Animal survival 3A The need for food Why do living things need food in order to survive? There are three main food groups. Elements present Basic Units Diagram Carbohydrates Carbon Hydrogen Oxygen Fats Carbon Hydrogen Oxygen Glucose molecules Fatty acids and glycerol Gl Gl Gl Gl Gl G L Y C E R O L Protein Carbon Hydrogen Oxygen Nitrogen Amino acids fatty acid fatty acid fatty acid Carbohydrates are needed for energy Fats are needed for energy and for storage of energy. Proteins are needed for growth and repair. Mammal diets Mammals are specially adapted for the wide variety of food they eat. There are three main groups of mammals whose teeth are specialised for the food they eat: Herbivores Herbivores eat vegetation such as grass, leaves and fruit. Examples are cattle, zebra, camel, and sheep. Herbivore teeth are specialised by the molars having ridges which help to grind the food. Carnivores Carnivores eat the flesh of other animals. Examples are lions, dogs, otters and seals. Carnivore teeth are specialised by having sharp canine teeth to stab and rip open their prey and by having sharp premolar and molar teeth to slice through bones and flesh. Omnivores Omnivores’ diet is made up of both flesh and vegetation. Examples are humans, chimpanzees, bears and pigs. Omnivore teeth are not particularly specialised as their teeth have to be able to cope with all kinds of food. Why do you need to digest your food? Your food is a mixture of solid and liquids containing vitamins, minerals, fibre, and water as well as carbohydrates, fats and proteins. The food materials have to reach every cell in your body and are carried by the blood system. How does the food reach your blood? The following experiment was set up: Visking tubing represents gut wall Starch and glucose represents food Water represents the blood When the surrounding water (blood) is tested for glucose and starch it is discovered that only glucose has got through the Visking tubing because it is a smaller molecule than starch. Another difference between starch and glucose is that glucose is soluble in water but starch isn’t. Therefore only small and soluble molecules can pass through into the bloodstream. Digestion is the breakdown of large and insoluble foods into small and soluble molecules so that they can be absorbed into the bloodstream through the gut wall. The human gut The human gut is sometimes called the alimentary canal. It is a muscular tube about 5 metres long, running from the mouth to the anus. Part of the tube is coiled up to fit into the body. Moving food Food cannot move along the tube itself. It has to be pushed. Muscular contractions of the gut wall force food along. This wave of muscular contraction is called peristalsis. The wall of the gut constricts (gets narrower) behind the food to push it along. Meanwhile, in front of the food, the gut gets wider to let the food through. The stomach The stomach is a muscular bag. Its wall produces a gastric juice which chemically breaks down some protein molecules. For digestion to work properly the food needs to be thoroughly mixed with the gastric juice. This is doe by the muscles in the wall of the stomach contracting and squeezing and moving the contents about. Small intestine After the food has been churned and mixed with the gastric juices in the stomach for a while, the partly digested food is moved, a small amount at a time, into the small intestine. The final products of digestion are then absorbed through the intestine wall. Absorption happens more quickly if the surface area of the inside of the small intestine is increased. Lining the inside of the small intestine are finger-like projections called villi. There are 3 ways the small intestine’s surface area can be increased: 1. the thousands of villi significantly increase the surface area 2. the small intestine is the longest part of the gut. 3. the inside of the small intestine is folded. Large intestine Any undigested food leaves the small intestine and passes into the large intestine. No digestion takes place here. The large intestine removes a lot of water from the undigested food. Once the undigested material (faeces) reaches the rectum, they will be stored until they are eliminated from the anus. anus Enzyme action Digestion in the gut involves the chemical breakdown of food. Each type of food is broken down by a different chemical, an enzyme. Amylase Starch maltose Protein Fat Pepsin Lipase peptides fatty acids and glycerol The main digestive juices are produced by the salivary glands, the stomach, the liver the small intestine and the pancreas. Most digestive juices contain enzymes. Bile which is produced by the liver and stored in the gall bladder, has no enzymes. There are three groups of enzymes involved in digestion. Each group of enzymes acts on a different type of food called a substrate. Each substrate gets broken down by the enzyme to substances called products. Enzyme group Amylases Proteases Lipases Enzyme salivary amylase pepsin lipase Substrate starch Product maltose protein fat peptides fatty acids Bile does not contain any digestive enzymes but it is necessary for digestion. It emulsifies fats to make it easier for lipase and other fat digesting enzymes to breakdown the fat molecules ie Large fat droplet Small fat droplets Absorbing food After enzyme action, the digestion products become absorbed by the blood. Most absorption takes place in the small intestine, mainly by the villi. A villus The villus is well adapted for the job of absorbing digested food: a) its wall is only one cell thick allowing digested food to pass through quickly. b) it has its own blood supply (blood capillary) to carry away glucose and amino acids. c) the lacteal carries away fatty acids and glycerol. Summary of digestion Region of gut Digestive juice Mouth saliva Made by Enzymes substrate product in the juice Salivary starch Maltose amylase pepsin protein Peptides Salivary glands Stomach Gastric Gastric juice glands Small