Photosynthesis and Respiration Flashcards
1
Q
Structure of Leaf
A
- Network of xylem and phloem
- Photosynthesis takes place largely in leaf- adapted to bring together raw materials of photosynthesis and remove it’s products
- Large surface area- absorbs lots of sunlight
- Arrangement of leave that minimises overlapping so shadowing of one leaf over another
- Thin as light is absorbed easily and short diffusion pathway for gases
- Transparent cuticle and epidermis that let light through to photosynthetic mesophyll cells beneath
- Long narrow upper mesophyll cells packed with chloroplasts that collect sunlight
- Numerous stomata for gaseous exchange so all mesophyll cells are only a short diffusion pathway from one
- Stomata that open and close in response to changes in light intensity
- Many air spaces for rapid diffusion of oxygen and carbon dioxide
2
Q
Why is energy important?
A
- Plants need energy for photosynthesis, active transport, DNA replication, cell division and protein synthesis
- Animals need energy for things like muscle contraction, maintenance of body temperature, ative transport, DNA replication, cell division and protein synthesis
3
Q
What do non-photosynthetic organisms do?
A
Feed on molecules produced by plants and then also use them to make ATP during respiration
4
Q
What is photosynthesis?
A
- Enery from light is used to make glucose from water and carbon dioxide
- Light energy is converted to chemical energy in the form of glucose
- Photosynthesis is a metabolic pathway (series os small reactions controlled by enzymes)
5
Q
How is energy stored and used in photosynthesis?
A
- Energy is stored in the glucose until plants release it by respiration
- Animals obtain glucose by eating plants or eating animals that have eaten plants
- They then respire the glucose to release energy
6
Q
What is respiration?
A
- When plants and animal cells release energy from glucose
- This energy is used to power all biological processes in a cell
- Aerobic uses oxygen- produces carbon dioxide and water (releases energy)
- Anaerobic doesn’t use oxygen
- Anaerobic in plants and yeast- produces carbon dioxide and ethanol (releases energy)
- Anaerobic in humans- produces lactate and releases energy
- Anaerobic and aerobic respiration are both examples of metabolic pathways
7
Q
ATP
A
- (adenosine triphosphate) is the immediate source of energy in a cell
- A cell can’t get energy directly from glucose
- So in respiration, energy released from glucose is used to make ATP
- Made from adenine, ribose sugar and 3 phosphate groups
- ATP carries energy to where it’s needed
8
Q
ATP Synthesis and Hydrolysis
A
- ATP is synthesised via condensation reaction between ADP and Pi using energy from an energy-releasing reaction (breakdown of glucose in respiration)
- Chemical energy stored in phosphate bond
- ATP synthase catalyses this reaction
- Also known as phosphorylation
- ATP then diffuses to the part of the cell that needs energy
- Here, it’s broken down back into ADP and Pi
- Chemical energy is released from the phosphate bond and used by the cell
- ATP hydrolase catalyses this hydrolysis reaction
- ADP and Pi are recycled and process starts again
9
Q
ATP Properties
A
- Stores or releases only a small, manageable amount of energy at at time, so no energy wasted as heat
- Small, soluble molecule that can easily be transported around the cell
- Easily broken down, so energy release is instantaneously
- Can be quickly remade
- Can make other molecules more reactive by phosphorylation
- ATP can’t pass out of the cell, so cell always has an immediate supply of energy
10
Q
Compensation Point
A
Particular level at which the rate of photosynthesis exactly matches the rate of respiration
11
Q
Chloroplasts in Photosynthesis
A
- Photosynthesis takes place in the chloroplasts
- They contain photosynthetic pigments (chlorophyll a, b and carotene)
- These are coloured substances that absorb light energy needed for photosynthesis
- Pigments are found in thylakoid membranes- they are attached to a protein (this makes a photosystem)
- Photosystems capture light energy
- PSI absorbs light best at a wavelength of 700nm
- PSII absorbs light best at 680nm
- Contained within inner membrane is a gel-like substance called stroma (contains enzymes, sugars and organic acids)
- Carbohydrates produced by photosythesis that are not used are stored as starch grains in the stroma
12
Q
Redox Reactions
A
- Reactions that involve oxidation and reduction
- If something is reduced it has gained electrons, gained hydrogen or lost oxygen
- If something is oxidised it has lost electrons, lost hydrogen or gained oxygen
- Oxidation of one molecule always involves reduction of another
- Oxidation- energy given out
- Reduction- energy taken in
13
Q
What is a coenzyme?
