Plants and Society

EARLY LIFE ON EARTH, AND THE ORIGIN OF LAND PLANTS

When did life first appear on Earth?

• 3.6 billion years ago 

  • The first life → simple cells (prokaryotes)

 When did eukaryotic cells first appear, and how? 

• 2.2 billion years ago 

  • In the theory of symbiogenesis, a merger of an archaean and an aerobic bacterium created the eukaryotes, with aerobic mitochondria 

When did Oxygen-producing photosynthesis first evolve, and in what organisms? How did our atmosphere change after that? 

• 3.4 billion years ago → photosynthesis occurs in cyanobacteria 

  • Oxygen enters the atmosphere as a waste product 

  • Ozone layer formed; as ionizing radiation so terrestrial organisms don’t get fried (protects organisms from sun)

• 2.4 billion years ago → Great oxidation effect → significant rise in oxygen levels

• Second merger 1.6 billion years ago adding chloroplasts 

• Origin of photosynthesis in eukaryotes was around 1.2 billion years ago

Where did chloroplasts come from (i.e., what is their evolutionary history), and what is the evidence for an endosymbiotic origin?

• A second merger, 1.6 billion years ago, added chloroplasts, creating the green plants 

• Primary endosymbiosis → heterotrophic eukaryote engulfed cyanobacterium (prokaryote) 

• Evidence: 

  • Structure of organelles 

    • 2 membranes (bacterial and host)

    • Antibiotics can block protein synthesis 

    • Binary fission 

  • Chloroplast DNA, rRNA, and ribosomes resemble cyanobacterial DNA

    • Circular organization 

    • No histones 

  • DNA sequence based phylogeny 

How did multicellular algae make the transition to life on land (i.e., what kinds of features had to evolve?) 

• Adaptations for life on land:

  • Fungal associations 

    • Plants moved onto land about 500 mya, accompanied by fungal partners to help absorb water and nutrients 

  • Regional specialization 

    • On land, resources are spatially segregated

      • Soil provides water and minerals to ROOTS, photosynthesis takes place in aerial SHOOT system  

  • Transport 

    • Vascular system → movement of water and minerals from roots to rest of plant (in xylem); of sugars from leaves to rest of plant (in phloem) 

  • Water conservation

    • Waxy cuticle prevents water loss 

  • Gas exchange 

    • Stomata allows for gas exchange 

  • Support 

    • Support in herbaceous tissue provided by turgor pressure

    • In woody tissues, lignin (a hard material embedded in cellulose matrix of plant cell walls) provides support 

  • Reproduction and dispersal 

    • Reproductive structures protected from desiccation (moisture removal): gametes produced in gametangia (protective structure that produces and houses gametes); retention of the embryonic sporophyte within the female gametophyte → providing nutrients and protection 

    • Dispersal by protected spores, and later, seeds

How do multicellular plants, animals, and fungi get their food?

• Consumers

  • Animals are heterotrophs 

  • They INGEST food; mostly internal digestion 

• Decomposers

  • Fungi are heterotrophs 

  • They live inside their food; secrete enzymes that digest macromolecules into smaller molecules; they ABSORB nutrients 

• Producers

  • Plants and algae are autotrophs

  • They use CO2 and sunlight to MAKE their own food

    • Thanks to their endosymbiotically-acquired chloroplasts 

How much of the tree of life is multicellular?

• Eubacteria and archaea are almost entirely unicellular 

• Eukaryotes → multicellularity evolved independently in 6 eukaryotic linears, but overall mostly unicellular

PHOTOSYNTHESIS

Be able to explain the ‘Big picture’ of photosynthesis (summary slide in power-point): inputs, outputs, connections, locations (thylakoid, stroma)

• Light reactions occur in thylakoid membrane 

  • Inputs: H2O, light, NADP+, ADP

  • Outputs: O2

  • Connections → ATP and NADPH

• Calvin cycle → stroma 

  • Inputs: CO2, ATP, NADPH 

  • Outputs: sugar (glucose, sucrose…)

  • Connections → NADP+, ADP

Why is photosynthesis so important (for plants, for you, for all life on earth?)

