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Lecture 23


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Lecture 23

  1. 1. Lecture 23: Plant Anatomy/Nutrient Transport & Photosynthesis Covers Chapters 7 & 43
  2. 2. Vascular seed plants • Gymnosperms: non-flowering plants • Seeds develop on surface of leaves or in a cone – Pine, eucalyptus trees • Angiosperms: flowering plants • 2 types, depending on number of cotyledons: a structure in the plant embryo that becomes the first leaf/leaves – Monocots: ONE COTYLEDON » some flowers, palm trees, grasses, wheat, rice, corn, oats – Dicots: TWO COTELYDONS » trees, other vegetables, some flowers
  3. 3. Gymnosperm
  4. 4. Monocot vs Dicot
  5. 5. Angiosperms
  6. 6. Angiosperms
  7. 7. Let’s stick to angiosperms only! • Since 80% of all living plant species are angiosperms, we will focus our anatomy lecture and reproductive lecture on angiosperms only! • There are a number of different types of cells in plants, but let’s just say that just like in humans, cells combine to form tissues.
  8. 8. Cells form Tissues • Plant cells, as they divide and differentiate, can form different tissues (one or more type of specialized cell that perform a specific function): – Dermal Tissue* – Ground Tissue* – Vascular Tissue*
  9. 9. 3 types of plant tissues* – In general, go from outside of plant to inside – Dermal Tissue System: covers outer surface of plant body • Primary purpose: reduce evaporation of water – Waxy cuticle (waterproof covering on leaves) – Periderm (waterproof covering on stems & roots) – Ground Tissue System: aka cortex • Primary purpose: photosynthesis, storage and support • Fruit and flowers arise from ground tissue – Parenchyma: photosynthesis, secretion of hormones, food storage – Collenchyma & Sclerenchyma: support and strengthen plant (take out?) – Vascular Tissue System: aka vascular bundle • Primary purpose: transports fluids and dissolved substances throughout plant body – Xylem: transports water and dissolved minerals (K, Ca, phosphate, Cl) FROM ROOTS TO TOP OF PLANT – Phloem: transports a solution of sugars, amino acids and hormones from structures that made it IN ALL DIRECTIONS (up and down plant, to or from leaves)
  10. 10. Plant Tissue
  11. 11. Xylem/Phloem
  12. 12. Tissues combine to form systems* • Two systems: – Root System: consists of all of the roots – Shoot System: all structures above ground
  13. 13. Root System • *Roots: branched portions of plant body, usually embedded in soil. • Have either – taproot system: central root with many branches (dicots) – fibrous system: many roots of equal size (monocots) • *Contain all three types of tissue – Dermal Tissue: periderm – Ground Tissue • *Store surplus food (carbs) manufactured in the shoot during photosynthesis • *Anchor the plant • *Produce some hormones Absorb water and minerals (vascular tissue) – Vascular Tissue: vascular bundle (X&P) • *Absorb water and minerals • *Transport water, minerals, sugars and hormones to and from the shoot
  14. 14. How do roots acquire water/nutrients? • Plants acquire: – Carbon from CO2 in the air – Oxygen from the air or from O2 dissolved in water – Hydrogen from H20 – Minerals and water from the soil (water by osmosis, minerals by active transport)
  15. 15. root hair epidermis cortex endodermis of cortex pericycle xylem phloem apical meristem vascular cylinder root cap Roots Fig. 43-13
  16. 16. Shoot System* • Two basic parts: – Buds: • Give rise to – Leaves: principle site of photosynthesis – Flowers & Fruit: contain plant reproductive organs & gametes – Stems: • elevate, support and separate leaves, flowers and fruit above the ground
  17. 17. Leaves • *Major photosynthetic structure of most plants • *Contain all three types of tissue – *Dermal Tissue: waxy cuticle and STOMATA – *Ground Tissue: Mesophyll cells (photosynthesis here!) – *Vascular Tissue: vascular bundle (X&P), called VEIN • Sugars made in mesophyll cells travel in vein to other areas of the plant • Many plants have evolved specialized leaves depending on climate/location/predators, etc
  18. 18. Stomata* • Stomata: adjustable pores that can open/close and let CO2 and water in, let O2 out – Leaves cannot entirely close stomata, because then CO2 cannot get in….therefore, transpiration happens: loss of water through stomata (plant lose 90% of water taken in by roots this way!) – The water being lost from stomata creates tension that pulls water up from roots (this is how water can get to the top of a 350-foot tall tree!) – Guard cells line the stomata and can change shape, size and volume, causing stomata to open/close – Like humans and oxygen, plants need CONTINUOUS CO2!
