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

The light reaction

• Light energy is being converted to chemical energy in the form of ATP and a reduced electron carrier (NADPH + H+)

Light Reactions

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. 10.8

(A) When a molecule absorbs the energy of a photon, it is raised from a ground state to an excited state. (B) In the excited state, an electron is boosted to a more distant shell, where it is held less firmly.

Fig. 10.6

Energy Transfer and Electron Transport  - Rather than being lost as fluorescence, energy from a photon may be transferred from one pigment molecule to another. In an antenna system, an excited pigment molecule can transfer energy through a series of other pigment molecules to a pigment molecule in the reaction center. That molecule may become sufficiently excited that it gives up its excited electron, which can then be passed on to an electron acceptor.

Chlorophyll

• Absorbs light and excites electrons• Passes those electrons to an

electron acceptor: NADP+ (nicotinamide adenine dinucleotide phosphate)

NADP+ + e− → NADPH + H+

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 Phosphate

NADP+ accepts a pair of high energy electrons and a Hydrogen ion to become NADPH

• light-independent reactions do not use light directly, but instead use ATP, NADPH + H+ (made by the light reactions), and CO2 to produce sugars. There are three different forms of the light-independent pathway that reduces CO2: the Calvin cycle, C4 photosynthesis, and crassulacean acid metabolism.

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