Unit 2: Plants Grade 11 AP Bio

Evolution of Plants

Plants evolved from red algae and green algae

Relation between green algae and land plants

- Contain chlorophyll a & b

- Have cellulose cell walls

- Stores food as starch

- Genetic similarities

- Similar reproductive strategies - sexual sporic reproduction

General Characteristics of Plants

- Cellulose cell walls

- Sessile

- Eukaryotic

- Multicellular

Vascular tissue

Tissue that transports water and sugars throughout an entire plant

(xylem & phloem)

Phloem

vascular tissue that transports sugars

Xylem

- Transports water and minerals

- Allows plants to grow higher

- Contains lignin - anchors plant, aids absorption

Cuticle

A non cellular layer on the top of the leaf

Secreted by epidermal cells to protect it from drying out

Stomata

Pores within the epidermis of the plant

Permits gas exchange between plant and air

Plant life cycle

Alternation of haploid gametophyte & diploid sporophyte stage (Alternation of Generations)

Alternation of Generations

1. Sporophyte produces haploid spores (meiosis)

2. Spore grows into gametophyte

(Produces male and female gametes)

3. Fuses and develops another sporophyte

Bryophytes

- Contains all seedless non vascular plants (mosses, liverworts, hornworts)

- Dependent on diffusion and osmosis for transport

- Rhizoids

- Helps plant attach to ground

- Helps to absorb water

- Dominant stage of life is gametophyte generation(haploid cells)

- Helps with nutrient cycling

Tracheophytes (vascular plants)

- Ferns, gymnosperms, angiosperms

- Sporophyte dominated life cycle

- Divided into seedless(spore bearing) & seeded plants

- Can grow much taller

Tracheophyte Reproduction

Spores - club mosses, horsetails, ferns

Seeds - gymnosperms & angiosperms

Ferns (seedless vascular plants)

- Reproduces through spores

- Most diverse seedless vascular plant

- Alternation of generations - dominated by sporophyte life cycle

2 Types of Seed-Producing Tracheophytes

gymnosperms + angiosperms

Gymnosperms

- Cone-bearing plants

- Has seeds exposed on the cone scales

- Mostly coniferous trees

- Have a reduced need for moisture

Gymnosperm Survival Adaptations

Reproduction with male pollen & pollen tubes - removes need for moisture

Protective bark - prevents water loss

Shape - prevent snow/ice damage, increases area for photosynthesis

Needle-like leaves - thick cuticle & sunken stomata prevents water loss

Doesn't loose needles - photosynthesis begins earlier, no need for extra nutrients

Angiosperms

- Plant has protected reproductive structure

- Adaptations increase likelihood of reproduction

- Can self pollinate or cross-pollinate

Angiosperm Survival Adaptations

Plant protects seeds within a fruit

Cotyledon (monocot/dicot)

a structure that stores food in the seed (tracheophyte only)

Monocot

- One cotyledon

- Floral parts in multiples of three

- Parallel array of leaf veins

- 1 pore in pollen grain

- Vascular bundles distributed evenly throughout

Dicot

- Two cotyledons

- 4/5 floral parts

- Netlike array of leaf veins

- 3 pores in pollen grain

- Vascular bundles arranged in a ring shape

4 Reasons for Success of Angiosperms

1. Presence of specialized structures

2. Protected seeds

3. Fruit

4. Specialized tissue

Seed

- a multicellular structure containing an embryo and a food source

- Contains hard protective structures

- Can survive without water for years

Plant Embryo

- An immature root

- An immature shoot

- One or two seed leaves

Pollination

When pollen from male flower parts is transferred to the female parts

Steps of Self Pollination

1. Pollen grains are moved to the stigma

2. Pollen goes down the pollen tube, enters the ovaries

3. Ovules are fertilized

4. Petals fall off of the flower

5. Fruit begins to form

a. Sepals & anthers dry up

a. Seeds form inside

Steps of Cross Pollination

1. Pollen from a different plant is moved to the stigma

2. Pollen goes down the pollen tube, enters the ovaries

3. Ovules are fertilized

4. Petals fall off of the flower

5. Fruit begins to form

a. Sepals & anthers dry up

a. Seeds form inside

Hormone

an organism's chemical messenger

Hormone Function

- Carries instructions from one set of cells to another

- Produced in one cell, modulates cellular processes in another

- Interacts with specific proteins (proteins act as receptors)

