Lecture 1- Plants and the Colonization of Land Flashcards
What is the importance of plants
- Agriculture
- Conversion of the sun’s energy
- Energy in the form of fossil fuels
- Clothing
- Drugs, medicines
- Ecosystem functioning
- Biodiversity
What is the basis of energy
Plants
Secondary compound
- Protect plants from predators
- Poison that wards off potential predators from consuming plant
- Found in many drugs like caffeine or marijuana
Botany
- the study of plants
- also called plant science
How does pollination work?
1) Bee probes into flowers and obtains nectar
2) Flower puts pollen (sperm) on bee
3) Bee travels to other flowers and cross fertilizes
Pollination of the Cardinal Flower by the Hummingbird
The Cardinal flower needs the hummingbird to pollinate
- Each flower is initially female, and then transitions to be male
- Hummingbird does not move enough pollen around, all flowers are competing and have specific adaptions because of this.
- Some flowers taller than others, etc
Flower is in either:
Male phase: produces pollen, top of plant
Female phase: receives pollen, bottom of plant
Formation of Plants and red algae (Plastids)
- Plastids first appeared when a eukaryote engulfed a cyanobacterium, giving rise to the red algae, green algae, and land plants
- Resulted formation of chloroplast
Plants defined
- Include chlorophytes, charophytes, and embryophytes
- Photosynthesis occurs in all of these
Chlorophytes
green algae
Charophytes
green algae
Embryophytes
land plants
Why does photosynthesis occur in plants and red algae
From primary endosymbiosis
Primary endosymbiosis
- A non-photosynthetic eukaryote engulfed a photosynthetic prokaryote (cyanobacterium/plastid) allowing photosynthesis to arise
- Prokaryote + eukaryote = eukaryote
Why does photosynthesis occur in other eukaryotes (strange names)
From secondary endosymbiosis
Secondary endosymbiosis
- Non-photosynthetic eukaryote engulfs the photosynthetic eukaryote produced by primary endosymbiosis (green or red algae)
- Eukaryote + eukaryote
Plants split from the red algae approximately
1500 my (1.5 by)
The Oxygen Revolution
Cyanobacteria constantly produced oxygen during photosynthesis, increasing the amount of O2 in the atmosphere and setting it off balance. Increased levels of O2 is toxic to certain organisms, resulting in one of the Earth’s most significant mass extinctions.
Major Events in the History of Plant Life
4550 MY- Earth forms
3500 MY- Photosynthesis appears (cyanobacteria)
1500 MY- 1st Plastid, Plants and red algae diverge
(when plants were invented)
700 MY- Further oxygen increase
Features of All Plants: Chlorophytes, Charophytes, and Embryophytes
1) Starch is the main energy source and storage molecule for plants
2) Contain Chlorophyll b
3) Cellulose in cell walls
4) Stacked thylakoids (“grana”)
Starch
- Polysaccharide of glucose residues
- Made up of two polysaccharides: amylose and amylopectin
Amylose
- Makes up 20% of starch
- unbranched
Amylopectin
- Makes up 80% of starch
- branched
Sugar as a storage molecule
Not very reactive
Easily metabolized
Absorbs and holds water
Why is starch a good storage molecule
Plant cells do not want to deal with absorbing water since sugar holds water
Starch does not hold water, it is insoluble and therefore good for storage
Chl a
found in all photosynthetic eukaryotes
Chl b
Chl b: an accessory pigment, passes energy to Chl a
Chl b absorbs slightly different wavelengths, extends wavelengths
Accessory pigment
- Light absorbing compounds found in photosynthetic organisms
- Work with chlorophyll a
Cellulose
- Polysaccharide, unbranched glucose residues (different bonds from starch)
- Most common organic polymer on Earth
- Cotton is 90% cellulose
- Used to make paper, rayon and cellophane
Thylakoids
- Membranes inside chloroplasts that contain chlorophyll
- Arranged in stacks rather than simple bands
- Where photosynthesis occurs
The stacked feature of thylakoids is unique to plants
What is the closest relatives of land plants
Charophytes: a type of green alga
Evidence:
- Both contain nuclear and chloroplast genes
- Structure is similar
*** Land plants are not descended from modern charophytes, BUT share a common ancestor with modern charophytes
Features of Charophytes and Land Plants
- Form Cell plates and phragmoplasts
- Plasmodesmata
- Sperm structure
- Peroxisome enzymes
