How does a seed grow into a tree? Where does all the mass come from???

Photosynthesis

• Plants convert the energy of sunlight into the energy of chemical bonds of carbohydrates

Importance of Photosynthesis

But that’s not all..

But wait, there’s more..

Photosynthesis:

6 CO2 + 6 H2O C6 H12 O6 + 6 O2

carbon dioxide + water = sugar + oxygen

STARCH

photosynthetic products often stored as starch•Starch = glucose polymer

CO2+H20 C(H2O)+ O2

Photosynthesis

Respiration

Sun

The BIG Picture

Leaf Structurecuticle - waxy, water resistant layer on

the surface of the leaf

Epidermis - transparent, colourless cell layer below the cuticle

mesophyll cells - pallisade: are elongated cells located just below the epidermal tissue

- spongy mesophyll consists of loosely packed cells where gas exchange takes place

Fig. 10.2a

Leaf structure

Chloroplasts

Fig. 10.2b

Chloroplasts• plant cell organelles where photosynthesis

takes place, found mainly in mesophyll layers in leaves

• have an inner and outer membrane

• the liquid material in the chloroplast is called the stroma

• Stroma contains a series of membrane bound sacs called thylakoids which are stacked on top of one another to form grana

• adjacent grana are linked together by lamellae

• Photosynthesis occurs partly within the stroma and partly within the thylakoid membrane

• The thylakoid membrane contains light-gathering pigments and an electron transport chain

• Thylakoid membranes enclose an interior space called the thylakoid lumen

Overview of Photosynthesis

1. Light reactions2. Dark reactions – Calvin Cycle

Fig. 10.4

• When light strikes an object it can be:1) Reflected2) Transmitted3) Absorbed

• Substances that absorb light are called pigments

• Different pigments absorb at different wavelengths

Pigments

Chlorophyll

• Chlorophyll is a pigment that absorbs in the red and blue regions of the visible spectrum

• Most of the green wavelengths are reflected so a sample of chlorophyll appears green

Chlorophyll

•Absorbs red & blue light

•Reflects green light

Fig. 10.6

Fig. 10.8

Energy Storing Compounds

Energy trapped by molecules can be used to lift electrons to a higher energy level.

From that higher energy level the electrons can fall down to their original energy level and do work along the way.

Example – a solar cell that powers a calculator

Or…

The high-energy electrons can be bound to an electron carrier.

Nicotinamide Adenine Dinucleotide PhosphateNADP+ accepts a pair of high energy electrons

and a Hydrogen ion to become NADPH

And of CourseATP – Adenosine TriphosphateEnergy storing compound used by every

living cellProvides the energy for almost all cellular

functions

Function of ATP

Light Reactions

Calvin CycleProducts from the light reactions and CO2

from the atmosphere are used to produce carbohydrates

Autotrophs• Self-feeders:

– sustain themselves without eating or decomposing other organisms

• Plants are photoautotrophs– They use light

• Some bacteria are chemoautotrophs– Produce organic compounds

without light from substances such as S or NH3

Heterotrophs

• Live on compounds produced by other organisms

• Eat other plants or animals or are decomposers (bacteria or fungi) that eat fallen leaves, feces, dead animals