plant phys for REAL

Trees are distinguished by secondary growth (producing wood and bark), a single, woody trunk, and a raised canopy to compete for sunlight.

What makes trees unique? 🌳

Lignin provides structural rigidity, allowing trees to grow tall. Vascular tissues (xylem) enable efficient transport of water and nutrients over long distances, supporting their large size.

What is the evolutionary significance of lignin and vascular tissues? 🌲

No, trees are polyphyletic, meaning the tree form has evolved independently multiple times in different plant lineages, showing convergent evolution.

Are trees monophyletic? 🤔

Transcription factors and signaling components control the activity of the shoot apical meristem (upward growth) and vascular cambium (secondary growth), dictating the tree's shape.

What genes determine tree form? 🧬

The vascular cambium produces secondary xylem (wood) inward and secondary phloem (part of the bark) outward, causing the trunk to thicken and grow in diameter.

Describe secondary growth. 🪵

Trees are a major carbon sink. They absorb atmospheric CO2​ through photosynthesis, storing carbon in their biomass (wood, leaves, roots) and helping to mitigate climate change.

How do trees impact the carbon cycle? 🌍

Trees act as keystone species, providing habitat and food for biodiversity, influencing microclimate, and stabilizing soil with their root systems.

What are the key ecological roles of trees? 🐿️

Photosynthesis removes CO2​ (a global cooling effect). Evapotranspiration cools local air and increases humidity, influencing local weather patterns.

How do trees influence climate? 🌤️

People use trees for timber, food, fibers, biofuels, medicines, and cultural purposes. They also provide environmental benefits like shade and erosion control.

What are the diverse uses of trees? 🏡

It is the primary process for converting solar energy into bioenergy, sustaining the biosphere and holding potential for human energy needs.

What is the global significance of photosynthesis? 🌎

Jan van Helmont showed plants get mass from water; Joseph Priestley found plants "restore" air; Jan Ingenhousz proved sunlight is necessary; and Melvin Calvin traced the carbon path in the cycle.

What are some key historical milestones in the discovery of photosynthesis? 📜

Cuticle prevents water loss; stomata allow gas exchange (CO2​ in, O2​ out); and vascularization transports water and nutrients; air space ensures that CO2​ can diffuse rapidly from the stomata to every photosynthetic cell within the leaf

How are leaves optimized for photosynthesis (cuticle, stomata, vascularization, air space)? 🍃

Chloroplasts have a double envelope, a fluid-filled stroma (where the Calvin Cycle occurs), and stacks of flattened sacs called thylakoids (where the light reactions occur). The stacks are known as grana.

What is the structure and function of a chloroplast? 🌱

Proplastids are precursors; chloroplasts perform photosynthesis; chromoplasts produce and store pigments (like in flowers and fruits); amyloplasts store starch; and etioplasts are chloroplasts that haven't been exposed to light.

Differentiate between different types of plastids. 🔬

They originated from an ancient cyanobacterium that was engulfed by a eukaryotic cell, a process called endosymbiosis. This is supported by molecular evidence showing genetic similarities between chloroplasts and cyanobacteria.

What is the evolutionary origin of chloroplasts? 🦠

Light is electromagnetic energy characterized by its wavelength (distance between waves), frequency (waves per second), and photon energy (quantifiable energy of a light particle).

Describe the key properties of light. ☀️

Photosynthetically Active Radiation (PAR) is the range of light wavelengths (400–700 nm) used by plants for photosynthesis. Photon energy within this range is sufficient to excite electrons and initiate chemical reactions, breaking and forming chemical bonds.

What is PAR and how does it relate to photon energy? 💡

Pigments like chlorophyll are essential for light capture. The absorption spectrum shows the wavelengths a pigment absorbs; the action spectrum shows the rate of photosynthesis at those wavelengths. A pigment's color is the wavelength of light it reflects, not absorbs.

How do pigments function in photosynthesis? 🎨

Bacterial rhodopsin is a protein found in some microorganisms that captures solar energy without chlorophyll. When it absorbs light, it pumps protons across a membrane, creating a pH gradient that can be used to generate energy.

