The Importance of Photosynthesis: Energy Production and Cell Function

1. 04/01/2020 Photosynthesis Starter • Why do we need energy within the cell? • Where does this energy come from? • Why is photosynthesis so vital for all living things? • Write down everything you can remember about photosynthesis from GCSE. • Word and symbol equations!! • What features do you think a chloroplast needs to effectively do it’s job?

2. Why is energy needed within cells? • Allows chemical reactions to take place • BUILD UP (synthesis) or BREAKDOWN of molecules • In order to do this, energy is required to make and break bonds

3. Where does the energy come from? • The SUNis the ultimate source of energy for nearly all living organisms (the exceptions being a few deep sea chemosynthetic bacteria)

4. What provides the energy within cells? • ATP…Adenosine Tri Phosphate • Common to ALL living things • Any chemical that interferes with the production or breakdown of ATP is fatal to the cell and therefore the organism • Chemical energy is stored in the phosphate bonds

5. Photosynthesis All the food we eat has originated from plants Plants use energy from the sun and convert it to chemical energy Chemical energy is used to synthesise large organic molecules from inorganic molecules Such as carbohydrates / sugars

6. Photosynthesis Autotrophic or heterotrophic? Autotrophic – ability to synthesise complex organic molecules from simpler molecules and an energy source Heterotrophic – ability to digest complex organic molecules and break them down into simpler ones

7. Photosynthesis Autotrophic organisms can be split into 2 groups: Chemo-autotrophs – use the energy from exergonic reactionsfor synthesis of complex molecules Photo-autotrophs - use the energy from light for synthesis of complex molecules

8. Photosynthesis 6CO2 + 6H20 + light C6H1206 + 02 The products of photosynthesis are glucose (C6H1206) and oxygen This can then be used by plants and animals for aerobic respiration C6H1206 + 602 6CO2 + 6H20 + some ATP

9. Task • Describe the process of photosynthesis. • You must refer: • The reactants and products, • How they enter and leave the leaf, • What transport process is used • Remember all your keywords from the transport module from AS Biology

10. Plant cells undergo the biochemical processes of photosynthesis (in daylight) and respiration.(at all times) : Sun provides energy for photosynthesis and evaporation of water • Carbon dioxide (CO2) • Required for photosynthesis • Enters leaf through open stomata (pores) Glucose produced in chloroplasts in leaf palisade cells by photosynthesis Sugars and other organic substances are transported through sieve tubes (phloem) Oxygen (O2 ) – waste; some used in respiration Removed through open stomata (pores) – located mainly on underside of leaf Water is lost through open stomata by evaporation (transpiration) down a water vapour potential gradient; some water is lost through lenticels (in stem) • Leaf • Organ adapted for photosynthesis – e.g. • Flat– large surface area – absorbs sunlight • Thin – short distance for diffusion and penetration of light Water enters root hair cells by osmosis, down a water potential gradient Minerals enter by active transport and diffusion Water and dissolved minerals are transported upwards through xylem vessels

11. Definition • Write a detailed definition for photosynthesis. • It MUST NOT be the GCSE definition but must contain more advanced scientific words that you have learnt in AS Biology when referring to the types of molecules

12. Photosynthesis (in chloroplasts in leaves) Definition Process whereby light energy from the Sun is transformed into chemical energy, and used to synthesise larger (complex) organic molecules from inorganic substances Forms the basis of most food chains Chemical equation (overall - simplified) Light energy 6H2O + 6CO2 C6H12O6 + 6O2 ChlorophyllGlucose Respiration in plants & animals depends upon the products of photosynthesis – i.e. organic substances and oxygen

13. Photosynthesis and Respiration Respiration C6H12O6 + 6O2 CO2 + 6H2O + Energy (ATP)

14. The Structure of the Leaf • From your previous GCSE and AS knowledge • Write how the structure of the leaf is related to its function in performing the process of photosynthesis

