Midterm 2

Leaf Modifications

• bud scales: protect perennial plants dormant shoot apical meristems

  • waxy, tight seal covering buds

  • buds underneath are tender modified stems

  • scales protect against wind, temperature, and herbivory

• bracts: associated with flowers and inflorescenses

  • colorful part of the plant closest to inflorescense

• tendrils: climbing modifications

  • sense touch of objects they grow around and increase/decrease growth accordingly

• spine: pointed modified leaves

• thorn: pointed modified stem

• prickle: outgrowth of epidermis and/or cortex

• bulb: enlarged leaves underground for storage of next seasons reproductive growth

  • store starch and sugar to be broken down into ATP

Reproduction

• asexual reproduction: generation of genetically identical plants produced via mitosis

  • examples are rhizomes and cuttings

• sexual reproduction: increases genetic diversity

  • fights disease resistance, allows evolution to genetically advantaged plants

• natural selection: survival of the fittest

• artificial selection: humans select for desired traits as opposed to what might actually be beneficial to the plant itself

• adaptation: changes in structure and function to become better suited to the environment over successive generations

  • example of adaptation are hydrophyte and xerophyte plants

• phenotype: observable physical traits

• genotype: genetic makeup having to deal with genes and alleles

Chromosomes and Genetics

• homolog: chromosomes coming in pairs that go together in the first stage of meisis

  • contain same genes at same gene locus

  • alleles come from mutations and determine phenotype, which happen when mistakes are made in the first mitotic stage

• quantitative trait: controlled by genes and influenced by environment

• Meiosis: reduces chromosomes by half and creates gametes

  • separates homologous pairs in diploid to form haploid

• fertilization: recombines chromosomes to original number

  • haploid cells recombine to form diploid zygote

• haploid: 1n, containing one set of homologs

• diploid: 2n, containing two sets of homologs

Meiosis Specifics

• prophase I: chromosomes condense, nuclear envelope dissolves, crossing over occurs

  • crossing over: swapping genetic material of homologous chromosomes

• metaphase I: homologous chromosomes line on metaphase plate as homologous pairs instead of sister chromatids

• anaphase I: homologous chromosomes are pulled apart by spindle fibers to opposite poles

• telophase I & cytokinesis: chromosomes condense at poles and cytoplasm splits

• prophase II: new spindle forms around chromosomes

• metaphase II: chromosomes line up at sister chromatids

• anaphase II: sister chromatids are pulled apart and centromeres divide

• telophase II & cytokinesis: nuclear envelope reforms and cytoplasm divides

New Genetic Variation

• crossing over: exchanges corresponding segments of DNA between chromatids of homologous chromosomes, which mixes up the alleles

• independent assortment: the way homologs align in the middle, determining combinations of alleles in haploid cells equalling 2 to the nth power

Fertilization

• self-fertilization: limited combinations of alleles

• outcrossing: increases genetic variation by increasing number of alleles present

Flowers & Pollination

• flower structures evolve to promote outcrossing and increase genetic diversity

  • sometimes the goal is to attract specific pollinators

• pedicel / peduncle: stalk supporting flower head

• receptacle: organs attached at the base

• whorls

  • sepals: modified leaves which protect the bud

  • petals: delicate, thin, pigmented and can release compounds as fragrance

  • stamen: male reproductive organ

    • filament: attaches anther to rest of plant

    • anther: produces pollen

  • pistil / carpel: female reproductive organ

    • stigma: hairs and sugars which make it sticky, produce nutrients and allow pollen to germinate

    • style: connects to ovary

    • ovules: house eggs

      • ovary develops into seeds

alterations of generations life cycle

• diploid generations alternate with haploid generations in a single life cycle

  • zygote has 2 copies of chromosomes and develops into a sporophyte

• sporophyte: diploid individuals

  • during meiosis, sporophytes create haploid spores, which then undergo mitosis to create gametophytes

  • diploid, produced asexually, begins with a 2n zygote and end with n spores from meiosis

• gametophyte: create gametes, which are sperm and eggs

  • haploid, produced sexually, contain n spores, end with n gametes producing a 2n zygote

• pollen grain: mature male gametophyte made of 3 cells

• sporopollenin: decay-resistant and chemical-resistant biopolymer making pollen yellow

  • pollen produces protein helping protect from environment

female parts

• ovules are part of the sporophyte, which is diploid

  • meiosis produces spores

• spores undergo mitosis, producing the gamete egg

• egg plus sperm equals diploid zygote, which becomes a seed

  • endosperm is then formed within the seed

pollination

• pollen from the same species lands on the stigma

• there are 3 cells in pollen

  • 1 cell elongates down style to ovule, forming the pollen tube

  • sperm is at the base of the ovule

double fertilization

• pollen grains land on stigma, then the pollen tube elongates to egg

• 1 sperm combines with the egg to form a zygote, and eventually the embryo

• 2nd sperm combines with central cell in the ovule creating a triploid or 3n cell

