Size does matter!

1. Size does matter! • Size plays a vital role in the ammount of heat loss or gain that an organism has with its environment. • Look at the diagram above. What is the relationship between size and heat loss?

2. As the body mass of an animal gets larger, the rate of heat production for each unit of body mass gets smaller. • So again, which of the two animal loses more heat to the environment? • The answer is… • The Long-tailed planigale. • The larger animal, the Tammar wallaby maintains its body temperature than the planigale as it has a smaller surface are to volume ratio over which it will lose heat to the environment.

3. Tolerance limits • As we have discussed, different animals have different rates of tolerance to environmental pressures. • Tolerance to temperature depends largely on the heat source for an organims. • In other words, whether the animal is ectothermic or endothermic.

4. Ectothermic • This describes animals that are unable to produce their own body heat. These animals must obtain their body heat from an external source. • They are also incapable of maintaining a constant internal environment (poikilothermic). • Reptiles provide us with an example of animals that are ectothermic.

5. Answer the following questions. • - What behavior do reptiles undertake to uptake heat from their environment? • - What would happen to a reptile if the temperature stays very low for a long period of time?

6. Endothermic • Endothermic animals are those which have a built in supply of body heat – internal energy releasing chemical reactions that produce heat as energy. • These animals also maintain a constant internal environment (they are homeothermic). • Examples of endothermic animals are mammals and birds. • Why do you think endotherms are able to tolerate greater variation to their external environment in comparison to ectotherms?

7. Questions • - Various terms are used to describe animals in relation to their temperature. Distinguish between the following terms and use named examples for each: ectotherm, endotherm, homeotherm, poikilotherm. • Do you think the terms ‘warm-blooded’ and ‘cold-blooded’ are appropriate descriptions for organisms? Justify your answer. • Apply the negative feedback model to explain thermoregulation in mammals. • What organs are involved in thermoregulation in mammals?

8. Key ideas

9. Animals surviving on land • Organisms that live successfully in a habitat would be expected to show particular structural, behavioraland physiological features or characteristics that assist them to survive in the range of environmental conditions that exist in that habitat.

10. Read pages 317-320 and explain several characteristics that allow animals to survive in • the heat, and • the cold

11. Animals surviving in water • The range of temperature variation in water is far less than it is in terrestrial habitats. • Whales and other mammals do not have fur, they do however have very thick layers of blubber, a special type of fat that acts like a layer of insulation, keeping the heat in. • Many fish produce anti-freeze, which keeps the liquid in their cells from freezing in really cold temperature waters.

12. Countercurrent systems • Whales and mammals also maintain their body temperature by using a countercurrent exchange system. This is a fine network of vascular tissues (capillaries) within fins and tails. • An artery leading to the fin is paired with and connected to a vein coming back from the fin. Blood flowing back from the skin is cool, as it has lost heat to the environment. In this system, the cool blood returning gains heat from the warm blood in the paired artery, so that this blood returning to the vital organs does not cool them too much.

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15. Plant response to temperature change • Plants in a hot environment • - radiation • transpiration • convection • leaf shape • heat shock protein • leaf orientation • structure • leaf fall

16. Plants in a cold environment • Unlike animals, plants cannot produce anti-freeze. • Because of the higher concentration of dissolved ions in the cytosol of the plant cells, the freezing point of the cytosol is lower. • Ice forms in the air space • surrounding the cells. The • ice pushes through the cell • walls, but does not break • the cell membrane.

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18. Water balance in living organisms • Water balance (osmoregulation) in mammals • Kidneys control water balance in all vertebrates. Water balance and blood pressure are closely linked: • increased water raises blood pressure • decreased water lowers blood pressure • The two significant compounds involved in water regulation are: • antidiuretic hormone (ADH) also known as vasopressin and • - renin

19. Vasopressin • Vasopressin is released by the hypothalamus as a response to low blood pressure. • It travels through the bloodstream to the kidney. • Vasopressin acts specifically on the distal tubules of the kidney, where it increases the amount of water reabsorbed back into the blood stream at this site. • Increase water in the blood = increased blood pressure • Increased drinking results in a feedback mechanism to reduce the secretion of vassopressin.

20. Renin • Renin is secreted by the kidneys when a person becomes dehydrated, when their blood pressure and blood volume falls. • Renin works by increasing the active transport of sodium ions from the urine being formed, back into the blood. • In accordance to the rules of osmosis, water will follow the sodium, re-entering the bloodstream and increasing the concentration of water in the blood, which ultimately increases blood pressure.

21. So, vassopressin and renin, although secreted by different organs, work independantly towards the same goal of increasing the amount of water in the blood, thus increasing blood pressure. • They work together to restore water balance as quickly as possible.

23. Water balance in other animals • Amoeba • Osmosis controls the movement • of water in and out of these single • celled organisms. • Fish

24. Sea birds • Birds conserve water by excreting uric acid – this form of nitrogenous waste is the least toxic and requires little water to be excreted with it. • Sea birds also have salt glands above their eyes so they can remove the salt from the salt water which they drink and eliminate it from this gland. • Reptiles • Terrestrial goannas have a large number of kidney tubules, to reabsorb water. • Amphibians • Frog have the problem of water coming in through their skin. To combat this, they produce a lot of urine.

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27. Water balance in plants • Water makes up about 90-95% of the living tissues of plants. Most leaves are covered by a waterproof waxy cuticle, through which relatively little water is lost. • Although, when stomata are • open for gas exchange (CO2 in • and O2 out), water vapour is • lost to the atmosphere via the • process of transpiration.

28. Ion concentration also play an important role in stomatal aperture. • What is the relationship between ion concentration and stomatal aperture?

29. Factors that affect transpiration • Humidity is a major • factor that affects • movement of water out • of the leaves of plants. • If the air is dry, water • loss is far greater than • if the air is humid. • Why do you think this is?

30. Wind also affects transpiration, whereby if it is windier, the rate of water loss will be greater. • Temperature is another factor that affects transpiration, with higher the temperatures resulting in greater water loss.

31. Structures to reduce water loss • - waxy cuticle • sunken stomata • rolled up leaves • succulents • cylindrical leaves • no leaves • Chose two of these to explain in detail (p332-334)

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