BI 122 Exam 2

Plant Structure and Function

Plant Evolution

• 1st prokaryotes: 3.5 bya

• 1st eukaryotes: 2.1 bya

• 1st simple multicellulars: 1.8 bya

• 1st: complex multicellulars: 575 mya

• adhesion (simple communication) → complex communication → bulk transport → coordinate growth/development

Bryophytes

“moss plants;” non-vascular - no bulk transport; don’t get very large

• mosses

• liverwarts

• hornworts

Vascular Plants

vascular - bulk transport

Lycophytes

“club mosses,” spore reproduction

Ferns and Horsetails

spore reproduction

Gymnosperms

seed reproduction, reproductive organs → cones

Angiosperms

seed reproduction, flowers

• first land plants weren’t vascular

Vascular Plant Structures

Leaves

photosynthesis

Epidermis (Palisade and Spongy)

Veins

vascular tissue

Stomata

tiny openings present on the epidermis of leaves to let CO₂ in and H₂O out

Guard Cells

specialized plant cells on the epidermis that are used to control gas exchange

cellulose: structural component of plant cell walls

• with high pressure guard cells open; with low pressure guard cells close

• uptake of solutes by guard cells causes water to be drawn in by osmosis (as the guard cells swell, they bow apart, opening the stoma)

• release of solutes causes water to flow out of the guard cells, closing the stoma

Calvin Cycle (Photosynthesis)

CO2 + RuBP →(Rubisco) 1×3 PGA (3c) + 1 x glycolate (2c)

• ATP breaks the glycolate into 2 x CO2

• normal Calvin

  • CO2 (1c) + RuBP (3c) → 2×3 PGA = C3 photosynthesis = typical

    • RuBP = ribulose 1,5 biphosphate

    • 3 PGA = 3 phosphoglycerate

    • enzyme = rubisco (ribulose biphosphate carboxylase)

Photorespiration

Calvin Cycle + C4 Cycle

RUBISCO

an enzyme present in plant chloroplasts, involved in fixing atmospheric carbon dioxide during photosynthesis and in oxygenation of the resulting compound during photorespiration

CAM Photosynthesis

In this pathway, stomata open at night, which allows CO₂ to diffuse into the leaf to be combined with PEP and form malate. This acid is then stored in large central vacuoles until daytime. During the day, malate is released from the vacuoles and decarboxylated.

CAM plants keep their stomata open at night

CO2 + H2O → HCO3- + H-

PEP = phosphoend pyruvate (3c)

CO2 (1c) + PEP (3c) → acid (4c)

enzyme = proteins that catalyze reactions

PEP and PEP Carboxylase

PEP: Phosphoenolpyruvate (PEP) is a 3-carbon compound present in mesophyll cells. It acts as a primary carbon dioxide acceptor and is converted into OAA by the action of PEP carboxylase. The enzyme RuBisCO is absent in the mesophyll cells of C₄ plants.

PEP carboxylase: plays a role in binding CO2 in the form of bicarbonate with PEP to create oxaloacetate in the mesophyll tissue (makes 4c acid)

C4 Photosynthesis

• makes a 4 carbon compound

• sunlight is required to produce ATP and NADPH

• C4 plants are rare in shade areas because it takes extra ATP compared to C5

Mesophyll Cells (Columnar and Spongy)

photosynthesis

Bundle Sheath Cells

between mesophyll cells and the vein

• PEP (3c) + CO2 → 4c acid (PEP carboxylase has no affinity for oxygen)

Stems

• angiosperms (flowers)

  • dicots: 2 leaf sprouts (3/4 of all plants)

  • monocots: one leaf sprout (1/4 of all plants and leaves are in groups of 3)

  • cotyledon: an embryonic leaf in angiosperms

Dicot Structure vs. Monocot Structure Roots

Dicot Structure vs. Monocot Structure Stems

Dicot Structure vs. Monocot Structure Stems

Epidermis

outside

Parenchyma Cells

filler cells, thin-walled, not specialized

Vascular Bundle

groups of cells all around the cross-sections of a stem; specialized

Xylem

vascular tissue that transports water and nutrients from roots to shoots

• made up of vessel elements, tracheids, and parenchyma cells

• primary cell wall: cellulose

• secondary cell wall: lignin

Phloem

responsible for transporting carbohydrates

• made up of sieve tubes and companion cells

Sclerechyma Cells

protect vascular tissue

Monocot Structure

vascular bundles

• atactostele: bundles are arranged in a ring

  • xylem and phloem

Tracheids and Vessel Elements

smaller single celled; bundled together

• water enters the xylem sap, this enters the pits, then goes up through the next pits?

