Biology Form 4 Page 32 Ms. R. Buttigieg UNIT 3 Conditions supporting life In this unit we shall be seeing how an important condition that supports life is the ability of the organism to maintain a constant internal environment this is referred to as homeostasis. Examples of homeostasis include: Keeping the body temperature constant Controlling blood sugar level. Controlling the amount of water in the body. We shall be looking mainly at the: Osmoregulation and Control of water 3.1 Availability of water '''Osmoregulation''' is the active regulation of the osmotic pressure of body fluids to maintain the homeostasis of the body's water content, that is it keeps the body from becoming too dilute or too concentrated. The activity of the contractile vacuole in a named protist Osmoregulation in the amoeba occurs by means of the contractile vacuole, where water is stored and eventually removed. Its cytoplasm contains a greater concentration of solutes than the surroundings and so it absorbs water by osmosis. The excess water is collected into a contractile vacuole which swells and finally expels water through an opening in the cell membrane.
Biology Form 4 Page 33 Ms. R. Buttigieg Excretion in humans occurs from several structures: The SKIN excretes excess water and salts, and a small amount of urea in sweat The LUNGS excrete most of the carbon dioxide and water vapour The KIDNEYS excrete urea, excess water and salts. The human kidney Make sure you re capable of drawing and labelling the various parts of the urinary system, the kidney and the nephron structure (see Fig 14.1, 14.2, 14.3, 14.6 on pg. 132-3) The function of the kidneys: (see pg. 133) Ultrafiltration Selective reabsorbtion of glucose, mineral ions and water Know the major components of urine (see Table 14.2, pg. 133) The Human Urinary System The Kidneys There are two kidneys situated towards the back of the body, just above the waist. The kidneys are essentially blood filters. Blood is brought to the kidneys to be filtered by the renal artery. After filtering, the blood is taken away again by the renal vein. The kidneys have four functions: 1. Regulation of blood water levels 2. Reabsorption of useful substances into the blood 3. Adjustment of the levels of salts and ions in the blood 4. Excretion of urea and other metabolic wastes
Biology Form 4 Page 34 Ms. R. Buttigieg So we can say that these are the organs of excretion; they remove the waste products urea, excess water and ions such as salt. They first filter the blood, then reabsorb what the body needs. Structure of the kidney If you cut into a kidney you see two distinct parts, the dark red outer zone called the cortex and the lighter inner zone, the medulla. If you then use a microscope and look at the cortex you begin to see lots of structures called nephrons. There are about 750,000 of them in each kidney. Blood enters the kidney through the renal artery. It is filtered and the clean blood leaves via the renal vein. Any waste material leaves through the ureter, then to the bladder and the world outside!
Biology Form 4 Page 35 Ms. R. Buttigieg How the kidney works The kidney works by a combination of three processes: It filters 20 % of the plasma and non-cell elements from the blood into the inside of the nephron (the lumen). It reabsorbs the components that the body needs from the lumen back into the blood. It secretes some unwanted components from the blood into the lumen of the nephron. Anything (fluid, ions, small molecules) that has not been reabsorbed from the lumen gets swept away to form the urine, which ultimately leaves the body. Through these processes, the blood is maintained with the proper composition, and excess or unwanted substances are removed from the blood into the urine.
Biology Form 4 Page 36 Ms. R. Buttigieg Ultrafiltration The blood arrives at the kidney in the renal artery at high pressure and enters the group of capillaries called the glomerulus. The high pressure squeezes water, urea, ions and glucose out of the blood into the Bowman s capsule. Large molecules stay in the blood. Reabsorbtion As blood flows along the nephron, useful substances including water, all glucose, amino acids and salts are reabsorbed by active transport using energy. The cleaned blood enters the renal vein and leaves the kidney. The amount of water reabsorbed depends on a hormone called ADH (antidiuretic hormone). Secretion of unwanted substances Urea and excess ions are not reabsorbed and pass into the collecting duct. The fluid continues out of the nephron into the ureter and down the bladder as urine. Urine contains water, urea and some salts in the form of ions. It should not contain protein or glucose. Protein molecules are too large to be filtered out of the blood and all the glucose is reabsorbed back into the blood from the kidney tubules.
Biology Form 4 Page 37 Ms. R. Buttigieg If you drink more fluids: 1. 2. 3. 4. The effect of climate and diet on urine composition A high protein diet increases the urea content in urine Hot dry weather decreases the body water content and the urine volume is small. This is because a lot of water is lost in sweating. The urine is yellow-brown and concentrated. Cold weather increases the water content in the body and therefore the total urine volume is larger. The urine is pale yellow and dilute. Answer the following: 1a) Draw a clear well labeled diagram to show the structure of the human urinary system. (4) b) In mammals the kidneys control the amount of water in the body. Describe how fresh water protists control the amount of water in their body. (3) JL 2003
Biology Form 4 Page 38 Ms. R. Buttigieg 2. The diagram below shows a mammalian kidney tubule (nephron). a. Name the parts labelled A, B, C, D, E, F. A: ; B: ; C: ; D: ; E: ; F: ; (6) b. What is the importance of the difference in diameter between tube A and tube F in the functioning on the kidney. (2) c. Name the process occurring at the region between D and E. (1) d. Name the fluid passing at point B (1) e. Name two major constituents present in the fluid named in question (d): (i) (ii) (2) (total 12 marks) JL 2002 3. Draw a longitudinal section of the kidney, showing clearly, the cortex, pelvis and medulla.
Biology Form 4 Page 39 Ms. R. Buttigieg 4. The following question is related to the Urinary System. Study the two diagrams below and answer the questions set. i) Which structures related to the Urinary System are shown in the above diagrams? Diagram X ; Diagram Y (1,1) ii) Fill in the labels in Diagram X (4) iii) Diagram Y shows the filtering unit of the organ shown in Diagram X. The concentration of some on the substances found in the blood (B), the filtrate (F) and the urine (U) are given in the table below. a) Which substance did not pass from B to F? (1) b) Which substance was completely reabsorbed into the bloodstream? (1) c) If a person produced 150 litres of filtrate and 1.5 litres of urine in one day, what percentage (%) of filtrate was passed as urine? (Show your workings) (2) d) Apart from the substances shown in the table, what is the major constituent of Urine? (1) (total 11 marks) JL 2001