Tutor profile: Dianne W.
Subject: Environmental Science
What is a J-curve and what does this mean in environmental science?
A J-curve is also known as the exponential growth curve. This happens when the population doubles in size in every generation. For example, a bacterium can divide into 2 after 20 min. It will continue dividing doubling its number in every 20 minutes. This type of population growth is best represented by a J-curve. Human population is also experiencing exponential growth that threatens the sustainability of resources in our environment. Rapid exponential growth is unsustainable because organisms are bound to use the resources around them which leads to environmental degradation. The slowly decreasing amount of resources around us becomes a limiting factor for human population to increase further. Limiting factors are also called environmental resistance. This slows down or controls population growth. Normally limiting factors can be either density independent or density dependent. Density independent limiting factors include natural disasters such as volcanic eruption, fire, pollution, etc. The chances of dying from these factors do not depend on population size or the number of individuals in a population. On the other hand, density dependent factors include diseases, competition, food, and predation. These factors can affect population size as more of these limiting factors can drop the population's per capita growth rate. In the long run, in a normal population, the J-curve will later plateau as environmental resistance/limiting factors increases. This plateau is called the carrying capacity of the environment. A sustainable ecosystem must operate below its carrying capacity.
What will happen to a cell in a hypertonic solution?
First we need to define what is a hypertonic solution. A solution is composed of solute (dissolved particles) and solvent (like water). In a hypertonic solution, there are more dissolved particles or solute than solvent (water). To imagine this more, say there are two cups of water.-sugar solution. Cup A contains, 50ml sugar syrup and 190ml of water. Cup B on the other hand, contains 150ml of sugar syrup and 90ml of water. Since cup B contains more sugar to water ratio, cup B is more hypertonic or more concentrated. When you taste cup B, it is sweeter than cup A. Now, what will happen to a cell when submerged in glass B- a more hypertonic solution. Let's assume that our cell is 70% water. The inside environment of the cell is hypotonic, meaning less concentrated as there are more water molecules (70%). We now need to apply the concept of osmosis. It states that water moves from an area of high water concentration to an area of low water concentration. The inside of the cell, again, has high water concentration (70%) but the outside of the cell which is now your glass of water where you submerge this cell has low water concentration (37.5%). You get this percentage value from the water content of cup B which is 90ml divided by the sum of all the solution in ml which is 150+90=240 multiply by 100. The water from the cell will move from the inside of the cell (70%) where there is a high water concentration to the outside of the cell where there is low water concentration. The cell is automatically doing this movement without using energy as the movement is done down the concentration gradient. We also call this passive transport. The cell will decrease in mass or will shrink. We also call this a crenated animal cell or for plants we call it a plasmolysed cell.
Subject: Physical Science
Using, Newton's second law of motion, describe the relationship between the mass of an object and its inertia.
Newton's 2nd law of motion states that F=ma. Where F is the force, m is the mass of the object and a is the acceleration. We are interested in knowing the relationship between mass and acceleration of the object or if the object will change position. If we look at the formula we can also say that, m=F/a. Then we know that mass is inversely proportional to its acceleration (inertia). This means that the more massive object, the harder it is for that object to change position or move or accelerate.
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