Lignin

a complex organic polymer deposited in the cell walls of many plants, making them rigid and woody

Pits

water moves in and out of the cell through here

Vessel Elements

form one on top of another

• when they’re done developing they dissolve and fuse together to form vessels

Poiseville Equation

flow rate is equal to the pressure on the side of the tube going in minus the pressure on the tube going out times pi/8 times 1/n times r raised to the 4/L or flow rate

• n = measure of viscosity

Transpiration

movement of water from the roots to the shoots

• hydrogen bonds between water molecules allow water to be pulled through the xylem; evaporate sucking force (water molecules evaporate to make room for more)

  • this force must be stronger than the force of the capillaries in the soil

• transpiration can be disrupted by:

  • collapse

  • cavitation (due to air leaks)

  • cavitation (due to freeze and thaw)

Mechanism for Water Transport

xylem

Cavitation

Due to air leaks: occurs when air bubbles from within the water in a xylem and the pressure quickly drops below the vapor pressure

Due to freeze and thaw: bubbles form as water freezes, once it thaws the bubbles and comes together to form a blockage

Phloem

transports the soluble organic compounds made during photosynthesis to the rest of the plant

Sieve Elements and Sieve Tubes

Elements: develop long and thin and a bundle of them is called a sieve tube

Companion Cells

support sieve elements by carrying out cell metabolism and regulation

Sieve Plates

forms to act as a filter and allows water and dissolved organic solutes to flow through

Phloem Sap

is made of sucrose which is made of fructose and glucose

Sucrose and Starch

plants move around sucrose but store it as starch

Osmotic Pump

moves sap from a source to a sink

Source and Sink

Source: makes or stores carbs or sugars

Sink: cells that need the carbs for photosynthesis

Translocation

movement of sap through the phloem

• companion cells pump sucrose from the source to the phloem

  • water moves from xylem to phloem and it creates pressure casing diffusion through the phloem wall

  • high pressure from the area near the source and low pressure from the area near the sink causes flow

  • xylem and phloem are always placed right next to each other

  • 50% of sugars used for energy and 50% is stored or used to build cell walls or feed organisms outside the plant

Roots

below ground, water & nutrient collection, support

• gets nutrients/H2O

• selective of what it lets in

  • outer part = epidermis

    • root hairs

  • cortex = filler doesn’t do a whole lot

    • parenchyma: cellular tissues

  • inner part = endodermis

    • casparian strip = can’t do H2O, has to then go into endoderm

Cortex

tissue of unspecialized cells lying between the epidermis (surface cells) and the vascular, or conducting, tissues of stems and roots

Root Hairs

Because they vastly increase the root surface area and effectively increase the root diameter, root hairs are generally thought to aid plants in nutrient acquisition, anchorage, and microbe interactions.

Endodermis

an inner layer of cells in the cortex of a root and of some stems, surrounding a vascular bundle

Casparian Strip

The Casparian strip is a waxy, hydrophobic band of suberin in the walls around the endodermal cells. It has the important job of blocking the apoplastic route of water and dissolved minerals.

Rhysosphere

all things living around plant roots that help them get nutrients

• little things get sugars

Mycorrhizae (Ecto and Endo)

a type of fungi

• phosphorus = trying to plant

• ecto = A symbiotic relationship between fungi and plants, where the fungal hyphae do NOT penetrate the cortical cells of the plant root.

• endo = Similar to Ectomycorrhizae, but the fungal hyphae penetrate the cortical cells of the plant root.

