Origin of land plants  

• All green algae and the land plants shared a common ancestor a little over 1 BYA. 

• Supported by DNA sequence data. 

• Not all photoautotrophs are plants (excludes red and brown algae) 

• Plants had many issues to overcome on land, including:  

• Water loss 

• Protection from harmful effects of the sun 

• Ability to effectively disseminate gametes for production  

• No soil on the land 488 Mya- rocks, beaches, ponds, oceans 

• No insects or other land animals  

• Fungi were probably present, along with bacteria 

• Fungi helps to makes nutrients and water available for plants 

Adaptions to terrestrial life 

• Moving water within plants 

• Bryophytes (mosses) are limited in size due to the lack of vasculature.  

• Tracheophytes have specialized vascular tissue for transport over long distances through plant body 

• Xylem: conducts water from roots 

• Phloem: transports sugars from leaves to other plants  

• Protection from desiccation and harmful effects of the sun:  

• Have a waxy cuticle and stoma  

• Shift to dominant diploid generation, meaning disastrous recessive mutations are masked 

• Haplodiplontic life cycle:  

• Multicellular haploid and diploid life stages  

• Also called the alternation of generations  

• All land plants are haplodiplontic.  

Halpodiplontic life cycle:  

• Multicellular haploid stage- gametophyte  

• Within gametangia gametes are produced by mitosis 

• Gametes from other plants fuse to form a diploid zygote  

• Zygote is the first cell of the sporophyte generation  

• Multicellular diploid stage- sporophyte 

• Within sporangia, diploid spore mother cells (sporocytes) undergo meiosis  

• Produces 4 haploid spores by meiosis  

• First cells of the gametophyte generation 

• Relative sizes of generations vary with phyla  

• Mosses 

• Large gametophyte 

• Small, dependent sporophyte  

• Angiosperm (flowering plants)   

• Small, dependent gametophyte  

• Large sporophyte  

• Evolutionary trend Is toward smaller haploid stage and dominant diploid stage  

• Diploid is better for eating with UV radiation caused mutations  

Bryophytes (mosses) 

• Closest living descendants of the first land plants  

• Called nontracheophytes because they lack tracheids.  

• Do have other conducting cells  

• Mycorrhizal associations important in enhancing water intake.  

• Symbiotic relationships between fungi and plants  

• Simple, but highly adapted to diverse terrestrial environments  

• Gametophytes- conspicuous and photosynthetic  

• Sporophytes- small and dependent  

• Require water for sexual reproduction 

• Flagellated sperm must swim in water 

• Gametophytes consist of small, leaf-like structures around stem-like axis  

• Not true leave-no vascular tissue  

• Anchored to substrate by rhizoids.  

• Multicellular gametangia form at the tips of gametophytes:  

• Archegonia- Female gametangia  

• Antheridia- Male gametangia 

Tracheophytes  

• Vascular tissues 

• Xylem 

• Phloem 

• Enable enhanced height and hormones throughout the plant  

• Develop in sporophyte (2n) but not gametophyte (n) 

• Gametophyte is reduced in size relative to the sporophyte 

• Cuticle and stomata found in all vascular plants  

• Roots  

• Provide transport and support 

• Lycophytes diverged before true roots appeared 

• Likely evolved twice 

• Leaves  

• Increased surface area for photosynthesis  

• Evolved twice  

• Euphylls found in ferns and seed plants 

• Lycophylls found in lycophytes  

Pterophytes:  

• Ferns and allies  

• True ferns  

• Horsetails  

• Whisk ferns  

• Conspicuous sporophyte and much smaller gametophytes are both photosynthetic  

• All form antheridia and archegonia on their gametophytes  

• All require free water for flagellated sperm.  

Fern morphology  

• Sporophytes have rhizomes  

• Modified stems that spread on ground 

• Fronds (leaves) develop at the tip of the rhizome as tightly rolled-up coils  

Seed plants  

• Seed plants are an important adaption  

• They maintain dormancy under unfavourable conditions  

• They protect the young plant when its most vulnerable  

• They provide food for the embryo until it can produce its own food 

• They facilitate dispersal of the embryo 

Conifers  

• Pines  

• Mores than 100 species, al of which are in the northern hemisphere  

• Produce tough needle like leaves in clusters  

• Leaves have thick cuticle and recessed stomata to retard water loss 

• Canals with resin deters insects and fungi 

Angiosperm abundance  

• The emergence of angiosperms changed the terrain of earth 

• Previously dominated by ferns, cycads, and conifers 

• Unique angiosperm features aided abundance  

• Flower production, insect pollination, broad leaves with thick veins 

Angiosperm evolution 

• It’s a mystery  

• As early as 145-208 MYA 

• Oldest known angiosperm is a Archaefructus (122-145 MYA)  

 Organization of the plant body: an overview  

• A vascular plant consists of:  

• Root system  

• Anchors the plant 

• Used to absorb water and ions from the soil  

• Shoot system  

• Consists of supporting stems, photosynthetic leaves, and productive flowers  

• Repetitive units consist of internode, node, leaf, and axillary bud  

Plant cell types  

• We distinguish plant cell types based on: 

• Size of vacuoles  

• Living or not at maturity  

• Thickness of secretions found in their cellulose cell walls  

• Some cells have only a primary cell wall of cellulose, synthesized at the protoplast 

• Some cells have more heavily reinforced walls with multiple layers of cellulose and or lignin.  

