Exam 2 Leaves, Fruits, and Flowers

CHAPTER 3.4 LEAVES, 2.6.3.1 FLOWERS AND FRUITS 2.7.3, AND PHOTOSYNTHESIS 4.1

Chapter 3.4 Leaves

Origin and Development of Leaves

• First leaves arise from the plumule portion of the embryo

• Other leaves originate as primordia in the apical bud area

Leaf and axillary buds originate from the apical meristem region

Parts of a typical leaf: Leaf lamina or blade and leaf veins

• Lamina: flattened blade

• Leaf veins: vascular bundles that collect water

Leaf arrangement and types

• Phyllotaxy: arrangement of leaves on a stem

  • Alternate

  • Opposite

  • Whorled

• Simple- single blade

• Compound leaves- blade is divided into leaflets

  • Pinnately compound

  • Palmately compound

  • Trifoliate leaves

• Leaf venation:

  • Netted or reticulate (common in dicot)

  • Parallel (grass)

  • Dichotomous (in ginkgo)

Leaf anatomy

• Stalk= petiole

• Stipules= leaflike on either side of petiole

• Sessile if lacking petiole (most monocots)

• Epidermis: upper and lower, epidermal cells, cuticle, stomata, and trichomes

• Stomata: a tiny pore bordered by two guard cells

• Veins: xylem, phloem, and bundle sheath

• Mesophyll: most photosynthesis here, chlorenchyma palisade mesophyll and spongy mesophyll

The internal structure of leaves: learn to differentiate between dicot and monocot leaf anatomy

• Monocot leaves:

  • Do not have mesophyll differentiated into palisade and spongy, only spongy

  • Bulliform cells- cause leaves to roll or fold, reducing transpiration

  • Kranz anatomy

  • Bundle sheath contains large, active chloroplasts in some monocots

Leaf adaptations

• Mesophytes (Buttercup)

• Xerophytes (Oleander)

  • Thick, leathery leaves

  • Multiple epidermis

  • Fewer stomata or sunken

  • Succulent, water-retaining leaves, or no leaves

  • Dense, hairy coverings

• Hydrophytes (Water lily)

  • Less xylem and phloem

  • Large air spaces

  • No differentiation of mesophyll

Leaf modifications

• Storage leaves: onion, fleshy layers, leafy vegetables

• Succulent leaves: cactus, store water

• Tendrils: pea plant, garden peas

• Spines: used to be leaflet, leaf blade, firethorn

• Floral leaves: Bracts, bougainvillea, helps pollination appear like flower

• Plantlets: kalanchoe

• Carnivorous plants: leaves modified to trap insects

  • Venus flytrap

  • Pitcher plant

  • Sundew

Leaf color change and abscission

• Chlorophylls- greens

• Carotenoids- yellows (orange)

• Water soluable anthocyanins (red or blue) and betacyanins (red) may also be present in the vacuole

• Abscission:

  • Not in photosynthesis

  • Separation of the leaves from the plant

  • Abscise at the base of the petiole, called abscission zone

  • Auxin and ethylene influence

  • Protective layer protects “infection”

  • Some leaf margins made of silica

Human relevance of leaves 

• Duckweed: smallest flowering leaf

• Giant water lily: largest

• Food- cabbage, celery, spices/herbs

• Dyes- henna

• Fuel- yareta plant (carrot family)

• Oil- eucalyptus

• Perfumes- orange, lavender

• Ropes and twine- agave, abaca (tea bags) manila

• Drugs- narcotics, medicines, hemp

• Mosquito repellents- citronella oil, neem

• Beverages- tea, tequila

• Waxes- carnauba

• Alfalfa leaf curd- yogurt

• Aesthetics- floral arrangements, gardens, landscape

Chapter 2.6.3.1 Flowers

Structure of flowers and all associated terminology

• Begin as an embryonic primordium that develops into a bud

• Occur in specialized branches at tips of peduncles

• Branchlets of pedicels (stalk or single flower)

• Whorls: sepals, petals, stamens, pistils

Peduncle (or pedicel), receptacle

Sepals - Outermost whorl

Collectively referred to as calyx

• Protects flower while in the bud

Petals - Next whorl inside sepals

Collectively referred to as Corolla

• Showy corollas attract pollinators

• Inconspicuous or missing corollas in many trees, weeds, grasses and wind-pollinated plants

