APS122 - Biodiversity - Wellman Flashcards
What is biodiversity?
The variety of life, in all its manifestations. It encompasses all forms, levels and combinations of natural variation
What are the 3 elements of biodiversity?
Ecological, genetic and organismal
- everyone thinks about populations
What is species richness?
Number of different species
What % of biomass (excluding microbes) is plant?
90%
What are the major primary producers on the planet?
Plants (base of all terrestrial food chains)
What do plants provide us with?
Food, drugs, materials to clothe and house us, fuel, jobs etc.
What can we use to work out the origin of land plant life?
- Evolutionary relationships of living plants
- molecular clock evidence
- Physiological/anatomical/genetic changes required to make transition from aqueous to subaerial existence
- fossil evidence (plants + spores/pollen)
Marine algae –> Pond/freshwater life –> ?
Land plants
Land plants (embryophytes) are a … group
Monophyletic
- evolved only once from a freshwater multicellular green algae
What are the problems associated with the transition to land?
- Water balance (evolve roots/rhizoids, transport systems, cuticle etc)
- availability of nutrients and gases (evolve stomata and roots)
- Support (no longer supported by aquatic medium - evolve lignified conducting tissue)
- UV protection (use cuticle)
- Reproductive strategy (spore wall evolved + dispersal by new vectors)
What is the most basal land plant group?
Liverworts
Bryophytes are…
The dominant phase is…
- non-vascular (do not have lignified) conducting tissues hydroids and leptoids
- Homosporous
- The gametophyte phase is dominant (sporophyte parasitic)
In vascular plants (tracheophytes) the dominant phase is the….
The conducting tissues are…
Sporophyte phase
- lignified
How many species of angiosperms are there?
250,000
Lycopsid –> ? –> ferns
Sphenopsids
What is the alteration of generations?
Gametophyte (haploid, n) phase and sporophyte (diploid, 2n) phase
Bryophytes require a … … … to reproduce
film of water
- sperm have 2 flagellae lol
What are the three main bryophyte groups?
Liverworts, mosses, hornwarts
What do epiphytes do?
Grow on other plants
What is the male sex organ of algae, mosses, ferns, fungi, and other non-flowering plants?
Antheridium
What is the female sex organ in mosses, liverworts, ferns, and most conifers?
Archegonium
In the sporophyte what do cells undergo?
Meiosis
What do elaters in sporophytes do?
Push out and release all of the spores
- spiral structures
What do mosses have at their base?
Leafy gametophyte structure
How do mosses disperse spores (considering they lack elaters)?
Use Peristome with teeth structures (which opens when it is dry) or other capsules (e.g. pepper-pot mechanism)
What are moss stomata for?
- liverworts do not have stomata
Some think they are for moving water around the sporophyte or drying out the sporophyte, or releasing spores
What sort of structure do bryophyte gametophytes often have?
Thalloid (particularly liverworts and hornworts)
Hornworts have basal … cells
Meristem
- “conveyor belts of spores”
When is it thought plants invaded the land?
475Ma
What are the most primitive basal vascular plants?
Lycopsids
In tracheophytes which stage is dominant?
Sporophyte phase
- sporophyte has lignified conducting tissues - can stand upright
What reproductive strategy can lycopsids use?
Both homosporous and heterosporous strategies
- gametophyte very small and short-lived
What are isospores?
All the same size
What is the most famous genera of lycopsid?
Lycopodium (200sp.)
- spine like leaves
- roots
- cones (with sporangia + produce isospores)
- homosporous
What is the most common genera of lycopsid?
Selaginella
- upright or along ground
- spiny leaves
- rhizophores
- heterosporous (sexual differentiation)
- female megaspores + male microspores
- still requires film of water
What are the advantages of heterospory?
- Encourages outbreeding (genetically healthier + more variation)
- Megaspores have reserves and can survive for much longer (even a couple years) + can dry out
- means can inhabit more seasonal and dry environments
What gave rise to the zosterophylls (which then gave rise to the lycopsids?
Rhyniophytes - simplest vascular plants
- bifurcate determinately (whereas zosterophylls + lycopsids indeterminate)
Why did lycopsid trees go extinct?
Environment dried out (require film of water for reproduction)
Sphenopsids are actually a highly derived group of…
ferns
Equisetum (a sphenopsid) has
nodes and whirls of leaves
- Rhizoids - nightmare for gardeners
- homosporous (produces isospores)
- sunken stomata
- “elaters” on outer layer of spores help to disperse them (4 per spore)
What are reasons why plants grow tall?
- intercept more sunlight
- shade out competitors
- better spore and seed dispersal
What are the marattiales?
Tree ferns
- trunk made of dead leaf bases with adventitious roots wrapped around
On ferns where are sporangia?
On the underside of leaves
What are hydropteridales?
Water ferns
- hairs repel water
- roots hang down
- the only heterosporous fern
- “velcro-like” system of megaspores and microspores
Are leaves homologous?
No - evolved several times independently - so did heterospory
How is it suggested megaphyll leaves evolved?
Webbing between branches
How is it suggested microphyll leaves evolved?
Either:
- Reduction
- Enation
- Sterilisation
What are the gymnosperms?
Seed plants
- gingkos
- cycads
- conifers
- gnetales
In gymnosperms the gametophyte grows inside…
the spore (called a pollen grain)
The pollen grain is … whereas the megaspore is …
male (microspores), female (ovule)
- when fertilised becomes seed
- dependence on water for reproduction removed
When was the plant equivalent of the cambrian explosion?
Devonian
What are cycads characterised by?
Big phat cones
What do gingkos and cycads have?
Both male and female plants
- can switch if not pollinated for a long period
What do conifers have on their pollen to help it fly and distribute?
