photosynthesis

Photosynthesis

Charissa Pretorius

2

This presentation is re-purposed from various

sources, which will be

referenced.

This presentation is re-purposed from various

sources, which will be

referenced.

3

LIFE ON EARTH

ULTIMATELY DEPENDS ON

ENERGY

LIFE ON EARTH

ULTIMATELY DEPENDS ON

ENERGY

4

THE SUN IS THE MAIN SOURCE OF ENERGY FOR LIFE ON EARTHTHE SUN IS THE MAIN SOURCE OF ENERGY FOR LIFE ON EARTH

What is ENERGY?What is ENERGY? Some define it as the ability to

work.

In physics it is the capacity of the body or a system to do work.

e.g. Growth and repair, active transport across membranes, reproduction, synthesis, etc.

PHOTOSYNTESISPHOTOSYNTESIS

Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water.

6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2

Almost all plants are photosynthetic autotrophs, as are some bacteria and protists.

Cyanobacteria

Euglena

Kelp

Mosses, ferns, andflowering plants

Sites of Photosynthesis Sites of Photosynthesis

Photosynthesis occurs in

chloroplasts, organelles in certain plants.

All green plant parts have chloroplasts and carry out photosynthesis.

The leaves have the most chloroplasts

The green color comes from chlorophyll in the chloroplasts

The pigments absorb light energy

ChloroplastsChloroplasts

10 to 100 chloroplasts10 to 100 chloroplasts

Enclosed by a Enclosed by a double membrane double membrane phospholipid inner and outer phospholipid inner and outer membrane.membrane.

Outer and inner membranes:Outer and inner membranes:  protective protective coverings that keep chloroplast structures enclosed.coverings that keep chloroplast structures enclosed.

Intermembrane space between them inside the membrane is the stroma.

Stroma: Site of conversion of carbon dioxide to sugar.

Stroma contains stacks (grana) of thylakoids.

Thylakoid: Site of conversion of light energy to chemical energy.

Grana: Dense layered stacks of thylakoid sacs.

Sites of conversion of light energy to chemical energy.

Chloroplasts

Location and structure of

chloroplasts

(overview)

LEAF CROSS SECTION MESOPHYLL CELL

LEAF

Mesophyll

CHLOROPLAST Intermembrane space

Outermembrane

Innermembrane

Granum

Grana StromaStroma Thylakoid

Thylakoidcompartment

Chloroplast

THE GENERAL PROCESS OF

PHOTOSYNTHESIS

(RECAP)

The chlorophyll in the chloroplasts in green plants absorbs the sunlight.

The sunlight is combined with water, Carbon Dioxide and nutrients from the soil.

The chlorophyll processes the ingredients and makes sugar (plant food) and oxygen.

Cellular respiration converts sugar into ATP.

PHOTOSYNTESIS PROCESSPHOTOSYNTESIS PROCESS

Involves:

Light reaction - photosystem 1 & 2

Dark reaction - calvin cycle

Light Reactions (H2O O2

+ ATP + NADPH2)

Light Reactions (H2O O2

+ ATP + NADPH2)

Water splits, giving off oxygen.

Dependent on sunlight for activation.

Light is absorbed by chlorophyll a and “excites” the electrons in the chlorophyll molecule.

Electrons are passed through a series of carriers and ATP is produced.

Takes place in thylakoids.

Dark Reactions (ATP + NADPH2 + CO2 C6H12O6)

Dark Reactions (ATP + NADPH2 + CO2 C6H12O6)

Carbon dioxide is split, providing carbon to make sugars.

Glucose is the final product.

Does not require light energy.

Includes the Calvin Cycle.

Takes place in the stroma.

The Calvin Cycle The Calvin Cycle STEP 1

CO2 is diffused into the stroma.

An enzyme combines CO2 with a five-carbon carbohydrate called RuBP.

The resulting six-carbon molecule splits into a pair of three-carbon molecules called PGA.

STEP 2

Each PGA molecule receives a phosphate group from ATP.

It also receives a proton from NADPH and releases a phosphate group producing PGAL.

This produces ADP, NADP+, and phosphate which are used in Light Reactions.

STEP 3

Some PGAL is converted to RuBP to continue the cycle.

Some PGAL leaves the cycle to create organic compounds.

Each turn of the cycle fixes one CO2 molecule and it takes six turns to make one glucose molecule.

CHLOROPLAST

ECOLOGICAL

PRINCIPLE…

Why is Photosynthesis important?Why is Photosynthesis important?

It makes organic molecules (glucose) out of inorganic materials (carbon dioxide and water).

It begins all food chains/webs. Thus all life is supported by this process.

It also makes oxygen gas!!

Photosynthesis starts ecological food webs

FACTORs AFFECTING

PHOTOSYNTHESIS

Rate of Photosynthesis Rate of Photosynthesis Light intensity – as intensity increases the rate

increases and eventually levels off into a plateau.

Temperature

Water shortage

Increasing amount of CO2 increases rate of photosynthesis.

WATER SHORTAGEWATER SHORTAGE

Water is one of the raw materials of photosynthesis, a shortage of water can slow or even stop photosynthesis.

Plants that live in dry conditions, such as desert plants and conifers, have a waxy coating on their leaves that reduces water loss.

TEMPERATURETEMPERATURE

Temperatures above or below 0°C and 35°C may damage enzymes, slowing down the rate of photosynthesis.

Very low temperatures - photosynthesis may stop entirely.

Very high temperatures - enzymes are denatured.

Optimum temperature: 25oC to 35oC

Reference list

(re-purposed from...)

Himarangan, R. T. (2010). Photosynthesis. Retrieved March 4, 2014, from http://www.slideshare.net/rthimarangan/photosynthesis-6396725 Kaur, N. (2010). Photosynthesis. Retrieved March 4, 2014, fromhttp://www.slideshare.net/shasha007/photosynthesis-5367674 Khan, B. (2013). Photosynthesis. Retrieved March 4, 2014, fromhttp://www.slideshare.net/baberrkhan/photosynthesis-26127233?v=default&b=&from_search=7 Phan, T. (2009). Photosynthesis. Retrieved March 4, 2014, fromhttp://www.slideshare.net/tinaphan/photosynthesis-2604600 Pointer, K. (2011). Photosynthesis. Retrieved March 4, 2014, fromhttp://www.slideshare.net/coachpointer/photosynthesis-7346091