Meristem cell division  

• Meristems are located at the tips of the stems and roots 

• Extensions of shoot and root produced by apical meristems  

• Lateral meristems produce an increase in shoot and root diameter  

• Differentiated cells do not divide further 

Plant meristems  

• Meristems produce hormones that repress the development of lateral bud 

• When the meristem is removed the plant with not be able to grow from that tip. 

• Lateral buds will now be released from the repression.  

Lateral meristems  

• Found in plants that exhibit secondary growth  

• Give rise to secondary tissues which are collectively called the secondary plant body  

Plant tissues  

• Three main types:  

• Dermal  

• On external surfaces that serves a protective function  

• Ground  

• Forms several different internal tissue types and can participate in photosynthesis, serve a storage function, or provide structural support  

• Vascular  

• Conducts water and nutrients  

Dermal Tissue 

• Forms the epidermis  

• One cell layer thick in most plants  

• Forms the outer protective covering of the plant  

• Covered with a fatty cut in layer constituting the cuticle  

• Mostly epidermal cells  

• Also special cells, including guard cells, trichomes, and root hairs  

Dermal tissue:  

Trichomes: 

• Cellular or multicellular hair-like outgrowths of the epidermis  

• Keep leaf surfaces cool and reduce evaporation by covering stomatal openings  

• Some are glandular, secreting substances that deter herbivory by glueing insects to the surface of the plant  

Root hairs:  

• Tubular extensions of individual epidermal cells  

• Greatly increase the roots surface area and efficiency of absorption  

• Should not be confused with lateral roots 

Ground tissue  

3 cell types:  

1. Parenchyma  

• Function In storage, photosynthesis, and secretion  

2. Collenchyma  

• Provide support and protection.  

3. Sclerenchyma  

• Provide support and protection  

Parenchyma Cells  

• Most common type of plant cell 

• Living protoplasts  

• Function in storage, photosynthesis, and secretion  

• Most have only primary cell walls  

• Less specialized than other plant cells  

Collenchyma cells  

• Provide flexible support for plant organs  

• Allow bending without breaking  

• Living protoplasts 

• Lack secondary cell walls  

Sclerenchyma cells  

• Tough thick walls  

• Usually lack living protoplasts at maturity  

• Secondary cell walls often contain lignin 

• Two general types; 

• Fibers  

• Sclereids 

 Sclereids- vary in shape, branched, occur singly or in groups; strengthens tissue  

Vascular tissue  

Xylem: conducts water/ dissolved minerals, supports plant body, bundles include fibers and parenchyma cells.  

2 types of water conducting cells: 

1. Vessels; continuous tubes of dead cylindrical cells arranged end to end, very efficient, not present in gymnosperm, shorter and wider than tracheids  

2. Tracheids; dead cells that taper at the end and overlap one another  

Phloem: conducts a solution of carbohydrates (sucrose), transports hormones, amino acids, and other substances necessary for growth 

• Principal food conducting tissue in vascular plants  

• Sieve tube members  

• Living cells that contain clusters of pores called sieve areas or sieve plates  

• Alive buy without nucleus  

• Associated with companion cells to help with metabolic function  

• Gymnosperms have sieve cells  

• Not as efficient as sieve tube members  

• Sieve tube cells are separated by membranes  

• They require active transport to move sugars from cell to cell.  

Comparison:  

Tracheids: cells are joined at an angle; water passes from cell to cell through ‘pits’.  

Vessels: cells are joined butt-ended; water passes from cell to cell through perforated plates  

Roots: Anchoring and absorption structures  

Root structure  

• Simpler pattern of organization and development than stems  

• Four regions are commonly recognized: boundaries not clearly defined;  

1. Root cap 

3. Zone of cell division  

4. Zone of elongation 

5. Zone of maturation 

Roots  

• Most plants produce either… 

• Taproot system  

• Fibrous root system  

• Some pants however produce modified roots with specific functions  

• Some are adventitious roots that arise from any place other than the plants root.  

