Photosynthesis

• light energy is converted into chemical energy

• large organic molecules are made from inorganic substances

• provides chemical energy for consumers and decomposers

• provides oxygen for respiration

• occurs in chloroplasts inside the leaves of photosynthesis

Autotrophs

Organisms that use light energy or chemical energy and inorganic molecules (carbon dioxide and water) to synthesise complex organic molecules

Heterotrophs

Organisms that indigest and digest complex organic molecules, releasing the chemical potential energy stored in them

Autotrophs

Heterotrophs

Do they respire

yes

no

Can they synthesise complex organic molecules from simple inorganic molecules

yes

no

Do they use light energy

yes

no

Can they hydrolyse complex organic molecules

yes

yes

examples

Plants/algae

Animals/fungi

Organisms that used respiration first developed when oxygen in the atmosphere first appeared after being released from photosynthesis. The endocrine theory suggests the photosynthetic bacteria were acquired possibly by endocytosis by early eukaryotic cells, to form the first algal or plant cells.

• 2-10

• surrounded by a double membrane

• outer membrane is permeable to many ions

• inner membrane Is less permeable . Is folded into lamalle. Each stack of a lamelle= a granum

• inter membrane space is 10-20 mm

Stroma- fluid filled matrix. Where the light independent rections take place

Grana- flattened sacs called thylakoids. The site of light absorption and ATP synthesis during light dependant reactions

Are molecules that absorb light energy. Each pigment absorbs a range of wavelengths in the visible region and has its own distinct peak of absorption. Other wave length are reflected.

They appear as the colour they are reflecting.

They are held in the thylakoid membrane arranged in funnel shaped structures called photo-stems

• P680+ P700= 2 forms of chlorophyll

  Both absorb red light and appear yellow and green

• P680- in photo stems II- peak absorption 680nm

• P700- in photo-stems I- peak absorption 700nm

  Both also absorb blue light (450nm)

• Chlorophyll b absorbs light at 500nm and 640nm and appears blue-green

• phytol (hydrocarbon tail)

• prophyrin group- similar to what haem has

• magnesium atom instead of iron

• light energy excites a pair of electrons associated with magnesium

Inner membrane with transport proteins

Control entry and exit of substances between the cytoplasm and stroma inside the chloroplasts

Many grana

Provide a large surface area for photosynthetic pigments, electron carriers and ATP synthase enzymes all in which are involved in the light dependant reaction

Photosynthetic pigments arranged in photo-stems

Allow maximum absorption of light energy

Proteins embedded in the grana

Hold photostems in place

Fluid filled stroma

Contain enzymes needed to catalyse the reactions of the light independent stage of photosynthesis

• Caratenoids absorb blue light- carotene is orange and xanthophyll is yellow

• not directly involved in the light dependant reaction

• absorb wavelengths that are poorly absorbed by chlorophylls and pass the light energy to chlorophyll a