Cellular Respiration

Question 1

catabolism / catabolic pathway

Answer 1

a metabolic pathway that releases energy by breaking down complex molecules to simpler compounds
Cellular respiration is a catabolic pathway

Question 2

anabolic pathway (biosynthetic pathways)

Answer 2

metabolic pathway that consumes energy to build complicated molecules from simpler ones
Photosynthesis is an anabolic pathway

Question 3

fermentation

Answer 3

breakdown of sugars or other organic fuel without oxygen

Question 4

aerobic respiration

Answer 4

oxygen used to break down fuels

Question 5

break down of sugars - chemical equation

Answer 5

C 6 H 12 O 6 + 6 O2 gives 6 CO2 + 6 H20 + Energy (ATP and heat)

Question 6

how is energy created in pathways

Answer 6

transfer of electrons from one reactant to another
the relocation of electrons releases energy stored in organic molecules and this energy is ultimately used to synthesise ATP

Question 7

redox reactions

Answer 7

chemical reaction that involve a transfer of one or more electrons from one reactant to another

Question 8

oxidation

Answer 8

A redox reaction is one that involves the transfer of electrons from one reactant to another
Oxidation is when a substance loses electrons

Question 9

reduction

Answer 9

Redox reactions involve the transfer of electrons from one substance to another
reduction is when electrons are added to another substance
adding electrons is called reduction - adding negatively charged electrons to an atom reduces the amount of positive charge of that atom

Question 10

cellular respiration as a redox reaction

Answer 10

Glucose becomes oxidised to form carbon dioxide (loses the hydrogens)
the oxygen becomes reduced to form water (gains the hydrogens)
Hydrogen is transferred from glucose to oxygen

Question 11

NAD / NADH

Answer 11

nicotinamide adenine dinucleotide (derivative of the vitamin niacin)
Electron carrier / electron shuttle
cycles between oxidised NAD to reduced NADH
functions in several of the redox steps during the breakdown of glucose

Question 12

electron transport chain

Answer 12

the electron transport chain consists of a number of molecules, mostly proteins, built into the inner membrane of the mitochondria of eukaryotic cells.
Electrons removed from glucose are shuttled by NADH to the top higher energy end of the chain. At the bottom lower energy end oxygen captures these electrons along with hydrogen nuclei forming water

Question 13

where is the electron transport chain located

Answer 13

in the inner membrane of the mitochondria of eukaryotic cells and the plasma membrane of respiring prokaryotes

Question 14

how is energy released in the electron transport chain

Answer 14

multistep
electrons cascade down the chain from one carrier molecule to the next in a series of redox reactions, losing a small amount of energy with each step until they finally reach oxygen, the terminal electron acceptor

Question 15

what is the role of oxygen in the electron transport chain

Answer 15

oxygen is very electronegative

oxygen pulls electrons down the chain

Question 16

three stages of cellular respiration

Answer 16

glycolysis
pyruvate oxidation and the citric acid cycle (krebs)
oxidative phosphorylation - electron transport and chemiosmosis

Question 17

where does glycolysis occur

Answer 17

in the cytosol

Question 18

what processes occur in the mitochondria

Answer 18

pyruvate oxidation
citric acid cycle
oxidative phosphorylation - electron transport and chemiosmosis

Question 19

how many molecules of ATP are created for each molecule of glucose

Answer 19

For each molecule of glucose degraded to carbon dioxide and water by respiration the cell makes up to 32 molecules of ATP

Question 20

what are the two energy phases of glycolysis

Answer 20

glycolysis can be divided into two phases - the energy investment phase and the energy payoff phase
During the energy investment phase the cell spends ATP
This is paid off
The net energy yield from glycolysis, per glucose molecule, is 2 ATP plus 2 NADH

Question 21

what happens to glucose during glycolysis

Answer 21

glucose, a six carbon sugar, is split into two three carbon sugars. these small sugars are oxidised and their remaining atoms rearranged to form two molecules of pyruvate

Question 22

is oxygen required for glycolysis

Answer 22

glycolysis occurs whether or not oxygen is present

Question 23

glycolysis outputs

Answer 23

2 pyruvates + 2 H20
2 ATP
2 NADH + 2H

Question 24

how does the pyruvate enter the mitochondrion

Answer 24

pyruvate is a charged molecule so in eukaryotic cells it must enter the mitochondrion via active transport with the help of a transport protein

Question 25

what happens when pyruvate enters the mitochondrion

Answer 25

pyruvate is oxidised (electrons lost) to a compound called acetyl coenzyme A or acetyl CoA which is further oxidised in the citric acid cycle

Question 26

what gas is released during the change from pyruvate to acetyl CoA

Answer 26

carbon dioxide is released. this is the first step in which carbon dioxide is released during respiration

