SAC 2 Test (3A,3B,5A,5B,5C,6A,6B,6C)

Question 1

Enzyme:

Answer 1

an organic molecule which catalyses a specific reaction

• They bind to a substrate when undergoing an enzyme facilitated reaction
• After an enzyme facilitated reaction, the enzyme is left unchanged

Question 2

Substrate:

Answer 2

the reactant of a reaction catalyzed by an enzyme

• After a reaction, the substrate forms a product

Question 3

Active Site:

Answer 3

the part of an enzyme where the substrate binds to

• A pocket like area which is complementary in shape to a substrate
• Must undergo a conformation change to accept the substrate

Question 4

Enzyme Substrate Complex:

Answer 4

the structure formed when an enzyme and substrate bond together

• To write an enzyme-catalysed reaction:
  
  • The reactant is called the substrate
  • Enzyme is written above the arrow

Question 5

Activation Energy:

Answer 5

the energy required to start a reaction

- All reactions need a minimum amount of energy to energize atoms and molecules into a chemical change
- Enzymes work to lower the activation energy threshold allowing reactions to happen quicker

Question 6

Type of Reactions:

Answer 6

Anabolic Reaction: when two or more smaller molecules join to form a larger molecule

- They are Endergonic: require an input of energy

Catabolic reaction: when a larger molecule is broken down to form two smaller molecules

• They are exergonic: releasing energy

Question 7

Biochemical pathway/metabolic pathway:

Answer 7

a series of enzyme-catalysed biochemical reactions in which the product of one reaction becomes the substrate of the next reaction

- A chain reaction of enzyme-catalysed reactions - Works like this as enzymes are specific to their substrate and so must work in pathways to get the desired product

Question 8

Factors affecting Enzyme Functioning

Answer 8

1. Enzymes have optimum temperatures and pH levels at which they function best at however in extreme conditions, the enzymes can be denatured
   - optimal temperature for enzymes is 36-38 degrees
   - optimal pH depends on where in the body the enzymes are
2. if everything else is kept constant, increasing substrate and enzyme concentrations will increase the rate of reaction up to a certain point
   - this will continue until the saturation point is reached at which the enzymes are working at maximal capacity and cannot increase

Question 9

Denaturation

Answer 9

The disruption of a molecules structure by an external factor

- E.g. heat
- As enzymes are proteins, they can be denatured
- This process is irreversible, cannot be fixed

Question 10

What happens to an Enzyme if it is too hot

Answer 10

• If temperature goes beyond optimal, the bonds in an enzymes tertiary and quaternary structures can break down
  
  • This leads to a conformation change in the activation site meaning the substrate can no longer fit

Question 11

What happens to an enzyme if it is too cold

Answer 11

• If below optimal level, enzymic reactions decrease as the molecules are moving slower and therefore colliding less often
  
  • If too cold, enzymes can show no activity and freeze

Unlike denaturing in heat, frozen enzymes can regain functionality after being reheated

Question 12

Competitive Inhibition:

Answer 12

the hindrance of an enzyme by blocking the active site and preventing the substrate from binding

- Competitive as this binding directly occupies the active site, preventing a substrate from binding
- Must have a complementary shape to bind

Question 13

Non-competitive inhibition:

Answer 13

the hindrance of an enzyme by binding to an allosteric site and changing the shape of the active site, therefore preventing the substrate binding

Allosteric Site: any other site other than the active site

Question 14

Coenzyme:

Answer 14

a non-protein organic cofactor that assists enzyme function. They release energy and are recycled during a reaction.

• E.g. ATP, NADH, NADPH

Question 15

Photosynthesis

Answer 15

The process of capturing light energy to power the production of glucose and oxygen from carbon dioxide and water

6 CO2 + 12 H20 (sunlight)–> C6H12O6 + 6 O2+ 6 H2O

stages:

• light dependent
• Light independent

Question 16

Light Dependent Stage

Answer 16

first stage of photosynthesis where light energy splits water molecules into hydrogen and oxygens.

• Only occurs when light is present
• Occurs in the thylakoid membranes

Inputs
12 H2O
12NADP+
18ADP + Pi

Outputs:
6 O2
12NADPH
18 ATP

Question 17

Process of Light Dependent Stage

Answer 17

1. .
   
