PHOTOSYNTHESISChapter 3

INTRODUCTION

Plants, algae, some protists, some bacteria capture about 5% of Sun’s energy.

Absorb CO2, water, and radiant energy chemical potential energy (glucose)

PHOTOSYNTHETIC ORGANISMS

Plants, algae, some protists, and cyanpbacteria. Contain green-coloured pigment called

_____________________: absorbs light energy and begins the process of photosynthesis.

Chlorophyll a (blue-green) (contains –CH3) at position –R

Primary light-absorbing pigment Chlorophyll b (yellow-green) (contains –COH at

–R)

CHLOROPHYLL Contains a porphyrin ring

attached to a long HC tail. Porphyrin: contains a

magnesium atom at center surrounded by a HC ring with – and = bonds.

Delocalized electrons in single-double bonds absorb light energy.

Different functional groups affect type of light energy molecules can absorb.

PROKARYOTIC AUTOTROPHS: CYANOBACTERIA

“blue-green algae”: largest group of photosynthesizing prokaryotes. Evolved between 2.5 and 3.4 billion y.a.

Probably the first organisms to use sunlight in the production of organic compounds.

Produced oxygen: paved way for heterotrophic life on Earth.

Unicellular, but may grow in visible colonies

Live in oceans, freshwater lakes and rivers, rocks, and soil... And polar bear fur.

Rocks? Cyanobacteria + fungi lichens Cyanobacterial blooms: rapid-growing

colonies in water rich in nitrates and phosphates (fertilizer, detergent runoff from homes, farms, industry)

May be toxic to fish, birds, humans, and other mammals.

Produce toxin called microcystin.

EUKARYOTIC AUTOTROPHS: ALGAE, PHOTOSYNTHETIC PROTISTS, AND PLANTS

Endosymbiosis: ancestor of cyanobacteria engulfed by ancestor of today’s eukaryotic cells. Mutually beneficial relationship.

Cyanobacteria protected from harsh environment Eukaryotic host obtained food molecules from

bacterium Cyanobacteria lack membrane-bound

organelles: have infoldings of cell membrane used as sites of photosynthesis and respiration.

Algae, some protists, plant cells: Contain chlorophyll within chloroplasts.

Leaves, stems, unripened fruit: green! Chloroplasts: possible ancestors of

_______________.

LEAVES: PHOTOSYNTHETIC ORGANS OF PLANTS

Thin and broad, or thin and narrow Structure and arrangement on stems and

branches maximizes SA exposed to sunlight

Limits distance that gases need to travel to reach chloroplasts.

STRUCTURE OF LEAVES

Cuticle: waxy water-resistant coating Protection against excessive absorbtion of light and evaporation of water.

Epidermis: transparent Mesophyll: abundant with chlorplasts Guard cells: create microscopic openings called stomata

Regulate the exchange of CO2 and O2 with atmosphere Allow water to escape by transpiration

Vascular bundles: ‘veins’ Transport water and minerals from roots and leaves and carry carbs from leaves to

roots.

TRANSPIRATION AND PHOTOSYNTHESIS Stomata: responsible for more than 85% of

water lost by plant. Two ways transpiration assists in photosynthesis:

Creates ‘transpiration pull’ that helps move water, minerals, and other substances from roots leaves.

Prevents leaves from heating to temperatures that could inhibit or denature enzymes.

Stomata open and close depending on environmental conditions. Closed:________________________________ Open:_________________________________

OPENING AND CLOSING OF STOMATA

Guard cells control the size of a stoma by changing their shape in response to changes in environmental conditions.

Open: guard cells turgid (swollen) Day-time: when photosynthesis can occur

(light energy) need of CO2 (diffusion) and H2O (transpiration pull)

Closed: guard cells flaccid (limp) Night-time: when photosynthesis cannot occur

(limited light energy).

CHLOROPLASTS

Photosynthetic factories of plants and algae. Have own DNA and can replicate by fission.

Two-membranes Stroma: protein-rich semiliquid material in the ‘middle’ Thylakoids: membrane-bound sacs that form columns.

About 30-50 per... Grana: column of thylakoids.

About 60 in each chloroplast Lamallae: connection between thylakoids.

Thylakoid Lumen: inside of the thylakoid fluid-filled .

SEATWORK/HOMEWORK

Pg. 145 #1,2,3,4,5,6,7