Biology topic 5.5- 5.9 photosynthesis

Mrs Peel year 2

Define and give examples for autotophs and heterotrophs.

Autotrophs are organisms that can make their own food or turn inorganic into organic carbon using energy. (Eg. Plants, Algae, Kemoautotrophs.)

Heterotrophs are organism that can’t make their own food and need to eat/ absorb organic matters for energy. (Eg. animals, fungi, bacteria)

Give the equation of photosynthesis.

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

What happens to the products of photosynthesis?

Glucose will be used as a fuel or turn into other compounds to be used by the plant.

Oxygen is a waste product which will be released into the atmosphere

What kind of reaction is photosynthesis and why?

Endothermic reaction because energy is needed to break the bonds between CO₂ and H₂O.

This energy is bigger than the energy released from new bonds forming.

What happens when plants respire?

Hydrogen that is stored in glucose can be used to react with oxygen and release a large amount of energy.

The equation is opposite photosynthesis.

Why is photosynthesis important in the ecosystem? (2)

1. Food webs where energy/ biomass can pass down to consumers

2. Oxygen are used by organisms to carry out aerobic respiration

Describe the two main types of reaction in photosynthesis in terms of the reactants and products involved?

1. light dependent reaction (needs light)- H2O is used while Oxygen, NAPDH and ATP are produced

2. light independent reaction (doesn’t rely on light) - CO2 is used while Glucose is produced

Define ATP.

ATP stands for Adenosine triphosphate and it is the energy currency of cells.

What does ATP consist of?

ATP consist of

1. A purine nucleotide base group- Adenine

2. A ribose sugar

3. 3 phosphate groups

Explain how ATP can turn into ADP.

The third phosphate group is loosely bonded so it can be removed to form ADP with only 2 phosphate groups ( Adenosine Diphosphate ). This process is assisted by a catalyst, ATPase

How does ATP turning into ADP release a lot of energy?

The lonely phosphate reacts with water molecules/ becomes hydrated, releasing energy.

What is the process called when ATP is formed from ADP?

Phsophorylation.

Explain why does making ATP from ADP is an endothermic reaction.

Because energy is required to break bonds between the lonely phosphate and water molecules.

What is NADPH?

Reduced NADP with the gain of hydrogen atom (consisting a hydrogen ion and an electron)

What is a co-enzyme and give an example.

Co- enzyme is a non-protein molecule that work alongside (or bind to) enzymes, transferring chemical groups or atoms to help with catalysing chemical reactions. (eg. NADP⁺- it is the final electron acceptor)

What are electron transfer chains (ETC)?

A series of protein complexes and organic molecules embedded in a cell membrane that transfer electrons through a sequence of redox reactions to generate chemical energy.

they have electron carrier proteins inside.

Define photosystems.

A specialized protein and pigment complex found in autotrophs that turn light energy into chemical energy during photosynthesis

Describe and compare the 2 types of photosystems.

Photosystem I and II have different photosynthetic pigments that absorb different wavelengths, maximising light absorbtion.

Photosystem II splits water into oxygen, protons and electrons through photolysis

Photosystem I receives electrons from PSII, re-energizes them using light, and uses them to reduce NADP⁺ into NADPH

Compare photolysis and hydrolysis.

• Photolysis is a chemical reaction in which a chemical compound is broken down into smaller units or fragments after absorbing light energy. (Eg. the split of water by light)

• Hydrolysis is a chemical reaction in which a molecule of water splits a chemical compound into two or more new substances.

• Photolysis requires light while hydrolysis don’t and photolysis can have different kinds of compound whereas hydrolysis is mainly about water.

Give the equation for photolysis in photosynthesis.

H₂O → ½ O₂ + 2e^- + 2H⁺

Where does photosynthesis take place and which part of the leaf is it?

in the chloroplast

In the palisade mesophyll cell of the leaf (after waxy cuticle and upper epidermis)

List the 11 organelles in a chloroplast cell.

1. Stroma

2. Thylakoid space

3. Thylakoid membrane

4. Granum

5. Stroma lamella

6. Outer membrane

7. Inner membrane

8. Intermembrane space

9. Starch grains

10. DNA loop

11. Ribosome

Describe the structure and function of stroma. (2)

• Gel like fluids surrounding thylakoid membrane

• Contains enzymes (eg. Rubisco) that catalyst light independent reactions

Describe the structure and function of thylakoid space. (2)

• Fluids within the thylakoid sacs

• Contains enzymes for photolysis

Describe the structure and function of thylakoid membrane. (3)

• A system of interconnected flattened sacs

• With electron carrier proteins and phtosynthetic pigment chlorophyll embedded within the membrane

• For light dependent reactions

Describe the structure and function of granum. (2)

• Stacks of thylakoid sacs joined together

• Have a large surface area which maximise light absorption

Describe the structure and function of stroma lamella. (2)

• Connecting bridges that links grana

• Space the grana out for larger surface area

Describe the structure and function of outer membrane. (2)

• Freely permeable to CO2 and H2O

• Makes up the envelope

Describe the structure and function of inner membrane. (2)

• contains transporter molecules which regulates the passage of substances in and out of the chloroplast.

