Plants Flashcards
Lectures 5-8
Create a timeline of when certain plant types evolved.
- First land plants 500 mya
- First vascular plants 420 mya
- First seed plants 360 mya
- Gymnosperms 245 mya
- Angiosperms 50 mya
How did colonisation of land plants allow for animal life?
They reduced the hostility of the land by:
- Increasing oxygen content
- Lowering temperatures
- Habitat provision both physically and via organic matter
- Food source provision
Describe the ancestral relationship of algae.
- Closest related are the Charophytes and Embrophytes (land plants)
- Then chlorophytes
- Then red algae
What are the 9 traits charophytes and land plants share?
- Both multicellular and eukaryotic
- Chloroplasts with chlorophyll a & b shared in plants, green algae
- Cell walls all contain cellulose with rosette complexes of 6 glucose molecules. Non charophyte algae have linear complexes.
- Share enzymes that minimise loss of organic compounds using photorespiration. Other algae lack them.
-Share the structure of flagellated sperm - Share the process of phragmoplast formation
- Similar gene sequences
- Presence of sporopollenin, a tough polymer protecting exposed zygotes
What are the 4 problems faced by plants colonising land?
- Dessication
- Lack of structural support
- Lack of nutrients
- Access and transport of water
How have land plants overcome these 4 problems?
Dessication: Cuticle layer over stomata that opens and closes based on hormones, allowing for gas exchange with minimal water loss
Lack of structural support: Thick cell wall with cellulose and lignin
Lack of nutrients: Root systems, symbiotic association with mycorrhizal fungi
Access and transport of water: Xylem and phloem
What are the 4 main traits land plants posses but charophytes do not?
- Root Apical Meristem and Shoot Apical Meristem
- Multicellular gametangia (organ/cell in which gametes are formed)
- Alternation between haploid/diploid in life
- Walled spores produced in sporangia which is only released in correct conditions.
What are cryptograms?
- Lower plants
- Seedless plants
- Spore bearing plants
- Non flowering plants
Two types: Vascular (ferns etc) and non vascular (mosses etc)
What are bryophytes?
Small plants without vascular systems. They must be kept in moist environments due to the fact they rely on capillary movement of water.
Do bryophytes have leaves or roots?
They have neither. They are anchored by rhizoids and have microphylls instead of leaves.
How have some bryophytes evolved to grow up to 2m?
Mosses such as polytrichum has conducting tissues in the middle of their stems.
In moss, what produces sperm cells? What does it require?
The antheridia releases sperm cells and requires water to release them, such as raindrops.
What produces the egg cell in moss?
The egg cell is in the archegonium.
When does the life cycle become diploid?
moss
When the sperm and egg cell fuse within the archegonium, creating a diploid zygote.
Describe the process from the zygote to the release of haploid spores.
moss
Zygote undergoes mitosis, eventually growing into an embryo. It then forms capsules (sporangium) which undergo meiosis and release haploid spores.
How does the plant grow from these spores?
moss
They are blown in the wind away from the parent plant and grow into new male/female gametophytes.
Give a summary of liverworts.
- Hepatophyta
- Some have simple thallus
- Similar lifecycle to moss with dominant gametophyte
- Some have complex gamete bearing structures
- Some reproduce asexually via budding
Give a summary of hornworts.
- Antherocerophyta
- Have simple gametophyte thallus
- Each cell has single large chloroplast
- Symbiotic with N2 fixing blue-green algae
- Sporophyte has 2 horns, grows from base
What are vascular cryptograms and their characteristics?
- Ferns, horsetails, club mosses
- Have vascular tissue
- Have dominant sporophyte
- Reduced gametophyte known as a prothallus.
What is the first known vascular land plant?
Cooksonia, extinct since the Devonian 380 Mya.
- First plant to show apical dichotomous branching, maximising offspring from one fertilisation.
What is the dominant phase of a fern life cycle?
Sporophytic diploid.
What does the prothallus contain?
- Archegonium (egg)
- Anteridium (sperm)
What is dishiscence?
The process in which spores are ejected from sporangium. Dead water filled cells known as annulus loses water via evaporation, is distorted. Annulus peels back, air forms a bubble as water is lost and eventually snaps back and dislodges spores.
Describe the stages of a fern life cycle from a spore to an adult.
- Spores are released from sporangium.
- Germinate and grow into a prothallus, which houses both the archegonium (egg) and anteridium (sperm)
- Sperm needs water to travel to egg, they fuse to become a diploid embryo.
- Grow into adult sporophyte and release new spores after meiosis via dishiscence.
Give a summary of ferns.
- Pteridophyta
- Large pinnate leaves
- Sporangia under leaf surface
- Stem often a rhizome but true roots present.
- Homosporous (not separated into M and F)
Give a summary of whisk ferns.
- Originated in Devonian, known as living fossils
- Green stems, microphylls, rhizoids
- Dichotomous branching
- High chromosome number
- Gametophyte stage is saprophytic meaning it obtains nutrients from decaying matter
Give a summary of horsetails.
- Sphenophyte
- 4 appendages attached to the spore. In dry conditions this is unfurled, dispersing spores. In wet conditions it is tightly furled and spores are dispersed.
- Dominant sporophyte, just like ferns
- Silica rich
- Distinct strobili (cones) that look very spiky all over
Give a summary of club mosses.
- Lycophyta
-True leaves (megaphylls) and roots - Reproductive shoots on sporophyte modified into strobilus (literally just a pinecone)
- Similar life cycle to fern
- Some species heterosporous (like moss)
What was the significance of the evolution of seedless vascular plants?
