plants continuity notes

8/10/2019 Plants Continuity Notes

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Overarching ThemeContinuity

PLANTSHow do plants ensure success for their diverse species?

Big IdeaThe life cycles of plants include various methods of reproduction,

however all demonstrate some form of alternation of generations.

Continuity = to ensure survival of a species, all organisms produce new organisms through the

process of reproduction. Genetic information is transferred from parents to offspring through

DNA via gametes; this DNA is responsible for genetic continuity.

The life cycles of plants are complex and ensure continuity through a process called

alternation of generations, which first evolved in aquatic plants

In general,an alternation of generations life cycle involves two generations - a

multicellular diploid generation and a multicellular haploid generation. The diploid (2n)

generation of the life cycle has 2 sets of chromosomes and the haploid (n) generation of

the life cycle has 1 set of chromosomes.

The diploid generation is called the sporophyte, because it produces spores. Thehaploid generation is called the gametophyte, because it produces gametes.

Haploid gametes from two different organisms combine to form a diploid zygote with

two complete sets of chromosomes.

The zygote develops into the diploid sporophyte; in the sporophyte, some cells divide by

meiosis and become haploid spores.

Spores are reproductive cells that develop into gametophytes

An alternation of generations life cycle is a common characteristic of ALL phyla in the

plant kingdom!

- Watchhttp://www.youtube.com/watch?v=iWaX97p6y9U

The Sex Lives of Nonvascular Plants: Alternation of Generations, Crash Course Biology #36
http://www.youtube.com/watch?v=iWaX97p6y9Uhttp://www.youtube.com/watch?v=iWaX97p6y9Uhttp://www.youtube.com/watch?v=iWaX97p6y9Uhttp://www.youtube.com/watch?v=iWaX97p6y9U


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Non-Seed Producing PlantsAlgae (also includes Mosses and Ferns, which we

will look at later)

- We will look at specific examples of how alternation of generations is displayed in the

life cycle of plants as well as begin looking at the overarching theme of Adaptation, but

first lets examine the characteristics of the first plants to evolve on this planet -Algae- Keep in mind the requirements of living things and how plant behaviour and structures

have evolved to ensure survival

- In particular, pay attention to how plants get water and gases, make nutrients, move

water and nutrients throughout their bodies, remove wastes and reproduce

ALGAEAquatic Plants

Characteristics

- Photosynthetic organisms, with no true roots, stems or leaves

- lack vascular tissue (tube-like cells that transport water and other materials within a plant and also provide

support for plant cells), therefore algae rely on simple diffusion from their water habitats to get dissolvedCO2and water

- can grow to large sizes (kelp forests) but require water to support them since they do not have vascular

tissue

- multicellular forms have floatation devices to hold them upright in water and blades, which are broad

photosynthetic structures that float on or near surface of water to maximize capture of light

- require water for reproduction

- also may have holdfasts, anchoring devices to keep them in place despite wave movement

- contain pigment molecules (chlorophyll) required for capturing light during photosynthesis

Habitats

- marine or fresh water environments, oceans, lakes, ponds

- possibly in very moist soil, tree trunks, snow and on rocks

- range of habitats in differing depths of water related to type of chlorophyll algae species contains and the

wavelength of light it absorbs; green algae in shallower water, brown in shallow to medium depths, red in

deeper water

Ecological Roles

Major roles

- as phytoplankton (unicellular forms)

o number one food producers (act as a food source for many organisms)

o supply 50%+ of global oxygen supply through photosynthesis

o symbiotic relationships with some corals

-as seaweed (multicellular forms)

o provide food source and habitat for marine organisms

o for human uses - source of agar, carrageenan, nori, etc.

Taxonomy

- 3 main phyla (green, brown and red algae)

- classified based on type of chlorophyll they contain


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-algal classification is constantly changing: some biologists are not convinced that all algae are plants and

prefer all unicellular algae to be placed in Kingdom Protista, with only some multicellular phyla (seaweed)

remaining as plants, so there is a bit of confusion with classification to the present day

Phylum Chlorophyta (Green Algae)

-predominantly freshwater habitats, but are some marine forms

-contain chlorophylls a and b-store food in form of starch

-have evolved into many diverse forms

i) Single-celled Green Algae(e.g. Chlamydomonas)

