BIO1PS
Protists;
▪ diverse group of eukaryotic organisms
▪ mostly unicellular and aquatic
▪ autotrophic and heterotrophic
▪ photosynthetic protists produce 40 – 50% of the world’s oxygen
- Diatoms;
▪ autotrophic, unicellular and composed of two intricate halves
▪ cell wall composed of silica
▪ major component of phytoplankton
- Dinoflagellates (whirling algae);
▪ unicellular
▪ heterotrophic or autotrophic (chlorophyll a + accessory pigments chlorophyll c + xanthophyll)
▪ 2 flagella give characteristic whirling motion
▪ some bioluminescent dinoflagellates create phosphorescence in the ocean
▪ endosymbiotic dinoflagellates in the tissues of corals (zooxanthallae) – give coral their colour and
supply nutrition. Under stress corals expel their zooxanthallae > coral bleaching
Green Algae;
▪ unicellular, colonial, filamentous and multicellular
▪ marine and freshwater (from which land plants emerged)
▪ Green algae and land plants have;
- chlorophyll a & b and carotenoids
- similar cell wall structure (containing cellulose)
- chloroplasts have a double-membrane envelope
- by product of photosynthesis (starch) stored in the chloroplast
Red Algae;
▪ mostly multicellular and marine
▪ Red and green seaweeds more closely related to each other than the brown seaweed
▪ Chlorophyll a (green algae have chlorophyll a & b) and accessory pigment – phycobiliproteins
(green algae have carotenoids)
▪ Chloroplasts have a double-membrane envelope
▪ some have calcium carbonate in their cell walls (coralline algae)
Brown Algae;
▪ mostly multicellular and marine
▪ Chromists (same as Diatoms) - Chorophyll a & c and accessory pigment fucoxanthin (gives them the
yellow/brown colour)
▪ Distinguished by chloroplasts surrounded by four membranes- originated from an ancestor
acquiring the chloroplast from a red alga
▪ includes giant kelp
Photosynthetic Pigments;
▪ protists may or may not be photosynthetic. If photosynthetic they have chlorophyll a, but may
differ in accessory pigments
▪ chlorophyll accessory pigments -> chlorophyll b, c and d
▪ non-chlorophyll accessory pigments -> carotenoids or phycobiliproteins
▪ different chlorophyll and non-chlorophyll pigments have different absorption spectra = different
colours
▪ Green algae look green because they absorb red light to photosynthesis and reflect green light
back to your eyes.
Conversely, red algae reflect the red light back to your eyes and use blue and green light to
photosynthesise
Transition to dry land;
▪ most protists are aquatic
▪ transition to land required adaptations for;
- nutrient supply
- physical support
- reproduction
Nutrient supply;
▪ aquatic – water surrounds algae and passive diffusion of water gases and nutrients occurs
- no need for specialised absorbing or transport tissues
- no true roots – only holdfasts or rhizoides anchor algae
▪ terrestrial – water and inorganic compounds are in soil and O2 and CO2 in atmosphere which is dry
- Roots - below ground absorptive structures
- Vascular transport tissues between different parts of plant
- Cuticle - Waterproofing of above ground parts
- Stomata - to allow gas exchange through cuticle
Physical Support;
▪ aquatic – water supports entire structure. No need for strengthened tissues except for those in
rough waves regions
▪ terrestrial – above ground parts have to be supporting and self-supported
- requires cellulose and lignin to strengthen tissues
- roots anchor above ground structure
Reproduction;
▪ aquatic – water transports gametes and spores (some motile (with flagella) to aid transport)
- water prevents gametes from desiccation
▪ terrestrial - external water only available intermittently to allow dispersal of gametes and dry air
desiccates gametes and spores
Requires; - spores with a tough water-proof walls and UV protective polymers (melanin)
- evolution of pollen to allow protection and dispersal of gametes
- evolution of seeds, flowers and fruits to allow protection and dispersal of spores and
embryos
Classification of Land Plants;
▪ Non-vascular spore forming plants eg. mosses
▪ Vascular plants
- spore forming plants eg. ferns
- seed forming plants;
- non-flower forming plants eg. pines
- flowering and fruit forming plants
Algae v. Land Plants;
▪ Algae have a great diversity of photosynthetic pigments, life cycles & forms of carbohydrate
storage
▪ Land plants have one combination of photosynthetic pigments (chlorophyll a, b & carotenoids;
‘grass green’ colour), store carbohydrate as starch, & one basic life-cycle pattern
Basic Life-cycle of Plants;
▪ Of the many life-cycles seen in algae & fungi, land plants show one basic life-cycle pattern, which is
changed as plants become more adapted to life on dry land
▪ Land plants show an alternation of heteromorphic diploid (sporophyte) & haploid (gametophyte)
generations
▪ Sporophytes (‘spore-forming plants’ - diploid - 2N chromosomes)
- Meiosis
▪ Spores (haploid) [always meiospores – sporic meiosis]
- Germination of spores
▪ Gametophytes (‘gamete forming plants’ - haploid -N chromosomes)
»[note difference from human life cycle – gametic meiosis]
▪ Male & female gametes (haploid - N chromosomes)
- Fertilisation
▪ Zygotes (diploid - 2N chromosomes)
▪ Sporophytes (diploid - 2N chromosomes)
Mosses – Phylum Bryophyta;
Gametophyte life stage of moss plant;
▪ Leafy, independent, photosynthetic gametophyte (‘gamete forming plant’ - haploid)
▪ Little protection from desiccation - most common in moist environments
▪ plants have no roots (only rhizoids) – absorb H2O, CO2 and nutrients through their surface (hence
their restricted size)
▪ Water required for sperm to swim from antheridium on male plants to the eggs in the
archegonium on female plants
▪ many reproduce vegetatively – a small piece of moss gametophyte can grow into an entire, new
plant
Sporophyte life stage of moss plant;
▪ spore forming diploid plant
▪ dependent on gametophyte
▪ short-lived but shows first development of cuticle & stomata
▪ Consists of a thin stem (seta) which elongates & then forms a bulbous sporangium or capsule
(spore forming structure)
▪ Obtain most of its sugar from the photosynthesis of the gametophyte