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A solution is composed of a solute dissolved in a solvent. In the sugar water described in Figure 5-1, the solute was sugar and the solvent was water, and the solute molecules diffused through the solvent. It is also possible for solvent molecules to diffuse. In the case of cells, the solutes are organic and inorganic compounds, and the solvent is water. The process by which water molecules diffuse across a cell membrane from an area of higher concentration to an area of lower concentration is called osmosis (ahs-MOH-sis). Because water is moving from a higher to lower concentration, osmosis does not require cells to expend energy. Therefore, osmosis is the passive transport of water. Direction of Osmosis The net direction of osmosis depends on the relative concentra- tion of solutes on the two sides of the membrane. Examine Table 5-1. When the concentration of solute molecules outside the cell is lower than the concentration in the cytosol, the solution outside is hypotonic to the cytosol. In this situation, water diffuses into the cell until equilibrium is established. When the concentration of solute molecules outside the cell is higher than the concentration in the cytosol, the solution outside is hypertonic to the cytosol. In this situation, water diffuses out of the cell until equilibrium is established. Observing Diffusion Materials 600 mL beaker, 25 cm dialysis tubing, funnel, 15 mL starch solution (10 percent), 20 drops Lugol’s solution, 300 mL water, 100 mL graduated cylinder, 20 cm piece of string (2) Procedure 1. Put on your disposable gloves, lab apron, and safety goggles. 2. Pour 300 mL of water in the 600 mL beaker. 3. Add 20 drops of Lugol’s solution to the water. CAUTION: Lugol’s solution is a poison and eye and skin irritant. 4. Open the dialysis tubing, and tie one end tightly with a piece of string. 5. Using the funnel, pour 15 mL of 10 percent starch solution into the dialysis tubing. 6. Tie the other end of the dialysis tubing tightly with the second piece of string, forming a sealed bag around the starch solution. 7. Place the bag into the solution in the beaker, and observe the setup for a color change. Analysis What happened to the color in the bag? What happened to the color of the water around the bag? Explain your observations. Quick Lab www.scilinks.org Topic: Osmosis Keyword: HM61090 mb06se_homs01.qxd 11/27/07 8:52 AM Page 98 HOMEOSTASIS AND CELL TRANSPORT 99 When the concentrations of solutes outside and inside the cell are equal, the outside solution is said to be isotonic to the cytosol. Under these conditions, water diffuses into and out of the cell at equal rates, so there is no net movement of water. Notice that the prefixes hypo-, hyper-, and iso- refer to the relative solute concentrations of two solutions. Thus, if the solution outside the cell is hypotonic to the cytosol, then the cytosol must be hyper- tonic to that solution. Conversely, if the solution outside is hypertonic to the cytosol, then the cytosol must be hypotonic to the solution. Water tends to diffuse from hypo- tonic solutions to hypertonic solutions. How Cells Deal with Osmosis Cells that are exposed to an isotonic external environment usually have no difficulty keeping the movement of water across the cell membrane in balance. This is the case with the cells of ver- tebrate animals on land and of most other organ- isms living in the sea. In contrast, many cells function in a hypotonic environment. Such is the case for unicellular freshwater organisms. Water constantly diffuses into these organisms. Because they require a relatively lower concentration of water in the cytosol to function normally, unicel- lular organisms must rid themselves of the excess water that enters by osmosis. Some of them, such as the paramecia shown in Figure 5-2, do this with contractile vacuoles (kon-TRAK-til VAK-y ̄ ̄o ̄ ̄o-OL), which are organelles that remove water. Contractile vacuoles collect the excess water and then contract, pumping the water out of the cell. Unlike diffusion and osmosis, this pumping action is not a form of passive trans- port because it requires the cell to expend energy. Copyright © by Holt, Rinehart and Winston. All rights reserved. (a) (b) Vacuole filling with water Vacuole contracting TABLE 5-1 Direction of Osmosis Condition External solution is hypotonic to cytosol External solution is hypertonic to cytosol External solution is isotonic to cytosol Net movement of water into the cell out of the cell none H2O H2O H2O H2O H2O H2O The paramecia shown below live in fresh water, which is hypotonic to their cytosol. (a) Contractile vacuoles collect excess water that moves by osmosis into the cytosol. (b) The vacuoles then contract, returning the water to the outside of the cell. (LM 315) FIGURE 5-2 100 CHAPTER 5 (a) HYPOTONIC Cell walls (b) HYPERTONIC (a) ISOTONIC (b) HYPOTONIC (c) HYPERTONIC Other cells, including many of those in multicellular organisms, respond to hypotonic environments by pumping solutes out of the cytosol. This lowers the solute concentration in the cytosol, bring- ing it closer to the solute concentration in the environment. As a result, water molecules are less likely to diffuse into the cell. Most plant cells, like animal cells, live in a hypotonic environ- ment. In fact, the cells that make up plant roots may be surrounded by water. This water moves into plant cells by osmosis. These cells swell as they fill with water until the cell membrane is pressed against the inside of the cell wall, as Figure 5-3a shows. The cell wall is strong enough to resist the pressure exerted by the water inside the expanding cell. The pressure that water molecules exert against the cell wall is called turgor pressure (TER-GOR PRESH-er). In a hypertonic environment, water leaves the cells through osmosis. As shown in Figure 5-3b, the cells shrink away from the cell walls, and turgor pressure is lost. This condition is called plasmolysis (plaz-MAHL-uh-sis), and is the reason that plants wilt if they don’t receive enough water. Some cells cannot compensate for changes in the solute con-

