Biology – unit 3 examiners report; photosynthesis and cellular respiration
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• you have the accompanying Masterclass documents in front of you for reference If you are having any issues, please send us a message in the chat feed Exam Pitfalls • Some Common Pitfalls in Exam answers.
1. Not answering the question a. Always read the question in totality. Then go back and read it again to check that you have understood what is been asked. b. You interpret the question differently and you start to answer it, but you are off topic. Why? Some students haven’t had time to revise correctly, they have a set of pre-prepared answers that they fall back on or they have panicked into thinking they have understood the question.
2. Not looking at the mark scheme or the space provided a. Both the mark scheme and the space provided (if there is one) will provide clues about how much the examiners are expecting to see. Dot points are acceptable. A 4 mark question is not going to be answered by a one word response!
3. Panicking a. Some students go blank when they see the exam and it’s not what they think it should be. Step back. Take a deep breath, count to ten and then look at the paper again. Now read the question and write an answer down in your head. Examine the answer. Does it satisfy the criteria for the question? Write it down. A blank answer sheet will get no marks.
4. Time Management a. Look at the exam paper. How many multiple-choice questions and marks are there? Short answers? Plan your response time to each section and stick to it. If you finish early you can always go back and check the ones that you had doubts about. Photosynthesis the purpose of photosynthesis chloroplasts as the site of photosynthesis, an overview of their structure and evidence of their bacterial origins inputs and outputs of the light dependent and light independent (Calvin cycle) stages of photosynthesis in C3 plants (details of the biochemical pathway mechanisms are not required) factors that affect the rate of photosynthesis, including light, temperature and carbon dioxide concentration
Cellular respiration
the purpose of cellular respiration the location of, and the inputs and outputs of, glycolysis including ATP yield (details of the biochemical pathway mechanisms are not required) mitochondria as the site of aerobic cellular respiration, an overview of their structure and evidence of their bacterial origins the main inputs and outputs of the Krebs (citric acid) cycle and electron transport chain including ATP yield (details of the biochemical pathway mechanisms are not required) the location of anaerobic cellular respiration, its inputs and the difference in outputs between animals and yeasts including ATP yield factors that affect the rate of cellular respiration, including temperature, glucose availability and oxygen concentration Photosynthesis and Cellular Respiration
Chapter 5 Photosynthesis
Key knowledge • the purpose of photosynthesis • chloroplasts as the site of photosynthesis – Structure – Evidence of bacterial origins • inputs and outputs of the light dependent and light independent (Calvin cycle) stages of photosynthesis in C3 plants – details of the biochemical pathway mechanisms are not required • factors that affect the rate of photosynthesis – Light – Temperature – carbon dioxide concentration • What do these food webs have in common? • Where do we place Homo sapiens in these food webs? • What provides energy to all living things within our biosphere?
ATP energy
ATP used for: •Synthesis of anabolic reactions (such as synthesis of biomacromolecules) •Active transport •Other ‘active’ processes Endergonic and exergonic reactions
ATP ADP + Pi
ADP + Pi ATP Photosynthesis: importance
• Sunlight (light energy) is the ultimate source of energy for almost all living organisms • Chlorophyll (a green pigment molecule) in green plants traps light energy and transforms it into chemical energy by the process of photosynthesis • Plants, algae and some bacteria are called autotrophs or producers because they produce their own food (or organic matter) in the form of carbohydrates; from inorganic compounds (water and carbon dioxide) • Animal, fungi and many bacteria are heterotrophs or consumers because they cannot produce their own food; they must consume (ingest or absorb) food (organic matter) in order to survive
Red = photosynthesising organisms Photosynthesis: what is it?