- Changes metabolism within the cell after receiving messages

Gibberellins (GAs)

- 125 plant hormones

- Transported through vascular tissue

Synthesized in:

- Root and stem apical meristems

- Seed embryos

- Young leaves

Gibberellins(GAs) Effects

- Increase plant height - stimulates cell elongation and cell division

- Increases rate of seed germination and bud development

- Flower maturation

- Delays senescence in leaves and fruit (process of becoming older)

Auxin

- 5 naturally occurring auxins

- Prevents cell growth - inhibitor

- Cell ends up growing towards the sun

Located in:

- Apical meristem

- Seed embryos

- Young leaves

Auxin Effects

- Promotes cell elongation

- High concentration promotes formation of fruit

- Inhibits fruit dropping

- Leaf formation

- Phototropism

- Gravitropism

- Promotes apical dominance

Phototropism

the growth towards a light source, auxin builds up on the opposite side of the light, inhibits growth there

Gravitropism

auxin builds up towards the ground, plant grows in opposite direction

Apical dominance

Growing through the apical meristems, preventing the lateral meristems

Cytokinin

- 200 plant hormones - derivatives of adenine

- Promotes mitosis

- Transported through xylem

Synthesized in:

- Root tips

- Young structures (embryos, fruits)

- Wounded tissue

Cytokinin Effects

- Causes cell division

- Counters effects of auxin - inhibits apical dominance

- Promotes leaf formation

- Delays senescence in leaves and fruit

Ethylene Gas

- Volatile gas, smaller and simpler molecule

- Produced by aging tissues (ex. wilting/ripening, nodes of stems)

Ethylene Gas Effects

- Promotes breakdown of carbohydrates into sugars

- Causes fruit to soften

- Inhibits cell division - induces abscission of fruit and leaves

- Occurs when auxin levels go down

Abscisic Acid (ABA)

- Synthesized in the roots and leaves

- Occurs when a plant is stressed

- Mediates its adaptation to stress

Abscisic Acid (ABA) Effects

- Closes stomata

- Encourages root growth

- Converts apical meristem into stiff bud scales

- Wraps the meristem to protect it during winter

- Thickens waxy cuticle on leaves

- Promotes abscission(falling off) of leaves

Plant Foraging

- Extending and growing roots towards nutrients

- Speeds up towards, slows down in

Dodder vine

- Attaches to other plants to survive

- Uses green leaf volatiles

- Chemical scents released by leaves - unique to each species

- Released in response to mechanical damage

- Detects difference between wheat and tomato seedlings

- Picks tomato plant 9/10 times

- Tested through artificial odor experiments

Chemical stress signal

released when plant is stressed, ie freshly cut grass

Importance of plant sensing genes

- Respond to stimuli

- Needs nutrients

- Self defence

- Cannot move -> must be aware

Tobacco plant

Uses nicotine to poison predators

Hornworm caterpillar

- Lives on tobacco plant

- Immune to toxin

- Plant releases chemical signals to hornworm predators

Trichome

- Small structures deposited by plants as a defense mechanism

- Extremely sweet for caterpillars

- Causes an odor that signals to predators

Knapweed

- An invasive species of plant

- Kills off native grasses

- Releases chemicals in the roots that kills off other plants

- Takes over nutrients

- Other plants cannot grow

- Causes a drop in biodiversity

Countered by lupin plant

- Releases oxalic acid

- Shields against knapweed toxin(surrounding plants are shielded)

Kin recognition in plants

- Recognizing siblings or related organisms, sharing of resources

- Can result in lower root allocation with siblings

Kin selection in plants

- Sharing of resources with sibling

- Follows altruism - doing benefit to others at a cost to yourself

Competition

- Competing with foreign unrelated organisms

- Stronger competition between strangers

Relationship between Douglas fir trees & fungi

Tree

- Gains nutrients from fungi

- Roots cannot reach everywhere, reach is extended by fungus

Fungi

- Habitat - grows on tree roots underground

- Depends on tree for carbon-based sugars

- Uses tree's carbon - necessary for life

Scientific study

- Mother tree is exposed to radioactive carbon

- Carbon was traced in other nearby trees and plants