Stems: Support for above ground organs  

Shoot apex  

• Stems also undergo growth from cell division in apical and lateral meristems  

• Shot apical meristem initiates stem tissue and intermittently produces primordia 

• Develop into leaves, other shoots, and even flowers  

Stems:  

• Provide support for leaves  

• Leaves may be arranged in one of three ways  

• Phyllotaxy  

Stem vascular tissue  

• Major distinguishing feature between monocot and eudicot stems is the organization of the vascular tissue system  

• Monocot vascular bundles are usually scattered throughout ground tissue systems  

•  Eudicot vascular tissue is arranged in a ring with internal ground tissue and external ground tissue  

Leaves: Photosynthetic organs  

• Initiated as primordia by the apical meristems  

• Principal site of photosynthesis  

• Expand by cell enlargement and cell division  

• Determinate in structure- growth stops at maturity 

• Different patterns adaptive in different environments 

2 different morphological groups  

• Microphyll: leaf with one vein  

• Megaphylls: leaf with many veins (most plants) 

Eudicot leaves:  

• Most eudicot leaves have a flattened blade  

• Leaf flattening increases photosynthetic surface  

• Slender flattened stalk called petiole  

Stipules:  

• Leaves may have stipules  

• Outgrowths at base of petiole  

• May be leaf-forming or modified as spines  

Leaf veins:  

• Vascular bundles in leaves  

• Main veins are parallel in most monocot leaves  

• Veins of eudicot form an often-intricate network.  

Leaf morphology:  

• Simple leaves contain undivided blades  

• May have teeth indentations or lobes  

• Compound leaves have blades that are divided into leaflets  

March 6^th 

Lecture #3 

Transport in Plants  

Transport Mechanisms 

• Water and minerals first enter the roots—> then move to the xylem in the innermost vascular tissue—>water rises through the xylem —> most of that water exits through the stomata in the leaves  

Long distance movement  

• Local changes result in long distance movement of materials  

• Most of the force is ‘pulling’ caused by transpiration 

• Evaporation from thin films of water in the stomata  

Transport of water  

• Occurs due to: Cohesion (water molecules stick to each other) and Adhesion (water sticks to walls of tracheids or vessels)  

Movement of water at a cellular level 

• OSMOSIS  

Osmotic concentration  

• When two solutions have different concentrations  

• Hypertonic: higher solute concentration  

• Hypotonic: lower solute concentration  

• Isotonic: two solutions have the same concentration  

Osmosis and cellular changes  

• If a single plant cell is placed into pure water: 

• Water moves into cells by OSMOSIS  

• Cell expands and becomes turgid  

• If a cell is placed in a high concentration of sucrose:  

• Water leaves the cell 

• The cell shrinks (plasmolysis)  

Osmotic pressure  

• Force is needed to stop osmotic flow 

• A flaccid or plasmolyzed plant cell con not support its weight   

Water potential  

• Represents free energy of water  

• Especially useful for botany  

• Increase in solute concentration caused a decrease in water potential  

• Increase in turgor pressure causes an increase in water potential  

• Water potential is sued to predict which way water will move 

• Water moves freely via osmosis from an area of higher to lower water potential  

• Measured using the units MEGAPASCALS (Mpa) 

Water and Mineral Absorption  

• Most of the water absorbed by plants enters through the roots with root hairs 

• Once absorbed through the root hairs, water and minerals move across cell layers until they reach the vascular tissue 

• Water + dissolved ions enter the xylem and move throughout the plant 

Transport routes through cells  

• Three transport routes:  

1. Apoplast route – movement through cell walls and the space between cells; avoids membrane transport  

2. Symplast route – cytoplasm continuum between cells connected by plasmodesmata  

3. Transmembrane route – membrane transport between cells and across the membranes of vacuole within cells; permits the greatest control  

Inward movement of water  

• Water moves through the apoplast route through he ground tissue of the cortex 

• Water molecules reach the endodermis  

• Any further passage is blocked by the waterproof casparian strips  

• Molecules must pass through the cell membranes and protoplasts of the endodermal cells to reach the xylem. (Symplast or transmembrane routes)  

Movement of ions  

• Plasma membranes of endodermal cells contain a variety of protein transport channels  

•  Mineral concentration in the soil is much lower than it is in the plant  

• Active transport across endodermis is required for increased solute concentration in the stele  

• Symporters transport specific ions across even larger concentration gradients  

Regulation of water movement  

• Water potential regulates the movement of water through a plant  

• Water moves from the soil into the plant only If the water potential in the soil is greater than it is in the roots 

• Water in a plant moves along a water potential gradient from the soil to a more negative water potentials in the roots, stems, leaves, and atmosphere.  

Xylem transport  

• The aqueous solution that passes through the endodermal cells moves into the tracheids and the vessel elements of the xylem  

• As ions are pumped into the root or move via facilitated diffusion, their presence decreases the water potential, making a hypertonic environment.  

• Water then moves into the plant via osmosis, causing an increase in turgor pressure  

Root pressure  

• Caused by the accumulation of ions in the roots at times when transpiration from leaves is low or absent  

• At night 

• Causes water to move into plant and up the xylem despite the absence of transpiration.  

