Excretion and Homeostasis Questions and Answers - Biology Form 2 Topical Revision

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  1. In an investigation the pancreatic duct of a mammal was blocked. It was found that the blood sugar regulation remained normal while food digestion was impaired. Explain these observations. (2 marks)
    1. Explain why the body temperature of a healthy human being must rise up to 390c on a humid day. (2 marks)
    2. In an experiment a piece of brain was removed from rat. It was found that the rat had large fluctuations of body temperatures suggest the part of the brain that had been removed. (1 mark)
    1. Explain why sweat accumulates on a person’s skin in a hot humid environment. (2 marks)
    2. Name the specific part of the brain that triggers sweating. (1 marks)
  4. Explain why some desert animals excrete uric acid rather than ammonia. (2 marks)
  5. State the role of the following hormones in the body
    1. Insulin (3 marks)
    2. Antidiuretic Hormone (3 marks)
  6. What osmoregulatory changes would take place in a marine amoeba if it was transferred to a fresh water environment?
  7. Name two components of blood that are not present in glomerular filtrate. (2 marks)
  8. How would one find out from a sample of urine whether a person is suffering from diabetes mellitus? (2 marks)
  9. When is glycogen, which is stored in the liver, converted into glucose and released into the blood? ( 2 marks)
  10. A person was found to pass out large volumes of dilute urine frequently. Name the
    1. Diseases the person was suffering from (1 marks)
    2. Hormone that was deficient (1 mark)
  11. State the importance of osmoregulation in organisms ( 2 marks)
  12. What happens to excess fatty acids and glycerol in the body? (2 marks)
  13. Give reasons for each of the following
    1. Constant body temperature is maintained in mammals ( 1 mark)
    2. Low blood sugar level is harmful to the body ( 2 marks)
  14. The temperature of a person taken before during and after taking a cold bath. The results are shown in the graph
    1. Explain why the temperature fell during the bath ( 2 marks)
    2. What changes appeared in the skin that enabled the body temperature to return to normal. (2 marks)
    1. Name the fluid that is produced by sebaceous glands (1 mark)
    2. What is the role of sweat on the human skin? ( 2 marks)
  16. State the role of insulin in the human body? ( 1 mark)
    1. What is the meaning of the following terms:
      1. Homeostasis ( 1 mark)
      2. Osmoregulation (1 mark)
    2. Name the hormones involved in regulating glucose level in blood
    1. Explain what happens to excess amino acids in the liver of humans. (3 marks)
    2. Which portions of the human nephrons are only found in the cortex? (3 marks)
      1. What would happen if a person produced less antidiuretic hormone? (1 mark)
      2. What term is given to the condition described in (c) (i) above? (1 mark)
  19. Define the following terms
    1. Excretion
    2. Secretion
    3. Egestion ( 3 marks)
  20. Name the components of blood that do not enter the renal tubule in mammals (2 marks)
  21. The table below shows the approximate percent concentration of various components in blood plasma entering the kidney glomerular filtrate and urine of a healthy human being.
    Component Plasma  Glomerular  Urine Filtrate
    Amino Acids
    Plasma proteins
    In organic ions

    1. Name the process responsible for the formation of glomerular filtrate.
    2. What process is responsible for the absence of glucose and amino acids in urine?
    3. Explain why there are no plasma proteins in the glomerular filtrate
    4. Besides plasma proteins what other major component of blood is absent in the glomerular filtrate.
    5. Why is the concentration of urea in urine much higher than its concentration in the glomerular filtrate?
  22. When the environmental temperature is very high, some animals urinate on their legs or lick the sides of their body. How does this help in temperature regulation?
  23. Fish are able to use more of their food intake for growth than mammals. Suggest an explanation for this.
  24. Explain the term negative feedback
  25. Study the diagram below and answer the questions that follow.
    circulatory system representation
    1. Name the blood vessels labeled A, B and C.
    2. If the animals has recently fed on a diet which is rich in proteins and carbohydrates in which of the vessels labeled A, B, and C would you expect to find the highest concentration of:
      1. Glucose
      2. Amino acids
      3. Carbon (IV) oxide
      4. Oxygen
      5. Urea
    3. During fasting, the level of blood glucose in vessels C may be higher than the level in vessel B explain
  26. Describe how the human kidney functions. ( 20 marks)


