Download Section 3.1 From Algae to Terrestrial Plants ALGA (plural: ALGAE

Section 3.1 From Algae to Terrestrial Plants
ALGA (plural: ALGAE) – a unicellular or multicellular photosynthetic, aquatic protist
- Photosynthetic members of the kingdom Protista, may be uni or multicellular
- Multicellular algae commonly called seaweeds, classified into 3 phyla based on colour:
brown, red, green
- Plant is the only other kingdom that has multicellular photosynthetic members
- Controversy on whether green algae belongs in plant or protist kingdom
- Scientists agree that plants evolved from algae and green algae are the evolutionary link
Kingdom Protista
Algae
Kingdom Plantae
Green
Seaweeds Algae
Plants
The Multicellular
Algae
- All unicellular
plant-like protists
from Chapter 2 can be called algae
- Single celled, plant like protists: dinoflagellates, diatoms, euglenoids
- Three phyla of seaweeds: brown, green and red
Brown Algae (Phylum Phaeophyta)
- Largest and probably most complex protists
- Often abundant enough to be key components of marine and tidal
environments
- Some kelp can grow to over 60m in height
- Can form underwater forests in nutrient-rich cool waters (like off
Canada’s west coast) and provide food and shelter for more than 800
marine species of plants, animals and protists
- Rockweed can be found along rocky tidal flats on Canada’s east coast
- They are smaller than kelp but also form underwater forests in the
tidal zone for dozens small marine species
- Brown Algae don’t have true leaves or roots, but have specialized
tissues
HOLDFAST – structure that anchors algae to a rock or other hard structure
(ex. Shell)
STIPE – long, stem-like structure that extends from the holdfast
BLADE – flat, leaf-like, used to collect light, take in carbon dioxide and give
off oxygen
Red Algae (Phylum Rhotophyta)
- Red algae appear to have been the first multicellular organisms on Earth, existing
between 1.5 to 1.2 billion years ago
- Today there are about 6000 living species of red algae
- They can grow to a metre in length and are the most abundant large algae in the warm
coastal waters of tropical oceans
- Red algae have green chlorophylls and have an additional pigment called phycoerthyrin
that is sensitive to light waves that reach greater ocean depths
- This allows red algae to thrive at ocean depths 100m+
- Red algae appears red to the eye because their light sensitive pigments reflect red
wavelengths of light
- Red algae are economically important as food or food processing
Ex. Nori (sushi seaweed) is red algea, Carrageenan (gel-like substance used to help mix
ingredients and make them stay mixed) is used in dairy products like ice cream and milk
shakes
-
Green Algae (Phylum Chlorophyta)
Most green algae are aquatic, most commonly found in fresh water but some live in
saltwater environments
Green algae can also be found in a variety of other ecosystems such as living in sea ice,
attached to the surface of trees and even in the fur of sloths
They are structurally diverse
Some (like Chlamydomonas) are unicellular and move using flagella
Others (like Volvox) are also unicellular and flagellated but occur in ball-shaped colonies
that roll through the water
Multicellular species like Ulva (sea lettuce) can grow to be a metre in length but only 2
cells thick, during reproduction, they produce spores that swim using flagella
Green algae are most plant like because they have the same types of chlorophyll and the
same colour as most land plants
Their cell walls contain cellulose and store food reserves in the form of starch
The Shift to Land
PLANTS – multicellular photosynthetic eukaryote with cellulose-based cell walls
- Hypothesis that green algae are the closest evolutionary relatives of land plants based on
structures within cell
- Like green algae, plants have chlorophylls a and b in their cells
- They both have cellulose cell walls and store food energy in the form of starch (bacteria,
fungi and animals store food as glycogen)
- DNA sequences are similar
Adaptations to Life on Land
- Major needs of plants:
 Protection from drying out

-
Transportation system of water and dissolved substances from outside environments
to within the body
 Support system to lift plants into light and air
Earliest land plants were small
Grew in moist places, transferred water and dissolved substances from cell to cell by
osmosis and diffusion (slow and inefficient, limited maximum size of plants and types of
environments that they could live in)
Plant Embryos
- Plant evolution from terrestrial habitats from aquatic habitats happened 360 million years
ago
- Plants reproduce using embryos, unlike multicellular algae
EMBRYO – an organism’s early pre-birth stage of development
- Embryos are small, simple, multicellular plants that are depended on parent plant for a
time
- More recent developments in plant evolution include vascular tissue for transporting
materials, seeds for protecting the embryo and flowers
Vascular Tissue, Leaves and Roots
- The first land plants were small and relatively simple in structure
- They did not have tissues that allowed the transport of different materials over long
distances
- Vascular tissue evolved into the group known as vascular plants
- They have 2 types of vascular tissue: xylem and phloem
- Xylem carries water and minerals from the roots to the rest of the plant, this tissue
consists of dead, tube-shaped calls that contain lignin (tough material)
- Lignified xylem forms firm structure that allows water and minerals to be transported
throughout the plant
- Fortification of xylem tissue with lignin allowed development of trees and forests, thus
enabling the growth of trees to great heights
- Phloem tissue is made of living cells arranged in tubular form, used for transporting
larger molecules like sugars
- Vascular tissue allowed for the evolution of roots, thus providing strong and anchoring
ability and specialized cells for absorption and transportation of water and minerals
- Leaves evolved after plants developed vascular tissue
-
They increased surface area of the plant above ground, thus allowing for a better
exchange of gases in photosynthesis and larger surface for capturing sunlight
Alternation of Generations
- Plants and some green algae use sporic reproduction, also known as alternation of
generations
SPORIC REPRODUCTION – sexual reproduction that alternates between a gamete-making
individual and a spore-making individual
- Actually 2 multicellular stages in life cycle
- Haploid version of organism (GAMETOPHYTE) produces haploid gametes by mitosis
(haploids have only one set of chromosomes)
- When gametes fuse, they develop into the diploid version of the organism
(SPOROPHYTE)
GAMETOPHYTE – haploid plant in sporic reproduction that produces gametes by mitosis
SPOROPHYTE – diploid plant in sporic reproduction that produces spores by meiosis
- Diploid cell contains 2 sets of chromosomes
- Sporophyte produces spores by meiosis which develop into the haploid gametophyte