  19. 19. upper epidermis petiole blade mesophyll palisade layer spongy layer lower epidermis stoma guard cell chloroplasts xylem phloem vascular bundle cuticle cuticle bundle-sheath cell A Typical Leaf Fig. 43-6
  20. 20. Stomata Fig. 43-22
  21. 21. 2 1 3 water molecules Water evaporates through the stomata of leaves Water enters the vascular cylinder of the root Cohesion of water molecules to one another by hydrogen bonds creates a “water chain” flowofwater Water Flow from Root to Leaf in Xylem Fig. 43-21
  22. 22. Specialized Leaves Fig. 43-7
  23. 23. Stems* • Elevate, support and separate leaves • Transport water and dissolved minerals from roots to leaves • Transport sugars produced in photosynthetic parts of shoot to roots and other parts of shoot (buds, flowers, fruit) • Contain all three types of tissue – Dermal Tissue: periderm – Ground Tissue: Cortex & Pith – Vascular Tissue: Vascular bundle (X&P) plus cambium • Cambium differentiates into secondary X&P: this is the WOOD in the tree.
  24. 24. Stem Fig. 43-8 terminal bud apical meristem leaf primordia node lateral bud internode vascular bundle pith branch (sprouted lateral bud) petiole blade leaf epidermis epidermis cortex cortex cortex pith primary phloem vascular cambium vascular cambium dividing vascular cambium primary xylem secondary phloem cork new secondary xylem primary xylem new secondary phloem primary xylem primary phloem primary phloem pith pith cork cambium cork (a) Primary and secondary growth in a dicot stem (b) Stem cross-sections (c) Vascular bundles vascular bundle cork cambium secondary xylem secondarygrowthprimarygrowth
  25. 25. Photosynthesis • Solar energy is trapped and stored as chemical energy in the bonds of organic molecules as sugars.* • Occurs in plants, photosynthetic protists, and certain bacteria (we focus on plants) • Takes place in leaf cells (mesophyll) in chloroplasts: organelles like mitochondria (double-walled organelles in plant cytoplasm)*
  26. 26. Anatomy of a chloroplast* • Outer membrane • Intermembrane space • Inner membrane • Stroma: area inside inner membrane • Thylakoid: disc-shaped interconnected membranous sacs in stroma • Chlorophyll: photosynthetic pigment in thylakoid • Thylakoid space: space inside thylakoids
  27. 27. Chloroplast
  28. 28. Closeup of thylakoid
  29. 29. 2 stages of photosynthesis* • Light reactions: (IN THYLAKOID) – Chlorophyll captures sunlight energy and transfers it to ADP & NADP+ (energy carrier molecules..result is ATP & NADPH). Water is split and O2 gas is byproduct • Calvin cycle (aka dark reaction): IN STROMA) – CO2 from atmosphere is made into a 3-carbon sugar (that can be changed into glucose), using chemical energy from the light reaction
  30. 30. An Overview of the Relationship Between the Light Reactions and the Calvin Cycle Fig. 7-3
  31. 31. A little bit about light • Light is composed of individual units called photons • Energy of a photon corresponds to its wavelength: short-wave photons are very energetic, long-wave photons less energetic • Light hits leaf: could bounce back, pass through, or be captured • Any light that bounces back reaches our eyes • Chloroplasts contain pigment molecules that absorb (capture) different wavelengths – Chlorophyll reflects green, making plants look green! – Carotenoid pigment molecules reflect orange and yellow (leaves in fall have lost chlorophyll, appear red, yellow, orange!)
  32. 32. Light reaction* • Like cell respiration, electrons carry energy from one place to another. • Takes place within/across thylakoid membrane • Light hits chlorophyll molecule in thylakoid membrane • Light energy is transferred to electrons, which travel through two electron transport chains and then transfer the electrons (and a hydrogen ion) to NADP+, which converts it to NADPH. • H20 is split and this creates a high H+ concentration inside thylakoid space (and low H+ in stroma) • O2 is created and released from plant to atmosphere • This concentration gradient is utilized: as H+ moves down its gradient from thylakoid space to stroma, it powers the synthesis of ATP from ADP
  33. 33. Events of the Light Reactions Occur In and Near the Thylakoid Membrane H+ are pumped into the thylakoid space ATP synthase photosystem I photosystem II thylakoid membrane light energy + + P ATP NADP+ ADP NADPH Calvin cycle CO2 C6H12O6 sugar e– e– e– e– e– e– 1 /2 2 H2O chloroplast electron transport chain II electron transport chain I (stroma) (thylakoid space) thylakoid O2 A high H+ concentration is created in the thylakoid space The flow of H+ down their concentration gradient powers ATP synthesis H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ 1 2 3 Fig. 7-7
  34. 34. Dark reaction aka Calvin Cycle* • ATP and NADPH from light reaction are now positioned in the stroma • Calvin cycle is really THREE reactions: – Carbon fixation: CO2 (plant takes in from atmosphere) is incorporated into a larger molecule. • Each molecule of CO2 combines with a molecule of RUBP (a 5- carbon sugar) to form TWO molecules of PGA (a 3-carbon sugar), catalyzed by the enzyme RUBISCO – Synthesis of G3P: energy from ATP & NADPH is used to convert 6 PGA molecules to 6 molecules of G3P (also a 3-carbon sugar) – Regeneration of RUBP: 5 of the 6 molecules of G3P are used to regenerate RUBP, and 1 molecule of G3P combines with another to form glucose! • Glucose is then used by cell or stored.
  35. 35. Calvin Cycle