  1. Pancreatic juice containing digestive enzyme is prevented from reaching food.
    Insulin (and glucagons), which regulates sugar, is released directly into the blood stream.
    1. Heat from the body metabolism is not lost to the surrounding through sweating because evaporation of sweat will be low; as air is already saturated with moisture.
    2. Hypothalamus
    1. Sweat produces does not evaporate due to high humidity and the body does not cool, hence more sweat produces leading to accumulation
    2. Hypothalamus
  4. - Elimination of uric acid requires less water than ammonia, hence (more) water is conserved.
    - Uric acid is less toxic than ammonia hence safer to excrete where there is less water.
    1. Regulation of blood sugar lowers blood sugar level/controls the conversion of blood sugar to glycogen/maintain correct blood sugar level (90-100mg/100cc of blood)
    2. Controls the absorption of water in the kidney (tubules) nephron/regulation of water in the body/osmotic pressure in the blood.
  6. More water will enter the amoeba (by osmosis) rate of water discharge by contractile vacuole will increase. Contractile vacuoles will be formed to discharge the excess water.
    1. Proteins/plasma; protein/fibrinogen; albumin, globulin, prothrombin.
    2. Blood cells, RBC/white blood cells/Platelets.
  8. - Tests/React/Boil urine with Benedicts/Fehlings: positive results/Orange red precipitate is an indication of the disease diabetes mellitus.
    - Brick red instead of orange, use of Benedict’s solution with boiling/heating.
  9. After vigorous activity when blood glucose falls below normal.
    1. Diabetes insipidus
    2. Anti-diuretic Hormone/ADH/ vasopressin
  11. Maintenance of constant level of water, salts, osmotic pressure for optimum conditions for metabolism, suitable condition for cellular functions.
  12. Converted into fats and stored as adipose tissue.
    1. - Most enzymes in the body function with a narrow range of temperature
      - High temperature denatures enzymes
      - Low temperature inactivates/inhibit enzymes
    2. Sugar is a raw material for respiration therefore less sugar leads to low rate of respiration hence less energy available to the body/low rate of metabolism.
    1. Heat loss by conduction/convection from the blood vessels, the skin enters general circulation cooling the body.
    2. Vasoconstriction, thus less blood flowing to the skin surface thus reducing heat loss. Sweating ceases. Heat produced by shivering through metabolism is retained in the body.
    1. Sebum
    2. - Cooling the body when water content evaporates.
      - Excrete excess salts, lactic acid and urea.
  16. - Regulates the blood sugar level in the body by converting glucose into glycogen.
      1. Maintenance of a constant internal environment of cells.
      2. Regulation of the concentration of water and salts in the body fluid.
    1. - Insulin - Glucagon
    1. - The amino acids are broken into amino group (NH2) and carboxyl group (COOH). The amino group combines with hydrogen forming highly toxic ammonia. It immediately carbines with carbon (IV) oxide forming urea that is less toxic.
      - The carboxyl group are converted to carbohydrates and then oxidized or converted into neutral fats and deposited on parts of the human.
    2. - Bowman’s capsule
      - Proximal convoluted tubule
      - Distal convoluted tubule
      1. Less water reabsorbed in the blood stream and dilute urine is produced.
      2. Diabetes insipidus
    1. Excretion is the removal of metabolic waste products from the body of an organism.
    2. Secretion is the removal of a substance from a cell where it is formed and its transfer to another part of the body where it serves a useful function
    3. Egestion is the removal of undigested food material from the body of an organism.
  20. Blood cells and plasma proteins
    1. Ultra filtration
    2. Selective reabsorption
    3. Because the pores in the glomerular capillaries are too small for plasma protein to pass through.
    4. Blood cells
    5. Most of the water in the glomerular filtrate is reabsorbed by the urine is formed whereas very little urea is reabsorbed.
  22. As moisture from the urine or saliva evaporates from the surface of the skin, it reabsorbs latent heat of vaporization from the body thus cooling it.
  23. Being exothermic, fish do not spend any part of their food intake in the maintenance of body temperature. This is unlike the case with mammals which spend a significant part of their food on temperature maintenance. Therefore fish are able to spend more of their food intake on growth.
  24. Negative feedback refers to a regulatory mechanism whereby a deviation of the entity being regulated above or below the normal range triggers a sequence of event to bring it back to normal.
    1. A - Hepatic artery
      B - Hepatic portal vein
      C - Hepatic vein
      1. B
      2. B
      3. C
      4. A
      5. C
    3. During fasting there is no glucose from the alimentary canal making glucose concentration in vessel B low. Vessel C obtains glucose derived from the hydrolysis of glycogen in the liver.
  26. Kidney receives blood from the renal artery, a branch of the dorsal aorta, hence blood is under high pressure. The afferent arteriole which is the branch of the renal artery supplies blood to glomerulus; the afferent arteriole has a wider diameter than the efferent arteriole; this causes back resistance hence high pressure in the glomerulus leading to ultrafiltration. The walls/capsular barrier are one cell thick hence glucose, amino acids, vitamins, hormones, salts, (creatinine) urea and water filter into the Bowman's capsule to form the glomerular filtrate; white blood cells/red blood cells and plasma proteins such as (Globulin, fibrinogen, platelets) are too large to pass through the capillaries: the filtrate flows into the proximal convulated tubule, where all amino acids, vitamins and all glucose are selectively absorbed back into the blood stream by active transport. There are many mitocondria to provide energy for reabsorption of these substances agaisnt concentration gradient by active transport. The flomerular filtrate flow into loop of henle. Water in descending loop moves by osmosis into the blood capillaries; sodium chloride is actively pumped from the ascending limb of loop of henle into the blood capillaries with the help of alsdosterone hormone produced by adrenal gland. The glomerular filtrate flow into the distal convulated tubule, water is reabsorbed from the distal convulated tubule into blood capillaries; the glomerular filtrate flows into collection tube/duct from where more water is reabsorbed into the blood stream. Anti-diuretic hormone influences the amount of water reabsorbed depending on osmotic pressure of bood; The glomerular filtrate from the collecting duct now referred to as urine; is emptied into pelvis. The urine passes through pelvis and ureter into urinary bladder out of the body through urethra when sphincter muscles relax.
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