Plants - Unit 2 BSCI207

Plants and Multicellularity

Benefits of Multicellularity

• Can overcome diffusion in some ways

How can Multicellular organisms overcome Diffusion? (2)

• Link separate cells together by adhesion

• Task division (cells differentiate into different types)

How To Reproduce As Multicellular

• Binary Fission/Budding

• Produce single-celled spore or gamete

Binary Fission/Budding is _____ reproduction

Asexual

Producing a single-celled spore or gamete is ____ reproduction

• Sexual

Produce a single-celled spore or gamete (How do they differ?)

• Single-celled spore will grow up into a whole individual by itself

• Gamete will fuse with another gamete cell and form a diploid individual

How can reproduction work in Multicellular organisms?

• Some cells that must completely give up opportunity to pass on genes

• Some cede function of reproduction

• Needs to be tight control of mitotic and meiotic potential

Does an organisms need to have sex organs to have sex?

No!

Does an organism need to even be multicellular to have sex?

No!

What does an organism NEED to have sex?

• Diploid phase of life cycle

• Meiosis to form haploid gametes

• Union of haploid meiotic products (“'syngamy” or “fertilization”)

Syngamy

Synthesis of two gametes (fusing together)

Sexual Life Cycles (3)

• Haplontic life cycle

• Haplo-diplontic life cycle

• Diplontic life cycle

Haplontic life cycle

• Most time is spent as haploid cell

• Sometimes turns into gametes and are fertilized by other gametes

• Brief diploid phase

Haplo-diplontic life cycle

• Multicellular individual that is both haploid and diploid in life cycle

Diplontic life cycle

• Animals and many plants do this

• Most of adult life cycle spent as diploid cells

• Two copies, one from each parent (result of fertilization)

• Brief period as a haploid cell (formation of gametes that form next generation)

____ life cycle is typical for unicellular eukaryotes

Haplontic

Animals have ____ sexual life cycles

Diplontic

Male and Female Gametes defined by their _____

• Size

• Female gamete is bigger (Egg) than male gamete (Sperm)

Haploid

• Cell or organism that contains a single, complete set of chromosomes (n)

• Half the number of chromosomes found in normal body cells

Diploid

• Contains two complete sets of homologous chromosomes

• One set from each biological parent

______ are the origin of agriculture and civilizations

Plants

Colonization of terrestrial environments: FIRST

First: plants evolved as a new monophyletic lineage with novel adaptations for surviving on the land

Colonization of terrestrial environments: LATER

Later: plants made terrestrial environment more survivable, existing lineages of animals able to colonize

What are some challenges of living on land for a plant?

• Aquire oxygen differently

• Weather

• Lack of water

• Gravity

• Reproduction

• Direct Sunlight

Plants In Water (Characteristics)

• Bathed in nutrients

• Supported against gravity

• Extensive transport often not necessary (Moving water from one part of body to other, because surrounded by water instead)

• Gametes, offspring transmitted by water

• No problem with desiccation

Reasons Plants Became Terrestrial? (3)

• More direct sun for photosynthesis (sufficient ozone for UV protection)

• Inorganic nutrients available on land

• Initially, absence of herbivores

Challenges to become terrestrial (Plants)

• Ways to transfer gametes

• Protect vulnerable stages (Zygotes)

• Withstand gravity

• Conserve water

• Transport nutrients

Zygotes

Single, diploid cell formed when a sperm cell and an egg cell (ovum) combine during fertilization

Great Moment in plant evolution was when

• Plants “crawled” onto land

• Grow closer and closer to shore

• Also fungi

Plants are able to get more water and nutrients when grown together with ____

Fungi

Tree of Plants

• Algal-like multicellular or on steps to becoming multicellular

• Green algae (Called green algae because are green and multicellular or grow in mats)

• Land plants: embryophytes

Embryophytes have ____

A protective embryo

Plants didn’t evolve photosynthesis, they captured a _______

• Cyanobacteria

Cyanobacteria

Commonly known as blue-green algae, are a group of photosynthetic, gram-negative bacteria

Characteristics of Plants living on land (5)