Air sacs (2 of them would you beleive?!!) WOWWWW
What do gnetales have?
Flower-like structures
How many cell types occur throughout the plant kingdom?
Around 40 only
- plants have very basic needs
Since plants are sedentary reproductive propagules are dispersed…
vast distances
Plants can often … in times of stress
regenerate
e.g. from underground stems and rhizomes
What are the two types of polyploidy?
Autopolyploidy
Allopolyploidy (hybrid) - responsible for a lot of plant speciation
What is mosaic evolution?
Only evolving certain parts of plants at once - rest remains the same
What is the key driver of plant evolution?
Evolution of new more effective and efficient reproduction strategies
What are angiosperm seeds used for?
Food, vitamins, oils, spices, stimulants, drugs, waxes, vegetable ivory, dyes, ornaments
What are seeds?
Reproductive bodies formed from fertilised ovules
What is the endosperm?
Nutrient store
What are the functions of seeds?
Multiplication, perennation (survival), dormancy and dispersal
Why are seeds superior to spores?
Nutrient store, multicellular - headstart - better transfer of genetic material to the next generation
What is the biggest seed?
Smallest?
Coco de mer (Buoyant)
Slipper orchid
What makes a successful seed?
Seed number - some species can have a potential of 1 billion offspring
As seed mass increases, offspring survival…
increases
What is the tradeoff in angiosperm seeds between
seed mass and seed number
What are the advantages to bigger seeds?
More resources
Emergence from a greater depth
Aggressive early growth
Greater stress tolerance
BUT fewer seeds
In favourable environments … seeds are better
Small
In stressful environments … seeds are better
Large
Competition leads to … seed mass
Lower - due to more root mass investment
What determines seed size?
Size of parent + form of parent Dispersal mode Environment Predation risk Lifestyle
Why do seeds need to be dispersed?
Avoid competition with kin
Avoid inbreeding
Exploit new habitats
What is anemochory?
Seed dispersal by wind
- often pioneer vegetations
- flyers - balloons - plumes - wings - tumbleweed
What is hyrdochory?
Seed dispersal by water
- buoyant seeds (corky fruits or air-containing fruits)
What is zoochory?
Seed dispersal by animals
- endozoochory (in)
- Epizoochory (on)
- synzoochory (deliberately)
- sticky, useful or tasty
What is myrmecochory?
Chiropterochory?
Seed dispersal by ants
- By bats
Why do island seeds tend to have decreased dispersal?
So seeds don’t end up in the sea
Angiosperms bear seeds…
enclosed within an ovary (fruit)
What are internodes?
Gaps between leaves on stem
What are the two main plant systems?
Shoot system and root system
What is the end of the female part (pistil/carpel) of the flower called?
Stigma (on the end of the style)
What is the male part of angiosperms called?
Stamen (+anthers)
When did the angiosperms emerge?
Mesozoic era
Evidence suggests the angiosperms and gymnosperms are … …
Sister clades
What are the main groups of angiosperms?
Eudicots, monocots (grasses), magnolids
What are cotyledons?
Seed leaves
- formed in the seed
- Carry a food source for growing leaves
- very different to ‘true’ leaves
Monocots have … vascular tissue
Parallel
In monocots stomata are..
Present in lines and present on both surfaces of the leaf
more scattered in dicots and more on underside of leaf
Eudicots can make … as they have cambium
wood
Monocots have … roots
adventitious
+ fibrous
(eudicots have taproots)
Monocot flowers have multiples of … parts
3
4 or 5 in eudicots
Monocots have … pollen grains, whereas eudicots have … pollen grains
Monosulcate, tricolpate
What is the major factor determining seed size?
Size of the parent
Shrub has wood in it. What doesn’t?
Forb
If you can produce toxic seeds you can…
invest in larger seeds
What is iteroparity?
Semelparity?
Reproduces many times during life cycle (most perennial plants
- Reproduces once during lifestyle (large and fatal - most annual plants) - actually quite rare
- Synchronised flowering over vast areas known as masting
What is a perennial?
A plant that lives for over 2 years
Why does semelparity exist?
- Predator satiation (too many for predators to eat)
- Increase recruitment after fire (competitors will have been removed)
What is seed dormancy?
When a seed doesn’t germinate until environmental conditions are favourable (avoids unfavourable conditions)
What is the purpose of seed dormancy?
- avoid unfavourable periods (e.g. cold winter)
- Wait for favourable environment (cueing)
- Give dispersing agents time to act
- Reduce kin competition
What control seed dormancy?
- Hormones (auxin promotes dormancy, giberellins break dormancy)
- After-ripening (after set time)
- Abiotic factors such as light and temperature
- Physical dormancy (seed coat)
What is pollination?
The process of getting pollen (male gametes) onto stigma to facilitate fertilisation and reproduction
Where does female gametophyte production occur?
What happens?
In the ovary (produces ovules)
- single diploid nucleus –> four haploid nuclei
- only one of the nuclei survive
- splits by mitosis to form 8 haploid nuclei, in 7 cells, within a single embryo sac
Where does male gametophyte production occur?
What happens?
Microsporangium (anther) to produce pollen
- single diploid nucleus –> 4 haploid nuclei
- none wasted
- each haploid nuclei undergoes mitosis to produce pollen with one generative cell and one tube cell
Tube nucleus is responsible for…
burrowing into the style
- two generative cells follow to fertilise eggs
What does the second generative pollen nucleus do?
Fuses with two polar nuclei inside the ovule to form the TRIPLOID endosperm (2/3 maternal, 1/3 paternal DNA)
- endosperm feeds plant
Perfect plants have…
Both male and female parts
Most plants are self-
Incompatible
- if same copy of S gene, pollen tube is aborted
