Photosynthesis - Yr 2

Question 1

Glucose

Answer 1

C6H12O6 – a single sugar which is produced in photosynthesis.

Question 2

ATP

Answer 2

An activated nucleotide found in all living organisms, which is produced during respiration and acts as an energy carrier. ATP is produced during the light-dependent reaction of photosynthesis.

Question 3

Metabolism

Answer 3

the chemical processes that occur within a living organism in order to maintain life.

Question 4

Photosynthesis

Answer 4

A complex metabolic pathway involving many intermediate reactions. Some energy in light is conserved in the form of chemical bonds. There are three main stages: capturing the light energy, the light-dependent reaction and light-independent reaction.

Question 5

Photolysis

Answer 5

Light energy splits 2 water molecules into 4 electrons, 4 hydrogen ions (protons) and an oxygen molecule (light-dependent reaction). These electrons replace the electrons lost from a chlorophyll molecule when light strikes it.

Question 6

Oxidation

Answer 6

Loss of electrons or loss of hydrogen or gain of oxygen with a substance

Question 7

Reduction

Answer 7

Gain of electrons or gain of hydrogen or loss of oxygen from a substance

Question 8

Co-enzyme

Answer 8

A non-protein compound that is necessary for the functioning of an enzyme. (NOT AN ENZYME!) Play a huge role in photosynthesis and respiration where they carry hydrogen atoms from one molecule to another. E.g. NAD, FAD and NADP.

Question 9

NADP

Answer 9

An electron carrier that is important in photosynthesis. When it takes up protons the NADP becomes reduced.

Question 10

NADPH

Answer 10

Reduced NADP – it is the main produced of the light-dependent stage and it enters the light-independent reaction taking with it the electrons from the chlorophyll molecules.

Question 11

Chloroplast

Answer 11

Reduced NADP – it is the main produced of the light-dependent stage and it enters the light-independent reaction taking with it the electrons from the chlorophyll molecules.

Question 12

Thylakoid

Answer 12

Disc like structures which make up the grana in stacks of up to 100. Where the light-dependent stage of photosynthesis takes place. They contain the photosynthesis pigment chlorophyll. Some may have tubular extensions (intergranal lamellae) which join up with thylakoids in adjacent grana.

Question 13

Stroma

Answer 13

Fluid-filled matrix where the light-independent stage of photosynthesis takes place.

Question 14

Chlorophyll

Answer 14

Photosynthetic pigment inside thylakoids which absorbs light energy. Can become ionisied.

Question 15

Light-dependent reaction

Answer 15

Stage of photosynthesis in which light energy is required to produce ATP and reduced NADP

Question 16

Photoionisation

Answer 16

Process by which a chlorophyll molecule becomes ionised. Caused by the chlorophyll molecule absorbing light energy and boosting the energy of a pair of electrons within a chlorophyll molecule, raising them to a higher energy level and they become so energetic they leave the chlorophyll molecule altogether and are taken up by an electron carrier.

Question 17

Thylakoid membrane

Answer 17

Contains a transfer chain where electrons are passed along a number of electron carriers in a series of oxidation-reduction reactions. Where chemiosmotic theory happens – ATP is made.

Question 18

Proton pumps

Answer 18

A protein which actively transports protons into the thylakoid using energy from electrons from chlorophyll. They mean a concentration gradient of protons is maintained across the thylakoid membrane with a high concentration inside the thylakoid space a low concentration in the stroma.

Question 19

Electron carrier transfer chain

Answer 19

How electrons are passed along a number of electron carriers in a series of oxidation-reduction reactions. Each new carrier is at a slightly lower energy level than the previous one in the chain, and so the electrons lose energy at each stage, which is used to combine an inorganic phosphate molecule with an ADP molecule to make ATP.

Question 20

Chemiosmotic theory

Answer 20

Mechanism by which ATP is produced in the light-dependent stage of photosynthesis. How it works is that protons are pumped from the stroma using proton pumps in the thylakoid membrane. The energy to drive this process comes from electrons released when photolysis of water happens. The photolysis of water also produces protons which further increase their concentration inside the thylakoid space. A concentration gradient of protons is therefore maintained across the thylakoid membrane with a higher concentration inside the thylakoid space and lower concentration in the stroma. Protons can only cross the thylakoid membrane through ATP synthase channel proteins and when they pass through they cause changes to the structure of the enzyme which then catalyses the combination of ADP with inorganic phosphate to form ATP.

Question 21

ATP synthase

Answer 21

An enzyme which is embedded in the thylakoid membrane through which protons pass through and cause changes to the structure of the enzyme which then catalyses the combination of ADP with inorganic phosphate to form ATP.

Question 22

Light-independent reaction

Answer 22

Stage of photosynthesis which does not require light energy directly, but does need the products of the light dependent reaction to reduce CO2 and form carbohydrate

Question 23

Calvin cycle

Answer 23

A biochemical pathway (part of the light-independent reaction) where CO2 is reduced to form carbohydrate. It takes 6 turns of the Calvin cycle (6 CO2, 18 ATP and 12 NADPH) to make one hexose sugar (because 1/6 molecules of TP are used to make useful substances e.g. glucose and 5/6 molecules of TP are used to make RuBP).
1 CO2 (1C) + 1 RuBP (5C)  2 GP (2 x 3C) + (2 NADPH + 2 ATP) 2 TP (2 x 3C)  Glucose (6C) or RuBP (needs 1 ATP to make RuBP) (5C)

Question 24

Ribulose bisphosphate (RuBP)

Answer 24

A 5 carbon sugar (in the Calvin cycle) which reacts with carbon dioxide in the stroma to produce two molecules of GP. This reaction is catalysed by rubisco (ribulose biphosphate caryboxylase).

Question 25

Glycerate 3 phosphate (GP)

Answer 25

A 3 carbon acid (in the Calvin cycle) which reduced NADP is used to reduce to TP using energy supplied by ATP.

Question 26

Triose Phosphate (TP)

Answer 26

A 3 carbon sugar (in the Calvin cycle) which can be converted to organic substances that the plant requires such as starch, cellulose, lipids, glucose, amino acids and nucleotides, but most are used to regenerate ribulose biphosphate using ATP from the light-dependent reaction.

Question 27

Limiting factor

Answer 27

A variable that limits the rate of a chemical reaction