5 - ICH - Photosynthesis Flashcards by Michelle Yick

What is:

Autotrophic nutrition
Heterotrophic nutrition

Autotrophic nutrition = The synthesis of complex organic molecules from inorganic molecules using external sources of energy e.g. photosynthesis/ light

Heterotrophic nutrition = Aquiring nutrients by the ingestion of other organisms e.g. animals and fungi

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What are photoautotrophs?

Photoautotrophs = Example of autotrophic nutrition in which plants need light to photosynthesise

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Simple equation for photosynthesis

Why is this an oversimplification?

6CO₂ + 6H₂O + Light energy → C₆H₁₂O_{6 +}6O₂

Photosynthesis is actually a complex series of chemical reactions
Photosynthesis is split into 3 distinct stages
The stages occur in different parts of the chloroplast

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How is photosynthesis related to respitation?

They are reverses of each other:

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What happens to the the levels of photosynthesis, respiration and glucose from day to night?

DAY:

Both photosynthesis and respiration happen.

Rate of photosynthesis > Rate of respiration

CO₂ entering the plant and O₂ leaving the plant.

Plant makes excess glucose, NET ↑ of glucose production.

NIGHT:

Photosynthesis stops (no light available) but respiration continues.

Rate of photosynthesis < Rate of respiration

O₂ entering the plant and CO₂ leaving the plant.

Use glucose for respiration but not making any to replenish it, NET ↓ of glucose.

DAWN/ DUSK:

At the compensation point: Rate of photosynthesis = Rate of respiration.

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What is the compensation point?

Rate of photosynthesis = Rate of respiration

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Name the 3 main stages of photosynthesis + where does each stage occur?

Light harvesting/ capturing of light energy -
Light dependant reaction - Thylakoid membrane
Light independant reaction - Stroma

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What is photolysis?

The splitting of water using light energy

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What are photosynthetic pigments?

Name 3 types of photosynthetic pigments + give examples of each

Chemicals that absorb light energy. As a result of the light energy being absorbed the chemicals become “excited”.

Chlorophyll - a and b

Carotinoids - carotene

Xanthophyll

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Why do plants have a range of different pigments?

Allows them to absopt a greater range of light wavelengths

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What metal is present in the centre of the complex iron in chlorophyll?

What does the metal bonded to the 4 N’s make?

Magnesium

Porphyrin ring

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Where are chloroplasts in the cell?

What is the purpose of their tail?

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What is thin layer chromatography?

A technique for seperating different pigments through the rate at which they move across an inert surface carried by a slovent

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What is a photosystem?

They are collections of pigments in the thylakoid membrane

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What is the photosynthetic pigment in the center of photosystem 1 and photosystem 2?

Photosystem 1 = P700

Photosystem 2 = P680

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Define chromatography

A technique for seperating molecules from a mixture according to their different solubility in a particular solvent

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What does Rf stand for?

Equation for working out the Rf value?

Rf = Retention factor

Rf = distance moved by pigment / distance moved by solvent

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What is the stroma?

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Fluid-filed matrix where the light independant reactions of photosynthesis take place.

Within the stroma a number of structures such as starch grains and oil droplets occur.

What is the grana?

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Stacks of disc like structures called thylakoids.

Within the thylakoid membranes chloroplast pigments are embedded and arranged in such a way to form complexes called photosystems.

This is where the light dependant reactions occur.

How are chloroplasts adapted to absorbing (harvesting) sunlight and carrying out the light dependant/ light independant reactions of photosynthesis? (6)

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Small + disc shape. Materials are easily exchanged with surrounding cytoplasm (max SA:VOL + short diffusion distance).
Chloroplasts are not static so they can be moved around the cytoplasm, allowing them to occupy the optimum position to carry out photosynthesis.
Granal membranes provide large SA to hold photosynthetic pigments, electron carriers and enzymes in precise positions.
Granal membranes have many ATP synthase attached to them. This helps with synthesis of ATP by chemiosmosis.
Stroma contains all enzymes needed to carry out light independant reactions.
Stroma fuild surrounds grana, light dependant reactions cana easily pass into the stroma.

Name 2 types of accessory pigment

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Carotenoids

Xanthophyll

How do electrons leave the photosystem?

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Absorbed light raises the energy levels of the electrons in the pigment molecules.
These electrons then become “excited” and then leave the parent molecule.

Where are photosystems located in the cell?

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Thylakoid membranes

Where does the light dependant reaction occur?

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Thylakoid membranes

Briefly describe what happens in the light dependant stage in 3 bullet points. What is **photophosphorylation**?

- Light energy is absobred, electron's energy levels are raised and they become excited. They leave their parent molecule. - Energy from these excited electrons is used to synthesise ATP from ADP and Pi (**photophosphorylation**) and to reduce NADP. - Water undergoes **photolysis** in PSII.

