Biology Packets 13-17 / Test 4

what is an autotroph?

an organism that converts light energy into chemical energy to make its own food

what is a heterotroph?

an organism that eats the food made by autotrophs

define photosynthesis

the conversion of light energy to chemical energy that is stored in glucose or other organic compounds

where does the light energy for photosynthesis come from?

the sun

where is chemical energy stored in glucose and other organic compounds?

in the covalent bonds / electrons

what is the equation for photosynthesis?

6CO2 + 6H2O + light energy --> C6H12O6 + 6O2

how does CO2 get into plants?

through the stoma (plural stomata)

how does H2O get into plants?

through the roots

what is the site of photosynthesis?

green plant - leaf - mesophyll layer - palisade cells and spongy cells - chloroplast - thylakoid

label the parts of a chloroplast

what part of the chloroplast attracts sunlight?

thylakoids

what do the thylakoid membranes contain?

chlorophyll

why are plants green?

they reflect green light

what is photophosphorylation?

the generation of ATP from ADP and inorganic phosphate with an input of light

what causes phosphorylation?

light

what are the two parts of photosynthesis?

light reactions and calvin cycle

where do the light reactions occur?

thylakoid membranes

where does the calvin cycle take place?

stroma of the chloroplast

what do the light reactions produce?

ATP through photophosphorylation and a reducing agent

what reducing agent does the light reactions produce?

NADPH

what is the reduced form of NADP?

NADPH

what does NADP stand for?

nicotinamide adenine dinucleotide phosphate

what kind of reaction is the light dependent reactions?

endergonic, requires energy to drive the electron transfer chain and produce ATP and NADPH

light is a form of what?

energy

a unit of light energy is called what?

a quantum or photon

what does light travel as?

waves

what determines the color of light?

its wavelength

what is the relationship between energy and wavelength of a photon?

inverse, shorter wavelength has more energy

what 3 things can happen when a photon of light hits a molecule?

can be reflected, transmitted, or absorbed

what is the result of an absorbed photon?

energy in the photon of light is transferred to an electron in the molecule
- molecule becomes excited

what does it mean when a molecule becomes excited?

it loses electrons
- one of the electrons moves to a higher energy level or to another molecule

what types of molecules become excited?

pigments

what are pigments?

molecules that can absorb visible light, each absorbs light of a specific wavelength

what colors of light are most important to photosynthesis?

red and blue

what are the two pigments most important to photosynthesis?

chlorophyll a (more important) and chlorophyll b

what is the difference between chlorophyll a and b?

chlorophyll a is blue-green, chlorophyll b is yellow-green
chlorophyll a absorbs violet and orange light, chlorophyll b absorbs blue and yellow light

what are accessory pigments?

ex: carotenoids
absorb intermediate wavelengths (blue) and transfer energy to chlorophyll

how is a photosystem formed?

clusters of chlorophyll a and accessory pigments absorb photons

where are photosystems located?

within a protein matrix on the surface of the thylakoid membrane

what are the two parts of a photosystem?

light harvesting complex - pigment molecules (accessory) that absorb photons and pass energy to reaction center
reaction center - one or more chlorophyll a molecules that enables it to use light energy to boost one electron to a higher energy level

what is noncyclic photophosphorylation?

a specific process within the light-dependent reactions of photosynthesis where electrons flow in a linear pathway through both photosystems to generate ATP and NADPH

what are the two components of noncyclic photophosphorylation?

photosystem I and photosystem II
- photosystem I is second but was discovered first

what is different about the two systems?

each contains pigments and proteins unique to that system and is activated by a different wavelength of light

what wavelength of light does chlorophyll a absorb in photosystem I?

700nm

what happens in photosystem I?

P700 becomes excited (loses electrons), transfers electrons to primary electron acceptor, transfers electrons to another electron acceptor, transfers electrons to enzyme NADP reductase, NADP is reduced to NADPH

what is the end result of photosystem I?

reduced NADP (for the Calvin cycle)
excited P700 (must be returned to non-excited/ground state)

what wavelength of light does chlorophyll a absorb in photosystem II?

680nm

what happens in photosystem II?

P680 becomes excited (loses electrons), transfers electrons to primary electron acceptor, transfers electrons to another electron acceptor, transfers electrons to cytochrome complex (proton pump) and H+ move from stroma to thylakoid space, transfers electron to electron acceptor, transfers electron to P700 in photosystem I

what is the end result of photosystem II?