• is a reduction reaction (involves the removal of oxygen from an organic compound) – ‘reduction of carbon dioxide’ • is an anabolic, endergonic chemical reaction (i.e. requires energy)
Reactant involved in photosynthesis: Products of photosynthesis:
carbon dioxide (CO2) Glucose (C6H12O6) light energy Oxygen (O2) water (H2O) OR
6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O
Source of the reactants in plants? Source of the reactants in water dwelling photosynthetic organisms? Photosynthesis: where does
it occur? Generally within cells in green leaves MESOPHYLL CELL
grana stroma
CHLOROPLAST
CROSS-SECTION OF A LEAF
http://www.robinsonlibrary.com/science/botany/anatomy/insideleaf.htm Stomata (stoma - plural)
• Pores in a plant’s cuticle (protective surface) through
which gases (including water vapor, CO2 and O2) are exchanged between the plant and the atmosphere
Oxygen
(O2)
Carbon Dioxide (CO ) 2 Guard Cell Guard Cell Mesophyll Cell
http://pixgood.com/mesophyll-cell-diagram.html Chloroplast
• organelle in cytosol of plant cells Stroma (fluid matrix – contains enzymes for photosynthesis) – not present in non- also contains ribosomes and DNA photosynthesising cells (e.g. root Thylakoids (contain chlorophyll) hair cells) Outer Membrane stacks of flattened discs • contains a series of flattened Inner Membrane Granum (internal layers of membrane sacs (thylakoids) membrane) arranged into stacks called grana • Chlorophyll is found in the grana – light dependent reactions of photosynthesis occur here • Fluid of chloroplast is called the stroma and contains enzymes – light independent reactions of photosynthesis occur here – DNA and ribosomes also found Grana (plural) within http://www.vce.bioninja.com.au/aos-1-molecules-of-life/biochemical-processes/photosynthesis.html Endosymbiosis theory origin of chloroplasts • Chloroplasts were probably free-living prokaryotes in ‘ancient times’ since they contain ribosomes and DNA like cyanobacteria • Chloroplasts have a double membrane – Suggests they lived endosymbiotically within another cell Thylakoids contain chlorophyll
Thylakoid Membrane
Thylakoid Space Granum Chlorophyll molecules
• Located in the thylakoid membranes.
• Chlorophyll pigment molecules trap light energy by absorbing certain wavelengths of light (blue - 420 nm and red - 660 nm are most important). • Plants are green because green light is reflected from them, not absorbed. Wavelength of Light (nm) Photosynthesis reaction Involves two main chemical reactions
1. Light Reaction or Light Dependent Reaction
Produces energy from sunlight in the form of ATP and NADPH.
2. Dark reaction or Light Independent Reaction or The Calvin cycle
Uses energy (ATP and NADPH) from the light dependent reaction to make carbohydrates (glucose) from carbon dioxide and water http://www.vce.bioninja.com.au/aos-1-molecules-of-life/biochemical-processes/photosynthesis.html Light-dependent stage Light-independent stage What affects the rate of photosynthesis?
Cellular Respiration
Key knowledge • the purpose of cellular respiration • the location of, and the inputs and outputs of glycolysis including ATP yield • mitochondria as the site of aerobic cellular respiration, an overview of their structure and evidence of their bacterial origins • the main inputs and outputs of the Krebs (citric acid) cycle and electron transport chain including ATP yield • the location of anaerobic cellular respiration, its inputs and the difference in outputs between animals and yeasts including ATP yield • factors that affect the rate of cellular respiration, including temperature, glucose availability and oxygen concentration Cellular respiration
• Cellular respiration is the controlled release of energy, via a series of enzyme-catalysed reactions, from organic compounds in cells to form ATP • The main organic compound used for this process is glucose, however lipids and proteins can also be broken down via modified processes – Animals must consume food to provide them with a constant supply of energy – When an animal is starved it obtains its energy from its own body tissues – when glucose (and all glycogen stores) is used up, fats and then proteins are used (97% of fat tissue, 31% of skeletal muscle tissue and 27% of blood can be used) • Two types of cellular respiration – Aerobic respiration – occurs in the presence of oxygen; involves the oxidation of glucose – Anaerobic respiration - occurs in the absence of oxygen
Nature of Biology 2 Jacaranda Plus http://www.vce.bioninja.com.au/aos-1-molecules-of-life/biochemical-processes/cell-respiration.html Cellular respiration
