BIO AND PLANT life week 1-3

What is the primary function of the root epidermis?

It is the outermost layer responsible for the uptake of water and nutrients from the soil.

What structures significantly increase the surface area of the root epidermis?

Root hairs.

Where is the endodermis located?

It is the innermost layer of the cortex, surrounding the vascular cylinder.

What is the primary function of the Casparian strip?

It is a waxy, suberized band that forces water and solutes to move through the symplast, regulating uptake into the vascular tissue.

What tissue type is the pericycle?

It is meristematic tissue located in the outermost layer of the stele.

What is the function of the pericycle?

It acts as the origin point for the formation of lateral roots.

Describe the arrangement of xylem in a typical dicot root.

It forms a star-shaped core in the center of the root.

Describe the arrangement of vascular tissue in a typical monocot root.

It consists of a ring of vascular bundles surrounding a central pith.

What determines whether an epidermal cell becomes a root hair cell or a non-hair cell?

Positional signaling based on contact with underlying cortical cells.

In root hair patterning, what is the "h" position?

A cell in contact with two cortical cells, which triggers differentiation into a root hair cell.

In root hair patterning, what is the "n" position?

A cell in contact with only one cortical cell, which differentiates into a non-hair cell.

What are the three primary stages of lateral root emergence?

Initiation in the pericycle, division to form a primordium, and emergence through the cortex and endodermis.

What is the function of the root cap?

It protects the root apical meristem and senses gravity (gravitropism).

How does the root cap sense gravity?

Through the settling of starch-filled amyloplasts known as statoliths.

Where does active cell division occur in the root?

In the root apical meristem (RAM).

What distinguishes monocot roots from dicot roots regarding the pith?

Monocot roots have a central pith, while it is usually absent or very small in dicot roots.

What is the apoplast?

The space outside the plasma membrane, including cell walls and intercellular spaces.

What is the symplast?

The continuous network of cytoplasm connected by plasmodesmata.

What is the stele?

The central vascular cylinder of the root.

Why must water travel through the symplast at the endodermis?

Because the Casparian strip blocks the apoplastic pathway.

What are the primary functions of plant roots?

Anchor plants, explore soil, uptake water/minerals, and typically require oxygen for respiration.

What are the four distinct zones of activity in a typical plant root?

Root Cap, Meristematic Zone (cell division), Elongation Zone (cell expansion), and Differentiation/Maturation Zone.

What happens to root cap cells as the root grows?

They are continually shed or lost, sometimes serving as a nutrient source for soil microbes.

What are adventitious roots and what triggers them?

Roots forming from non-root tissues (stems/leaves), triggered by environmental stress and mediated by auxin.

Beyond lateral root initiation, what is the role of the pericycle?

Contributes to secondary growth, giving rise to vascular cambium and part of cork cambium.

What is the function of the mucigel secreted by the root cap?

Acts as a lubricant for soil penetration and facilitates nutrient uptake and microbe interactions.

What characterizes the differentiation (maturation) zone of a root?

Cells lose meristematic capacity, specialize into cell types, and form prominent root hairs.

What are mycorrhizae?

Ancient symbiotic relationships between plant roots and fungi that facilitate nutrient and water exchange.

Define Ectomycorrhizae

A type of mycorrhizal association where fungi form an external sheath around the root but do not penetrate the plant cell walls.

Define Endomycorrhizae

A type of mycorrhizal association where fungal hyphae penetrate the plant cell walls to form specialized structures called arbuscules for nutrient exchange.

What do plants provide to fungi?

Carbohydrates (sugars) produced through photosynthesis.

What do fungi provide to plants?

Solubilized minerals (such as phosphorus) and water, which are essential for survival in nutrient-poor soils.

What is biological nitrogen fixation?

A process where atmospheric nitrogen (N₂) is converted into ammonia (NH₃) by specialized bacteria, such as Rhizobia.

Where does nitrogen fixation occur in legumes?

Within specialized structures on the roots known as nodules.

What enzyme is required for nitrogen fixation?

Nitrogenase, which catalyzes the conversion of atmospheric nitrogen.

What is the role of leghaemoglobin?

It regulates oxygen levels within the nodule to protect the oxygen-sensitive nitrogenase enzyme.

What is the primary function of roots?

To facilitate the uptake of water and essential mineral macronutrients required for plant growth.

What is the role of root hairs?

They significantly increase the root surface area to maximize the absorption of water and nutrients.

How do plants modify the rhizosphere?

They release chemical exudates, such as organic acids, which alter soil chemistry to help mobilize nutrients.

How do plants actively take up minerals?

Through specific membrane transporters located in the root cells.

What creates soil horizons?

A combination of abiotic processes (like weathering and deposition) and biological activity.

What determines soil fertility?

It is shaped by the interaction of abiotic processes and the biological community within the soil.

Why is the rhizosphere important?

It is the narrow zone of soil surrounding the roots where complex interactions occur between plant roots, soil microbes, and environmental conditions to sustain plant life.

