Forest Bio Exam 3

Photosynthetically Active Radiation (PAR)

wavelengths of light between 400 and 700 nm that photosynthetic organisms use as a source of energy

Chlorophyll

green pigment responsible for capturing light (within chloroplasts)

Stack of thylakoids

grana

Where are the grana found?

Found in the stroma (inner liquid)

2 type of reactions

- light dependent

- light-independent

Light-dependent reactions

energy from the sun is used to "split" water to produce 2 important energy storage molecules called ATP and NADPH, oxygen is a byproduct (splitting of H2O)

Light-independent reactions

energy derived from the light-dependent reaction is used to produce glucose in the calvin cycle

Where do the light-dependent reactions occur?

thylakoid membrane

Input of the LDR

Sinlight, H2O

Output of the LDR

O2, NADPH, ATP

Photosystem 2 (step 1)

- energy absorbed by the chlorophyll P680

- electron in chlorophyll get excited

- water splits producing protons, electrons and o2

Photosystem 2 (step 2)

- electrons move along the electron transport chain (electrons lose energy through transport)

- protons accumulate in the thylakoid lumen

Photosystem 2 (step 3)

- protons pass through ATP synthase

- ATP synthesized from ADP and inorganic phosphorus

Photosystem 1 (step 1)

- energy absorbed by the chlorophyll P700

- electron gets excited

- hydrogen binds to the NADP with the electron catalyzing formation of NADPH

Calvin cycle

involves a series of chemical reactions which utilize energy from the LDRs and occurs in the chloroplast stroma

Catalyzer in C3 plants?

RuBisCO (acts as a carboxylase and oxygenase)

First product in C3 plant carbon fixation?

3 carbon molecules

Stages of calvin cycle?

1. carbon fixation

2. reduction

3. regeneration

What happens in carbon fixation?

3(CO2) molecules combine with a 5-carbon acceptor (RuBP) which is catalyzed by RuBisCO and produces a 6-carbon compound that splits into two molecules of a 3-carbon compound (3PGA)

What happens in Reduction?

ATP and NADPH are used to convert the 3PGA molecules into a 3-carbon sugar (G3P), the reduction process occurs when NADPH donates electrons to the 3-carbon intermediate to make G3P

What happens in Regeneration?

Some G3P molecules go to make glucose, while others must be recycled to regenerate the RuBP acceptor. This step requires ATP.

Oxygenase

an enzyme that catalyzes the incorporation of oxygen from O2, CO2 released instead of fixed

Remember C3 takes the path from ___ to ___

Mesophyll, vascular tissue

In C4 it takes the path from the ___ to ___ to ___

Mesophyll, bundle sheath cell, vascular

C4 photosynthesis

Incorporates CO2 into 4-carbon acids using PEP carboxylase

3 Fates of glucose

Priority 1 - Respiration

Priority 2 - Construction

Priority 3 - Excess

Cellular respiration

the process by which living things convert oxygen and glucose to carbon dioxide and water (yields energy and does not require sunlight)

2 major steps of respiration

- glycolysis

- krebs cycle

3 multiple choice options

Glycolysis

- breakdown of glucose

- occurs in the cytoplasm

What is produced in glycolysis?

- 6-carbon glucose is split into two 3-carbon pyruvate molecules

- ATP (net gain of 2) and NADH

Krebs cycle

- second stage of cellular respiration, in which pyruvic acid is broken down into carbon dioxide

- NADH and FADH2 enter the electron transport chain where ATP and water are generated

- occurs in the mitochondria

What is produced in the krebs cycle?

- pyruvate is broken into CO2

- NADH and FADH2 are released

- ATP and water are generated at the end

Total respiration

Composed of maintenance and growth respiration

Maintenance respiration

The respiration needed to support the function and turnover of existing tissue (priority 1)

Growth respiration

respiration associated with synthesis of new materials (priority 2)

A plant must ... in order to stay alive

break even

Light compensation point (LCP)

the light level where carbon input from photosynthesis offsets losses from respiration

What happens to the carbon balance at light levels above the LCP?

The carbon balance is usually positive.

How does the angle of the sun change with distance from the equator?

The farther you are from the equator, the more angular the sun becomes.

Which slope receives more sunlight and is typically drier?

South-facing slopes receive more sunlight and are drier.

Which slope receives less sunlight?

North-facing slopes receive less sunlight.

What is the difference between East and West aspects regarding sunlight?

East aspects receive morning sunlight, while West aspects receive sunlight during the warmer part of the day and are typically drier.

Why is water important to plants?

It is essential for chemical reactions, particularly in photosystem II (PS2), and helps maintain cell wall structure.

What regulates the opening and closing of stomata in plants?

Turgor pressure, which is the pressure within the cell vacuole.

What is osmosis in the context of plant cells?

The movement of water across the cell membrane to mix with more concentrated solute.

How does water move between plant cells?

Water moves along gradients of 'water potential,' progressing from high energy (less concentrated solute) to low energy (more concentrated solute).

What is osmotic potential in plant cells?

Osmotic potential is lower when solute is dissolved in water, influencing water movement.

What is turgor potential and its significance in living plant cells?

Turgor potential is typically positive in living plant cells due to high solute concentration, which helps maintain cell structure.

What happens to turgor potential in wilted leaves?

Wilted leaves have zero turgor potential, indicating a lack of water.

What does the cohesion-tension theory explain?

It explains how water moves from areas of high water concentration to low concentration, driven by evaporation.

What is cohesion in relation to water molecules?

Cohesion refers to water molecules sticking together.

What is adhesion in the context of water movement?

Adhesion is the tendency of water to stick to other objects.

What role does gravitational potential play in water movement in plants?

Gravitational potential pulls water down, while adhesive forces create friction that must be overcome for upward movement.

What is required for sufficient negative water potential in trees?

A sufficient amount of water is needed to create enough negative water potential to overcome downward forces.

How does insufficient water affect tree size?

Trees are generally smaller when there is not enough water, as it becomes harder to create the necessary negative water potential.

Hormones that promote growth

- Auxins

- gibberellins

- cytokinis

Etioliation

due to growth in dark:

stem elongation

poor leaf development

lack of chlorophyll

Hormones that inhibit growth

abscisic acid and ethylene

Auxin

Indoleacetic acid (IAA), a natural plant hormone that has a variety of effects, including cell elongation, root formation, secondary growth, and fruit growth

Phototropism

A growth response to light

Gravitropism

response of a plant to the force of gravity

Gibberellins

A class of related plant hormones that stimulate growth at the internodes

Cytokinins

Promote cell division and differentiation

Ethylene

The only gaseous plant hormone. Among its many effects are response to mechanical stress, programmed cell death, leaf abscission, and fruit ripening.

Abscisson

Process of leaf or fruit fall

When is the carbon balance not positive?

It is not positive except under certain conditions.

How does respiration change with increasing temperature?

Respiration, especially maintenance respiration, increases rapidly with increasing temperature.