What is an alternative solar energy capture mechanism? 🔋

Antenna complexes capture light energy and pass it to the reaction centers (P680 or P700) via resonance energy transfer, where the energy is funneled to a chlorophyll molecule.

How is light harvested and transferred in photosynthesis? 💡

The Z-scheme illustrates the flow of electrons from water through Photosystem II (PSII) and Photosystem I (PSI). PSII splits water and uses light energy to energize electrons, while PSI uses a second photon to re-energize the electrons for NADPH synthesis.

Describe the Z-scheme and the roles of PSI and PSII. ⚡

After water is split, electrons move through a series of carriers: plastoquinone, cytochrome b6f, plastocyanin, and ferredoxin, ultimately leading to the production of NADPH and a proton gradient.

Explain the electron transport chain in the light reactions. ⛓️

The electron transport chain creates a proton motive force (ΔpH and ΔE) across the thylakoid membrane. This force powers ATP synthase to produce ATP. The electrons themselves are used to create NADPH.

How are ATP and NADPH made in the light reactions? 🔋

The two main products are ATP and NADPH, which are both essential for the Calvin Cycle (the light-independent reactions) to produce sugars.

What are the key products of the light reactions? ✨

Energy starts as photonic energy from sunlight, which is converted to electronic energy by exciting electrons. This leads to charge separation in the reaction center, and this energy is finally captured in the stable covalent bonds of ATP and NADPH.

Trace the energy transformations in photosynthesis. ➡️

It has three phases: carboxylation (CO2 is fixed by RuBisCO), reduction (ATP and NADPH convert the molecule to G3P), and regeneration (more ATP is used to regenerate the RuBP molecule).

Describe the C3 Calvin Cycle. 🔄

The key inputs are CO2​, ATP, and NADPH. The main output is Glyceraldehyde 3-phosphate (G3P), which is used to make sugars.

What are the inputs and outputs of the Calvin Cycle? ➡️

Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) is the enzyme that catalyzes the initial step of the Calvin Cycle, fixing CO2​ by attaching it to RuBP.

What is the role of Rubisco? 🌱

When oxygen levels are high, RuBisCO acts as an oxygenase, attaching O2​ to RuBP instead of CO2​. This produces a toxic compound that the plant must process, which is an energetically costly and inefficient process.

Explain photorespiration. 💨

High O2​ to CO2​ ratio, high temperature, and water stress (which causes stomata to close, trapping O2​ and blocking CO2​) increase photorespiration rates.

What factors influence photorespiration?🌡️

It's a CO2​ concentrating mechanism that uses a spatial separation of fixation. PEP carboxylase fixes CO2​ in mesophyll cells, and then the CO2​ is transported to the bundle sheath cells where the Calvin Cycle occurs. This is enabled by a specialized leaf anatomy called Kranz anatomy.

What is C4 photosynthesis? 🌾

It minimizes photorespiration by concentrating CO2​ around RuBisCO. This makes it more efficient in hot, high-light environments and gives it a very high water use efficiency.

What are the advantages of C4 photosynthesis? 👍

It's a water-conserving mechanism that uses a temporal separation of fixation. CO2​ uptake occurs at night when stomata are open. It is stored as malate and released during the day for the Calvin Cycle, when stomata are closed.

What is CAM photosynthesis?🌵

They are well-adapted to arid environments, have extremely high water use efficiency, and typically have low productivity due to the limited time for CO2​ uptake.

What are the characteristics of CAM plants? 🐌

The two major products are starch, synthesized and stored in the plastids (chloroplasts), and sucrose, synthesized in the cytoplasm.

What are the two major products of photosynthesis and where are they made? 🍚

Starch is a large, insoluble polymer used for long-term energy storage in the cell. Sucrose is a smaller, soluble sugar used as the main transport molecule to move energy throughout the plant.