Root Nodules and Nitrogen Fixation

Root nodules are full of nitrogen fixing bacteria and nitrogen oozes out into the soil.

Content of xylem sap maintained by edodermal cells.

• N2 = atmosphere = can’t see

  • plants need

  • N2 → NH3 or NO2- or NO3-

Vascular Plant Reproduction

• haploid: 1n (1 chromosome)

• diploid: 2n (2 sets of chromosomes)

• mitosis: exact copy, same chrom. (1n to 1n or 2n to 2n)

• meiosis 2n to 1n

• gamete: haploid reproductive cell 1n

• spore: haploid cell that gives rise to a new organism

  • gametophyte: plant that makes gametes

  • sporophyte: plant that makes a spore

• fertilization: 2 gametes making a diploid

• dispersal: getting diploid out into the world

Life Cycles

dioecious: male and female parts are on different plants

monoecious: male and female parts are located in the same area of one plant

Aquatic Algae (e.g. Chara)

Bryophyte (e.g. Polytrichum)

Fern (e.g. Pteridium)

the diploid sporophyte generation is the obvious dominant organism

• there is no advantage for the gametophyte to grow tall because gametes must be produced near the ground where the water needed for their free-swimming sperm is most likely to be found

Gymnosperm

seed plants

• cones

  • ovule cone = female (pinecones); female gametophyte

  • pollen cone = male

  • surface of leaves has sporangium to make haploid spores

    • these go through meiosis and produce the male gametophyte, pollen

  • wind picks up the pollen and pollinates an ovule cone of the same species

    • develops a pollen tube for the sperm to implant itself in the egg (ovule)

    • seed coat over the female gametophyte which covers the embryo to make the seed

Angiosperm

seed plants

• flowers: help recruit animals to carry pollen from one individual to another

• carpal: female

  • ovary → ovules (ovary houses the gametopyte)

  • style = stalk

  • stigma = landing platform of pollen

• stamen: male

  • filament = stalk

  • anther = sporangium

• petals

• sepals: photosynthesize

• flowers have different colors and shapes to attract different animals for different modes of transportation

  • nectar

  • shelter

  • pollen

Angiosperm

Angiosperm

Sporophyte vs. Gametophyte Generations

The sexual phase, called the gametophyte generation, produces gametes, or sex cells, and the asexual phase, or sporophyte generation, produces spores asexually. In terms of chromosomes, the gametophyte is haploid (has a single set of chromosomes), and the sporophyte is diploid (has a double set).

Sporangia, Sori, Spores

Sporangia: an enclosure in which spores are formed

Sori: plural of sorus

Sorus: a cluster of sporangia in ferns and fungi

Spores: a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions

Pollination and Pollen Tubes

Co-evolution with Pollinators

some plants adapt to different pollinators to bring them in and then stick with the animal so that way the animal can deposit the pollen on a female of the same species; plants want reliable pollinators

• pheramones: a chemical signal, scent, that an organism released into the environment to communicate with other members of the same pecies

• pollinia: packets of pollen

Self-compatible and Self-incompatible

• self-incompatible: most angiosperms cannot pollinate themselves (no genetic diversity)

• self-compatible: can pollinate themselves

Double Fertilization

• 1 nucleus from the male gametophyte (pollen) fuses with the egg, forming a zygote, the other unites with the diploid cell of the female gametophyte (ovule) to form a triploid cell that gives rise to endosperm

  • triple tissue: endosperm

  • cotyledons: first leaves of a new sprout (part of the embryo)

Double Fertilization

in angiosperms, gametophytes are contained in the anthers and ovaries and the sporophytes consist of the rest of the plant

• double fertilization results in a diploid embryo and a triploid endosperm

Endosperm

the part of a seed which acts as a food store for the developing plant embryo, usually containing starch with protein and other nutrients

Fruit

the mature ovary wall

• recepticle: the part of the plant that acts as the base for the carpal and sepals

  • in fruit the recepticle grows around the ovary

• artificial selection allows for modern fruits to be bigger with more edible flesh