What is the primary function of the Casparian strip in root anatomy?

It is a suberized, waterproof barrier in the endodermis that forces water and solutes to move through the symplast (plasma membranes) rather than the apoplast, allowing the plant to selectively regulate nutrient uptake.

What distinguishes the Hartig net in ectomycorrhizal associations?

It is a complex network of fungal hyphae that grows between the root epidermal and cortical cells, facilitating nutrient exchange without penetrating the cell walls.

Which specific nitrogen-fixing enzyme complex is highly oxygen-sensitive and why?

Nitrogenase; it is sensitive to oxygen because the Fe-protein and MoFe-protein components are permanently inactivated by O₂ exposure.

How does leghaemoglobin protect nitrogenase within legume nodules?

It acts as an oxygen buffer, binding free oxygen with high affinity to maintain a low-oxygen environment (microaerobic) suitable for nitrogenase activity while delivering oxygen to the bacterial electron transport chain for respiration.

What is the difference between arbuscules and vesicles in endomycorrhizae?

Arbuscules are highly branched structures within cortical cells for nutrient exchange; vesicles are lipid-rich storage organs formed by some fungi.

What role do root exudates like organic acids (e.g., citrate, malate) play in the rhizosphere?

They acidify the soil and act as chelating agents, solubilizing tightly bound minerals like phosphorus and iron, making them bioavailable for root uptake.

How does the GL2 gene influence root hair development?

It is a transcription factor that acts as a negative regulator of root hair formation; epidermal cells expressing GL2 become non-hair cells (atrichoblasts).

Define the "symplastic" vs. "apoplastic" pathways in nutrient movement.

The symplastic pathway moves nutrients through the cytoplasm of connected cells via plasmodesmata; the apoplastic pathway moves through the porous cell walls and extracellular spaces.

What characterizes the "O horizon" in a soil profile?

The organic horizon, consisting primarily of decomposing leaf litter and organic matter at the surface.

What are the two primary protein subunits of the nitrogenase enzyme?

The Fe protein (dinitrogenase reductase) and the MoFe protein (dinitrogenase).

What is the main nutritional benefit of ectomycorrhizae to trees in forest ecosystems?

They facilitate the uptake of nitrogen and phosphorus from organic matter that the plant roots could not otherwise access.

Why are root hairs essential for water uptake?

They provide a massive increase in surface area, allowing for the absorption of water even when moisture levels in the soil are low.

What occurs during the process of "cation exchange" in soil?

Roots release H⁺ ions (often via H⁺-ATPases) into the soil, which displace positively charged mineral nutrients (like K⁺ or Mg²⁺) from negatively charged soil particles so they can be absorbed.

What is the difference between macronutrients and micronutrients?

Macronutrients (e.g., N, P, K, Ca, Mg) are required in relatively large concentrations, while micronutrients (e.g., Fe, Mn, Zn, Cu) are required in trace amounts but are equally essential.

What is the primary role of the pericycle in root development?

It is the tissue layer that gives rise to lateral (branch) roots.

How do Rhizobia bacteria initially recognize a host legume?

Through a molecular dialogue: the plant releases flavonoids, which induce the bacteria to produce Nod factors, which are then recognized by the plant root.

What happens to soil pH when plants undergo intensive nitrogen uptake?

It often changes; uptake of ammonium (NH₄⁺) releases H⁺ into the soil (acidifying), while uptake of nitrate (NO₃⁻) consumes H⁺ or releases OH⁻/HCO₃⁻ (alkalinizing).

What is the "rhizosphere"?

The narrow zone of soil surrounding the root, where biological and chemical activity is heavily influenced by root exudates.

Describe the benefit of endomycorrhizal (arbuscular) fungi regarding stress resistance.

They can confer systemic resistance against drought and soil-borne pathogens by improving plant water status and inducing defensive chemical pathways.

How does phosphorus availability typically limit plant growth in older, weathered soils?

Phosphorus often reacts with iron and aluminum oxides to form insoluble complexes, making it chemically unavailable for root uptake without fungal or exudate assistance.

What is the role of H⁺-ATPases in root plasma membranes?

They pump protons out of the cell to create an electrochemical gradient (proton motive force), which drives the secondary active transport of nutrients into the cell.

How do root nodules maintain structural integrity?

Through coordinated cell division and differentiation of both plant and bacterial cells, creating a specialized organ protected by a nodule cortex.

What is weathering in the context of soil formation?

The breakdown of rocks and minerals into smaller particles via physical (temperature, wind) or chemical (water, acids, biological) processes.

Why are mycorrhizal networks sometimes called the "Wood Wide Web"?

Because they can link multiple plants of the same or different species, allowing for the potential transfer of carbon and nutrients between plants.

What is the importance of the zone of maturation in roots?

It is the region where root cells differentiate into specialized tissues (like xylem and phloem) and where most functional root hairs appear.

what is the definition of a meristem?

A small region of undifferentiated, self-renewing stem cells in a plant that gives rise to all mature plant tissues and organs.

