chloroplast structure and leaf adaptations

Photosynthesis #1

Learning objectives...•Link leaf structure to efficiency in photosynthesis

•Review chloroplast structure•Describe and explain the role of photosynthetic

pigments in light harvesting

Photosynthesis overview and chloroplast structure

• (d) state that in plants photosynthesis is a two-stage process taking place in chloroplasts;

• (e) explain, with the aid of diagrams and electron micrographs, how the structure of chloroplasts enables them to carry out their functions;

Stages of photosynthesis...

• Light harvesting

• Light independent

• Light dependent

Leaf adaptations…

Why might a plant be variegated?

Cross-section of a leaf

100 m

Mesophyll cells

How are chloroplasts positioned?

• http://www.saps.org.uk/secondary/teaching-resources/795-video-clip-chloroplasts-and-starch

Chloroplast structure…

a

hg f

e

dcb

Schematic chloroplast

sealed thylakoid membrane

membrane-enclosed stroma

Thylakoid membrane

• chlorophyll• light-harvesting• electron transfer

• O2 evolution

• energy production

Stroma

• Rubisco

• CO2 fixation

• sugar and starch synthesis

Peachloroplast

1 m

a) Membrane-bound sacs containing chlorophyll moleculesb) Liquid that contains a variety of photosynthetic enzymes and

starch grains.c) Stacks of membrane bounded, flattened, discoid sacs,

arranged like neat piles of coins.

A. ThylakoidsB. StromaC. Grana (1 granum)

Summary test...• Leaves are the main site of photosynthesis which occurs

mainly in the (1) cells. They have numerous (2) that allow exchange of gases between themselves and the air around them and a network of veins that make up the tissue (3) that brings water to the leaf and (4) that carries away (5) produced in photosynthesis. Chloroplasts are surrounded by a double membrane or (6) and possess both (7) and (8) that enable them to make their own proteins. Inside, there is a fluid-filled matrix called the (9) that carries out the (10) reaction and also contains structures like (11) grains and oil droplets. Within this matrix are disc-like structures called (12) stacked in groups called (13) where the (14) reaction of photosynthesis takes place.

Light is absorbed by individual chlorophylls in the light-harvesting complexes

Energy is transferred from one pigment to another via Resonance Energy Transfer

This transfer funnels the energy to a reaction centre

where electron transfer starts

Energy transfer in light-harvesting complexes