Pancreatic Pancreas Lipase intestine juice bile Large intestine liver Its job is to absorb water Fat Fatty acids and glycerol Protease Peptides amino acids and glycerol Amylase maltose starch Its job is to emulsify fats 3B Reproduction All living things reproduce and produce offspring similar to them. If living things did not reproduce, then their numbers would decrease and they would become extinct. Sperm and eggs Sperm and eggs are called gametes. They are the specialised cells involved in reproduction. Sperm Nucleus the male sex cell Can swim Smaller then the egg tail Egg The female sex cell Contains a food store Much larger then the sperm cytoplasm nucleus Cell membrane Fertilisation Fertilisation is when one sperm fuses with an egg. The sperm loses its tail and the male nucleus fuses with the female nucleus. A membrane called the fertilisation membrane then forms around the fertilised egg preventing other sperm from entering. The fertilised egg is called a zygote. A zygote Fertilisation membrane Internal and external fertilisation Internal fertilisation is when sperm and eggs meet inside the female’s body. All mammals, birds and reptiles and most land invertebrates carry out internal fertilisation. Eternal fertilisation is when eggs and sperm meet outside the body usually in water. Fish, amphibians and water living invertebrates carry out external fertilisation. Internal fertilisation is more efficient because the eggs are protected inside the female, fewer eggs are produced and the gametes are closer together so the chances of fertilisation are greater. After fertilisation After fertilisation the fertilised egg begins to divide. Cell divisions continue until a ball of cells is formed: Trout development Trout breed once per year during the month of November. The female makes a hollow in the small stones in the river bed. She lays about 3000 eggs and then the male releases sperm onto them. After fertilisation takes place, the trout eggs begin to develop. Newly hatched trout feed on yolk from the yolk sac. After the yolk sac is used up, the young fish (fry) to feed on small water animals. No protection is given to the trout embryo before and after hatching. The human female reproductive system oviduct The human male reproductive system Human development The ova (eggs) develop in the ovary. At puberty, an ovum is released once a month. The egg passes through the oviduct where it must be fertilised, and on into the uterus. If a sperm fuses with an egg in the oviduct, the fertilised egg or zygote starts to divide as it is passed down the oviduct. When the ball of cells reaches the uterus, it becomes embedded or implanted into the spongy wall of the uterus. The embryo will spend the next 9 months developing here. After the human egg has implanted into the wall of the uterus, it begins to grow and develop. A special structure called the placenta develops, allowing the blood of the mother and the blood of the embryo become very close without mixing. The embryo is attached to the mother by the umbilical cord. The placenta allows the mother and the embryo to exchange essential materials. Exchange at the placenta Mother’s blood Oxygen and food CO2 and waste Embryo’s blood Oxygen and food pass from the mother’s blood to the placenta, down the umbilical cord to the embryo. Carbon dioxide and waste materials are passed along the umbilical cord to the placenta and across to the mother’s blood. During pregnancy, a mother should avoid alcohol and smoking because the alcohol and nicotine can be passed through the placenta to the embryo and affect its development. Unlike the trout eggs, human eggs and embryos are well protected during development by the amniotic sac and fluid, by the uterus wall and the pelvic bones of the mother. After birth, human babies are protected for many years by their parents. Survival chances During reproduction many sex cells and young are destroyed. Only the ‘fittest’ survive to reproduce more of the offspring. Species No of No of No of eggs eggs fertilised produced fertilised eggs diseased Rabbit 8 8 0 Trout 3000 2000 200 Pheasant 15 12 2 Human 1 1 0 Frog 1000 750 50 No of fertilised eggs eaten 0 800 2 0 200 No of young eaten 0 850 3 0 400 % survival 100 5 33 100 10 Mammals have the highest survival rate while fish have the lowest. This is because fish and amphibians do not normally care for their young, and therefore they have to lay many eggs in the hope that some survive to adulthood. Birds and mammal take care of their young before and after birth so they do not have to produce as many eggs and their young have a better chance of survival. C Water and Waste Water gain Our bodies gain water in three different ways: Food Water loss drink metabolic Water Our bodies lose water in four different ways: Sweat through skin urine water loss faeces breath through lungs You gain and lose water in various ways. To maintain water balance in your body, water gain must equal water loss. The kidneys are the main organs for controlling the water content of your bodies. The urinary system In humans the kidneys are solid, oval structures found towards the back of the body below the rib cage. The kidney has two main functions: 1. 