3.5 energy transfers in and between organisms

where does photosynthesis occur

in the chloroplasts of a leaf

adaptations of the leaf

• large surface area for maximum absorption of light

• leaves grow outwards not on top of each other for maximum absorbtion by all leaves

• thin for short diffusion pathway for substances

• long and narrow tightly packed upper mesophyll cells are packed with numerous chloroplasts

• numerous stomata for gas exchange

• stomata open and close to control water loss

• many airspaces in lower mesophyll to allow diffusion of CO2 and O2

• network xylem and phloem for transport of water and glucose

3 main stages of photosynthesis

1. capturing of light energy

2. light dependent reaction

3. light independent reaction

structure of chloroplasts

• disk shaped, 2-10 um long, 1 um wide

• double membrane

• grana = stacks of 100 thylakoids where light dependent reaction occurs

• thylakoids have tubular extensions that join up with thylakoids in adjacent grana

• stroma is a fluid filled matrix where light independent reaction occurs (starch grains also in Stroma)