M.1.2 Flashcards
Photosynthesis and Cellular Respiration
Carbon fixation
- Changing of inorganic carbon molecule into organic sugars that combine to form glucose
Inorganic molecule
- Not produced by an organism
- Occurs readily in nature, e.g. carbon dioxide, water, oxygen, mineral salts
Organic molecule
- Chemicals produced by an organism
- e.g., lipids, proteins, carbohydrates, nucleic acid
Heterotrophs
- Organisms that can’t make organic material
- Consumes organic material for energy
Chloroplast
- Disc shaped organelle
- contains stacks of thylakoid (grana)
Mesophyll
- Green tissue of the cell, where chloroplasts are located
Stoma(ta)
- Pores in the leaf that allows carbon dioxide to enter and oxygen to leave
- Opened/closed by guard cells on either side of it
Photosynthesis basic formula
Water + Carbon Dioxide → (in presence of sunlight through a chloroplast) Glucose + Oxygen Gas
H20 + CO2 (with sunlight) → C6H12O6 + O2
Light reaction
- 1st stage of photosynthesis
- Generates energy (ATP, NADPH) needed for dark reaction, oxygen and hydrogen by splitting water
- Chlorophyll absorbs light energy, splits water to produce H+ ions
- Oxygen released as a byproduct
- Occurs in thylakoid membrane’s photosystem
Calvin Cycle overview
- 2nd stage of photosynthesis
- Produces glucose from CO2 using the ATP + NADPH energy from the light cycle
- RuBP combines with CO2 to form G3P. One G3P is converted into glucose, the rest is converted back into RuBP for the next cycle
Chlorophyll
- Pigment that traps light energy
- Chlorophyll A: blue-violet and red wavelengths
- Chlorophyll B: blue and orange wavelengths, reflects yellow-green wavelengths
- Doesn’t capture green wavelengths
Obligate anaerobes
- Die if exposed to oxygen, as they don’t produce enzymes necessary to detoxify reactive oxygen species.
e.g. bacteroides (obligate anaerobic bacteria)
Facultative anaerobes
- Can live with or without oxygen, as it produces ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent.
e.g. e. coli and yeast
Guard cells
- Cells surrounding the stomata, changing the size of pores by turgor pressure (due to the large vacuole in guard cells)
Turgid: fills with water, stretching the guard cells to curve outwards, causing it to open
Flaccid: as water leaves the vacuole, the guard cells deflate, collapsing inwards and closing the stomata. - If the environment is hot and dry, this causes a steeper concentration gradient for water vapour to diffuse out of the leaf. This loss of water in the guard cells cause them to become flaccid and close the stomata. This reduces further water loss.
Enzymes
- special proteins: biological catalysts (in this case) that speeds up photosynthesis
Stroma
- Fluid inside chloroplast surrounding thylakoid system and grana
- Contains starch, chloroplast DNA, ribosomes, and enzymes needed for Calvin Cycle
ATP
adenosine triphosphate
NADPH
nicotinamide adenine dinucleotide phosphate hydrogen
- Created by adding hydrogen ions (H+) to NADP
G3P
- Glyceraldehyde-3-phosphate
- Raw material for production of fatty acids, amino acids, glucose, nucleotides
- Often immediately converted into glucose phosphate then starch
Calvin Cycle steps
- CO2 + RuBP → 3PGA (3-phosphoglyceric acid)
- 3PGA → G3P (enzymes convert using energy from ATP and NAPDH)
- CO2 exits cycle as G3P sugar (carbon fixation)
- RuBP regenerated via rearrangement of leftover G3P molecules
3PGA
- 3-phosphoglyceric acid
- Product of: carbon + RuBP (+ ATP and NADPH energy)
RuBP
- Ribulose biphosphate
- 5-carbon sugar
- Combines with carbon: CO2 + RuBP → 3PGA
- Replenished by rearrangement of leftover G3P molecules from end of 1 Calvin Cycle
Alcohol fermentation
- Glucose → carbon dioxide + ethanol
Lactic acid fermentation
Glycolysis occurs, and then if still not in presence of oxygen:
- pyruvate + NADH –> lactic acid, which can be broken down in glycolysis again to produce another 2 net ATP
glucose –> lactic acid + 2 ATP
Used for fermentation of kimchi, yoghurt.
Also in muscle cells, where after extended periods of exertion there is a shortage of oxygen in muscle cells, causing them to respire anaerobically. The presence of lactic acid causes a cramp.
Glycolysis main idea
- 1 Glucose → 2 pyruvates
- Begins both aerobic and anaerobic respiration as does not need oxygen to occur
- Occurs in cytoplasm
Phosphorylation
- Adding of a phosphate group to a molecule
Krebs Cycle
- Found by Hans Kreb in 1930s
- Pyruvate converted into acetyl co-enzyme (acetyl co-A)
- Acetyl co-A degraded to CO2 and H2O with release of ATP
- Occurs in matrix of mitochondria
Main stages of cellular respiration
- Glycolysis
- Krebs cycle
- Electron transport chain (ETC)
ETC
- Occurs in inner membrane of mitochondria
ATP production light reaction
- Electrons energised by splitting of water travel down an electron transport chain to NADPH-producing photosystem
- Chloroplast uses energy released by this electron “fall” to make ATP
No.of ATP produced in cellular reaction
- Aerobic: 32 ATP molecules/1 glucose
- Anaerobic: 2 ATP molecules/1 glucose
Light intensity photosynthesis
- The rate of photosynthesis increases with light intensity, BUT will plateau eventually when it reaches plant’s optimum level as every chloroplast is saturated with sunlight energy, and is operating at maximum capacity.
- Also plateaus as carbon dioxide concentration or temperature become limiting
- Remember this is different to temperature, as temperature can result in inefficient loss of water vapour, but higher temperature is accompanied with high light intensity
Relationship between photosynthesis and cellular respiration
- Photosynthesis: inorganic molecules –> energy dense compound (anabolic reaction)
- Cellular respiration: energy dense compound –> inorganic molecules + energy (catabolic)
- Also cellular respiration occurs at a slower rate as it is a more complex reaction
