Photosynthesis and Cellular Respiration - Detailed Notes

The Great Plains

• The interaction between producers and consumers demonstrates how the Sun's energy enters, is transformed, and exits living systems.
• Chemicals like water, carbon, nitrogen, and sulfur cycle continuously, connecting organisms with each other and their environment.
• The Prairie landscape contains products of technology, such as the petroleum industry extracting crude oil and natural gas.
• These resources formed over time as natural chemical processes altered ancient producers and consumers into compounds that fuel society and create synthetic materials.
• Unit 1 focused on interactions between living and non-living systems at a macroscopic level, while this unit considers the same interactions at a microscopic level.
• This unit will cover the cellular processes of photosynthesis and cellular respiration, which provide the energy and matter organisms need to survive.

Unit 3 General Outcomes

• Relate photosynthesis to the storage of energy in organic compounds.
• Explain the role of cellular respiration in releasing potential energy from organic compounds.

Focussing Questions

• How does light energy from the Sun enter living systems?
• How is the energy from light used to synthesize organic matter?
• How is the energy from organic matter released for use by living systems?

Unit 3 Preparation: Prerequisite Concepts

• This unit builds on prior knowledge of photosynthesis and cellular respiration from Chapters 1 and 2.

Plant and Animal Cells

• Plants and animals, along with fungi and protists, are eukaryotic organisms with cells containing a nucleus.

• Cells are microscopic components that make up all organisms, exhibiting characteristics of life and specializing in specific tasks.

• Plant and animal cells have structural differences; plant cells have a rigid cell wall, which animal cells lack.

• Both cell types share basic structural and functional similarities, including organelles that perform specific functions within the cell.

• Organelles are often surrounded by a membrane and work together as a cellular system to carry out essential life-related tasks.

  Plant cells

  • Plant cells are generally larger than animal cells.
  • Plant cells have cell walls and chloroplasts, which are not found in animal cells.

Common structures in plant and animal cells:

• Cell Membrane: Separates the cell interior from the outside world and controls the movement of materials in and out of the cell.
• Cytoplasm: Gel-like material, mainly water, containing dissolved materials that create the chemical environment for other cell structures.
• Nucleus: The cell's command center contains DNA blueprints for making proteins and is surrounded by a double membrane to protect the DNA from biochemical reaction byproducts.
• Nuclear Pores: Pores in the nuclear membrane are large enough to allow macromolecules to enter and ribosomes to leave the nucleus.
• Chromatin: Uncoiled chromosomes (DNA).
• Nucleolus: A specialized area of chromatin inside the nucleus that produces ribosomes.
• Ribosome: Tiny two-part structures throughout the cytoplasm help assemble proteins.
• Endoplasmic Reticulum (ER): A system of flattened membrane-bound sacs and tubes continuous with the outer membrane of the nuclear envelope.
  • Rough ER: Studded with ribosomes and synthesizes proteins.
  • Smooth ER: Synthesizes phospholipids and packages macromolecules in vesicles for transport.
• Golgi Apparatus: A stack of flattened membrane-bound sacs that receive vesicles from the ER, contain enzymes for modifying proteins and lipids, and package finished products into vesicles for transport.
  • Transport to the cell membrane for secretion out of the cell.
  • Transport within the cell as lysosomes.
• Mitochondrion: The powerhouse of the cell where organic molecules like carbohydrates are broken down inside a double membrane to release and transfer energy.
• Lysosome: A membrane-bound vesicle filled with digestive enzymes that can break down worn-out cell components or materials brought into the cell.
• Peroxisome: A membrane-bound vesicle containing enzymes that break down lipids and toxic waste products, like alcohol.
• Centrosome: An organelle located near the nucleus organizes the cell’s microtubules, contains a pair of centrioles (made up of microtubules), and helps organize the distribution of cell components during division.
• Vesicle: A small membrane-bound transport sac.
• Vacuole: A large membrane-bound, fluid-filled sac for the temporary storage of food, water, or waste products.
• Cytoskeleton: A network of interconnected fibers (actin filaments, intermediate filaments, and microtubules) that maintain cell shape and allow for movement of cell parts.

