Plants: Lecture 2 Flashcards
What is alternation of generations?
Alternation of generations refers to instances where there is a multicellular haploid and diploid component/stage/phase in the life cycle.
What types of plants have alternation of generations?
Alternation of generations occurs in all land plants.
How did alternation of generations arise in plant groups?
It arose independently in evolutionary history many times, also occurring in other groups.
What is the name of the haploid generation?
The haploid generation is called the Gametophyte.
What does the gametophyte make?
The gametophyte directly makes gametes.
What is the diploid structure?
The diploid structure is called the sporophyte.
What does the sporophyte make?
The sporophyte makes spores by meiosis.
In land plants, what does meiosis make?
In land plants, meiosis results in the making of spores.
What process do spores undergo to create the gametophyte?
Spores undergo mitosis to create the multicellular gametophyte.
What is a spore?
A spore is a single cell that can divide to produce a multicellular organism that often has a protective coat (called sporopollenin).
- Can develop into another entity without cells needing to unite.
What is a gamete?
A single cell that can and must unite with another gamete to create a diploid zygote.
- Cannot develop without unification
Example of a green alga without alternation of generations?
Chlamydomonas (Chlorophyta) spend most of their lives as single-celled, haploid organisms. They live in ponds or moist soils and have two flagella.
- Cannot undergo alternation of generations because they do not have a true multicellular haploid and also have no multicellular diploid.
- Instead they have + and - individuals that do not undergo alternation of generations.
How did alternation of generations originate?
Alternation of generations originated when a zygote delays meiosis and instead continues to grow and divide.
- The result of this is a multicellular diploid.
What does the origination of alternation of generations mean?
The multicellular haploid (archegonium & gametophyte) contains the zygote, which undergoes delayed meiosis and instead undergoes mitotic divisions, producing the multicellular sporophyte (multicellular diploid). This also results in the embryophyte condition of a multicellular haploid housing a multicellular diploid.
How many divisions of land plants are there?
There are 10 divisions of land plants or embryophytes.
What are the 4 main divisions of land plants?
The 4 main divisions are Mosses, Ferns, Conifers, and Angiosperms.
How many species of mosses are there?
The division of Bryophyta (mosses) contains around 15,000 species.
Basic facts about division Bryophyta?
- They are low growing (cm tall)
- They are confined to damp areas
- They have no true leaves
- They are gametophyte dominant
- They are homosporous
Why are mosses confined to damp areas?
They are confined to damp areas for two reasons:
- They have swimming sperm, meaning water must be present for the sperm to reach the egg. This is why they are low growing.
- They have no true vascular tissue and only contain a rudimentary vascular system. It is not well developed enough to be large and cannot support the whole plant by sending nutrients.
Why don’t they have true leaves?
True leaves need to have a vascular system, which mosses lack.
What does it mean to be sporophyte or gametophyte dominant?
The state that is more dominant is the more long-lived state. This means that it is what we see when we look at the plant.
Where do moss sporophytes arise from?
Moss sporophytes arise from the gametophytes. They are dependent on the gametophyte and live for a short period of time.
Moss life cycle?
- Spore germinates, and grows into the gametophyte.
- Male gametophyte contains sperm that undergo mitosis and divide.
- A raindrop (water in general) moves the sperm from the antheridium to meet the female egg.
- The female gametophyte develops in the archegonia
- Egg and sperm meet when raindrop lands on female structure. Fertilization occurs.
- The zygote (sporophyte) sits in the archegonium as it develops (embryophyte condition)
- The sporophyte is dependent on the gametophyte which photosynthesizes and gives nutrients to the sporophyte.
- Sporangium (top of plant) is a vessel that creates and contains spores, and is responsible for undergoing meiosis to make more spores.
- Repeat
Where do moss sporophytes grow out of?
Moss sporophytes grow out of the top of gametophytes.
How is sperm made in the antheridia?
Sperm is made by mitosis in the antheridia (male gametophyte)
Where is the egg contained?
The egg is contained in the archegonium (female gametophyte)
What is the sporangium?
The sporangium is where cells undergo meiosis (each cell creating 4 new cells)
What was the next big step in evolution?
The next big step in evolution was vascular tissue.
What is the importance of vascular tissue?
Vascular tissues provides support and supply through its structures: Xylem and Phloem.
- Allows plants to grow taller due to increased rigidity and hormones, sugar, water and more.
What was the first plant to be recorded as having vascular tissues?
Cooksonia was the first plant group to be recorded as having a vascular system in the fossil record. Roughly 410 mya
What plants are in division pterophyta?
Ferns, Horsetails, and other “Winged Plants” are part of division pterophyta.
How many species are in division pterophyta?
There are roughly 20,000 species, with most of them being tropical.