• Make up the envelope

Describe the structure and function of intermembrane space (2)

• Inbetween outer and inner membrane

• Fluid inside have various enzymes, proteins and ions which helps the cell functions.

Describe the function of starch grains (1)

Storage of glucose

Describe the function of DNA loop.

Have genetic informations for some proteins

Describe the function of ribosomes.

Builds protein

Explain what happens in non- cyclic light dependent reaction.

This happens in the thylakoid membrane

1. Electrons are excited by the light source in chlorophyll of PSII

2. Electrons moves out of the chlorophyll into the ETC (redox reactions happens inside electron carrier proteins)

3. Electrons lost in the chlorophyll will be replaced by an electron formed by the photolysis of water

4. Chemiosmosis happens- When electrons move along the ETC, energy is lost and this energy is being used to pump hydrogen ions (protons) through the membrane from stoma to thylakoid space, against a conc gradient, creating a proton gradient. - The hydrogen ions eventually diffuse back to the stroma from thylakoid space through a channel called the ATPsynthase within the membrane. This movement catalyst the formation of ATP from ADP and a phosphate group.

5. By the time the electrons reached PSI, it has lost all of its energy. It will be excited by the light again in PSI and move along the ETC.

6. When it has reached the end of the chain, the electrons will be used to reduce NADP+ where NADPH is formed.

Give the equation for when NADP⁺ is reduced to form NADPH.

NADP⁺ + e^- + H⁺ → NADPH

Where does the hydrogen ion when making NADPH comes from?

Photolysis of water

Compare non cyclic and cyclic light dependent reaction. (4)

• Cyclic only happens in PSI whereas non cyclic happens in PSI and PSII

• Cyclic only produce ATP whereas non cyclic produce both ATP and NADPH

• Cyclic only happens when the plant needs a lot of energy

• In cyclic, there is no photolysis and electrons recycle back to PSI

Describe what happens in cyclic light dependent reaction. (3)

1. Electrons are excited in PSI which moves along the ETC

2. Chemiosmois happens and ATP is synthesised

3. Electrons recycle back to PSI instead of producing NADPH

Describe what happens in the light independent reaction/ Calvin cycle. (3)

1. Carbon fixation- RuBP (5 carbons) adds a carbon from CO2 to form an unstable 6- carbon chain which then breaks into 2 GPs with 3 carbons each.

2. Reduction of GP- GP is reduced by NADPH (NADP⁺ formed) and energy is supplied from ATP (ADP and P) formed to form GALP

3. Regerneration- Most of the GALP use energy from ATP to regenerate back to RuBP while a small amount make Glucose.

What are the compounds that can be made from glucose in plants? (4)

1. Lipids/ glycerol

2. Proteins/ amino acids

3. Starch/ Sucrose/ Cellulose

4. Nucleic acid

Suggest how glucose can be used to synthesis lipids or glycerols. (2)

1. Glucose can be made into triglycerides for the food store in seeds

2. Glucose can also join with a phosphate group to make phospholipids in the cell membrane

Suggest how glucose can be used to synthesis proteins and amino acids.

Glucose can join with nitrate ions (NO3^- turning into an amino group NH₂) absorbed from roots to make an amino acid.

The amino acid then goes through polymerisation to make protein

Suggest how glucose can be used to synthesis nucleic acid.

Nucleic acid (eg. DNA and RNA) is made up of repeating monomer units of nucleotides:

they are made up of:

1. Pentose- ribose/ deoxyribose

2. A phosphate group

3. A nitrogenous base

Glucose can join a nitrate group (NO₃⁻) and a phosphate group (PO₄^3-)

Suggest how glucose can be used to synthesis starch for food storage. (5)

• A polysaccharide

• starch is an alpha glucose

• amylose and amylopectin

• forming glycosidic bonds

• In condensation reactions

Suggest how glucose can be used to synthesis cellulose for plant cell wall. (5)

• A polysaccharide

• Cellulose is a beta glucose

• They are long, straight, unbranched chains

• Form glycosidic bonds and hydrogen bonds( microfribrils)

• In condensation reactions

Suggest how glucose can be used to synthesis sucrose for the transportation of carbohydrates. (3)

• A disaccharide

• Made by glucose and fructose

• It is transported by phloem

Briefly describe the hill reaction and its point of a core practical. (1)

To investigate photosynthesis in different light conditions using isolated chloroplast and DCPIP

List and explain different equipments needed in this experiment. (9)

1. Spinach leaves and blender to break cell walls and outer membranes to get chlorplasts- where photosynthesis happens

2. Filter funnel and muslin cloth- to filter out large unbroken cell debris

3. DCPIP solution- which acts as the redox indicator to replace NADP+ and receive electrons to change blue colour to colourless

4. Cold isolation medium- A solution that helps to extract preserve cell components like chloroplast from crushed tissues without damaging them. The solution includes buffer solution to maintain stable pH, salt to maintain ionic balance and keep the structure and sucrose to keep the solution isotonic so cells don’t shrink or burst. Coldness of the solution prevents the enzymes from denaturing the cell

5. Centrifuge- seperate mediums with different densities. This includes the lighter cytoplasm liquid (supernatant) and denser chloroplast pellets.