- Development of vascular tissues, roots and leaves increased photosynthesis.
= 5x less co2
= global cooling and glacial formation
= generally less death
What are gymnosperms?
Cone bearing plants with enclosed ovules.
Why are seeded plants so successful?
- Embryo is protected from the environment
- Seed can travel further from parent, increasing areas of colonisation.
- Seeds retain viability for a long time and can hatch when conditions are right.
What is the patterns of life cycles across evolution?
As evolution has continued, gametophytic stages have become less dominant - with ferns/seedless vascular plants having macroscopic gametophytes but seeded plants having microscopic gametophytes.
Are seeded plants hetero or homosporous?
Hetero.
- However closest relative of seed plants are homosporous, meaning they evolved from homosporous ancestors.
What determines whether a male or female gamete will be produced?
Megasporangia from megaspores = female
Microsporangia from microspores = male
How are eggs protected in seeded plants?
- Integuments, which are sporophyte tissue that envelopes the megasporangium (outer later of ovule that holds the egg).
- Gymnosperms have 1
- Angiosperms have 2 = more protection
What are the main differences between seedless and seeded plants? (you can’t say seeds)
Seedless vs seeded:
Flagellated sperm/non flagellated
Require water to move/require animals or wind
Travel few cm/ travel vast distances
Sensitive to dessication/Survive long periods
What is the first example of a species transitioning to seeds?
Archaeopteris:
- Fern like leaves
- No seeds
But!!!
- Heterosporous
- Up to 30m tall
Give a summary of Ginkophyta
- Phyla within gymnosperms
- 1 extant species that is diecious.
- Females produce rotting smelling fruit
Give a summary of cyadophyta.
- Phyla within gymnosperm
- 100 extant species, all diecious
Give a summary of Gnetophyta.
- Phyla within gymnosperms
- Closest relative to angiosperms
- 69 extant species
Give a summary of ephedra.
- Phyla within gymnosperms
- 40 extant species
- Desert shrub
Give a summary of conifera.
- Phyla within gymnosperms.
- 610 extant species, some up to 5000 yrs old.
Are pines hetero or homosporous?
Hetero.
Describe the process of growth in both male and female pine sporophytes.
Female: Ovulate cone contains many ovules which contain megasporocytes (2n), surrounded by a megasporangium and 1 integument.
Male: Pollen cone contains many microsporangia (2n) which undergoes meiosis 2 times to create many pollen grains (n, haploid, gametophytic)
- Megaspore and pollen then fuse
What happens to the now fused gametes?
pines
- Undergo meiosis twice to form 4 haploid cells
- Only 1 survives as a megaspore (n)
- Female gametophyte develops, containing 2/3 archaegonia which all form eggs.
- Endosperm forms around now growing zygote, until they are grown enough to fall from the cone and become a new plant.
What is an angiosperm?
A single phylum known as flowering plants that produce seeds contained within fruits (ovaries).
What develops into the male and female gametes in angiosperms?
Male: The stamen (made of anther and filament) produce microspores that develop into pollen grains
Female: Carpel (made of stigma, style and ovary) produce megaspores that develop into female gametophytes.
Describe the journey from a mature flower to an egg nucleus.
- Ovary in mature flower holds 2n ovules that divide by meiosis. It holds a megasporangium that holds a megaspore.
- It grows into an egg nucleus inside the female gametophyte after double fertilisation, and eventually into a new zygote.
Describe the journey from a mature flower to a new pollen grain with new sperm. Do not describe double fertilisation.
- An anther on the mature flower holds a microsporangium with holds diploid microsporocytes.
- These have two cell types (generative and tube) and grow to form pollen grains in the stigma.
- The generative cell divides to form 2 sperm cells during transit along the pollen tube.
- Double fertilisation occurs, new zygote formed. baby plant.
What is an endosperm?
Tissue that surrounds and nourishes the embryo in the seeds of flowering plants.
What is double fertilisation?
- Pollen tube discharges 2 sperm cells into egg sac.
- 1 fertilises egg to form diploid zygote (baby).
- 1 fuses with 2 polar nuclei to form a triploid cell. This divides to form the endosperm.
What are the benefits of double fertilisation?
- Co ordinates embryogenesis and endosperm formation
- Conservation of resources
What is a cotyledon? How many do monocots/dicots have?
An embryonic leaf in seed-bearing plants, one or more of which are the first leaves to appear from a germinating seed.
- Monocots have 1, dicots 2.
What are the differences between monocot/dicot leaves?
Monocot leaves: Parallel veins
Dicot leaves: Net/web like veins.
What are the differences between monocot/dicot stems?
Monocot - Scattered vascular tissue
Dicot - Vascular tissue arranged into rings
What are the differences between monocot and dicot roots?
Monocot - Fibrous root systems, no main root
Dicot - Have a taproot, a main root with smaller ones coming off it.
What are the differences between monocot and dicot flowers and pollen?
Monocot - Pollen grain with one opening on a flower with organs of 3x.
Dicot - Pollen grain with three openings with organs in 4 or 5x.
How to monocot root caps develop, and what is their purpose?
- Functions as a crash helmet, helping to force its way through soil
- Constantly replenished with new cells and protects stem cells in root
Do all dicots share an ancestor?
No, they are paraphyletic.
Give a summary of bennetittales.
- Extinct
- Closer to angiosperm
Give a summary of Archaefructus sinensis.
- Transition fossil, around 125 mya
- Anthers but no pets or sepals
- Bulbous structure alongside being found with fish bones indicates aquatic species
