Homeostasis

1. Homeostasis Week Five

2. Energy • Energy is the ability to do work. Living things get energy from food. • Plants and some other types of organisms are able to use light energy from the sun to produce food. • Organisms that make their own food are called autotrophs. • Organisms that obtain energy from the food they consume are called heterotrophs.

3. ATP • Energy can come in many different forms, and can be stored in many different ways. • Living things can use chemical fuels. One of the principal chemical compounds that cells use to store and release energy is adenosine triphosphate. (ATP) • ATP consists of adenine, a 5-carbon sugar called ribose, and three phosphate groups (key to ability to store and release energy).

4. ATP • To store energy, a compound called adenosine diphosphate (ADP) is used. It only has two phosphate groups. A cell can add a phosphate group to ADP, producing ATP, and storing a little energy as well. • When a cell needs that energy, the bond is broken with the third phosphate group, and the energy is released.

5. ATP • The characteristics of ATP make it exceptionally useful as the basic energy source of all cells. • ATP provides energy for many cell functions, including active transport. • ATP is great for transferring energy; it is not very good for long-term storage.

6. Thylakoids • Thylakoids are saclike photosynthetic membranes inside the chloroplasts. They are arranged in stacks called grana. • Proteins in the thylakoids organize chlorophyll and other pigments into clusters called photosystems. These are the light collecting units of the chloroplast. • The stroma is the region outside the thylakoid membranes, where light-independent reactions take place.

7. Photosynthesis • Sunlight excites electrons in chlorophyll. These high-energy electrons require special carriers. • A carrier molecule is a compound that can accept a pair of high-energy electrons and transfer them, along with most of their energy, to another molecule. This is called electron transport. • NADP+ is one of these carrier molecules. The electrons will convert it into NADPH.

8. Photosynthesis • Light dependent reactions require light. These reactions produce ATP and NADPH. • The light dependent reactions produce oxygen gas and convert ADP and NADP+ into the energy carriers ATP and NADPH. • H+ ions cannot cross the membrane directly. However, the membrane contains a protein called ATP synthase that allows the crossing. • A calorie is the amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius.

9. Glycolysis • Cellular respiration is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen. • Glycolysis is the process where cells gradually release small amounts of energy from glucose and other food compounds. One molecule of glucose is broken in half, producing two molecules of pyruvic acid, a 3-carbon molecule. • NAD+ is an electron carrier that accepts 4 high-energy electrons during glycolysis.

10. Fermentation • Fermentation releases energy from food molecules by producing ATP in the absence of oxygen. This is an anaerobic process. • The two main types of fermentation are alcoholic fermentation and lactic acid fermentation. • In the absence of oxygen, glycolysis can produce 2 ATP molecules. With oxygen, the Krebs cycle and electron transport can produce an additional 34 ATP molecules, for a total of 36 ATP molecules. • The 36 ATP molecules the cell makes per glucose is about 38 percent of the total energy of glucose. Where is the other 62%? • It is released as heat, which is why your body is warmer after exercise.

11. Energy Needs • For quick energy, glycolysis will supply a few seconds of energy for intense activity. Then lactic acid fermentation kicks in for the next 90 seconds. Lactic acid is a by-product, and this is what causes muscle soreness. • When a body needs long-term energy, the body uses cellular respiration. Glycogen is used for the first 15-20 minutes of activity. After that, the body starts breaking down other molecules, like fat. This is one reason why aerobic exercise is beneficial for weight control. • Cellular respiration and photosynthesis work in opposite directions.

12. Surface Area/Volume • The larger a cell becomes, the more demands the cell places on its DNA. In addition, the cell has more trouble moving enough nutrients and wastes across the cell membrane. • Ratio of Surface Area to Volume • Surface Area equals length × width × number of sides • If you have a 1cm cube, surface area = 1cm × 1cm x 6 = 6cm2 • Volume equals length × width × height • If you have a 1cm cube, volume = 1cm × 1cm × 1cm = 1cm3 • The ratio of surface area to volume is 6/1, or 6 : 1 • If the cube grew to be 2cm, what is the ratio? • If the cube grew to be 3cm, what is the ratio?

13. Surface Area/Volume • The volume increases faster than the surface area and the ratio decreases. This decrease creates serious problems for the cell. • Suppose a small town has a two lane main street. What would happen if that town doubled in size, but didn’t increase the size of the main street? What would happen if it tripled in size and didn’t increase the size of the main street? • If a cell gets too large, it would be difficult to get sufficient amounts of oxygen and nutrients in and waste products out. • The cell avoids this by going through the process of cell division.

14. Animal Homeostasis • Amphibians maintain homeostasis by living in water part of the time, and on land the other part. • The control of body temperature is important for maintaining homeostasis in vertebrates, particularly in habitats where temperature varies widely with time of day and with season. • Ectotherm- An animal whose body temperature is controlled primarily by picking up heat from, or losing heat to, its environment. • Endotherm- An animal that can generate and retain heat inside its body.