The Cell Membrane

• The cell membrane separates the internal environment of a cell from its external environment.
• Cell membranes are composed mainly of a double layer of phospholipid molecules (lipids that don't dissolve in water, like fats, oils, and steroids).
• Each phospholipid molecule has a head region (dissolves easily in water) and a tail region (insoluble in water).
• Phospholipid molecules arrange themselves in water into a two-layered structure with head ends exposed to water and tail ends facing each other away from water.
• Cell membranes include double-layer phospholipids, proteins, and other embedded molecules.
• Some embedded proteins create passageways for water-soluble molecules and ions, while others help transport substances across the membrane.

Passive Transport: Diffusion and Osmosis

• The cell membrane is selectively permeable, allowing some molecules to pass through while preventing others.
• Diffusion is the natural movement of molecules or ions from a region of higher concentration to one of lower concentration.
• Small, uncharged molecules like oxygen can move easily through the cell membrane by diffusion; this is a passive process that doesn't require energy.
• Substances move down their concentration gradient, referring to a difference in quality between adjacent regions (concentration, pressure, electrical energy, pH).
• Osmosis is the diffusion of a solvent (water) across a semi-permeable membrane separating two solutions.
  • The direction of osmosis depends on the relative concentration of water molecules on either side of the cell membrane.

Osmosis scenerios

• Isotonic: If the water concentration inside the cell equals the water concentration outside the cell, equal amounts of water move in and out of the cell at the same rate.
• Hypotonic: If the water concentration outside the cell is greater than that inside the cell, water moves into the cell.
• Hypertonic: If the water concentration inside the cell is greater than that outside the cell, water moves out of the cell.
• The cell membrane cannot prevent the movement of water, thus osmosis is a passive process.

Facilitated Diffusion

• Substances like water, oxygen, and carbon dioxide can pass through the cell membrane without assistance.
• Other substances, like glucose, require help to pass through the cell membrane.
• Specialized transport proteins in the cell membrane help different kinds of substances move in and out of the cell.
• A particular transport protein will recognize and help to move only one type of dissolved molecule or ion based on its shape, size, and electrical charge.
• Carrier proteins facilitate the movement of glucose molecules from high to low concentration and allow molecules to move both in and out of the cell.
• Channel proteins transport charged particles across the membrane; ions must be small enough and have the right charge to fit through the tunnel.
• Diffusion, osmosis, and facilitated diffusion do not require energy from the cell.

Active Transport

• Active transport uses energy to enable a cell to take in a substance that is more concentrated inside the cell than outside the cell.
• Energy for active transport often comes from adenosine triphosphate (ATP).
• The splitting of one of the three phosphates from ATP releases energy that is harnessed to power a cellular function, often moving a molecule through a membrane against its concentration gradient.

Endocytosis and Exocytosis

• Some substances are too large to cross the cell membrane, so the cell uses vesicles to "swallow" or expel substances.
• Endocytosis involves the cell membrane folding inward, trapping and enclosing a small amount of matter from outside the cell.
  • Types of endocytosis: pinocytosis, phagocytosis, and receptor-assisted endocytosis.
    • Pinocytosis intakes a small droplet of extracellular fluid with dissolved substances or tiny particles and occurs in almost all cell types.
    • Phagocytosis intakes a large droplet of extracellular fluid, often including bacteria or bits of organic matter, and occurs only in specialized cells like white blood cells.
    • Receptor-assisted endocytosis intakes specific molecules that attach to special proteins in the cell membrane, like cholesterol.
• Exocytosis removes substances from the cell; a vesicle from inside the cell moves to the cell surface, fuses with the cell membrane, and releases its contents into the extracellular fluid.

Mechanisms for the Movement of Substances across the Cell Membrane