17- energy for biological processes

Question 1

What is an autotroph?

Answer 1

organisms that use light energy(phototroph) or chemical energy( chemotroph) and inorganic molecules to synthesise complex organic molecules

Question 2

What is a hetrotroph?

Answer 2

Organisms that gain their nutrients from complex organic molecules. It digests them to simpler soluble molecules and then respires some of them to obtain energy, or uses the products of digestion to synthesise organic molecules it needs.

Question 3

What is photosynthesis?

Answer 3

A series of chemical reactions in which light energy is transferred into chemical energy. Light energy is used to produce other organic compounds and substrates for respiration. Produces; Glucose- used to produce other organic compounds and substrates for respiration.
Oxygen- released into atmosphere so all aerobes depend on it for respiration.

Question 4

Where does photosynthesis happen?

Answer 4

Within chloroplasts
Chlorophyll are found in photosystems on thylakoid membranes
Chloroplasts are abundant in palisade mesophyll cells.

Question 5

What are the 2 main steps of photosynthesis?

Answer 5

-Light dependant reaction, which takes place across the thylakoid membranes.
-Light independent reaction, which takes place in the stroma; this process is dependent on there being enough light and water to create ATP and NADP.

Question 6

Explain how carbon dioxide can be measured in an aquatic system.

Answer 6

Hydrogencarbonate indicator can be used. It is red in equilibrium with atmospheric air.
It becomes orange/ yellow with increased CO2 levels.
It becomes deep purple as CO2 is removed.
Can be used to show CO2 is being used during photosynthesis.

Question 7

How are the cells in a leaf arranged for maximum photosynthetic activity?

Answer 7

-Regular arrangement so gaps between cells for light to filter through
- Tightly packed so higher chance of light hitting cells
- lengthways so that light travels through cell; more likely to hit chloroplasts.

Question 8

What are some leaf adaptations to maximise photosyntesis?

Answer 8

-Large flat shape to absorb sunlight
- branching network of veins to supply water
- Lots of stomata to allow CO2 into the plant and prevent water loss
- Air spaces between cells for gas diffusion
-Chloroplasts

Question 9

What are the adaptations of a palisade cell?

Answer 9

-Large number of chloroplasts
- No air spaces between them to trap as much light as possible
- thin cell walls and cytoplasm
- chloroplasts on edge and can move in the cell

Question 10

What are chloroplasts?

Answer 10

Most are disc shaped and 2-10 picometers long
Contain DNA and ribosomes so can make enzymes for photosynthesis.
Photosynthesis occurs entirely within them .

Question 11

What is the structure of a chloroplast?

Answer 11

Stacks of flattened membrane compartments- each stack is called a granum, each compartment is a thylakoid.
Membrane extensions called lamella connect the grana.
The grana provide a large SA for the attachment of photosystems in the membranes of thylakoids. These contain photosynthetic pigments such as chlorophyll.
The fluid in the chloroplast is the stroma- it contains enzymes for the second stage of photosynthesis
The sugars produced are stored in starch grams.

Question 12

What are photosynthetic pigments?

Answer 12

Light travels in energy packets called photons.
Photosynthetic pigments absorb light energy at specific wavelengths of light.
Each pigment absorbs a specific wavelength and reflects the others. - Green leaves reflect green light however seaweed can be brown as different wavelengths reach different depths of the sea. Also means that light can be absorbed at dawn and dusk, increasing time photosynthesising.

Question 13

What is chlorophyll a?

Answer 13

Main photosynthetiic pigment- appears yellow green, known as the primary pigment reaction centre. It is in the centre of a photosystem
- There are 2 types that absorb red light
-P680; found in PSII- peak wave length 680nm
-P700; found in PSI, peak wave length 700nm

Question 14

What are accessory pigments?

Answer 14

• Embedded in thylakoid membranes; Arranged randomly in photosystem funnel, form a light harvesting system, absorb light energy of different wavelengths and direct it to the reaction centre.
  -Chlorophyll b = blue/green
• carotene= orange
• Xanthophyll = yellow
  Different types of accessory pigments to absorb as much light as possible and direct it to chlorophyll a; primary pigment reaction centre.