  • containing 3 copies of genetic material

  • the triploid cell creates the endosperm

• fertilized endosperm divides rapidly and cytoplasm gathers outside the nucleus

  • cell forms around each nucleus and then they harden

  • ovules become seed, zygote becomes embryo, ovary becomes fruit and the placenta provides nutrients

• self pollination: plants with both the pistil and stamen can do this to themselves

  • examples are soybeans, peanuts, rice, wheat, and tomatos

• cross pollination: pollen comes from the anther of a different plant

  • examples are corn, cotton, apples, raspberries and strawberries

  • these plants have more genetic diversity than self-pollinators, and therefore are more resistant to disease / unfavorable conditions

Genetic incompatibility

• prevents self pollination from the same plant or clones

• inside carpels, specific proteins are produces and the pollen tube wont allow pollen with matching proteins inside

Imperfect flowers

• have either only male or only female parts

  • dioecious: individual plants are entirely male or female

  • monoecious: parts of the plant are entirely male or female

• Dichogamy: stamens and pistils mature at different times

  • protandry: anther produces pollen before stigma can take it

  • protogyny: stigma are ready for pollen before anther produces it

• dehiscense: controlled cell death

Co-Evolution

• plants evolve specific traits to attract specific pollinators such as pigments or fragrances while pollinators evolve traits to move the pollen

• bees: attracted to blue and yellow flowers and to sweet smells

  • plants co-evolve to have nectar and extra pollen for the bees

  • also have nectaries, which contain nectar guides

• birds: attracted to red and orange flowers, which are usually unscented because birds can’t smell

• butterflies: attracted to red, blue and yellow flowers with strong scents that are sweet or mimic pheromones

• moths: attracted to white flowers because they are nocturnal

• beetles: attracted to dull colored flowers with strong odors of fermentation and decay

• bats: attracted to plants with many nectaries, dull colors, and strong odors of decay or bat pheromones

• wind: plants have no nectar, petals or scent

Embryo Development and Fruit

• double-fertilization: diploid zygote and triploid cell

• seed: ovules connected to placenta by funiculus

• embryogenesis: establishes plant body

  • 1st division creates embryo and suspensor

  • next few divisions create globular stage and suspensor

  • a few more stages create the heart stage and hypophysis

  • torpedo stage: root meristem and cotyledons established

• Embryo Structures

  • plumule: shoot inside seed

  • epicotyl: node above cotyledon

  • hypocotyl: node below coytledon

  • radicle: leaves seeds during germination

  • scuttelum: grass only, is the cotyledon

  • coleoptile: grass only, is the sheath

  • seed coat: comes from ovule, intermediate

  • micropyle: where sperm enters ovule through pollen tube

  • hilum: scar where ovule attached to ovary

Fruits - mature ovary containing seeds

• pericarp: fruit wall developing from mature ovary wall

  • exocarp: skin or peel

  • mesocarp: fruit flesh

  • endocarp: touch inner layer just outside seed

• accessory fruit: fruit derived from flower tissue instead of seed

• parthenocarpic: very rare mutation where ovary develops into seedless fruit

• fleshy fruit: can be simple, aggregate or multiple with layered pericarp

  • simple fruit - develop from one or multiple united carpels

  • aggregate fruit - many carpels from one carpel in a flower producing fruitlets

  • multiple fruit - multiple flowers attached together that become one connected fruit

• dry fruit: can be dehiscent or indehiscent with dry, unlayered pericarp

  • dehiscent - mature ovary wall breaks open once seed matures after controlled cell death

  • indehiscent - seeds remain in pericarp after maturity

seed dispersal

• wind-borne: dry, lightweight seeds with modified structures allowing them to float in the wind

• water-borne: buoyant, water-resistant seeds

• explosive dehiscence: seeds explosively open at maturity to spread

• animal dispersal: seeds stick to animals or are excreted

• self-planting: parent plant physically transfers seeds to surrounding soil

Seed germination

1. radicle: first structure to emerge

2. taproot: first root emerges

3. hypocotyl: leads through soil as stem to protect leaves and is beneath the cotyledon

4. epicotyl: stem above cotyledons

• post-emergence, hypocotyl and epicotyl are grouped together and called the stem

Types of germination

• epigeous: cotyledons are carried aboveground with the hypocotyl

• hypogeous: cotyledons remain beneaht the soil

Seed Dormancy

• seeds wont germinate even in favorable conditions to prevent vivipary

  • vivipary: seeds germinate while attached to parent plant

• After-Ripening: takes a few months to occur and needs to happen in warm and dry conditions as opposed to hot and humid climates