• For plants → allows plants to produce their own food (glucose) and energy, allowing them to grow and produce

• For you → oxygen to breathe and food that you eat (by consuming plants or indirectly consuming animals that eat plants)

• For life on Earth → photosynthetic organisms form the base of the food chain, supporting other forms of life, removes CO2 from atmosphere, 

Van Helmont experiment – what did he test, how did he do it, what did he conclude? 

• Took an earthenware vessel, placed in it 200 pounds of soil dried in an oven, soaked this with rainwater, and planted in it a willow branch weighing 5 pounds 

• At the end of five years, the tree grown from it weighed 169 pounds and about 3 ounces

• He dried the soil in the vessel again, and the same 200 pounds were found, less than 2 ounces

• Conclusion → 164 pounds of wood, bark, and root had arise from water only

What do we mean when we say that “trees are made of air”?  

• This means that majority of trees mass comes from CO2 in the air, not soil or water

• CO2 is converted into glucose using sunlight, and that glucose is then used to build cellulose/lignin/other organic molecules that make up plants mass

How is the H+ gradient built up inside the thylakoid space, and what is the consequence?

• Transport of H+ into thylakoid during flow of electrons from PSII to PSI

• Splitting of water inside thylakoid 

• Use of H+ to reduce NADP+ in stroma 

• Consequence: buildup of H+ ions in the thylakoid creates a proton gradient → H+ ions diffuse down their gradient → convert NADP+ to NADPH and ADP to ATP → these are used for sugar synthesis in the Calvin cycle 

Why are plants green?

• Contain chlorophyll, which absorbs red and blue light but reflects green light 

Rubisco – what is it? What does it do? In what ways is it inefficient?

• Rubisco is an enzyme that catalyzes the first step of the Calvin cycle, fixing CO2

  • Combines CO2 with RuBP to form 3-PGA, which is used to make glucose 

• Inefficient:

  • Slow: slow turnover rate of 2-3 reactions per second

  • Oxygenase activity: rubisco also catalyzes the opposing reaction (binding O2 for photorespiration instead of binding CO2 for the calvin cycle) causing it to reverse its own work 

  • Rubisco has a 100x higher affinity for CO2 than O2, but the atmosphere has more O2 than CO2 → 20-50% of C fixed by photosynthesis is lost to photorespiration (even more in warm climates)

Photorespiration – problem and solutions

Pep Carboxylase, C3, C4, CAM

• Problem: photorespiration occurs when the Rubisco enzyme binds O2 instead of CO2 during the Calvin cycle, wasting energy and reducing the efficiency of photosynthesis 

• C3: no adaptations, prone to photorespiration 

  • Hot conditions → stomata close to decrease water loss → photorespiration increases → reduced efficiency 

• C4: spatial separation of photosynthesis stages 

  • Mesophyll cell chloroplasts (light dependent reactions); PEP carboxylase turns CO2 into a 4 carbon compound 

  • Bundle sheath cell chloroplasts: the 4 carbon compound is transported here and releases higher CO2 concentrations as Rubisco is sequestered from O2 

• CAM: temporal separation of light-dependent reactions and Calvin cycle 

  • Night: plants open stomata → PEP carboxylase fixed CO2 into a 4 carbon acid → malate/aspartate builds up through the night until saturated with carbon → plant tissue becomes acidified 

  • Day: stomata close → light reactions begin → malate is decarboxylated and the Calvin cycle operates 

  • Growth is limited by how much CO2 can be stored 

Why did I bring dry ice to class? 

What is the composition of our atmosphere?

• 21% oxygen 

• 78% nitrogen 

• 0.9% argon 

• 0.04% carbon dioxide 

Where does your fat go when you lose weight? 

• Fat is broken down into CO2 and water when you lose weight 

• CO2 is exhaled and the water is excreted as urine or sweat

• Fat goes into the air 

PLANT NUTRITION

How is plant nutrition similar to that of animals? Different?