What are the roles of starch and sucrose? ➡

Key limiting steps include the rate of CO2​ uptake through stomata, the efficiency of the Calvin cycle, and the speed of electron transport. These limitations can be assessed using gas exchange measurements and chlorophyll fluorescence.

What are the limiting steps of photosynthesis? 🚦

Strategies include improving Rubisco's efficiency, creating photorespiratory bypasses, introducing or enhancing the C4 cycle, and modifying the activity of Calvin cycle enzymes and electron transport components.

What are some genetic engineering strategies to enhance photosynthesis? 🧬

Plants adapt to varying light, temperature, and water conditions through developmental (e.g., changing leaf shape), biochemical (e.g., enzyme regulation), and behavioral (e.g., stomatal closure) changes.

How do plants adapt to environmental changes? 🏞

Sun leaves are thicker, with more palisade mesophyll and high Rubisco content to handle high light. Shade leaves are thinner and have larger antenna complexes to capture limited light more efficiently.

How do sun and shade leaves differ? 🌞

These curves show how the photosynthetic rate changes with light intensity. The light saturation point is where the rate plateaus, indicating photosynthesis is no longer limited by light but by other factors like Rubisco activity.

What do light-response curves show? 📈

Leaves maintain thermal balance and dissipate heat through transpiration (evaporative cooling) and by changing their orientation to the sun.

How do leaves avoid heat damage? 🥵

High temperatures can denature enzymes and increase photorespiration. Water stress causes stomatal closure to conserve water, which reduces CO2​ availability and starves the Calvin cycle, decreasing efficiency.

How do high temperatures and water stress impact photosynthesis? 💧

Efficiency is limited by factors such as CO2​ availability (through stomatal or mesophyll conductance), Rubisco activity, and the capacity of the Calvin cycle and electron transport chain. Photoprotection mechanisms like nonphotochemical quenching can also limit efficiency.

What limits photosynthetic efficiency? 🛑

C4 plants have an advantage in hot, high-light environments with low CO2​ because their CO2-concentrating mechanism minimizes photorespiration. C3 plants are more efficient in cooler climates with high CO2​ because their process is less energy-intensive. This is due to the lower CO2​ compensation point of C4 plants.

Compare C3 and C4 plants' performance. ⚖

Plants use chloroplast movements to change their position within cells and leaf movements (e.g., sun-tracking) to optimize light absorption.

Describe behavioral adaptations to light. 🕺

C3 plants are predicted to benefit more from rising atmospheric CO2​ because it reduces photorespiration, a major inefficiency for them. The competitive advantage of C4 plants in hot climates may diminish. These effects have been studied using FACE (Free Air CO2​ Enrichment) experiments.

How does rising CO2​ and temperature affect C3 and C4 plants? 📈

primary wall

the outermost layer of a plant cell, thin and flexible with cellulose and pectin, laid down by cells that are dividing and growing

middle lamella

layer that holds the primary and secondary walls together, contains lots of pectins

tonoplast

membrane that surrounds the central vacuole, selectively permeable, regulates cell turgor

plasmodesmata

channels that pass through the cell walls of plants, linking them together, used for intercellular transport

golgi body

packages proteins into vesicles so that they can be sent to their desired location

mitochondrion

produce ATP through cellular respiration

plasma membrane

layer that separates the cell wall from the cytoplasm

oil body

lipid storage compartments mainly found in seeds, provide energy for the seed to grow

ribosomes

where proteins are synthesized in the cell from mRNA

chloroplast

where photosynthesis takes place in the cell to produce sugar, contains chlorophyll

peroxisome

breaks down fatty acids and hydrogen peroxide (helps with photorespiration) and synthesized plant hormones

cortical microtubule

network of tubules beneath the plasma membrane which help determine cell shape, part of the cytoskeleton

cortical actin microfilamen

plays a role in cell wall organization and division, supports cytoskeletal structure

smooth endoplasmic reticulum

network of membranes that helps synthesize various necessary substances (lipids), lacks ribosomes

rough endoplasmic reticulum

produces proteins that are necessary for the cell to function, contains ribosomes

