Biology Homeostasis, Passive and Active Transport in Cells

Homeostasis The balance maintained within a living thing Specifically, with respect to cells: – how a cell maintains a balance of materials (food, water, waste, minerals, salts, etc.) inside.

Transport How a cell brings needed materials (food, water, mineral etc.) in across the cell membrane How a cell sends other materials (waste, excess water, secreted hormones) out across the membrane How a cell moves materials from place to place within the cell.

Two Types of Transport Passive Transport: requires no energy expenditure by the cell –Examples: diffusion, osmosis, facilitated diffusion, diffusion through ion channels Active Transport: requires the cell to use energy to transport materials –Examples: Membrane pumps, endocytosis, exocytosis, pinocytosis.

Passive Transport: Diffusion In a solution, materials will move from an area of high concentration to an area of lower concentration, until an equilibrium is reached The difference in concentration between two areas is called the concentration gradient or diffusion gradient. In diffusion, materials always move from higher concentration to lower concentration.

Passive Transport (diffusion) Normal diffusion. The solute particles gradually spread out evenly through the solution. Note: The water molecules also spread into the solute.

Passive Transport: Osmosis The cell membrane is selectively permeable– some materials can cross it more easily than others. Remember: Water also diffuses. It goes into the places that have less water (and more solutes) Water can easily move across the cell membrane

Osmosis Osmosis is when water diffuses across a membrane into, or out of, a cell. –Which direction osmosis takes depends on the solution the cell is placed in Hypotonic solutions contain less dissolved solutes than the cell. Osmosis is inwards (water enters the cell) Hypertonic solutions contain more dissolved solutes than the cell. Osmosis is outwards (water leaves the cell) Isotonic solutions contain the same amount of dissolved solutes as the cell. There is no net osmosis.

Effects of Osmosis on cells Effect on animal cells  Effect on plant cells  Animal very Thirsty! Animal Healthy Animal Cells Damaged! Serious Wilting! Temporary Wilting Plant cells firm

Video of Osmosisand egg experimentOsmosisegg experiment an Osmometer

Passive Transport: Facilitated Carrier proteins may assist certain materials across the cell membrane Ion Channels provide small pathways through the membrane for some ions to move through. –Ions couldn’t otherwise pass through the lipid bilayer.

 Ion channels allow some small ions to pass, but block larger molecules Carrier proteins help some materials pass through the membrane 

Active Transport Materials are pumped, pulled or pushed through the membrane. Energy is required.

Ion Pumps Ion pumps push ions across the membrane. Example (Na+/K+ pump) –A protein embedded in the membrane binds to three sodium ions from inside the cell –ATP causes the protein to change shape, pushing the sodium through the membrane –Potassium from outside the cell can now bind to the protein –The protein changes shape again, pushing the potassium into the cell.

Ion Pumps Classroom video on active transport.(9:00)active transport Sodium/Potassium pump video.(1:36)pump Sodium/Potassium pump video by non- science students ( 56 sec)non- science students Another short animation (24 sec)animation

Endo-, Exo-, and Pinocytosis Endocytosis and exocytosis are both variations of a process called pinocytosis. In all forms of pinocytosis, materials cross the cell membrane in small vesicles

Exocytosis and Endocytosis Exocytosis pushes things out of the cell. Endocytosis brings things into the cell.

Phagocytosis Phagocytosis is endocytosis on a larger scale. Large molecules or even entire cells are surrounded and brought inside the cell. In humans, phagocytosis mostly occurs in white blood cells, when they engulf bacteria. Video of Phagocytosis Edible Video of Phagocytosis

Endocytosis video (35 sec)video Endocytosis & exocytosis animation made by students using string. (27 sec)animation

Diagram of Onion Cell

Onion Skin Cells (low power)

Onion Cells (high power)

Test Friday Chapters 1, (2), 3, 4 and 5 in textbook Topics –Chapter 1: What is Life? Features and properties of life. –Chapter 3: Biochemistry Proteins, Carbohydrates, Lipids, Nucleic Acids. Their properties, sub-units, and biological uses. –Chapter 4: The Cell Membrane: The lipid bilayer, other features of the cell membrane Cytoplasm: cytosol; organelles-- their structures and functions The Nucleus: Nuclear membrane, nucleoplasm, chromosomes and nucleolus Eukaryotic vs. Prokaryotic cells –Chapter 5: Transport in Cells Passive Transport: Diffusion and Osmosis Osmosis and the Cell Membrane: ion channels, facilitated diffusion. Effects of osmosis on cells. Active Transport: ion pumps, endo and exocytosis, phagocytosis

Typical Test Format About 50% fact based questions (multiple choice / fill in blank / short answer) About 30 % identification and brief explanation (labelling diagrams, identifying structures and describing functions) About 20% longer answer questions: Explaining concepts and justifying opinions

Multiple Choice Answers 6.BMolecules tend to move down their concentration gradients (ie. from higher concentration to lower concentration) 7.DThe cell membrane helps maintain homeostasis 8.CIon channels help ions move across the cell membrane 9.AGlucose often enters the cell by facilitated diffusion using carrier molecules. 10.C Low turgor pressure causes a plant to wilt. 11.BThe Sodium-Potassium pump usually pumps sodium out of the cell and potassium into it. 12.AA cell expends energy on membrane pumps (a form of active transport) 13.BPhagocytosis is when cells engulf and destroy other cells 14.DCarrier proteins are most important in facilitated diffusion 15.CThe solution outside the cell is probably hypertonic, because the membrane appears to have pulled back from the cell walls.

Review One Describe the most important features of living things Be able to list characteristics of living things Be able to justify opinions about what should and should not be considered alive. You should be able to describe the scientific methods, and distinguish between experiment, hypothesis and theory. You should be able to identify good experimental procedures, including use of controls and single variable procedures.

Review 2 There will be no test questions from chapter 2, HOWEVER: you will be expected to know the difference between atoms, molecules and ions, and to know what mixtures and solutions are.

Review 3 Importance of Water and Carbon Carbohydrates Lipids Proteins Nucleic Acids Constituents (monomers or subunits) Structure (how are they bonded together) Sources (where do we get them?) Uses (what does our body do with them?)

Review 4 Cells Membrane –Lipid Bilayer (hydrophilic, hydrophobic) –Protein inclusions Cytoplasm –Organelles Mitochondrion Ribosomes ER Nucleus

The Organelles Know the Structure & Function! Mitochondiron Ribosome Endoplasmic Reticulum Golgi Apparatus (Golgi Body) Vacuoles Lysosomes