• Protected embryo

• Cuticle

• Multicellular sporophyte

• Gametangia

• Thick-walled spores

*Traits help plants not lose water

4 major plant groups

• Bryophytes

• Pteridophytes

• Gymnosperms

• Angiosperms

4 groups are defined by

• Traits that they have or don’t have

• (Ex. Bryophytes don’t have vascular tissue)

Bryophytes

Nonvascular

Pteridophytes

Vascular Seedless

Gymnosperms

Seeded Non-flowering

Angiosperms

Seeded Flowering

4 Successive radiations of land plants/The evolution of land plants can be seen as ____

A series of major adaptations to terrestrial challenges for plants to live on land

Plant Life Cycle

• Haploid generation = Gametophyte generation

• Diploid generation = Sporophyte generation

Bryophyte life cycle

• Haploid cells for most of life cycles

Plant Life Cycle (Haploid)

Gametophyte generation

Plant Life Cycle (Diploid)

Sporophyte generation

Bryophytes Traits

• Need to live near water or in a very wet environment

• Rely on water for fertilization

• Abundant in moist habitats

• Persistent gametophytes protect the short-lived sporophytes

• Zygotes develop into diploid embryos (young sporophytes)

Bryophytes Traits that allow them to live on land

• Waxy cuticle (around leaves - reduces amount of evaporation of water)

• Enclosed Embryo

• Stomates

*All land plants have these traits, but these are the ONLY traits Bryophytes have

Stomates

• Special cells that form pores

• Open and close depending on water and gas needs of plants

• Allow plant to regulate opening of body to get more CO2 and close so they don’t evaporate water

Pteridophytes Evolutionary Traits

• Evolved Vascular Tissue

• Xylem and Phloem

• Xylem fortified with lignin

• Small free-living gametophytes without vascular tissue

• Have vascular tissue but NOT seeds

Xylem is fortified with _____ so can increase in ____size

• Lignin

• Size

• Can get large sporophytes with vascular tissue

Xylem transports _____

Water and Ions

Phloem transports ____

Sugars

Xylem and Phloem in Pteridophytes

• Organized in little bundles

• Vascular bundles (Xylem cells in middle, Phloem cells on outside of bundle)

Xylem in Pteridophytes

• Long, wide cells with no cytoplasm

• Form tubes

Phloem in Pteridophytes

• Long, narrow cells with limited cytoplasm

• Not as wide

Pteridophytes are limited by ____ (2)

• Requirement for water to accomplish fertilization

• Presence of a vulnerable gametophytes (phase)

Fern Life Cycle

Sporangium

• Where sporophyte is made

Bryophyte

• Mostly gametophyte (haploid)

Pteridophyte

• Mostly sporophyte

Gymnosperms are ___

Vascular plants with naked seeds

Gymnosperms have two major innovations: ___ and ____

• Seeds

• Pollen

4 Major Gymnosperms:

• Cycads

• Ginkgoes

• Conifers

• Gnetophytes

Gymnosperms are ___

Heterosporous

Megaspore = ____

Egg

Microspore = _____

• Sperm

• Ex. Pollen

Anisogamous

Not same size gametes

Gymnosperms are ____

Anisogamous

Parts of A Seed (4)

• Seed coat

• Spore wall

• Food Supply

• Embryo

“In situ” means

In that location (In that situation)

Evolution of Seed

1. Megaspore → Female Gametophyte (egg) retained on sporophyte

2. Egg fertilized in situ

3. Embryo supplied with food

4. Seed (fertilized ovule) - a three generation package deal

5. Germination can wait for favorable conditions!

Germination favorable conditions include (2)

• Carried by wind

• Carried by animals

(Seed) Seed Coat

• Derived from integument

• Part of the mother plant

• 1st Generation

(Seed) Spore Wall

• Surrounded by megasporangium remnant

(Seed) Food Supply

• Haploid Female Tissue

• Supply food to the egg

• Female Gametophyte tissue (n)

(Seed) Embryo

• 2nd Generation

• New sporophyte (2n)

Do Gymnosperms need water for reproduction?

• No

• Now free from water for reproduction

Drawbacks of wind pollination:

• Inefficient (must produce a lot of pollen)

• No reliable

Pine cone