A
A molecule that aids the function of an enzyme by transferring a chemical group from one molecule to another
14
Q
Coenzymes in Photosynthesis
A
- NADP- transfers hydrogen from one molecule to another
- Means it can reduce or oxidise a molecule
15
Q
Light-dependent reaction
A
- Needs light energy
- Takes place in thylakoid membranes of chloroplasts
- Light energy is absorbed by chlorophyll and photosynthetic pigments
- Light energy excites electrons in chlorophyll, electrons are released and chlorophyll becomes a positive molecule (photoionisation)
- Chlorophyll is oxidised and electron carrier is reduced
- Energy from released electrons helps make ATP by photophosphorylation (transfers energy) and reduced NADP from NADP(transfers hydrogen to L.I reaction)
- H2O is oxidised to O2- photolysis of water into protons, electrons and oxygen
- Photolysis of water…
- 2h2o = 4H+ + 4e- + o2
16
Q
Non-cyclic photophosphorylation
A
- Produces ATP, NADPH and oxygen
- Photosystems are linked by electron carriers (proteins that transfer electrons)
- Photosystems and electron carriers form an electron transport chain- a chain of proteins through which excited electrons flow
- Light energy is absorbed by PSII and this excites the electrons in chlorophyll
- Electrons move to a higher energy level as they have more energy
- High-energy electrons are released from the chlorophyll and move down the electron transport chain to PSI
- Electrons that have left must be replaced by photolysis
- Excited electrons lose energy as they move down the electron transport chain
- This energy is used to transport protons into the thylakoid so the thylakoid has a higher concentration of protons than the stroma (proton gradient across thylakoid membrane formed)
- Protons move down their concentration gradient, into the stroma via ATP synthase which is embedded in the thylakoid membrane
- Energy from this movement combines ADP and Pi to form ATP
- Light energy is absorbed by PSI, which excites electrons to an even higher energy level
- Electrons are transferred to NADP along with a proton from the stroma to form NADPH
17
Q
Chemiosmotic theory
A
- Process of electrons flowing down the electron transport chain and creating a proton gradient across the membrane to drive ATP synthesis is chemiosmosis
- Energy to drive this comes from energy released during photolysis
- Each new carrier has slightly lower energy as energy lost is used to make ATP
18
Q
Cyclic Photophosphorylation
A
- Produces ATP and only uses PSI
- Electrons from chlorophyll aren’t passed back to NADP but back to PSI via electron carriers
- Electrons are recycled and can repeatedly flow through PSI
- Process produces only small amounts of ATP
- Thylakoid membrane is impermeable to protons
- As protons pass through ATP synthase, it’s structure changes to form ATP
19
Q
Chloroplast Adaptations for L.D
A
- Thylakoid membranes provide large surface area for attachment of chlorophyll, electron carriers and enzymes
- Proteins in grana hold chlorophyll in a way where their is maximum absorption of light
- ATP synthase catalysed production of ATP and establishes proton gradient
- Chloroplasts contain DNA and ribosomes to make proteins for the L.D reaction
- Protons taken up by NADP which is needed for L.I reaction
- Oxygen by-product is either used by respiration or diffuses out of the leaf
20
Q
Calvin Cycle (Light-independent reaction)
A
- Takes place in the stroma of chloroplasts
- Needs ATP and H+ ions to keep it going
- CO2 enters the leaf through the stomata and diffuses into the stroma of the chloroplast where it’s combined with ribulose bisphosphate (RuBP)- catalysed by enzyme rubisco
- This gives an unstable 6-carbon compound which quickly breaks down into 2 molecules of a 3-carbon compund called glycerate-3-phosphate (GP)
- Hydrolysis of ATP (from L.D) provides energy to reduce GP to a different 3-carbon compound called triose phosphate (TP)- this requires H+ ions which come from NADPH from L.D- reduced NADP is recycled back to NADP for L.D
- Some TP is converted into useful organic compunds (e.g.glucose) and rest regenerates RuBP
- 5/6 molecules of TP regenerate RuBP
- Regenerating RuBP uses the rest of ATP made by the L.D reaction
21
Q
How does the calvin cycle make a hexose sugar?
A
- Hexose sugars are simple 6-carbon sugars (glucose)
- One hexose sugar is made by joining 2 molecules of TP
- Cycle needs to turn 6 times to make one hexose sugar
- 3 turns of the cycle produces 6 molecules of TP
- 5/6 TP regenerate RuBP
- This means that for 3 turns of the cycle, only 1 TP is produced that’s used to make a hexose sugar
- Hexose sugar has 6 carbons, so 2 TP molecules are needed to form one hexose sugar
- This means the cycle must turn 6 times to produce 2 molecules of TP that can make one hexose sugar
- 6 turns need 18 ATP and 12 NADPH from the L.D reaction
- Keeps the cycle going and makes sure there’s always enough RuBP ready to combine with CO2 taken in from the atmosphere
22
Q
How are Carbohydrates made?
A
- Hexose sugars are made from 2 TP molecules
- Larger carbohydrates (sucrose,starch, cellulose) are made by joining hexose sugars together in different ways
23
Q
How are lipids made?
