Photosynthesis

Ch. 8

Photosynthesis• Occurs in the Chloroplast • Photosynthesis = building glucose by using

the sun’s energy• Requires sunlight, water, CO2, chlorophyll, • Makes glucose (chemical energy) and oxygen

(waste product)

(chlorophyll) (released)6CO2 + 6H2O + Light C6 H12 O6 + 6O2

REACTANTS PRODUCTS

Composed of 2 main reactions• 1. Light-Dependent Reaction

– The “light” phase– Light energy (electromagnetic) is

absorbed by pigments in the thylakoids

– The light excites the electrons in the thylakoids and energy is transferred to the chlorophyll and photosynthesis can begin

1. Light-Dependent Reaction cntd.• Electrons continued to be made but

how?•The water that was absorbed from the roots and needed for photosynthesis is broken down here.

•The Hydrogen ions are used and the Oxygen atoms are released

• Chemical energy has now been made (some ATP and NADPH)

2. Light Independent

• The “synthesis” phase• Also know an the Calvin cycle or Dark

Reaction

• Makes glucose from CO2 and H

• Occurs in the stroma

• The CO2 and NADPH created in the Light Reaction is now converted into Glucose.

Thylakoids

H2O

e H2 \ O

NADP + H2

C6H12O6

CO2

Stroma

Chloroplast

Factors Affecting Photosynthesis • Light Intensity

– As light intensity increases, photosynthesis increases

• Carbon Dioxide– As CO2 increases, photosynthesis

increases• Temperature

– All chemical reactions are dependent on temperature

2 Concerns for plants

• Getting water & Getting water & keepingkeeping water. water.• Plants developed roots in order to Plants developed roots in order to

get water and they developed a get water and they developed a cuticle to keep water in the leaves.cuticle to keep water in the leaves.– CuticleCuticle: waxy covering that : waxy covering that

surrounds the leaf and reduces surrounds the leaf and reduces transpiration.transpiration.

TranspirationTranspiration

• Water loss by plants.Water loss by plants.• Cuticle was a good AND bad thing Cuticle was a good AND bad thing

because how will plants get CObecause how will plants get CO2 from from the atmosphere?the atmosphere?

StomataStomata

• Solved the problem!Solved the problem!• A stomata is a A stomata is a holehole on the underside on the underside

of a leaf that allows gas exchange. It of a leaf that allows gas exchange. It is surrounded by is surrounded by guardguard cells. cells.

Plants need water for 2 Plants need water for 2 reasons:reasons:• For photosynthesis and plumps guard For photosynthesis and plumps guard

cells – open up and allow for gas cells – open up and allow for gas exchange.exchange.

• LowLow water, guard cells may keep stomata water, guard cells may keep stomata closed.closed.

• Stomata are open during the day when Stomata are open during the day when photosynthesis is happening.photosynthesis is happening.

• Stomata are closed at Stomata are closed at nightnight when when photosynthesis is not happening (& to photosynthesis is not happening (& to reduce transpiration.)reduce transpiration.)

How fast does a plant photosynthesise? This question is very important to farmers and growers.

We can use this apparatus to measure the rate of photosynthesis. How?

We might count the oxygen bubbles per minute, or collect the gas given off in one minute and measure its volume.

What would happen if we increased the light level?

light source

oxygen collects

test tube

water

pondweed (Elodea)

beaker

funnel

Here are some results from the pondweed experiment.

What effect does light have on the rate of photosynthesis?

What would happen if we put a layer of oil on the water?

light level bubbles of oxygen per minute

very high 24

high 22

medium 15

low 7

very low 0

This stops carbon dioxide from the air dissolving in the water.

The Energy Currency for the cell is

___

How well did you do today?

Where does photosynthesis take place?

A. Chlorophyll

B. Chloroplast

C. Stroma

D. Thylakoids