Photosynthesis

Question 1

Autotrophs

Answer 1

• producer
• Is an organism that makes complex organic compounds (food) from inorganic molecules using energy (chemical or light)
• A photoautotroph makes its own food using light energy and inorganic materials (carbon dioxide, water and minerals) by some bacteria, and some Protista

Question 2

Heterotrophs

Answer 2

• consumer
• an organism that cannot make inorganic compounds from inorganic sources. It needs a ready made supply of organic compounds (carbon compounds)
• Heterotrophs obtain their organic compounds by consuming other organisms. Almost all animals, fungi and some Protista and bacteria

Question 3

Compensation point

Answer 3

When both photosynthesis and respiration are taking place at the same rate.
- there is no net loss or gain of carbohydrates

Question 4

Compensation period

Answer 4

The time at which it takes for the plant to reach the compensation point
- varies between species

Question 5

Evolution of chloroplast

Answer 5

Believed that photosynthetic bacteria were acquired by eukaryotic cells by endocytosis to produce the first algae/plant cell
- this is called endosymbiont theory

Question 6

Size of chloroplast

Answer 6

Between 2-10um (length)

Question 7

Structure of a chloroplast

Answer 7

double membrane
- outer membrane highly permeable, inner membrane less permeable and has transport proteins embedded in it

thylakoids and lamella
- inner membrane is folded into lamellae AKA thylakoids
- thylakoids are staked into piles called grana
- Intergranal lamellae link different stacks of thylakoids / Grana

grana
- first stage of photosynthesis takes place (LDS)
- creates large SA for: distribution of photosystems that contain pigment to trap light, electron carriers and ATP synthase needed for LDS

stroma
- products made in LDS can pass into the stroma to be used in LIS

Question 8

How are photosynthetic pigments arranged

Answer 8

Photosystems in thylakoid membranes
- absorb certain wavelengths of light
- reflect other wavelengths (colours we see)

Question 9

Chlorophyll a

Answer 9

• primary pigment reaction centre

2 forms:
- P₆₈₀ in PS2
- P₇₀₀ in PS1

• appears blue-green
• absorbs red light
  contains a magnesium atom- when light hits this, a pair of electrons become excited

Question 10

Accessory pigments

Answer 10

chlorophyll b
- absorbs light at wavelengths between 400-500 and 640nm
- It appears yellow-green

carotenoids
- absorbs blue light of wavelengths 400-500nm
- Reflects yellow and orange light

xanthophyll
- absorb blue and green light (370-550nm) and reflect yellow

Question 11

Cyclic photophosphorylation (LDS)

Answer 11

1. Light hits accessory pigments and transfer energy to primary pigment (or hits primary pigment)
   - photolysis occurs where water is split into O₂ and H⁺ ions. Oxygen is given off as a waste product (the H⁺ ions move down the electrochemical gradient in chemiosmosis)
2. Primary pigment reaction centre emits 2 excited electrons from PS2 to the ETC
3. 2 electrons travels down the ETC, losing energy which is used to form ATP
4. At the same time as 2 electrons are given off from PS2, 2 electrons are emitted from PS1 and combine with NADP and hydrogen ions to form reduced NADP

Question 12

LDS: non-cyclic photophosphorylation

Answer 12

1. Light hits water and splits it into oxygen and hydrogen ions (O₂ given off as waste product) PHOTOLYSIS
2. As light hits PS2, 2 electrons are excited and emitted and move down an ETC, gradually losing energy to produce ATP
3. At the same time, light strikes PS1 and 2 electrons are excited and emitted down an ETC
4. The electrons combine with NADP and the H⁺ ions to form reduced NADP

Question 13

Where does the Light Dependent Stage occur

Answer 13

Thylakoid membrane

Question 14

Where does the light independent stage occur

Answer 14

Stroma

Question 15

LDS: cyclic photophosphorylation