2. maintaining water balance getting rid of poisonous waste substances from the body Filtration and absorption Blood enters the kidney through the renal artery and leaves through the renal vein. The blood contains useful substances such as glucose and a poisonous substance, urea. Somehow the kidney has to keep the useful substances and get rid of the poisonous ones. The blood entering the kidney is filtered removing water, useful substances and harmful urea. Useful substances are then reabsorbed back into the blood, leaving some water and the urea. The amount of water reabsorbed depends on the body’s requirements. If we compare the blood going in and out of the kidney and urine for the presence of glucose and urea: Sample Renal artery (in) Renal vein (out) Urine Urea present? Yes No yes Glucose present? Yes Yes No This means that the kidney has removed the urea that was in the renal artery coming into the kidney and placed it in the urine. The renal vein leaving the kidney should be urea free. No glucose should escape in the urine; it should be reabsorbed back into the blood and leave in the renal vein. To explain the process of filtration and reabsorption you have to look at the kidney’s structure in more detail. The kidney is made up of about one million tiny tubes called nephrons that filter the blood and then reabsorb the useful substances. Proteins are broken down to amino acids during digestion. They can be used to build new cells or repair tissues. Any extra amino acids not needed at the time are broken down in the liver to a poisonous waste called urea and a carbohydrate. The urea is transported by the blood to the kidney where it is removed from the blood and leaves the body in the urine. Below is a diagram of one nephron or kidney tubule: 1. 2. 3. 4. 5. Blood is filtered through the glomerulus. All molecules small enough pass through into the Bowman’s capsule eg glucose, amino acids water and urea. Large molecules like protein or blood cells do not get through. As the filtrate moves along the nephron, useful substances are absorbed back into the blood ie glucose salt and water are reabsorbed. The nephron is surrounded by a network of blood capillaries that carry the now cleaned blood away to rejoin the renal vein. the collecting duct now contains urine which is the urea and some water. How much water depends on what the body needs. The urine is carried by the ureter down to the bladder for storage. Eventually it is passed out through the urethra. Water regulation No matter how much liquid the body gains, the kidney adjusts urine output to maintain water balance. The regulation of water balance by the kidneys is under the control of the brain. The brain produces a hormone called ADH (anti diuretic hormone) that controls how much water is reabsorbed by the kidney. Water content of blood too low Water content of blood too high too much salt or sweating drinking Brain produces more ADH Brain produces less ADH water content of blood normal High volume of Water reabsorbed by the kidney Low volume of water water reabsorbed by the kidney Low volume of concentrated urine High volume of dilute urine In other words The lower the water content of the blood >> The more ADH is released by the brain >> The more water is reabsorbed by the kidney >> And a small amount of concentrated urine is produced. The higher the water content of the blood >> The less ADH is released by the brain>> The less water is reabsorbed by the kidney >> And more dilute urine is produced. When kidneys go wrong If kidneys are damaged or diseased, they may cease to function. This can lead to a build up of the poisonous waste urea in their bloodstream. This can be fatal if untreated. If total kidney failure occurs, there are two possible treatments. Each of these treatments will save the life of the patient but there are certain disadvantages to each form of treatment. Treatment How it works The blood is Dialysis filtered through a machine over a number of hours several times a week to remove the urea. The patient Transplant receives a donor kidney Advantages It saves the patient’s life allowing them to live until a donor kidney is available to Disadvantages It’s expensive to run. It limits the patient’s lifestyle A successful transplant means the patient can go back to a normal life The patient’s body may reject the new kidney. There is a shortage of kidney donors. D responding to the environment Animals are continually being subjected to signs or signals coming from the environment around them. Environmental signals are called stimuli and the animal will respond to them in a variety of ways. The way in which an animal responds to a stimuli makes up an animal’s behaviour. This behaviour is important for an animal’s survival. Some examples: Woodlice A woodlouse is the land’s equivalent of a shrimp. It has to keep its self moist in order to breathe. It tends to stay in damp dark places where it can breathe and avoid predators. Flatworm Flatworms live on the bottom of ponds and rivers. They cannot see but are attracted by chemical signals from their food. Investigating the response of woodlice to light We know that woodlice prefer damp conditions to dry and dark conditions to light. Can we show this in an experiment? Dark side light side Hole sellotape When woodlice are put through the central hole and all holes are sealed with sellotape, they are left for awhile. After 10 minutes you would expect to see more woodlice in the dark side of the chamber. This is because in the wild they will be safer in a dark place. You can also use this chamber to investigate whether the woodlice prefer damp conditions to dry. Rhythmical behaviour Some environmental; conditions vary regularly eg light during the day, dark at night, long warm days in summer and short cold days in the winter. There are three main rhythmical changes in the environment: daily, tidal and annual. Daily Some animals are nocturnal, some are diurnal eg owls usually hunt at night whilst humans are usually active during the day. The owls have less competition for food if they hunt at night. Tidal Seashore animals coordinate their activity according to high or low tide. Shore crabs tend to hide under rocks while the tide is out and become active only when the tide comes in. This will happen twice a day. Annual This is behaviour that usually occurs only at one specific time of the year. The two best examples are courtship and migration. Most animals only mate once a year often involving an elaborate courtship. Many animals migrate long distances at certain times of the year, usually in search of food or warmer living conditions or a safe place to bring up young. These two behaviours are predominantly triggered by changes in the hours of light and dark.