• Two types – Aerobic respiration (requires oxygen and mostly takes place in mitochondria) – Anaerobic respiration (does not require oxygen and takes place in cytosol of cell) • Aerobic respiration can be divided into three main stages: – Glycolysis (occurs in cytosol of cell) – Kreb’s cycle (occurs in mitochondria) – Electron transport chain (occurs in mitochondria) • Aerobic respiration of one molecule of glucose releases energy that is coupled to the production of 36 molecules of ATP. In cells of your heart, liver and kidneys, two additional molecules of ATP are generated to give a total of 38 ATP • General (overall) equation for aerobic respiration:
36 ATP (sometimes 38 ATP)
Nature of Biology 2 Jacaranda Plus http://www.vce.bioninja.com.au/aos-1-molecules-of-life/biochemical-processes/cell-respiration.html C6H12O6 + 6O2 → 6CO2 + 6H2O + ~36ATP Mitochondria – essential for aerobic respiration
• Singular = mitochondrion • Are membrane-bound organelles in the cytosol of eukaryotic cells (not found in prokaryotic cells) • Matrix (fluid part) contains DNA (every human has the same mitochondrial DNA as their mother) and ribosomes • Highly folded inner membrane to increase surface area – enzymes involved in respiration found here • Many mitochondria are found in cells that require a lot of energy such as skeletal muscle • Millions of years ago, mitochondria were probably free-living prokaryotes since they contain DNA and ribosomes, similar to ancient bacteria • They have a double membrane (like chloroplasts), suggesting they lived endosymbiotically inside another cell
Nature of Biology 2 Jacaranda Plus http://micro.magnet.fsu.edu/cells/mitochondria/mitochondria.html http://www.vce.bioninja.com.au/aos-1-molecules-of-life/biochemical-processes/cell-respiration.html Stage 1: Glycolysis Where What Overall Inputs Overall Outputs Occurs in cytosol of Glucose 2 NADH cells 2 NAD+ 2 ATP
2 ADP + 2 Pi 2 Pyruvate (enzymes required for series of reactions in glycolysis are found in the cytosol) + 4Pi
• DOES NO NEED MITOCHONDRIA
• Anaerobic reaction (does not require 02 to happen) • Requires 2 molecules of ATP to occur, but produces 4 molecules of ATP as a result – therefore there is a net release of 2 ATP molecules • Releases hydrogen (H+) which is taken up by the unloaded hydrogen carrier NAD+ to form NADH • Glycolysis cannot occur without a ready supply of NAD+ • NAD = Nicotinamide adenine dinucleotide (an unloaded hydrogen carrier that collects hydrogen ions and their electrons) • NAD+ = unloaded hydrogen carrier • NADH = loaded hydrogen carrier
Nature of Biology 2 Jacaranda Plus http://www.vce.bioninja.com.au/aos-1-molecules-of-life/biochemical-processes/cell-respiration.html Stage 2: Krebs cycle Where Inputs Outputs
Occurs in mitochondria in 2 Pyruvate 6 CO2 mitochondrial matrix 8 NAD 8 NADH
(the fluid part of the 2 FAD 2 FADH2 mitochondria) 2ADP + 2Pi 2 ATP
This is for one glucose molecule This is for one glucose molecule
• Also known as the citric acid cycle • Pyruvate leave the cytosol and enters the mitochondrion where it is used in the Krebs cycle + • H is gathered by unloaded carriers (FAD and NAD) to produce loaded carriers (FADH2 and NADH) • FAD = flavine adenine dinucleotide
Nature of Biology 2 Jacaranda Plus http://www.vce.bioninja.com.au/aos-1-molecules-of-life/biochemical-processes/cell-respiration.html Stage 3: Electron transport Where What Inputs Outputs
Inner membrane of Oxygen (O2) Water (H2O) mitochondria e.g. NADH 32-34 ATP + Cytochrome FADH2 FAD + molecules are also ADP + Pi NAD involved Note: Quantities have not been included
• Requires oxygen to take place • Electron transport chain involves reactions with the loaded hydrogen carriers
• Electrons from the loaded hydrogen carriers (NADH and FADH2) are brought to inner membranes of mitochondria where the electrons are transferred from one cytochrome to another and finally ‘accepted’ by oxygen. • Oxygen combines the electrons with H+ ions to form water molecules • The electron transport chain produces the majority of the ATP molecules in the three stages of aerobic respiration (32-34 out of 36-38 ATP in total produced via aerobic respiration)
Nature of Biology 2 Jacaranda Plus http://www.vce.bioninja.com.au/aos-1-molecules-of-life/biochemical-processes/cell-respiration.html This is what the cytochromes look like Cytochromes within the inner membrane of mitochondria, where electron transport occurs
http://genetics.wayne.edu/mitomed/research.php Summary of three stages of aerobic respiration • Aerobic Respiration: Occurs in the cytoplasm (glycolysis) and mitochondria in the presence of oxygen • Overall: Glucose and oxygen are converted into water, carbon dioxide and ATP (net gain of 36 - 38 ATP molecules) • Note: while glycolysis does not require oxygen (i.e. it is an anaerobic reaction), it is still considered one of the stages of aerobic respiration
Nature of Biology 2 Jacaranda Plus http://www.vce.bioninja.com.au/aos-1-molecules-of-life/biochemical-processes/cell-respiration.html Other diagrams representing the three stages of aerobic respiration
Stage 1: glycolysis Stage 2: Krebs cycle Stage 3: electron transport e.g.