Question 27

what is the yield from the citric acid cycle

Answer 27

6 NADH 2 FADH2 and 2ATP + 2 Carbon dioxide the cycle generates 1ATP per turn but most of the chemical energy is transferred to NAD and FAD

Question 28

NADH and FADH

Answer 28

Glycolysis and citric acid cycle produce only 4 ATP per glucose molecule after the CAC the molecules of NADH and FADH account for most of the energy extracted from each glucose molecule

Question 29

structure of the electron transport chain

Answer 29

the ETC is a collection of molecules embedded in the inner membrane of the mitochondrion the folding of the inner membrane to form cristae increases its surface area providing space for thousands of copies of each component of the electron transport chain in a mitochondrion most components of the chain are proteins which exist in multiprotein complexes I to IV Tightly bound to these proteins are prosthetic groups - cofactors and coenzymes

Question 30

how does the electron transport chain work

Answer 30

electron carriers alternate between reduced and oxidised states as they accept and then donate electrons

Question 31

what are some of the proteins involved in the electron transport chain

Answer 31

``` flavoprotein iron sulphur protein ubiquinone cytochromes - contains a haem group the electron transport chain has several types of cytochromes ```

Question 32

what happens at the end of the electron transport chain

Answer 32

the last protein (cytochrome) of the chain passes its electrons to oxygen which is very electronegative Each oxygen atom also picks up a pair of hydrogen ions (protons) from the aqueous solution neutralising the -2 charge of the added electrons and forming water

Question 33

does the electron transport chain make ATP

Answer 33

the electron transport chain makes no ATP directly instead it eases the fall of electrons from food to oxygen breaking the energy drom into a series of smaller steps that release energy in smaller more manageable amounts

Question 34

chemiosmosis

Answer 34

pumping hydrogen ions across a membrane to make ATP

Question 35

what is ATP synthase

Answer 35

an enzyme that makes ATP from ADP and inorganic phosphate located in the inner membrane of the mitochondrion a molecular mill - hydrogen ions enter from the intermembrane space and bind within a rotor that changes shape and spins they hydrogen ion exits into the mitochondrial matrix turning the rod of the rotor produces ATP from ADP and P

Question 36

Hydrogen gradient that drives ATP synthesis

Answer 36

As electrons move down the chain, energy is released and used to pump protons (hydrogen) out of the matrix, forming a gradient. Protons flow back into the matrix through an enzyme called ATP synthase, making ATP. At the end of the electron transport chain, oxygen accepts electrons and takes up protons to form water.

Question 37

what would happen in cellular respiration if oxygen was not available

Answer 37

without the electronegative oxygen to pull electrons down the transport chain oxidative phosphorylation would cease

Question 38

anaerobic respiration

Answer 38

certain prokaryotic organisms that live in environments without oxygen have an electron transport chain but do not use oxygen as the final electron acceptor at the end of the chain some sulphate reducing marine bacteria use sulphate

Question 39

fermentation

Answer 39

does not use oxygen or an electron transport chain an extension of glycolysis that allows the continuous generation of ATP glycolysis plus reactions that regenerate NAD by transferring electrons from NADH to pyruvate

Question 40

alcohol fermentation

Answer 40

carried out by many bacteria in anaerobic conditions yeast ( a fungus) in addition to aerobic respiration also carries out alcohol fermentation (bread) pyruvate is converted into acetaldehyde and then ethanol - carbon dioxide is released (beer)

Question 41

lactic acid fermentation

Answer 41

pyruvate reduced to form lactate no carbon dioxide released lactic acid fermentation by certain fungi and bacteria is used to make cheese and yoghurt human muscle cells make ATP by lactic acid fermentation when oxygen is scarce

Question 42

how are fermentation, anaerobic respiration and aerobic respiration similar

Answer 42

all use glycolysis to oxidise glucose to pyruvate with a net production of 2 ATP by substrate level phosphorylation NAD is the oxidising agent that accepts electrons during glycolysis

Question 43

how much ATP is produced through fermentation

Answer 43

fermentation yields 2 molecules of ATP produced by substrate level phosphorylation in the absence of an electron transport chain the energy stored in pyruvate is unavailable (in cellular respiration pyruvate is completely oxidised (all electrons transferred) in the mitochondrion - 32 molecules of ATP

Question 44

what organisms photosynthesise

Answer 44

plants algae - unicellular and multicellular e.g. kelp certain unicellular eukaryotes - e.g. euglena some prokaryotes - cyanobacteria other bacteria

Question 45

where does photosynthesis occur

Answer 45

chloroplasts in leaves (mesophyll) | 1 mm squared of leaf = 500,000 chloroplasts

Question 46

stomata

Answer 46

microscopic pores in a leaf | carbon dioxide enters and oxygen leaves through stomata

Question 47

how many chloroplasts in a cell

Answer 47

30-40

Question 48

structure of a chloroplast

Answer 48

two membranes surround the dense fluid called stroma (inner and outer membrane) third membrane system within the stroma called thylakoids inside the thylakoids is the thylakoid space (separated from the stroma) thylakoids can be stacked into grana thylakoids contain chlorophyll between the two outer membranes is the intermembrane space

Question 49

chlorophyll

Answer 49

light energy absorbed by chlorophyll drives the synthesis of organic molecules in the chloroplast

Question 50

where does the oxygen given off by plants during photosynthesis come from

Answer 50

derived from H2O not from CO2 | the chloroplast splits water into hydrogen and water

Question 51

photosynthesis as a redox reaction

Answer 51

water is split and its electrons are transferred along with hydrogen ions from the water to the carbon dioxide reducing it to sugar

Question 52

is photosynthesis an endergonic or exergonic reaction

Answer 52

the process is endergonic - it requires energy | the energy for photosynthesis comes from light

Question 53

what are the two stages of photosynthesis

Answer 53

