EXAM 2

Question 1

How is the structure of an individual xylem cell appropriate for its role in water transport?

Answer 1

The structure of xylem cells allows for the efficient and unidirectional transport of water and dissolved nutrients in plants due to their thick walls from their lignin.

Question 2

How about for an individual root hair cell?

Answer 2

Individual root hairs, rather than xylem cells, have thin walls to allow nutrients to sink in, while xylem is more of just a transport

Question 3

Spongy mesophyll cells in leaves, how do they work?

Answer 3

They are specialized for gas exchange and photosynthesis. Their structure is characterized by large intercellular spaces and thin cell walls, which allow for the diffusion of gases such as carbon dioxide, oxygen, and water vapor

Question 4

What’s the difference between roots and shoots?

Answer 4

Roots absorb water and key nutrients
Shoots absorb light

Question 5

Why is surface area so important for plants?

Answer 5

Absorption takes place across a surface, but the cells that use the absorbed light and molecules occupy a volume
A plant is efficient in absorption if it has a large surface area relative to its volume

Question 6

What are guard cells?

Answer 6

They are specialized dermal cells in leaves that regulate gas exchange and water loss through small openings called stomata. The structure of guard cells is characterized by a thickened outer wall and a thinner inner wall.

Question 7

What is a taproot and how does it function?

Answer 7

A taproot is a central root that grows downward for structural support, and grows deep to grab hard to reach nutrients

Question 8

What are lateral roots and what do they do?

Answer 8

These are supplemental roots that grow laterally to the ground, and also provide structural support

Question 9

What are the ways that water can enter the xylem cell?

Answer 9

The apoplast pathway involves water entering the root via the spaces between the plant cell walls, also known as the apoplast. Water can move freely through the apoplast until it reaches the endodermis, the innermost layer of the cortex in the root.

The symplast pathway involves water entering the root through the cytoplasm of root cells. Water can pass from cell to cell through the plasmodesmata, which are small channels that connect the cytoplasm of neighboring cells. Once water reaches the endodermis, it must again pass through the selectively permeable membranes of the endodermal cells.

The transmembrane pathway involves water moving across the selectively permeable membranes of root cells. This pathway involves both the apoplast and symplast pathways, as water can enter the cell wall and move through the apoplast, or enter the cytoplasm of root cells and move through the symplast.

Question 10

What is the primary mechanism that drives water up trees?

Answer 10

The primary mechanism is transpiration, which is the loss of water vapor from the leaves and other aerial plant parts. Transpiration creates a negative pressure, or tension, within the xylem vessels, which pulls water up from the roots.

Question 11

What is cohesion?

Answer 11

Water molecules are attracted to each other by hydrogen bonding, creating a cohesive force that helps to maintain the integrity of the water column within the xylem vessels.

Question 12

What is adhesion?

Answer 12

Water molecules are also attracted to the walls of the xylem vessels, creating an adhesive force that helps to keep the water column in place as it is pulled upwards.

Question 13

What is surface tension?

Answer 13

The cohesive forces between water molecules create surface tension, which helps to keep the water column intact and prevent it from breaking apart under tension.

Question 14

What is evaporation?

Answer 14

As water evaporates from the leaves and other aerial plant parts, it creates a negative pressure within the xylem vessels, which helps to pull water up from the roots.

Question 15

What is stomatal conductance?

Answer 15

Stomata are the small pores on the surface of leaves that allow for gas exchange, including the release of water vapor during transpiration. The opening and closing of stomata is regulated by environmental and physiological factors, which can affect the rate of transpiration and the water potential gradient between the leaves and roots.

Question 16

What is root pressure?

Answer 16

Root pressure occurs when water is actively pumped into the xylem vessels of the roots, creating a positive pressure that can help to push water upwards.

Question 17

What is water potential?

Answer 17

Water potential is a measure of the potential energy of water in a system, relative to pure water at atmospheric pressure and temperature. It is expressed in units of pressure (such as kilopascals or megapascals), and is a measure of the tendency of water to move from one place to another.

Question 18

How does water potential affect fluid transport in plants?

Answer 18

Water moves from high potential to low potential spaces which creates a gradient for water to travel

Question 19

What is cavitation?

Answer 19

Cavitation occurs when air bubbles form within the xylem vessels, breaking the continuous water column and blocking the flow of water. This can happen when water is under tension, such as during periods of high transpiration demand or when the water supply is limited.

Question 20

What is an embolism?

Answer 20

Embolism occurs when air bubbles or other materials enter the xylem vessels, blocking the flow of water. This can happen due to damage to the plant’s vascular system, such as from frost or physical injury.

Question 21

What is the difference between cavitation and embolism?

Answer 21

Cavitation is the initial formation of air bubbles in the xylem due to a sudden drop in pressure, while embolism is the permanent blockage of xylem vessels due to the presence of air bubbles.

Question 22

In what ways are the mechanisms used to transport water and translocate sugars similar? In what ways to they differ?

Answer 22

The mechanisms used to transport water and translocate sugars in plants are similar in that they both rely on pressure differences to move fluids through the plant. Specifically, both processes are driven by a combination of transpiration (the loss of water vapor from leaves) and root pressure (the force exerted by the roots on the soil solution).

Question 23

What are chloroplasts and why are they important?

Answer 23

They are organelles for photosynthesis, with two distinct compartments, the thylakoid membrane and stroma. The thylakoids are the stacks called grana, and the flat surface helps them collect ATP.

