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Photosynthesis and Cellular Respiration Biology – unit 3 examiners report; photosynthesis and cellular respiration We will be starting at 4:30pm. In the meantime, please check the following: • your computer speakers are on and volume is up, and your microphone is muted • click the chat icon to open the chat feed – use this to ask us questions • 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
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