``` light reactions (photo) - occurs in the thylakoid membranes Calvin cycle (synthesis) - occurs in the stroma ```

Question 54

why is the calvin cycle referred to as dark reactions (light independent)

Answer 54

do not require light | however do occur during the day because the reaction requires the NADPH and ATP made by the light reactions

Question 55

why do we see green when we look at a leaf

Answer 55

chlorophyll absorbs violet blue and red light and reflects green light

Question 56

photosystem

Answer 56

in the thylakoid membrane chlorophyll molecules are organised along with other small organic molecules and proteins into a complex called a photosystem composed of a reaction centre complex and a light harvesting complex

Question 57

what are the two photosystems in the thylakoid membrane

Answer 57

photosystem II - P680 | photosystem I - P 700

Question 58

what is the light harvesting complex

Answer 58

consists of various pigment molecules including chlorophyll a, chlorophyll b and multiple carotenoids bound to proteins the range of chlorophylls and carotenoids enables the photosystem to harvest light from a broader spectrum

Question 59

what happens in the light harvesting complex

Answer 59

pigment molecule absorbs a photon energy passed from pigment molecule to pigment molecule until it is passed to a chlorophyll a molecule in the reaction centre complex

Question 60

what happens when the electron from the light harvesting complex gets to the reaction centre complex

Answer 60

special pair of chlorophyll a molecules transfer one of their electrons to the primary electron acceptor

Question 61

why are the photosystems called P680 and P700

Answer 61

this is the wavelength they best absorb P680 pigment is best at absorbing wavelength of 680nm (red) P700 - far red (different proteins in each account for slight differences in light absorbing properties

Question 62

path of electrons in light reactions - linear electron flow

Answer 62

photon strikes pigment molecule in light harvesting complex of PS II - boosts electron electrons excite each other until one reaches P680 chlorophyll a molecules in the PSII reaction centre complex transferred to primary electron acceptor enters electron transport chain from PSII to PS I(this drives chemiosmosis) the electron enters the reaction centre of P700 exciting chlorophyll a molecules there and they become electron acceptors enter second electron transport chain through the protein ferredoxin NADP is reduced to NADPH by NADP reductase

Question 63

chemiosmosis in photosynthesis

Answer 63

in Photosystem II an enzyme catalyses the splitting of water molecule into two electrons, two hydrogen ions and a oxygen atom electrons feed into the primary electron acceptor the oxygen is released and joins another oxygen to form O2 (released by leaf) the hydrogen is released into the thylakoid space (interior of the thylakoid) as electrons flow down the electron transport chain energy is released that pumps protons (hydrogens) from the stroma into the thylakoid space makes a proton gradient across the thylakoid membrane Stroma low hydrogen concentration / thylakoid space high concentration ATP is sythesised as hydrogen ions diffuse from the thylakoid space back to the stroma through ATP synthase complexes ATP forms in the stroma where it is used to help drive sugar synthesis during the calvin cycle

Question 64

how are the citric acid cycle and the calvin cycle alike

Answer 64

they are both cycles | starting material is regenerated after some molecules enter and others exit the cycle

Question 65

how are the citric acid cycle and the calvin cycle different

Answer 65

citric acid cycle is catabolic - breaks down molecules | calvin cycle is anabolic - makes more complex molecules out of simpler ones - builds carbohydrates

Question 66

what occurs during the calvin cycle

Answer 66

carbon enters the cycle in the form of carbon dioxide and leaves as sugar the cycle spends ATP as a energy source and consumes NADPH as a reducing power (to add electrons) for adding electrons to make the sugar

Question 67

what carbohydrate is released at the end of the calvin cycle

Answer 67

G3P - glyceraldehyde 3 phosphate

Question 68

how many molecules of carbon dioxide are needed to make one molecules of G3P

Answer 68

3