• Similar: amino acids, nucleic acids, sugars and with a few exceptions, and the same lipids (plants never use cholesterol). Small molecules such as ATP and vitamins perform same functions in both types of organisms 

• Different: plants make everything organic within their own bodies while animals have to digest 

Selective uptake of minerals – how is it regulated?

• Active transport (at a cost of ATP)

Difference between macro and micronutrients 

• Macronutrients: form the basic structure of plant cells and are involved in growth, energy storage, and metabolism

  • Primary nutrients are N, P, K

  • Secondary nutrients are Ca, Mg, S 

• Micronutrients: elements essential for plant growth that are needed in only very small (micro) quantities 

  • B, Cu, Fe, Cl, Mn, Mo, Zn

Basics of N cycle – what kinds of organisms can process N₂ in the atmosphere directly?

• Nitrogen-fixing bacteria 

  • Nitrogen fixation → N₂ → NH₃/NH₄⁺

    • By nitrogen fixing bacteria 

  • Nitrification → NH₄⁺ → NO₂⁻ → NO₃⁻

    • By nitrogen fixing bacteria

  • Assimilation → NO₃⁻/NH₄⁺ → organic nitrogen in plants/animals

    • Plants absorb nitrogen for growth 

  • Ammonification → organic nitrogen → NH₄⁺

    • Decomposers recycle nitrogen from dead organisms 

  • Denitrification → NO₃⁻ → N₂ 

    • Done by bacteria to return nitrogen to the atmosphere 

Mycorrhizae – what are they? How does each party benefit?   

Why don’t plants defecate?

• Symbiotic association between plant and fungus

• Important for uptake of phosphorus

• Fungus collects water, N, P for plant

• Plants pay fungus with sugar 

• Plants don’t defecate because they efficiently recycle or remove waste through leaves, bark, root, and gases

Carnivory in plants - function? Mechanisms of prey capture? Evolution?

• Function: carnivorous plants augment their N by eating insects 

• Mechanism of prey capture:

  • Snap traps: rapid leaf movement triggered by sensory hairs snaps shut on prey

  • Flypaper traps: sticky glandular hairs trap and digest insects

  • Suction traps: vacuum like bladders in small aquatic organisms 

• Evolution: Convergent evolution and adaptation to specific ecological niches

TRANSPORT AND GAS EXCHANGE

Water movement – how does water get to the top of a tree? 

• Water is pulled, under tension, through plants in a continuous stream from soil out through leaves

• Water movement can be explained by water potential

• Water moves from an area of less to more solute (osmosis) → passive transport 

• Plant cells have walls, so pressure is also involved 

Structure and function of endodermis?

• Function: Prevents water and solutes from passing through this layer via the apoplastic pathway 

• Structure: Tightly packed cells and casparian strips 

Relationship between gas exchange, water loss, photosynthesis, stomata

SUMMARY:

• Uptake of water and minerals by root hairs and/or mycorrhizae 

• Diffusion through cortex to xylem (must pass through membrane) 

• Vertical transport through xylem (bulk flow) into stems and leaves 

• Cuticle/bark reduces evaporation from above ground parts

• In leaves, water used in photosynthesis, enters phloem, or evaporates (most water lost by evaporation (transpiration))

• Water vapor passes from intercellular spaces in mesophyll through stomates, which regulate loss of water and CO2 uptake 

Transpiration-to-photosynthesis ratio

• The amount of water lost per gram of CO2 assimilated into organic material created by photosynthesis 

• Transpiration rate / photosynthesis rate 

• C4 plant ratio is 300:1 vs C3 ratio is 600:1

  • Can close stomata when losing too much water but stockpile CO2 inside

Why do plants 'drink' so much more than animals?

• Photosynthesis → key reactant, and especially important since plants lose water through transpiration 

• Nutrients → dissolve and transport nutrients absorbed through the roots 

• Root pressure → as water flows upward, need constant intake through the roots 

• Structural support → plants hold their shapes through turgor pressure 

Water potential - solute, pressure potential

• Potential of water to do work; incorporates solute concentration and pressure 

• Solute potential + pressure potential = water potential 

Which way will water move?