A
- Glycerol is made from triose phosphate
- Fatty acids are made from glycerate 3-phosphate
24
Q
How are amino acids made?
A
Made from glycerate 3-phosphate
25
Q
Chloroplast Adaptations in L.I
A
- Fluid of stroma contains all enzymes needed to carry out L.I reaction
- Stroma fluid surrounds grana- products of L.D in grana can readily diffuse into the stroma
- Contains both DNA and Ribosomes- quickly and easily manufacture some of proteins in L.I reaction
26
Q
High light intensity of a certain wavelength (optimum conditions)
A
- Light needed for light-dependent reaction (higher intensity, more energy provided)
- Only certain wavelengths of light are used for photosynthesis
- Photosynthetic pigments chlorophyll a, chlorophyll b and carotene only absorb red and blue light in sunlight
- Green light is reflected, which is why plants look green
38
Q
Principles of chromatography
A
- Mobile phase moves through or over the stationary phase
- Components in the mixture spend different amounts of time in the mobile phase and the stationary phase
- Components that spend longer in the mobile phase travel faster or further
- Time spent in different phases is what separates out the components of the mixture
45
Q
Stages of Glycolysis
A
- Phosphorylation= Glucose is phosphorylated using a phosphate from 1 molecule of ATP to create 1 molecule of glucose phosphate and 1 molecule of ADP
- ATP is then used to add another phosphate, forming hexose bisphosphate
- Hexose bisphosphate is then split into 2 molecules of triose phosphate
- Adding phosphates makes glucose more reactive and lowers activation energy
-
Oxidation= Triose phosphate is oxidised, forming 2 molecules of pyruvate
- NAD collects the hydrogen ions, forming 2 reduced NAD
- 4 ATP are produced, but 2 were used up in stage 1 so net gain of 2 ATP
52
Q
The Link Reaction
A
- Pyruvate + NAD +CoA = acetyl CoA + NADH + CO2
- Converts pyruvate produced in glycolysis to acetyl coenzyme A
- Pyruvate is decarboxylated, so 1 carbon atom is removed from pyruvate in the form of carbon dioxide
- At the same time, pyruvate is oxidised to form acetate and NAD is reduced to form reduced NAD
- Acetate is then combined with coenzyme A to form acetyl coenzyme A
- No ATP is produced in this reaction
54
Q
Products of the link reaction
A
55
Q
Krebs Cycle
A
- Produces reduced coenzymes and ATP
- Cycle happens once for every pyruvate molecule in the matrix of the mitochondria
- Acetyl CoA from the link reaction combines with a 4-carbon molecule (oxaloacetate) to form A 6-carbon molecule (citrate)
- Coenzyme A goes back to the link reaction to be used again
- Citrate is converted to a 5-carbon molecule
- Decarboxylation occurs where CO2 is removed
- Dehydrogenation also occurs- hydrogen is used to produce reduced NAD from NAD
- 5-carbon molecule is then converted to a 4-carbon molecule
- Decarboxylation and dehydrogenation occur, producing 1 molecule of reduced FAD and 2 of reduced NAD
- ATP is produced by the direct transfer of a phosphate group to ADP (substrate-level phosphorylation)
- Citrate has now been converted into oxaloacetate
57
Q
Oxidative phosphorylation
A
- Process where the energy carried by electrons, from reduced coezymes (NADH and FADH2) is used to make ATP
- Occurs at the site of mitochondria (cristae)
- Great numbers of mitochondria in active cells
- Hydrogen atoms are released from reduced NAD and reduced FAD as they’re oxidised to NAD and FAD (H atoms split into protons and electrons)
- Electrons move down the electron transport chain (made up of electron carriers), losing energy at each carrier
- Energy is used by the electron carriers to pump protons from the mitochondrial matrix into the intermembrane space (space between inner and outer mitochondrial membranes)
- Concentration of protons is now higher in the intermembrane space than in the mitochondrial matrix- this forms an electrochemical gradient (concentration gradient of ions)
- Protons then move down the electrochemical gradient, back across the inner mitochondrial membrane and into the mitochondrial matrix via ATP synthase (which is embedded in the inner mitochondrial membrane)
- Movement drives synthesis of ATP from ADP and Pi
- Process of ATP production driven by movement of H+ ions across a membrane due to electrons moving down an electron transport chain is called chemiosmosis
- In the mitochondrial matrix, at the end of the transport chain, the protons, electrons and oxygen (from the blood) combine to form water
- Oxygen is the final electron acceptor
- Without oxygen’s role in removing hydrogen, protons and electrons would back up along the chain and respiration would come to a halt
58
Q
How can a cell make 32 ATP from one molecule of glucose?
A
- 2.5 ATP are made from each recuced NAD and 1.5 ATP are made from each reduced FAD
- For each glucose molecule, 28 ATP is produced by oxidative phosphorylation