15. Leaf - Organ of Photosynthesis - Adaptations Flat – large surface area - maximum light absorption Thin– short diffusion distance between palisade mesophyll cells & external environment (for CO2, H2O and O2); palisade mesoophyll cells are near the upper surface – maximises light absorption; upper epidermal cells are transparent –allows light to reach the palisade mesophyll cell Waxy transparent cuticle– allows light to enter; prevents loss of water for photosynthesis Lower epidermis contain stomata (pores) – allows gas exchange – intake of CO2 and release of O2 Leaf mosaicarrangement– exposure of maximum number of leaves to light Chloroplasts Contain light absorbing pigments in membranes of Thylakoids - chlorophylls (a and b) + carotenoids + xanthophylls Pigments absorb light energy and convert it into chemical energy (ATP) through photophosphorylation Contain enzymes for synthesis of hexose sugars (carbohydrates) Vascular (transport) tissue Xylem – transports H2O (and minerals) to leaf mesophyll cells (chloroplasts) for photosynthesis Phloem transports organic molecules made in the leaf to rest of the plant Palisade mesophyll cells (upper layer) Contain many chloroplasts – large amount of chlorophyll; Closely packed columnar cells arranged with long axis perpendicular to surface – reduces number of light absorbing cross walls and increases surface area; Chloroplasts moved by cytoskeleton (cyclosis) - to absorb maximum light or to protect from excessive light Thin cell walls – reduces diffusion pathway; efficient light penetration Chloroplasts at periphery of cell – short diffusion pathway Non pigmented vacuole – allow light penetration Spongy mesophyll (lower layer) Spherical cells; less chloroplasts; larger intercellular air spaces for movement of gases and H2O vapour); store carbohydrates (and other organic substances) made by photosynthesis – which are taken into the phloem.

16. Incident Light More cell wall to cross Incident Light Mosaic arrangement Of leaves – maximum number of leaves exposed to sunlight Columnar arrangement Few cell wall to cross H2O O2 CO2

17. 04/01/2020 Chloroplasts Starter • What does a chloroplast do? • What features do you think a chloroplast needs to effectively do it’s job?

18. Objectives • Explain how the structure of chloroplasts enables them to carry out their functions • Define the term “photosynthetic pigment” • Explain the importance of photosynthetic pigments in photosynthesis

19. Photosynthesis Takes place in specialised plant organelles called chloroplasts that contain photosynthetic pigments Absorb light energy & have their own peak of absorption Occurs in 2 main stages Light – dependantstage Light – independentstage

20. Evolution of the chloroplast • It is believed that photosynthetic bacteria were acquired by eukaryotic cells • By endocytosis (engulfing) • To produce the first algal/plant cell • This is called the “endosymbiont theory” • They were then passed on to the next generation

21. Current organisms trying endosymbiosis to get chloroplasts • Two types of marine molluscs current engulf algae and incorporate their chloroplasts to allow them to make complex molecules • However, they have not yet found a way of passing these to the next generation

23. Size and Shape • Can vary • Usually between 2-10µm in length • Usually disc shaped

24. Chloroplast structure

25. Task • You have got 10 minutes • You need to annotate the diagram of the chloroplast and think of how each adaptations help it to carry out its function

26. Membranes Double membrane (envelope); • Outer membrane – permeable to many small ions • Inner membrane – less permeable and has transport proteins embedded in it Intermembrane space is 10–20nm wide between the inner and outer membrane Photosynthetic pigments – arranged in photostems

27. Lamellae and thylakoids • The inner membrane is folded into lamellae (thin plates) aka thylakoids • The lamellae (thylakoids) are stacked in piles called granum (increases SA) • Between the grana are intergranal lamellae

28. Stroma (viewed with LM) • Fluid-filled matrix • The light-independent stage of photosynthesis occurs here (contains enzymes for this) • Contains starch grains, oil droplets, DNA and ribosomes

29. Grana (viewed with LM) • Contains stacks of thylakoids • Where the light-dependant stage of photosynthesis takes place • Absorb light and ATP synthesised • Thylakoids are only seen under electron microscope