• Water moves across the membrane from solution with higher to lower water potential (down the water potential gradient)

• Water under pressure has a positive pressure potential 

• Water under tension has a negative pressure potential 

• Flaccid cell has pressure potential of 0

• Turgid cell has a positive pressure potential 

Be able to solve basic WP problems

Water potential gradients in a living plant

• Water moves down water potential gradient from less negative to more negative 

• Water always moves from regions of higher water potential (less negative) to regions of lower water potential (more negative)

How is water potential involved in the opening and closing of stomata?

• Water potential changes within the guard cells, driven by osmotic movements of water, are crucial in controlling the opening and closing of stomata

• Presence of solute → less free water available for movement → water potential is more negative 

• Opening: negative water potential in guard cells → water moves into guard cells

• Closing: less negative water potential in guard cells → water moves out of guard cells 

Turgor and wilting – causes?

• Turgor pressure → water in vacuole pushes the cell membrane against the cell wall

• Wilting → empty vacuole causes the cell walls to shrink and to pull away from the neighboring cells

  • Results in droopy appearance 

• Causes:

  • Water loss from transpiration 

  • Dehydration 

  • Root damage 

  • High temperature and increased transpiration 

How is sugar translocated from source to sink? 

• Source: where sugar is made and stored

• Sink: where the sugar is sent to 

• Translocated: organic material synthesized in leaves but most of it is stored or used elsewhere

  • Organic materials transported in living phloem cells 

  • Largely transported as sucrose (also amino acids and other compounds) 

Pressure-flow hypothesis 

• Active uptake of sucrose from source into phloem (“loading”)

• Water follows (enters sieve cells from xylem by osmosis)

• At sink, sugar is transported out of sieve cell, water follows (diffuses out) 

• Flow created by water entering sieve cells at source and leaving cells at sink

• Movement of sugars can be bi-directional 

Changes in sources and sinks over the seasons

• Spring → active growth phase 

  • Source: storage organs

  • Sink: leaves, shoots, flowers 

• Summer → peak photosynthesis

  • Source: mature leaves 

  • Sink: developing fruits, seeds, storage organs

• Fall → preparation for dormancy

  • Source: leaves

  • Sinks: storage organs

• Winter → dormancy 

  • Source: minimal photosynthesis 

  • Sink: few active sinks 

Differences between sugar and water transport

• Location:

  • Sugar in the phloem

  • Water in the xylem 

• Direction:

  • Water is upward from roots to leaves

  • Sugar is bi-directional 

• Mechanism:

  • Phloem is alive → doing active work → sieve tube elements 

  • Xylem → made up dead, hollow cells

• Transport:

  • Water is mostly a passive process

  • Sugar is an active process that requires ATP

PLANT GROWTH AND MORPHOLOGY

Plants vs animals - differences in type /mode/ timing of growth and development   

• Type: 

  • Animal growth → determinate

  • Plant growth → indeterminate 

• Mode:

  • Animals → growth is more uniform and occurs throughout the body

  • Plants → growth occurs at meristems (root and shoot tips) 

• Timing:

  • Animals → Specific life stages

  • Plants → seasonal/continuous 

Determinate vs indeterminate growth

• Determinate: overall shape of adult animal is genetically determined from its earliest development stages 

• Indeterminate: retain tiny regions of embryonic tissue (meristems) that are capable of developing into new parts of the plant, so that the plant grows new shoots and roots for as long as it is alive

  • Overall shape of plant is not determined in advance

Meristems – SAM and RAM, vascular cambium

• Meristems: regions of undifferentiated cells capable of continuous cell division 

• Plant growth:

  • Primary growth - elongation 

    • Shoot apical meristem (SAM)

    • Root apical meristem (RAM)

  • Secondary growth - thickening 

    • Vascular cambium

Why/how do beet and carrot greens grow from the top of a cut-off root in a 'trash garden'?