Calyx and corolla form perianth (both in dicots and monocots)

• non essential parts

Androecium

• Stamens

• Each stamen consists of a filament with an anther at the top

• Pollen grains developed in anthers

Gynoecium

• Carpels

• Each carpel consists of a stigma, style, and ovary

• One or more carpels make up a pistil

• Simple ovary (beans)

• Compound ovary multiple carpels, okra

Flower diversity

• Solitary flower

  • Single and arises at the tip of stem or branch

  • Stalk is the peduncle

• Inflorescence

  • Peduncle is stalk to multiple flowers or florets

  • Pedicel is the stalk of the floret

  • Raceme- based continues growth, oldest at the bottom

  • Cyme based- stop growing oldest at top

• Bracts are present in both solitary and in inflorescence (leafs are closer to flower)

Hypogynous, epigynous and perigynous flowers.

Learn all related terminology regarding ovary position.

• Superior ovary (flower hypogynous) ORANGE

• Inferior ovary (flower epigynous) BLUEBERRY

• Semi-inferior (flower perigynous) ROSEHIPS and Hypanthium

Complete and Incomplete flower

• Complete: all 4 whorls

• Incomplete: 1 or more whorls missing

Perfect and imperfect flowers

• Perfect: bisexual both stamen and carpal

• Imperfect: unisexual either stamen or carpal

Flower symmetry

• Actinomorphic (radially symmetrical) regular

• Zygomorphic (bilaterally symmetrical) irregular

Chapter 2.7.3 Frutis and Dispersal

Changes in a fertilized flower and fruit formation.

• Ovary= fruit

• Ovule= seed

• Ovary wall= fruit wall

• Stamens, petals, and styles fall off

• Parthenocarpic fruits- fruits without visible seeds (pineapple)

Learn all types of fruits: derived from one flower, many flowers, one ovary or many pistils, etc.

• Simple fruits

  • Develop from a flower with one ovary (simple or compound)

  • Beans/tomato

• Aggregate fruits

  • Develop from a flower with several ovaries

  • Strawberry, blueberry

• Multiple fruits

  • Develop from an inflorescence

  • Figs, pineapple

Parts of a typical fruit.

• Pericarp

  • Exocarp- skin

  • Endocarp- inner boundary around seeds

  • Mesocarp- tissue between exocarp and endocarp

• Seeds

Fruit diversity: Fleshy and dry

• Fleshy- the pericarp fleshy at maturity

  • Tomato

• Dry- pericarp is dry at maturity

  • Nuts

Learn the fruit types and relevant examples.

• Simple fleshy fruits develop from a flower with a single pistil

• Berry- with thin skin and relatively soft pericarp

  • Tomatoes, grapes, peppers, blueberries, bananas

• Drupe- A single seed enclosed by a hard, stony endocarp (pit)

  • Peach, olive

• Pepo- Relatively thick exocarp, numerous seeds

  • Pumpkins, melons

• Hesperidium- leathery exocarp containing oils

  • Citrus

• Pome- Flesh comes from the receptacle that grows up around the ovary

  • Apples, pears

Dehiscent and Indehiscent dry fruits.

• Dehiscent- split at maturity

  • Legume, milkweed, iris

  • Follicle- splits along one seed (milkweed)

  • Legume- splits along two sides

  • Siliques- split along two sides, but seeds on the central partition (mustard family: broccoli, cabbage)

  • Capsules- Split in variety of ways (irises, poppies, okra)

• Indehiscent- do not split at maturity

  • Corn, acorn, dandelion

  • Achene- base of seed (attached to the pericarp) buckwheat

  • Nut- single seed inside a harder and thicker pericarp (acorn)

  • Grain (caryopsis)- pericarp tightly united with seed (Corn)

  • Samara- pericarp extends as wings for dispersal (elms)

  • Schizocarp- twin fruit that breaks into one-seeded segments called mericarps- ex. carrots

Aggregate fruits

• Derived from a single flower with many ovaries

• Clustered units on a single receptacle

• Raspberries, blackberries, strawberries

Multiple fruits

• Derived from a single inflorescence

• Mulberries, Osage orange, pineapples, figs

Seed dispersal:

wind (entire dry fruit or seeds only), animals, ants (elaiosomes)

• Water

• Ballistic

Dormancy and Scarification.