   • Inside the thylakoid, light energy excites the electrons in chlorophyll
   • The excited electrons move along the proteins in the thylakoid membrane which powers the pumping of H+ into the thylakoid lumen.
   • H2O molecules breakdown to 2H+ and one O2, causing the release of electrons into the chlorophyll to replace the others.
   2. .
      - The oxygen is released from the chloroplast which will either diffuse out of the stomata and into the environment or be used in aerobic cellular respiration.
   3. .
      - H+ from the water molecules are used to generate the high energy coenzyme NAPDH by attaching to NADP+
   • The movement of H+ down the concentration gradient generates the high energy coenzyme ATP
     
     • ATP and NAPDH coenzymes then move on to the light independent stage

Question 18

Light Independent Stage(Calvin Cycle)

Answer 18

second stage of photosynthesis where carbon dioxide is used to form glucose

• Occurs in the stroma of chloroplast

Inputs
6 CO2
12NADPH
18ATP

Outputs:               
C6 H12 O6
12NADP+
18 ADP + Pi
H2O

Question 19

Process of the Light Independent Stage(Calvin Cycle)

Answer 19

1. .
   
   • 3 Carbon dioxide molecules enter the Calvin Cycle in the mesophyll cells and undergo initial reactions
   • The Carbon from CO2 combines with 3x 5-Carbon Molecule(RuBP), forming 18 carbon molecules
   • then splits into 6x 3-Carbon Molecules
   2. .
      - 6 NADPH and 6 ATP molecules are used to turn the 6x 3-PGA carbon molecules into 6x3 G3P molecules by changing the arrangement of the carbon molecules
   • NADPH becomes NADP+ and ATP becomes ADP + Pi
   3. .
      - 1x G3P molecule then exits the cycle and is used to create 1 half of the glucose molecule
   • The remaining 5x G3P molecules, using 3 ATP molecules are arranged again to form RuBP(15 carbons) beginning the cycle again to create the second G3P molecule to create 1 whole glucose
   4. .
      Some of the oxygen molecules leftover from the breaking of CO2 at the beginning of the cycle combine with H+ from NADPH to create the output water

Question 20

Thylakoids

Answer 20

A flattened sac-like structure housed inside the
chloroplast.

Each thylakoid is made up of a chlorophyll-containing membrane enclosing a lumen.

Thylakoids are the location of the light-dependent stage of photosynthesis

Question 21

Stroma

Answer 21

The fluid substance that makes up the interior of
chloroplasts.

It is the site of the light-independent stage of photosynthesis

Question 22

Chlorophyll

Answer 22

A chemical found in the thylakoids of chloroplasts. It is responsible for absorbing light energy in photosynthesis

Question 23

Rubisco

Answer 23

a pivotal enzyme involved in initial carbon fixation during the Calvin Cycle/light-independent stage of photosynthesis

- Stands for Ribulose 1,5 Bisphosphate Carboxylase/Oxygenase - its role is to catalyze the calvin cycle

Question 24

Factors influencing whether Rubisco binds to CO2 or O2

Answer 24

Temperature:
- At regular temperatures, Rubisco’s affinity for CO2 is greater than for O2

- At higher temperatures, the affinity for O2 is higher, leading to rubisco binding to oxygen more often

Substrate Concentration:
- The more substrate is present, the greater chance it will bind to Rubisco

- Plants try and expose a high concentration of CO2 and a low concentration of O2 to Rubisco 
    - The stomata of the plant regulates this by opening up to allow CO2 to enter while O2 and other water vapor simultaneously diffuse out

Question 25

C3 Plants

Answer 25

plants with no evolved adaptation to minimize photorespiration

- Considered 'normal plants'
- All of the light independent stage occurs within mesophyll cells

E.g. Trees, wheat, rice

Question 26

Photorespiration

Answer 26

a wasteful process in plants initiated when Rubisco uses O2 as a substrate rather than CO2, limiting photosynthesis

- Photosynthesis is disrupted as CO2 loses an opportunity to bind with Rubisco.
- Less photosynthesis = less glucose produced + wasted energy used = negative impacts on a plants ability to grow

Question 27

Factors Affecting the Rate of Photosynthesis(all vice versa)