• Beet and carrot greens regrow from top of a cut-off root due to meristematic tissue that remains active 

• Stored nutrients in the root provide energy for new leaf growth, while water absorption and hormonal signals trigger shoot regeneration 

• Plant cannot grow its taproot → will eventually stop once energy reserves are depleted

• Process used in trash gardens to regrow edible greens from vegetable scraps

Primary and secondary growth

• Plant growth:

  • Primary growth - elongation 

    • Shoot apical meristem (SAM)

    • Root apical meristem (RAM)

  • Secondary growth - thickening 

    • Vascular cambium

Modular growth – implications for diversification of function?

• Implications:

  • In animals, the rudiments of all organs form in the embryo and so are all the same age

  • Plants add organs at their tips for as long as they live, so the modules of a plant vary in age, in proportion to their distance from the SAM

    • Youngest organs are near the shoot tip while older organs are farther away 

  • Because plants can make many copies of their organs, they can vary in functions

Alternative functions of structures – leaves, stems, roots

• Modified leaves:

  • Water storage 

  • Defense 

  • Reproduction 

• Modified stems:

  • Photosynthesis 

  • Water storage

  • Defense 

• Modified roots:

  • Support

  • Climbing

  • Storage

How can you tell a simple leaf from a leaflet on a compound leaf? 

• Simple leaf: a single blade attached to a stem, one petiole  

• Leaflet on a compound leaf: Multiple leaflets, one petiole, bud at base of whole leaf

Plant ‘immortality’ – what, how? 

• Meristems: active meristems provide the ability to keep growing indefinitely as long as the environment allows 

• Perennial growth: some plants can grow back each year from same root system 

Grocery store botany – what’s what?

• Look at a variety of plants, each used for different purposes

• Cabbage → leaf 

• Brussels sprouts → bud 

• Celery → petiole

• Cloves → flower

• Capers → flower

MUTUALISMS between plants and animals – pollination, seed and fruit dispersal, defense (e.g., ant-plants). What does each party get out of the deal?

• Pollination 

  • Plant: reproduction and genetic diversity 

  • Animal: food (nectar and pollen) 

• Seed and fruit dispersal

  • Plant: spread offspring, reduce competition 

  • Animal: Food (fruit and seeds) 

• Defense 

  • Plant: protection from herbivores, improved health 

  • Ant: food (nectar, food bodies), and shelter

PLANT SENSES AND BEHAVIOR

Categories of behavior – e.g., foraging, reproduction, defense, etc.

• Foraging: for light, nutrients, water 

  • (host/victims for parasitic plants)

• Reproduction: germination, pollination, sex change 

  • (functional gender) 

• Defense: physical and chemical induced responses 

• Kin recognition: role of modular construction and dispersed mechanisms 

What do plants forage for?

• Light, nutrients, water

• (Host/victims for parasitic plants)

How is plant behavior similar to / different from animal behavior?

• Similarities:

  • Both plants and animals respond to environmental stimuli and external cues 

  • Both communicate with other organisms 

  • Both exhibit behaviors related to reproduction, survival, and defense 

• Differences:

  • Movement 

    • Plants → growth based movement 

    • Animals → rapid, locomotion based movement 

  • Nervous system

    • Plants → no nerves 

    • Animals → complex nervous system 

  • Reproduction 

    • Plants → typically stationary 

    • Animals → active mating 

  • Communication methods 

    • Plants → chemical signaling 

    • Animals → vocalization 

Having read the Light Eaters, what do you think about the ‘intelligence’ (agency? consciousness?) of plants? Are these concepts useful? Misleading? What surprised you the most? 

• Intelligence: Plants exhibit complex behaviors and problem-solving abilities (e.g., foraging for resources, defending against herbivores), but this is not the same as consciousness or agency. The concept of plant "intelligence" can be useful for understanding their adaptive capabilities but may be misleading if it implies human-like cognition.

• What surprised me: The extent to which plants can communicate with each other and other organisms (e.g., releasing volatile compounds to warn neighbors of herbivores) and their ability to remember past experiences (e.g., exposure to stress).

• YAMASHITA and WHITE paper

How do plants sense their environments? (ie, what sensory modalities do they use?)