• Guttation: the loss of water from leaves when root pressure is high 

Cohesive water forces  

• Water has an inherent tensile strength that arises from the cohesion of its molecules  

• Tensile strength of a water column varies inversely with its diameter  

• Since tracheids and vessel are tiny in diameter, they have strong cohesive water forces  

• The long column of water is further stabilized by adhesive forces  

Effect of cavitation  

• Tensile strength depends on the continuity of the water column  

• A gas bubble can expand and block the tracheid or vessels (cavitation) 

Mineral transport  

• Tracheids and vessels are essential for the bulk transport of minerals  

• Minerals are relocated through the xylem from the roots to other metabolically active parts of the plant  

• Phosphorus, potassium, nitrogen, and sometimes iron may be abundant in xylem 

• Calcium can not be transported elsewhere once it has been deposited in a particular plant part  

Rate of transpiration  

• Over 90% of water taken by the plants roots is lost to the atmosphere  

• Photosynthesis requires carbon dioxide supply from the atmosphere  

• Closing the stomata can control water loss on a short term basis 

• Stomata must open to allow carbon dioxide entry  

Guard cells  

• Only epidermal cells containing chloroplasts  

• Have thicker cell walls on the inside and thinner cell walls elsewhere  

• Bulge and bow outward when they become turgid  

• This causes the stoma between two guard cells to open 

Stomatal opening  

• Turgor in guard cells result from the active uptake of potassium, chloride and malate  

• Addition of these solutes cause water potential to drop 

• Water enter osmotically and cells become turgid 

Stomatal opening and closing  

• Closed when carbon dioxide concentrations are high 

• Open when blue wavelengths of light promote uptake of potassium by the guard cells 

• Closed when temperature exceeds 34 degrees and water relations are unfavourable  

• CAM plants conserve water in dry environments by opening the stomata and taking in carbon dioxide at night. 

Water-stress response  

Plant adaptions to drought  

• Many morphological adaptions allow plants to limit water loss in drought conditions  

• Such as 

• Dormancy  

• Loss of leaves  

• Covering leaves with cuticle and wooly trichomes 

• Reducing the number of stomata 

• Having stomata in pits on the leaf surface  

Plant response to flooding  

• Flooding may lead to abnormal growth 

• Oxygen deprivation most significant problem 

• Plants have also adapted to life in fresh water  

• Form aerenchyma.  

Growth in saline soil 

• Halophytes are plants that can tolerate soils with high salt concentrations  

• Some produce high concentrations of organic molecules in their roots  

Phloem transport 

• Most carbohydrates produced in leaves are distributed through the phloem to the rest of the plant 

• This process is called translocation, which provides building blocks for actively growing regions of the plant  

Other phloem transports: 

• Hormones 

• MRNA 

• Sugars 

• Amino acids  

• Organic acids  

• Proteins 

• Ions 

Pressure flow hypothesis 

• Most widely accepted model describing the movement of carbohydrates in phloem  

• Dissolved carbohydrates flow from a source to a sink 

• Sources include photosynthetic tissues  

• Sinks include growing root and stem tips as well as developing fruit ‘ 

• Food storage tissue can be sources or sinks 

Lecture 3  

March 11^th 

Soil:  

• Highly weathered out layer of the earths crust  

• The earths crust includes about 92 naturally occurring elements  

• Full of microorganisms  

Mineral availability  

• Only minerals dissolved in water in spaces among soil particles are available for uptake by roots  

• Membrane potential maintained by the root, as well as the water potential difference inside and outside the root, affects root transport of minerals.  

Pores in soil 

• About half the soil volume is occupied by pores 

• May be filled with air or water 

• Some of this water is not available because it drains immediately due to gravity  

• However, Water that is held in small pores is readily available for plant 

Topsoil 

• Most roots are found in TOPSOIL 

• Mixture of mineral particles of varying sizes, living organisms, and humus  

• Sand, silt, and clay. 

• Soil composition determines the degree of water and nutrients binding to soil particles  

Topsoil loss 

• If topsoil is lost, soils water holding capacity and nutrient content is adversely affected 

• “Dust bowl” 

Prevention of erosion  

• Whenever the vegetative cover of soil is disrupted, such as plowing or harvesting, erosion by water and wind increases.  

• Measures to prevent erosion include: 

• Intercropping  

• Conservation tillage 

• No-till 

Prevention of fertilizer runoff 

• Overuse of fertilizers can cause significant water pollution and have negative effects; overgrowth of algae.  

Acid soils  

• The pH of a soil affects the release of minerals from weather rock 

• Can stunt he growth of plants if there is a low pH. 

• Most plants grow best at a slightly acidic pH.  

• Ex: Brazilian pampas  

Saline soils  

• Accumulation of salt alter water potential in soil 

• Leading to water loss and turgor in plants  

• Saline soil is most commonly found in dry areas where salts are introduced through irrigation.  

