorophyll A and B and beta-carotene
• Both algae and land plants have stacked thylakoids in chloroplasts, for efficient photosynthesis
• Both contain flagellated sperm
• Both store glucose as starch

Land Plants

• Land plants evolved from algae
• Chloroplasts contain chlorophyll a & b and B-carotene
• Land plants have a similar arrangement of thylakoids as algae
• Sperm is flagellated
• Chloroplasts synthesize starch as a storage product

Characteristics of Land Plants

• Plants are eukaryotic organisms, therefore they have nuclei
• Plants are autotrophic, making their own food via photosynthesis
• Plants are multicellular
• Plants are terrestrial, and live on land
• Undergo alternation of generations (complex life cycle)
• Plants are known as embryophytes, and protect the embryo within the parent plant
• Cell walls are made of cellulose, a structural carbohydrate

Alternation of Generations

• All land plants undergo alternation of generations
• The relationship between gametophyte and sporophyte is variable
• Stages include:
  • A haploid stage (1 set of chromosomes) → gametophyte plants alternate between these two stages
  • A diploid stage (2 sets of chromosomes) → sporophyte creating a repeating cycle
• Gametophyte: produces gametes (egg and sperm) through mitosis that produces 2 identical daughter cells (for growth and repair)
• Each gamete is haploid, meaning it has half the genetic material
• The haploid sperm swims and travels through pollen (in seeded plants) to the egg
• The egg and sperm fuse and form a zygote
• The zygote is now diploid (2n), and has a full set of chromosomes (½ egg, ½ sperm)
• The zygote divides and grows into the next stage
• Sporophyte: diploid stage with 2 sets of chromosomes
• Multicellular, one plant is made of multiple diploid cells
• Sporophytes produce haploid spores through meiosis by cutting chromosomes in half (2n to n)
• Spores grow into gametophytes
• Fertilization methods for non-vascular plants (moss or fern):
  • Sperm travels through water to reach the egg They need moist environments
• Fertilization methods for vascular plants (flowers or conifers):
  • Sperm is carried in pollen which travels by wind, insects, or other animals

Moving From Water to Land:

• Advantages:
  • Lack of predators and reduced competition
  • Abundant resources like sunlight, CO2 , and nutrients
  • Fungal assistance in symbiotic relationship helping plants absorb nutrients from the soil
• Disadvantages:
  • Desiccation (drying out)
    • Adaptation: cuticle which is a waxy layer on leaves and stems, reduces water loss, and stomata, small opening controlled by guard cells allowing for gas exchange while managing water retention
  • UV Radiation
    • Adaptation: Plants produce UV absorbing pigments, flavonoids or anthocyanins and some fungi evolved UV-blocking pigment
  • Nutrient Access and circulation: Water nutrient diffused easily and plants evolved roots and internal system to transport resources
  • Support against gravity: Plants need rigid structure to remain upright
  • Reproduction in dry conditions
    • Adaptation:
    • Development of pollen for transferring sperm without water
    • Spores and seeds allow offspring dispersal and survival in dry conditions
    • Embryo Retention: Offspring develop while still attached to and nourished by the parent plant this marks their emergence of embryophytes

Preventing Water Loss

• Stomata- Where gas exchange occurs
• Cuticle- a waxy, watertight sealant that gives plants the ability to survive outside of the water

Protection from UV Light

• Compounds or pigments were developed to absorb UV light acting as sunscreen

Nonvascular Plants (“Bryophytes”)

• Three lineages with living representatives include liverworts, hornworts, and mosses, but do not form a monophyletic group
• They do not have a true vascular system, but are small
• They do not have xylem or phloem
• They lack structural support and internal water transport
• They rely on osmosis and diffusion to absorb water and nutrients
• Possess very diverse adaptation, despite the need for water for reproduction
• They can survive in deserts, Arctic, Antarctica, and dry conditions
• Rhizoids: root-like structures that anchor mosses to surface
• They do not absorb nutrients/water, therefore they are not true-roots like in vascular plants
• Hydroids: simple conduction cells mosses use to move water
• Leptoids: simple conducting cells that mosses use to move sugar
• Some mosses are used in traditional medicine for medicinal uses
• Sphagnum Moss (Peat Moss) are common in cool, wet areas like bogs and wetlands and can be uses practically Mosses and liverworts are sensitive to air and water pollution, so they are used to monitor environment health
• 16,000 species in 3 clades
• gametophyte and sporophyte
• Rely on osmosis and diffusion to uptake water and nutrients
• Simple conducting tissue
• Sporophyte is small and dependent