Module 8

What are the 6 essential macronutrients required by plants?

CHNOPS —>

1. Carbon (C)

2. Hydrogen (H)

3. Nitrogen (N)

4. Oxygen (O)

5. Phosphorus (P)

6. Sulfur (S)

What is a major determinant of plant distribution & growth?

Soil is a major determinant of plant distribution and growth. The balance of water, air in soil pore space dictates root respiration and nutrient availability.

What are three major soil horizons?

A horizon (top soil): The zone with mostly organic material with mineral components that is freshly decomposed. B horizon (subsoil) where the collection of the above materials accumulate, like humus, clay, and aluminum. (PCMA by clay) C horizon (Soil base): consists of weathered rock or sediment deposits above the bedrock.

Describe the role of cationic exchange in plant uptake of soil nutrients.

Clay particles in the topsoil carry negative electrical charges that attract potassium, calcium, magnesium, and ammonium (PCMA). The roots pump up HYDROGEN IONS during root respiration (acidifying the surrounding soil) These hydrogen ions bind to the clay particles bumping off the mineral cations, which the root hairs absorbed the mineral cations dispersed.

How does soil affect water availability?

Healthy soil is composed of 25% water and 25% air the size of the particles range from clay, silt, and sand. Water moves from the soil into root hairs. Soil water potential is higher than the water potential in roots so water flows naturally towards the roots. Soil must maintain a balance between water retention and air pockets if it wants to do transpiration. If the soil water potential drops below the root water potential, the plant can no longer extract that bound water, leading to a loss of turgor pressure and causing the plant to wilt.

Transpiration

The process by which water and dissolved mineral nutrients move from the soil into the roots, travel upward through the xylem, and evaporate out through the stomata in the leaves

Why are legumes efficient at obtaining nitrogen? How does Rhizobium benefit from its relationship with plants?

Legumes are efficient at obtaining nitrogen because they form a mutualistic symbiotic relationship with soil bacteria belonging to the genus Rhizobium. Rhizobium benefits from this relationship by receiving carbohydrates, organic compounds, and protection inside the host plant's root nodule

Mycorrhizal Fungi

A mutualistic symbiotic partnership between soil fungi and plant roots

What is the major contributor to the dry biomass of a plant?

Dry biomass is the total weight of a plant's tissue after all the water has been removed. Around 96% comes from carbon and oxygen obtained from CO2 during photosynthesis. And at a elemental level the CHNOPS macronutrients make up for 98% of it.

Rhizosphere

The specific layer of soil directly surrounding and influenced by a plant's root system

Mycorrhizal symbiosis

Fungal hyphae act as physical extensions of the plant's root system, dramatically increasing the surface area for absorbing water and soil minerals and expanding the plant's effective rhizosphere. The fungi can also produce antibiotics.

What is water potential? How do solute potential and pressure potential affect it?

Water naturally moves toward regions of higher solute concentration via osmosis. As water enters a plant cell through osmosis, internal pressure builds up, causing the cell to become firm or turgid. If a plant loses water, its pressure potential drops, causing the plant to wilt.

Describe the steps involved in water transport.

Water enters root hairs from the soil solution via osmosis, moving down a water potential gradient (from a higher water potential in the soil to a lower water potential in root tissues). Water enters the xylem. Water travels from high to low water potential continuously. Inside the mesophyll water evaporates this process is driven by solar evaporation requiring no energy expenditure.

How do stomata open & close?

Sunlight activates membrane pumps that actively move potassium ions from nearby cells INTO the guard cells. These potassium ions make the inside very salty/sugary, and because now its higher solute inside water rushes inside. When light is more scarce water leaves because the potassium goes back to neighboring cells, closing the pore.

Cohesion

The attraction between identical molecules

Adhesion

The attraction between different substances

Apoplastic

Water travels OUTSIDE cell walls

Symplastic

Water travels INSIDE cell walls

Casparian strip

A waxy wall inside the endodermis that BLOCKS the outside route

Compare symplastic and apoplastic flow of water in roots.  What is the function of the casparian strip?