Question 24

How do plants obtain their CO2?

Answer 24

Through their stomata, which they can control their openness. During the day they open up to absorb, and close at night to save water.

Question 25

How do plants absorb light?

Answer 25

The chloroplasts contain pigments such as chlorophyll that absorb light energy from the sun. Additionally, some plants may have specialized structures such as thorns or hairs that can also intercept light. Since the pigments are green, it collects red and blue light the best.

Question 26

What are phenophytin molecules?

Answer 26

Pheophytin molecules play a critical role in the light-dependent reactions of photosynthesis, where they act as electron acceptors in the electron transport chain. A decrease in the number of pheophytin molecules would lead to a reduction in the efficiency of the light-dependent reactions, which could result in a decrease in the production of ATP and NADPH.

Question 27

What are redox reactions and why are they important?

Answer 27

Pigments such as chlorophyll absorb light energy and use it to generate high-energy electrons. These electrons are then transferred through a series of redox reactions in the electron transport chain, which ultimately generates ATP and NADPH

Question 28

What type of reactions occur during photosynthesis?

Answer 28

Light dependent (absorption) and non-light dependent (Calvin cycle)

Question 29

What is C4, and what are its benefits?

Answer 29

C4 is a carbon fixation cycle, with carbon dioxide is first fixed into a four-carbon compound in mesophyll cells, which are then transported to bundle sheath cells where the Calvin cycle occurs. This spatial separation of carbon fixation and the Calvin cycle allows for a reduction in photorespiration and an increase in photosynthetic efficiency, particularly in environments with high temperatures and intense light. C4 plants are also able to maintain high rates of photosynthesis under low CO2 concentrations and water stress.

Question 30

What is CAM and its benefits?

Answer 30

In the CAM pathway, plants fix carbon dioxide during the night when their stomata are open, and store it as organic acids. During the day, the stored carbon dioxide is released and used in the Calvin cycle. CAM plants are adapted to arid environments with low water availability, as the closed stomata during the day reduce water loss through transpiration. This pathway also allows CAM plants to take advantage of the cooler temperatures during the night for carbon fixation, which reduces the risk of photorespiration.

Question 31

What are the 3 phases of the Calvin cycle?

Answer 31

The process by which plants convert carbon dioxide into glucose during photosynthesis. It occurs in the stroma of chloroplasts and has three phases: carbon fixation, reduction, and regeneration. In the carbon fixation phase, carbon dioxide is combined with a five-carbon sugar called ribulose bisphosphate (RuBP) to create two three-carbon molecules called 3-phosphoglycerate (3PG). In the reduction phase, ATP and NADPH from the light-dependent reactions are used to convert 3PG into a three-carbon sugar called glyceraldehyde 3-phosphate (G3P). In the regeneration phase, some G3P is used to regenerate RuBP, while the rest is used to create glucose and other organic compounds.

Question 32

What is RUBISCO?

Answer 32

It’s a catalyst for the Calvin Cycle

Question 33

What is osmoregulation?

Answer 33

The process by which organisms maintain the balance of water and solutes (such as ions and molecules) inside their cells and tissues, despite fluctuations in their external environment. Osmoregulation is necessary for proper cell function, as changes in the concentration of solutes can disrupt cellular processes. Osmoregulation can involve mechanisms such as ion transport, active transport, and diffusion to regulate the concentration of solutes inside the cell. In organisms that live in hypertonic or hypotonic environments, osmoregulation can involve specialized adaptations such as salt glands, ion channels, and transporters. Overall, osmoregulation is an essential process that helps maintain cellular homeostasis and allows organisms to survive in a variety of environments.

Question 34

How do salt glands work?

Answer 34

They are specialized cells found in the tissues of some animals that allow them to excrete excess salts from their bodies. These cells actively transport sodium and chloride ions out of the animal’s body, creating a concentration gradient that drives the movement of water out of the cells as well. This water, along with the excess salts, is then excreted from the animal’s body.

Question 35

Does the location of the cotransporter proteins on the cell’s membrane be important

Answer 35

The location of the Na+-K+-2Cl- cotransporter proteins on the cell’s plasma membrane can be important for their function, as their location can affect the direction and efficiency of ion transport. Similarly, the location of K+-channels and Cl- channels can also be important for their function, as their location can affect the direction and efficiency of ion movement across the membrane.

Question 36

What is a resting membrane potential?

Answer 36

It is the electric potential between the interior and exterior of a neuron at rest, typically around -70 mV. It is formed by the unequal distribution of ions across the membrane, with more K+ inside and more Na+ outside due to the Na+/K+ ATPase.

Question 37

Why is the Nernst equation important and what is it?

Answer 37

It is important for calculating the equilibrium potential for a specific ion and helps determine the contribution of each ion to the resting membrane potential. The equation is E = (RT/zF) * ln([ion]outside/[ion]inside), where E is the equilibrium potential, R is the universal gas constant, T is the temperature in Kelvin, z is the valence of the ion, F is the Faraday constant, and [ion]outside and [ion]inside are the concentrations of the ion outside and inside the cell, respectively.

Question 38

What is the difference between photosystem I and II

Answer 38

Photosystem II functions to capture light energy and use it to split water molecules into oxygen and hydrogen ions. The hydrogen ions are then used to create a proton gradient that powers ATP synthesis. Photosystem I uses the energy from light to generate high-energy electrons, which are used to reduce NADP+ to NADPH, a molecule that plays a key role in the synthesis of sugars during the Calvin cycle.