Energy transfers in and between organisms

Question 1

What is the simple explanation of photosynthesis?

Answer 1

Energy from light is used to make glucose from H2O and CO2.

Question 2

What is the overall equation for photosynthesis?

Answer 2

6CO2 + 6H2O + energy ——> C6H12O6 + 6O2

Question 3

Energy is stored in glucose until plants release it by…

Answer 3

…respiration.

Question 4

What are the two types of respiration?

Answer 4

Aerobic respiration, using oxygen

Anaerobic respiration, not using oxygen.

Question 5

What is the overall equation for aerobic respiration?

Answer 5

C6H12O6 + 6O2 ——> 6CO2 + 6O2 + energy

Question 6

Anaerobic respiration in plants and yeast produces _______ and ______ _______ and releases energy

Answer 6

Ethanol

Carbon dioxide.

Question 7

In humans, anaerobic respiration produces ______ and releases energy.

Answer 7

Lactate.

Question 8

What is ATP?

What does an ATP molecule consist of?

Answer 8

Adenosine triphosphate. ATP carries energy around the cell by diffusing through the cell to wherever it’s needed.
An ATP molecule consists of a ribose sugar, an adenine base and three phosphate groups.

Question 9

What type of reaction synthesises ATP from ADP and Pi? What enzyme catalyses the synthesis of ATP? Where is the energy in ATP stored?

Answer 9

ATP is formed by a condensation reaction between ADP and an inorganic phosphate, which is catalysed by ATP synthase. The energy is stored as chemical energy in the phosphate bonds.

Question 10

What happens to ATP when its energy needs to be released?

Answer 10

ATP is hydrolysed into ADP and Pi in a hydrolysis reaction catalysed by ATP hydrolase. Chemical energy is released from the phosphate bond and used by the cell. The ADP and Pi are recycled and the process can restart.

Question 11

What are 6 properties of ATP that make it a good energy source?

Answer 11

• ATP stores and releases a small manageable amount of energy, so no energy is wasted as heat.
• ATP is a small, soluble molecule so it can be easily transported around a cell.
• ATP is easily broken down, so energy can be released instantaneously.
• ATP can be quickly remade.
• ATP can make other molecules more reactive by transferring one of its phosphate groups to them (phosphorylation).
• ATP can’t pass out of a cell, so the cell always has an immediate supply of energy.

Question 12

Whats a metabolic pathway?

Answer 12

A series of small reactions controlled by enzymes.

Question 13

Define metabolism.

Answer 13

The chemical processes that occur within living cells or organisms that are necessary for the maintenance of life. In metabolism, some substances are broken down to release energy for vital processes, while other substances, necessary for life, are synthesised.

Question 14

What is photophosphorylation?

Answer 14

Adding a phosphate group to a molecule using light energy.

Question 15

What is photoionisation?

Answer 15

When light energy ‘excites’ electrons in an atom or molecule, giving them more energy and causing them to be released. The release of electrons causes the atom or molecule to become a positively-charged ion.

Question 16

Define hydrolysis.

Answer 16

The splitting of a molecule using a molecule of water.

Question 17

Define decarboxylation.

Answer 17

The removal of carbon dioxide from a molecule.

Question 18

Define dehydrogenation.

Answer 18

The removal of hydrogen from a molecule.

Question 19

What is a coenzyme?

Answer 19

A molecule that aids the function of an enzyme.

Question 20

How do coenzymes work?

Answer 20

They work by transferring a chemical group from one molecule to another.

Question 21

Name a coenzyme used in photosynthesis.

Answer 21

NADP- Nicotinamide adenine dinuceotide phosphate.

Question 22

How does NADP work as a coenzyme?

Answer 22

NADP transfers hydrogen from one molecule to another, meaning it can reduce (give hydrogen to) or oxidise (remove hydrogen from) a molecule.

Question 23

Name 3 coenzymes used in respiration.

Answer 23

NAD- Nicotinamide adenine dinucleotide
FAD- Flavin adenine dinucleotide
Coenzyme A

Question 24

What are the roles of NAD and FAD in respiration?

Answer 24

NAD and FAD transfer hydrogen from one molecule to another, meaning they can reduce or oxidise a molecule.

Question 25

What is the role of coenzyme A in respiration?

Answer 25

Coenzyme A transfers acetate between molecules.

Question 26

In what part of plant cells does photosynthesis take place?

Answer 26

The chloroplasts.

Question 27

What are chloroplasts?

Answer 27

Flattened organelles surrounded by a double membrane. They have thylakoids (fluid-filled sacs) stacked up in the chloroplast into structures called grana. The grana are linked together by pieces of thylakoid membrane called lamellae.

Question 28

Name 3 photosynthetic pigments found in chloroplasts.