• Can occur when overwatering pulls salts from the lower soil levels to topsoil.  

Plant nutrients 

• Photosynthesis; CO2 into sugar  

• Also need: 

• Macronutrients (9) 

• Micronutrients (7) 

Mineral deficiencies in plants  

• Can cause differences in colour in plant leaves.  

Identifying nutritional requirements  

Hydroponics  

• soil provides nutrients and support but these functions can be replaced in hydroponic systems to maximize growth  

• Allows plants to be grown all year around  

Food security  

• Focuses on ways to increase a plants uptake and storage of minerals  

• Some plants have been genetically modified  

Special nutritional strategies  

• Plants need ammonia or nitrate to build amino acids  

• They lack the biochemical pathways necessary to convert nitrogen gas to NH3 

• Symbiotic relationships have evolved between plants and nitrogen fixing bacteria  

• Legumes form nodules that house the bacterium rhizobium 

• Rhizobium bacteria require oxygen and carbohydrates to support their energetically expensive lifestyle as nitrogen fixers  

• Formed in legumes mainly  

Mycorrhizae  

• Symbiotic associations with mycorrhizal fungi are found in about 90% of vascular plants  

• Expand surface area available for nutrient uptake  

• Enhances phosphate transfer to the plant  

Carnivorous plants  

• Often grow in acidic soils that lack nitrogen  

• Trap and digest small animals, primarily insects, to obtain adequate nitrogen supplies  

• Having modified leaves adapted for luring and trapping prey  

• Prey is digested with enzymes secreted from specialized glands 

• Ghost pipe   

Carbon-nitrogen balance  

• Increased CO2 levels may alter C—N ratio in plants  

Carbon dioxide and photosynthesis  

• Calvin cycle fixes CO2 into sugar 

• Ribulose 1,5-bisphosphate carboxylase  

• Rubisco can bind CO2 or 02  

Photorespiration 

• If CO2 levels are low then O2 may bind to rubisco  

• This causes photorespiration 

• Which results in neither nutrients or energy storage  

• Plants must keep O2 away from rubisco  

C3 Photosynthesis  

• Occurs in mesophyll cells    

• In C3 plants, as CO2 increases, the Calvin cycle becomes more efficient  

• But the C3 plants have less nitrogen and minerals per unit mass 

• Which results in lower nutritional value for herbivores  

• Meaning more plant must be eaten 

C4 photosynthesis 

• This photosynthesis uses an extra pathway to shuttle carbon deep within the leaf 

• This reduces photorespiration  

Free air CO2 enrichment studies  

• FACE  

• Rings of towers that release CO2 toward the center of the ring 

• Allow studies to be conducted at the ecosystem level 

Increasing CO2 levels  

• As CO2 levels rise, less nitrogen and other macronutrients are found in leaves 

• Herbivores must eat more to obtain the optimal amount of nutrients  

Phytoremediation  

• Use of plants to concentrate or breakdown pollutants  

• Phytodegradation- contaminant is taken up from soil and broken down  

• Phytovolatilization- contaminant is taken up from soil and released through the stomata  

• Phytoaccumulation-  contaminant is taken up from soil and concentrated in shoots  

Mechanisms of phytoremediation  

• Trichloroethylene  

• Maybe be removed from the soil by poplar trees  

• Degraded into CO2 and chlorine  

• A fraction moves rapidly through the xylem and is released through stomata  

• Phytoaccumulation  

4^th lecture 

March 13^th 

Plant defence 

Physical defences: 

• Many abiotic factors threaten plants  such as fires and weathers  

• Plants do not have much defence against fire, except some advantages of the new ground after the fire  

Plant Pests:  

• Other threats such as pathogenic viruses, bacteria, fungi, animals, and other plants  

• Can tap into nutrient resources of plants 

• Viruses use DNA replicating mechanisms to self replicate 

• Kill plants immediately, leading to necrosis  

Invasive species  

• Big problem with nonnative invasive species, such as emerald ash borer.  

Dermal tissue system 

• First line of defence  

• Epidermal cells throughout the plant secrete wax to protect plant surfaces from water loss and attack 

• Above ground parts also covered with cutin. 