• Light Promotion: light is required for the seeds to germinate

• Light Inhibition: seeds can only have a certain amount of light to germinate and will remain dormant in sunny conditions

• stratification: seeds must be exposed to cold (NOT freezing) conditions to germinate

• scarification: seeds must be scratched in order to open and germinate through a tough seed coat

• high temperatures: seeds in chapparal regions must be exposed to the heat of fire in order to kill the competition and promote germination

• chemical promoters: seeds in chapparal regions must be exposed to compounds in wildfire smoke to germinate

  • parasitic plants must sense a hormone from their host plant in order to germinate

• chemical inhibitors: desert plants store chemicals, but after a heavy rainfall washes the chemicals away they germinate

Photosynthesis and Carbon Assimilation

• growth - irreversible increase in size

• primary growth - occurs at meristems of roots and shoots as well as axillary buds

  • increase in length

  • stem length determined by internode length, internode length determined by length of internode cells

  • biomass crops heavily depend on internode and stem length

• secondary growth - growth in diameter of nonvascular plants from vascular cambium and cork cambium

  • mostly xylem, which is wood

• development - sequence of changes and milestones in organisms

  • seedling = germination

  • vegetative = primary growth

  • reproduction = sexual and asexual

  • senescence = death

measures of growth

• productivity - dry matter

• RGR - relative growth rate measuring increase of dry matter per unit of time

• yield - dry matter accumulated at the harvestable unit

• harvest index - dry weight of harvestable unit divided by the total plant dry weight

photosynthesis - 6 carbon dioxide plus 12 water → C6H12O6 (glucose) + 6 water + 6 oxygen

respiration - glucose + 6 oxygen → 6 carbon dioxide + 6 water + 686 kCal

• plants get carbon from atmosphere and hydrogen from water

• photoautotroph - plants using sunlight to produce energy

• heterotroph - organisms eating plants to extract energy and produce macros

• productivity = photosynthesis - respiration - photorespiration

  • photosynthesis is the net gain of carbon

  • respiration and photorespiration are the net losses of carbon

• carbon cycle: inputs come from photoautotrophs, are consumed and excreted by heterotrophs

• chlorophyll: captures and conducts light energy and converts to CO2 via light reactions

  • the 686kCal produced by respiration builds molecules, produces heat and powers mechanical work

• light reactions: convert solar to chemical energy

  • potential energy stored in chlorophyll is converted to ATP and NADPH, fueling dark reactions

• dark reactions: convert chemical energy to sugar

  • use CO2 to produce sugar (CH2O)

    • each CO2 fixed needs 3 ATP and 2 NADPH

• ATP - stores potential energy in phosphate groups, which release a lot of potential energy when broken

  • converts to ADP, which doesnt have as much chemical energy

• NADPH - NADP+ bonds with H to store lots of potential energy and is more stable than ATP

  • ATP: 7.3kCal

  • NADPH: 52kCal

  • Glucose: 686kCal

Leaves and Photosynthesis

• chloroplasts: contain thylakoids, grana, and stroma and are the site of light reactions

  • in light reactions within thylakoids, water, light, NADP+, ADP, and a phosphate group are taken in and produce O2, ATP and NADPH

  • in dark reactions within the stroma, the Calvin Cycle takes CO2, ATP and NADPH to produce sugar

Chlorophyll

• Chlorophyll A: blue and green pigmented, are 2-3x more prevalant than Chlorophyll B and are the reaction center

• Chlorophyll B: yellow and green pigmented, accessory pigment

  • accessory pigment - allow plant to absorb more wavelengths of light

• Photosystem - complex of proteins, chlorophyll and carotenoids on the thylakoid membrane

  • Photosystem I: provide electrons for NADPH, which are replenished by Photosystem II, have many Chlorophyll A and few Chlorophyll B

  • Photosystem II: replenish electrons of Photosystem I, reduce H2O to oxygen, 2 electrons and 2 protons and contain equal amounts of Chlorophyll A and B

• Chemiosmosis: concentrated protons in the thylakoid move down the concentration gradient via ATP synthase to produce ATP

• Calvin Cycle: ATP + NADPH used to build glucose from carbon dioxide and hydrogen

Dark Reactions

1. Carbon Fixation: incorporates CO2 into RuBP by enzyme RUBISCO, splitting into two three-carbon sugars

   1. RUBISCO: most prevalent protein on earth, doesn’t require ATP, has an oxygenase activity

2. Reduction: input of phosphate group from ATP and electrons from NADPH to form G3P sugar

   1. every three CO2 form 6 G3P

3. Regeneration of RuBP from G3P by using ATP

• mesophyll cells are the site of fructose and glucose production from G3P

  • sucrose is made in the cytoplasm

Allocation Regulation

• sucrose is tightly regulated by cell depending on needs

Transport of Assimilates

• fixed carbon produces sucrose for transport, respiration, storage, structure and defense