• Some seeds require a period of dormancy (reduced physiological activity can’t germinate)

• Vivipary- when seeds germinate while still attached to the parent plant

Imbibition & Germination.

• Imbibition- absorption of water by seed (enzymes are activated)

• Scarification- artificially breaking the dormancy

Photosynthesis Chapter 4.1

Key metabolic pathways in plants.

• Photosynthesis – Captures solar energy and convert it into carbohydrates by combining carbon dioxide and water

• Anabolism - Forming chemical bonds to build molecules

• Catabolism - Breaking chemical bonds

• Cellular respiration - Releases energy held in chemical bonds by breaking down carbohydrates, producing carbon dioxide and water

Discovery of Photosynthesis

• 17th century Jan Baptist van Helmont

  • Rejected the idea that plants take most of their biomass in through soil, instead through water

  • Used willow trees

• Joseph Priestley ran experiments in 1772 using a mouse and a candle sealed in a jar, plant revived air for mouse

The photosynthetic process

• Requires:

  • Water, solar light, CO2, photosynthetic pigments

• Products:

  • Water

  • Oxygen

  • Sugars and other primary metabolites (carbohydrates, proteins, lipids)

  • Secondary metabolites (alkaloids (caffeine), essential oils CITRUS)

Summary equation of photosynthesis

• CO2 + H2O + light → C6H12O6 + O2 + H2O

• IN PLASMID

Understanding pigments

• Carotenoids (yellow and orange) absorb excess energy

• Phycobilins (blue or red in cyanobacteria and red algae)

• 250-400 pigment molecules = photosynthetic unit

• Chlorophyll a: blue-green color

• Chlorophyll b: yellow-green

• B transfers energy from light to chlorophyll A

Absorption of light

• Plants only use visible light

• Shortest: violet

• Longest: red

• 40 percent of radiant energy is from visible light

• Wavelengths 400-700 nm

• If light intensity is too high:

  • Photooxidation occurs, which destroys chlorophyll

• If water is in short supply or light intensity is too high:

  • Stomata close and thus reduce the supply of carbon dioxide available for photosynthesis

• If light and temperatures are too high:

  • The ratio of carbon dioxide to oxygen inside the leaves may change

  • Accelerates photorespiration which uses oxygen and releases carbon dioxide

Steps of photosynthesis

• Light-dependent reactions by Robin Hill

• Light-independent reactions Calvin Cycle “Dark”

• Both processes may occur simultaneously

Light dependent

• Thylakoid (packets of light) membranes of chloroplasts: light energy strikes chlorophyll molecules

• Water molecules split apart, releasing electrons and hydrogen ions, oxygen gas is released

• Photolysis (split light)

• Electrons pass along the electron transport system

• Products derived from light-dependent reactions are used in light-independent reactions

Light independent reactions

• Within stroma of chloroplasts

• ATP and NADPH, electrons (products of light-dependent) and carbon dioxide form a 3-carbon compound, PGA PhophoGlyceric Acid

• RuBP- ribulose 1,5-biphosphate

• Rubisco- an enzyme

C4 and CAM pathways

• C4 plants:

  • Tropical grasses and plants of arid regions (hot and tropical)

  • Sugarcane, corn

  • Kranz anatomy

  • Mesophyll cells with smaller chloroplasts with well-developed grana

  • Produces 4-carbon compound (oxaloacetic acid)

  • Bundle sheath cell with large chloroplasts with numerous starch grains

  • Organic acids accumulate at night (STOMATA OPEN)

• CAM plants:

  • Cacti, bromeliads, orchids

  • Crassulacean Acid Metabolism

  • C4 pathway at night, Calvin Cycle in day

  • Function under limited water supply, high light

Products from secondary metabolic pathway

• Codeine, nicotine, lignin, Salicin, Camphor, Menthol, and Rubber

Assimilation and Digestion

• Assimilation: Conversion of organic matter produced in photosynthesis to build protoplasm and cell walls

• Sugars are transformed into lipids, proteins, and other carbohydrates such as sucrose, starch, cellulose

• Digestion: Conversion of starch and other insoluble carbohydrates to soluble forms

• Always hydrolysis process

ROLES OF:

RuBp- acts as the primary carbon dioxide acceptor in plants

RuBisCO- Fixes carbon dioxide into organic compounds

PGA- first stable compound formed during carbon fixation

GA3P- primary end product of photosynthesis Calvin cycle (crucial three carbon sugar)