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Chapter 8


8.1 - HOW ORGANISMS OBTAIN ENERGY

Transformation of energy
  • Energy- the ablility to work
  • Thermodynamics - the study of the flow and transformation of energy in the universe

Laws of Thermodynamics
  • 1st Law - energy can be converted from one form to another, but it cannot be destroyed.
  • 2nd Law - energy cannot be converted without the loss (or disippation) of energy (heat, friction, sound, light, etc.).

Autotrophs and Heterotrophs
  • Autotrophs are organisms that make their own food. Exs: plants, some protists (algae), and some bacteria.
  • Heterotrophs are organisms that need to ingest food to obtain energy. Exs: animals, fungi, some protists (amoeba, paramecia), and some bacteria.

Trophic Levels: Sun -> Autotroph -> Heterotroph -> Heterotroph

Metabolism
  • Metabolism - all of the chemical reactions in a cell
  • Photosynthesis - light energy from the sun is converted to chemical energy (glucose) for use by the cell
  • Cellular respiration - organic molecules (glucose) are broken down to release energy for use by the cell
  • Glucose - C6 H12 O6 (C H2 0-carbohydrate)
  • Sun is source of energy

ATP: The Unit of Cellular Energy
  • ATP - the "energy currency" of the cell
  • ATP stores and releases a small amount ($1) of energy for movement, transport, and other active processes in the cell.
  • ATP is Adenosine Triphosphate
  • Both heterotrophs and autotrophs use ATP as an energy storage molecule in their cells.
  • ATP stores energy in third phosphate, which breaks off to release energy and attaches to absorb
  • ATP is used to power cell processes in the cell such as the Calvin Cycle of photosynthesis in which carbon dioxide is converted into glucose.
  • ATP is also used for movement within the cell
  • It is produced during cell respiration when carbohydrates such as glucose are broken down
  • Energy is realeased when the third phosphate on ATP is removed and transferred to another molecule.
  • This leaves behind ADP
  • ADP is Adenosine Diphosphate


8.2 - PHOTOSYNTHESIS

Photosynthesis
  • Photosynthesis - the process by which the energy of the sun is used to convert H2O and CO2 into high energy sugars (glucose).
  • Importance: we need glucose and other carbohydrates for energy but we cannot produce them ourselves. We also need oxygen and this is produced during photosynthesis by plants and algae.

Light Energy
  • Light - is a form of energy that travels in the form of PARTICLES or WAVES
  • The waves are measured in WAVELENGTHS, which can vary in length. Humans can see violet through red wavelengths. (Remember ROY G. BIV?)
  • Color - reflected light
  • Pigment - a molecule that absorbs light
  • Whatever colors the pigment does NOT absorb are that we see.

Pigments
  • Chlorophyll is a pigment that ABSORBS violet, red, and blue wavelengths of light.
  • Green is REFLECTED by chlorophyll a. That's why most leaves appear green to us.
  • Other pigments called ACCESSORY PIGMENTS (chlorophyll a, xanophyll, and carotene) help chlorophyll a absorb a greater spectrum of light.

Chloroplast
  • Photosynthesis takes place in the chloroplast
  • Chloroplast - 1. double membraned, disk-shaped organelle 2. located inside this disk are stacks of sacks
  • Each stack is called a thylokoid
  • Inside each thylakoid is chlorophyll and other pigments
  • Stacks of sacks are called grana
  • Surrounding the grana is a fluid called stroma

Balanced Photosynthesis Equations
  • Photosynthesis occurs in two phases.
  • Light-dependent reactions
  • Light-independent reactions

Phase One: Light Reactions
  • The absorbtion of light is the first step in photosynthesis
  • Chloroplast capture light energy
  • GOAL: To convert light energy into chemical bond energy (ATP, NADPH)
  • What goes in: H2O, light, pigments, (chlorophyll), ADP, P, NADP+
  • What comes out: O2, ATP, NADPH
  • Location: in the thylakoids

Electron Transport
  • Light energy excites electrons in photosystem II and also cause a water molecule to split, releasing an electron transport system, H+ into the thylakoid space, and O2 as a waste product.
  • The excited electrons move from photosystem II to an electron-acceptor molecule in the thylakoid membrane
  • The electron-acceptor molecule transfers the electrons along a series of electron-carriers to photosystem I.

The Calvin Cycle
  • Happens in stroma
  • Goal: to turn CO2 into glucose using energy from ATP and NADPH
  • What comes in: ATP, NADPH, RuBP,
  • What goes out: Glucose (stored by plant), ADP, P, and NADP+ (shipped back to light reactions)
  • Step 1: 6 CO2 molecules combine with 6 RuBP's to form 12 3-carbon molecules called 3-PGA.
  • Step 2: ATP provides energy and NADPH provides protons to transorm the 3-PGA molecules into twleve high-energy molecules called G3P. One molecule of G3P is a half glucose. Two of the twelve G3P leave cycle to become glucose.
  • Step 3: An enzyme called rubisoc onverts the remaining ten G3P molecules back into 6 molecules of RuBP.
  • Step 4: Th 6 RuBP's combine with 6 new CO2's to continue the cycle.
  • Factors influencing the rate of photosynthesis: (1) availability of water (2) intensity of sunlight (3) temperature

Alternative Pathways - the H2O/CO2 problem
C4 Plants
  • Adaptation to conserve water in hot regions.
  • Instead of 3-CArbon stages (3-PGA and G3P), these plants fix CO2 into a 4-carbon molecule
  • Able to keep stomata closed on hot days and Calvin cylce occurs only in special cells.
  • Used by sugar cane and corn
CAM Plants
  • Conserves water in dry regions.
  • Only open stomata for CO2 at night.
  • Holds the CO2 until daytime. Calvin cycle proceeds while stomata are closed.
  • Used by pineapple and cacti.
Bell Curve - optimum zone, tolerance zone

8.3 CELLULAR RESPIRATION
  • Overall Goal: to completely break down glucose and tranfer the energy to ATP
  • Location: in the cytoplasm and mitochondria of all eukaryotic cells.
  • C6 H12 O6 -> 6CO2 + 6H2O + Energy
  • Cellular Respiration occurs in two main parts: glycolysis and aerobic respiration

Glycolysis
  • Glucose is broken down in the cytoplasm through the process of glycolysis
  • Two molecules of ATP and two molecules of NADH are forned for each molecule of glucose that is broken down.
  • Happens in cytoplasm
  • Goal: to break glucose ($100) into 2 pyruvates ($50). Does not require Oxygen therefore it is ANAEROBIC
  • What goes in: Glucose + 2 ATP's ("invested")
  • What comes out: 2 pyruvates ($50 each), 2 ATP's ($1) (net), 2 NADH's ($10)
  • 9 step process with 2 phases: energy consuming/investing, energy releasing
  • Glucose enters the cell by facilitated diffusion
  • 2 ATP's PHOSPHORYLATE (add a phosphate one each side) glucose which makes it more reactive
  • Glucose breaks down into two 3-Carbon molecules