-grows in ponds, ditches and wet soil

-small, egg-shaped cell with two flagella

-light sensitive eyespot that can sense bright light or darkness

-large, cup-shaped chloroplast that photosynthesizes to produce starches

-two contractile vacuoles (to get rid of excess water)

-because are unicellular, do NOT have a multicellular haploid generation and a multicellular

diploid generation, so their life-cycle is not a true example of Alternation of Generations

-no cellulose in cell wall

-characteristics of Protists, Plants and Animals

ii) Colonial Green Algae(e.g. Volvox)

-many identical cells living together

-each cell functions independently

-colonies can have anywhere from 500 to 50,000 cells

-individual cells are connected by strands of cytoplasm that allow them to communicate when

colony needs to swim

-a few cells are specialized for reproduction

iii) Threadlike Green Algae(e.g. Spirogyraand Oedogonium)

-create long, threadlike colonies called filaments

-grow and reproduce asexually

-if filaments are broken, the cells continue to divide and grow

-attach to the bottom of a lake or pond by a specialized holdfast cell so are sessile, compared to

motile Chlamydomonas

iv) Multicellular Green Algae(e.g. Ulva or sea lettuce)

-live in marine environments-are only 2 cells thick, so easy diffusion of gases

-holdfasts attach Ulvato rocks

-have both a multicellular haploid generation and a multicellular diploid generation

-no difference in appearance of each generation (sporophyte and gametophyte), are virtually

indistinguishable from each other! (refer to diagram)


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1. The mature diploid sporophyte (2n) produces haploid spores (n), via meiosis. These

spores are flagellated and are called zoospores.

2. The zoospores germinate and grow into haploid gametophytes (n). The gametophytes

grow into haploid maleand femalealgae plants.

3.

The male gametophyte produces haploid flagellated male gametes. The femalegametophyte produces haploid flagellated female gametes. Fertilization occurs when

the male and female gametes swim together and fuse.

4. Fertilization results in a diploid zygote (2n). The zygote grows into a diploid sporophyte

algae plant through mitosis.

Phylum Rhodophyta (Red Algae) (e.g. Chrondrus crispus)

-almost exclusively marine habitats

-red because of the presence of pigment phycoerythrin, a pigment that reflects red light and

absorbs blue light

-since blue light penetrates water to a greater depth than light of longer wavelengths, these

algae can live at greater depths than other algae, up to 260 m.

- rhodophytes are important sources of food, such as nori (Poryphyra) and dulse (Palmaria) and

also used as fertilizers on coastal agricultural land

-some rhodophytes are important in the formation of tropical reefs (e.g. coralline algae)

Phylum Phaeophyta (Brown Algae)

-mostly marine habitats


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-brown colour results from the dominance of the xanthophyll pigment

-contains chlorophylls a and c

-brown algae generally larger and more species found in colder waters than other seaweeds

-common forms include kelps (Sargassum) and wracks (Fucus)

-also some forms use for food such as Japanese kombu (Laminaria japonica)

-kelps grow in underwater forests, some grow to more than 60 m. long and are secured to rockswith holdfast structures

-Fucuskeeps upright with help of air bladders

-Reproduction in Fucus(refer to diagram)

1. Female gamete =egg (n) is large and cannot swim

2. Male gamete=sperm (n) is small and swims with help of flagella

3. Diploid sporophyte plant (large seaweed structure) is the only multicellular part of

the life cyclethis shows an evolution of alternation of generations from its first

form in algae into what we see in more complex land plants.

4. The blades(leaves) of the sporophyte plant contain specialized reproductive

structures (conceptacles, in little pockets called receptacles), one produces eggs(oogonia) and one produces sperm (antheridia), both are produced on the same

plant.

5. The eggs and sperm are released into the water and if sperm find some of the

floating eggs, fertilization occurs and a zygote (2n) is formed

6. The zygote sinks to the ocean bottom and, with luck attaches to an object such as a

rock where the zygote will grow by mitotic division into a new diploid (2n)

sporophyte


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Learning ActivityAlgae Life Cycle Review Sheets, Algae: Structures and Uses Lab

Confirm your learningAlgae Brochure Project, due ___________

Connection to Biological ThemeHow does each phase in Alternation of Generations provide continuity for

algae? Explain the benefits provided by each phase. Consider the means by which the cells divide

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Asexual phase (sporophyte) allows species to increase in numbers since they double every time the cell divides

during mitosis.

Sexual phase (gametophye) increase genetic variation by combining chromosomes from different individuals

during meiosis.

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