Give the equation for the photolysis of water in the light dependant stage. Which is the waste product?

H₂O → 2H⁺ + 2e^- + ½O₂ O₂ = Released as a waste product

Outline the sequence of events that occur in the light dependant stage (7)

1. PSI + PSII absorb light. 2. Light energy raises the energy of the electrons which become excited. PSI and PSII each lose a pair of electrons. 3. Electrons from PSI pass down an ETC, ATP is formed by photophosphorylation. 4. Water undergoes photolysis in PSII. H₂O → 2H⁺ + 2e^-+ ½O₂. Oxygen is released as a waste product. 5. 2 protons and 2 electros combine to make 2H **atoms**. 2H⁺ + 2e^-→ 2H 6. 2H is picked p by an electron carrier molecule NADP to produce reduced NADP. 7. Some electrons emitted by PSI return directly to PSI via the ETC and ATP is formed by photophosphorylation.

What is: 1. **Non cylic photophosphorylation**? 2. **Cyclic photophosphorylation**? What does each one produce as products?

**Non cylic photophosphorylation** = Involves PSI. Electrons start and finish in PSI. Produces ATP, oxygen and reduced NADP. **Cyclic photophosphorylation** = Involved PSII. Electrons don't cycle. They enter from H₂O and leave through reduced NADP. Produces ATP only.

Define **chemiosmosis**

The diffusion of protons from a region of high conc to a reagion of low conc across a partially permeable membrane

How is chemiosmosis involved with the synthesis of ATP?

1. H⁺ diffuse into thylakoid membrane from stroma by chemiosmosis. This makes the thylakoid membranes more acidic (lowers the pH). They can't diffuse back out. The only way to leave is through ATP synthase. 2. Water undergoes photolysis. H₂O → 2H⁺ + 2e^- + ½O₂. Oxygen is released as a waste gas. 2H⁺ travels through thylakoid space through **ATP Synthase**. 3. ATP synthase is broken down into 3 steps (because the head rotates in sections of 3) - pick up Pi + ADP, join them together, dump them. 4. 2H⁺ passes through ATP synthase and joins with NADP + 2e^- to produce reduced NADP.

Name the products made in the light dependant reaction. Which ones are useful and which ones are waste products?

_Useful:_ Reduced NADP and ATP _Waste:_ Oxygen

What do you need to put into the light independant reaction for it to work?

Carbon and oxygen from CO_2. Energy from ATP. Hydrogen from reduced NADP.

What do these stand for? 1. RuBP 2. RuP 3. GP 4. TP

RuBP = Ribulose bisphosphate RuP = Ribulose phosphate GP = Glycerate-3-phosphate TP = Triose phosphate

The number of carbons and phosphates in: 1. CO₂ 2. RuBP 3. RuP 4. GP 5. TP

What is the name of the cycle involved with the light independant reaction?

Calvin cycle

Outline the steps in the light independant reaction

1. **Carbon fixation** - Addition of carbon to a molecule. RuBP is the acceptor molecule for CO_2. This occurs in the presence of an enzyme called **Rubisco**. **RuBP + CO₂ – (rubisco) → GP** 2. GP is a unstable 6C compound. It uses ATP and the hydrogen from reduced NADP to break down into TP, a more stable 3C compound. **GP + energy + 2H⁺ → TP** 3. Some of TP combines in pairs to form 6C sugars. These can then be polymerised into starch BUT the majority of the TP will have their atoms rearranged to form RuP **TP –rearangement of atoms→ RuP** 4. RuP reacts with the Pi of ATP to form RuBP (the starting point of the calvin cycle). **RuP + Pi → RuBP**

What are the uses of TP? (3)

Produce hexose sugars (glucose, fructose, these then can react to make sucrose) Hexose sugars can be polymerised: ß glucose = cellulose α glucose = starch TP also produces Glycerol which reacts with Fatty acids (produced by GP) to form lipids.

What are the uses of GP?

Produce amino acids. GP converts to pyruvic acid which then forms the 2C compound **acetyl coenzyme A (acetyl coA)**. Many of acetyl coA are produced to form faftty acids which react with glycerol (produced by TP) to produce lipids.

Define **limiting factor**

A factor which limits the rate of a process

List 3 limiting factors of photosynthesis

Light intensity Temperature CO₂ concentration

What does the graph of a limiting factor and rate of photosynthesis look like and why is it?

what would happen to the amount of: RuBP, RuP, GP and TP 1. Removal of light 2. Removal of CO₂

How can you overcome limiting factors?

Greenhouses

5 - ICH - Photosynthesis Flashcards

(43 cards)