Nature of Biology 2 Jacaranda Plus Anaerobic respiration
• Chemical breakdown of glucose in the absence of oxygen • Occurs in the cytosol of cell • Organisms have capacity to carry out anaerobic respiration under conditions when oxygen is not available (lack of oxygen for short periods or permanently). This ability enables organisms to continue functioning under these conditions or to live in habitats where oxygen is absent – Mammalian tissue can switch to anaerobic respiration during short periods of strenuous exercise when the oxygen supply to the muscles cannot keep up with demand – During rest or moderate activity mammalian tissue undergoes aerobic respiration • Outputs of anaerobic respiration are different depending on the organism and the enzymes they have – Animals: Glucose is converted into lactic acid (and 2 molecules of ATP). Anaerobic respiration is called LACTOSE FERMENTATION in these organisms – Plants and Fungi: Glucose is converted into ethanol and carbon dioxide (and 2 molecules of ATP) – Anaerobic respiration is called FERMENTATION in these organisms ➢ These reaction are reversible, so when oxygen is present, these by-products can be converted back into pyruvate for use in aerobic respiration
Nature of Biology 2 Jacaranda Plus http://www.vce.bioninja.com.au/aos-1-molecules-of-life/biochemical-processes/cell-respiration.html Anaerobic respiration
• also called fermentation in plants and yeast Aerobic vs anaerobic respiration
Heineman Biology 2 Aerobic vs Anaerobic respiration
• Anaerobic Respiration: Occurs in the cytosol in the absence of oxygen and produces 2 molecules of ATP in cytosol – Animals: Glucose is converted into lactic acid (and 2 molecules of ATP) – Plants and Fungi: Glucose is converted into ethanol and carbon dioxide (and 2 molecules of ATP) in cytosol • Aerobic Respiration: Occurs in the cytosol and mitochondria in the presence of oxygen – Overall: Glucose (and oxygen) is converted into water, carbon dioxide and ATP (36 - 38 ATP molecules)
Nature of Biology 2 Jacaranda Plus http://www.vce.bioninja.com.au/aos-1-molecules-of-life/biochemical-processes/cell-respiration.html Aerobic vs Anaerobic respiration
and plants)
NOTE: Aerobic and anaerobic respiration involve different steps but both types of cellular respiration begin with the breakdown of glucose via glycolysis Nature of Biology 2 Jacaranda Plus Factors that affect the rate of cellular respiration Involvement of coenzymes in photosynthesis and cellular respiration
Photosynthesis
http://www.gtac.edu.au/module-1/the- colours-of-photosynthesis-introduction/ Respiration
https://www.youtube.com/watch?v=7J4LXs- oDCU Or try Khan Academy https://www.youtube.com/watch?v=- rsYk4eCKnA More Detailed Explanations
Following are more detailed explanations of the chemical pathways.
Try not to remember the details but rather the connections between the objects in the diagrams.
Can you follow the pathway(s)? Macromolecules ADP Energy-rich nutrients Carbohydrates NAD+ Carbohydrates Lipids NADP+ Lipids Proteins FAD+ Proteins Nucleic acids
+ - Pi H e
Anabolism Catabolism
ATP Small precursor molecules NADH Energy-depleted products monosaccharides NADPH CO Fatty acids FADH 2 2 H O Amino acids 2 NH Nitrogenous bases 3 Oxidation and reduction of co-enzymes Reduction Oxidation NAD+ + 2e- + H+ → NADH NADH → NAD+ + 2e- + H+ NADP+ + 2e- + H+ → NADPH NADPH → NADP+ + 2e- + H+
NAD+ NADH Organic Organic or or molecule + molecule + + NADP+ NADPH
electron proton Hydrogen atom More Detailed Explanations
Photosynthesis and Respiration Photosynthesis
+ - 2H2O → O2 + 4H + 4e Photosystem II
NADP+ + H+ + 2e- → NADPH Photosystem I
Low energy High energy Light Dependent Stage Light Independent Stage Light Independent Stage
+ 3 CO2 + 6 NADPH + 6 H + 9 ATP → + glyceraldehyde-3-phosphate (G3P) + 6 NADP + 9 ADP + 3 H2O + 8 Pi
To make one glucose molecule (which can be created from 2 G3P molecules) would require 6 turns of the Calvin cycle. Respiration Glycolysis Pyruvate 3C
CoA ETC