Unit 6

Purpose of Photosynthesis

To convert solar/light energy into chemical energy (glucose)

Formula of Photosynthesis

**6**CO__2__ + **6**H__2__O + light energy → C__6__H__12__O__6__ + 6O__2__

For photosynthesis, plants need?

1. Energy from sun
2. Carbon Dioxide (CO__2)__
3. Water (H__2__O)
4. Chlorophyll

What part of the plant does photosynthesis take place?

The leaves

Cuticle

Waxy covering on surface of stems & leaves; prevents water loss in land plants

Upper Epidermis

Thin layer of cells, permits most light to through to the underlying cells

Mesophyll

Interior leaf tissue

* Where majority of chloroplasts are found
* 2 types of cells

2 types of cells in the mesophyll

Palisade & Spongy

Palisade Cells

Lots of chloroplasts & photosynthesis

Spongy Cells

Fewer chloroplasts; store sugars & amino acids, aid in gas exchange

Lower Epidermis

Similar to upper, but contains lots of stomata

Stomata

Microscopic pores that allow gas exchange between the environment & interior of the plant

* CO2 enters leaf & O2 exits
* Opening & closing of stomata is controlled by guard cells

Cells of mesophyll must be close to air supply to…

* Obtain CO2
* Release O2

2 types of plant veins

Xylem & Phloem

Xylem

Transports H2O & dissolved minerals from roots → shoots

Phloem

Transports food made in leaves → roots & developing structure

Parts of a Chloroplast

Stroma, Thylakoids and Grana

Stroma

Thick fluid within membrane

Thylakoids

Disk shaped sacs inside (where most of photosynthesis occurs)

Grana

Stacks of thylakoids (Granum = 1 stack

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Pigments are..

Molecules that absorb specific wavelengths (energies) of light and reflect all others

Chlorophyll

A pigment found in the thylakoids; responsible for capturing light for photosynthesis

* It contains electrons that absorb the light energy
* Found in chloroplasts of eukaryotic cells & cytoplasm of prokaryotic cells

What are the 2 stages of photosynthesis?

1. Light Dependent Reaction
2. Calvin Cycle (Aka light Independent Reaction/dark reaction)

Light Dependent Reactions

* Sunlight energy is changed to chemical energy
* Oxygen is produced and released
* NADPH & ATP are produced
* NADPH is an electron carrier/acceptor molecule

Calvin Cycle

* Does not need light
* Occurs stroma (insides) of the chloroplast
* CO2 combines with the hydrogen (H) released from NADPH to produce C6H12O8 (Sugars)
* Uses ATP
* Produces NADPH+ and ADP + P
* These go back to the the light reactions & are recycled back into NADPH & ATP

Why is photosynthesis important?

* It takes the suns energy to make glucose
* Serves as the basis of the food chain
* Removes CO2 and release o2

Who uses photosynthesis?

Plants, Algae(Protista), Bacteria

Autotrophs

Organisms that produce their own food

Factors that affect the rate of photosynthesis

* Light intensity
* Carbon Dioxide Concentration
* Temperature

Light Intensity Effect on Photosynthesis

As light intensity increases, the rate of light dependent reactions also increase

* If the light dependent reactions increase in speed, then photosynthesis overall is increasing

Eventually the rate of photosynthesis is limited by some limited factor

* The rate of photosynthesis plateaus because of the chlorophyll is saturated with light

At very high light intensities, photosynthesis slows down but theses light intensities don’t occur in nature

Carbon Dioxide Concentration Effect on Photosynthesis

* As incresements in the amount of CO2, it increases the rate at which carbon is incorporated in glucose in the light - independent reaction/calvin cycle
* The rate eventually plateaus when the enzymes involved in building glucose are saturated/working at their max rate

Temperatures Effect on Photosynthesis

* Light dependent reactions are not affected by changes in temperature, but the calvin cycle is
* As temperature increases, reaction rate will increase; reactants have more kinetic energy & more molecular collisions as result
* Photosynthesis is controlled by enzymes, when the temperature is to high they denature


* If the temperature gets too high, the rate of photosynthesis decreases because the enzymes involved begin to denature

Layers of Leaf in Order

1. Cuticle
2. Upper Epidermis
3. Mesophyll
4. Lower epidermis
5. Lower cuticle

What do thylakoids do?

They spilt water and produce oxygen

All organisms require energy for ?

* Building molecules
* Active Transport
* Cellular division
* Movement

Where is energy is stored ?

ATP

ATP meaning

Adenosine TriPhosphate

What is ATP made of ?

Adenosine

* Made of adenine & ribose (a 5-C sugar)

Triphosphate tail

* Made of 3 phosphate groups
* The tail is source of energy used for celluar work

Where is energy specifically stored in ATP?

In the bonds between the phosphates

* The last bond has the most energy

When ATP is involved in a chemical reaction…

The last phosphate of the ATP breaks off, releasing energy

ADP

The ATP molecule after losing/breaking off its phosphate turning it into ADP

* ADP = Adenosine Diphosphate

What happens to the broken off phosphate of ATP?