When did division pterophyta appear?
They appeared roughly 400 mya.
Features of division pterophyta plants?
- They have vascular tissue: called xylem and phloem which are in charge of support and supply
- Swimming sperm
- Sporophyte dominant
- Can be homosporous or heterosporous
Fern/Pterophyta life cycle?
- spore is dispersed
- spore germinates and grows
- one side of structure produces sperm (antheridium) and the other produces eggs (archegonium).
- sperm is released into the archegonium and fertilizes the egg, forming a zygote/sporophyte
- gametophyte disintegrates
- sporophyte matures and their sporangium undergo meiosis.
- repeats
How do “vacuum” sporangium work?
They throw their spores when the outside layer bursts open. It is under tension until it busts open and throws the spores a few centimetres.
What is the other method of dispersing spores?
The cinnamon fern contains 2 kinds of leaves: photosynthesizing leaves and sporangia leaves.
- The release of spores is more like a clam shell opening as it quickly opens, flings the spores, and closes once again.
What is homospory?
Homospory is when a plant has one size of spore coming from meiosis.
What is heterospory?
Heterospory is when meiosis results in 2 sizes of spores.
Process of homosporous spore production?
- Sporangium
- Single type of spore
- Typically a bisexual gametophyte (both female and male structure together)
- Creates egg and sperm
Heterosporous spore production?
Female side:
- Megasporangium
- Megaspore
- Female gametophyte
- Egg (large)
Male side:
- Microsporangium
- Microspore
- Male gametophyte
- Sperm (small)
What plants tend to be homosporous?
Mosses and most ferns
What plants tend to be heterosporous?
Some ferns and all seed plants
What change led to land plant evolution?
The development of pollen and seeds (If you have seeds you have pollen) led to land plants being what we know them as.
What are the 5 divisions of seed plants?
- Cycadophyta
- Ginkgophyta
- Gnetophyta
- Coniferophyta
- Anthophyta
What do seed plants have?
Seed plants have both seeds and pollen
What is a seed made up of?
A seed is made up of an embryo, nutrients, and a seed coat.
What does a seed develop from?
A seed develops from an ovule (an immature seed).
What is an ovule?
- A novel structure appearing in seed plants
- The site of female meiosis
- Contains the female gametophyte, female sex organs, egg and embryo
- Where fertilization occurs
- Where embryo arises and matures
What is meant by the ovule being the site of female reproduction?
This means that it needs a female gametophyte and an egg. To do this it needs to make a spore which is made from a sporangium.
What happens to cells inside the megasporangium?
These cells undergo mitosis, forming the embryo
What is the micropyle?
The micropyle is the opening where pollen enters the seed
What is the integumentary?
It is the structure that eventually becomes the seed coat.
What does the megasporangium create?
It creates a cell that will undergo meiosis, where 3 of 4 cells will die and leave one viable.
What becomes the megagametophyte?
A single functional megaspore becomes the megagametophyte.
What does a mature ovule become?
A mature ovule becomes the seed.
- Integument = seed coat
- Female gametophyte = food
- Megaspore = embryo
What is a seed composed of?
It is composed of an embryo, nutrition ad a seed coat
- Develops from the ovule
Where does pollen come from?
Pollen makes/contains sperm, and also the mature multicellular male gametophyte
- it is only a few cells in size
How many species are there of division Coniferophyta?
There are roughly 50,000 species of conifers
Facts about conifers?
- Their reproductive organs are in cones
- Sporophyte dominant
- Heterosporous
- Microgametophyte = pollen
- Megagametophyte is within ovule, making the egg and nourishing embryo.
Main difference of the conifer life cycle?
The conifers wait roughly a year between sperm/pollen arrival and fertilization.
What is the “nutrition” in conifers?
In conifers, the nutrition for the embryo is the megagametophyte.
What is the megagametophyte?
Structure that makes the egg in the archegonium and nourishes the embryo
What is the microgametophyte?
The pollen grain that makes sperm.
Why do male cones make and release so much pollen?
They release and make a lot of pollen because it travels by wind and you need a lot of pollen for this method to ensure that the maximum amount of fertilization occurs.
Summary of conifers?
- Seeds and pollen
- Separate male and female cones
- Naked seeds called gymnosperms
- Seed embryo is nourished by megagametophyte
- Slow reproduction
Why might there only be 550 species of conifers?
Many think this may be due to the slow reproduction time for the trees
Jack pine reproduction example?
Summer 1:
- Initiate male and female cones
Summer 2:
- Male meiosis (pollen)
- Pollination
- Female meiosis after pollination
Summer 3:
- Fertilization (summer)
- Mature seeds (late summer/fall)
When do conifer seeds germinate?
They will only germinate/release when a fire comes.