Question 15

What is an absorbtion spectra?

Answer 15

-Shows wavelengths of light that are absorbed and reflected by each pigment, all of the pigments together give the net absorption spectra.

Question 16

What is an action spectra?

Answer 16

Indicates the relative efficiency at which the different wavelengths of light can carry out photosynthesis.

Question 17

What are the main steps of the light dependant photosynthesis reaction?

Answer 17

Light harvesting, electron moves to higher orbital, random walk, electron transport chains.

Question 18

What happens during step 1- light harvesting- of the light dependant reaction?

Answer 18

Occurs in PSI- P700 and PSII- P680.
These are embedded in the thylakoid membranes
When a photon hits the accessory pigment, if there is an electron that resonates at that energy level (with the exact wavelength of light), the electron will move to a higher orbital.

Question 19

What happens during step 2- electron moving to higher orbital- of the light dependant reaction?

Answer 19

After the electron has moved to a higher orbital; it isnt stable so the electron ‘flops’ back to it’s original place.
A packet of light energy is released, however there is less energy as some has been used to move the electron to a higher shell, the lower amount of energy is a different wavelength of light and can be absorbed by a different accessory pigment.

Question 20

What happens during stage 3- Random walk- of the light dependant reaction?

Answer 20

• energy bounces around the accessory pigments in the photosystem- random walk
• Eventually this may reach the primary pigment reaction centre.
• When the energy hits the primary pigment reaction centre it must have the wavelength of the reaction centre to excite the electron-P700 or P680
• An electron is released if the electron is excited.

Question 21

What happens during stage 4- Electron transport chains- of the light dependent reaction?

Answer 21

The electrons are released from the reaction centres and passed to the electron transport chains
-PSII electron goes to PSI
- PSI electron goes to the production of reduced NADP- the coenzyme that transfers one hydrogen from 1 reaction to another.

Question 22

What is photolysis?

Answer 22

Water molecules are split in an enzyme catalysed reaction, it uses light energy and occurs in PSII
1. Hydrogen ions released into lumen of the thylakoid- used for chemiosmosis
2. Once in the stroma, the protons are combined with NADP to produce NADPH with an electron from PSI.
3. Waste products used for respiration or released via diffusion through the stomata.

Question 23

What are the main things that happen during the light independent stage?

Answer 23

-Carbon dioxide is converted to carbohydrate. Reduced NADP is the reducing power, ATP is the energy source.
- occurs in the stroma of the chloroplast.

Question 24

What are the 3 main stages of the light independent stage?

Answer 24

1. Carboxylation- Carbon dioxide fixation with ribulose biphosphate (RuBP)
2. Reduction - Reduction of glycerate 3-phosphate (GP) to triose phosphate (TP)
3. Re-formation of the CO2 acceptor molecules.

Question 25

What is an electron transport chain?

Answer 25

It takes an electron from PSII to PSI. The electron from PSI is then used in the formation of NADPH.

Question 26

How do electron transport chains work?

Answer 26

• Electron carriers have progressively lower energy levels, a series of proteins along the chain.
• As the electron moves from one to the next, energy is released.
• The energy is used to pump protons into the thylakoid lumen; used in active transport for chemiosmosis.
• The protons build up on one side of the membrane as it is impermeable to H+.
• The H+ move down their concentration gradient through hydrophilic channels linked to ATP synthase, which drive the production of ATP= chemiosmosis.

Question 27

What is photophosphorylation? What are the 2 types?

Answer 27

• The formation of ATP in the presence of light energy.
• Takes place in the thylakoid membranes of chloroplasts during the light independent stage.
• 2 types; Cyclic- used in times of stress to release ATP only, and Non-cyclic, normal photosynthesis.
• It is an example of substrate level phosphorylation; the phosphate is transferred directly from a donor to the ADP.

Question 28

Explain the process of cyclic phosphorylation

Answer 28

• Electron leaving ETC after PSI can be returned to PSI, instead of being used to form NADPH.
• This means that PSI can still lead to the production of ATP without any electrons being supplied from PSII.
  -NADPH isn’t produced

Question 29

What happens during the first step of the Calvin cycle, carboxylation?