• Sight → 3 kinds of photoreceptors 

• Taste → response to compounds dissolved in water 

• Smell → response to volatile compounds 

• Touch → response to touch, vibration 

• Hearing → CONTROVERSIAL!!!!!!!

• Response to gravity 

• Ability to keep time → daily (circadian) and yearly (photoperiodic) cycles

• Pollan article → 15-20 distinct senses 

Tropisms and nastic responses - examples

• Thigmotropism: 

  • Response to touch 

  • Tendrils detect contact via sensory epidermal cells called tactile blebs 

  • Tendrils coil around objects they touch 

• Phototropism:

  • Stems grow toward light (positive) while roots grow away from light (negative)

• Gravitropism:

  • Roots grow downward (positive) while stems grow upward (negative)

• Nastic responses: Non directional movements in response to stimuli 

  • Nyctinasty: leaf movements in response to day/night cycles

  • Thigmonasty: rapid movements in response to touch 

Gravitropism in roots vs shoots; how do roots sense gravity?

• Stems are negatively gavitrophic 

• Roots are positively gavitrophic 

• How roots sense gravity: Starch filled plastids called amyloplasts sink towards the gravitational field. This stimulates the release of the growth hormone auxin

Camouflage plant – Observations? Evidence? Do you buy it?

• Observation/evidence: various instances of plants mimicking other plants 

  • Farmers pulled out rye weed to keep crops healthy 

  • So rye weed took on a form similar to wheat to avoid the selective pressure 

• I buy it → solid defense mechanism 

HERBIVORY AND PLANT DEFENSE

What parts of plants get eaten?

• Leaves → eaten by herbivores

• Stems → eaten by insects 

• Roots → eaten by insects 

• Flowers and seeds →  eaten by insects

Who eats plants?

• Mammals: Deer, rabbits, elephants, etc.

• Insects: Caterpillars, beetles, aphids, etc.

• Birds: Some birds eat seeds, fruits, and leaves.

• Other herbivores: Snails, slugs, and even some fish.

How do plants defend themselves?  Physical / chemical? 

• Spines/thorns

• Hairs

• Toxic chemicals

• Latex

• Crypsis or mimicry 

• Mutualistic relationships with ants 

• Help from predators or parasitoids 

• Chemical communication between plants and animals

Direct / indirect defenses

• Direct defenses: constitutive (always present) or induced (produced following herbivory)

  • Physical → spines, hairs, thorns, waxes, latex 

  • Chemical → toxic chemicals, digestibility reducers, egg killers 

• Indirect defenses: constitutive or induced

  • 3rd trophic level → EFNS, mutualism with ants, domatia, release of volatiles 

Detection of eggs 

• Chemical detection: plants recognize specific chemical compounds left behind when insects lay eggs

• Mechanical detection: some plants sense physical presence of eggs via changes in leaf pressure or local cell damage 

• Light detection: some plants can sense light pattern changes caused by eggs blocking sunlight 

Pollination 

What, broadly, is the role of a flower?

• Attract and reward pollinators 

• Facilitate reproduction in angiosperms 

Be able to describe the process of pollination

• Pollen production: anther produces pollen grains

• Pollen transfer: pollen is carried by wind, water, or pollinators to another flowers stigma 

• Pollen adhesion: pollen sticks to the sticky stigma of the flower 

• Pollen tube formation: a pollen tube grows down the style to reach the ovary 

• Fertilization: sperm cells travel through the tube to fertilize the ovule, forming a seed

Significance of POLLEN, FLOWERS (innovations in Angiosperms)

• Pollen: Allows for the delivery of sperm without water, enabling seed plants to colonize diverse habitats.

• Flowers: Innovations in angiosperms that attract pollinators and increase reproductive efficiency. Flowers provide rewards (e.g., nectar, pollen) and have co-evolved with pollinators to ensure successful pollination.