vacuole

storage compartment in the plant cell that stores nutrients, water, and waste, also helps maintain pressure in cell

nucleus

contains genetic material and controls many different aspects of the cell

nuclear pore

transport molecules between the nucleus and the cytoplasm

nucleolus

produce and assemble ribosomal RNA and ribosomes in the cell

chromatin

forms chromosomes and packages genetic material

plastid

a class of plant cell organelles surrounded by a double membrane (envelope) and possessing specialized functions such as photosynthesis, pigment synthesis, and storage of starch or lipids

chloroplast

green plastid specialized for photosynthesis

amyloplast

plastid that synthesizes and stores starch

chromoplast

plastid that synthesizes and stores pigments (ex: carotenoids)

proplastid

undifferentiated precursor to other plastid types

structure of chloroplast and functions of key structures

chlorophyll

what is the key pigment of photosynthesis?

magnesium

what metal does chlorophyll contain?

carotenoids

what is the other major class of pigment found in chloroplasts?

it is an accessory photosynthetic pigment: absorbs light and passes the energy to chlorophyll, protection against excess light: quenches the excited state of chlorophyll for nonphotochemical quenching

what are two functions of carotenoids?

it is the incorporation of CO2 into organic molecules via the Calvin cycle

what is meant by CO2 fixation?

in the stroma of the chloroplast

where does CO2 fixation occur?

in the light harvesting complexes of the two photosystems embedded in the thylakoid membrane

where in the chloroplast does light capture occur?

transfers electrons to NADP+ to form NADPH

what is the function of photosystem I?

splits water and generates electrons and O2

what is the function of photosystem II?

200-300

how many antennae chlorophylls are associated with each reaction center chlorophyll?

increase light absorption efficiency and energy transfer to the reaction center

what are the advantages of antennae chlorophylls?

water → PSII → plastoquinone (PQ) → cytochrome b6f → plastocyanin (PC) → PSI → ferrodoxin (Fd) → NADP+ reductase → NADPH

identify the path of electrons in the photosynthetic light reactions from water to NADPH

Patterns of cell division and directional cell enlargement

The development of a plant from a sessile, immobile organism to a complex structure is primarily a result of what two processes?

Diploid and haploid

A plant's life cycle alternates between which two generations?

Ground tissue

Which plant tissue system includes cell types like parenchyma, collenchyma, and sclerenchyma?

Plasmodesmata; symplasm

The cytoplasm of adjacent plant cells is connected by channels called ______, which form a continuous network known as the ______

Water transport; dead

What is the primary function of mature xylem cells, and what is their state at maturity?

Glycoproteins destined for secretion are processed first in the ER and then in the Golgi apparatus.

Which of the following describes the role of the endoplasmic reticulum (ER) and the Golgi apparatus in protein processing?

it reduces atmospheric CO2 into carbohydrates (triose phosphates)

what is the primary function of the Calvin-Benson cycle?

ATP and NADPH which are generated by the light-dependent reactions of photosynthesis

what energy sources does the Calvin-Benson cycle use?

In the cytoplasm

In a plant cell, where does the translation of mRNA into proteins occur?

Primary walls are synthesized during active growth, and secondary walls are deposited later on the inner surface of the primary walls

what is the key difference between primary and secondary cell walls?

carboxylation (rubisco catalyzes the reaction of CO2 with ribulose 1,5-bisphosphate (RuBP) to produce 3-phosphoglycerate)

what is the first phase of the Calvin-Benson cycle?

reduction (converts 3-phosphoglycerate to triose phosphates)

what is the second phase of the Calvin-Benson cycle?

regeneration (restores the CO2 acceptor molecule, ribulose 1,5-bisphosphate)

what is the third phase of the Calvin-Benson cycle?

rubisco (ribulose, 1,5-bisphosphate carboxylase/oxygenase)

name the key enzyme involved in the carboxylation phase

a process where rubisco binds and reacts RuBP with O2 instead of CO2, producing 3-phosphoglycerate and the toxic compound 2-phosphoglycolate

define photorespiration