Highway A: The apoplastic route water travels OUTSIDE from non-living cell walls. Highway B: The symplastic route, water crosses the outer cell membrane to enter the living cytoplasm inside a cell. Neighboring root cells are linked by microscopic internal doorways (called plasmodesmata). Inside the endodermis the Casparian strip acts as a FILTER, it must leave the cell walls and cross the plasma membrane INSIDE the endodermis.

Describe the steps involved in sugar translocation in plants.

Sucrose is produced by photosynthesis, these are transported by sieve-tube cells using ATP provided by companion cells. Solute concentration increases because of the sucrose, drawing water FROM the xylem by osmosis. This forces the sucrose to go down, sucrose exits the sieve tube to be consumed by sink cells. Water goes back to the xylem once the solute is gone, reducing the turgor.

Passive transport

Movement down concentration gradients without energy expenditure

Active transport

Movement against concentration gradients requiring energy (for example moving from low to high concentration).

Water potential

Incorporates solute potential and pressure potential to govern the direction of water movement

Osmosis

A specialized form of passive transport where water diffuses across a selectively permeable membrane toward areas of higher solute concentration (or lower water potential)

Diffussion

Applies to any type of particle or molecule (such as solutes, gases, or dyes) spreading out from an area of high concentration to low concentration

Describe solute transport across plasma membranes in plants.

Passive transport is solute going from an area of high concentration to an area of low concentration. Active transport is when ATP is required and solute needs to move from an area of low concentration to an area of high concentration. Through H+ hydrogen ions co-transport the solute is going along the hydrogen ions. Sugar is produce with photosynthesis, and companion cells spend ATP to make run the H+ and sucrose co-transporting into the phloem sieve-tube cells.

What is the main photosynthetic pigment? What are the accessory pigments?

Chlorophyll a, the main photosynthetic pigment. It absorbs mostly red and blue wavelengths. Accessory pigments broad the spectrum light can absorb, chlorophyll b(blue, red-orange), carotenoids, and xanthophylls (blue-green).

What is an absorption spectrum? Action spectrum?

Ah absorption spectrum is just how much light absorbs at which wavelengths. Action spectrum is how much that light performs photosynthetic activity. The action spectrum shows all the photosynthetic work driven by the primary and accessory pigments working together.

Thylakoid

Tiny membrane-bound inside the chloroplasts

Granum

A whole stack of these thylakoid disks piled on top of each other

Stroma

The dense, thick liquid that fills the open space inside the chloroplast

Photosynthesis consists of light and light-independent reactions—describe the major steps in each reaction and where they occur.  Why do we consider photosynthesis a redox process?

The light-dependent reactions happen Inside the Grana(stacks) the solar energy is stored in ATP and NADPH. ATP is made through chemiosmosis, sunlight hits photosystem I giving the electron energy to create the NADPH. The light independent reactions happen in the stroma (the surrounding area) using the ATP and NADPH to turn carbon dioxide into sugar. The CO2 is used by the enzyme RuBisCo the cell uses ATP and the electrons from NADPH to convert the carbon into 3-carbon sugar molecule called G3P and the pairs combine to form glucose. The leftover G3P is used to repeat the cycle.

Photorespiration

When plants close their stomata down, Under these conditions, the enzyme RuBisCO mistakenly binds O2 instead of CO2

How do C4 and CAM plants minimize photorespiration?  How are CAM plants especially adapted to hot, dry environments?

C4 separate initial carbon into 2 different cell locations; the mesophyll cells, it is efficient at capturing carbon into a 4-carbon called malate (it can capture it even when internal CO2 levels are low). By keeping stomata completely sealed during the scorching heat of the day and taking in CO2 only at night,

About ____% of a plant’s water escapes through the stomata, although the stomata account for just a small percent of the external leaf surface.

95

Inputs to the light-dependent reactions include

Light,water

Photosynthetic pathways

Are the specific biochemical mechanisms plants use to capture and fix carbon dioxide