• Suberin is found in cell walls of subterranean plant organs  

• Silica inclusions, trichomes, bark, and even thorns can also offer protection 

Invaders and dermal defences 

• Physical damage to the dermal surface can create an entry site for pathogens   

• Parasitic nematodes use their sharp mouth parts to get through the plant cell walls, some form tumors 

• Wounding may make it easier for pathogens to infect the plant 

Fungal invasion 

• Fungi seek out the weak spot in the dermal system, or stomata, to enter the plant 

• Phases of fungal invasion include: 

1. Windblown spore lands on leaves  

2. Spore germinates and forms adhesion pad 

3. Hyphae grow through cell walls and press against cell membrane 

4. Hyphae differentiate into haustoria  

Chemical defences  

• Many plants employ toxins that kill herbivores or deter their grazing behaviour  

• Some are unique to plants  

• Others called defensins are found in plants and animals  

Secondary metabolites  

• Metabolic pathways needed to sustain life are modified to produce chemicals that adversely affect herbivores  

• Alkaloids  

• Caffeine, nicotine, cocaine, morphine 

• Tannins  

• Bind to and inactivate proteins 

• Plant oils  

• Repel insects with strong odors, particularly those found in the mint family 

• Avoid these metallics by eating a varied diet 

Allelopathic plants  

• Plants also secret chemicals to block seed germination or inhibit growth of nearby plants  

• This strategy minimizes competition for resources 

• Very little vegetation grows under black walnut trees due to allelopathy  

Poison: Ricin 

• An alkaloid produced by the castor bean plant  

• Single seed can kill a small child if ingested 

• May protect plants from aphids  

• In the endosperm of a seed, it is found as a nontoxic dimer composed of ricin A and B joined by a single disulphide bond 

• When this bond is broken by an animals digestive enzymes, ricin A binds to ribosomes, cleaving an adenine and changing the structure of rRNA 

• A single ricin A molecule can inactivate 1500 ribosomes per minutes, blocking out translation of proteins  

Animals that protect plants   

• Ants protect their acacia tree 

• Small armies of ants protect the tree from harmful herbivores  

• Done by attacking a katydid that would otherwise feed on the leaves of the acacia that shelter them 

• Ants attack small shrubs that grow too close to the tree 

Parasitoid wasps, caterpillars, and leaves  

• As a caterpillar chew on a leave a wound response leads a release of volatile compound  

• Female parasitoid wasp is attracted  

• Lays egg in caterpillar 

• Eggs hatch and larvae kill caterpillar 

Plant sensory systems  

Response to light  

• Pigments are molecules that are capable of absorbing light energy  

• Some used for photosynthesis 

• Other detect light and mediate the plants response to it 

• Photomorphogenesis 

• Nondirectional, light triggered development 

• Phototropism  

• Directional growth response to light 

• Both compensate for inability to move 

Photomorphogenesis: Phytochrome  

• The pigment containing protein phytochrome is present in all groups of plants  

• Phytochrome exists in 2 interconvertible forms  

• Phytochrome’s are involved in many signalling pathways that lead to gene expression  

• Pr Is found in the cytoplasm 

• When out is converted to Pfr it enter the nucleus  

• When in the nucleus the Pfr binds with other proteins that form a transcription complex leading to the expression of light regulated genes  

• Seed germination  

• Shoot elongation  

• Detection of plant crowding  

Phototropism  

• Tropisms are directional growth responses  

• Phototropism’s contribute to the variety of forms we see within a species as shoots grow towards light  

• Many plants bend toward blue light  

Blue light receptors  

• Blue light receptor phototropin 1  

• Blue light stimulates PHOT1 to autophosphorylate 

• Regulates the flux of auxin in shoots  

• Auxin is expressed onside of shoot not exposed to light 

• Elongation on one side of a shoot can lead to bending towards the light 

Response to gravity 

Gravitropism  

• Response of a plant to the gravitational field of the earth  

• Shoots exhibit negative gravitropism  

• Roots have a positive gravitropic response  

Response to gravity 

• 4 general steps lead to gravitropic response:  

1. Gravity is perceived by the cell; falling amyloplasts  

2. A mechanical signal is transduced into a physiological signal; amyloplasts touch ER membranes  

3. Physiological signal is transduced inside the cell and to other cells  

4. Differential cell elongation occurs in the “up” and “down” sides of root and shoot 

Amyloplasts  

• Starch storing organelles  

• Modified chloroplasts, have no chlorophyll 

Root response to gravity 

• In roots, the cap is the site of gravity perception  

• Signalling triggers differential cell elongation and division in the elongation zone 

Hormones and sensory systems  

Auxin: a plant hormone  

Darwins experiment: 

• In conclusion: in response to light, an influence that caused bending was transmitted from the tip of the seedling to the area below, where bending normally occurs  

Auxin promotes cell growth 

• Auxin accumulated on the side of a seedling away from light  

• Auxin promoted these cells to grow faster than those on the lighted side  

• Cell elongation causes the plant to bend towards the light  

Auxin 

• Indoleacetic acid is the most common natural auxin 

• Probably synthesized from tryptophan  

• The synthetic auxin   

Plant reproduction 

Life cycle of an Angiosperm  

• Angiosperm represent an evolutionary innovation with their production of flowers and fruits. 

• Plants go through developmental changes leading to reproductive maturity by adding structures to existing ones within meristems. 