Biotic and abiotic pollination

• Biotic - by insects, birds, mammals, etc 

  • Pollination ‘syndromes’

• Abiotic - wind, water 

  • Thought to be a secondary reduction or loss of petals and rewards 

Cheating by plants and animals in pollination 'mutualisms'

• Nectar robbing: insects remove nectar from flowers without contacting sexual structures

• Plants cheat: Flowers look and smell like rotting meat, attract carrion flies 

• Floral mimicry: a non-rewarding flower resembles a rewarding one 

Seed and fruit dispersal

In what groups of plants are seeds found (i.e., what are the SEED plants?)

• Gymnosperms: seeds not enclosed in a fruit, they develop on the surface of cones or other structures 

• Angiosperms: seeds are enclosed inside a fruit, which develops from the ovary of a flower 

What are the 3 main components of a seed?

• Seed coat → protective outer layer 

• Embryo → developing plant

• Endosperm → provides nutrients / cotyledons → in dicots, are modified leaves that store nutrients for the growing plant, initial food source during germination  

Evolutionary innovations of seed plants 

• Seeds: Protect and nourish the embryo, allowing dispersal in space and time.

• Pollen: Enables sperm delivery without water, expanding habitat range.

• Flowers: attract pollinators 

• Fruits: help seed dispersal 

Further innovations of angiosperms

• Flowers → specialized reproductive structures

  • Increase pollination efficiency 

• Fruits → enhanced seed dispersal

  • Seeds are enclosed within fruits (aid in protection and dispersal)

• Double fertilization → energy efficiency 

  • One sperm fertilizes the egg (forming the embryo) and another sperm fertilizes polar nuclei 

• Xylem with vessel elements → faster water transport 

  • Wider/more efficient at transporting water

Distinction between fruit and seed; function and developmental origin of each

• Seed: Develops from a fertilized ovule; contains the embryo and food supply. Function: Protects and nourishes the embryo, aids dispersal.

• Fruit: Develops from the ovary; protects seeds and aids in their dispersal. Function: Enhances seed dispersal through various mechanisms (e.g., wind, animals).

Orchid seeds vs coconuts – different strategies; how does each embryo get its start?

• Orchid seeds: Tiny, dust-like, and lack food reserves. They rely on mycorrhizal fungi to provide nutrients for germination.

• Coconuts: Large, with a significant food reserve (endosperm). The embryo uses this stored energy to germinate and grow.

What does it mean to say that seeds can travel in time and space?

• Traveling in space refers to the movement of seeds across different locations, enabling plant species to expand and adapt to new environments.

• Traveling in time refers to seeds’ ability to remain dormant and survive through unfavorable conditions, effectively allowing them to "wait" until the right time to germinate.

Selective advantages of seed dispersal (departure and arrival benefits)

• Departure benefits:

  • Avoid competition with the parent plant.

  • Escape from natural enemies (e.g., herbivores, pathogens).

• Arrival benefits:

  • Colonize new habitats.

  • Reach microsites favorable for germination and growth.

Modes of seed dispersal – biotic, abiotic, inside or outside of animals

• Biotic: Dispersal by animals (e.g., birds, mammals) either inside (e.g., ingested fruits) or outside (e.g., hitchhiking on fur).

• Abiotic: Dispersal by wind (e.g., winged seeds), water (e.g., drift seeds), or explosive mechanisms (e.g., seed pods).

Indehiscent / dehiscent fruits

• Dehiscent fruits: Split open at maturity to release seeds (e.g., pea pods).

• Indehiscent fruits: Do not split open; seeds are dispersed within the fruit (e.g., acorns).

Simple vs accessory fruits

• Simple fruits: Develop from a single ovary (e.g., peach, tomato).

• Accessory fruits: Develop from tissues other than the ovary (e.g., apple, strawberry).

4 red fruits; what is the reward in tomatoes, strawberries, pomegranates, raspberries?

• Tomato: Fleshy pericarp (fruit tissue) is the reward.

• Strawberry: The fleshy receptacle (not the ovary) is the reward.

• Pomegranate: The juicy arils (seed coverings) are the reward.

• Raspberry: The aggregate of drupelets (small fleshy fruits) is the reward.