Answer 27

1. increased light increases photosynthesis rate until a plateau is reached
2. increased temperature when below the optimal will increase the rate whereas if above the optimal, it will decrease rate
3. Increased pH levels will increase the rate when below the optimal and decrease the rate when above the optimal
4. Increase CO2 levels increases rate until a plateau is reached
5. Increasing water levels will increase the rate of photosynthesis as it will avoid the stomata closing, allowing more CO2 to enter
6. increase in inhibitors lead to a decrease in photosynthesis rate

Question 28

Cellular Respiration

Answer 28

`the process by which cells create useable energy in the form of ATP from a series of biochemical reactions involving the breakdown of glucose

As glucose carries a lot of energy, it must be broken down into smaller ATP packages

Question 29

Structures of the Mitochondrion relating to Aerobic Cellular Respiration

Answer 29

Cytosol: the aqueous fluid that surrounds the cells organelles inside the plasma membrane
- site of glycolysis

Mitochondrial matrix: the space inside the inner membrane of a mitochondrion
- the site of the Krebs cycle

Crista: the folds of the inner membrane of a mitochondrion
- Site of the electron transport chain

Question 30

Stage 1 of Aerobic Cellular Respiration: Glycolysis

Answer 30

the first stage of Aerobic cellular respiration in which the 6 carbon glucose is converted to two 3 carbon pyruvate molecules via a sequence of ten enzyme reactions

        - Located in the cytosol 

Inputs:

• 1 glucose
• 2 ADP + 2 Pi
• 2 NAD+ + 2 H+

Outputs:

• 2 pyruvates
• 2 ATP
• 2 NADH

Question 31

Stage 2 of Aerobic Cellular Respiration: Krebs Cycle

Answer 31

the second stage of Aerobic cellular respiration where multiple reactions occur to create ATP, NADH, FADH2 and CO2.

- Located in the mitochondrial matrix
    - Via a series of eight reactions, energy is extracted from acetyl(2 carbons), breaking it down to allow coenzyme A to be recycled back for use in the link reaction

Inputs:

• 2 Acetyl-CoA(derived from 2 pyruvate)
• 2 ADP + 2 Pi
• 6 NAD+ + 6 H+
• 2 FAD + 4 H+

Outputs:

• 2 CO2
• 2 ATP
• 6 NADH
• 2 FADH

Question 32

Stage 3 of Aerobic Cellular Respiration(Electron Transport Chain):

Answer 32

the third stage of aerobic cellular respiration where energy from the electrons unloaded by NADH and FADH2 generates a proton gradient, driving significant ATP production

- Located in the cristae(inner membrane)
- Produces the greatest amount of ATP, 34-36
    - Continually recycles the high energy enzymes NAD+ and FAD back into NADH and FADH2 to be able to use them again in glycolysis and the Krebs cycle

Inputs:

• 6 O2
• 26-28 ADP + 26-28 Pi
• 10 NADH
• 2 FADH2

Outputs:

• 6 H2O
• 26-28 ATP
• 10 NAD+ + 10 H+
• 2 FAD + 4 H+

Question 33

Link Reaction

Answer 33

• A reaction that links glycolysis and the Krebs cycle by transporting pyruvate to the mitochondria matrix to combine with coenzyme A to form acetyl-CoA
  - This reaction produces 1 CO2 as a waste product and NADH

Question 34

Process of Electron Transport Chain

Answer 34

1. NADH and FADH2 molecules unload protons and electrons at the first and second protein complexes through the reactions:
   
   • NADH -> NAD+ + H+ + 2 e-
   • FADH2 -> FAD + 2 H+ + 2 e-
   2. The excited released electrons are transferred through a number of different protein complexes powering the active transport of H+ from the mitochondrial matrix into the narrow intermembrane space
   3. This leads to a build up of protons in the intermembrane space creating a high concentration and in turn creating a steep concentration gradient across the inner mitochondrial matrix
   4. In order to move down the gradient, protons must travel through ATP synthase, specialised protein channels. As they move through, they cause the enzyme to spin creating kinetic energy which produces the reaction
      - ADP + Pi -> ATP
      Creating 26-28 ATP per glucose molecule
      5. This process can lead to lots of free protons and electrons building up in the matrix which if remaining unbound, can cause problems for cells in large concentrations. They can damage DNA, interfere with enzyme reactions and create dysfunctional proteins. This is prevented by O2 binding to the free electrons and protons to form harmless water