Its transferred to another molecule that undergoes a change during the cellular work

3 Types of Cellular Work

1. Chemical Work
2. Mechanical Work
3. Transport Work

Chemical Work Example

Ex: Building molecules like proteins

;ATP provides the energy for dehydration synthesis to link amino acids

Mechanical Work Example

Ex: Contraction of Muscles

;ATP transfers phosphate groups to proteins that change shape & cause muscle cells to contract

Transport Work Example

Ex: The Sodium Potassium Pump

; ATP changes the shape of the pump proteins so ions can move across the membrane

The ATP cycle

ATP is recyclable

* Energy is released when ATP breaks and forms ADP + Phosphate
* Energy is stored when a phosphate attaches to ADP forming ATP

ATP Synthase

An enzyme that makes ATP from ADP & phosphates

* Process called chemiosmosis

Chemiosmosis

Flow of H+ across a membrane

* The flow of H+ through the enzyme powers ATP synthase
* Occurs in mitochondrial membrane

Where Does ATP Come From?

Carbohydrates & Fats

* Cells break down the carbs and fats
* Cells then use it for life processes by breaking ATP into ADP

Where do all carbohydrates come from?

Producers/autotrophs through photosynthesis

Cellular Respiration Purpose

To convert chemical energy stored in organic molecules into ATP

* (To be released by the chemical energy stored in glucose)

Cellular Respiration Formula

C6H12 + 6O2 → 6H2O + 6CO2 + ATP energy

Cellular Respiration

* Cellular respiration occurs in all living things (both plant and animal cells)
* Even though autotrophs like plants make their own food they still need to break it down and release energy to make more
* Most cellular respiration occurs in mitochondria
* There is a step which occurs in the cytoplasm

2 Types of Cellular Respiration

Aerobic Respiration & Anaerobic Respiration

Aerobic Respiration

* Requires oxygen
* Aerobic respiration produces more ATP when oxygen is present/available
* Occurs in mitochondria
* There are 3 steps/stages of Aerobic Respiration

3 Steps of Aerobic Respiration

1. Glycolysis
2. Krebs/Citric Acid Cycle
3. Electron Transport Chain

1. Glycolysis

Breakdown of glucose

* Occurs in cytoplasm of cell
* Does not require oxygen (Anaerobic)
* 1 glucose splits & forms 2 pyruvic acid
* Also creates an electron carrier molecule - NADPH
* Produces 2 ATP’s

2. Krebs Cycle

Breakdown of pyruvic acid to CO2

* Occurs in the mitochondrial matrix
* CO2 is released
* Produces more NADPH and FADH2 - more electron carrier molecules
* Produces 2 more ATP

3. Electron Transport Chain

* Occurs in the inner membrane of the mitochondria
* NADPH and FADH pass their electrons down the chain, producing ATP along the way
* Oxygen is the final electron collection
* Oxygen is released along with water
* Produces 32 - 34 ATP

Net ATP Gain of Aerobic Respiration

Glycolysis = 2

Krebs Cycle = 2

Electron Transport Chain = 32 - 34

ATP Total = 36 - 38

* About 36 ATP per molecule of glucose
* CO2 & H2O are produced as waste products

Anaerobic Respiration

Occurs without oxygen

* The Electron Transport Chain does not function because there is not enough o2 to serve as the final electron acceptor
* Therefore we cannot recycle NAD+ back in NADH
* Bur it can via fermentation

Fermentation

Making ATP without oxygen

* Makes ATP entirely from glycolysis
* Only produces 2 atp molecules for every 1 molecule of glucose
* (This is enough ATP for short bursts of activity)

2 Types of Fermentation

Lactic Acid Fermentation & Alcoholic Fermentation

Lactic Acid Fermentation

* Occurs in muscle cells
* Pyruvic acid produced by glycolysis is converted to 2 molecules of lactic acid
* Produces 2 ATP’s
* Recycles NAD+ back into NADH (which the ETC would have done if oxygen was present)
* Used by some fungi & bacteris

Lactic Acid Fermentation May Cause…

Muscle pain & soreness

* Blood removes excess lactic acid from muscles
* It can build up if not removed fast enough, causing pain
* When oxygen levels return to normal, blood is able to remove lactic acid again

Alcoholic Fermentation

* Occurs in yeast
* Pyruvic acid produced by glycolysis converted to 2 molecules of ethyl alcohol
* CO2 is released
* Produces 2 ATP’s
* Recycles NAD+ back into NADH
* Used in making food and beverages
* Ex: Beer & wine, CO2 makes it bubbly
* Ex: Bread, released CO2 by yeast causes dough to rise

How is energy transferred ?

Through one level to another

* Only \~10% actually moves to the next level
* Much of the energy is lost at a given level is lost as heat \~90%

Light

The intial energy source for most biological systems/levels

How Cellular Respiration & Photosynthesis Help Cycle Carbon Through These Levels?

* Cellular Respiration releases CO2 into the atmosphere; Photosynthesis removes it
* Photosynthesis releases O2 into the atmosphere; Cellular respiration removes it
* This exchange helps keep global CO2 & O2 levels in the atmosphere constant

General Characteristics of Photosynthesis

* Takes place in chloroplasts
* Takes place in plant cells
* Produces oxygen as byproduct
* Makes food for plants
* Food is a product (glucose)
* Energy from light is used

General Characteristics of Aerobic Respiration

* Takes place in mitochondria
* Takes place in both plant & animal cells
* Releases energy from food molecules
* Produces carbon as a byproduct
* Produces water as byproduct
* 36 - 38 ATP’s produced

General Characteristics of Anaerobic Respiration

* Takes place in cytoplasm
* Takes place in both plant & animal cells
* Releases energy from food molecules
* Produces carbon dioxide as byproduct (only alcoholic fermentation)
* 2 ATP’s produced