P700 from photosystem I in ground state
excited P680 (has to be brought back to ground state by accepting low energy level electrons)

how is P680 restored to its ground state?

enzyme bound to photosystem II catalyzes splitting of water, removes an electron, and transfers the electron to P680, bringing it to the ground state

what happens to oxygen and H+ after this?

oxygen diffuses out of the cell through stomata and H+ pump out of thylakoid space into stroma through ATP synthase

how is ATP formed?

protons move through channels from thylakoid space to stroma forming ATP (stroma side) via ATP synthase (chemiosmosis)

what is the end result of noncyclic photophosphorylation?

reduced NADP (photosystem I)
ATP formation (photosystem II)

summarize the light dependent reactions/noncyclic photophosphorylation

light goes into photosystem II (chlorophyll a), P680 is excited, loses an electron to an electron acceptor in the reaction center, passed to cytochromes, energy is lost, moves H+ from stroma into thylakoid space, have electrons with low energy.
chlorophyll a (P680) lost electrons so needs to be brought to ground state, water splits releasing oxygen to do this.
light hits chlorophyll in photosystem I, P700 is excited, loses an electron to an electron acceptor in the reaction center, moves down and loses little energy, electron joined with NADP reductase to form NADPH (used in the Calvin cycle).
high H+ conc in the thylakoid space, H+ move through ATP synthase, ADP and Pi pick up energy from potential to kinetic to form ATP

what is the next step of photosynthesis?

the Calvin Cycle

what does the Calvin Cycle generally do?

trap CO2 and reduce material to glucose

what is another name for the Calvin Cycle?

light independent reactions

what drives the calvin cycle?

the reducing power of NADPH and ATP

what is the first step of the Calvin Cycle?

carbon fixation

what is carbon fixation?

1 CO2 molecule from the air at a time is accepted by 5C RuBP which is enzyme mediated by rubisco, the unstable 6C molecule breaks down rapidly to form 2 3C molecules, ATP phosphorylates the molecule to make it energy rich, NADPH reduces the molecule to G3P, a 3C molecule (reduction phase)

what is RuBP?

ribulose bisphosphate

what is rubisco?

ribulose bisphosphate carboxylase

what is G3P?

glyceraldehyde 3-phosphate

what is reduced and what is oxidized in carbon fixation?

NADPH is oxidized to NADP and a molecule is reduced to make G3P

how many molecules of CO2 are needed to output one molecule of G3P?

3
3 turns of the Calvin Cycle

how many turns of the calvin cycle are needed to produce one molecule of glucose?

6

what are the two pathways for G3P after carbon fixation and reduction?

make glucose or regenerate ribulose bisphosphate (RuBP)

what happens in the regeneration of RuBP?

G3P (3C) is converted back into RuBP (5C), using energy from the oxidation of ATP

what is the first organic product of CO2 fixation?

3-C molecule called 3-phosphoglycerate

what are plants that use this pathway known as?

C3 plants

what is photorespiration?

when there is not enough CO2 for the calvin cycle, O2 jumps in using rubisco to form useless chemicals that the cell has to break down

when would CO2 be scarce?

on hot days when plants don't want to open because they will lose water, but don't want to stay closed because they can get CO2

what are CAM plants?

plants that open their stomata during the night and store CO2 as malic acid and close them during the day to break down malic acid

what are C4 plants?

start calvin cycle with an alternate mode of carbon fixation that forms a 4C compound as its first product
ex: sugarcane and corn

where are CAM and C4 plants found?

super warm areas, require lots of energy

quick summary of light reactions

carried out by molecules in the thylakoid membranes, convert light energy to the chemical energy of ATP and NADPH, split H2O and release O2 to the atmosphere

quick summary of Calvin Cycle reactions

take place in the stroma, use ATP and NADPH to convert CO2 to the sugar G3P, return ADP, inorganic phosphate, and NADP to the light reactions

what is the cell cycle?

an ordered sequence of events in the life of a eukaryotic cell, from its origin in the division of a parent cell until its own division into 2 cells

what are the phases of the cell cycle?

1. Interphase
2. Mitotic Phase

what happens in interphase?

90% of the cycle
cell grows
duplicates its chromosomes in prep for cell division

what are the phases of interphase?

G1, S, G2

what is the G1 phase?

first gap, cell grows by producing proteins and cytoplasmic organelles

what is the S phase?

synthesis, cell grows and duplicates chromosomes

when the chromosomes are duplicated, what results?

each duplicated chromosome has two sister chromatids

how many chromatids are left after the S phase?

92

what is the major attachment site of sister chromatids?

centromere

what is a kinetochore?

specialized protein structure at the centromere that links each sister chromatid to the mitotic spindle

what is the G2 phase?

second gap, cell grows and completes prep for cell division

what are the specifics of what happens in the G2 phase?

a nuclear envelope encloses the nucleus, the nucleus contains one or more nucleoli (sg. nucleolus), centrosomes form

what does each centrosome contain?

a pair of centrioles

how do the chromosomes appear in G2 phase?

chromatin, not condensed

what happens in the mitotic phase?

very short, cell divides

what are the parts of the mitotic phase?

mitosis and cytokinesis

what is mitosis?

division of the nucleus

what is cytokinesis?

division of the cytoplasm

define cell division

the continuity of life based on the reproduction of cells

what are the three key roles of cell division?

1. asexual reproduction
2. growth and development
3. tissue renewal

what is the result of cell divison?

genetically identical daughter cells (exact copy of genetic material, DNA)

what is DNA in a cell called?

genome

what is DNA packaged into?

chromosomes