30. Task • Complete the table to describe each function of the chloroplast and how it is related to its function

31. How chloroplasts are adapted

32. Chloroplast Outer membrane Permeable Intermembrane space Inner membrane Selectively permeable Transport proteins present Lipid droplet Intergranal lamella Starch grain (storage) Storage polysaccharide (made of glucose) • Thylakoid membrane • Increase surface area • Pigments arranged in clusters termed photosystems (PS) • Allow maximum absorption of light • Electron carriers present • Proton pumps present • ATP synthase complex (for ATP synthesis by photophosphorylation) • Photolysis (splitting) of water • Products of light-dependant reactions (ATP + reduced NADP + O2) pass into stroma Stroma (fluid) Enzymes for light-independent (dark) reactions – Calvin cycle Products – glucose + NADP + ADP Granum Stack of thylakoids (~ 100) Large surface area Site of light-depemdent reactions Products – ATP + reduced NADP + O2 Ribosome (70S) Site of protein synthesis Circular DNA Codes for proteins (enzymes) - e.g. rubisco Biconvex shape Increases surface area

34. Photosynthesis Photosynthetic pigments are arranged in structures called photosystems Photosystems – found in the thylakoid membranes

35. Photosynthetic pigments • Absorb certain wavelengths of light • Reflect other wavelengths (these are the colours we see)

36. Chlorophyll Mixture of pigments, all have a similar structure: Long hydrocarbon chain & pophyrin ring Similar to the haem group in haemoglobin but has magnesium (Mg) rather than iron (Fe)-electrons are excited

37. Chlorophyll • Found within chloroplasts • Absorb and capture light • Made up of a group of five pigments • Chlorophyll a • Chlorophyll b • Carotenoids; xanthophyll and carotene • Phaetophytin • All absorb light at different wavelengths • Chlorophyll a is the most abundant • Proportions of other pigments accounts for varying shades of green found between species of plants

38. Photosystem I and Photosystem II • These are distinct chlorophyll complexes • Each contains a different combination of chlorophyll pigments

39. Chlorophylls • Chlorophyll a • Is in the “Primary pigment reaction centre” • Two forms • P680 – in photosystem 2 • P700 – in photosystem 1 • Appears yellow-green • Absorbs red light (and blue at 450nm) • contains a Mg atom – when light hits this, a pair of electrons become excited

41. Chlorophyll a Found at the base of the photosystem in the primarypigmentreactioncentre p680 – in photosystem II-particles found on the grana p700 – in photosystem I- particles found on the intergranal lamellae

42. Arrangement of Pigments in Thylakoid Membrane Pigments are arranged in clusters (photosystems) in the thylakoid membranes There are two types of photosystems – with each containing a reaction centre containing the principal light absorbing pigment (the primary acceptor) – i.e. chlorophyll a P700 (PS I) – Absorbs orange light Absorption peak ~ 700 nm P680 (PS II) – Absorbs red light Absorption peak ~ 680 nm Absorption of light by chlorophyll a causes electrons to be excited and move to a higher energy level The electrons are accepted by an electron acceptor and passed onto electron carriers Depending on the photosystem, the electrons have different fates

43. Chlorophyll • Accessory pigments • Other forms of chlorophyll a • Chlorophyll b • Carotenoids • Xanthophylls

44. Accessory Pigments Absorb the wavelengths of light that are not easily absorbed by chlorophyll and funnel the photons to chlorophyll a at the base of the photosystem (reaction centre) Don’t contain a porphyrin group – not directly involved in the light dependent reactions

45. Accessory pigments • Chlorophyll b • Absorbs light at wavelengths between 500-640nm • It appears blue-green • Is one of the accessory pigments • Carotenoids • Absorb blue light • Reflects yellow (xanthophyll) and orange (carotene) light • They absorb light not normally absorb by chlorophylls – then pass

46. Light Chlorophyll solution Electrons excited to a higher energy level Electrons return to their original (ground) state Energy transferred to surrounding as: Heat, and, Light at a longer (less energetic) wavelength – seen as red fluorescence Light Chlorophyll in leaf Electrons excited to a higher energy level Electrons accepted by an electron acceptor and passed onto electron carriers arranged at progressively lower energy levels Energy generated by electron transfer is used to phosporylate ADP to form ATP – by PHOTOPHOSPHORYLATION – through chemiosmosis Light energy is converted to a usable form of chemical energy (ATP) ATP used for biosynthesis and physiological processes