- Rose-shaped cellulose-synthesizing proteins
- Sporopellenin
Phragmoplast
- Microtubules that forms between the daughter nuclei of the dividing cell
- A cell plate then develops in the middle of the phragmoplast, separating the two cells
Plasmodesmata
- Extensions of cell membrane through pores in the cell wall
- Bridges that connect cytoplasm of neighbouring plant cells to each other
- Allow for transport and communication between cells
Sperm structure
Land plants flagellated sperm closes resembles charophyte sperm
Peroxisome enzymes
- Detoxify
- Converts fatty acids into sugar and assists chloroplasts in photorespiration
Rose-shaped cellulose-synthesizing proteins
- Cells of land plants and charophytes have distinctive circular rings of proteins in the plasma membrane
- These protein rings create the cellulose microfibrils of the cell wall
- Non-charophyte algae have linear proteins that synthesize cellulose
Sporopellenin
- Durable polymer that prevents zygotes from drying out and attacks from viruses
- Most durable organic product on earth
- Covering of many spores in charophytes and land plants
- A similar chemical adaptation is found in plants that allowed them to live permanently above the waterline
Advantages of the Movement of Plants to Land
- Air filters less sunlight than water. More light for photosynthesis.
- Air has more CO2 than water. More fuel for photosynthesis.
- Early terrestrial habitats lacked pathogens or predators/herbivores.
- Terrestrial soil is richer in nutrients than aquatic soil.
Adaptations to living in water
- the easy life
- supportive
- retain water
reproduction easier:
>sperm swim in water
> dispersal easy (float)
> Eggs not dry out
Adaptations to living on land
- the hard life
- not supportive
- lose water
reproduction harder:
>sperm cannot fly
> young not dispersed
> eggs and embryos need protection from drying out, predators
Land plant adaptations
- Turgor: positive pressure, cell walls with xylem, stems
- Cuticle, vascular tissue, roots, stomates
- Sporopollenin: protected embryo, seed coat, pollen, flower, fruit
Features of all land plants
- cuticle
- gametangia
- embryophyte condition
- alternation of generations
Cuticle
- Waxy covering of epidermis
- Prevents excessive water loss from the above ground plant organs, while also providing protection from microbial attack
Gametangia
- Multicellular, jacketed sex organs
- Haploid
Antheridium
Male sex organ
Produces sperm
Archegonium
Female sex organ
Produces egg
Embryophyte condition
- Zygote retained in maternal tissue
- Embryos develop from zygotes that are retained within the tissues of the female parent (a gametophyte)
- Parental tissues protect the developing embryo from harsh environmental conditions and provide nutrients
Land plants are also called
embryophytes
Alternation of generations
- The life cycles of all land plants alternate between two generations
- Each generation gives rise to the other
- Does not occur in charophytes
- Life cycle includes both multicellular haploid organisms and multicellular diploid organisms
- Not the same as the haploid and diploid stages in sexual reproducing organisms
*** There is a generation that is haploid and multicellular- that’s whats unique about land plants
There are two generations:
Sporophyte and Gametophyte
Arose independently in evolution several times
Phyte
plant
Gametophyte
- “Gamete producing plant”
- Multicellular haploid, n
- Makes gametes, egg and sperm
Sporophyte
- “Spore producing plant”
- Multicellular diploid, 2n
- Makes spores
Spores
- Produced by meiosis in a mature sporophyte
- Reproductive cells that can develop into a new haploid organism without fusing with another cell
- Mitotic division of the spore cell produces a new multicellular gametophyte, and the cell cycle begins again
Alternation of generations in five generalized steps
1) The gametophyte produces haploid gametes by mitosis
2) Two gametes unite (fertilization) and form a diploid zygote
3) The zygote develops into a multicellular diploid sporophyte
4) The sporophyte produces unicellular haploid spores by meiosis
5) The spores develop into multicellular haploid gametophytes
How did the alternation of generations originate?
The zygote delays meiosis, mitosis occurs before, cells divides and grows
Result: Multicellular diploid
Arose independently in evolution several (or many) times
Does not occur in charophytes!
