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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