Answer 29

CO2 from the atmosphere enters intracellular spaces. It diffuses into cells and stroma of chloroplasts where it is combined with a 5-carbon molecule, ribulose biphosphate (RuBP). The CO2 is now fixated.
-Rubisco catalyses the reaction and an unstable 6-carbon molecule is formed.
-Rubisco is competitively inhibited by oxygen.

Question 30

What happens during step 2 of the Calvin cycle, reduction?

Answer 30

• The unstable 6 carbon molecule breaks down immediately forming 2, 3-carbon GP molecules.
• Each GP molecule is converted to another 3-C molecule TP, using an H from NADPH and energy supplied the phosphorylation of ATP.
• These are both supplied from the light- dependent reactions of photosynthesis.

Question 31

What happens during the 3rd stage of the Calvin cycle, Regeneration?

Answer 31

TP is a carbohydrate, a 3-C sugar, the majority of which is recycled to regenerate RuBP so that the Calvin cycle can continue.

Question 32

How many full turns of the Calvin cycle are needed to produce one glucose molecule? Why?

Answer 32

6. For one glucose molecule to be produced, 6 CO2 molecules with have to enter the Calvin cycle. This results in 12 TP molecules, 2 of which will be removed to make the glucose molecule.
   10 TP molecules are recycled to regenerate 6 RuBP molecules.

Question 33

What are the 3 main factors that affect the rate of photosynthesis?

Answer 33

• Light intensity
• carbon dioxide concentration
• temperature

Question 34

Why does light intensity affect the rate of photosynthesis?

Answer 34

Light is needed as an energy source. As light intensity increases, ATP and NADPH are produced at a higher rate.

Question 35

How does CO2 conc. affect the rate of photosynthesis?

Answer 35

CO2 is needed as a source of C’s, so if all other conditions are met, increasing the CO2 conc will increase the rate of carbon fixation in the Calvin cycle, and therefore, the rate of TP production.

Question 36

Why does temperature affect the rate of photosynthesis?

Answer 36

• Affects rate of enzyme controlled reactions. Increase in temp= increase in rate of enzyme controlled reactions e.g. carbon fixation.
• Rate of photorespiration. Stomata close to avoid water loss by transpiration during dry spells when plants undergo water stress. However, this stops CO2 entering the plant, reducing the rate of the light- independent reaction, and eventually stopping photosynthesis.

Question 37

What are the effects of reducing light intensity on the Calvin cycle?

Answer 37

• Will reduce rate of light dependent stages of photosynthesis- will reduce quantity of ATP and NADPH produced. As they’re needed to convert GP to TP, conc. of GP will increase and conc. of TP will decrease. Less TP to regenerate RuBP, so conc. decreases.

Question 38

What is chemiosmosis?

Answer 38

The ATP produced in photosynthesis and respiration is synthesised primarily by chemiosmosis. It involves the diffusion of protons from a region of high conc. to a region of low conc. through a partially permeable membrane. The movement of protons as they flow down their conc. gradient releases energy that is used in the attachment of an inorganic phosphate to ADP to form ATP.
It depends on the creation of a proton conc. gradient The energy to do this comes from the excited electrons.

Question 39

How can electrons become excited?

Answer 39

• Electrons present in pigment molecules e.g. chlorophyll are excited by absorbing light from the sun.
  -high energy electrons are released when chemical bonds are broken in respiratory substrate molecules.
  The excited electrons pass into an electron transport chain and are used to generate a proton gradient.

Question 40

How does an electron transport chain work?

Answer 40

It is made up of a series of electron carriers, each with progressively lower energy levels. As high energy electrons move from one carrier to another, energy is released. This is used to pump protons across a membrane and therefore a proton gradient. The proton gradient is maintained as a result of the impermeability of the membrane to H+ ions, which is why active transport is needed.

Question 41

How are electrons able to move back through the membrane down their concentration gradient?

Answer 41

Through hydrophilic membrane channels liked to the enzyme ATP synthase( catalyses the formation of ATP). The flow of protons through these channels provides the energy used to synthesise ATP from ADP and Pi.