6. Distilled water- act as the control

7. Lamp- light source

8. Ice bath- needed in the extraction process to prevent chloroplast being denatured by unwanted enzyme activities

9. Colorimeter- measure absorbance values

Describe how you would carry out the experiment for the Hill’s reaction.

1. Extraction of chloroplast: 1. Blend the spinach and filter it with a muslin cloth inside the filter funnel. 2. Centrifuge the mixture to get the chloroplast pellet and resuspend it in a cold isolation buffer while keeping it in an ice bath.

2. Setting up test tubes: Tube A= Chloroplast + DCPIP +bright light. Tube B= Chloroplast + DCPIP + no light. Tube C= Chloroplast + distilled water + bright light. Tube D= Supernatant liquid + DCPIP + bright light.

3. Recording results: 1 method= Use a stop watch to measure time taken for the blue colour to dissappear in each test tubes. Other method= Read the absorbance value at regular intervals using a colourimeter with red and orange filter.

Explain the results that should occur in different test tubes in this (HIll’s reaction) experiment. (4)

Tube A= Turns colourless + have reaction as light is not a limiting factor

Tube B= Only slightly react as light is the limiting factor

Tube C= No colour change shown as DCPIP is not added

Tube D= No reaction as no chloroplast present

What are the controlled variables in this reaction? (4)

1. Plant species and the age of leaf

2. Volume and concentration of DCPIP and chloroplast extract

3. Temperature

4. pH

What is the independent variable in this reaction?

Light conditions

What is the dependent variable in this reaction?

Rate of light dependent reaction

What are the hazards and solutions in the experiment? (3)

1. DCPIP is an irritant- wear goggles and lab coats

2. Plant juices may cause an allergy- wear gloves, goggles and lab coats

3. Hot lamps may cause skin burns- switch off when not in use

Explain the three main limiting factors of photosynthesis.

1. Temperature- denature enzymes such as RuBP in the calvin cycle

2. CO₂ Concentration- Affects carbon fixation

3. Light intensity- Affects product froming in the light dependent reaction and preventing reduction of GP in the calvin cycle

Breifly describe the point of the calvin’s experiement.

To track the path of carbon in a light independent reaction using radioactive tracers and green algae.

Suggest the apparatus appears in the calvin’s experiment (5).

1. Lollipop flask- maximise the aborbance of light by algae duw to large and flat surface area. Transparent so light can directly pass through

2. Air hole which lets air and CO2 to enter inside the flask

3. An area wheere a syringe can inject radioactive Carbon 14 isotope to track the carbon

4. Valve/ tap that allows small quantities of algae and solution to be released from the flask- allow to acheive sample in precised time

5. Hot methanol directly placed beneath the tap- Stop any chemical reactions/ photosynthesis from happening to be able to analyse the solution to see how much C14 is in each molecule.

Why is using unicellular algae more suitable than using leaves. (4)

1. No need to damage leaves

2. Waxy cuticle in the leave delays the time that stops chemical reaction happening in leaves which destroys accuracy

3. Every cells in the algae is exposed to C-14 and light while leaves only allow OC2 to diffuse slowly into the leaf while outer layers may affect light to pass

4. Algae is suspended in the liquid so concentration C-14 can be easily adjusted while for leaves, gas concentration is harder to control

Explain why the levels of GP rises in darker environments. (2)

• GP cannot be reduced by light dependent products (NADPH and ATP) to turn into GALP in the calvin cycle

• While the remaining RuBP kept on producing GP, causing the continueous rise without being used up

Explain why the levels of glucose drops in darker environments. (2)

• GALP cannot be made due to the lack of light dependent products to reduce GP

• Remaining GALP is being used up eventually

Explain why the levels of RuBP drops in darker environments. (2)

• GALP cannot be made due to the lack of light dependent products to reduce GP which affect regeneration

• RuBP is being turned into GP until eventually being used up

Explain why level of RuBP rise in lower concentrations of CO₂ conditions. (2)

• Because it is being regenerated from GALP (light is not the limiting factor)

• Low CO2 environments affects carbon fixation which preventss GP being formed from RuBP

Explain why levels of GP drops in lower concentrations of CO₂ conditions. (2)

• Less carbon fixation happens so less GP is being formed from RuBP

• While it is being reduced into GALP until eventually being used up