F Communication By Ms Cullen

Survival In order to survive living organisms must respond to their external environment. They can respond by their behaviour or their physiology. Organisms also need to respond to changes in their internal environment, as conditions need to be optimal for their metabolism. Any change in the internal or external environment of an organism is called a stimulus.

Give some examples of both external and internal stimuli that organisms have to respond to and their responses.

Receptors detect stimuli Receptors are specific. Some receptors are cells eg rods and cones on the retina of the eye are photoreceptors. Some receptors are proteins on cell surface membranes eg glucose receptors are proteins found on cell membranes of some pancreatic cells. Effectors will bring about a response to a stimuli and therefore produce an effect. Effectors can be muscle cells or cells found in glands.

Enzymes What internal conditions are needed to be kept constant to allow enzymes to work efficiently?

Maintaining the internal environment - Homeostasis Homeostasis is Greek meaning ‘steady state’. In animals, cells and tissues are surrounded by tissue fluid – so this is the internal environment. Cells will alter their own internal environment as they use up substrates and release products. For example: CO 2 as it is released as waste will change the pH of the tissue fluid and this could inhibit enzyme action. The blood maintains the composition of the tissue fluid, transporting substances and making sure waste products are excreted. This of course needs to be closely monitored.

Homeostasis What conditions need to be kept constant in the human internal environment?

Coordination Multicellular organisms are more efficient as their cells are able to differentiate. However, this means that there needs to be good communication between different parts of the body. What qualities do you think a communication system should have?

Cell Signalling Cells communicate by one cell releasing a chemical, which is detected and responded to by another cell. There are 2 major systems of communication that work by cell signalling: 1.The neuronal system 2.The hormonal system Compare and contrast the 2 systems.

Thermoregulation

Maintaining body temperature - Thermoregulation Enzymes control metabolic reactions and they work at an optimum temperature. Therefore bodies need to be kept as close to that temperature as possible. The optimum core body temperature (areas more than 2.5cm below the body surface) for humans is about 36.9˚C. There are 2 main methods of thermoregulation for organisms. 1.Ectothermy (=outside heat) 2.Endothermy (=inside heat)

Ectotherms Ectotherms maintain their body temperature by their behaviour. They derive their body heat from their immediate external environment, which of course fluctuates daily and seasonally.

Ectotherms - lifestyle 1.The North American horned lizard spends nights buried in the sand to prevent heat loss. 2.Early morning the lizard basks on a rock, with its back 90˚ to the sun to get maximum heat absorption. 3.When body temperature is reached the lizard will become active and feed. 4.When the ground becomes very hot the lizard lies in shade. 5.The lizard will dig into the sand early in the evening whilst it is still warm.

Endotherms All mammals and birds are endotherms. Most of their heat is derived internally from respiration. They control their core body temperature by a combination of physiology and behaviour. As they are able to maintain a body temperature independent of their immediate environment this has allowed endotherms to colonise areas of extreme temperatures.

Endotherms Emperor penguins can maintain a body temperature of 38˚C in the Antarctic where temperatures regularly fall as low as -60˚C

Can you think of advantages and disadvantages of being an endotherm?

Advantages of being endothermic

Disadvantages of being endothermic

How does size affect endotherms? Heat is lost from the body surface. So a small endotherm with a large surface area to volume ratio will lose heat more quickly. Therefore smaller endotherms must respire more rapidly to release enough heat energy to balance the heat loss. This requires a higher metabolic rate and intake of food.

How does size affect endotherms? There is a minimum size that an endotherm can be, below which it would be impossible to eat enough food to maintain body temperature. Savi’s Pygmy Shrew is thought to be the smallest mammal, weighing between 1.2 and 2.7g. The smallest bird is the Bee Humming bird, weighing about 2g.

How does size affect endotherms? Once endotherms are a certain volume body shape can influence the surface area to volume ratio and therefore heat loss. The rounder the shape, the smaller the surface area to volume ratio and the easier it is to conserve heat. Animal which live in hotter areas tend to have long noses, big ears and flaps of skin which increase their surface area to volume ratio and heat loss. Elongated extremities also have larger surface areas aiding heat loss.

How does size affect endotherms? Which cow lives in the hot climate? How is it adapted?

How does size affect endotherms?

Endotherms – Physiological mechanisms to maintain body temperature Explain how the following respond if core body temperature is too low and too high. Sweat glands Lungs, mouth and nose Hairs on skin Arterioles leading to capillaries in the skin Liver cells Skeletal muscles

Week 1 (a) Vasodilaton; (b) vasoconstriction

Endotherms – Behavioural mechanisms to maintain body temperature Can you think of behavioural mechanisms which endotherms use if they are too hot or too cold?

The hypothalamus in the brain monitors blood temperature. If core body temperature drops then the hypothalamus sends signals to reverse this change; Increase in metabolic rate, increased muscle contraction & decrease in loss of heat to the environment. If core temperature rises above the optimum the hypothalamus sends signals to bring about opposite changes. This is an example of negative feedback.

Week 1 Controlling body temperature by negative feedback Name the effectors involved

Peripheral temperature receptors These are in the skin and they monitor the temperature of the extremities. This information is sent to the hypothalamus. If the brain receives information that the external environment is too hot or too cold then it can initiate behavioural mechanisms to rectify this.