17 Photosynthesis

Question 1

what is the formula for photosynthesis?

Answer 1

6CO2 + 6H2O —-> C6H12O6 + 6O2

Question 2

what is photosynthesis?

Answer 2

THE PROCESS BY WHICH LIGHT ENERGY IS USED TO SYNTHESISE COMPLEX ORGANIC MOLECULES (GLUCOSE) FROM SMALL INORGANIC MOLECULES (CARBON DIOXIDE AND WATER) WITH A BY-PRODUCT OF OXYGEN ALSO PRODUCED

Question 3

what is the name for an organism that can photosynthesise and define what it does

Answer 3

A PHOTOAUTOTROPH EG. PLANTS AND ALGAE,
IT CAN SYNTHESISE ITS OWN FOOD BY CAPTURING LIGHT ENERGY FROM THE SUN TO SYNTHESISE ORGANIC MOLECULES FOR USE IN CELLULAR FUNCTIONS EG. RESPIRATION AND BIOSYNTHESIS

Question 4

what is an heterotrophic organism?

Answer 4

AN ORGANISM THAT OBTAINS COMPLEX ORGANIC MOLECULES BY EATING OTHER HETEROTROPHIC OR AUTOTROPHIC ORGANISMS. DURING RESPIRATION, THE COMPLEX ORGANIC MOLECULES (GLUCOSE) ARE BROKEN DOWN TO RELEASE ENERGY AS ATP FOR METABOLIC REACTIONS

Question 5

what are the two stages of photosynthesis?

Answer 5

THE LIGHT-DEPENDENT STAGE AND THE LIGHT-INDEPENDENT STAGE

Question 6

summarise the two stages of photosynthesis

Answer 6

THE LDS: ABSORBING LIGHT ENERGY, SYNTHESISING ATP AND PRODUCING NADPH
THE LIS: SYNTHESISING CARBOHYDRATES USING THE PRODUCTS FROM THE LDS

Question 7

where do the two stages of photosynthesis take place?

Answer 7

LDR: GRANA/THYLAKOID MEMBRANES
LIR: STROMA

Question 8

what is a photosystem?

Answer 8

A COLLECTION OF PHOTOSYNTHETIC PIGMENTS, LOCATED IN THE THYLAKOID MEMBRANE, ANCHORED BY PROTEINS

Question 9

describe the structure of a photosystem

Answer 9

1. FUNNEL/ANTENNA COMPLEX CONTAINING ACCESSORY PIGMENTS, WHICH HAVE NO PORPHYRIN RING
   2.

Question 10

what are the roles of the antenna complex and the PPRC?

Answer 10

AC: ABSORB DIFFERENT WAVELENGTHS OF LIGHT AND TRANSFER THIS LIGHT ENERGY EFFICIENTLY AND RAPIDLY TO THE PPRC
NOT DIRECTLY INVOLVED IN LDR.

Question 11

what are the steps in the LDR?

Answer 11

1. Mg2+ ATOM IN PORPHYRIN RING OF CHL A IS EXCITED IF CORRECT WAVELENGTH OF LIGHT STRIKES, EXCITING 2 ELECTRONS WHICH ARE ACCEPTED BY AN ELECTRON ACCEPTOR.
2. THE 2 EXCITED ELECTRONS ARE PASSED DOWN PROTEINS AT SEQUENTIALLY LOWER ENERGY LEVELS IN THE ETC BY ELECTRON CARRIERS.
3. THE ELECTRONS LOSE ENERGY AS THEY ARE PASSED DOWN THE CHAIN OF ELECTRON CARRIERS, AND THE ENERGY RELEASED IS USED TO SYNTHESISE SOME ATP BY PROCESS OF CHEMIOSMOSIS.
4. MEANWHILE, LIGHT HAS ALSO STRUCK PSI AND TWO EXCITED ELECTRONS ARE ACCEPTED BY AN ELECTRON ACCEPTOR, LEAVING ROOM FOR THE ORIGINAL TWO ELECTRONS FROM PSII TO BE ACCEPTED BY PSI.
   5.

Question 12

what is the structure of a chlorophyll molecule?

Answer 12

A LONG PHYTOL/HYDROCARBON CHAIN AND A PORPHYRIN GROUP SIMILAR TO A HAEM GROUP, BUT MG2+ ATOM INSTEAD OF AN FE3+ ATOM

Question 13

what are accessory pigments, give examples, where are they found, which colours do they reflect

Answer 13

A NON-CHLOROPHYLL PIGMENT INSIDE THE CHLOROPLAST OF PHOTOSYNTHETIC ORGANISMS, THAT HELPS IN ABSORBING OTHER LIGHT ENERGY ESSENTIAL DURING THE LIGHT REACTIONS OF PHOTOSYNTHESIS

FOUND IN THE FUNNEL/ANTENNAE COMPLEX OF A PHOTOSYSTEM

CHL B- absorbs blue light below 500nm and red light at 640nm- AND CAROTENOID PIGMENTS SUCH AS CAROTENE- ORANGE -AND XANTHOPHYLL- YELLOW

Question 14

describe photorespiration

Answer 14

STOMATA CLOSE WHEN TEMPERATURE IS HIGH AND HUMIDITY IS LOW TO PREVENT WATER LOSSS THROUGH TRANSPIRATION
ENTRY OF CO2 PREVENTED, INSIDE LEAF CO2 CONC DECREASES, O2 CONC INCREASES
OXYGEN COMPETITIVELY INHIBITED BY RUBISCO
2-PHOSPHOGLYCOLATE (2C) PRODUCED INTEAD OF GP (3C) WHICH IS TOXIC AND CONVERTED TO OTHER ORGANIC MOLECULES USING ATP