Vascular Plant Growth and Development

the shoots are made of repeating units of nodes and internodes; one or more leaves are attached at each node

Stem Development

• totipotent stem cells: embryonic stem cells that are present during the first few cell divisions; can form any of the different types of cells in the body

• meristems: groups of totipotent stem cells; a population of cells

  • cambium: type of meristem

Primary (1^o) Growth

a result of rapidly-dividing cells in the apical meristems at the shoot tip and root tip

Shoot Apical Meristem

primary growth = up

leaf primordials on the sides

Totipotent Cells

can form all the cell types in the body

Meristem Identity Proteins

made by the cell at the tip of a meristem

• cells can keep going through mitosis to make more cells

Zone of Cell Elongation

the cells take on water and solutes and fills the vacuoles to elongate

Zone of Cell Maturation

the cells will age

Leaf Development

• early vascular plants lost their apical meristems on their side branches and flattened into a single plain

  • the development of new meristems allowed tissues to form between these side branches, this led to leaves

Leaf Primordial: Evolution of Leaf Structure

groups of cells that will form into new leaves

• at the tip of each branch, the leaf primordial covers the shoot apical meristem

Branch Development

• splitting at apical meristems

  • more sporangium being produced

• grow from axillary buds: meristems that form at the base of each leaf

Flower Development

• grow from specialized floral meristems

  • florigen is the hormonal signal that changes an apical meristem to a floral meristem

  • homeotic genes: genes that specify a body part during development

Hormones

• made in meristems; can affect any cell in the plant

• change gene expression to propogate cell development and differentiation

  • auxin

  • gibberellic acid

  • cytokinins

  • ethylene

  • abscisic acid → closes stomata

  • florigen → triggers flowering

Auxins and Shoot Development

• guides vascular differentiation

• moved through a process called polar transport from the tips to the vascular tissue

• no charge on the auxin in the cell walls

  • gets into the cell and becomes negative

    • PIN proteins: polar integral network proteins

      • channels that allow the negative auxin to travel through the cell wall

      • found on the basal side, away from the tip

      • procambial cells = pre-xylem/phloem

Polar Transport

Directional cell-to-cell transport of functional molecules enables plants to sense and respond to developmental and environmental signals.

Vascular Differentiation

Vascular tissues, xylem and phloem, are differentiated from meristematic cells, procambium, and vascular cambium.

Apical Dominance

when vertical growth supersedes lateral growth

Gibberelic Acid & Internodal Elongation

“green revolution”

• agricultural revolution where plants were bred for short, stout stalks that wouldn’t fall over

  • gibberelic acid controls internodal elongation and decreases the force on the cells and makes the cell wall weaker so the plant can grow higher

    • low gibberelic acid = short plants

Cytokinins & Branch Development

if you have a plant growing really well and you cut off the tip, the plant will start to branch (apical meristem is gone)

• apical dominance

• apical → auxins = suppressed axillaries (auxins in meristems got cut off)

• auxins inhabit cytokinins

  • cytokinins cause cell division

    • made in auxillary buds

Ethylene & Fruit Ripening

gaseous hormone that causes fruit ripening

• enzyme activation (catalyzes a reaction)

• activates the enzymes that ripen the fruit, production increases as it matures and it can cause other nearby fruits to ripen

Secondary (2^o) Growth

increase in diameter

woody (primary and secondary) vs. herbaceous (primary only)

Lateral Meristems

cells that never stop dividing; consists of actively dividing cells forming new tissue; responsible for the rise in the thickness of the plant

Vascular Cambium

makes vascular tissue, forms where xylem and phloem come together

• inside = xylem and outside = phloem (grows both ways

• wood = secondary xylem (outer layers of xylem are the only xylem carrying water)

• bark = secondary phloem (from the vascular cambium out)

• dark, hard heartwood (resin) in the middle of the cross-section acts as a form of structure

• light, soft sapwood is full of functional xylem (outside rings)

• dendrochronology = study of growth rings

  • wide growth rings = higher growth rate

  • narrow growth rings = slow growth rings