What is "continual organogenesis"?

The plant's ability to produce new organs (leaves, flowers, roots) throughout its entire lifespan, driven by the activity of meristems.

What are the two primary zones within the SAM that maintain meristem identity?

The Central Zone (contains the stem cells) and the Organizing Center (maintains the stem cell fate).

What is the primary role of the Peripheral Zone (PZ) in the shoot apical meristem?

It is the region surrounding the central zone where new organ primordia (like leaf buds) are initiated.

Adaxial vs. Abaxial surface

Adaxial: The leaf surface adjacent (closest) to the shoot apical meristem. Abaxial: The surface furthest from the shoot apical meristem.

What is Phyllotaxy?

The geometric pattern of leaf arrangement on a stem (e.g., spiral, opposite, or whorled).

Difference between Primary and Secondary growth?

Primary growth (apical meristems) increases length/height. Secondary growth (lateral meristems) increases radial width/girth.

what is the role of the vascular cardium?

A lateral meristem that divides to produce xylem (inward) and phloem (outward), facilitating radial growth in woody plants.

Why do Brassica oleracea variants (broccoli/cauliflower) have unusual architecture?

They possess mutations that cause meristems to stall or repeatedly branch rather than differentiating into normal, mature organs.

How do the AP1 and CAL genes affect flower development?

They are transcription factors; when both are mutated, the plant fails to form normal flowers and instead produces proliferating, cauliflower-like meristematic tissue

What is the function of the CLV3 (CLAVATA3) gene?

It regulates the size of the meristem; mutations in this gene, combined with others, contribute to the fractal-like meristematic growth seen in Romanesco.

Why is the ability to create new meristems an evolutionary advantage?

Because plants are sessile, they cannot escape threats; meristems allow them to regenerate lost organs and adapt their body plan to environmental damage.

What is the biological significance of "Floral Homeotic Genes"?

They act as the "master switches" that assign a specific identity to undifferentiated cells in the floral meristem. They determine whether a primordium develops into a sepal, petal, stamen, or carpe

How does the ABC model function as a "Combinatorial Code"?

It proposes that floral identity is not determined by a single gene, but by the presence or absence of three overlapping protein functions (A, B, and C). The specific combination in each whorl dictates the organ's fate.

What is the specific combinatorial code for each floral whorl?

• Whorl 1: A alone = Sepals

• Whorl 2: A + B = Petals

• Whorl 3: B + C = Stamens

• Whorl 4: C alone = Carpels

How does the "A-B-C" model explain the phenotype of a C-mutant (Agamous)?

If C is missing, A expands into the inner whorls. Since A normally dictates sepals/petals, the inner whorls (normally stamens/carpels) transform into petals and sepals. Additionally, because C is required to "stop" the meristem, the flower becomes indeterminate (a flower-within-a-flower

Why do some mutations (like Apetala) cause a two-whorl transformation rather than just one?

Because A, B, and C functions are expressed in broad, overlapping domains. When one function is deleted, the boundary of the remaining functions shifts, affecting the identity of both whorls where that gene was normally expressed.

How do plants "tweak" the ABC model to create floral diversity (e.g., Roses, Tulips)?

They utilize spatial expansion of gene expression. In tulips, the B-function expands into the first whorl, turning sepals into petals. In roses, the A-function expands, creating more A+B overlap (petals) at the expense of stamens.

Aside from identity, what other factors determine the final morphology (size/number) of floral organs?

Organ size and number are regulated downstream of identity genes by:

1. Meristem Size: Larger meristems provide more space for additional primordia to initiate.

2. Cell Dynamics: Separate genetic programs that control the rate of cell division and the degree of cell expansion.

What is the role of the "E" function in the expanded ABCDE model?

The E-function genes are required for the activity of the A, B, and C proteins. Without E-function genes, the identity genes cannot function, and the plant defaults to producing only leaf-like structures.

What is the "why" behind the ABC model's conservation across different species?

It is an evolutionarily ancient and robust "developmental module." It provides a simple, reliable framework that flowering plants can easily modify to adapt their flower shape to different pollinators without needing to invent an entirely new genetic system.

What is another term used interchangeably with plant hormone?

Phytohormone.

Why must plants be highly adaptable to their external environment?

Because they cannot move.

What are three examples of seasonal processes regulated by plant hormones?

Dormancy, germination, and flowering.

What are three examples of environmental factors plants respond to via hormones?

Light, temperature, and wind.

At what typical concentrations are plant hormones effective?

Low concentrations, from micromolar to nanomolar.

Where are plant hormones typically synthesized?

In small amounts, often in specific tissues.

How do plant hormones reach their site of action?

They are transported, often concentrated by specific transporters.

What cellular components perceive plant hormones?

Specific receptors or binding proteins.

What process is triggered immediately after a hormone binds to its receptor?

Signal transduction.

What are the two primary cellular targets altered by signal transduction?

Gene expression and protein activity.

What is phototropism?

Plant growth or movement in response to light.