WWW 11-14 study set

WWW List #11

Cohesion and Adhesion Water molecules stick to each other as a result of hydrogen bond- ing. An attractive force that holds molecules of a single substance together is known as cohesion. Cohesion due to hydrogen bonding between water molecules contributes to the upward movement of water from plant roots to their leaves. Related to cohesion is the surface tension of water. The cohe- sive forces in water resulting from hydrogen bonds cause the mol- ecules at the surface of water to be pulled downward into the liquid. As a result, water acts as if it has a thin “skin” on its sur- face. You can observe water’s surface tension by slightly overfill- ing a drinking glass with water. The water will appear to bulge above the rim of the glass. Surface tension also enables small crea- tures such as spiders and water-striders to run on water without breaking the surface. Adhesion is the attractive force between two particles of differ- ent substances, such as water molecules and glass molecules. A related property is capillarity (KAP-uh-LER-i-tee), which is the attrac- tion between molecules that results in the rise of the surface of a liquid when in contact with a solid. Together, the forces of adhe- sion, cohesion, and capillarity help water rise through narrow tubes against the force of gravity. Figure 2-11 shows cohesion and adhesion in the water-conducting tubes in the stem of a flower. Temperature Moderation Water has a high heat capacity, which means that water can absorb or release relatively large amounts of energy in the form of heat with only a slight change in temperature. This property of water is related to hydrogen bonding. Energy must be absorbed to break hydrogen bonds, and energy is released as heat when hydrogen bonds form. The energy that water initially absorbs breaks hydro- gen bonds between molecules. Only after these hydrogen bonds are broken does the energy begin to increase the motion of the water molecules, which raises the temperature of the water. When the temperature of water drops, hydrogen bonds reform, which releases a large amount of energy in the form of heat. Therefore, during a hot summer day, water can absorb a large quantity of energy from the sun and can cool the air without a large increase in the water’s temperature. At night, the gradually cooling water warms the air. In this way, the Earth’s oceans stabilize global temperatures enough to allow life to exist. Water’s high heat capac- ity also allows organisms to keep cells at an even temperature despite temperature changes in the environment. As a liquid evaporates, the surface of the liquid that remains behind cools down. A relatively large amount of energy is absorbed by water during evaporation, which significantly cools the surface of the remaining liquid. Evaporative cooling prevents organisms that live on land from overheating. For example, the evaporation of sweat from a person’s skin releases body heat and prevents over- heating on a hot day or during strenuous activity. Adhesion Cohesion Hydrogen bonds Cohesion, adhesion, and capillarity contribute to the upward movement of water from the roots of plants. FIGURE 2–11 www.scilinks.org Topic: Hydrogen Bonding Keyword: HM60777 mb06se_cols03.qxd 5/18/07 10:47 AM Page 41 42 CHAPTER 2 Density of Ice Unlike most solids, which are denser than their liquids, solid water is less dense than liquid water. This property is due to the shape of the water molecule and hydrogen bonding. The angle between the hydrogen atoms is quite wide. So, when water forms solid ice, the angles in the molecules cause ice crystals to have large amounts of open space, as shown in Figure 2-12. This open space lattice structure causes ice to have a low density. Because ice floats on water, bodies of water such as ponds and lakes freeze from the top down and not the bottom up. Ice insulates the water below from the cold air, which allows fish and other aquatic crea- tures to survive under the icy surface.