Answer 28

Chlorophyll a
Chlorophyll b
Carotene

Question 29

What are photosynthetic pigments?

Where are they found?

Answer 29

Coloured substances that absorb the light energy needed for photosynthesis. The pigments are found in the thylakoid membranes attached to proteins.

Question 30

What are photosystems?

Answer 30

Chlorophyll-protein complexes that sit on the thylakoid membranes in chloroplasts. In each photosystem there’s a central, primary pigment surrounded by several hundred other pigment molecules referred to as accessory pigments. The various accessory pigments absorb light of all different wavelengths and pass the energy down the photosystem to the primary pigment, which acts as the reaction centre.

Question 31

Where does the light dependent stage of photosynthesis occur?

Answer 31

The thylakoid membranes.

Question 32

What is the first step of the LDR?

Answer 32

Light energy is absorbed by photosystem II. This light energy excites electrons in chlorophyll so the electrons move to a higher energy level. These high-energy electrons are then released from PSII chlorophyll and move down the electron transport chain to PSI.

Question 33

Photosystems are linked by electron carriers. What are these?

Answer 33

Proteins that transfer electrons.

Question 34

The photosystems and electron carriers form an electron transport chain. What is an ETC?

Answer 34

A chain of proteins through which excited electrons flow.

Question 35

What happens after the excited electrons leave PSII?

Answer 35

The excited electrons that have left PSII must be replaced. Light energy splits water into protons (H+), electrons (e-) and oxygen by photolysis.
H2O ——> 2H+ + 1/2O2

Question 36

What happens with the excited electrons that left PSII?

Answer 36

The excited electrons lose energy as they move down the electron transport chain. This energy is used to actively transport protons into the thylakoid so that the thylakoid has a higher concentration gradient of protons than the stroma. This forms a proton gradient across the thylakoid membrane.

Question 37

What happens as result of the formation of the proton gradient between the thylakoid and the stroma?

Answer 37

Protons move down their concentration gradient into the stroma by facilitated diffusion through ATP synthase embedded in the membrane. The energy from this movement combines ADP with inorganic phosphate (Pi) to form ATP.

Question 38

How is reduced NADP generated in photosynthesis?

Answer 38

Light energy is absorbed by photosystem I, which excites the electrons again to an even higher energy level. Finally, the electrons are transferred to NADP, along with a proton (H+) from the stroma, to form reduced NADP.

Question 39

What is chemiosmosis?

Answer 39

The process of electrons flowing down the electron transport chain and creating a proton gradient across the thylakoid membrane to drive ATP synthesis

Question 40

What is cyclic photophosphorylation?

Answer 40

Cyclic photophosphorylation only uses PSI. It’s called ‘cyclic’ because the electrons from the chlorophyll molecule aren’t passed onto NADP, but are passed back to PSI via electron carriers. This means the electrons are recycled and repeatedly flow through PSI. This process doesn’t produce and reduced NADP or O2, it only produces small amounts of ATP.

Question 41

What is another name for the light independent reaction of photosynthesis (LIR)?

Answer 41

The Calvin cycle

Question 42

Where does the LIR of photosynthesis take place?

Answer 42

The stroma of the chloroplasts.

Question 43

What are the products of the LIR?

Answer 43

Triose phosphate and RuBP- ribulose biphosphate (a 5 carbon compound). Triose phosphate can be used to make glucose and other useful substances.

Question 44

What is the first step of the Calvin cycle?

Answer 44

Carbon dioxide is combined with ribulose biphosphate to form 2 molecules of gylcerate 3-phosphate.
CO2 enters the leaf through stomata and diffuses into the stroma of the chloroplast. Here, it is combined with ribulose biphosphate (RuBP)(5C). This reaction is catalysed by the enzyme rubisco. This gives an unstable 6-carbon compound which quickly breaks down into 2 molecules of a 3-carbon compound called glycerate 3-phosphate.

Question 45

What is the second step of the Calvin cycle, after 2 molecules of glycerate 3-phosphate are formed?

Answer 45

ATP and reduced NADP are required for the reduction of GP to triose phosphate.
The hydrolysis of ATP from the LDR provides energy to turn the GP (3C) into a different 3-carbon compound called triode phosphate (TP). This reaction also requires H+ ions, which come from reduced NADP (from LDR). Reduced NADP is recycled to NADP.

Question 46

What happens with the triose phosphate formed from GP?

Answer 46

Some triose phosphate is then converted into useful organic compounds like glucose and some continues in the Calvin cycle to regenerate RuBP.
5 out of every 6 molecules of TP produced in the cycle aren’t used to make hexose sugars, but to regenerate RuBP. Regenerating RuBP uses the rest of the ATP produced by the LDR.