Making flowers  

Flower production  

• Four genetically regulated pathways to flowering have been identified 

1. The light dependent pathway 

2. The temperature dependent pathway 

3. The gibberellin dependent pathway  

4. The autonomous pathway  

• Plants rely primarily on one pathway, but all four pathways can present. 

Light dependent pathway  

• The photoperiodic pathway 

• Keyed to changes in the proportion of light to dark in the daily 24-hr cycle. 

Day length affects flowering  

• Long day plants flower when daylight becomes longer than a critical  

• Short day plants flower when daylight becomes shorter than a critical length  

• Day neutral plants flower when mature regardless of day length 

Darkness is the real flowering signal  

• The duration of uninterrupted darkness determines when flowering will occur  

• If the long nighttime is interrupted with a short flash of light, plants behave as a “long day” 

Manipulation of photoperiod  

• Using light as a cue allows plants to flower when abiotic conditions are optimal  

• Manipulation of photoperiod in greenhouses ensures that short day poinsettias flower in time for the winter.  

Phytochrome and cryptochrome 

• Change in phytochrome or cryptochrome light receptor molecule triggers a cascade of events that lead to the production of a flower.  

• Phytochrome= red light sensitive  

• Cryptochrome= blue light sensitive   

• Arabidopsis uses gene CONSTANS (CO) which turns on the genes that are needed for flowering  

• Leads to expression of LFY 

• Phytochrome regulates the transcription of CO 

CONSTANS  

• CO protein is produced day and night 

• Levels of CO are maintained by the circadian clock  

• Levels of CO mRNA are lower at night because of targeted protein degradation by ubiquintin  

• Phytochrome causes an increase in transcription at daybreak 

• Cryptochrome prevents degradation by the ubiquintin dependent pathway during the day 

Temperature dependent pathway 

• Some plants require a period of chilling before flowering (vernalization)  

• Winter wheat  

• Seeds were chilled and then planted in the spring ‘ 

Gibberellin dependent pathway 

• Gibberellin is a plant hormone  

• Decreased levels of this hormone have shown to delay flowering in some species  

• Has been shown to bind to the promoter of the LFY gene, which supports a model where gibberellin induces an increase in LFY gene expression 

• This would directly affect flowering 

Autonomous pathway  

• Does not depend on external cues except for basic nutrition  

• Delays flowering 

• Balance between floral promoting and inhibiting signals may regulate when flowering occurs  

Flowering pathways  

• The four flowering pathways lead to an adult meristem becoming a floral meristem  

• They either activate or repress the inhibition of floral meristem identity genes  

• LFY and AP1 

• Turn on organ identity genes  

• Define four concentric whorls: sepals, petals, stamens, and carpels  

Structure and evolution of flowers  

Flower morphology: four whorls 

• Calyx= consists of flattened sepals  

• Corolla= consists of petals  

• Androecium= collective term for all the stamens of a flower  

• Consists of filament and a anther  

• Gynoecium= collective term for all carpels of a flower 

• Consist of ovary, style, and stigma  

Trends in floral specialization  

• 2 major trends  

1. Floral parts have grouped together  

2. Floral parts lost or reduced  

• Modification often relate to pollination mechanisms  

• Primitive flowers are radially symmetrical  

• Advanced flowers are bilaterally symmetrical  

Embryo development  

Double fertilization  

• The growing pollen tube enters angiosperm embryo sac and releases two sperm cells  

• One sperm fertilizes the central cell with its polar nuclei and initiates endosperm development  

• Other sperm fertilizes the egg to produce a zygote  

Embryo development  

• First zygote division is asymmetrical, resulting in cells with two different fates  

• The root-shoot axis also forms at this time  

• First cells division gives rise to a single row of cells, cells soon begin dividing in different directions, producing a solid call of cells  

• Primary meristems differentiate while the plant embryo is still at the globular stage 

Formation of tissue systems  

• Apical meristems establish the root-shoot axis in the globular stage, from which the three basic tissue systems arise  

• Outer protoderm develops into dermal tissue that protects the plant  

• Ground meristem develops into ground tissue that stores food and water  

• Inner procambium develops into vascular tissue that transports water and nutrients  

Embryo development  

• The globular stage gives rise to heart shaped embryo with bulges called cotyledons  

• These bulges are produced by embryonic cells, and not by the shoot apical meristems  

• Three basic tissues are now developed 

• These tissues are organized in three dimensions radically around the root shoot axis  

• Early embryonic development, most cells can give rise to a wide range of cell and organ types, including leaves  

• After germination, apical meristems continue adding cells to the growing root and shoot tips  

Critical developmental events  

• During embryogenesis, angiosperm undergo three critical events  

1. Development of food supply; endosperm 

2. Development of seed coat; differentiation of ovule tissue  

3. Development of fruit surrounding seed; developed from carpel wall surrounding ovule  

Endosperm variation  

• In corn: solid  

• In peas and beans; used up during embryogenesis 

Seeds  

• In many angiosperm, development of the embryo is arrested soon after meristems and cotyledons differentiate  