Question 35

Anaerobic Fermentation

Answer 35

a metabolic pathway that occurs in the absence of O2. Involves glycolysis, followed by further reactions that convert pyruvate into lactic acid in animals or ethanol and CO2 in yeasts

- The electron transport chain and Krebs cycle are disrupted under anaerobic conditions, losing a key source of ATP
- Consists of just glycolysis generating 2 ATP which recycles NADH from a steady supply of NAD+
- In order to rely indefinitely off glycolysis, cells need a way to convert NADH back to NAD+ without O2

Question 36

Lactic Acid Fermentation

Answer 36

the process of anaerobic fermentation in animals where pyruvate produced via glycolysis is converted to lactic acid

• C6H12O6 -> 2 C3H6O3 + 2 ATP

Question 37

Process of Lactic Acid Fermentation

Answer 37

• glycolysis occurs where glucose is broken down into two pyruvates
• causes at the same time ADP+Pi to resynthesize into ATP and causes NAD+ resynthesize into NADH
• the 2 pyruvates are then broken down further into 2 lactic acid molecules
• this process requires NADH to unload turning it into NAD+

Question 38

Ethanol Fermentation

Answer 38

the process of anaerobic fermentation in yeasts where pyruvate produced via glycolysis is converted to ethanol and carbon dioxide

• C6H12O6 -> 2 C2H5OH + 2 CO2 + 2 ATP

Question 39

Process of Ethanol Fermentation

Answer 39

• glycolysis occurs where glucose is broken down into two pyruvates
• causes at the same time ADP+Pi to resynthesize into ATP and causes NAD+ resynthesize into NADH
• the 2 pyruvates are then converted into 2 acetyl-CoA molecules producing 1 waste CO2 molecule
• the acetyl-CoA molecules are then converted into 2 ethanol molecules
• this process requires NADH to unload its high energy electrons turning it into NAD+

Question 40

Factors Affecting the Rate of Cellular Respiration

Answer 40

1. Temperature: cellular respiration will occur at the highest rate when the temperature aligns with the enzymes optimal temperature
2. pH Optimal levels for Aerobic Cellular Respiration
   - Cytoplasm(glycolysis) = 7.2
   - Mitochondrion Matrix(Krebs Cycle) = 7-7.4
   - Intermembrane space of the Mitochondrion = 7.8
3. As glucose is an input for ACR, increasing glucose will increase the rate up until the enzymes saturation point, conversely decreasing glucose will decrease the rate
4. as oxygen is an input for the ETC, increasing oxygen increases the rate up until the enzymes saturation point, conversely decreasing oxygen will decrease the rate

Question 41

Precision

Answer 41

How closely two or more measurements closely align with each other

• indicates your method is valid and reliable
• wide spread data means results are imprecise and data that is close together is precise

Discussion of Errors/improvements:
- what equipment could be changed

Question 42

Accuracy

Answer 42

How close is the measurement to the true value of the quantity being measured

• true value refers to the value obtained if you performed a perfect experiment

Discussion of Errors/improvements:

• what systematic errors could have occurred?
• was the equipment calibrated correctly?

Question 43

Validity

Answer 43

The measurement of the experiment actually testing what it is meant to test

• there can only be one IV and DV and all other variables must be accounted for

Discussion of Errors/improvements:

• were there any variables not controlled for
• improve by suggesting how to control for variable

Question 44

Reliability

Answer 44

a measurement, tool or experiment that produces similar results when repeated and can be trusted

Discussion of Errors/improvements:
- if not reliable, what potential random errors could have occurred

• how can the method be improved

Question 45

Personal Errors

Answer 45

Mistakes or miscalculations made by the experimenter

How to Avoid:
- repeat the experiment again

• get 2 or 3 people to help count if relying on human accuracy

Question 46

Systematic Errors

Answer 46

errors which cause results to differ from the true value by a consistent amount each time, due to faulty equipment

• affects the accuracy and cannot be minimized through replication

How to Avoid:
- recalibrate your equipment

Question 47

Random Errors

Answer 47

errors which are caused by unpredictable variations in the measurement process and result in an spread of readings

• reduce precision

How to Avoid:
- replicate experiments or increase sample size

• refine the measurement process
• use more precise equipment