Animal Rights and Diet Success Criteria I can explain key terms which describe the type of diets people have I can explain the advantages and disadvantages of different types of diet Animal Rights and Diet Match up the terms with the meaning Term Meaning Omnivore - eats fish but no other type of meat Vegetarian - eats most types of meat and vegetables Pescetarian - doesn’t eat any products that come from animals Vegan - doesn’t eat meat but will eat dairy products like milk Place the different diets on a spectrum All meat No animal products at all Vegetarian Vegan Omnivore Pescetarian Omnivore Omnivore Most people in the UK are omnivores Match the countries with the amount of meat eaten per person per year Country Meat per person per year India 9.9 kg USA 4.4 kg Bangladesh 120 kg UK 111.5kg Nepal 84.2 kg Australia 4 kg Numeracy How much meat is consumed in the UK per year? (Amount of meat eaten X the UK population) 2. How much meat is consumed in Bangladesh per year? (Amount of meat eaten X the Bangladesh population) Country Meat per person per year USA 120 kg Australia 111.5kg UK 84.2 kg Nepal 9.9 kg India 4.4 kg Bangladesh 4 kg UK – 64 million Bangladesh – 165 million http://www.telegraph.co.uk/travel/maps-and-graphics/world-according-to-meat-consumption/ 7 Why do people eat meat? Discuss Tradition (their family has always done it) Culture (celebrations) Taste Convenience Nutrients such as B12, protein and iron Consumption of meat is rising across developing countries because higher incomes generally mean more meat eating. Pescetarian "Yeah, I'm a vegetarian." "But that looks like fish you're eating." "Oh yeah, I eat fish.“ An estimated 5% - 6% of people in the UK are pescetarians. How many people is this? Approx. 3.6 million Calculation – 66,000,000 /100 x 5.5 = 3,630,000 9 Which group is cuter? Animals Fish 10 People often don’t feel as much love for fish as they do for fluffy, cute mammals. The may think fish don’t feel pain. They may be fussy. They think fish isn’t meat. Not farmed as much as mammals; can be wild. To get nutrients they wouldn’t get from just vegetables and grains. (Omega 3 is in plants but in higher concentrations in oily fish) Why are people pescetarians? https://www.vegsoc.org/sslpage.aspx?pid=753 http://articles.mercola.com/omega-3.aspx Fish – In a perfect world, fish can provide you all the omega-3s you need. Unfortunately, the vast majority of the fish supply is now heavily tainted with industrial toxins and pollutants, such as heavy metals which include mercury, lead, arsenic, and cadmium, PCBs, and radioactive poisons. These toxins make eating fish no longer recommended. 11 Vegetarianism Vegetarians will not eat any meat or product that comes from the slaughter of animals e.g. gelatine. About 3% of the UK population are vegetarian. How many people is this? 1.9 million 12 Why are people vegetarian? They don’t like the idea that animals are killed so they can eat Health reasons Don’t like meat Brought up vegetarian Environmental reasons Religious reasons (e.g. some Buddhist, Hindus) Watch the following clip twice. The second time, write down the fact which surprises you the most. https://www.youtube.com/watch?v=VW6wfpHFdaI The World Health Organization has classified processed meats – including ham, salami, sausages and hot dogs – as a Group 1 carcinogen (same as smoking/alcohol) which means that there is strong evidence that processed meats cause cancer. Red meat, such as beef, lamb and pork has been classified as a 'probable' cause of cancer. 13 Veganism Not just a diet Around 1% of the population of UK are vegans. A vegan is described by the Vegan Society as “a philosophy and way of living which seeks to exclude—as far as is possible and practicable—all forms of exploitation of, and cruelty to, animals for food, clothing or any other purpose; and by extension, promotes the development and use of animal-free alternatives for the benefit of humans, animals and the environment. In dietary terms it denotes the practice of dispensing with all products derived wholly or partly from animals” Why are people vegan? Why are people vegan? James Aspey: https://www.youtube.com/watch?v=a22XxXP3nU8 Warning: some of the content in this video clip may upset some viewers from 7:14 – 8:11 https://www.youtube.com/watch?v=BtqXeym7H8A Why are people vegan? “Don’t want bad karma” Feel healthier Reduce chances of diseases. Example heart disease. Don’t want to exploit animals Believe in animal rights Sustainability Environment Create a Table of Pros & Cons of Veganism Pros √ Cons - Create a Table of Pros & Cons of Veganism Pros Cons No animals have died for you to eat Some people think it is healthier Help the environment Fewer antibiotics/chemicals that are given to some animals Makes you feel good No vitamin B12 so have to supplement Harder to find food at shops or restaurants May be harder to get enough iron May be more expensive to get substitute meats Judged by family and friends Could put farmers out of business Group Work Source 1 Summarise it in your jotter Explain what the source is/what it says What does it suggest? What is your opinion? Feedback to rest of class https://www.youtube.com/watch?v=SYyjel5VuHg Farmer’s Poem

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