• Integumentary develop into a relatively impermeable seed coat 

• Encloses the seed with its dormant embryo and stored food  

Fruits  

• Most simply defined as mature ovaries  

• During seed formation the flower ovary begins to develop into fruit 

• It is possible to for fruits to develop with seed development 

Germination  

• Germination: the emergence of the radicle through the seed coat  

• Germination requires signals: light, warmth, time  

• The main trigger of germination is water imbibition  

• Oxygen must reach the embryo  

• Germination and early seeding growth require utilization of metabolic reserves stored as starch in amyloplasts and protein bodies  

• The events in the seed at germination are regulated by hormones especially gibberellic acid  

• In kernels of cereal grains, the single cotyledon is modified into scutellum  

March 25^th  

Behavioural biology  

Why do animals do what they do?  

• Proximate causation  

• Mechanisms that are the reason for behaviour 

• Increased levels of hormone 

• Neural connections  

• Ultimate or evolutionary causation  

How do we study behaviour?  

1. Physiology 

2. Ontogeny  

3. Phylogeny  

4. Adaptive significance  

Ethology: study of the natural history of behaviour 

• Emphasis on innate behaviour  

• Instinctive, does not require learning  

• Preset paths in nervous system  

• Genetic- fixed action pattern  

• Goose replacing an egg from her nest  

Innate behaviour  

• Egg retrieval behaviour is triggering by a key or sign stimulus  

• Innate release mechanism:  

• Perception of key stimulus plus triggering of motor program  

• Once patterns begins, it goes to completion; even if the egg is removed  

Nerve cells, neurotransmitter, hormones, and behaviour 

• Behaviours that occur rapidly are controlled by simple neural mechanisms that involve just a few neurons.  

• Hormones influence some behaviours 

• Reproduction 

• Parental care 

• Aggression 

• Stress 

• Testosterone: regulates territorial behaviour and courtship 

• Estrogen: regulates mating behaviour  

• Glucocorticoid: stress hormone  

• Neurotransmitters also influence some behaviours  

• Serotonin 

• Dopamine  

• fMRI: used to measure neuron activity  

• Nucleus accumbens: reward and pleasure  

Behavioural genetics  

• Nature  

• Genetics  

• Nurture  

• Social environment  

• Vasopressin and Oxytocin are released during mating  

• Neuropeptides that control many aspects of behaviour including reward and pleasure  

• Vasopressin: regulates body retention of water 

• Oxytocin: stimulates birth contractions  

Learning habituation 

• Habituation: decrease in response to a repeated stimulus  

• No positive or negative consequences  

• Animal learns to not respond  

Associative learning, or conditioning  

• Association between two stimuli or between a stimulus and a response  

• Behaviour is conditioned through association  

• ‘Differ in the way association are established  

• TWO major types:  

• Classical conditioning: stimulus and behaviour  

• Operant conditioning: behaviour and response  

Operant conditioning 

• Trial and error  

• Animals learn to associate its behavior response with a reward or punishment  

• Operant is the action or behaviour  

• Operator is the animal 

• Paired presentation of two different kinds of stimuli causes the animal to form an association between the stimuli 

• Ex: toads learn not to eat a bumblebee  

Instincts  

• Instinct govern learning preparedness  

• Instinct guides learning by determining what type of information can be learned  

• Animals may have innate predispositions toward forming certain associations and not others  

• Learning Is only possible within the boundaries set by evolution  

Development of behaviour  

• Imprinting  

• Form social attachment to other individuals or develop preferences that influence behaviour later in life.  

• Filial imprinting- attachment between parents and offspring  

• Interaction between parents and offspring are key to the normal development of social behaviour  

Quiz questions:  

Q: Frequency of a particular allele within a population can be changed over generations by which factor or process?  

A: Selection  

Q: for natural selection to occur within a population certain conditions must be met  

A: reproduction, heredity, variation in characteristics, variation in fitness of organisms.  

Q: Which agent of evolutionary change is the ultimate source of genetic variation? 

A: Mutation  

Q: A bird's wing and a bats wing are examples of what kind of structures? 

A: Analogous structures 

Q: Which is not an example of prezygotic isolation? 

A: Hybrid inviability 

Q: Which concept states that a species is a group of organisms that are reproductively isolated from other such groups? 

A: Biological species concept  

Q: which type of speciation results from geographic isolation?  

A: Allopatric speciation  

Q: situation where a new species is produced by interbreeding two members of a distinct species. 

A: sympathies allopolyploidy  

Q: Which factors contribute to adaptive radiation? 

A: New environment with few species, Abundant resources  

Q: the science of classifying things? 

A: Taxonomy 

Q: group of organisms that consists of the most recent common ancestor and all of its descendants?  

A: Monophyletic group