• sucrose is water soluble, transported in the phloem, makes ATP, stored as starch in roots, can make cellulose / lignin or be a secondary metabolite

  • transported through leaf mesophyll cells via plasmodesmata

  • vascular bundles transport sugar through plants

  • mesophyll cells are very close to vascular bundles

• diffusion - movement of solute from high to low concentration

• osmosis - movement of water from low to high concentration with the purpose of dilution

• semipermeability - membranes are permeable to water and small nonpolar molecules

  • plants can withstand high turgor pressure because of the cell wall

  • this means the plants should have higher concentrations of sucrose within the cell to promote osmosis and turgidity

  • plants prefer to be turgid rather than equilibrium

• facilitated diffusion: cell membranes have channel and pump proteins allowing certain molecules to diffuse across without ATP

• Active transport: cell membranes have carrier proteins that require ATP to form around the molecule and actively carry it across the membrane

Phloem - transports sucrose from source to sink

• source: area of high solute concentration and high pressure

• sink: area of a low solute concentration and low pressure

  • rate of phloem transport depends on pressure gradient

  • trees have a slow rate due to their size, while herbaceous annuals such as corn and other forage crops have high rates

• sieve tube element: living cells, made for long distance water and sucrose transport

• companion cell: living cells, loads sucrose into sieve tube element

• sieve pore: dead cell with no cell wall

Assimilate Partitioning

• yield: total dry matter in harvestable unit

• harvest index: sucrose should be going to the harvestable portions of the plant rather than the unconsumed parts

• sink strength: sink size (size of harvestable unit) divided by sink activity

• sink activity: sucrose is unloaded

  • greater rate of unloading, stronger sink and lower pressure in sieve tube elements

Phloem Repair

• p proteins: plug leaks in sieve tube elements like blood clots

• callose: carbohydrates that act as scabs to cover the sieve tube element wound after p-proteins clot them

  • both of these prevent phloem assimilates from leaking out of the sieve tube element

• phloem feeding insects - aphids, leafhoppers and whiteflies are the most common due to their piercing-sucking mouthparts, which consume the assimilates. Then they spit out chemicals that repair the wound they created

Chemicals

• Systemic Chemicals: water soluble, taken up by phloem and move the chemicals from source to sink

  • examples include glyphosate and paraquat

Fate of Assimilates

• respiration and storage, structure, and secondary metabolites

• sucrose used in dark respiration to produce ATP is used in respiration compounds; glucose and oxygen are used to create CO2, water and energy

  • energy builds molecules, releases heat and conducts mechanical work

• respiration begins in the cytosol and ends in the mitochondria

  • glycolysis - breaks hexoses into pyruvate and produces a little bit of ATP to kick off the reactions

  • pyruvate oxidation - produces acetyl CoA, which is used in the Citric Acid Cycle

  • Citric Acid Cycle - breaks carbon bonds to release ATP

  • Oxidative Phosphorylation: runs the electron transport chain and conducts chemiosmosis, producing the most ATP

• respiration is only 34% effective in capturing the energy stored in glucose

  • remaining 76% is lost as heat

  • reduces the relative growth rate by 30-60%

• temperature - influences growth rate due to effect on respiration rate

  • less dry weight is lost on cool nights, which slow the plants metabolism and use less energy

Without oxygen, what will happen to the electron transport chain?

A. nothing, it will stay the same

B. it will happen at a faster rate

C. it will happen at a slower rate

D. it will stop completely

• the answer is D because it won’t undergo chemiosmosis and the system backs up

Fermentation

• converts NADH to NAD+ in absence of oxygen to produce ethanol

• flooding: some crops such as corn can tolerate temporarily flooded conditions due to highly active alcohol dehydrogenase (ADH)

  • this type of fermentation supplies just enough ATP for growth, but cannot remain in that state for long

• in wine and beer fermentation, yeast ferment glucose and excretes CO2 and ethanol

Storage Compounds

• starch: a carbohydrate glucose polymer that is stored in amyloplasts, water insoluble and digestible

• inulin: fructose polymer, stored. in vacuole, water soluble and indigestible

• sucrose: stored in some forms and give fruits more calories

• triglyceride: lipids, which are high energy and used for long-term storage

Structural Compounds

• phospholipids: cell membranes

• cutin, suberin and waxes: act as physical barriers from environment

• cell walls: composed of cellulose, hemicellulose and pectin

• lignin: tough secondary cell walls

Defense Compounds

• secondary metabolites such as fragrances or poisons

• Jasmonate: defends against herbivory

• Citronellate: defends against insects